--- 1/draft-ietf-mmusic-media-loopback-16.txt 2012-03-12 23:14:08.826671648 +0100 +++ 2/draft-ietf-mmusic-media-loopback-17.txt 2012-03-12 23:14:08.886672451 +0100 @@ -1,149 +1,152 @@ - Internet Draft K. Hedayat - Expires: March 6, 2012 EXFO + Internet Draft H. Kaplan (ed.) + Expires: August 12, 2012 Acme Packet + K. Hedayat + EXFO N. Venna Saperix P. Jones Cisco Systems, Inc. A. Roychowdhury Hughes Systique Corp. C. SivaChelvan Cisco Systems, Inc. N. Stratton BlinkMind, Inc. - September 6, 2011 + March 10, 2012 An Extension to the Session Description Protocol (SDP) for Media Loopback - draft-ietf-mmusic-media-loopback-16 + draft-ietf-mmusic-media-loopback-17 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- - Drafts. + Drafts. The list of current Internet-Drafts is at + http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. - This Internet-Draft will expire on March 6, 2012. + This Internet-Draft will expire on August 12, 2012. Copyright Notice - Copyright (c) 2009 IETF Trust and the persons identified as the + + Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without - warranty as described in the BSD License. + warranty as described in the Simplified BSD License. Abstract - The wide deployment of Voice over IP (VoIP), Real-time Text and - Video over IP services has introduced new challenges in managing - and maintaining voice/real-time Text/video quality, reliability, - and overall performance. In particular, media delivery is an area - that needs attention. One method of meeting these challenges is + The wide deployment of Voice over IP (VoIP), Text and Video over IP + services has introduced new challenges in managing and maintaining + real-time voice/real-time Text/video quality, reliability, and + overall performance. In particular, media delivery is an area that + needs attention. One method of meeting these challenges is monitoring the media delivery performance by looping media back to the transmitter. This is typically referred to as "active monitoring" of services. Media loopback is especially popular in ensuring the quality of transport to the edge of a given VoIP, Real-time Text or Video over IP service. Today in networks that deliver real-time media, short of running 'ping' and 'traceroute' to the edge, service providers are left without the necessary tools to actively monitor, manage, and diagnose quality issues with their service. The extension defined herein adds new SDP media attributes which enables establishment of media sessions where the media is looped back to the transmitter. Such media sessions will serve as monitoring and troubleshooting tools by providing the means for measurement of more advanced VoIP, Real-time Text and Video over IP performance metrics. Table of Contents 1. Introduction .................................................. 3 1.1 Use Cases Supported ....................................... 4 - 2. Terminology ................................................... 6 + 2. Terminology...................................................5 3. Offering Entity Behavior ...................................... 6 4. Answering Entity Behavior ..................................... 6 - 5. SDP Constructs Syntax ......................................... 6 - 5.1 Loopback Type Attribute ................................... 6 + 5. SDP Constructs Syntax..............Error! Bookmark not defined. + 5.1 Loopback Type Attribute...................................7 5.2 Loopback Mode Attribute ................................... 7 - 5.3 Generating the Offer for Loopback Session + 5.3 Generating the Offer for Loopback Session.................8 5.4 Generating the Answer for Loopback Session ................ 9 5.5 Offerer Processing of the Answer ......................... 11 5.6 Modifying the Session .................................... 11 - 5.7 Establishing Sessions Between Entities Behind NAT ........ 11 - 6. RTP Requirements ............................................. 11 + 5.7 Establishing Sessions Between Entities Behind NAT........12 + 6. RTP Requirements.............................................12 7. Payload formats for Packet loopback .......................... 12 - 7.1 Encapsulated Payload format .............................. 12 + 7.1 Encapsulated Payload format..............................13 7.2 Direct loopback RTP payload format ....................... 15 8. RTCP Requirements ............................................ 16 - 9. Congestion Control ........................................... 16 + 9. Congestion Control...........................................17 10. Examples .................................................... 