User guide

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Cisco H.323 Signaling Interface User Guide
OL-2156-04 Rev. A1
Chapter 1 Cisco H.323 Signaling Interface Overview
Cisco HSI System Description
RUDP
RUDP transports the E-ISUP messages between the PGW 2200 and the Cisco HSI.
RUDP is a Cisco proprietary, connection-oriented, packet-based transport protocol.
RADVision H.323
The Cisco HSI uses the RADVision H.323 stack. The system uses the H.225 (Q.931 and registration,
admission, and status [RAS] protocol) and H.245 protocols to implement the H.323 endpoint signaling
function.
RADVision H.323 enables the creation of real-time voice H.323 calls over IP networks.
E-ISUP
E-ISUP is a proprietary Cisco protocol based on ISUP. E-ISUP is used for inter-PGW 2200 call control.
E-ISUP uses a subset of ISUP messages. The main differences between ISUP and E-ISUP are as follows:
• E-ISUP is for the control of packet voice connection. It does not have circuit management messages
such as circuit reset and blocking.
• E-ISUP is transported over RUDP in an IP network.
• E-ISUP enables PGW 2200s to transport Session Description Protocol (SDP) information (such as
endpoint IP address and codec specifications) for call endpoints.
The Cisco HSI provides a conversion between the E-ISUP call control protocol originating from the
PGW 2200 and the H.323 call control protocol originating from the IP network (see Figure 1-1).
New Features Introduced in HSI Release 2.21
The following four features are introduced in Cisci HSI, Release 2.21.
Asymmetric Codec Treatment
The Asymmetric Codec Treatment feature averts the potential for inconsistencies in codec selection,
which might otherwise result when endpoints attempt to use different codecs for the transmission path.
Empty Capability Set
Empty Capability Set support enables the HSI to close opened logical channels, without releasing the
call. Subsequently, the HSI can open a new logical channel, potentially to a different endpoint, or use a
different codec.
H.323 Hairpin
The H.323 Hairpin feature can be used to connect a call between two H.323 endpoints without using
resources on the media gateway. For example, the PGW can respond to the dialled number in an
incoming H.323 call by routing the call to another HSI (perhaps the same HSI) rather than routing the