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Network Working Group                                           J. WelchRequest for Comments: 4445                        IneoQuest TechnologiesCategory: Informational                                         J. Clark                                                           Cisco Systems                                                              April 2006A Proposed Media Delivery Index (MDI)Status of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2006).IESG Note   This RFC is not a candidate for any level of Internet Standard.   There are IETF standards which are highly applicable to the space   defined by this document as its applicability, in particular, RFCs   3393 and 3611, and there is ongoing IETF work in these areas as well.   The IETF also notes that the decision to publish this RFC is not   based on IETF review for such things as security, congestion control,   MIB fitness, or inappropriate interaction with deployed protocols.   The RFC Editor has chosen to publish this document at its discretion.   Readers of this document should exercise caution in evaluating its   value for implementation and deployment.  SeeRFC 3932 for more   information.Abstract   This memo defines a Media Delivery Index (MDI) measurement that can   be used as a diagnostic tool or a quality indicator for monitoring a   network intended to deliver applications such as streaming media,   MPEG video, Voice over IP, or other information sensitive to arrival   time and packet loss.  It provides an indication of traffic jitter, a   measure of deviation from nominal flow rates, and a data loss   at-a-glance measure for a particular flow.  For instance, the MDI may   be used as a reference in characterizing and comparing networks   carrying UDP streaming media.   The MDI measurement defined in this memo is intended for Information   only.Welch & Clark                Informational                      [Page 1]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 20061.  Introduction   There has been considerable progress over the last several years in   the development of methods to provide for Quality of Service (QoS)   over packet-switched networks to improve the delivery of streaming   media and other time-sensitive and packet-loss-sensitive applications   such as [i1], [i5], [i6], [i7].  QoS is required for many practical   networks involving applications such as video transport to assure the   availability of network bandwidth by providing upper limits on the   number of flows admitted to a network, as well as to bound the packet   jitter introduced by the network.  These bounds are required to   dimension a receiver`s buffer to display the video properly in real   time without buffer overflow or underflow.   Now that large-scale implementations of such networks based on RSVP   and Diffserv are undergoing trials [i3] and being specified by major   service providers for the transport of streaming media such as MPEG   video [i4], there is a need to diagnose issues easily and to monitor   the real-time effectiveness of networks employing these QoS methods   or to assess whether they are required.  Furthermore, due to the   significant installed base of legacy networks without QoS methods, a   delivery system`s transitional solution may be composed of networks   with and without these methods, thus increasing the difficulty in   characterizing the dynamic behavior of these networks.   The purpose of this memo is to describe a set of measurements that   can be used to derive a Media Delivery Index (MDI) that indicates the   instantaneous and longer-term behavior of networks carrying streaming   media such as MPEG video.   While this memo addresses monitoring MPEG Transport Stream (TS)   packets [i8] over UDP, the general approach is expected to be   applicable to other streaming media and protocols.  The approach is   applicable to both constant and variable bit rate streams though the   variable bit rate case may be somewhat more difficult to calculate.   This document focuses on the constant bit rate case as the example to   describe the measurement, but as long as the dynamic bit rate of the   encoded stream can be determined (the "drain rate" as described below   inSection 3), then the MDI provides the measurement of network-   induced cumulative jitter.  Suggestions and direction for calculation   of MDI for a variable bit rate encoded stream may be the subject of a   future document.   Network packet delivery time variation and various statistics to   characterize the same are described in a generic approach in [i10].   The approach is capable of being parameterized for various purposes   with the intent of defining a flexible, customizable definition that   can be applied to a wide range of applications and furtherWelch & Clark                Informational                      [Page 2]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 2006   experimentation.  Other approaches to characterizing jitter behavior   are also captured such as in [i12].  A wide-ranging report format   [i11] has been described to convey information including jitter for   use with the RTP Control Protocol (RTCP) [i12].  The MDI is instead   intended to specifically address the need for a scalable,   economical-to-compute metric that characterizes network impairments   that may be imposed on streaming media, independent of control plane   or measurement transport protocol or stream encapsulation protocol.   It is a targeted metric for use in production networks carrying large   numbers of streams for the purpose of monitoring the network quality   of the flows or for other applications intended to analyze large   numbers of streams susceptible to IP network device impairments.  An   example application is the burgeoning deployments of Internet   Protocol Television (IPTV) by cable and telecommunication service   providers.  As described below, MDI provides for a readily scalable   per-stream measure focused on loss and the cumulative effects of   jitter.2.  Media Delivery Index Overview   The MDI provides a relative indicator of needed buffer depths at the   consumer node due to packet jitter as well as an indication of lost   packets.  By probing a streaming media service network at various   nodes and under varying load conditions, it is possible to quickly   identify devices or locales that introduce significant jitter or   packet loss to the packet stream.  