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Chapter 5 – Gatekeeper Software
IP Parameter Definitions
Values
Description
Diff Serv PHB (Per Hop Behavior) values pertain
to a differential prioritizing system for IP packets
as handled by Diff Serv-compatible routers. There
are 64 values, each with an elaborate technical
description. These descriptions are found in
TCP/IP standards RFC2474, RFC2597, and, for
present purposes, in RFC3246, which describes
the value 34 (34 decimal; 22 hex) for Assured
Forwarding behavior (default for Call Control
PHB) and the value 46 (46 decimal; 2E
hexadecimal) for Expedited Forwarding behavior
(default for Voip Media PHB). Before using
values other than these default values of 34 and
46, consult these standards documents and/or a
qualified IP telecommunications engineer.
To disable Diff Serv, configure both fields to 0
decimal.
The next page explains Diff Serv in the context of
the IP datagram.
0 – 63
Value is used to prioritize call
default = 34
setup IP packets.
0 – 63
Value is used to prioritize the
RTP/RTCP audio IP packets.
default = 46
Type II,
Must be set to match network’s
SNAP
frame type. Default is Type II.
Field Name
Diff Serv Parameter
fields
Call Control PHB
Voip Media PHB
Frame Type
The IP Datagram with Header, Its Type-of-Service Field, & DiffServ
bits =>
0
4
VERS
HLEN
8
16
TYPE OF
SERVICE
IDENTIFICATION
TIME TO LIVE
19
24
31
TOTAL LENGTH
FLAGS
PROTOCOL
FRAGMENT OFFSET
HEADER CHECKSUM
SOURCE IP ADDRESS
DESTINATION IP ADDRESS
IP OPTIONS (if any)
PADDING …
end of header
DATA
…
The TOS field consists of eight bits, of which only the first six are used. These six bits are called the
“Differentiated Service Codepoint” or DSCP bits.
Multi-Tech Systems, Inc. MultiVOIP Gatekeeper User Guide
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