Huawei U-SYS MRS6100 Technical Manual page 71

Technical Manual
U-SYS MRS6100 Media Resource Server
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Max-Forwards
The Max-Forwards field serves to limit the number of hops a request can transit on the
way to its destination. It consists of an integer that is decremented by one at each hop.
If the Max-Forwards value reaches 0 before the request reaches its destination, it will
be rejected with a 483 (Too Many Hops) error response.
The purpose of inserting this field is to avoid consuming proxy server resources in an
event of loop. The default field value is 70.
The Max-Forwards field has a generic format:
Max-Forwards: decimal integer
Allow
The Allow field gives a list of request types that can be supported by the proxy server.
An example of Allow field:
Allow: INVITE, ACK, OPTIONS, CANCEL, BYE
Content-Length
The Content-Length field indicates the size of the message body, in decimal format.
Applications use this field to indicate the size of the message body to the transferred,
regardless of the media type of the entity. If the used transport protocol is based on
streams, TCP for example, this field must be used.
The size of the message body does not include the carriage return line feed (CRLF)
that separates the message header from the message body. The value of
Content-Length must be equal to or greater than 0. If a message does not contain a
message body, the value of the Content-Length field must be set to 0.
SDP serves to construct the message body of a request or 2xx response.
The Content-Length field has a generic format:
Content-Length: decimal value
An example of Content-Length field:
Content-Length: 349
The example indicates the length of the message body is 349 bytes.
Content-Type
The Content-Type field indicates the media type of the message body. If the message
body is not null, the Content-Type field must be present. If the body is empty and a
Content-Type field is present, it indicates that the body length of the specific type is
zero (an empty audio file for example).
An example of Content-Type field:
Content-Type: application/sdp
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Chapter 5 MGCP and SIP