17 10.1 Offer for specific media loopback type .................. 17 - 10.2 Offer for choice of media loopback type ................. 17 - 10.3 Response to INVITE request rejecting loopback media ..... 18 + 10.2 Offer for choice of media loopback type.................18 + 10.3 Response to INVITE request rejecting loopback media.....19 11. Security Considerations ..................................... 19 - 12. Implementation Considerations ............................... 19 + 12. Implementation Considerations...............................20 13. IANA Considerations ......................................... 20 13.1 SDP Attributes .......................................... 20 13.2 MIME Types .............................................. 21 14. Normative References ........................................ 30 1. Introduction The overall quality, reliability, and performance of VoIP, Real-time Text and Video over IP services rely on the performance and quality of the media path. In order to assure the quality of the delivered media there is a need to monitor the performance of the media transport. One method of monitoring and managing the - overall quality of VoIP, Real-time Text and Video over IP Services + overall quality of real-time VoIP, Text and Video over IP Services is through monitoring the quality of the media in an active session. This type of "active monitoring" of services is a method of proactively managing the performance and quality of VoIP based services. The goal of active monitoring is to measure the media quality of a - VoIP, Real-time Text or Video over IP session. A way to achieve - - endpoint and to provide media statistics (e.g., RTCP and RTCP XR - information). Another method involves deployment of special - endpoints that always loop incoming media back for sessions. - Although the latter method has been used and is functional, it does - not scale to support large networks and introduces new network - management challenges. Further, it does not offer the granularity - of testing a specific endpoint that may be exhibiting problems. + VoIP, Text or Video over IP session. A way to achieve this goal is + to request an endpoint to loop media back to the other endpoint and + to provide media statistics (e.g., RTCP and RTCP XR information). + Another method involves deployment of special endpoints that always + loop incoming media back for sessions. Although the latter method + has been used and is functional, it does not scale to support large + networks and introduces new network management challenges. + Further, it does not offer the granularity of testing a specific + endpoint that may be exhibiting problems. The extension defined in this memo introduces new SDP media attributes that enable establishment of media sessions where the media is looped back to the transmitter. The offer/answer model - [RFC3264] is used to establish a loopback connection. Furthermore, this extension provides guidelines on handling RTP [RFC3550], as well as usage of RTCP [RFC3550] and RTCP XR [RFC3611] for reporting media related measurements. 1.1 Use Cases Supported As a matter of terminology in this document, packets flow from one peer acting as a "loopback source", to the other peer acting as a "loopback mirror", which in turn returns packets to the loopback @@ -149,27 +152,20 @@ "loopback mirror", which in turn returns packets to the loopback source. In advance of the session, the peers negotiate to determine which one acts in which role. The negotiation also includes details such as the type of loopback to be used. This specification supports three use cases: "encapsulated packet loopback", "direct loopback", and "media loopback". These are distinguished by the treatment of incoming RTP packets at the loopback mirror. - As a supplement to these use cases, this specification also allows - the loopback source to request the loopback mirror to begin sending - a media stream to the loopback source, ending when the mirror - begins to receive packets from the source. This facility is needed - in some circumstances to establish the media path through - middleboxes lying between the peers. - 1.1.1 Encapsulated Packet Loopback In the encapsulated packet loopback case, the entire incoming RTP packet is encapsulated as payload within an outer payload type that is specific to this use case and specified below (Section 7.1). The encapsulated packet is returned to the loopback source. The loopback source can generate statistics for one-way path performance up to the RTP level for each direction of travel by examining sequence numbers and timestamps in the outer header and the encapsulated RTP packet payload. The loopback source can also @@ -219,60 +215,81 @@ This usage allows trouble-shooting at the codec level. The capability for path statistics is limited to what is available from RTCP reports. 