Nortel ISDN Signaling Link, Описание, установка и эксплуатация

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Page 46 of 378 Description
553-3001-202 Standard 1.00 April 2000
On large systems, the DCH interface to the Meridian 1 uses the MCDN or
QSIG GF protocols and their variants to transmit call and feature control
messages to the DCHIP card. Small systems use only MCDN because the
NTAK02BB SDI/DCH card does not support QSIG protocols for ISL. The
DCH interface uses these protocols and their variants, as they have the
following advantages:
• ISL configuration support
• symmetry (incoming and outgoing call messaging is the same)
• near H.323 standard
QSIG GF Name Display is the only supported QSIG supplementary service.
The ITG feature complies with H.323 Basic Call Q.931 signaling. This part
of the H.323 standard (H.225) defines the messaging used to setup and release
basic calls. A mechanism is implemented to enable the passing of ISDN
messaging through the IP network between the two end points. The call is set
up using the H.323 standard signaling with encapsulated ISDN-specific
information. This mechanism allows interworkings with other gateways.
The DCHIP card provides the tandem between the ISDN signaling and the
H.323 protocol. If the DCHIP functionality is combined with the Follower
card, messages are sent between the DCH Processor and the H.323 Processor.
Most configurations split this functionality between the DCHIP and Follower
cards. Figure 8 shows the signal flow from the DCH to the H.323 stack.