SS7 Stack Overview

The SS7 Stack has been the principle focus of the OpenSS7 project for some time. The SS7 stack components provide the various protocol levels of the SS7 protocol. These include MTP Level 2, MTP Level 3, SCCP, TCAP, ISUP and BICC.

(Click on any of the components below for an overview of the component.)

As illustrated above, the OpenSS7 SS7 Stack provides all of the necessary components of the Signalling System No. 7 (SS7) protocol. Protocol components are implemented as SVR 4.2 STREAMS drivers and modules. The protocol components are as follows:

Signalling Link Device Drivers
Message Transfer Part Level 3 (MTP3)
Integrated Services Digital Network (ISDN) User Part (ISUP)
Signalling Connection Control Part (SCCP)
Transaction Capabilities Application Part (TCAP)
Base Station System (BSS) Application Part (BSSAP)
Bearer Independent Call Control (BICC)
Applications
SS7 Stack Manager

Status: The status of the varions SS7 stack components can be found here.
Designs: Designs for the varions SS7 stack components can be found here.
Conformance: Conformance of the varions SS7 stack components can be found here.
Performance: Performance of the varions SS7 stack components can be found here.
References: References for the varions SS7 stack components can be found here.
Man Pages: Manual Pages for the varions SS7 stack components can be found here.

Signalling Link Device Drivers

Signalling Link Device Drivers are provided for a number of hardware devices and a low-level driver framework exists for the rapid development of new device drivers.

Signalling Link Device drivers can implement a number of interfaces that can have pushable modules inserted to provide conforming SS7 operation without the need for significant retesting of the new device driver. Any of these levels can be implemented in the device driver and then the missing modules pushed on top to form a compliant signalling link device driver. These levels are as follows:

The Channel Interface (CHI) documented in chi(7), provides direct access to a 56kbps, 64kbps, 1.536Mbps, or 2.048Mbps channel. Octets received on the channel are delivered directly to the stream and octets written to the stream are delivered directly to the transmission channel. This is the easiest way to incorporate a new driver into the OpenSS7 framework. sdt(4) and sl(4) modules can be pushed on a ch(4) stream to form a complete and compliant SS7 signalling link. The sdt(4) module provided SS7-HDLC framing of the bit-stream and the sl(4) module provides the SS7 signalling link state machines.

The Signalling Data Link Interface (SDLI) documented in sdli(7), provides direct access to the channel as does the channel interface above, however, the SDLI interface provides some additional capabilities for statistics, the control of V.35 interface leads, and the detection of E1/T1 alarm conditions on the group carrier. Device drivers that implement the sdli(7) interface directly can have sdt(4) and sl(4) modules pushed to form a complete signalling link.

The Signalling Data Terminal Interface (SDTI) documented in sdti(7), provides a signalling data terminal access. Devices that have on-board HDLC framing that meets SS7 needs can implement the sdti(7) interface directly and push the sl(4) module to provide a complete signalling link.

The Signalling Link Interface (SLI) documented in sli(7), provides signalling link access. Devices implementing the sli(7) interface provide all the SS7 Signalling Link functions in the device driver.