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P-2302R Series User’s Guide

Chapter 8 VoIP Screens 110

8.5.1 Type Of Service (ToS)

Network traffic can be classified by setting the ToS (Type Of Service) values at the data

source (for example, at the Prestige) so a server can decide the best method of delivery, that is

the least cost, fastest route and so on.

8.5.2 DiffServ

DiffServ is a class of service (CoS) model that marks packets so that they receive specific per-

hop treatment at DiffServ-compliant network devices along the route based on the application

types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs) indicating the

level of service desired. This allows the intermediary DiffServ-compliant network devices to

handle the packets differently depending on the code points without the need to negotiate

paths or remember state information for every flow. In addition, applications do not have to

request a particular service or give advanced notice of where the traffic is going.

8.5.2.1 DSCP and Per-Hop Behavior

DiffServ defines a new DS (Differentiated Services) field to replace the Type of Service

(TOS) field in the IP header. The DS field contains a 2-bit unused field and a 6-bit DSCP field

which can define up to 64 service levels. The following figure illustrates the DS field.

DSCP is backward compatible with the three precedence bits in the ToS octet so that non-

DiffServ compliant, ToS-enabled network device will not conflict with the DSCP mapping.

Figure 39 DiffServ: Differentiated Service Field

The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior), that each

packet gets across the DiffServ network. Based on the marking rule, different kinds of traffic

can be marked for different priorities of forwarding. Resources can then be allocated

according to the DSCP values and the configured policies.

8.5.3 VLAN

Virtual Local Area Network (VLAN) allows a physical network to be partitioned into multiple

logical networks. Only stations within the same group can communicate with each other.

Your Prestige can add IEEE 802.1Q VLAN ID tags to voice frames that it sends to the

network. This allows the Prestige to communicate with a SIP server that is a member of the

same VLAN group. Some ISPs use the VLAN tag to identify voice traffic and give it priority

over other traffic.

1. The Prestige does not support DiffServ at the time of writing.

DSCP

(6-bit)

Unused

(2-bit)

1 2 ... 106 107 108 109 110 111 112 113 114 115 116 ... 383 384

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