Sridhar, Please do not try to learn SIP from RFC2543.
RFC3261 replaced and obsoleted RFC2543 long ago. It is authoritative, but do please note that it has been extended and revised many times. (See the "Updated by" list at the top of https://tools.ietf.org/html/rfc3261.)
If you are just getting started then you will benefit greatly by reading a tutorial book such as:
SIP - Understanding the Session Initiation Protocol https://www.amazon.com/SIP-Understanding-Session-Initiation-Protocol/dp/1608078639/ref=sr_1_1?keywords=understanding+the+session+initiation+protocol&qid=1567523861&s=gateway&sr=8-1 Good Luck, Paul On 9/3/19 6:58 AM, Sridhar Kumar N wrote:
Dear All Good Day, While Studying SIP protocal, Stuck at FROM-TAG usage. TO-TAG usage is clearly explained in RFC2543. But FROM -TAG usage is written in 2lines. Can you please elaborate for understanding. If the From address can appear in requests generated by other user agent clients for the same call, the caller MUST insert the tag parameter in the From field.
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