SIP
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... SIP [1] client sending a request to a SIP server typically performs
a DNS lookup for the domain name ...
... UDP, TCP or SCTP). A SIP
server that supports, for instance, three different transport
protocols, will have three different DNS ...
... present, this solution is not considered scalable any longer.
A SIP element that supports compression will need to be prepared to
receive compressed and uncompressed messages on the same port ...
... There are two types of SIP messages; SIP requests and SIP responses.
Clients send SIP requests ...
... header
field.
We define two parameters, one for SIP URIs and the other for the Via
header field ...
... sip:alice@atlanta.com;comp=sigcomp
Via: SIP/2.0/UDP server1.foo.com:5060;branch=z9hG4bK87a7;comp=sigcomp
...
...
Therefore, the presence of comp=sigcomp indicates that the SIP entity
identified by the URI or by the Via header field ...
... sigcomp mean
"willingness" as well as "support" allows the receiver of a SIP
message to influence the decision of whether or not to use SigComp at
a given time.
...
...
Every SIP implementation that supports SigComp MUST implement the
procedures described in this document.
...
... dialog is established. A client sending a request outside a dialog
can also obtain SIP URIs with comp=sigcomp in a Contact header field ...
... to wait until the dialog is established in order to begin compressing
messages. One of the biggest gains that SigComp can bring to SIP is
the ability to compress the initial INVITE of a dialog, when the user
...
... sometimes it is necessary to have clients configured in an automatic
fashion. Unfortunately, current mechanisms for SIP client
configuration (e.g., using DHCP ...
... uncompressed OPTIONS request to its outbound proxy. The outbound
proxy can provide an alternative SIP URI with the comp=sigcomp
parameter in a Contact header field ...
... compressed is not a problem, since user agents can REGISTER a SIP URI
with comp=sigcomp in their registrar. All incoming requests for the
...
... with comp=sigcomp in their registrar. All incoming requests for the
user will be sent to this SIP URI using compression.
...
...
In order to avoid asymmetric compression (i.e., two SIP entities
exchanging compressed requests in one direction and uncompressed
requests in the other direction) proxies ...
... Route rewriting. A typical example of double Record-Routing is a SIP
proxy that acts as a firewall ...
...
If a compressed SIP request arrives to a SIP server that does not
understand SigComp, the server will not have any means to indicate
...
... The Via compression parameter is a "via-extension", as defined by the
SIP ABNF (Section 25.1 of [1]):
...
...
A SIP entity receiving a compressed message has to decompress it and
to parse it. This requires slightly more processing power ...
... An attacker inserting the parameter comp=sigcomp in a SIP message
could make a SIP entity send compressed messages to another SIP
entity ...
... sigcomp in a SIP message
could make a SIP entity send compressed messages to another SIP
entity that did not support SigComp. Appropriate integrity
mechanisms ...
... SIP message
could make a SIP entity send compressed messages to another SIP
entity that did not support SigComp. Appropriate integrity
mechanisms should be used to avoid this attack ...
... Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261prop, June 2002. ...