| draft-ietf-sigtran-m3ua-04 Description: Request For Comments
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Network Working Group G. Sidebottom, L. Ong, Guy Mousseau
INTERNET-DRAFT Nortel Networks
Ian Rytina
Ericsson
Hanns-Juergen Schwarzbauer, Klaus Gradischnig
Siemens
Ken Morneault
Cisco
Mallesh Kalla
Telcordia
Normand Glaude
Performance Technologies
Expires in six months Sept 2000
SS7 MTP3-User Adaptation Layer (M3UA)
<draft-ietf-sigtran-m3ua-04.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC 2026. Internet-Drafts are working
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Abstract
This Internet Draft defines a protocol for supporting the transport of
any SS7 MTP3-User signalling (e.g., ISUP and SCCP messages) over IP
using the services of the Stream Control Transmission Protocol. Also,
provision is made for protocol elements that enable a seamless
operation of the MTP3-User peers in the SS7 and IP domains. This
protocol would be used between a Signalling Gateway (SG) and a Media
Gateway Controller (MGC) or IP-resident Database. It is assumed that
the SG receives SS7 signalling over a standard SS7 interface using the
SS7 Message Transfer Part (MTP) to provide transport.
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TABLE OF CONTENTS
1. Introduction.......................................................3
1.1 Scope.........................................................3
1.2 Terminology...................................................3
1.3 M3UA Overview.................................................5
1.4 Functional Areas.............................................10
1.5 Sample Configurations........................................18
1.6 Definition of M3UA Boundaries................................21
2. Conventions.......................................................22
3. M3UA Protocol Elements............................................22
3.1 Common Message Header........................................22
3.2 Variable-Length Parameter Format
3.3 Transfer Messages............................................24
3.4 SS7 Signalling Network management (SSNM) Messages............26
3.5 Application Server Process Maintenance Messages..............32
3.6 Management Messages..........................................40
4. Procedures........................................................44
4.1 Procedures to Support the Services of the M3UA Layer.........44
4.2 Procedures to Support the M3UA Services in Section 1.4.2.....44
4.3 Procedures to Support the M3UA Services in Section 1.4.4.....45
4.4 Procedures to Support the M3UA Services in Section 1.4.3.....52
5. Examples of M3UA Procedures.......................................54
5.1 Establishment of Association and Traffic
Between SGs and ASPs.........................................54
5.2 ASP traffic Fail-over Examples...............................56
5.3 M3UA/MTP3-User Boundary Examples.............................57
6. Security..........................................................61
6.1 Introduction.................................................61
6.2 Threats......................................................61
6.3 Protecting Confidentiality...................................62
7. IANA Considerations...............................................62
8. Acknowledgements..................................................62
9. References........................................................62
10. Author's Addresses...............................................65
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1. Introduction
1.1 Scope
There is a need for SCN signalling protocol delivery from an SS7
Signalling Gateway (SG) to a Media Gateway Controller (MGC) or IP-
resident Database as described in the Framework Architecture for
Signalling Transport [1]. The delivery mechanism should meet the
following criteria:
* Support for the transfer of all SS7 MTP3-User Part messages (e.g.,
ISUP, SCCP, TUP, etc.)
* Support for the seamless operation of MTP3-User protocol peers
* Support for the management of SCTP transport associations and
traffic between an SG and one or more MGCs or IP-resident Databases
* Support for MGC or IP-resident Database process fail-over and load-
sharing
* Support for the asynchronous reporting of status changes to
management
In simplistic transport terms, the SG will terminate SS7 MTP2 and MTP3
protocol layers and deliver ISUP, SCCP and/or any other MTP3-User
protocol messages over SCTP transport associations to MTP3-User peers
in MGCs or IP-resident Databases.
1.2 Terminology
Application Server (AS) - A logical entity serving a specific Routing
Key. An example of an Application Server is a virtual switch element
handling all call processing for a unique range of PSTN trunks,
identified by an SS7 DPC/OPC/CIC_range. Another example is a virtual
database element, handling all HLR transactions for a particular SS7
DPC/OPC/SCCP_SSN combination. The AS contains a set of one or more
unique Application Server Processes, of which one or more is normally
actively processing traffic.
Application Server Process (ASP) - A process instance of an Application
Server. An Application Server Process serves as an active or standby
process of an Application Server (e.g., part of a distributed virtual
switch or database). Examples of ASPs are processes (or process
instances) of MGCs, IP SCPs or IP HLRs. An ASP contains an SCTP end-
point and may be configured to process signalling traffic within more
than one Application Server.
Association - An association refers to an SCTP association. The
association provides the transport for MTP3-User protocol data units
and M3UA adaptation layer peer messages.
IP Server Process (IPSP) - A process instance of an IP-based
application. An IPSP is essentially the same as an ASP, except that it
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uses MU3A in a peer-to-peer fashion. Conceptually, an IPSP does not
use the services of a signalling gateway.
Signalling Gateway Process (SGP) - A process instance of a Signalling
Gateway. It serves as an active, standby or load-sharing process of a
Signalling Gateway.
Signalling Process - A process instance that uses M3UA to communicate
with other signalling process. An ASP, a signalling gateway process
and an IPSP are all signalling processes.
Routing Key: A Routing Key describes a set of SS7 parameter and
parameter values that uniquely define the range of signalling traffic
to be handled by a particular Application Server. For example, where
all traffic directed to an SS7 DPC, OPC and ISUP CIC_range(s) or SCCP
SSN is to be sent to a particular Application Server, that SS7 data
defines the associated Routing Key. Routing Keys are unique in the
sense that a received SS7 signalling message cannot be directed to more
than one Routing Key. Also, a Routing Key cannot extend across more
than a single SS7 DPC, in order to more easily support SS7 Management
procedures. It is not necessary for the parameter range values within
a particular Routing Key to be contiguous. For example, an ASP could
be configured to support call processing for multiple ranges of PSTN
trunks that are not represented by contiguous CIC values.
Routing Context - An Application Server Process may be configured to
process signalling traffic related to more than one Application Server,
over a single SCTP Association. At an ASP, the Routing Context
parameter uniquely identifies the range of signalling traffic
associated with each Application Server that the ASP is configured to
receive. There is a 1:1 relationship between a received Routing
Context value and a Routing Key entry at the sending node. Therefore
the Routing Context can be viewed as an index into a sending node's
Message Distribution Table containing the Routing Key entries.
Fail-over - The capability to re-route signalling traffic as required
to an alternate Application Server Process, or group of ASPs, within an
Application Server in the event of failure or unavailability of a
currently used Application Server Process. Fail-back may apply upon
the return to service of a previously unavailable Application Server
Process.
Signalling Point Management Cluster (SPMC) - The complete set of
Application Servers represented to the SS7 network under one specific
SS7 Point Code of one specific Network Appearance. SPMCs are used to
sum the availability / congestion / User_Part status of an SS7
destination point code that is distributed in the IP domain, for the
purpose of supporting MTP3 management procedures at an SG. In some
cases, the SG itself may also be a member of the SPMC. In this case,
the SG availability / congestion / User_Part status must also be taken
into account when considering any supporting MTP3 management actions.
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MTP - The Message Transfer Part of the SS7 protocol.
MTP3 - MTP Level 3, the signalling network layer of SS7
MTP3-User - Any protocol normally using the services of the SS7 MTP3
(e.g., ISUP, SCCP, TUP, etc.).
Network Appearance - The Network Appearance identifies an SS7 network
context for the purposes of logically separating the signalling traffic
between the SG and the Application Server Processes over a common SCTP
Association. An example is where an SG is logically partitioned to
appear as an element in four separate national SS7 networks. A Network
Appearance implicitly defines the SS7 Point Code(s), Network Indicator
and MTP3 protocol type/variant/version used within a specific SS7
network partition. A physical SS7 route-set or link-set at an SG can
appear in only one network appearance. The Network Appearance is not
globally significant and requires coordination only between the SG and
the ASP. Therefore, in the case where an ASP is connected to more than
one SG, the same SS7 network context may be identified by different
Network Appearances depending over which SG a message is being
transmitted/received.
Network Byte Order: Most significant byte first, a.k.a Big Endian.
Layer Management - Layer Management is a nodal function that handles
the inputs and outputs between the M3UA layer and a local management
entity.
Host - The computing platform that the ASP process is running on.
Stream - A stream refers to an SCTP stream; a uni-directional logical
channel established from one SCTP endpoint to another associated SCTP
endpoint, within which all user messages are delivered in-sequence
except for those submitted to the un-ordered delivery service.
1.3 M3UA Overview
1.3.1 Protocol Architecture.
The framework architecture that has been defined for SCN signalling
transport over IP [1] uses multiple components, including a common
signalling transport protocol and an adaptation module to support the
services expected by a particular SCN signalling protocol from its
underlying protocol layer.
Within the framework architecture, this document defines an MTP3-User
adaptation module suitable for supporting the transfer of messages of
any protocol layer that is identified to the MTP Level 3 layer, in SS7
terms, as a user part. The list of these protocol layers include, but
is not limited to, ISDN User Part (ISUP) [2,3,4], Signalling Connection
Control Part (SCCP) [5,6,7] and Telephone User Part (TUP) [8]. TCAP
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[9,10,11] or RANAP [12] messages are transferred transparently by the
M3UA as SCCP payload, as they are SCCP-User protocols.
