Nortel Networks NN43001-563 - Manual (Page 77)

Type of Service 77
The data ToS is placed in every voice or fax data packet sent from the IP
trunk card. To optimize the speech quality, ToS is usually configured for
low-latency and high-priority.
The control ToS is placed in every signaling message packet sent from the
IP trunk card. Signaling links use Transmission Control Protocol (TCP)
which provides a retransmission mechanism. In addition, the latency of the
control packets is not as critical as it is for the data packets.
Each entry in the routing table has a configurable ToS. ToS values are
configured in the DSP Profile window. For a route entry to be selected for
an outgoing packet, both the configured route and the ToS must match. Two
cases must be considered: local subnet traffic and remote traffic.
The remote subnet packets is the H.323 call data for an IP Trunk 3.01 (and
later) node which is not on the local subnet and must go through a router.
There is a default gateway entry (0.0.0.0) that specifies the gateway address
for this traffic. The ToS does not matter for this route. If the route and ToS
do not match any of the other route entries, the packet is routed here. The
entry is configured for the TLAN network interface.
Local subnet packets is the H.323 call data intended for another IP Trunk
3.01 (and later) node connected to the same subnet. This can be the
immediate subnet. For traffic to be sent on the local subnet, the routing
table entry for the TLAN network interface must be selected. Each table
entry (except the default route) has a ToS value configured against it. Since
there are two ToS values configured (one for control data and one for voice
data), there must be two route entries for the local subnet in the table.
If both table entries are not present, a condition occurs where packets for
voice, control, or both can be sent to the default route because the ToS
does not match the local subnet entry. These packets go to the router and
then back on the subnet, wasting router resources and increasing traffic on
the subnet.
The IP trunk card configures two route table entries for the local subnet if a
different ToS is configured for the voice and control packets. Otherwise, a
single entry is created.
CAUTION
Service Interruption
Only technical personnel with detailed knowledge of router
capabilities should make changes to ToS. Improper changes to
ToS can degrade network performance.
Nortel Communication Server 1000
IP Trunk Fundamentals
NN43001-563 01.01 Standard
Release 5.0 30 May 2007
Copyright © 2007, Nortel Networks
.