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119. - 3. Offering Entity Behavior + SDP: Session Description Protocol, as defined in [RFC4566]. This + document assumes the SDP offer/answer model is followed, per + [RFC3264], but does not assume any specific protocol for carrying + the SDP. - An offering entity compliant to this memo and attempting to - establish a media session with media loopback MUST include - "loopback" media attributes for each individual media description - in the offer message. The offering entity MUST look for the - "loopback" media attributes in the media description(s) of the - response from the answering entity for confirmation that the - request is accepted. + The following terms are borrowed from [RFC3264] definitions: offer, + offerer, answer, answerer, and agent. - 4. Answering Entity Behavior + 3. SDP Offerer Behavior - An answering entity compliant to this specification and receiving - an offer containing media descriptions with the "loopback" media + An SDP offerer compliant to this memo and attempting to establish a + media session with media loopback MUST include "loopback" media + attributes for each individual media description in the offer + message. The offerer MUST look for the "loopback" media attributes + in the media description(s) of the response from the answer for + confirmation that the request is accepted. + + 4. SDP Answerer Behavior + + An SDP answerer compliant to this specification and receiving an + offer containing media descriptions with the "loopback" media attributes MUST acknowledge the request by including the received "loopback" media attributes for each media description in its - response if it agrees to do the loopback. If the answerer does not + asnwer if it agrees to do the loopback. If the answerer does not want to do loopback or wants to reject the "loopback" request for - specific media types, it MAY do so as defined in section 5.4.1 of - this specification. + specific media types, it MAY do so as defined in section Error! + Reference source not found. of this specification. - An answering entity that is not compliant to this specification and - which receives an offer with the "loopback" media attributes MAY - ignore the attribute and treat the incoming offer as a normal - request. + An answerer MAY reject an offered stream (either with loopback- + source or loopback-mirror) if the loopback-type is not specified, + the specified loopback-type is not supported, or the endpoint + cannot honor the offer for any other reason. The loopback request + MUST be rejected by setting the stream's media port number to zero + in the answer as defined in RFC 3264 [RFC3264], or by rejecting the + entire offer (e.g., by rejecting the session request entirely). - 5. SDP Constructs Syntax + Note that an answerer that is not compliant to this specification + and which receives an offer with the "loopback" media attributes + would ignore the attribute and treat the incoming offer as a normal + request. If the offerer does not wish to establish a "normal" RTP + session, it would need to terminate the session upon receiving such + an answer. - Two new media attributes are defined: one indicates the type of - loopback and the other indicates the mode of the loopback. + 5. New SDP Attributes + + Three new SDP media-level attributes are defined: one indicates the + type of loopback, and the other two define the mode of the + loopback. 5.1 Loopback Type Attribute - The loopback type is a property media attribute with the following + This specification defines a new 'loopback' attribute, which + indicates the type of loopack that the agent is able to do. The + loopback type is a property media attribute with the following syntax: a=loopback: Following is the Augmented BNF [RFC5234] for loopback-type: + Loopback-attr = "a=loopback:" loopback-type = loopback-choice [1*SP loopback-choice] loopback-choice = loopback-type-pkt / loopback-type-media loopback-type-pkt = "rtp-pkt-loopback" loopback-type-media = "rtp-media-loopback" The loopback type is used to indicate the type of loopback. The loopback-type values are rtp-pkt-loopback, and rtp-media-loopback. rtp-pkt-loopback: In this mode, the RTP packets are looped back to the sender at a point before the encoder/decoder function in the @@ -285,28 +302,30 @@ new payload type and format. Section 7 describes the payload formats that MUST be used for this type of loopback. rtp-media-loopback: This loopback is activated as close as possible to the analog interface and after the decoder so that the RTP packets are subsequently re-encoded prior to transmission back to the sender. 