It is recommended that the M3UA use the services of the Stream Control
Transmission Protocol (SCTP) [13] as the underlying reliable common
signalling transport protocol. This is to take advantage of various
SCTP features such as:
- Explicit packet-oriented delivery (not stream-oriented);
- Sequenced delivery of user messages within multiple streams,
with an option for order-of-arrival delivery of individual
user messages,
- Optional multiplexing of user messages into SCTP datagrams;
- Network-level fault tolerance through support of multi-homing
at either or both ends of an association;
- Resistance to flooding and masquerade attacks; and - Data
segmentation to conform to discovered path MTU size.
Under certain scenarios, such as back-to-back connections without
redundancy requirements, the SCTP functions above may not be necessary.
In these cases, it is acceptable to use TCP as the underlying common
transport protocol.
1.3.2 Services Provided by the M3UA Layer
The M3UA Layer at an ASP provides the equivalent set of primitives at
its upper layer to the MTP3-Users as provided by the MTP Level 3 to its
local users at an SS7 SEP. In this way, the ISUP and/or SCCP layer at
an ASP is unaware that the expected MTP3 services are offered remotely
from an MTP3 Layer at an SG, and not by a local MTP3 layer. The MTP3
layer at an SG may also be unaware that its local users are actually
remote user parts over M3UA. In effect, the M3UA extends access to the
MTP3 layer services to a remote IP-based application. The M3UA does
not itself provide the MTP3 services. In the case where an ASP is
connected to more than one SG, however, the M3UA must maintain the
status of configured SS7 destinations and route messages according to
availability/congestion status of the routes to these destinations.
The M3UA Layer may also be used for point-to-point signalling between
two IP Server Processes (IPSPs). In this case, the M3UA provides the
same set of primitives and services at its upper layer as the MTP3.
However, in this case the expected MTP3 services are not offered
remotely from an SG. The MTP3 services are provided but the procedures
to support these services are a subset of the MTP3 procedures due to
the simplified point-to-point nature of the IPSP to IPSP relationship.
1.3.2.1 Support for the transport of MTP3-User Messages
The M3UA provides the transport of MTP-TRANSFER primitives across an
established SCTP association between an SG and an ASP and between
IPSPs.
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The MTP-TRANSFER primitives are encoded as MTP3-User messages with
attached MTP3 Routing Labels as described in the message format
sections of the SCCP and ISUP recommendations. In this way, the SCCP
and ISUP messages received from the SS7 network are not re-encoded into
a different format for transport to/from the server processes. As
well, all the required MTP3 Routing Label information (OPC, DPC, SIO)
is available at the ASP and the IPSP as is expected by the MTP3-User
protocol layer.
At an ASP, in the case where a destination is reachable via multiple
SGs, the M3UA must also choose via which SG the message is to be routed
or support load balancing across the SGs, ensuring that no mis-
sequencing occurs.
The M3UA does not impose a 272-octet user information block limit as
specified by the SS7 MTP Level 3 protocol. Larger information blocks
can be accommodated directly by M3UA/SCTP, without the need for an
upper layer segmentation/re-assembly procedure as specified in recent
SCCP or ISUP versions. However, in the context of an SG, the maximum
272-octet block size must be followed when inter-working to a SS7
network that does not support the transfer of larger information blocks
to the final destination. This avoids potential ISUP or SCCP
fragmentation requirements at the SG. However, if the SS7 network is
provisioned to support the Broadband MTP [20] to the final SS7
destination, the information block size limit may be increased past 272
octets.
1.3.2.2 Native Management Functions
The M3UA provides management of the underlying SCTP transport protocol
to ensure that SG-ASP and IPSP-IPSP transport is available to the
degree called for by the MTP3-User signalling applications.
The M3UA provides the capability to indicate errors associated with
received M3UA messages and to notify, as appropriate, local management
and/or the peer M3UA.
1.3.2.3 Inter-working with MTP3 Network Management Functions
At the SG, the M3UA must also provide inter-working with MTP3
management functions to support seamless operation of the user SCN
signalling applications in the SS7 and IP domains. This includes:
- Providing an indication to MTP3-Users at an ASP that a remote
destination in the SS7 network is not reachable.
- Providing an indication to MTP3-Users at an ASP that a remote
destination in the SS7 network is now reachable.
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- Providing an indication to MTP3-Users at an ASP that messages to a
remote MTP3-User peer in the SS7 network are experiencing SS7
congestion.
- Providing an indication to MTP3-Users at an ASP that a remote MTP3-
User peer is unavailable.
The M3UA layer at an ASP may initiate an audit of the availability or
the congested state of remote SS7 destinations. This information is
requested from the M3UA at the SG.
The M3UA layer at an ASP may also indicate to the SG that the M3UA
itself or the ASP or the ASP's host is congested.
1.3.2.4 Support for the management of SCTP associations between the SG
and ASPs.
The M3UA layer at the SG maintains the availability state of all
configured remote ASPs, in order to manage the SCTP Associations and
the
traffic between the SG and ASPs. As well, the active/inactive state of
remote ASPs is also maintained - Active ASPs are those currently
receiving traffic from the SG.
The M3UA layer may be instructed by local management to establish an
SCTP association to a peer M3UA node. This can be achieved using the
M-SCTP ESTABLISH primitive to request, indicate and confirm the
establishment of an SCTP association with a peer M3UA node. In order
to avoid multiple SCTP associations between two IPSPs, one side must be
designated to establish the association or the mutual SCTP endpoint
addresses must be pre-configured.
The M3UA layer may also need to inform local management of the status
of the underlying SCTP associations using the M-SCTP STATUS request and
indication primitive. For example, the M3UA may inform local management
of the reason for the release of an SCTP association, determined either
locally within the M3UA layer or by a primitive from the SCTP.
Also the M3UA layer may need to inform the local management of the
change in status of an ASP or AS. This can be achieved using the M-ASP
STATUS or M-AS STATUS primitives.
1.3.2.5 Support for the management of connections to multiple SGs
As shown in Figure 1 an ASP may be connected to multiple SGs. In such a
case a particular SS7 destination may be reachable via more than SG,
i.e., via more than one route. As MTP3 users only maintain status on a
destination and not on a route basis M3UA must maintain the status
(availability and/or congestion of route to destination) of the
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individual routes, derive the overall status of the destination from
the status of the individual routes, and inform the MTP3 users of this
derived status whenever it changes.
1.3.3 Signalling Network Architecture
A Signalling Gateway is used to support the transport of MTP3-User
signalling traffic received from the SS7 network to multiple
distributed ASPs (e.g., MGCs and IP Databases). Clearly, the M3UA
protocol is not designed to meet the performance and reliability
requirements for such transport by itself. However, the conjunction of
distributed architecture and redundant networks does allow for a
sufficiently reliable transport of signalling traffic over IP. The
M3UA protocol is flexible enough to allow its operation and management
in a variety of physical configurations, enabling Network Operators to
meet their performance and reliability requirements.
To meet the stringent SS7 signalling reliability and performance
requirements for carrier grade networks, Network Operators should
ensure that no single point of failure is present in the end-to-end
network architecture between an SS7 node and an IP-based application.
This can typically be achieved through the use of redundant SGs,
redundant hosts, and the provision of redundant QOS-bounded IP network
paths for SCTP Associations between SCTP End Points. Obviously, the
reliability of the SG, the MGC and other IP-based functional elements
also needs to be taken into account. The distribution of ASPs within
the available Hosts must also be considered. As an example, for a
particular Application Server, the related ASPs should be distributed
over at least two Hosts.
Here is one example of a physical network architecture relevant to SS7
carrier-grade operation, in the IP network domain, shown in Figure 1
below:
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SG MGC
Host#1 ************** ************** Host#1
= * ********__*__________________________*__******** * =
SG1 * * SGP1 *__*_____ _______________*__* ASP1 * * MGC1
* ******** * \ / * ******** *
* ********__*______\__/________________*__******** *
* * SGP2 *__*_______\/______ _____*__* ASP2 * *
* ******** * /\ | | * ******** *
* : * / \ | | * : *
* ******** * / \ | | * ******** *
* * SGPn * * | | | | * * ASPn * *
* ******** * | | | | * ******** *
************** | | | | **************
| | \ /
Host#2 ************** | | \ / ************** Host#2
= * ********__*_____| |______\/_______*__******** * =
SG2 * * SGP1 *__*_________________/\_______*__* ASP1 * * MGC2
* ******** * / \ * ******** *
* ********__*_______________/ \_____*__******** *
* * SGP2 *__*__________________________*__* ASP2 * *
* ******** * * ******** *
* : * SCTP Associations * : *
* ******** * * ******** *
* * SGPn * * * * ASPn * *
* ******** * * ******** *
************** **************
Figure 1 - Physical Model
In this model, each host has many application processes. In the case
of the MGC, an ASP may provide service to one or more application
server, and is identified as an SCTP end point. In the case of the SG,
a pair of signalling gateway processes may represent, as an example, a
single network appearance, serving a signalling point management
cluster.