By monitoring a network   continuously, deviations from nominal jitter or loss behavior can be   used to indicate an impending or ongoing fault condition such as   excessive load.  It is believed that the MDI provides the necessary   information to detect all network-induced impairments for streaming   video or voice-over-IP applications.  Other parameters may be   required to troubleshoot and correct the impairments.   The MDI is updated at the termination of selected time intervals   spanning multiple packets that contain the streaming media (such as   transport stream packets in the MPEG-2 case).  The Maximums and   Minimums of the MDI component values are captured over a measurement   time.  The measurement time may range from just long enough to   capture an anticipated network anomaly during a troubleshooting   exercise to indefinitely long for a long-term monitoring or logging   application.  The Maximums and Minimums may be obtained by sampling   the measurement with adequate frequency.Welch & Clark                Informational                      [Page 3]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 20063.  Media Delivery Index Components   The MDI consists of two components:  the Delay Factor (DF) and the   Media Loss Rate (MLR).3.1.  Delay Factor   The Delay Factor is the maximum difference, observed at the end of   each media stream packet, between the arrival of media data and the   drain of media data.  This assumes the drain rate is the nominal   constant traffic rate for constant bit rate streams or the piece-wise   computed traffic rate of variable rate media stream packet data.  The   "drain rate" here refers to the payload media rate; e.g., for a   typical 3.75 Mb/s MPEG video Transport Stream (TS), the drain rate is   3.75 Mb/s -- the rate at which the payload is consumed (displayed) at   a decoding node.  If, at the sample time, the number of bytes   received equals the number transmitted, the instantaneous flow rate   balance will be zero; however, the minimum DF will be a line packet's   worth of media data, as that is the minimum amount of data that must   be buffered.   The DF is the maximum observed value of the flow rate imbalance over   a calculation interval.  This buffered media data in bytes is   expressed in terms of how long, in milliseconds, it would take to   drain (or fill) this data at the nominal traffic rate to obtain the   DF.  Display of DF with a resolution of tenths of milliseconds is   recommended to provide adequate indication of stream variations for   monitoring and diagnostic applications for typical stream rates from   1 to 40 Mb/s.  The DF value must be updated and displayed at the end   of a selected time interval.  The selected time interval is chosen to   be long enough to sample a number of TS packets and will, therefore,   vary based on the nominal traffic rate.  For typical stream rates of   1 Mb/s and up, an interval of 1 second provides a long enough sample   time and should be included for all implementations.  The Delay   Factor indicates how long a data stream must be buffered (i.e.,   delayed) at its nominal bit rate to prevent packet loss.  This time   may also be seen as a measure of the network latency that must be   induced from buffering, which is required to accommodate stream   jitter and prevent loss.  The DF`s max and min over the measurement   period (multiple intervals) may also be displayed to show the worst   case arrival time deviation, or jitter, relative to the nominal   traffic rate in a measurement period.  It provides a dynamic flow   rate balance indication with its max and min showing the worst   excursions from balance.   The Delay Factor gives a hint of the minimum size of the buffer   required at the next downstream node.  As a stream progresses, the   variation of the Delay Factor indicates packet bunching or packetWelch & Clark                Informational                      [Page 4]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 2006   gaps (jitter).  Greater DF values also indicate that more network   latency is necessary to deliver a stream due to the need to pre-fill   a receive buffer before beginning the drain to guarantee no   underflow.  The DF comprises a fixed part based on packet size and a   variable part based on the buffer utilization of the various network   component switch elements that comprise the switched network   infrastructure [i2].   To further detail the calculation of DF, consider a virtual buffer VB   used to buffer received packets of a stream.  When a packet P(i)   arrives during a calculation interval, compute two VB values,   VB(i,pre) and VB(i,post), defined as:   VB(i,pre) = sum (Sj) - MR * Ti; where j=1..i-1   VB(i,post) = VB(i,pre) + Si   where Sj is the media payload size of the jth packet, Ti is the   relative time at which packet i arrives in the interval, and MR is   the nominal media rate.   VB(i,pre) is the Virtual Buffer size just before the arrival of P(i).   VB(i,post) is the Virtual Buffer size just after the arrival of P(i).   The initial condition of VB(0) = 0 is used at the beginning of each   measurement interval.  A measurement interval is defined from just   after the time of arrival of the last packet during a nominal period   (typically 1 second) as mentioned above to the time just after the   arrival of the last packet of the next nominal period.   During a measurement interval, if k packets are received, then there   are 2*k+1 VB values used in deriving VB(max) and VB(min).  After   determining VB(max) and VB(min) from the 2k+1 VB samples, DF for the   measurement interval is computed and displayed as:   DF = [VB(max) - VB(min)]/ MR   As noted above, a measurement interval of 1 second is typically used.   If no packets are received during an interval, the last DF calculated   during an interval in which packets did arrive is displayed.  The   time of arrival of the last previous packet is always retained for   use in calculating VB when the next packet arrives (even if the time   of the last received packet spans measurement intervals).  For the   first received measurement interval of a measurement period, no DF is   calculated; however, packet arrival times are recorded for use in   calculating VB during the following interval.Welch & Clark                Informational                      [Page 5]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 20063.2.  