Multi-Tech Systems MVP-2410 User Manual

 

 
 
The IP Datagram with Header, Its Type-of-Service field, & DiffServ 
 
bits => 

0 

4 

8 

 

16     19 

 

24 

31 

VERS HLEN 

TYPE OF 

SERVICE 

TOTAL LENGTH 

IDENTIFICATION 

FLAGS

 

FRAGMENT OFFSET 

TIME TO LIVE 

PROTOCOL 

HEADER CHECKSUM 

SOURCE IP ADDRESS 

DESTINATION IP ADDRESS 

IP OPTIONS (if any) 

PADDING … 

 

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 6 7 

PRECEDENCE D T R unused 

 
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.