This example model can also be applied to IPSP-IPSP signalling. In
this case, each IPSP would have its services distributed across 2 hosts
or more, and may have multiple server processes on each host.
In the example above, each signalling process (SGP, ASP or IPSP) is the
end point to more than one SCTP association, leading to many other
signalling processes. To support this, a signalling process must be
able to support distribution of M3UA messages to many simultaneous
active associations. This message distribution function is based on
the status of provisioned routing keys, the availability of signalling
points in the SS7 network, and the redundancy model (active-standby,
load-sharing, n+k) of the remote signalling processes.
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For carrier grade networks, Operators should ensure that under failure
or isolation of a particular signalling process, stable calls or
transactions are not lost. This implies that signalling processes
need, in some cases, to share the call or transaction state information
with other signalling processes. In the case of ASPs performing call
processing, coordination may also be required with the related Media
Gateway to transfer the MGC control for a particular trunk termination.
However, this sharing or communication is outside the scope of this
document.
This model serves as an example. M3UA imposes no restrictions as to
the exact layout of the network elements, the message distribution
algorithms and the distribution of the signalling processes. Instead,
it provides a framework and a set of messages that allow for a flexible
and scalable signalling network architecture, aiming to provide
reliability and performance.
1.4 Functional Areas
1.4.1 Signalling Point Code Representation
Within an SS7 network, a Signalling Gateway is charged with
representing a set of nodes in the IP domain into the SS7 network for
routing purposes. The SG itself, as a physical node in the SS7
network, must be addressable with an SS7 Point Code for MTP3 Management
purposes. The SG Point Code may also be used for addressing any local
MTP3-Users at the SG such as an SG-resident SCCP function.
An SG may be logically partitioned to operate in multiple SS7 network
Appearances. In such a case, the SG must be addressable with a Point
Code in each network appearance, and represents a set of nodes in the
IP domain into each SS7 network. Alias PCs may also be used within an
SG network appearance.
The M3UA places no restrictions on the SS7 Point Code representation of
an AS. Application Servers can be represented under the same PC of the
SG, their own individual Point Codes or grouped with other applications
for Point Code preservation purposes. A single Point Code may be used
to represent the SG and all the ASPs together, if desired.
Where Application Servers are grouped under a Point Code address, an
SPMC will include more than one AS. If full advantage of SS7 management
procedures is to be taken (as is advisable in carrier grade networks)
care must be taken that, if (the connection to) one AS of an SPMC
fails, all AS of the SPMC fail or become unreachable from the SG. If
this is not the case, usage of SS7 transfer prohibited procedures by
the SG becomes problematic as either traffic to the failed AS cannot be
stopped/diverted or traffic to a still available AS will unnecessarily
be stopped/diverted. (Depending on the network configuration it may
even be necessary to assign an individual SS7 point code to each AS.)
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Observing these principles is of particular importance if alternative
routing possibilities exist on the SS7 level (e.g. via mated SGs) or
application level (e.g. via another MGC/MG).
If an ASP or group of ASPs is available to the SS7 network via more
than one SG, each with its own Point Code, the ASP(s) should be
represented by a Point Code that is separate from any SG Point Code.
This allows these SGs to be viewed from the SS7 network as "STPs", each
having an ongoing "route" to the same ASP(s). Under failure
conditions where the ASP(s) become(s) unavailable from one of the SGs,
this approach enables MTP3 route management messaging between the SG
and SS7 network, allowing simple SS7 re-routing through an alternate SG
without changing the Destination Point Code Address of SS7 traffic to
the ASP(s).
Where an AS can be reached via more than one SG it is equally important
that the corresponding Routing Keys in the involved SGs are identical.
(Note: It is possible for the Routing Key configuration data to be
temporarily out-of-synch during configuration updates).
+--------+
| |
+------------+ SG 1 +--------------+
+-------+ | SS7 links | "STP" | IP network | ----
| SEP +---+ +--------+ +---/ \
| or | | ASPs |
| STP +---+ +--------+ +---\ /
+-------+ | | | | ----
+------------+ SG 2 +--------------+
| "STP" |
+--------+
Note: there is no SG-to-SG communication shown, so each SG can be
reached only via the direct linkset from the SS7 network.
The following example shows a signalling gateway partitioned into two
network appearances.
SG
+-------+ +---------------+
| SEP +--------------| SS7 Ntwk |M3UA| ----
+-------+ SS7 links | "A" | | / \
|__________| +-----------+ ASPs |
| | | \ /
+-------+ | SS7 Ntwk | | ----
| SEP +--------------+ "B" | |
+-------+ +---------------+
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1.4.2 Message Distribution
1.4.2.1 Address Translation and Mapping at the SG
In order to direct messages received from the SS7 MTP3 network to the
appropriate IP destination, the SG must perform address translation and
mapping functions using information from the received MTP3-User
message.
To support this message distribution, the SG must maintain the
equivalent of a network address translation table, mapping incoming SS7
message information to an Application Server for a particular
application and range of traffic. This is accomplished by comparing
elements of the incoming SS7 message to provisioned Routing Keys in the
SG. These Routing Keys in turn make reference to an Application Server
that is enabled by one or more ASP. These ASPs provide dynamic status
information to the SG using various management messages defined in the
M3UA protocol. Possible SS7 address/routing information that comprise
a Routing Key entry includes, for example, the OPC, DPC, SIO found in
the MTP3 routing label, or other MTP3-User specific fields such as the
ISUP CIC, SCCP subsystem number, or TCAP transaction ID. Some example
routing keys are: the DPC alone, the DPC/OPC combination, the
DPC/OPC/CIC combination, or the DPC/SSN combination. The particular
information used to define an M3UA Routing Key is application and
network dependent, and none of the above examples are mandated.
An Application Server contains a list of one or more ASPs that are
capable of processing the traffic. This list is assumed to be dynamic,
taking into account the availability status of the individual ASPs in
the list, configuration changes, and possible fail-over mechanisms. The
M3UA protocol includes messages to convey the availability status of
the individual ASPs as input to a fail-over mechanism.
Normally, one or more ASPs is active in the ASP (i.e., currently
processing traffic) but in certain failure and transition cases it is
possible that there may not be an active ASP available. Both load-
sharing and backup scenarios are supported.
When there is no Routing Key match for an incoming SS7 message, a
default treatment must be specified. Possible solutions are to provide
a default Application Server at the SG that directs all unallocated
traffic to a (set of) default ASP(s), or to drop the messages and
provide a notification to management. The treatment of unallocated
traffic is implementation dependent.
1.4.2.2 Address Translation and Mapping at the ASP
In order to direct messages to the SS7 network, the ASP must also
perform an address translation and mapping function in order to choose
the proper SG or SGP for a given message. This is accomplished by
observing the Destination Point Code and other elements of the outgoing
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message, SS7 network status, SG and SGP availability, and network
appearance configuration tables.
A remote Signalling Gateway may be composed of one or more SGPs that
are capable of routing SS7 traffic. As is the case with ASPs, a
dynamic list of SGPs in an SG can be maintained, taking into account
the availability status of the individual SGPs, configuration changes
and fail-over mechanisms. There is, however, no M3UA messaging to
manage the status of an SGP. Whenever an SCTP association to an SGP
exists, it is assumed to be available. Also, every SGP of one SG
communicating with one ASP regarding one AS provides identical SS7
connectivity to this ASP.
1.4.3 SS7 and M3UA Interworking
In the case of SS7 and M3UA inter-working, the M3UA adaptation layer is
designed to provide an extension of the MTP3 defined user primitives.
1.4.3.1 Signalling Gateway SS7 Layers
The SG is responsible for terminating MTP Level 3 of the SS7 protocol,
and offering an IP-based extension to its users.
>From an SS7 perspective, it is expected that the Signalling Gateway
(SG) transmits and receives SS7 Message Signalling Units (MSUs) to and
from
the PSTN over a standard SS7 network interface, using the SS7 Message
Transfer Part (MTP) [14,15,16] to provide reliable transport of the
messages.
As a standard SS7 network interface, the use of MTP Level 2 signalling
links is not the only possibility. ATM-based High Speed Links can also
be used with the services of the Signalling ATM Adaptation Layer (SAAL)
[17,18]. It is possible for IP-based links to be present, using the
services of the MTP2-User Adaptation Layer (M2UA) [19]. These SS7
datalinks may be terminated at a Signalling Transfer Point (STP) or at
a Signalling End Point (SEP). Using the services of MTP3, the SG may
be capable of communicating with remote SS7 SEPs in a quasi-associated
fashion, where STPs may be present in the SS7 path between the SEP and
the SG.
Where ATM-based High Speed Links are used in the SS7 network, it is
possible for the SG to use the services of the MTP-3b [20] for reliable
transport to and from an SS7 SEP or STP. The maximum Service Data Unit
(SDU) supported by the MTP-3b is 4096 octets compared to the 272-octet
maximum of the MTP3. However, for MTP3-Users to take advantage of the
larger SDU between MTP3-User peers, network architects should ensure
that MTP3-b is used end-to-end between the SG and the SS7-resident
peer.
