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ISDN Backhaul Support Using IUA/SCTP
Revised: January 31, 2008, OL-12436-02
This chapter describes the support of ISDN backhaul using ISDN Q.921-User Adaptation (IUA) and the
Stream Control Transmission Protocol (SCTP). This support applies to both the user and network
interfaces of an ISDN PRI configuration for facility associated signaling (FAS) as defined in RFC 3057.
At this time, only FAS is supported for IUA. Using the Reliable User Datagram Protocol (RUDP) for
PRI backhauling is not impacted by IUA/SCTP support. An ISDN trunking gateway can be configured
to use either RUDP or IUA, but not both at the same time.
IUA/SCTP Protocols
IUA and SCTP are two protocols defined for the transportation of telephony signaling over a packet
network. SCTP is a reliable transport protocol like RUDP. IUA is the adaptation layer that makes SCTP
services available to Q.921 services users, such as Q.931 and NI2. There are several benefits to using
IUA/SCTP in place of Session Manager (SM)/RUDP, including the following:
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In a typical network topology, one SCTP association is established between the gateway and each Call
Agent. Multiple SCTP streams are carried out within each association. One stream is always dedicated
for management purposes, and separate SCTP streams are used for each D-channel. Two IP addresses
for each side are designated to the same SCTP association for multi-homing.
The IUA manager (IUM) process provides an interface to the IUA and SCTP stacks and communicates
with the gateways. The Cisco SCTP and IUA stacks are used for this feature.
OL-12436-02
the multi-streaming feature of SCTP allows each D-channel to use a different stream to prevent
head-of-line blocking.
the multi-homing feature of SCTP provides more efficient network redundancy compared to RUDP.
SCTP allows a configurable maximum outstanding receive window in number of bytes to get data
through the network faster. RUDP supports a fixed value of 32 datagrams.
SCTP uses dynamic timers based on calculated round trip time; RUDP has fixed timers.
SCTP provides a cookie mechanism for better security.
C H A P T E R
Cisco BTS 10200 Softswitch ISDN Provisioning and Troubleshooting
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