Cisco Unified Contact Center Enterprise Solution Reference ...

Unified CCE Network Architecture Overview
RSVP
11-6
Cisco Unified Contact Center Enterprise 7.x SRND
Chapter 11 Bandwidth Provisioning and QoS Considerations
you to specify keep-alive parameters on a per-connection basis. For Unified ICM public connections, the
keep-alive timeout is set to 5∗400 ms, meaning that a failure can be detected after 2 seconds, as was the
case with the UDP heartbeat prior to Release 5.0.
The reasons for moving to TCP keep-alive with QoS enabled are as follows:
In a converged network, algorithms used by routers to handle network congestion conditions can
have different effects on TCP and UDP. As a result, delays and congestion experienced by UDP
heartbeat traffic can have, in some cases, little correspondence to the TCP connections.
The use of UDP heartbeats creates deployment complexities in a firewall environment. The dynamic
port allocation for heartbeat communications makes it necessary to open a large range of port
numbers, thus defeating the original purpose of the firewall device.
Cisco Unified CallManager 5.0 introduces support for Resource Reservation Protocol (RSVP) between
endpoints within a cluster. A protocol for Call Admission Control (CAC), RSVP is used by the routers
in the network to reserve bandwidth for calls.
To calculate bandwidth usage before RSVP was introduced, it was necessary for each CallManager
cluster to maintain local counts of how many active calls traversed between locations. If more than one
Cisco Unified CallManager cluster shared the same link, it was necessary to dedicate bandwidth for each
cluster, leading to inefficient use of available bandwidth.
RSVP solves this problem by tracing the path between two RSVP agents that reside on the same LAN
as the phones. The RSVP agent is a software media termination point (MTP) that runs on Cisco IOS
routers. The RSVP agents are controlled by Cisco Unified CallManager and are inserted into the media
stream between the two phones when a call is made. The RSVP agent of the originating phone will
traverse the network to the RSVP agent of the destination phone, and reserve bandwidth. Since the
network routers keep track of bandwidth usage instead of CallManager, multiple phone calls can traverse
the same RSVP controlled link even if the calls are controlled by multiple CallManagers.
Figure 11-2 shows a scenario in which two different CallManager clusters provide service to phones at
the same remote site. This may occur if a CallManager cluster is assigned to handle an IP call center. In
the scenario, two users at the same office are serviced by different clusters. RSVP offloads the bandwidth
calculation responsibilities of CallManager to the network routers.
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