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1.4.3.2 SS7 and M3UA Inter-Working at the SG
The SG provides a functional inter-working of transport functions
between the SS7 network and the IP network by also supporting the M3UA
adaptation layer. It allows the transfer of MTP3-User signalling
messages to and from an IP-based Application Server Process where the
peer MTP3-User protocol layer exists.
The Signalling Gateway must maintain knowledge of SS7 node and
Signalling Point Management Cluster (SPMC) status in their respective
domains in order to perform a seamless inter-working of the IP-based
signalling and the SS7 domains. For example, SG knowledge of the
availability and/or congestion status of the SPMC and SS7 nodes must be
maintained and disseminated in the respective networks, in order to
ensure that end-to-end operation is transparent to the communicating
SCN protocol peers at the SS7 node and ASP.
When the SG determines that the transport of SS7 messages to an SPMC
(or possibly to parts of an SPMC) is encountering congestion, the SG
should inform the MTP3 route management function (by an implementation-
dependent mechanism). This information is used by the MTP3 to mark the
"route" to the affected destination as congested and to trigger MTP
Transfer Controlled (TFC) messages to any SS7 SEPs generating traffic
to the congested DPC, as per current MTP3 procedures.
When the SG determines that the transport of SS7 messages to all ASPs
in a particular SPMC is interrupted, then it should similarly inform
the MTP3 route management function. This information is used by the
MTP3 to mark the "route" to the affected destination as unavailable,
and in the case of the SG acting as a signalling transfer point (i.e.,
the Point Code of the SG is different from that of the SPMC), to send
MTP Transfer Prohibited (TFP) messages to the relevant adjacent SS7
nodes, according to the local SS7 network procedures.
When the SG determines that the transport of SS7 messages to an ASP in
a particular SPMC can be resumed, the SG should similarly inform the
MTP3 route management function. This information is used by the MTP3
to mark the route to the affected destination as available, and in the
case of a signalling transfer point, to send MTP Transfer Allowed (TFA)
messages to the relevant adjacent SS7 nodes, according to the local SS7
network procedures.
For SS7 user part management, it is required that the MTP3-User
protocols at ASPs receive indications of SS7 signalling point
availability, SS7 network congestion, and remote User Part
unavailability as would be expected in an SS7 SEP node. To accomplish
this, the MTP-PAUSE, MTP-RESUME and MTP-STATUS indication primitives
received at the MTP3 upper layer interface at the SG need to be
propagated to the remote MTP3-User lower layer interface at the ASP.
(These indication primitives are, of course, also made available to any
existing local MTP3-Users at the SG, if present.)
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It is important to clarify that MTP3 management messages such as TFPs
or TFAs received from the SS7 network are not "encapsulated" and sent
blindly to the ASPs. Rather, the existing MTP3 management procedures
are followed within the MTP3 function of the SG to re-calculate the
MTP3 route set status and initiate any required signalling-route-set-
test procedures into the SS7 network. Only when an SS7 destination
status changes are MTP-PAUSE or MTP-RESUME primitives invoked. These
primitives can also be invoked due to local SS7 link set conditions as
per existing MTP3 procedures.
In case where the MTP in the SG undergoes an MTP restart, event
communication to the concerned ASPs should be handled as follows:
When the SG discovers SS7 network isolation, the SG sends an indication
to all concerned available ASPs (i.e., ASPs in the "active" or
"inactive" state), using a DUNA message. For the purposes of MTP
Restart, all SPMCs with point codes different from that of the SG with
at least one ASP that is active or has sent an ASPAC message to the SG
during the first part of the restart procedure should be considered as
available. If the M3UA at the SG receives any ASPAC messages during
the restart procedure, it delays the ASPAC-ACK messages until the end
of the restart procedure. During the second part of the restart
procedure the M3UA at the SG informs all concerned ASPs in the "active"
or "inactive" state of any unavailable SS7 destinations. At the end of
the restart procedure the M3UA sends an ASPAC-ACK message to all ASPs
in the "active" state.
1.4.3.2 Application Server
A cluster of application servers is responsible for providing the
overall support for one or more SS7 upper layers. From an SS7
standpoint, a Signalling Point Management Cluster (SPMC) provides
complete support for the upper layer service for a given point code.
As an example, an SPMC providing MGC capabilities must provide complete
support for ISUP for a given point code, according to the local SS7
network specifications.
This measure is necessary to allow the SG to accurately represent the
signalling point on the local SS7 network.
In the case where an ASP is connected to more than one SG, the M3UA
must maintain the status of configured SS7 destinations and route
messages according to availability/congestion status of the routes to
these destinations.
When an ASP enters the "Inactive" state towards an SG the M3UA must
mark all SS7 destinations configured to be reachable via this SG as
available.
When the M3UA at an ASP receives a DUNA message indicating SS7 network
isolation at an SG, it will stop any affected traffic via this SG and
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clear any unavailability state of SS7 destinations via this SG. When
the M3UA subsequently receives any DUNA messages from an SG it will
mark the effected SS7 destinations as unavailable via that SG. When
the M3UA receives an ASPAC-ACK message it can resume traffic to
available SS7 destinations via this SG, provided the ASP is in the
active state towards this SG.
1.4.3.3 IPSP
Since IPSPs use M3UA in a point-to-point fashion, there is no concept
of routing of messages beyond the remote end. Therefore, SS7 and M3UA
inter-working is not necessary for this model.
1.4.4 Redundancy Models
The network address translation and mapping function of the M3UA layer
supports signalling process fail-over functions in order to support a
high availability of call and transaction processing capability.
1.4.4.1 Application Server Redundancy
All MTP3-User messages (e.g., ISUP, SCCP) incoming to an SG from the
SS7 network are assigned to a unique Application Server, based on the
information in the message and the provisioned Routing Keys.
The Application Server is, in practical terms, a list of all ASPs
configured to process a range of MTP3-User traffic defined by one
Routing Key. One or more ASPs in the list are normally active (i.e.,
handling traffic) while any others may be unavailable or inactive, to
be possibly used in the event of failure or unavailability of the
active ASP(s).
The fail-over model supports an "n+k" redundancy model, where "n" ASPs
is the minimum number of redundant ASPs required to handle traffic and
"k" ASPs are available to take over for a failed or unavailable ASP. A
"1+1" active/standby redundancy is a subset of this model. A simplex
"1+0" model is also supported as a subset, with no ASP redundancy.
At the SG, an Application Server list contains active and inactive ASPs
to support ASP load-sharing and fail-over procedures. The list of ASPs
within a logical Application Server is kept updated in the SG to
reflect the active Application Server Process(es).
To avoid a single point of failure, it is recommended that a minimum of
two ASPs be in the list, resident in separate hosts, and therefore
available over different SCTP Associations. For example, in the
network shown in Figure 1, all messages to DPC x could be sent to ASP1
in Host1 or ASP1 in Host2. The AS list at SG1 might look like this:
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Routing Key {DPC=x) - "Application Server #1"
ASP1/Host1 - State=Up, Active
ASP1/Host2 - State=Up, Inactive
In this "1+1" redundancy case, ASP1 in Host1 would be sent any incoming
message with DPC=x. ASP1 in Host2 would normally be brought to the
active state upon failure of, or loss of connectivity to, ASP1/Host1.
In this example, both ASPs are Up, meaning that the related SCTP
association and far-end M3UA peer is ready.
The AS List at SG1 might also be set up in load-share mode:
Routing Key {DPC=x) - "Application Server #1"
ASP1/Host1 - State = Up, Active
ASP1/Host2 - State = Up, Active
In this case, both the ASPs would be sent a portion of the traffic.
For example the two ASPs could together form a database, where incoming
queries may be sent to any active ASP.
Care must be exercised by a Network Operator in the selection of the
routing information to be used as the Routing Key for a particular AS.
For example, where Application Servers are defined using ranges of ISUP
CIC values, the Operator is implicitly splitting up control of the
related circuit groups. Some CIC value range assignments may interfere
with ISUP circuit group management procedures.
In the process of fail-over or fail-back, it is recommended that in the
case of ASPs supporting call processing, stable calls do not fail. It
is possible that calls in "transition" may fail, although measures of
communication between the ASPs involved can be used to mitigate this.
For example, the two ASPs may share call state via shared memory, or
may use an ASP to ASP protocol to pass call state information.
1.4.4.2 Signalling Gateway Redundancy
Signalling Gateways may also be distributed over multiple hosts. Much
like the AS model, SGs may be comprised of one or more SG Processes
(SGPs), distributed over one or more hosts, using an active/standby or
a load-sharing model. An SGP is viewed as a remote SCTP end-point from
an ASP perspective. There is, however, no M3UA protocol to manage the
status of an SGP. Whenever an SCTP association to an SGP exists, the
SGP is assumed to be available. Also, every SGP within an SG
communicating with an ASP provides identical SS7 connectivity to this
ASP. Should an SGP lose all or partial SS7 connectivity and other SGPs
exist, the SGP must terminate the SCTP associations to the concerned
ASPs.
