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Chapter 9 Voice
P-2612HNU-Fx User’s Guide
179
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 56 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.
VLAN Tagging
Virtual Local Area Network (VLAN) allows a physical network to be partitioned into
multiple logical networks. Only stations within the same group can communicate
with each other.
Your ZyXEL Device can add IEEE 802.1Q VLAN ID tags to voice frames that it
sends to the network. This allows the ZyXEL Device to communicate with a SIP
server that is a member of the same VLAN group. Some ISPs use the VLAN tag to
identify voice traffic and give it priority over other traffic.
9.7.4 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 Hold
• Call Waiting
• Making a Second Call
• Call Transfer
• Three-Way Conference
DSCP
(6-bit)
Unused
(2-bit)