5.2 Loopback Mode Attribute - The loopback mode is a value media attribute that is used to - indicate the mode of the loopback. These attributes are additional - mode attributes like sendonly, recvonly, etc. The syntax of the - loopback mode media attribute is: + The loopback mode defines two value media attributes that are used + to indicate the mode of the loopback. These attributes are + additional mode attributes like sendonly, recvonly, etc. The + syntax of the loopback mode media attributes are based on the + following: a=:... - The loopback-mode values are loopback-source and loopback-mirror. + The loopback-mode values are 'loopback-source' and 'loopback- + mirror'. loopback-source: This attribute specifies that the entity that generated the SDP is the media source and expects the receiver of the SDP message to act as a loopback-mirror. loopback-mirror: This attribute specifies that the entity that generated the SDP will mirror (echo) all received media back to the sender of the RTP stream. No media is generated locally by the looping back entity for transmission in the mirrored stream. @@ -320,83 +339,90 @@ MUST include all the payload types that will be used during the loopback session including those specified in the loopback-mode attribute line. The complete payload space for the call is specified in the "m=" line and the rtpmap attribute is used to map from the payload type number to an encoding name denoting the payload format to be used. 5.3 Generating the Offer for Loopback Session If an offerer wishes to make a loopback request, it MUST include - both the loopback-type and loopback-mode parameters in a valid SDP + both the loopback-type and loopback-mode attributes in a valid SDP offer: Example: m=audio 41352 RTP/AVP 0 8 100 a=loopback:rtp-media-loopback a=loopback-source:0 8 100 a=rtpmap:0 pcmu/8000 a=rtpmap:8 pcma/8000 a=rtpmap:100 G7221/16000/1 - Note: A loopback offer in a given media description MUST NOT - contain the standard mode attributes sendonly, recvonly, sendrecv, - or inactive. The loopback-mode attributes (loopback-source and - loopback-mirror) replace the standard attributes. + A loopback offer in a given media description MUST NOT contain the + standard mode attributes sendonly, recvonly, sendrecv, or inactive. + + The loopback-mode attributes (loopback-source and loopback-mirror) + replace the standard attributes. The offerer may offer more than one loopback-type in the SDP offer. - The port number and the address in the offer (m= line) indicate + The port number and the address in the offer (m/c= lines) indicate where the offerer would like to send and receive the media stream. The payload type numbers indicate the value of the payload the offerer expects to send and receive. If the offerer is the loopback-source, the subset of payload types indicated in the a=loopback-source line are the payload types for the codecs the offerer is willing to send. However, the answer might indicate a different payload type number for the same codec in the loopback- mirror line. In that case, the offerer MUST send the payload type received in the answer. If the offerer is the loopback-mirror, the subset of payload types indicated in the a=loopback-mirror line are the payload types for the codecs the offerer is willing to receive. If loopback-type is rtp-pkt-loopback, the loopback-mirror MUST send and the loopback-source MUST receive the looped back packets encoded in one of the two payload formats (encapsulated RTP or - payload loopback) as defined in section 7. + direct loopback) as defined in section 7. Example: m=audio 41352 RTP/AVP 0 8 112 a=loopback:rtp-pkt-loopback a=loopback-source:0 8 a=rtpmap:112 encaprtp/8000 Example: m=audio 41352 RTP/AVP 0 8 112 a=loopback:rtp-pkt-loopback a=loopback-source:0 8 a=rtpmap:112 rtploopback/8000 5.4 Generating the Answer for Loopback Session - As with the offer, a loopback answer in a given media description - MUST NOT contain the standard mode attributes sendonly, recvonly, - sendrecv, or inactive. The loopback-mode attributes (loopbackThe - port number and the address in the answer (m= line) indicate where - the answerer would like to receive the media stream. The payload - type numbers indicate the value of the payload types the answerer - expects to send and receive. If the offerer is the loopback- - source, the answerer MUST be a loopback-mirror and the subset of - payload