| High-Level Data Link Control (HDLC)Description: OpenSS7 Project Manual Pages ISDN StackHDLCSection: OpenSS7 SS7 Stack Devices (4)Updated: 2008-10-31 Index Return to Main Contents NAMEhdlc - High-Level Data Link ControlSYNOPSIS#include <sys/stropts.h>
DESCRIPTIONHDLC
HDLC is implemented as a pushable STREAMS(4) module. The HDLC mdoule can be pushed over a stream conforming to the Channel Interface (CHI) as described in chi(7). The HDLC module provides HDLC access to the bit stream from the channel provided by the chi(7) Stream below it, by performing HDLC functions on the raw bit stream. The upper interface provided by the HDLC module is the Communications Device Interface (CDI) as described in cdi(7). HDLC streams can be linked under dl(4) drivers lapd(4), lapb(4), lapf(4), gr303(4), v52(4), using the I_LINK or I_PLINK commands of streamio(7), to provide a complete Data Link that can then be linked under an isdn(4), fr(4), idlc(4), dpnss(4), iua(4), gr303ua(4), v5ua(4) or dua(4) driver using the I_LINK or I_PLINK commands of streamio(7), to provide data link services to the Layer 3 protocol. This is normally performed, as required, by the ISDN Configuration Daemon, isdnconfd(8). NOTICESHDLC has been implemented as a pushable module to ease the development of ISDN Data Link drivers for various cards. All that is required is for the card to provide a Channel Interface (CHI), chi(7), and push the hdlc(4) and dl(4) modules to provide a complete and compliant Q.921[3] Data Link. HDLC is implemented internally as a soft-HDLC using host-based table lookups. While this is fairly efficient, devices that are capable of performing this function in hardware should provide the Communications Device Interface (CDI), cdi(7), directly. An example of a device that does not include HDLC is the x400p(4) driver. An example of one that does, is the acb56(4) driver. NOTICESHDLC modules are not normally pushed or accessed directly by user-level programs. The HDLC module is used directly by some test and monitoring programs. IOCTLSThe HDLC module responds to Local Management Interface (LMI), lmi_ioctl(4), IO controls as interpreted for HDLC operation as described in hdlc_ioctl(4). FILES<ss7/cdi.h>, <ss7/cdi_hdlc.h>, <ss7/hdlc_ioctl.h>. MODULESSEE ALSOISDN(4), cdi(7), dl(4), hdlc_ioctl(4), isdnconfd(8). VERSIONSThe HDLC module conforms to the CDI Specification, Revision 1.0[4]. The HDLC module does not appear until strss7 release 0.8.4. REFERENCES
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