QSIG Protocol Stack

The QSIG protocol stack specifies a signaling system at reference point Q and is illustrated in Table 3-14. QSIG has an identical structure to that of ISDN, and at L1 and L2, these protocols can be the same. They differ at L3, however, where QSIG is split into the following three sublayers:

• QSIG BC—With this symmetrical protocol, the interfaces and messages for the user and network sides are identical. The messages and sequences of this protocol are more easily understood and demonstrated in the example at the end of this section.

• QSIG GF—This protocol specifies the control entities for supplementary services and ANFs. This protocol does not have the capability to control these services, but it does provide the generic layer capabilities to enable them. The protocol provides a connection-oriented and connectionless mechanism between the application entities of different PBXs.

• QSIG Supplementary Service and ANF Protocols—These define the procedures for individual or specific services and features. These services and ANFs are defined and detailed in separate specifications. Such organizations as the European Computer Manufacturers Association (ECMA) and the European Telecommunication Standards Institute (ETSI) are developing these protocol standards.

Table 3-14. QSIG Protocol Stack

OSI Reference

QSIG Protocol

QSIG Standard



Based on interface being used



Identical to ISDN L2 (LAPD)



ECMA 142/143; ETS300 171/172


ECMA 165; ETS300 239

QSIG protocols for supplementary services

Separate specifications, such as call forward (ECMA 173/174, ETS300 256/257) and call transfer (ECMA 177/178, ETS300 260/261)


Application-based service elements

Transparent to the network

*ETS300 is an ETSI-based standard.

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