It is therefore possible for an ASP to route signalling messages
destined to the SS7 network using more than one SGP. In this model, a
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Signalling Gateway is deployed as a cluster of hosts acting as a single
SG. A primary/back-up redundancy model is possible, where the
unavailability of the SCTP association to a primary SGP could be used
to reroute affected traffic to an alternate SGP. A load-sharing model
is possible, where the signalling messages are load-shared between
multiple SGPs.
It may also be possible for an ASP to use more than one SG to access a
specific SS7 end point, in a model that resembles an SS7 STP mated
pair. Typically, SS7 STPs are deployed in mated pairs, with traffic
load-shared between them. Other models are also possible, subject to
the limitations of the local SS7 network provisioning guidelines.
>From the perspective of the M3UA at an ASP, a particular SG is capable
of transferring traffic to an SS7 destination if an SCTP association
with at least one SGP of the SG is established, the SGP has received an
indication from the ASP M3UA that the ASP is actively handling traffic
for that destination, and the SG has not indicated that the destination
is inaccessible. When an ASP is configured to use multiple SGs for
transferring traffic to the SS7 network, the ASP must maintain
knowledge of the current capability of the SGs to handle traffic to
destinations of interest. This information is crucial to the overall
reliability of the service, for both active/standby and load-sharing
model, in the event of failures, recovery and maintenance activities.
The ASP M3UA may also use this information for congestion avoidance
purposes.
1.4.5 Flow Control
Local Management at an ASP may wish to stop traffic across an SCTP
association in order to temporarily remove the association from service
or to perform testing and maintenance activity. The function could
optionally be used to control the start of traffic on to a newly
available SCTP association.
1.4.6 Congestion Management
The M3UA Layer is informed of local and IP network congestion by means
of an implementation-dependent function (e.g., an implementation-
dependent indication from the SCTP of IP network congestion). When an
SG determines that the transport of SS7 messages to a Signalling Point
Management Cluster (SPMC) is encountering congestion, the SG should
trigger SS7 MTP3 Transfer Controlled management messages to originating
SS7 nodes. The triggering of SS7 MTP3 Management messages from an SG is
an implementation-dependent function.
At an ASP, congestion is indicated to local MTP3-Users by means of an
MTP-Status primitive indicating congestion, to invoke appropriate upper
layer responses, as per current MTP3 procedures.
The M3UA should indicate local ASP congestion to the SG with an SCON
message. When an SG receives an SCON message from an ASP it should
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trigger SS7 MTP3 Transfer Controlled management messages to concerned
SS7 destinations according to established MTP procedures.
1.4.7 SCTP Stream Mapping.
The M3UA at both the SG and ASP also supports the assignment of
signalling traffic into streams within an SCTP association. Traffic
that requires sequencing must be assigned to the same stream. To
accomplish this, MTP3-User traffic may be assigned to individual
streams based on, for example, the SLS value in the MTP3 Routing Label
or the ISUP CIC assignment, subject of course to the maximum number of
streams supported by the underlying SCTP association.
The use of SCTP streams within M3UA is recommended in order to minimize
transmission and buffering delays, therefore improving the overall
performance and reliability of the signalling elements. The
distribution of the MTP3 user messages over the various streams should
be done in such a way to minimize message mis-sequencing, as required
by the SS7 User Parts.
1.4.8 Client/Server Model
The SG takes on the role of server while the ASP is the client. ASPs
must initiate the SCTP association to the SG.
In the case of IPSP to IPSP communication, one side can be designated
as the initiator of the SCTP association and M3UA messaging.
The SCTP (and UDP/TCP) Registered User Port Number Assignment for M3UA
is 2905.
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1.5 Sample Configurations
1.5.1 Example 1: ISUP message transport
******** SS7 ***************** IP ********
* SEP *---------* SG *--------* ASP *
******** ***************** ********
+------+ +------+
| ISUP | (NIF) | ISUP |
+------+ +------+-+------+ +------+
| MTP3 | | MTP3 | | M3UA | | M3UA |
+------| +------+ +------+ +------+
| MTP2 | | MTP2 | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| L1 | | L1 | | IP | | IP |
+------+ +------+ +------+ +------+
|_______________| |______________|
SEP - SS7 Signalling End Point
SCTP - Stream Control Transmission Protocol
NIF - Nodal Inter-working Function
In this example, the SG provides an implementation-dependent nodal
inter-working function (NIF) that allows the MGC to exchange SS7
signalling messages with the SS7-based SEP. The NIF within the SG
serves as the interface within the SG between the MTP3 and M3UA. This
nodal inter-working function has no visible peer protocol with either
the MGC or SEP. It also provides network status information to one or
both sides of the network.
For internal SG modeling purposes, at the NIF level, SS7 signalling
messages that are destined to the MGC are received as MTP-TRANSFER
indication primitives from the MTP Level 3 upper layer interface and
are sent to the local M3UA-resident message distribution function for
ongoing routing to the final IP destination. MTP-TRANSFER primitives
received from the local M3UA network address translation and mapping
function are sent to the MTP Level 3 upper layer interface as MTP-
TRANSFER request primitives for on-going MTP Level 3 routing to an SS7
SEP. For the purposes of providing SS7 network status information the
NIF also delivers MTP-PAUSE, MTP-RESUME and MTP-STATUS indication
primitives received from the MTP Level 3 upper layer interface to the
local M3UA-resident management function.
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1.5.2 Example 2: SCCP Transport between IPSPs
******** IP ********
* IPSP * * IPSP *
******** ********
+------+ +------+
|SCCP- | |SCCP- |
| User | | User |
+------+ +------+
| SCCP | | SCCP |
+------+ +------+
| M3UA | | M3UA |
+------+ +------+
| SCTP | | SCTP |
+------+ +------+
| IP | | IP |
+------+ +------+
|________________|
This example shows an architecture where no Signalling Gateway is used.
In this example, SCCP messages are exchanged directly between two IP-
resident IPSPs with resident SCCP-User protocol instances, such as
RANAP or TCAP. SS7 network inter-working is not required, therefore
there is no MTP3 network management status information for the SCCP and
SCCP-User protocols to consider. Any MTP-PAUSE, -RESUME or -STATUS
indications from the M3UA to the SCCP should consider only the status
of the SCTP Association and underlying IP network.
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1.5.3 Example 3: SG resident SCCP layer, with remote ASP
******** SS7 ***************** IP ********
* SEP *---------* *--------* *
* or * * SG * * ASP *
* STP * * * * *
******** ***************** ********
+------+ +---------------+ +------+
| SCCP-| | SCCP | | SCCP-|
| User | +---------------+ | User |
+------+ | _____ | +------+
| SCCP | | | | | | SCCP |
+------+ +------+-+------+ +------+
| MTP3 | | MTP3 | | M3UA | | M3UA |
+------| +------+ +------+ +------+
| MTP2 | | MTP2 | | SCTP | | SCTP |
+------+ +------+ +------+ +------+
| L1 | | L1 | | IP | | IP |
+------+ +------+ +------+ +------+
|_______________| |______________|
STP - SS7 Signalling Transfer Point
In this example, the SG contains an instance of the SS7 SCCP protocol
layer that may, for example, perform the SCCP Global Title Translation
(GTT) function for messages logically addressed to the SG SCCP. If the
result of a GTT for an SCCP message yields an SS7 DPC or DPC/SSN
address result of an SCCP peer located in the IP domain, the resulting
MTP-TRANSFER request primitive is sent to the local M3UA-resident
network address translation and mapping function for ongoing routing to
the final IP destination.
Similarly, the SCCP instance in an SG can perform the SCCP GTT service
for messages logically addressed to it from SCCP peers in the IP
domain. In this case, MTP-TRANSFER messages are sent from the local
M3UA-resident network address translation and mapping function to the
SCCP for GTT. If the result of the GTT yields the address of an SCCP
peer in the SS7 network then the resulting MTP-TRANSFER request is
given to the MTP3 for delivery to an SS7-resident node.
It is possible that the above SCCP GTT at the SG could yield the
address of an SCCP peer in the IP domain and the resulting MTP-TRANSFER
primitive would be sent back to the M3UA for delivery to an IP
destination.
For internal SG modeling purposes, this may be accomplished with the
use of an implementation-dependent nodal inter-working function within
the SG that effectively sits below the SCCP and routes MTP-TRANSFER
messages to/from both the MTP3 and the M3UA, based on the SS7 DPC or
DPC/SSN
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address information. This nodal inter-working function has no visible
peer protocol with either the ASP or SEP.
Note that the services and interface provided by the M3UA are the same
as in Example 1 and the functions taking place in the SCCP entity are
transparent to M3UA. The SCCP protocol functions are not reproduced in
the M3UA protocol.
1.6 Definition of M3UA Boundaries
1.6.1 Definition of the boundary between M3UA and an MTP3-User.
>From ITU Q.701 [14]:
MTP-TRANSFER request
MTP-TRANSFER indication
MTP-PAUSE indication
MTP-RESUME indication
MTP-STATUS indication
1.6.2 Definition of the boundary between M3UA and SCTP
The upper layer primitives provided by the SCTP are provided in [13]
1.6.3 Definition of the Boundary between M3UA and Layer Management
M-SCTP ESTABLISH request
Direction: LM -> M3UA
Purpose: LM requests ASP to establish an SCTP association with an SG
or IPSP.
