Multi-Tech Systems MVP-2410/3010, MVP-410ST/810ST manual Type of Service or TOS field, 137

MultiVOIP User Guide					Technical Configuration (T1/E1)
The IP Datagram with Header, Its Type-of-Service field, & DiffServ
bits =>
0	4	8		16	19	24		31
VERS	HLEN	TYPE OF				TOTAL LENGTH
		SERVICE
	IDENTIFICATION			FLAGS		FRAGMENT OFFSET
TIME TO LIVE		PROTOCOL				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.

The Type of Service or “TOS” field

0		1	2	3	4	5
	PRECEDENCE			D	T	R

67 unused

The three precedence have eight values, 0-7, ranging from “normal” precedence (value of 0) to “network control” (value of 7). When set, the D bit requests low delay, the T bit requests high throughput, and the R bit requests high reliability.

Routers that support DiffServ can examine the six DSCP bits and prioritize the packet based on the DSCP value. The DiffServ Parameters fields in the MultiVOIP IP Parameters screen allow you to configure the DSCP bits to values supported by the router. Specifically, the Voip Media PHB field relates to the prioritizing of audio packets (RTP and RTCP packets) and the Call Control PHB field relates to the prioritzing of non-audio packets (packets concerning call set-up and tear-down, gatekeeper registration, etc.).

The MultiVOIP Call Control PHB parameter defaults to 34 decimal (22 hex; 100010 binary – consider vis-à-vis TOS field above) for Assured Forwarding behavior. The MultiVOIP Voip Media PHB parameter defaults to the value 46 decimal (2E hex; 101110 binary – consider vis-à-vis TOS field above). To disable DiffServ, configure both fields to 0 decimal.

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