Specifications

AT-VP504E FXS 63

Miscellaneous Configuration

This chapter describes other configuration settings not covered in the

previous chapters.

Using QoS QoS (Quality of Service) features enable network managers to decide

on packet priority queuing. The AT-VP504E FXS supports the

Differentiated Services (DS) field and 802.1q taggings. There are two

variables – one variable for media (T.38, RTP, etc.) and one for

signalling (SIP).

Differentiated

Services (DS)

Field

You can set various DIfferentiated Services parameters that will allow

you to control the network traffic.

Note: The AT-VP504E FXS does not support RSVP (Resource

Reservation Protocol).

What are Differentiated Services?

Differentiated Services (DiffServ, or DS) is a protocol for specifying and controlling network traffic by

class so that certain types of traffic get precedence – for example, voice traffic, which requires a

relatively uninterrupted flow of data, might get precedence over other kinds of traffic.

Unlike the earlier mechanisms of 802.1p tagging and Type of Service (ToS), Differentiated Services

avoids simple priority tagging and depends on more complex policy or rule statements to determine

how to forward a given network packet. An analogy is made to travel services, in which a person can

choose among different modes of travel – train, bus, airplane – degree of comfort, the number of stops

on the route, standby status, the time of day or period of year for the trip, and so forth.

For a given set of packet travel rules, a packet is given one of 64 possible forwarding behaviors –

known as per hop behaviors (PHBs). A six-bit field, known as the Differentiated Services Code Point

(DSCP), in the Internet Protocol (Internet Protocol) header specifies the per hop behavior for a given

flow of packets. The DS field structure is presented below:

0 1 2 3 4 5 6 7

+---+---+---+---+---+---+---+---+

| DSCP | CU |

+---+---+---+---+---+---+---+---+

•

DSCP

: Differentiated Services CodePoint.

•

: Currently Unused. The CU bits should always be set to 0.

For both signalling and media packets, the DSCP field is configurable independently. For future

extensibility, the entire DS field (TOS byte) will be configurable.

Note: It is the network administrator's responsibility to provision the AT-VP504E FXS with standard and

correct values.