On 12/7/18 5:12 AM, Hamza Mohamed Salman wrote:
Dear,
Good Day.
The trace result shows that The 480 arrives to the node, and it is rejected
(dropped) because there is a fault in the message. The following is seen in the
communication buffer of the TEST SYSTEM trace we receive yesterday.
SIP/2.0 480 Temporarily Unavailable
Via: SIP/2.0/UDP
BC00.RAHBC1.MSS.ALMADAR.NET:5060;branch=z9hG4bK0036926780904874;received=10.150.22.1
Allow: ACK,BYE,CANCEL,INFO,INVITE,MESSAGE,NOTIFY,OPTIONS,PING,REFER,UPDATE
Call-ID:
{acx8285710251vwbcghefemdm...@bc00.rahbc1.mss.almadar.net
Contact:
Content-Type: application/sdp
CSeq: 116019009 INVITE
From:
;tag=13000730723785
Record-Route:
To: ;tag=1543136248.891036.906647130
User-Agent: swengine v3.5 r16205
Content-Length: 0
While content-type header is present, the content-length is zero, what is not
acceptable. You can see the explanation below from SIP OPM before, but I copy
here again
For application/sdp type of body RFC 4566 is applicable, which specifies
mandatory and optional parts of the body.
In other words, application/sdp body itself is not expected to be empty."
Upto 16A (GSM_MSC SW), our software was allowing this message, but from 17A
onward, the software has been updated to adapt 100% to the standard.
Here I also attached the Network Impact Report of 16A to 17A. In page number
46, this impact on SIP request/response messages are mentioned.
* MSC-S releases call if SIP request/response is received with
following combination
of elements (not according to syntax rules):
- A message body part (e.g. SDP) is received, Content-Type header indicating
the body part presence is received and Content-Length header received
indicates zero (0) length of the body part,
- No message body part is received but the Content-Type header indicating
the body part presence is received.
Im asking if we can change the 480,486 messages and remove content-type header
or not??
IMO this case isn't clearly addressed in 3261.
But note that there is a "default" content type for the body of sip
messages, and that default varies based on the type of message. For
INVITE the default is application/sdp. (I forget if it says, but I think
the same default can assume to apply the responses to the message.)
So even if you omit a Content-Type, one is implied for every message,
independent of whether there is a body or not. Hence you should not be
troubled by having a content-type present in a message with no body.
For SDP, the syntax doesn't itself permit an empty body. But as used in
SIP, the presence or absence of an SPD body (or body part) is used to
discern whether an offer/answer is present.
To answer your question directly, you may include or omit the
'Content-Type:application/sdp/' header field for messages with no body.
Thanks,
Paul
BTW, there *could* be other content types that syntactically permit a
zero-length body. I suppose in principle that might present a specific
use for content-type with a missing body - especially when the
content-type is not the default for the message type. AFAIK this has not
been tested, and might have a high probability of failing in existing
implementations.
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