Specifications

Bandwidth, Codecs and Compression
173
Bandwidth Management
This section details the new bandwidth management solution.
Bandwidth management and call admission control
The terms “Bandwidth Management” and “Call Admission Control” are often used
interchangeably to mean the management, and potential re-routing, of calls across an IP
network between end devices. In reality these are two separate concepts. Bandwidth
management gathers information about the availability and use of bandwidth on particular
connections and links. Call Admission Control uses this information to decide whether a call
should be completed or not.
Although the IP network is often considered as a “cloud,” it is actually made up of many parts,
including LANs, MANs and WANs. There are constraints on the amounts of data that can be
handled at the transitions between the different networks, and often within the networks
themselves.
If a link is bandwidth limited, it is desirable to be able to determine the available bandwidth
across the link and manage it to ensure that it is available for voice use. Once the bandwidth
is known, it is possible to determine how many virtual channels can be established and to admit,
redirect or reject calls based on current available resources, that is, bandwidth. The latter is
the task of Call Admission Control between end nodes.
Call admission control updates
Currently, Call Admission Control is applied to calls that must pass between different controllers
and nodes, including when using IP Networking or IP Trunks. The same mechanism also applies
to SIP Trunks and TDM trunks, although the latter is predetermined through the type of trunk,
PRI, for example. In most cases, this is an appropriate way to limit and re-direct calls. This
mechanism is now being expanded across the entire installation through the use of common
zone numbering. This will provide finer control of call admission in situations including:
• multiple nodes that use a common network connection
• remote workers who don't use IP Networking, including hot desk users
• resilient/redundant switchover to a backup controller at a remote site with limited bandwidth
• identification of bandwidth usage
Call Admission Control works by:
• knowing the network topology and identifying bottlenecks such as edge routers
• tracking bandwidth usage at the bottleneck/gateway points
• specifying voice limits for a connection, e.g. voice may only be allowed to use 50% of the link
• following the media path connection, that is, the most direct path. Signalling may involve a
number of units and may follow a different path than the media does. When traversing
zones, however, the calls must go through a bandwidth controller to be counted.
The zones and network topology are defined and propagated between the controllers and the
Enterprise Manager. Some additional tuning may be required locally at controllers where