M-STCP ESTABLISH confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has established an SCTP
association with an SG or IPSP.
M-SCTP ESTABLISH indication
Direction: M3UA -> LM
Purpose: SG or IPSP informs LM that an ASP has established an SCTP
association.
M-SCTP RELEASE request
Direction: LM -> M3UA
Purpose: LM requests ASP to release an SCTP association with SG or
IPSP.
M-SCTP RELEASE confirm
Direction: M3UA -> LM
Purpose: ASP confirms to LM that it has released SCTP association
with SG.
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M-SCTP RELEASE indication
Direction: M3UA -> LM
Purpose: SG or IPSP informs LM that ASP has released an SCTP
association.
M-SCTP STATUS request
Direction: LM -> M3UA
Purpose: LM requests M3UA to report status of SCTP association.
M-SCTP STATUS indication
Direction: M3UA -> LM
Purpose: M3UA reports status of SCTP association.
M-ASP STATUS request
Direction: LM -> M3UA
Purpose: LM requests SG or IPSP to report status of remote ASP.
M-ASP STATUS indication
Direction: M3UA -> LM
Purpose: SG or IPSP reports status of remote ASP.
M-AS-STATUS request
Direction: LM -> M3UA
Purpose: LM requests SG or IPSP to report status of AS.
M-AS-STATUS indication
Direction: M3UA -> LM
Purpose: SG or IPSP reports status of AS.
M-NOTIFY indication
Direction: M3UA -> LM
Purpose: ASP reports that it has received a NOTIFY message
from its peer.
M-ERROR indication
Direction: M3UA -> LM
Purpose: ASP, SG or IPSP reports that it has received an ERROR
message from its peer.
M-ASP-DOWN request
Direction: LM -> M3UA
Purpose: LM requests ASP to stop its operation and send an ASP-DOWN
message to the SG.
M-ASP-UP request
Direction: LM -> M3UA
Purpose: LM requests ASP to start its operation and send an ASP-UP
message to the SG.
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M-ASP-INACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to stop data transfer and send an ASP-
Inactive message to the SG.
M-ASP-ACTIVE request
Direction: LM -> M3UA
Purpose: LM requests ASP to start data transfer and send an ASP-
Active message to the SG.
2.0 Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD
NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when they appear
in this document, are to be interpreted as described in [RFC2119].
3.0 M3UA Protocol Elements
The general M3UA message format includes a Common Message Header
followed by zero or more parameters as defined by the Message Type.
For forward compatibility, all Message Types may have attached
parameters even if none are specified in this version.
3.1 Common Message Header
The protocol messages for MTP3-User Adaptation require a message
structure that contains a version, message type, message length, and
message contents. This message header is common among all signalling
protocol adaptation layers:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Reserved | Message Class | Message Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ /
All fields in an M3UA message MUST be transmitted in the network byte
order, unless otherwise stated.
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M3UA Protocol Version: 8 bits (unsigned integer)
The version field contains the version of the M3UA adaptation layer.
The supported versions are:
1 Release 1.0
Message Class: 8 bits (unsigned integer)
The following list contains the Message Type Classes for the defined
messages.
0 Management (MGMT) Message
1 Transfer Messages
2 SS7 Signalling Network Management (SSNM) Messages
3 ASP State Maintenance (ASPSM) Messages
4 ASP Traffic Maintenance (ASPTM) Messages
5 to 255 Reserved
Message Type: 8 bits (unsigned integer)
The following list contains the message types for the defined
messages.
Management (MGMT) Message
0 Error (ERR)
1 Notify (NTFY)
2 to 255 Reserved for Management Messages
Transfer Messages
0 Reserved
1 Payload Data (DATA)
2 to 255 Reserved for Transfer Messages
SS7 Signalling Network Management (SSNM) Messages
0 Reserved
1 Destination Unavailable (DUNA)
2 Destination Available (DAVA)
3 Destination State Audit (DAUD)
4 SS7 Network Congestion State (SCON)
5 Destination User Part Unavailable (DUPU)
6 to 255 Reserved for SSNM Messages
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ASP State Maintenance (ASPSM) Messages
0 Reserved
1 ASP Up (UP)
2 ASP Down (DOWN)
3 Heartbeat (BEAT)
4 ASP Up Ack (UP ACK)
5 ASP Down Ack (DOWN ACK)
6 Heatbeat Ack (BEAT ACK)
7 to 255 Reserved for ASPSM Messages
ASP Traffic Maintenance (ASPTM) Messages
0 Reserved
1 ASP Active (ACTIVE)
2 ASP Inactive (INACTIVE)
3 ASP Active Ack (ACTIVE ACK)
4 ASP Inactive Ack (INACTIVE ACK)
5 to 255 Reserved for ASPTM Messages
Reserved: 8 bits
Should be set to all '0's and ignored by the receiver.
Message Length: 32-bits (unsigned integer)
The Message Length defines the length of the message in octets,
including the header.
3.2 Variable-Length Parameter Format
M3UA messages consist of a Common Header followed by zero or more
parameters, as defined by the message type. The variable-length
parameters contained in a message are defined in a Tag-Length-Value
format as shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter Tag | Parameter Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Parameter Value /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Parameter Tag: 16 bits (unsigned integer)
Tag field is a 16-bit identifier of the type of parameter. It takes
a value of 0 to 65534.
The value of 65535 is reserved for IETF-defined extensions. Values
other than those defined in specific parameter description are
reserved for use by the IETF.
Parameter Length: 16 bits (unsigned integer)
The Parameter Length field contains the size of the parameter in
bytes, including the Parameter Tag, Parameter Length, and Parameter
Value fields. The Parameter Length does not include any padding
bytes.
Parameter Value: variable-length.
The Parameter Value field contains the actual information to be
transferred in the parameter.
The total length of a parameter (including Tag, Parameter Length and
Value fields) MUST be a multiple of 4 bytes. If the length of the
parameter is not a multiple of 4 bytes, the sender pads the
Parameter at the end (i.e., after the Parameter Value field) with
all zero bytes. The length of the padding is NOT included in the
parameter length field. A sender should NEVER pad with more than 3
bytes. The receiver MUST ignore the padding bytes.
3.3 Transfer Messages
The following section describes the Transfer messages and parameter
contents.
3.3.1 Payload Data Message (DATA)
The Data message contains the SS7 MTP3-User protocol data, which is an
MTP-TRANSFER primitive, including the complete MTP3 Routing Label. The
Data message contains the following variable length parameters:
Network Appearance Optional
Protocol Data Mandatory
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The following format MUST be used for the Data Message:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bits (unsigned integer)
The optional Network Appearance parameter identifies the SS7 network
context for the message, for the purposes of logically separating
the signalling traffic between the SG and the Application Server
Process over a common SCTP Association. An example is where an SG
is logically partitioned to appear as an element in four different
national SS7 networks.
In a Data message, the Network Appearance implicitly defines the SS7
Point Code format used, the SS7 Network Indicator value, and the
MTP3/MTP3-User protocol type/variant/version used within the SS7
network partition. Where an SG operates in the context of a single
SS7 network, or individual SCTP associations are dedicated to each
SS7 network context, or the Network Indicator in the SIO of the MTP-
Transfer primitive is sufficient, the Network Appearance parameter
is not required.
The Network Appearance parameter value is of local significance
only, coordinated between the SG and ASP.
Where the optional Network Appearance parameter is present, it must
be the first parameter in the message as it defines the format of
the Protocol Data field.
Protocol Data: variable length
The Protocol Data field contains the SS7 MTP3-User application
message, including the complete Routing Label. The Protocol Data
parameter contains the following fields:
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Service Information Octet. Includes:
Service Indicator,
Network Indicator,
and Spare/Priority codes
MTP Routing Label. Includes:
Destination Point Code,
Originating Point Code,
And Signalling Link Selection Code (SLS)
User Protocol Data. Includes MTP3-User protocol elements:
ISUP, SCCP, or TUP parameters
The format is as defined in the relevant MTP standards for the SS7
protocol being transported. The format is either implicitly known
or identified by the Network Appearance parameter.
For the ANSI protocol example, the Protocol Data field format is
shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIO | DPC Network | DPC Cluster | DPC Member |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPC Network | OPC Cluster | OPC Member | SLS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB---------------------------------------------------------LSB|
For the ITU international protocol example, the Protocol Data field
is shown below.
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Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SIO | DPC | DPC | DPC | OPC | OPC |
| |Zone | Region | SP |Zone | Region |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|*| OPC | SLS | |
|*| SP | | |
+-+-+-+-+-+-+-+-+ +
\ \
/ Protocol Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB---------------------------------------------------------LSB|
* LSB of OPC Region
3.4 SS7 Signalling Network Management (SSNM) Messages
3.4.1 Destination Unavailable (DUNA)
The DUNA message is sent from the SG to all concerned ASPs to indicate
that the SG has determined that one or more SS7 destinations are
unreachable. It is also sent in response to a message from the ASP to
an unreachable SS7 destination. The MTP3-User at the ASP is expected
to stop traffic to the affected destination through the SG initiating
the DUNA as per the defined MTP3-User procedures.
