Quality Of Service - Nortel 1000 Description, Installation And Operation Manual

Page 98 of 644 System description

Quality of Service

553-3001-363 Standard 2.00
Quality of Service (QoS) is the gauge of quality of the IP network between
two nodes. As QoS degrades, existing calls suffer from poor voice and fax
quality. New calls will not be initiated if transmissions degrade below an
acceptable level.
Behavioral characteristics of the IP network depend on the following:
• Round Trip Time (RTT)
• latency
• queuing delay in the intermediate nodes
• packet loss
• available bandwidth
The Type of Service (ToS) bits in the IP packet header can affect how
efficiently data is routed through the network. For further information on
ToS, see "Type of Service" on
Packet jitter related to latency affects the quality of real-time IP
transmissions. For good voice quality, the IP trunk card reassembles the voice
packets in an ordered continuous speech stream and plays them out at regular
intervals despite varying packet arrival times.
The user configures a required QoS for the IP Trunk 3.01 (and later) node in
OTM. The QoS value determines when calls fallback to alternate facilities
due to poor performance of the data network. The QoS value is between 0.0
and 5.0, where 0.0 means never fallback to alternate facilities and 5 means
fallback to alternate facilities unless the voice quality is perfect. When the
QoS for outgoing calls, as measured by the Leader card, falls below the
configured value, calls fallback to alternate facilities. Once the QoS rises
above the configured value, all new outgoing calls are routed through the IP
network.
Note: QoS is measured for each remote gateway. For example, if a given
Leader has three remote leaders in its dialing plan table, it performs three
QoS measurements and calculations (one per remote gateway).
September 2004
page 105.