Manpage of MG

MG

Section: OpenSS7 STREAMS Channels Devices (4)
Updated: 2008-10-31
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NAME

mg, MG - Media Gateway (MG)

SYNOPSIS

#include <ss7/mgi.h>
#include <ss7/mgi_ioctl.h>

int mg_stream = open(device, flags);

DESCRIPTION

MG
is an implementation of a local switching matrix control for devices conforming to the mxi(7) and chi(7) interfaces. MG provides for the control of the switch matrix.

MG is implemented as a STREAMS(4) multiplexing driver. mx(4) or ch(4) Streams are linked under the MG multiplexing driver using the I_LINK(7) or I_PLINK(7) commands of streamio(7), to provide multiplex or channel services to MG. Once linked, the Streams must be configured using mgi_ioctl(4).

MG provides the following Stream types that are directly compatible with the Stream types provided by other MG(4) drivers. To select one of these Stream types, the device argument to the open(2) call can be one of the following:

/dev/mg: This device provides the MG protocol service interface using the MG-primitives of the Media Gateway Interface descrined in mgi(7), as interpreted for use with local switching drivers as descibed in mgi_mg(7). This interface is suitable both for use with other SS7 modules and drivers, as well as with the cframe(3) library using the OpenSwitch call framework.

USAGE

The MG driver is the switching workhorse of the OpenSS7 STREAMS Channels package. mgi(7) Streams can be opened on the upper multiplex. Both mxi(7) and chi(7) Streams can be linked on the lower multiplex. Any channel of any Stream, whether upper or lower, can be connected through the matrix to any other channel.

The MG driver can perform simple or complex conversion functions (e.g. mu-law to a-law), digital padding, echo cancellation, compression/decompression, rate adaption (e.g., 8-bit A-law to 5-bit GSM), that do or do not cause flow control considerations. Preestablished or canned tones and announcments are supported by the driver. Dynamic announcements need to be provided by an external module (using a Stream on the upper or lower multiplex) or in hardware.

The MG driver supports single-rate and multi-rate channels. It also supports multi-rate conversion and multiple audio channels per connection leg. The purpose of the MG driver is to perform both simple circuit switching and do it very fast, or to provide complex conversion and conferencing as efficiently as possible.

For simply matrix connections, the MG driver can be modelled as a hardware Time-Space-Time switch, only switching is performed primarily in software. Other, more specialized, mgi(7) drivers, such as mgcp(4), are intended on providing device control. The MG driver is a pseudo-device driver and performs switching functions in software.

Configuration

At boot time, or when a new span or circuit is brough into service and is to be switched through the MG software switching matrix, a management program opens a device or pseudo-device driver to obtain a Stream representing the new channel or span and links the Stream beneath the MG multiplexing driver. Input-output controls are then used to assign the channel or span (and timeslots within the span) to channel identification numbers within the switching matrix. These channel identification numbers and the mapping to specific hardware should be maintained in configuration files.

For example, when a T1 span is put into service on a v401p(4) card, the management program opens a Stream on the v401p(4) mxi(7) device that represents a T1 span, attaches the Stream to the T1 span, and then links the Stream beneath the MG driver. During linking, the MG driver issues a MX_INFO_REQ(7) or CH_INFO_REQ(7) primitive downstream to interrogate the Stream as to channel characteristics. After linking, the management program uses a configuration table to determine the channel number assignments for the card an T1 span selected. An input-output control is issued to the MG driver with the multiplex index of the linked span, and the channel number assignments for the span. The MG driver provides the ability for management programs to determine the lower multiplex identifier that is associated with any channel or channel group. This allows the management program to perform a I_PLINK(7) operation and close the Stream: it can then later discover the multiplex identifier from the channel assignment (contained in the configuration file) with an input-output control to the MG driver, so that it knows the multiplex identifier to use to remove the channel or channel group from service with a I_PUNLINK(7) operation.

NOTICES

Unlike other OpenSS7 protocol modules and drivers providing transport communications services, MG does not provide a sockets(3) interface. This is because the special needs of switch matrix control are divorced from the sockets paradigm.

IOCTLS

All interaces support a set of management IO controls using ioctl(2) and I_STR commands to the streamio(7) system calls on the mg_stream file descriptor. These management controls are documented in mg_ioctl(4).