diff --git a/trunk/doc/readme.txt b/trunk/doc/readme.txt
index 5219feac4..0ca6e4e33 100644
--- a/trunk/doc/readme.txt
+++ b/trunk/doc/readme.txt
@@ -83,6 +83,7 @@ kafka-160915-0553-82964.pdf
 STUN: https://tools.ietf.org/html/rfc5389
 TURN: https://tools.ietf.org/html/rfc5766
 ICE: https://tools.ietf.org/html/rfc5245
+SIP: https://tools.ietf.org/html/rfc3261
 
 Winlin
 
diff --git a/trunk/doc/rfc3261-2002-sip.pdf b/trunk/doc/rfc3261-2002-sip.pdf
new file mode 100644
index 000000000..1a4d0e2bd
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