The DUNA message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
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The format for DUNA Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length =8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 5 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Affected DPC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Network Appearance: 32-bit unsigned integer
The optional Network Appearance parameter identifies the SS7 network
context for the message, for the purposes of logically separating
the signalling traffic between the SG and the Application Server
Process over a common SCTP Association. An example is where an SG
is logically partitioned to appear as an element in four different
national SS7 networks.
In an SSNM message, the Network Appearance parameter defines the
format of the Affected DPC(s) in the Affected Destination parameter.
The DPC point code length (e.g., 14-, 16-, or 24-bit) and sub-field
definitions (e.g., ANSI 24-bit network/cluster/member, ITU-
international 14-bit zone/region/signal_point, many national field
variants, ...) are fixed within a particular Network Appearance.
Where an SG operates in the context of a single SS7 network, or
individual SCTP associations are dedicated to each SS7 network
context, the Network Appearance parameter is not required and the
format of the Affected DPC(s) is understood implicitly.
The format of the Network Appearance parameter is an integer, the
values used are of local significance only, coordinated between the
SG and ASP.
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Where the optional Network Appearance parameter is present, it must
be the first parameter in the message as it defines the format of
the Affected DPCs in the Affected Destination parameter.
Affected Destinations: n x 32-bits
The Affected Destinations parameter contains up to sixteen Affected
Destination Point Code fields, each a three-octet parameter to allow
for 14-, 16- and 24-bit binary formatted SS7 Point Codes. Affected
Point Codes that are less than 24-bits, are padded on the left to
the 24-bit boundary. The encoding is shown below for ANSI and ITU
Point Code examples.
ANSI 24-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask | Network | Cluster | Member |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB-----------------------------------------LSB|
ITU 14-bit Point Code:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mask |0 0 0 0 0 0 0 0 0 0|Zone | Region | SP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|MSB--------------------LSB|
It is optional to send an Affected Destinations parameter with more
than one Affected DPC but it is mandatory to receive and process it.
All the Affected DPCs included must be within the same Network
Appearance. Including multiple Affected DPCs may be useful when
reception of an MTP3 management message or a linkset event
simultaneously affects the availability status of a list of
destinations at an SG.
Mask: 8-bit unsigned integer
The Mask field associated with each Affected DPC in the Affected
Destinations parameter, used to identify a contiguous range of
Affected Destination Point Codes, independent of the point code
format. Identifying a contiguous range of Affected DPCs may be
useful when reception of an MTP3 management message or a linkset
event simultaneously affects the availability status of a series of
destinations at an SG. For example, if all DPCs in an ANSI cluster
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Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
are determined to be unavailable due to local linkset
unavailability, the DUNA could identify potentially 256 Affected
DPCs in a single Affected DPC field.
The Mask parameter represents a bit mask that can be applied to the
related Affected DPC field. The bit mask identifies how many bits
of the Affected DPC field are significant and which are effectively
"wildcarded". For example, a mask of "8" indicates that the last
eight bits of the DPC is "wildcarded". For an ANSI 24-bit Affected
DPC, this is equivalent to signalling that all DPCs in an ANSI
Cluster are unavailable. A mask of "3" indicates that the last
three bits of the DPC is "wildcarded". For a 14-bit ITU Affected
DPC, this is equivalent to signaling that an ITU Region is
unavailable. A mask value equal to the number of bits in the DPC
indicates that the entire network appearance is affected - this is
used to indicate network isolation to the ASP.
Info String: variable length
The optional INFO String parameter can carry any meaningful 8-BIT
ASCII character string along with the message. Length of the INFO
String parameter is from 0 to 255 characters. No procedures are
presently identified for its use but the INFO String may be used by
Operators to identify in text form the location reflected by the
Affected DPC for debugging purposes.
3.4.2 Destination Available (DAVA)
The DAVA message is sent from the SG to all concerned ASPs to indicate
that the SG has determined that one or more SS7 destinations are now
reachable, or in response to a DAUD message if appropriate. The ASP
MTP3-User protocol is expected to resume traffic to the affected
destination through the SG initiating the DUNA.
The DAVA message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
The format and description of the Network Appearance, Affected
Destinations and Info String parameters is the same as for the DUNA
message (See Section 3.4.1.)
3.4.3 Destination State Audit (DAUD)
The DAUD message can be sent from the ASP to the SG to audit the
availability/congestion state of SS7 routes to one or more affected
destinations.
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The DAUD message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
The format and description of DAUD Message parameters is the same as
for the DUNA message (See Section 3.4.1.)
3.4.4 SS7 Network Congestion (SCON)
The SCON message can be sent from the SG to all concerned ASPs to
indicate the congestion level in the SS7 network to one or more
destinations or in response to a DAUD message, if appropriate. For
some MTP protocol variants (e.g., ANSI MTP) the SCON may be sent when
the SS7 congestion level changes. The SCON message is also sent from
the M3UA of an ASP to the SG or IPSP indicating that the M3UA or the
ASP is congested.
The SCON message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
Info String Optional
The format for SCON Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length =8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 5 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cong. Level 1 | Affected DPC 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ ... /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cong. Level n | Affected DPC n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The Affected Destinations parameter differs from the Affected
Destinations parameter in the DUNA, DAVA, and DAUD in that a Congestion
Level field is included instead of a Mask field. Therefore ranges of
congested Affected DPCs cannot be signaled, but this is consistent with
operation in the SS7 network.
The format and description of the Network Appearance and Info String
parameters is the same as for the DUNA message (See Section 3.3.2.1.)
Congestion Level field: 8-bits (unsigned integer)
The Congestion Level field, associated with each Affected DPC in the
Affected Destinations parameter, contains one of the following
values:
0 No Congestion or Undefined
1 Congestion Level 1
2 Congestion Level 2
3 Congestion Level 3
The congestion levels are as defined in the national congestion
method in the appropriate MTP recommendation [14,15]. For MTP
congestion methods that do not employ congestion levels (e.g., the
ITU international method, the parameter is always "Undefined".
When an SCON is received at the SG, a TFC message is generated into the
SS7 network.
Editors Note: May need a different message type (ASPCON) and specify
more detailed procedures at the SG or IPSP upon reception.
3.4.5 Destination User Part Unavailable (DUPU)
The DUPU message is used by an SG to inform an ASP that a remote peer
MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is unavailable.
The DUPU message contains the following parameters:
Network Appearance Optional
Affected Destinations Mandatory
User/Cause Mandatory
Info String Optional
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The format for DUPU Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Appearance* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 5 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Affected DPC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 9 | Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cause | User |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
User/Cause: 32-bits
The Unavailability Cause and MTP3-User Identity fields, associated
with the Affected DPC in the Affected Destinations parameter, are
encoded as follows:
Unavailability Cause field: 16-bits (unsigned integer)
The Unavailability Cause parameter provides the reason for the
unavailability of the MTP3-User. The valid values for the
Unavailability Cause parameter are shown in the following table.
The values agree with those provided in the SS7 MTP3 User Part
Unavailable message. Depending on the MTP3 protocol used in the
network appearance, additional values may be used - the
specification of the relevant MTP3 protocol variant/version
recommendation is definitive.
0 Unknown
1 Unequipped Remote User
2 Inaccessible Remote User
MTP3-User Identity field: 16-bits (unsigned integer)
The MTP3-User Identity describes the specific MTP3-User that is
unavailable (e.g., ISUP, SCCP, ...). Some of the valid values for
the MTP3-User Identity are shown below. The values agree with those
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Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
provided in the SS7 MTP3 User Part Unavailable message and Service
Indicator. Depending on the MTP3 protocol used in the network
appearance, additional values may be used - the specification of the
relevant MTP3 protocol variant/version recommendation is definitive.
0 to 2 Reserved
3 SCCP
4 TUP
5 ISUP
6 to 8 Reserved
9 Broadband ISUP
10 Satellite ISUP
The Affected Destinations parameter differs from the Affected
Destinations parameter in the DUNA, DAVA, and DAUD in that a Reserved
field is included instead of a Mask field. Therefore, ranges of
congested Affected DPCs cannot be signaled, but this is consistent with
operation in the SS7 network. The Affected Destinations parameter in
the DUPU message can only contain one Affected DPC.
The format and description of the Network Appearance and Info String
parameters is the same as for the DUNA message (See Section 3.4.1.).
3.5 Application Server Process Maintenance (ASPM) Messages
3.5.1 ASP Up (ASPUP)
The ASP UP (ASPUP) message is used to indicate to a remote M3UA peer
that the Adaptation layer is ready to receive SSNM or ASPM management
messages for all Routing Keys that the ASP is configured to serve.
The ASPUP message contains the following parameters:
Adaptation Layer Identifier Optional
INFO String Optional
The format for ASPUP Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adaptation Layer Identifier* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.3.2.1.)
Adaptation Layer Identifier: 32-bits
The optional Adaptation Layer Identifier (ALI) is a string that
identifies the adaptation layer. This string must be set to "M3UA"
which results in a length of 8. The ALI would normally only be used in
the initial ASP Up message across a new SCTP association to ensure both
peers are assuming the same adaptation layer protocol.
Editors Note: Info in SCTP (Payload Identifier) could be used - is
there any need for ALI anymore?