types indicated in the a=loopback-mirror line are the - payload types for the codecs the answerer is willing to receive. - Similarly, if the offerere is the loopback-mirror, the answerer - MUST be aloopback-source and the subset of payload types indicated - in the a=loopback-source line are the payload types for the codecs - the answerer is willing to send. + As with the offer, an SDP answer for loopback MUST NOT contain the + standard mode attributes sendonly, recvonly, sendrecv, or inactive. + The port number and the address in the answer (m/c= lines) indicate + where the answerer would like to receive the media stream. The + payload type numbers indicate the value of the payload types the + answerer expects to send and receive. The loopback-mode attributes + (a=loopback-source or a=loopback-miror) MUST contain at least one + codec the answerer is willing to send or receive depending on + whether it is the loopback-source or the loopback-mirror. In + addition, the "m=" line MUST contain at least one codec that the + answerer is willing to send or receive depending on whether it is + the loopback-mirror or the loopback-source. + + If the offerer is the loopback-source, the answerer MUST be a + loopback-mirror and the subset of payload types indicated in the + a=loopback-mirror line are the payload types for the codecs the + answerer is willing to receive. Similarly, if the offerer is the + loopback-mirror, the answerer MUST be aloopback-source and the + subset of payload types indicated in the a=loopback-source line are + the payload types for the codecs the answerer is willing to send. If an answerer wishes to accept the loopback request it MUST - include both the loopback mode and loopback type attribute in the + include both the loopback mode and loopback type attributes in the answer. When a stream is offered with the loopback-source attribute, the corresponding stream in the response MUST be loopback-mirror and vice versa, provided that answerer is capable of supporting the requested loopback-type. For example, if the offer contains the loopback-source attribute: m=audio 41352 RTP/AVP 0 8 a=loopback:rtp-media-loopback a=loopback-source:0 8 @@ -446,79 +472,69 @@ m=audio 41352 RTP/AVP 0 8 112 a=loopback:rtp-pkt-loopback a=loopback-mirror:0 8 a=rtpmap:112 encaprtp/8000 m=audio 41352 RTP/AVP 0 8 113 a=loopback:rtp-pkt-loopback a=loopback-mirror:0 8 a=rtpmap:113 rtploopback/8000 - 5.4.1 Rejecting the Loopback Offer - - An offered stream (either with loopback-source or loopback-mirror) - MAY be rejected if the loopback-type is not specified, the - specified loopback-type is not supported, or the endpoint cannot - honor the offer for any other reason. The Loopback request may be - rejected by setting the media port number to zero in the answer as - per RFC 3264 [RFC3264]. + The previous examples used the 'encaprtp' and 'rtploopback' + encoding names, which will be defined in sections 7.1.3 and 7.2.3. 5.5 Offerer Processing of the Answer - The answer to a loopback-source MUST be loopback-mirror. The - answer to a loopback-mirror MUST be loopback-source. The - loopback-mode line MUST contain at least one codec the answerer is - willing to send or receive depending on whether it is the loopback- - source or the loopback-mirror. In addition, the "m=" line MUST - contain at least one codec that the answerer is willing to send or - receive depending on whether it is the loopback-mirror or the - loopback-source. - - If the answer does not contain a=loopback-mirror or + If the received answer does not contain a=loopback-mirror or a=loopback-source, it is assumed that the loopback extensions are - not supported by the target UA. + not supported by the remote agent. This is not a protocol failure, + and instead merely completes the SDP offer/answer exchange with + whatever normal rules apply; the offerer MAY decide to end the + established RTP session (if any) through normal means of the upper- + layer signaling protocol (e.g., by sending a SIP BYE). 5.6 Modifying the Session - At any point during the loopback session, either participant may + At any point during the loopback session, either participant MAY issue a new offer to modify the characteristics of the previous - session. In case of SIP this is defined in section 8 of RFC 3264 - [RFC3264]. This also includes transitioning from a normal media - processing mode to loopback mode, and vice a versa. + session, as defined in section 8 of RFC 3264 [RFC3264]. This also + includes transitioning from a normal media processing mode to + loopback mode, and vice a versa. 