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7.1.2. IPv4 – Internet Protocol Version 4 (RFC 791) upgradeable to v6 (RFC 1883)
7.1.3. ARP – Address Resolution Protocol
7.1.4. DNS – A Record (RFC 1706), SRV Record (RFC 2782)
7.1.5. DiffServ (RFC 2475) and ToS – Type of Service (RFC 791/1349)
7.1.6. DHCP Client – Dynamic Host Configuration Protocol (RFC 2131)
7.1.7. ICMP – Internet Control Message Protocol (RFC792)
7.1.8. TCP – Transmission Control Protocol (RFC793)
7.1.9. UDP – User Datagram Protocol (RFC768)
7.1.10. RTP – Real Time Protocol (RFC 1889) (RFC 1890)
7.1.11. RTCP – Real Time Control Protocol (RFC 1889)
7.2. Voice Features
7.2.1. SIPv2 – Session Initiation Protocol Version 2 (RFC 3261-3265)
7.2.1.1. 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 average SIP proxy server may handle 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
PHONE ADAPTER supports the use of backup SIP proxy servers so that service disruption should be
next to non-existent.
Static Redundancy:
A relatively simple way to support proxy redundancy is to configure a static list of SIP proxy servers to
the PHONE ADAPTER in its configuration profile where the list is arranged in some order of priority.
The PHONE ADAPTER will attempt to contact the highest priority proxy server whenever possible.
When the currently selected proxy server is not responding, the PHONE ADAPTER automatically
retries the next proxy server in the list.
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 PHONE
ADAPTER. One solution to this situation is through the use DNS SRV records. The PHONE
ADAPTER can be instructed to contact a SIP proxy server in a domain named in SIP messages. The
PHONE ADAPTER 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 PHONE
ADAPTER shall try to contact the list of hosts in the order of their stated priority.
7.2.1.2. Re-registration with Primary SIP Proxy Server
If the PHONE ADAPTER 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.
7.2.1.3. SIP Support in Network Address Translation Networks – NAT
7.2.2. Codec Name Assignment
© 2004 Linksys Proprietary (See Copyright Notice on Page 2)
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