SIP/2.0 415 Unsupported Media Type - in lync

ISSUE:  When a lync client make a call to a custom client this issue arise.

SIP/2.0 415 Unsupported Media Type
Via: SIP/2.0/TLS 192.168.0.3:5061;branch=z9hG4bKD46A59CA.99BC04A5AF342A99;branched=FALSE;ms-internal-info="beEdEaEIWfaYJeF8c6BZ3b0XKNdvQ3PyQaRPEpAEarjbWlBLyZ_eZHbgAA"
Via: SIP/2.0/TLS 192.168.0.4:55803;branch=z9hG4bK36072482.06B5227EC88DCA9A;branched=FALSE;ms-received-port=55803;ms-received-cid=162D00
Via: SIP/2.0/TLS 192.168.0.100:50797;received=x.x.x.x;ms-received-port=50797;ms-received-cid=8C00
Record-Route: <sip:FE.domain.local:5061;transport=tls;opaque=state:T:F:Ci.R16a800;lr;ms-route-sig=adlkYhe7OeBeVys8TvobWpLmx2HSLx-xldaLJ-jRlgx4mlBLyZI12ObwAA>;tag=D5120ECF36260EB267FB812D17DAE391
From: "Test User 3" <sip:test3@fe.local>;tag=be345768e2;epid=3bcd1d97b8
To: <sip:demouser@fe.local>;epid=13757352
Call-ID: ff8f03c39c46499db228eab1eb58fed9
CSeq: 1 INVITE
Authorization: NTLM qop="auth", realm="SIP Communications Service", opaque="E74376CA", targetname="FE.domain.local", version=4, crand="13757352", cnum ="5", response="01000000ed10b4deaa20de6f64000000"
Ms-client-diagnostics: 51004; reason="Action initiated by user"
Content-Length: 0

WHY?


This issue arise due to inability of providing support for specific media type. In short--

If you ask a media player to play media it can play.
But, if you ask a media player to open a pdf it is not possible ,because it doesn't have that feature.