Cisco Cisco Unified Intelligent Contact Management Software Leaflet

PG-to-CC (Central Controller) route diversity is maintained throughout the network. Be sure to 
avoid routes that result in common path selection (and, thus, a common point of failure) for the 
multiple PG-to-CC sessions (see 

For each of the WAN links in 

, a prioritization scheme is required. Two such prioritization 

schemes are supported: IP-based prioritization and QoS. Traffic prioritization is needed because it is 
possible for large amounts of low-priority traffic to get in front of high-priority traffic, thereby delaying 
delivery of high-priority packets to the receiving end. In a slow network flow, the amount of time a single 
large (for example, 1500-byte) packet consumes on the network (and delays subsequent packets) can 
exceed 100 ms. This delay would cause the apparent loss of one or more heartbeats. To avoid this 
situation, a smaller Maximum Transmission Unit (MTU) size is used by the application for low-priority 
traffic, thereby allowing a high-priority packet to get on the wire sooner. (MTU size for a circuit is 
calculated from within the application as a function of the circuit bandwidth, as configured at PG setup.) 

A network that is not prioritized correctly almost always leads to call time-outs and problems from loss 
of heartbeats as the application load increases or (worse) as shared traffic is placed on the network. A 
secondary effect often seen is application buffer pool exhaustion on the sending side, due to extreme 
latency conditions.

Unified ICM applications use three priorities: high, medium, and low. However, prior to QoS, the 
network effectively recognized only two priorities identified by source and destination IP address 
(high-priority traffic was sent to a separate IP destination address) and, in the case of UDP heartbeats, 
by specific UDP port range in the network. The approach with IP-based prioritization is to configure IP 
routers with priority queuing in a way that gives preference to TCP packets with a high-priority IP 
address and to UDP heartbeats over the other traffic. When using this prioritization scheme, 90% of the 
total available bandwidth should be granted to the high-priority queue

A QoS-enabled network applies prioritized processing (queuing, scheduling, and policing) to packets 
based on QoS markings as opposed to IP addresses. Unified ICM Release 7.x provides marking 
capability of both Layer-3 DSCP and Layer-2 802.1p (using the Microsoft Windows Packet Scheduler) 
for private and public network traffic. Traffic marking in Unified ICM implies that configuring dual IP 
addresses on each Network Interface Controller (NIC) is no longer necessary because the network is 
QoS-aware. If the traffic is marked at the network edge instead, however, dual-IP configuration is still 
required to differentiate packets by using access control lists based on IP addresses. For details, see 

.

The primary purpose of the UDP heartbeat design is to detect if a circuit has failed. Detection can be 
made from either end of the connection, based on the direction of heartbeat loss. Both ends of a 
connection send heartbeats at periodic intervals (typically every 100 or 400 milliseconds) to the opposite 
end, and each end looks for analogous heartbeats from the other. If either end misses 5 heartbeats in a 
row (that is, if a heartbeat is not received within a period that is 5 times the period between heartbeats), 
then the side detecting this condition assumes that something is wrong and the application closes the 
socket connection. At that point, a TCP Reset message is typically generated from the closing side. Loss 
of heartbeats can be caused by various reasons, such as: the network failed, the process sending the 
heartbeats failed, the machine on which the sending process resides is shut down, the UDP packets are 
not properly prioritized, and so forth.