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Using Enterprise Edge Services 33

P0910464 Issue 01 Enterprise Edge Networking Operations Guide

As a reference point: for a typical G.729 codec, each VoIP flow requires the

following WAN bandwidth, depending on the codec sample rate:

Note: The calculation is based on a full-duplex WAN link with HDLC overhead

and VoIP with silence suppression.

Nortel Networks recommends that for slow WAN links, such as a 56K leased line

or ISDN, H.323 video is not configured as premium traffic.

Packet Marking for DiffServ Networks

Enterprise Edge classifies traffic and marks packets by setting the IP header type of

service (TOS) field. By default, the following items are classified as premium

traffic:

• All VoIP flows

• RIP packets: routing packets are periodically exchanged between Enterprise

Edge and remote routers. These packets need higher priority than regular

packets to ensure that the routing protocol is working properly.

• ICMP packets: Enterprise Edge Net Link Manager uses the ‘ping’ command to

decide whether the primary WAN link is active or inactive. These packets are

not delayed by regular packets.

• UDP Port 5000 packets – Enterprise Edge VoIP QoS Monitor uses port 5000 in

a proprietary protocol to monitor the IP network delay and jitter. Since

Enterprise Edge assigns VoIP packets to the premium queue, it also gives these

monitor packets high traveling priority.

• Admitted RTP/RTCP packets.

In Enterprise Edge, there are two places a user can set up a TOS field in an IP

header:

TOS-for-Premium-Traffic – this field sets TOS bits for premium packets for

DiffServ networks. If this field is ignored, Enterprise Edge uses a default value

of 0xB8.

TOS-for-Priority-Filters– this field sets TOS for those packets matching a

specific priority filter.

Note: You can specify packets matched to a filter to go Priority Queue 0 – 8. The

Queue 0 is for premium packets, and Queue 1 – 8 correspond to best-effort

priority classes 1 – 8.

G.729 Sample Rate

30 ms

Sample Rate

20 ms

Sample Rate

10 ms

Compression

10.6 k 14 k 24 k

Data

Compression

8 k 10 k 16 k

RTP Hdr Comp. 5.8 k 6.8 k 9.6 k

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