Network Working Group I. Johansson Internet-Draft Ericsson AB Intended status: Standards Track Apr 8, 2009 Expires: October 10, 2009 Multicast-Based Rapid Acquisition of Multicast RTP Sessions draft-johansson-avt-mcast-based-rams-00 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. 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 October 10, 2009. Copyright Notice Copyright (c) 2009 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 in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document proposes an improvement to the unicast based Rapid Acquisition for Multicast based Streaming discussed in [ID-Versteeg]. The outline of the improvement is to gather up Rapid Acquisition Johansson Expires October 10, 2009 [Page 1] Internet-Draft Multicast-Based RAMS Apr 2009 requests for many users and transmit them in dedicated multicast streams. With this technique the peak load on the retransmission server and on the outgoing link from the retransmission server can be reduced. For a problem description of the channel change problem in multicast based IPTV the reader is encouraged to read [ID-Versteeg]. Requirements Language 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 [RFC2119]. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Description . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1. Informative References . . . . . . . . . . . . . . . . . . 6 6.2. Normative References . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Johansson Expires October 10, 2009 [Page 2] Internet-Draft Multicast-Based RAMS Apr 2009 1. Introduction Draft [ID-Versteeg] proposes a method for fast channel change in multicast RTP session that employs setting up separate unicast burst transmissions to set top boxes that changes channel. Draft [ID-Peilin] proposes an extension to this draft that essentially adds elements to make it possible to adjust the transmission rate of the unicast stream. The methods should considerably reduce the channel switch latency as experienced by the end user. There are a number of potential issues with the aforementioned methods. o Peaky load pattern: Viewers of popular IPTV channels may display a synchronized behavior in their channel change pattern , for instance when a commercial break sets in or a popular TV show ends. o High load on the retransmission server: The retransmission server will sometimes be exposed to high load, also the load on the outgoing link from the retransmission server can be very high. This means that the retransmission server and the outgoing link needs to be vastly over provisioned, something that may be costly for the implementer of the IPTV infrastructure. This draft explains how multiple rapid acquisition requests can be gathered up and served via a dedicated multicast channel and can be used as an improvement to the methods described earlier. The additional delay compared to a solely unicast based version depends on the gather up time which can be set quite low during low load conditions and set to higher values during high load conditions (giving graceful degradation). The benefit is that the peak load on the retransmission server is reduced considerably. Another method that is described is to setup multicast control channels that contains information about rapid acquisition multicast feeds that are active. 2. Description The proposed solution can serve as a complement to the solutions outlined in [ID-Versteeg] and [ID-Peilin]. During low load conditions the retransmission server (RS) will serve each RAMS-R request with an individual unicast RTP burst. As the load increases the RS will gather up RAMS-R for the same channels over a defined time window (Td) and set up a multicast stream that contains the same Johansson Expires October 10, 2009 [Page 3] Internet-Draft Multicast-Based RAMS Apr 2009 contents as the unicast stream would have done. The time window that is used to gather up RAMS-R requests for the same channel is made dependent on the load on the RS. During fairly low load conditions the time window is made small (e.g Td=50ms), as load gets higher the time window increases, thus the degradation in channel switching performance will become graceful. The figure below displays how this would work, the figures is somewhat simplified, for instance IGMP Leave is left out. RR-1 RR-2 RS | | | |--RAMS-R, ch X-------------------------------------->| - |<-RAMS-I m-cast 225.0.1.1----------------------------| | |--IGMP Join 225.0.1.1------------------------------->| | | |--RAMS-R, ch X ---------->| | | |<-RAMS-I m-cast 225.0.1.1-| Td | |--IGMP Join 225.0.1.1---->| | | | | | | | | | |<-------------------------|<-Stream buf on 225.0.1.1-| - | | | | |-IGMP Join m-cast ch X---------> |---------------------------------IGMP Join m-cast ch X----> RR-1 transmits a RAMS-R to RS, requesting rapid acquisition data for channel X, as RR-1 is the first to request this data, a timer is started in order to wait for a given timespan (Td) for other RAMS-R for the same channel from other RR's. RS sends a RAMS-I to RR-1 with instructions to listen in on 225.0.1.1 and thus RS-1 makes an IGMP Join to said multicast address. Later RR-2 sends a RAMS-R to RS, requesting rapid acquisition data for channel X. RS sends a RAMS-I to RR-2 with instructions to listen in on 225.0.1.1 and RS-2 also makes an IGMP Join to the said multicast address When the timer is expired, RS will stream the requested data on multicast channel 225.0.1.1 the data speed in the multicast channel can be either normal speed or a speed that is higher than normal (e.g 120%). When sufficient data has been received via the multicast channel, both RR-1 and RR-2 makes an IGMP Join to multicast channel X. As Td is made dependent on the load on the RS this method allows for graceful degradation. A special case occurs when the timer expires and only one STB has sent a request, this case is similar to the Johansson Expires October 10, 2009 [Page 4] Internet-Draft Multicast-Based RAMS Apr 2009 unicast streaming case. At severe load conditions the RAMS-R requests will be either ignored or responded with a negative acknowledgement, in which case the RR's will not receive any rapid acquisition data. Besides the methodology described above, another possibility is also that an STB joins a multicast control channel which contains information about which multicast channel contains rapid acquisition data for a given channel. Because of the limited amount of data that is carried in this multicast control channel reliable transmission techniques can possibly be used. There are a few different ways to determine when a switch from the rapid acquisition channel to the normal multicast channel: 1. A marker in the rapid acquisition media stream tells the STB to make a switch 2. A multicast control channel tells the STB that it is time to switch or can give the STB sufficient information necessary to make the switch 3. End of rapid acquisition media stream, indicated by an explicit End-Of-Stream symbol 4. Count of frames, the STB can itself decide to switch after receiving e.g 3 I-frames In certain cases it is preferable (for instance limited downlink bandwidth) that the rapid acquisition stream to a particular STB is terminated (e.g by means of IGMP Leave) before the normal multicast channel is joined. Depending on how the decision to switch is made there is a slight possibility that data will be missing, to alleviate this risk the normal multicast streams can be delayed a fraction of a second to allow for a certain switching time and a smooth transition from the rapid acquisition data to the normal multicast channel. 3. IANA Considerations T.B.D 4. Security Considerations T.B.D Johansson Expires October 10, 2009 [Page 5] Internet-Draft Multicast-Based RAMS Apr 2009 5. Acknowledgements The author wish to thank Mats Cedervall and Victor Souza for help with this draft. 6. References 6.1. Informative References [ID-Peilin] IETF, "Extensions to RTCP for Rapid Synchronization, http: //tools.ietf.org/id/draft-peilin-avt-rtp-burst-01.txt". [ID-Versteeg] IETF, "Unicast-Based Rapid Acquisition of Multicast RTP Sessions, http://tools.ietf.org/id/ draft-versteeg-avt-rapid-synchronization-for-rtp-02.txt". 6.2. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Author's Address Ingemar Johansson Ericsson AB Laboratoriegrand 11 SE-971 28 Lulea SWEDEN Phone: +46 73 0783289 Email: ingemar.s.johansson@ericsson.com Johansson Expires October 10, 2009 [Page 6]