ZyXEL VMG9823 User Guide - Page 234
Phone Services Overview
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Chapter 21 Voice 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 138 DiffServ: Differentiated Service Field DSCP (6-bit) Unused (2-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. 21.8.2 Phone Services Overview Supplementary services such as call hold, call waiting, and call transfer. are generally available from your VoIP service provider. The 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. VMG9823-B10A User's Guide 234
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