SIP¸¦ ÀÌ¿ëÇÏ¿© Ä÷¯¸µ ¼­ºñ½º³ª ¼ÒÀ§ ¸»ÇÏ´Â (Remote) Real Ringback toneÀ» Á¦°øÇÒ ¼ö ÀÖ´Ù.

ÀÌ·¸°Ô INVITE¿¡ ´ëÇÑ Final Response ÀÌÀü¿¡ ¹Ìµð¾î°¡ Àü¼Û,PlayµÇ´Â °ÍÀ» Early Media¶ó°í ÇÑ´Ù. Early Media¿¡ ´ëÇØ Å©°Ô 2°¡Áö ¸ðµ¨ÀÌ Àִµ¥, PSTN°ú ¿¬°èµÇ´Â °æ¿ì¿¡ ÇØ´çµÇ´Â Gateway¸ðµ¨°ú Application Server ¸ðµ¨ÀÌ ÀÖ´Ù.

Gateway ¸ðµ¨Àº SIP ½Ã±×³Î¸µ »ó¿¡¼­ Early Media¿¡ ´ëÇÑ Æ¯º°ÇÑ ¾ð±Þ¾øÀÌ µ¿ÀÛÇÏ´Â °ÍÀÌ´Ù. 180¸Þ½ÃÁö¸¦ ¹ÞÀº °æ¿ì, Local Ring BacktoneÀ» ¹ß»ý½ÃÅ°°í, ¸¸¾à »ó´ë¹æ¿¡¼­ RTP(Early Media)°¡ ¿À¸é Local Ringback tone ¹ß»ýÀ» Áß´ÜÇÏ°í, RTP¸¦ PlayÇÑ´Ù. »ó´ë¹æÀÌ ÀüÈ­¸¦ ¹ÞÀ¸¸é Session Media°¡ RTP·Î Àü´ÞµÇ°í, ÅëÈ­¸¦ ÇÏ°Ô µÈ´Ù. ÀÌ Gateway ¸ðµ¨ÀÇ ¹®Á¦Á¡Àº Forking ¹× Security ¹®Á¦°¡ ÀÖ´Â °ÍÀÌ´Ù.

Application Server ¸ðµ¨Àº SIP ½Ã±×³Î½Ã early media¿¡ ´ëÇÑ offer/answer¸¦ °¡´ÉÇÏ°Ô ÇÑ´Ù. ÀÌ´Â Content-Disposition Çì´õ¿¡ session°ú early-sessionÀ» »ç¿ëÇÔÀ¸·Î¼­ °¡´ÉÇÏ´Ù. ÀÌ·¯ÇÑ È®ÀåÀ» ÀÌ¿ëÇÏ¿© Early Media¿¡ ´ëÇÑ ½Ã±×³Î¸µÀ» Ãß°¡·Î ÇÒ ¼ö ÀÖ´Ù.

´ÙÀ½ ±×¸²°ú ¸Þ½ÃÁö´Â Application Server ¸ðµ¨¿¡¼­ÀÇ SIP ½Ã±×³Î¸µ ¿¹Á¦ÀÌ´Ù. (RFC 3959)

(1) INVITE¿¡ Æ÷ÇÔµÈ offer

   Content-Type: application/sdp
   Content-Disposition: session
   v=0
   o=alice 2890844730 2890844731 IN IP4 host.example.com
   s=
   c=IN IP4 192.0.2.1
   t=0 0
   m=audio 20000 RTP/AVP 0

(2) 183 Session Progress ¸Þ½ÃÁö¿¡ Æ÷ÇÔµÈ, Early offer¿Í session answer

   Content-Type: multipart/mixed; boundary="boundary1"
   Content-Length: 401
   --boundary1
   Content-Type: application/sdp
   Content-Disposition: session
   v=0
   o=Bob 2890844725 2890844725 IN IP4 host.example.org
   s=
   c=IN IP4 192.0.2.2
   t=0 0
   m=audio 30000 RTP/AVP 0
   --boundary1
   Content-Type: application/sdp
   Content-Disposition: early-session
   v=0
   o=Bob 2890844714 2890844714 IN IP4 host.example.org
   s=
   c=IN IP4 192.0.2.2
   t=0 0
   m=audio 30002 RTP/AVP 0
   --boundary1--

(3) PRACK¿¡ Æ÷ÇÔµÈ early answer

   Content-Type: application/sdp
   Content-Disposition: early-session
   v=0
   o=alice 2890844717 2890844717 IN IP4 host.example.com
   s=
   c=IN IP4 192.0.2.1
   t=0 0
   m=audio 20002 RTP/AVP 0

Âü°í:
RFC 3960 Early media and ringing tone generation in SIP
RFC 3959 Early Session Disposition Type in SIP