Huawei U-SYS MRS6100 Technical Manual page 72

Technical Manual
U-SYS MRS6100 Media Resource Server
Supported
Transportation of a 100 temporary response defined in SIP is not reliable. In other
words, it is not guaranteed that UAC can receive the provisional response sent by
UAS.
If the response is required to carry information about media, it must be guaranteed
that the message can be reliably transported to the peer. The 100rel extension
provides an appropriate mechanism for the reliable transportation of the 100
response. The acknowledgement request method for a provisional response in 100rel
is PRACK.
If UAC supports the extension, it adds the field of Supported: 100rel in the message
transmitted. If UAS supports the extension, it adds the field of Require: 100rel in the
100 response transmitted. Upon receipt of the response, UAC is required to send a
PRACK request to UAS, to notify it of the receipt of the provisional response. UAS
sends a 2xx response to UAC to terminate the acknowledgement process of the
provisional response.
If a UA wants to send a provisional response carrying a SDP message body, UAC and
UAS must support and use the 100rel extension to guarantee the reliable
transportation of the message.
An example of Supported field:
Supported: 100rel
User-Agent
The User-Agent field contains information about the UAC originating the request.
Revealing the specific software version of UA may set the user in a position of being
more vulnerable to attacks against software that is known to contain security holes.
Therefore, the User-Agent field should be set to be a configurable option.
An example of Use-Agent field:
User-Agent: Softphone Beta1.5
Expires
The Expires field gives the relative time after which the message (or content) will
expire.
An example of Expires field:
Expires: 5
Accept-Language
The Accept-Language field is used in requests to indicate the preferred languages for
reason phrases, session descriptions, or status responses carried as message
bodies in the response. If no Accept-Language field is present, the server assumes all
languages are acceptable to the client.
An example of Accept-Language field:
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Chapter 5 MGCP and SIP