| The Router interface may be implemented by the application to provide custom
routing logic. It is used to determine the next hop for a given request.
For backwards compatibility reasons, the default behavior of the stack is
to consult the application provided Router implementation for all requests
outside of a dialog. This is controlled through the stack property
javax.sip.USE_ROUTER_FOR_ALL_URIS which defaults to true
when not set.
This specification recommends to set the stack property
javax.sip.USE_ROUTER_FOR_ALL_URIS to
false. This will cause the stack to only consult the application
provided Router implementation for requests with a non-SIP URI as request URI
(such as tel: or pres:) and without Route headers. This enables an application
to implement DNS lookups and other resolution algorithms
When javax.sip.USE_ROUTER_FOR_ALL_URIS is set to
false, the next hop is determined according to the following algorithm:
- If the request contains one or more Route headers, use the URI of the
topmost Route header as next hop, possibly modifying the request in
the process if the topmost Route header contains no lr parameter(See Note below))
- Else, if the property
javax.sip.OUTBOUND_PROXY is set, use its
value as the next hop
- Otherwise, use the request URI as next hop. If the request URI is not a SIP
URI, call
javax.sip.address.Router.getNextHop(Request) provided by the application.
Note: In case the topmost Route header contains no 'lr' parameter
(which means the next hop is a strict router), the implementation will perform
'Route Information Postprocessing' as described in RFC3261 section 16.6 step 6
(also known as "Route header popping"). That is, the following modifications will be
made to the request:
- The implementation places the Request-URI into the Route header
field as the last value.
- The implementation then places the first Route header field value
into the Request-URI and removes that value from the Route
header field.
Subsequently, the request URI will be used as next hop target.
The location (classname) of the user-defined Router object is supplied in the
Properties object passed to the
javax.sip.SipFactory.createSipStack(Properties) method upon creation
of the SIP Stack object.
The Router object must accept a SipStack as an argument to the constructor in
order for the Router to access attributes of the SipStack
The constructor of an object implementing the Router interface must be
RouterImpl(SipStack sipStack, String outboundProxy) {}
The routing policy can not be changed dynamically, i.e. the SipStack needs to be
deleted and re-created.
Outbound proxy should be passed to the
javax.sip.SipFactory.createSipStack(Properties) method upon creation
of the SIP Stack object.
Application Notes
A UAC application which desires to use a particular outbound
proxy should prepend a Route header with the URI of that proxy (and 'lr' flag if
appropriate).
Alternatively, it may achieve the same result by setting the OUTBOUND_PROXY
property (although the Route header approach is more flexible and therefore RECOMMENDED)
A proxy application may either rewrite the request URI (if the proxy is
responsible for the domain), or prepend a Route header.
author:
BEA Systems, NIST
version:
1.2 |