3.5.2 ASP Up Ack
The ASP UP Ack message is used to acknowledge an ASP-Up message
received from a remote M3UA peer.
The ASPUP Ack message contains the following parameters:
Adaptation Layer Identifier (optional)
INFO String (optional)
The format for ASPUP Ack Message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =2 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Adaptation Layer Identifier* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.3.2.1.)
The format and description of the optional Adaptation Layer Identifier
(ALI) parameter is the same as for the ASP-UP message. (See Section
3.4.1)
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3.5.3 ASP Down (ASPDN)
The ASP Down (ASPDN) message is used to indicate to a remote M3UA peer
that the adaptation layer is not ready to receive traffic or
maintenance messages.
The ASPDN message contains the following parameters:
Reason Mandatory
INFO String Optional
The format for the ASPDN message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.3.2.1.)
Reason: 32-bit (unsigned integer)
The Reason parameter indicates the reason that the remote M3UA
adaptation layer is unavailable. The valid values for Reason are
shown in the following table.
0 Unspecified
1 User Unavailable
2 Management Blocking
3.5.4 ASP Down Ack
The ASP Down Ack message is used to acknowledge an ASP-Down message
received from a remote M3UA peer.
The ASP Down Ack message contains the following parameters:
Reason Mandatory
INFO String Optional
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The format for the ASPDN Ack message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reason |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.3.2.1.)
The format of the Reason parameter is the same as for the ASP-Down
message. (See Section 3.4.3)
3.5.5 ASP Active (ASPAC)
The ASPAC message is sent by an ASP to indicate to a remote M3UA peer
that it is Active and ready to process signalling traffic for a
particular Application Server. The ASPAC affects only the ASP state
for the routing keys identified by the Routing Contexts, if present.
The ASPAC message contains the following parameters:
Type Mandatory
Routing Context Optional
INFO String Optional
The format for the ASPAC message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag =6 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Type: 32-bit (unsigned integer)
The Type parameter identifies the traffic mode of operation of the
ASP within an AS. The valid values for Type are shown in the
following table.
1 Over-ride
2 Load-share
3 Over-ride (Standby)
4 Loadshare (Standby)
Within a particular Routing Context, Over-ride and Loadshare Types
cannot be mixed. The Over-ride value indicates that the ASP is
operating in Over-ride mode, and the ASP wishes to take over all
traffic in an Application Server (i.e., primary/back-up operation),
over-riding any currently active ASP in the AS. In Load-share mode,
the ASP wishes to share in the traffic distribution with any other
currently active ASPs. The Standby versions of the Over-ride and
Loadshare Types indicate that the ASP is declaring itself ready to
accept traffic but leaves it up to the sender as to when the traffic
is started. Over-ride (Standby) indicates that the traffic sender
continues to use the currently active ASP until it can no longer
send/receive traffic (i.e., the currently active ASP transitions to
Down or Inactive). At this point the sender may immediately move
the ASP to Active and commence traffic. Loadshare (Standby) is
similar - the sender continues to loadshare to the current ASPs
until there it is determined that there is insufficient resources in
the Loadshare group. When there is insufficient ASPs, the sender
may immediately move the ASP to Active.
Routing Context:
The optional Routing Context parameter contains (a list of) 4-byte
unsigned integers indexing the Application Server traffic that the
sending ASP is configured/registered to receive.
There is one-to-one relationship between an index entry and an SG
Routing Key or AS Name. Because an AS can only appear in one
Network Appearance, the Network Appearance parameter is not required
in the ASPAC message.
An Application Server Process may be configured to process traffic
for more than one logical Application Server. From the perspective
of an ASP, a Routing Context defines a range of signalling traffic
that the ASP is currently configured to receive from the SG. For
example, an ASP could be configured to support call processing for
multiple ranges of PSTN trunks and therefore receive related
signalling traffic, identified by separate SS7 DPC/OPC/CIC_ranges.
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The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.3.2.1.)
3.5.6 ASP Active Ack
The ASPAC Ack message is used to acknowledge an ASP-Active message
received from a remote M3UA peer.
The ASPAC Ack message contains the following parameters:
Type Mandatory
Routing Context Optional
INFO String Optional
The format for the ASPAC Ack message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 6 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.3.2.1.)
The format of the Type and Routing Context parameters is the same as
for the ASP-Active message. (See Section 3.4.5).
3.5.7 ASP Inactive (ASPIA)
The ASPIA message is sent by an ASP to indicate to a remote M3UA peer
that it is no longer processing signalling traffic within a particular
Application Server. The ASPIA affects only the ASP state in the
Routing Keys identified by the Routing Contexts, if present.
Sidebottom et al [Page 44]
Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
The ASPIA message contains the following parameters:
Type Mandatory
Routing Context Optional
INFO String Optional
The format for the ASPIA message parameters is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 6 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: 32-bit (unsigned integer)
The Type parameter identifies the traffic mode of operation of the
ASP within an AS. The valid values for Type are shown in the
following table.
1 Over-ride
2 Load-share
Within a particular Routing Context, only one Type can be used. The
Over-ride value indicates that the ASP is operating in Over-ride
mode, and will no longer handle traffic within an Application Server
(i.e., it is now a backup in a primary/back-up arrangement). The
Load-share value indicates that the ASP is operating in Load-share
mode and will no longer share in the traffic distribution with any
other currently active ASPs.
A node that receives an ASPIA with an incorrect Type for a
particular routing Context will respond with an Error Message
(Cause: Invalid Traffic Handling Mode.
The format and description of the optional Routing Context and Info
String parameters is the same as for the ASPAC message (See Section
2.3.3.3.)
Sidebottom et al [Page 45]
Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
3.5.8 ASP Inactive Ack
The ASPIA Ack message is used to acknowledge an ASP-Inactive message
received from a remote M3UA peer.
The ASPIA Ack message contains the following parameters:
Type Mandatory
Routing Context Optional
INFO String Optional
The format for the ASPIA Ack message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 6 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The format and description of the optional Info String parameter is the
same as for the DUNA message (See Section 3.3.2.1.)
The format of the Type and Routing Context parameters is the same as
for the ASP-Inactive message. (See Section 3.4.7).
3.5.9 Heartbeat (BEAT)
The Heartbeat message is optionally used to ensure that the M3UA peers
are still available to each other. It is recommended for use when the
M3UA runs over a transport layer other than the SCTP, which has its own
heartbeat.
The BEAT message contains the following parameters:
Heatbeat Data Optional
Sidebottom et al [Page 46]
Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
The format for the BEAT message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 8 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Heartbeat Data * /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Heartbeat Data parameter contents are defined by the sending node.
The Heartbeat Data could include, for example, a Heartbeat Sequence
Number and/or Timestamp. The receiver of a Heartbeat message does not
process this field as it is only of significance to the sender. The
receiver MUST respond with a BEAT-Ack message.
3.5.10 Heartbeat Ack (Beat-Ack)
The Heartbeat Ack message is sent in response to a received Heartbeat
message. It includes all the parameters of the received Heartbeat
message, without any change.
3.6 Management Messages
3.6.1 Error (ERR)
The Error message is used to notify a peer of an error event associated
with an incoming message. For example, the message type might be
unexpected given the current state, or a parameter value might be
invalid.
The ERR message contains the following parameters:
Error Code Mandatory
Diagnostic Information Optional
The format for the ERR message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 7 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Diagnostic Information* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
Error Code: 32-bits (unsigned integer)
The Error Code parameter indicates the reason for the Error Message.
The Error parameter value can be one of the following values:
1 Invalid Version
2 Invalid Network Appearance
3 Invalid Adaptation Layer Identifier
4 Invalid Message Type
5 Invalid Traffic Handling Mode
6 Unexpected Message Type
7 Protocol Error
8 Invalid Routing Context
Diagnostic Information: variable length
When included, the optional Diagnostic information can be any
information germane to the error condition, to assist in
identification of the error condition. In the case of an Invalid
Network Appearance, Adaptation Layer Identifier, Traffic Handling
Mode or Invalid Routing Context, the Diagnostic information includes
the received parameter. In the other cases, the Diagnostic
information may be the first 40 bytes of the offending message.
In the case of an Invalid Version Error Code, the Common Header
contains the supported Version.
Error messages are not generated in response to other Error messages.
3.6.2 Notify (NTFY)
The Notify message used to provide an autonomous indication of M3UA
events to an M3UA peer.
The NTFY message contains the following parameters:
Status Type Mandatory
Status Identification Mandatory
Routing Context Optional
INFO String Optional
Sidebottom et al [Page 48]
Internet Draft SS7 MTP3-User Adaptation Layer Sept 2000
The format for the NTFY message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status Type | Status Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 6 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ Routing Context* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ INFO String* /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Status Type: 16-bits (unsigned integer)
The Status Type parameter identifies the type of the Notify message.
Following are the valid Status Type values:
1 Application Server State Change (AS-StateChange)
2 Other
Status Information: 16-bits (unsigned integer)
The Status Information parameter contains more detailed information
for the notification, based on the value of the Status Type.
If the Status Type is AS_State_Change the following Status
Information values are used:
1 reserved
2 Application Server Inactive (AS-Inactive)
3 |
Documentation