[SIPForum-discussion] loose routing

[William Prusty]

Strict Routing and Loose Routing

The way how record routing works has evolved. Record routing according
to RFC2543 rewrote the Request-URIi
<http://www.iptel.org/glossary#term81> i
<http://www.iptel.org/glossary#term80> . That means the Request-URI
always
contained URI of the next hop (which can be either next proxy server
which inserted Record-Route header field or destination user agent).
Because of that it was necessary to save the original Request-URI as the
last Route header field. This approach is called strict routing.

Loose routing, as specified in RFC3261, works in a little bit different
way. The Request-URI is no more overwritten, it always contains URI of
the destination user agent. If there are any Route header field in a
message, than the message is sent to the URI from the topmost Route
header field. This is significant change--Request-URI doesn't
necessarily contain URI to which the request will be sent. In fact,
loose routing is very similar to IP source routing.

Because transit from strict routing to loose routing would break
backwards compatibility and older user agents wouldn't work, it is
necessary to make loose routing backwards compatible. The backwards
compatibility unfortunately adds a lot of overhead and is often source
of major problems.

Regards,

william

 



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