Avaya BSGX4e User's Guide download pdf (Page 201)

BSGX4e Business Gateway User Guide 201

Release 01.01 NN47928-102

GoS Configuration

 Management: SNMP polling does not require a very high bandwidth, 64 Kbps is

enough. SNMP traffic is not very sensitive to loss and delay. By assigning to this

traffic a bandwidth of 64 Kbps you can ensure too many packets are not dropped

(the rate can be higher at some times) so the SNMP applications can run normally

(no timeout).

 Other: The other traffic can be handled in best effort mode, for which no

bandwidth is allocated and nothing is required for the loss and delay.

Traffic management requires defining how to classify the traffic to distinguish the

different traffic types:

 VoIP (signalling and media): Because the SIP Session Controller controls the VoIP

calls established through the BSGX4e, it knows which packets (signalling and

media) belong to VoIP traffic type.

 Management: Assuming the SNMP agent is configured to listen and transmit SNMP

packets on port 161, this traffic type can be classified based on port (161) and

protocol (UDP).

 Other: You do not need to specify any classification rules for the other flows. By

default, flows are managed in best effort.

To conclude the analysis, you must define the bandwidth of the WAN T1 link. This

determines at which speed the routing engine can transmit packets from its WAN

interface. A T1 interface usually runs at 1.536 Mbps (taking into account the Frame

Relay header and Frame Check Sequence (FCS)). IP packets sent to the T1 link have

a Frame Relay overhead of 6 bytes in the case Data Link Connection Identifiers

(DLCI) are coded on 10 bits (four for the overhead and two for FCS) while packets

sent by the BSGX4e have a Ethernet overhead of 14 bytes. This means you can

configure the bandwidth of the Layer 3 QoS to a value greater than 1.536 Mbps, but

not too much to avoid overwhelming the T1 link. By experience, the value 1 684 450

Mbps is good.

Configuring Layer 2 QoS

The configuration of Layer 2 QoS requires the following steps:

1.Configuring the classification type.

Assume all VoIP signalling and media packets are tagged with a DiffServ/ToS byte

of 45.

BSG> config switch qos setting type ToSDiff

2.Configuring the queuing mechanism.

Strict priority and weighted round robin queuing mechanisms are supported.

Because real-time traffic such as VoIP is sensitive to packet loss and delay, strict

priority queuing is recommended.

*BSG*> config switch qos setting scheduling fixed

*BSG*> show switch qos setting

Switch QoS:

Type Scheduling

--------------------------

TOS* FIXED

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Avaya BSGX4e User's Guide Page 201

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