Network Working Group P. Riikonen Internet-Draft draft-riikonen-silc-multimedia-session-00.txt 15 January 2007 Expires: 15 July 2007 Multimedia Sessions in SILC protocol Status of this Draft By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of 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. 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/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document defines the use of multimedia protocols and the set up of multimedia sessions in the Secure Internet Live Conferencing (SILC) protocol [SILC1]. Table of Contents 1 Introduction .................................................. 2 1.1 Requirements Terminology .................................. 2 2 Recommended Protocol .......................................... 2 3 Session Description Protocol (SDP) ............................ 2 3.1 SDP field usage in SILC ................................... 3 3.2 SDP Examples .............................................. 5 4 Session Initiation Protocol (SIP) ............................. 6 5 Other Protocols ............................................... 6 6 Security Considerations ....................................... 7 Riikonen [Page 1] Internet-Draft 15 January 2007 7 References .................................................... 7 8 Author's Address .............................................. 7 9 Full Copyright Statement ...................................... 7 1 Introduction This document defines the use of multimedia protocols and the set up of multimedia sessions in the Secure Internet Live Conferencing (SILC) protocol [SILC1]. The SILC protocol supports multimedia messages with the Message Payload [SILC2] and SILC_MESSAGE_FLAG_DATA which has the ability to define what type of content is delievered within the payload. The Message Payload is used to encapsulate the multimedia session set up procedure and the actual multimedia session data. We define the recommended multimedia session protocol for SILC and also consider some other protocols in the scope of SILC. 1.1 Requirements Terminology The keywords MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this document, are to be interpreted as described in [RFC2119]. 2 Recommended Protocol Since SILC protocol can encapsulate practically any protocol for setting up a multimedia session we have selected the Session Description Protocol (SDP) as RECOMMENDED protocol. It was chosen for its maturity, simplicity and versatility. If multimedia features are implemented in SILC application it is recommended that at least support for SDP is added. 3 Session Description Protocol (SDP) The SDP [SDP] protocol defines a general purpose multimedia session description protocol. SDP is one of the simplest protocols to negotiate multimedia sessions and is suited perfectly for SILC protocol. Since SDP does not itself define how it is used to set up the session, we define it here for SILC. The definition is based on the [RFC3264] and [RFC4145]. In SILC the SDP messages are sent as data messages (MIME message). They can be destined directly to a client for direct conferencing, or to a channel for group conferencing. It is also possible to send the message directly to client to invite them to group conferencing before they have joined the channel. The MIME type used is application/sdp. Riikonen [Page 2] Internet-Draft 15 January 2007 To set up a multimedia session a client sends SILC message with SILC_MESSAGE_FLAG_DATA and SILC_MESSAGE_FLAG_REQUEST flags set and with MIME SDP message in the message payload. If the receiver wants to participate in the multimedia session it sends MIME SDP message back with SILC_MESSAGE_FLAG_DATA and SILC_MESSAGE_FLAG_REPLY flags set to the sender. If reply is not received after an application defined period of time the message may be retransmitted or the session set up may be terminated. After reply has been received the multimedia session is started according to the SDP and all multimedia data is sent using SILC data messages. When performing peer-to-peer connection the SDP defines which party initiates the connection. After initiation the SILC Key Exchange protocol MUST be performed. The resulted key material will be used to protect the multimedia session. Multimedia data transmission may start after the key exchange has been performed. When performing group conferencing all parties independently connect to the SILC server specified in the SDP. In other cases when performing the multimedia session inside the SILC network, any party may start transmitting the multimedia data after the SDPs have been exchanged. To terminate the session, or to reject incoming request, an MD5 digest MUST be computed from the original SDP data, and the digest is sent back with the SILC_MESSAGE_FLAG_DATA and SILC_MESSAGE_FLAG_STOP flags set. The receiver of such message should verify the MD5 digest and terminate the session if it matches any active session. The session may also be terminated by closing network connection. In group sessions simply by leaving the channel terminates the session. The original sender of the SDP message may send the terminating message to notify all clients on the channel to terminate the session. If the original sender on channel receives the terminating message it takes no action on it. 3.1 SDP field usage in SILC The Encryption Keys (k=) field describes encryption key to protect the multimedia session. As SILC protocol transport and the multimedia session is secured by default this field SHOULD NOT be used. The Origin (o=) field describes from where the session originates. The sub-field is the sender's SILC nickname. Examples: o=foobar 2890844521 2890842804 IN IP4 10.2.1.7 The Connection Data (c=) field describes the connection information for the multimedia session. When performing peer-to-peer multimedia session the is 'IN', indicating Internet connection. When Riikonen [Page 3] Internet-Draft 15 January 2007 performing multimedia session inside SILC network it is 'SILC'. When the 'SILC' network type is used the
