Information Technology Reference
In-Depth Information
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E&M (wink-start [Feature Group B, FGB], wink-start with wink acknowledge or double wink [Feature Group D, FGD],
Feature Group D Exchange Access North America [FGD-EANA], or immediate start)
E&M signaling is often the preferred option for CAS signaling because it avoids glare, it provides answer/disconnect supervision, it
can receive automatic number identification (ANI) with FGD, and it can send ANI with FGD-EANA.
E1 R2 is a CAS system whose signaling specifications are defined in ITU-T Recommendations Q.400 to Q.490. One advantage of R2
is that is can provide ANI.
Signaling System 7
The Cisco PGW 2200 PSTN gateway offers interconnection of Signaling System 7 (SS7) networks with H.323 and SIP networks.
SS7 was developed by the ITU in the 1970s and is a common channel signaling (CCS) system used in the PSTN that enables
functionality including call control, database queries, network operations, and transactions.
As part of the PGW 2200 PSTN gateway, Cisco offers Signaling Link Terminals (SLT) and PGW 2200 hosts. The Cisco SLTs
connect to the SS7 network via A or F links, and the SLT terminates Message Transfer Part (MTP) Layer 1 and 2.
Note that in an SS7 network, A-links provide connectivity between signal switching points/signal control points (SSP/SCP) and signal
transfer points (STP), with each SSP/SCP typically having at least two A-links to STPs for redundancy. In contrast, F-links provide
direct connectivity between signaling endpoints and are used when there are high traffic volumes or no STPs to provide intermediate
connectivity.
