Summary
This chapter focused on the key SigTran protocols and their role in a next-generation architecture of voice products. The SigTran work grew from a desire to decompose a traditional circuit switch into specialized components. It focused on the following two areas:
A transport protocol that is suitable for meeting the requirements of carrying telecommunication protocols, especially SS7, over a packet network. The creation of adaptation layers that support the primitives of SCN telephony signaling protocols.
SCTP was developed as the new generic transport protocol. It provides performance and reliability benefits for telephony signaling transport over the UDP and TCP transport protocols.
The common elements of the adaptation layers were introduced and described in some detail, as were the following key adaptation layers:
M3UA—
Provides for the transport of MTP Level 3 user part signaling (for example, ISUP and SCCP).
SUA—
Provides for the transport of SCCP user signaling (for example, TCAP).
M2UA—
Provides for the transport of MTP Level 2 user signaling (for example, MTP Level 3).
M2PA—
Provides a means of creating an IP SS7 link by replicating MTP Level 2 and supporting the MTP Level 2 primitive boundary to MTP Level 3.
IUA—
Provides for the transport of Q.921 user signaling (for example, Q.931).
In addition, two protocols related to SigTran were introduced: TALI and the early Cisco backhaul protocol stack. Finally, some examples of SS7 to SIP and H.323 interworking were provided to provide a context for how SigTran protocols can be used with other VoIP protocols.
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