DRAFT
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- Attended Call Transfer (no star code)
- Blind Call Transfer
Services that can be disabled (or enabled) by method (b) are any of the services that have a star code
assignment in the SPA941 configuration profile (see Section 21 on a complete list). Note that if service is
enabled, but the corresponding *code is emptied, the service can still be enabled/disabled by the end-
user from the phone GUI or web page.
If a service is disabled, any soft key associated with that service will be hidden from the GUI. These are:
SK(dnd), SK(-dnd), SK(cfwd) and SK(-cfwd). Any menu item associated with a disabled service will be
preceded with an exclamation mart (!) and no soft keys will be visible to select that entry.
• Voice and Signaling Features
SIPv2 – Session Initiation Protocol Version 2 (RFC 3261-3265)
SIP Proxy Redundancy – Static or Dynamic via DNS SRV
In typical commercial IP Telephony deployments, all calls are established through a SIP proxy server. An
typical SIP proxy server may serve tens of thousands subscribers. It is important that a backup server is
available so that an active server can be temporarily switched out for maintenance. The SPA supports the
use of backup SIP proxy servers so that service disruption should be next to non-existent.
SIP Proxy Dynamic Redundancy:
The dynamic nature of SIP message routing makes the use of a static list of proxy servers inadequate in
some scenarios. In deployments where user agents are served by different domains, for instance, it
would not be feasible to configure one static list of proxy servers per covered domain into an SPA. One
solution to this situation is through the use DNS SRV records. The SPA can be instructed to contact a SIP
proxy server in a domain named in SIP messages. The SPA shall consult the DNS server to get a list of
hosts in the given domain that provides SIP services. If an entry exists, the DNS server will return a SRV
record which contains a list of SIP proxy servers for the domain, with their host names, priority, listening
ports, etc. The SPA shall try to contact the list of hosts in the order of their stated priority.
Re-registration with Primary SIP Proxy Server
If the SPA is currently using a lower priority proxy server, it should periodically probe the higher priority
proxy to see if it is back on line and attempt to switch back to the higher priority proxy whenever possible.
It is very important that switching proxy server should not affect calls that are already in progress.
Codec Name Assignment
Negotiation of the optimal voice codec is sometimes dependent on the SPA device’s ability to “match” a
codec name with the far-end device/gateway codec name. The SPA allows the network administrator to
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