/mcpSDP Example 2 m=audio 54312 RTP/AVP 99 a=rtpmap:99 opus/48000/2 a=fmtp:99 maxplaybackrate=16000; sprop-maxcapturerate=16000; maxaveragebitrate=20000; stereo=1; useinbandfec=1; usedtx=0 Referred-By Header Support Cisco Unified Communications Manager transparently passes the Referred-By header, which is present in an incoming REFER message that a SIP endpoint sends, to the outbound initial INVITE (triggered by the REFER). When a SIP endpoint wants to blind transfer to a different endpoint, the SIP endpoint sends the REFER message to Cisco Unified Communications Manager with the Refer-To header and Referred-By headers populated. If Cisco Unified Communications Manager has to generate a brand new call to the Refer-To target, then Cisco Unified Communications Manager includes the Referred-By header in the outbound initial INVITE to the Refer-To target. If additional redirect features such as call forwarding are configured, the Referred-By header does not get included in any SIP INVITES that are communicated as a result of the supplementary feature. If the Refer-To destination endpoint does not understand the Referred-By header, it can respond with a 429 Provide Referrer Identity response. Cisco Unified Communications Manager passes this error response back to endpoint that initiated the REFER, and clears the call. Session ID Header Support Cisco Unified Communications Manager supports passing the SIP Session-ID headers through to all call legs. When Cisco Unified Communications Manager receives an inbound SIP INVITE message from a SIP endpoint, and the Session ID header is included, Cisco Unified Communications Manager passes the header through to the other call leg and includes it in the outbound INVITE dialog message that gets sent to the other endpoint. If the SIP endpoint does not provide the Session-ID header, Cisco Unified Communications Manager generates the header on behalf of the endpoint after the first inbound SIP message that is received. iX Channel Encryption Encryption support with DTLS is now added to the iX Channel for application media. This update ensures privacy for information transmitted using iX Channel. When iX Channel encryption is used in video conferences, this update ensures that the privacy of transmitted information, such as the identities of meeting participants is protected. There are two types of SDP offers for iX Channel encryption: • Best Effort Encryption—The SDP offer is for an encrypted iX Channel, but will fall back to a non-encrypted iX Channel if the SIP peers do not support it. This approach may be used if encryption is not mandatory in the solution. For example, encryption is usually mandatory within the cloud, but not within a single enterprise. • Forced Encryption—The SDP offer is for an encrypted iX Channcel only. This offer will be rejected if the SIP peers do not support iX Channel encryption. This approach may be used in deployments where encryption is mandatory between endpoints. SIP Line Messaging Guide (Standard Edition) for Cisco Unified Communications Manager 49 SIP Standard Line Interface Referred-By Header Support