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Chapter 23 Voice
VMG5313-B10A/-B30A Series User’s Guide
291
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.
3
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 150 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.
23.10.2 Phone Services Overview
Supplementary services such as call hold, call waiting, and call transfer. are generally available from
your VoIP service provider. The VMG supports the following services:
•Call Return
•Call Hold
• Call Waiting
• Making a Second Call
• Call Transfer
• Call Forwarding
• Three-Way Conference
• Internal Calls
• Call Park and Pickup
• Do not Disturb
•IVR
•Call Completion
•CCBS
• Outgoing SIP
3. The VMG does not support DiffServ at the time of writing.
DSCP
(6-bit)
Unused
(2-bit)