Version 6.6 507 October 2014
Installation & Operation Manual 38. Configuring the PSTN Subsystem
38.7 Configuring the CAS/ISDN Subsystem
CAS (Common Associated Signaling) is a telecommunication signaling protocol used
to interconnect PBXs or other legacy PSTN equipment. When using CAS, routing
information is encoded and transmitted in the same channel as the payload itself.
The Mediant 8000 supports “CAS interworking function” where signaling messages
arriving from the CAS trunk are relayed to the Softswitch (e.g. via the MEGACO or SIP
protocols), and vice versa.
ISDN (Integrated Services Digital Network) is an international communications
standard for sending voice and data over digital telephone lines or land-line telephone
wires. When using ISDN, voice and data are carried by bearer channels (B channels)
occupying a bandwidth of 64 kb/s. A data channel (D channel) handles signaling at 16
kb/s or 64 kb/s, depending on the service type.
The Mediant 8000 supports “ISDN interworking function” where signaling messages
coming from the ISDN trunk are relayed to the Softswitch (e.g. via the SIP protocols),
and vice versa.
Additionally, the Mediant 8000 supports the relay of ISDN signaling messages using
the SIGTRAN IUA (ISDN User Adaptation Layer) protocol. A signaling message
coming to the Mediant 8000 from the ISDN connection goes through the data link
layer and the Q.931 protocol data unit and is relayed to the SoftSwitch using IUA over
SCTP.
Figure
38-11: ISDN Relay via IUA
DPNSS (Digital Private Network Signaling System) is a network protocol used on
digital trunk lines for connecting two PABXs. It was originally defined by British
Telecom. The Mediant 8000 supports the relay of DPNSS signaling using SIGTRAN
DUA (DPNSS User Adaptation Layer) protocol.
The Mediant 8000 has the following IUA/DUA capabilities:
Up to 84 UAL Interfaces per Media Gateway Board
Up to 3 UAL Groups per Media Gateway Board
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