Chapter 22 Voice
EMG6726/8726-B10A User’s Guide
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You can continue to add, listen to, or delete tones, or you can hang up the receiver when you are
done.
22.8.1 Quality of Service (QoS)
Quality of Service (QoS) refers to both a network's ability to deliver data with minimum delay, and the
networking methods used to provide bandwidth for real-time multimedia applications.
Type of Service (ToS)
Network traffic can be classified by setting the ToS (Type of Service) values at the data source (for
example, at the EMG) so a server can decide the best method of delivery, that is the least cost, fastest
route and so on.
DiffServ
DiffServ is a class of service (CoS) model that marks packets so that they receive specific per-hop
treatment at DiffServ-compliant network devices along the route based on the application types and
traffic flow. Packets are marked with DiffServ Code Points (DSCP) indicating the level of service 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 152
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.
22.8.2 Phone Services Overview
Supplementary services such as call hold, call waiting, and call transfer. are generally available from
your VoIP service provider. The EMG supports the following services:
3.
The EMG does not support DiffServ at the time of writing.
DSCP
(6-bit)
Unused
(2-bit)
