Phone Services Overview - ZyXEL Communications EX5501-B0 User Manual

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.
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 163 DiffServ: Differentiated Service Field
DSCP
(6-bit)
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.

22.9.2 Phone Services Overview

Supplementary services such as call hold, call waiting, and call transfer. are generally available from
your VoIP service provider. The Zyxel Device 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 Zyxel Device does not support DiffServ at the time of writing.
Chapter 22 VoIP
3
Unused
(2-bit)
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