5.7 Establishing Sessions Between Entities Behind NAT ICE/STUN/TURN provide a general solution to establishing media sessions between entities that are behind NATs. Loopback sessions that involve one or more end points behind NATs SHOULD use these general solutions wherever possible. 6. RTP Requirements A loopback-mirror that is compliant to this specification and accepting a media with rtp-pkt-loopback loopback-type MUST loopback the incoming RTP packets using either the encapsulated RTP payload format or the direct loopback RTP payload format as defined in section 7 of this specification. An answering entity that is compliant to this specification and accepting a media with the loopback type rtp-media-loopback MUST - transmit all received media back to the sender. The incoming media - MUST be treated as if it were to be played (e.g. the media stream - MAY receive treatment from PLC algorithms). The answering entity - MUST re-generate all the RTP header fields as it would when - transmitting media. The answering entity MAY choose to encode the - loopback media according to any of the media descriptions supported - by the offering entity. Furthermore, in cases where the same media - type is looped back, the answering entity MAY choose to preserve - number of frames/packet and bitrate of the encoded media according - to the received media. + transmit all received media back to the sender, unless congestion + feedback or other lower-layer constraints prevent it from doing so. + The incoming media MUST be treated as if it were to be played (e.g. + the media stream MAY receive treatment from PLC algorithms). The + answering entity MUST re-generate all the RTP header fields as it + would when transmitting media. The answering entity MAY choose to + encode the loopback media according to any of the media + descriptions supported by the offering entity. Furthermore, in + cases where the same media type is looped back, the answering + entity MAY choose to preserve number of frames/packet and bitrate + of the encoded media according to the received media. 7. Payload formats for Packet loopback The payload formats described in this section MUST be used by a loopback-mirror when rtp-pkt-loopback is the specified loopback-type. Two different formats are specified here - an encapsulated RTP payload format and a direct loopback RTP payload format. The encapsulated RTP payload format should be used when the incoming RTP header information needs to be preserved during the loopback operation. This is useful in cases where loopback @@ -730,137 +746,135 @@ 10. Examples This section provides examples for media descriptions using SDP for different scenarios. The examples are given for SIP-based transactions and are abbreviated and do not show the complete signaling for convenience. 10.1 Offer for specific media loopback type - A client sends an INVITE request with offer SDP which looks like: + An agent sends an SDP offer which looks like: v=0 o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com s=Example i=An example session e=alice@example.com c=IN IP4 host.atlanta.example.com t=0 0 m=audio 49170 RTP/AVP 0 a=loopback:rtp-media-loopback a=loopback-source:0 a=rtpmap:0 pcmu/8000 - The client is offering to source the media and expects the server - to mirror the RTP stream per rtp-media-loopback loopback type. + The agent is offering to source the media and expects the answering + agent to mirror the RTP stream per rtp-media-loopback loopback + type. - A server sends a response with answer SDP which looks like: + An answering agent sends an SDP answer which looks like: v=0 - o=bob 2890844526 2890842807 IN IP4 host.biloxi.example.com + o=bob 1234567890 1122334455 IN IP4 host.biloxi.example.com s=Example i=An example session e=bob@example.com c=IN IP4 host.biloxi.example.com t=0 0 m=audio 49270 RTP/AVP 0 a=loopback:rtp-media-loopback a=loopback-mirror:0 a=rtpmap:0 pcmu/8000 - The server is accepting to mirror the media from the client at the - media level. + The answerer is accepting to mirror the media from the offerer at + the media level. 