Nortel Networks NN43001-563

Typeof Service 77

The TM 3.1 User Interface allows two ToSvalues to be conﬁgured: data and

control. Data packets transmit the voice or fax call’s data, while control

packets setup and maintain the call. Both can be conﬁgured for any value

in the range of 0 – 255 (0 is the default). When an IP Trunk 3.01 (and

later) node is conﬁgured, ToSbits are initially set to default values. The

TM 3.1 IP Trunk 3.01 (and later) node administration interface allows the

customer to conﬁgure these bits for potentially better interworking with

different manufacturers’routing equipment. The extent of any improvement

from setting these ToSbits depends on the network routing equipment.

Improvements can vary depending on the router’s prioritization algorithms.

The data ToSis placed in every voice or fax data packet sent from the IP

trunk card. To optimize the speech quality, ToSis usually conﬁgured for

low-latency and high-priority.

The control ToSis 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. ToSvalues are

conﬁgured in the DSP Proﬁle window. For a route entry to be selected for

an outgoing packet, boththe 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 foran IP Trunk 3.01 (and

later) node which is not on the local subnet and must go through a router.

There is a default gatewayentry (0.0.0.0) that speciﬁes thegateway address

for this trafﬁc. The ToS doesnot 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 ToSvalue conﬁgured against it. Since

there are two ToSvalues 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.

Nortel Communication Server 1000

IP TrunkFundamentals

NN43001-563 02.01 Standard

Release 5.5 21 December 2007