and sub-fields are omitted. Examples: c=SILC c=IN IP4 10.2.1.7 The Media Announcements (m=) field describes the media information for the multimedia session. If the network type in c= field is 'SILC' the sub-field MUST be set to 9 (discard). The for RTP over UDP is 'RTP/AVP', for RTP over TCP it is 'TCP/RTP/AVP', and for non-RTP protocol over UDP it is 'udp' and over TCP it is 'tcp'. The sub-field includes the RTP media payload number when using RTP. When using non-RTP protocol it includes MIME subtype. Examples: c=SILC m=audio 9 TCP/RTP/AVP 3 a=rtpmap:3 GSM/8000 c=SILC m=audio 9 tcp mpeg The Attributes (a=) field can be used to set various session and media specific attributes. For SILC we define attribute "silc". a=silc: The is either "direct" or "group". When it is "direct" and the c= field defines a connection point the connection will be peer-to-peer connection to the remote client. If it is "group" and the the c= field defines a connection point the connection will be to a remote SILC server for group conferencing. If c= field includes "SILC" network type, then "direct" is for direct session with a client in SILC network and "group" is for group conferencing in SILC network. If the "silc" attribute is omitted the session type is expected to be "direct". The following parameters are defined for attribute "silc". channel The name of the channel for group conferencing. Can be used only with "group" session type. More than one channel parameters may be defined. The [RFC4145] specifies a "setup" attribute that defines which party of the session will initiate the connection when performing peer-to-peer session. Its use in SILC is as specified in [RFC4145] and MUST be present in SDP when the c= field includes an actual connection point and when the "silc" Riikonen [Page 4] Internet-Draft 15 January 2007 attribute session type is "direct", or if the attribute is not present at all. When performing group conferencing each party always need to create the connection to the server and the "setup" attribute need not be present in SDP. 3.2 SDP Examples v=0 o=foobar 2890844521 2890842804 IN IP4 10.2.1.100 s=peer-to-peer example t=0 0 m=audio 5000 TCP/RTP/AVP 3 c=IN IP4 10.2.1.100 a=rtpmap:3 GSM/8000 a=silc:direct a=setup:active This example sets up a peer-to-peer session to remote client at 10.2.1.100 at port 5000. v=0 o=foobar 2890844521 2890842804 IN IP4 10.2.1.32 s=Group conferencing example c=IN IP4 10.2.1.7 t=0 0 a=silc:group channel=foobar m=audio 706 TCP/RTP/AVP 3 a=rtpmap:3 GSM/8000 This example sets up a session to a remote SILC server 10.2.1.7 at port 706. Once connected the channel "foobar" will be joined for group conferencing. v=0 o=foobar 2890844521 2890842804 IN IP4 10.2.1.32 s=SILC network chat example c=SILC t=0 0 m=audio 9 TCP/RTP/AVP 3 a=rtpmap:3 GSM/8000 This example sets up a session inside SILC network with the remote user "foobar". v=0 o=foobar 2890844521 2890842804 IN IP4 10.2.1.32 s=SILC network group conferencing example t=0 0 Riikonen [Page 5] Internet-Draft 15 January 2007 m=audio 9 TCP/RTP/AVP 3 c=SILC a=rtpmap:3 GSM/8000 a=silc:group channel=group-chat This example sets up a group conferencing session inside SILC network on channel "group-chat". 4 Session Initiation Protocol (SIP) The SIP [SIP] protocol is a general purpose protocol for setting up, modifying and terminating different kinds of sessions, including multimedia sessions. The SIP protocol use the SDP to describe the multimedia session. In SILC the SIP messages are sent as data messages (MIME message). They can be destined directly to a client for direct conferencing, or to a channel for group conferencing. It is also possible to send the message directly to client to invite them to group conferencing before they have joined the channel. The MIME type used is application/sip. The SILC_MESSAGE_FLAG_DATA flag must be set in each message and the message payload includes a MIME SIP message. The actual SIP session set up and termination is described in the SIP protocol specification, and SILC protocol merely provides a secure transport for the session. After the session is set up all multimedia data is sent using SILC data messages. The MIME type for the multimedia data messages is defined during the SIP session set up. The rules for SDP fields described in previous section also applies for SDP with SIP in the context of SILC. Proxy and redirection servers usually would not be used in the context of SILC, unless the sessions are redirected to outside SILC network. This may compromise the security of the session. The S/MIME need not be used when using SIP in SILC protocol. The SILC protocol transport and the created multimedia session is secured by default. 5 Other Protocols There are other open and proprietary protocols for setting up multimedia sessions. One important is H.323 using the H.225 to set up the session. This document should later define the use of H.323 with SILC. Practically any protocol to set up multimedia sessions may be used with SILC by using SILC as a secure transport to set up the session, and to use Riikonen [Page 6] Internet-Draft 15 January 2007 SILC data messages (MIME messages) to secure and deliver the actual multimedia data once the session has been established. 6 Security Considerations Security is central to the design of this protocol, and these security considerations permeate the specification. Common security considerations such as keeping private keys truly private and using adequate lengths for symmetric and asymmetric keys must be followed in order to maintain the security of this protocol. 7 References [SILC1] Riikonen, P., "Secure Internet Live Conferencing (SILC), Protocol Specification", Internet Draft, June 2003. [SILC2] Riikonen, P., "SILC Packet Protocol", Internet Draft, June 2003. [RFC3264] Rosenberg, J., et. al., "An Offer/Answer Model with the Session Description Protocol (SDP)", RFC 3264, June 2002. [RFC4145] Yon, D., et. al., "TCP-Based Media Transport in the Session Description Protocol (SDP)", RFC 4145, September 2005. [SIP] Rosenberg, J., et. al., "SIP: Session Initiation Protocol", RFC 3261, June 2002. 8 Author's Address Pekka Riikonen Helsinki Finland EMail: priikone@iki.fi 9 Full Copyright Statement Copyright (C) The Internet Society (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors Riikonen [Page 7] Internet-Draft 15 January 2007 retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Riikonen [Page 8]