10.2 Offer for choice of media loopback type - A client sends an INVITE request with offer SDP which looks like: + + An agent sends an SDP offer which looks like: v=0 o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com s=Example i=An example session e=alice@example.com c=IN IP4 host.atlanta.example.com t=0 0 m=audio 49170 RTP/AVP 0 112 113 a=loopback:rtp-media-loopback rtp-pkt-loopback a=loopback-source:0 a=rtpmap:0 pcmu/8000 a=rtpmap:112 encaprtp/8000 a=rtpmap:113 rtploopback/8000 - The client is offering to source the media and expects the server - to mirror the RTP stream at either the media or rtp level. + The offerer is offering to source the media and expects the + answerer to mirror the RTP stream at either the media or rtp level. - A server sends a response with answer SDP which looks like: + An answering agent sends an SDP answer which looks like: v=0 - o=box 2890844526 2890842807 IN IP4 host.biloxi.example.com + o=box 1234567890 1122334455 IN IP4 host.biloxi.example.com s=Example i=An example session e=bob@example.com c=IN IP4 host.biloxi.example.com t=0 0 m=audio 49270 RTP/AVP 0 112 a=loopback:rtp-pkt-loopback a=loopback-mirror:0 a=rtpmap:0 pcmu/8000 a=rtpmap:112 encaprtp/8000 - The server is accepting to mirror the media from the client at the - packet level using the encapsulated RTP payload format. + The answerer is accepting to mirror the media from the offerer at + the packet level using the encapsulated RTP payload format. - 10.3 Response to INVITE request rejecting loopback media + 10.3 Answerer rejecting loopback media - A client sends an INVITE request with offer SDP which looks like: + An agent sends an SDP offer which looks like: v=0 o=alice 2890844526 2890842807 IN IP4 host.atlanta.example.com s=Example i=An example session e=user@example.com c=IN IP4 host.atlanta.example.com t=0 0 m=audio 49170 RTP/AVP 0 a=loopback:rtp-media-loopback a=loopback-source:0 a=rtpmap:0 pcmu/8000 - The client is offering to source the media and expects the server - to mirror the RTP stream at the media level. + The offerer is offering to source the media and expects the + answerer to mirror the RTP stream at the media level. - A server sends a response with answer SDP which looks like: + An answering agent sends an SDP answer which looks like: v=0 - o=bob 2890844526 2890842807 IN IP4 host.biloxi.example.com + o=bob 1234567890 1122334455 IN IP4 host.biloxi.example.com s=Example i=An example session e=user@example.com c=IN IP4 host.biloxi.example.com t=0 0 m=audio 0 RTP/AVP 0 a=loopback:rtp-media-loopback a=loopback-mirror:0 a=rtpmap:0 pcmu/8000 - NOTE: Loopback request may be rejected by either not including the - loopback mode attribute (for backward compatibility) or setting the - media port number to zero, or both, in the response. - 11. Security Considerations - The security considerations of [RFC3261] and [RFC3264] apply. - Furthermore, given that media loopback may be automated without the - end user's knowledge, the server of the media loopback should be - aware of denial of service attacks. It is recommended that sessions - with media loopback are authenticated and the frequency of such - sessions is limited by the server. + The security considerations of [RFC3264] apply. Furthermore, given + that media loopback may be automated without the end user's + knowledge, the server of the media loopback should be aware of + denial of service attacks. It is recommended that sessions with + media loopback are authenticated and the frequency of such sessions + is limited by the server. 12. Implementation Considerations The media loopback approach described in this document is a complete solution that would work under all scenarios. However, it is believed that the solution may not be light-weight enough for the common case. In light of this concern, this section clarifies which features of the loopback proposal MUST be implemented for all implementations and which features MAY be deferred if the complete solution is not desired. @@ -1340,25 +1354,20 @@ defined at this time. Author: Kaynam Hedayat. Change controller: IETF Audio/Video Transport working group delegated from the IESG. 14. Normative References - [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., - Johnston, A., Peterson, J., Sparks, R., Handley, M. - and E. Schooler, "SIP: Session Initiation Protocol", - RFC 3261, June 2002. - [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with the Session Description Protocol (SDP)", RFC 3264, June 2002. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R. and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC3611] Almeroth, K., Caceres, R., Clark, A., Cole, R., Duffield, N., Friedman, T., Hedayat, K., Sarac, K. @@ -1380,20 +1389,29 @@ RFC 3551, July 2003. [RFC4566] Handley, M., Jacobson, V., Perkins, C., "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC4855] Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, February 2007. Authors' Addresses + Hadriel Kaplan + Acme Packet + 100 Crosby Drive + Bedford, MA 01730 + USA + + EMail: hkaplan@acmepacket.com + URI: http://www.acmepacket.com + Kaynam Hedayat EXFO 285 Mill Road Chelmsford, MA 01824 US Phone: +1 978 367 5611 EMail: kaynam.hedayat@exfo.com URI: http://www.exfo.com/