Nortel Networks Remote Gateway 50 - Manual (Page 68)

Page 68 of 258 Bandwidth Management
553-3001-207 Standard 2.00 January 2006
feedback. This dynamic bandwidth adjustment maintains a high level of
voice quality during network degradation.
The Adaptive Network Bandwidth Management feature dynamically adapts
to QoS in the network and reduces the bandwidth available for interzone calls
if QoS degrades. Typically, each Call Server in the network has a zone
assigned to it. The Call Server keeps track of the bandwidth being used
between its own zone and zones belonging to other Call Servers. If the QoS
degrades between the Call Server's zone and a particular zone belonging to
another Call Server, the available bandwidth is reduced automatically
between those two zones. When the QoS between the two zones improves,
then the bandwidth limit is allowed to return to normal.
When an IP Phone encounters degradation of the network, it informs the Call
Server through various QoS alarms. These QoS alarms (packet loss, jitter,
delay, and, for phase 2 IP Phones, R value) get reported to the Call Server.
Depending upon the rate of the incoming alarms and the value of the alarms,
the Call Server reduces the available bandwidth available to make new calls.
The Call Server will lower/limit the number of new calls allowed, based on
the available bandwidth. This prevents excessive calls being placed on a
network with limited bandwidth (resulting in poor voice quality). Once the
adjusted (lowered) bandwidth reaches its full capacity, new calls are either
routed to an alternate route (if available) using Network Alternate Routing
Service (NARS) or the Alternative Routing for NBWM feature (see
Branch Office: Installation and Configuration (553-3001-214)), or new calls
are blocked. The Call Server continues to monitor the network throughout the
network degradation period. When the degradation is removed or the
performance of the network improves, the allowable bandwidth returns to
provisioned levels and the Call Server gradually starts allowing new calls.
Essentially, Adaptive Network Bandwidth Management provides a fallback
to PSTN on QoS degradation for new calls. As a result, bandwidth is managed
and quality measured between all the zones across the entire network, and
when necessary corrective action is taken. Due to the real-time interaction
with the network, less maintenance is required for the network since the
system reacts automatically to network conditions.
With Adaptive Network Bandwidth Management, it is not necessary to
provision bandwidth parameters between every zone in the network. Rather,
the Call Server automatically learns of new zones in the network and applies