Media Loss Rate   The Media Loss Rate is the count of lost or out-of-order flow packets   over a selected time interval, where the flow packets are packets   carrying streaming application information.  There may be zero or   more streaming packets in a single IP packet.  For example, it is   common to carry seven 188 Byte MPEG Transport Stream packets in an IP   packet.  In such a case, a single IP packet loss would result in 7   lost packets counted (if those 7 lost packets did not include null   packets).  Including out-of-order packets is important, as many   stream consumer-type devices do not attempt to reorder packets that   are received out of order.3.3.  Media Delivery Index   Combining the Delay Factor and Media Loss Rate quantities for   presentation results in the following MDI:                                  DF:MLR    Where:                          DF is the Delay Factor                        MLR is the Media Loss Rate   At a receiving node, knowing its nominal drain bit rate, the DF`s max   indicates the size of buffer required to accommodate packet jitter.   Or, in terms of Leaky Bucket [i9] parameters, DF indicates bucket   size b, expressed in time to transmit bucket traffic b, at the given   nominal traffic rate, r.3.4.  MDI Application Examples   If a known, well-characterized receive node is separated from the   data source by unknown or less well-characterized nodes such as   intermediate switch nodes, the MDI measured at intermediate data   links provides a relative indication of the behavior of upstream   traffic flows.  DF difference indications between one node and   another in a data stream for a given constant interval of calculation   can indicate local areas of traffic congestion or possibly   misconfigured QoS flow specification(s) leading to greater filling of   measurement point local device buffers, resultant flow rate   deviations, and possible data loss.Welch & Clark                Informational                      [Page 6]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 2006   For a given MDI, if DF is high and/or the DF Max-Min captured over a   significant measurement period of multiple intervals is high, jitter   has been detected but the longer-term, average flow rate may be   nominal.  This could be the result of a transient flow upset due to a   coincident traffic stream unrelated to the flow of interest causing   packet bunching.  A high DF may cause downstream buffer overflow or   underflow or unacceptable latency even in the absence of lost data.   Due to transient network failures or DF excursions, packets may be   lost within the network.  The MLR component of the MDI shows this   condition.   Through automated or manual flow detection and identification and   subsequent MDI calculations for real-time statistics on a flow, the   DF can indicate the dynamic deterioration or increasing burstiness of   a flow, which can be used to anticipate a developing network   operation problem such as transient oversubscription.  Such   statistics can be obtained for flows within network switches using   available switch cpu resources due to the minimal computational   requirements needed for small numbers of flows.  Statistics for all   flows present on, say, a gigabit Ethernet network, will likely   require dedicated hardware facilities, though these can be modest, as   buffer requirements and the required calculations per flow are   minimal.  By equipping network switches with MDI measurements, flow   impairment issues can quickly be identified, localized, and   corrected.  Until switches are so equipped with appropriate hardware   resources, dedicated hardware tools can provide supplemental switch   statistics by gaining access to switch flows via mirror ports, link   taps, or the like as a transition strategy.   The MDI figure can also be used to characterize a flow decoder's   acceptable performance.  For example, an MPEG decoder could be   characterized as tolerating a flow with a given maximum DF and MLR   for acceptable display performance (acceptable on-screen artifacts).   Network conditions such as Interior Gateway Protocol (IGP)   reconvergence time then might also be included in the flow tolerance   DF resulting in a higher-quality user experience.4.  Summary   The MDI combines the Delay Factor, which indicates potential for   impending data loss, and Media Loss Rate as the indicator of lost   data.  By monitoring the DF and MLR and their min and max excursions   over a measurement period and at multiple strategic locations in a   network, traffic congestion or device impairments may be detected and   isolated for a network carrying streaming media content.Welch & Clark                Informational                      [Page 7]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 20065.  Security Considerations   The measurements identified in this document do not directly affect   the security of a network or user.  Actions taken in response to   these measurements that may affect the available bandwidth of the   network or the availability of a service is out of scope for this   document.   Performing the measurements described in this document only requires   examination of payload header information (such as MPEG transport   stream headers or RTP headers) to determine nominal stream bit rate   and sequence number information.  Content may be encrypted without   affecting these measurements.  Therefore, content privacy is not   expected to be a concern.6.  Informative References   [i1]  Braden, R., Zhang, L., Berson, S., Herzog, S., and S. Jamin,         "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional         Specification",RFC 2205, September 1997.   [i2]  Partridge, C., "A Proposed Flow Specification",RFC 1363,         September 1992.   [i3]  R. Fellman, `Hurdles to Overcome for Broadcast Quality Video         Delivery over IP` VidTranS 2002.   [i4]  CableLabs `PacketCable Dynamic Quality-of-Service         Specification`, PKT-SP-DQOS-I06-030415, 2003.   [i5]  Shenker, S., Partridge, C., and R. Guerin, "Specification of         Guaranteed Quality of Service",RFC 2212, September 1997.   [i6]  Wroclawski, J., "Specification of the Controlled-Load Network         Element Service",RFC 2211, September 1997.   [i7]  Braden, R., Clark, D., and S. Shenker, "Integrated Services in         the Internet Architecture: an Overview",RFC 1633, June 1994.   [i8]  ISO/IEC 13818-1 (MPEG-2 Systems)   [i9]  V. Raisanen, "Implementing Service Quality in IP Networks",         John Wiley & Sons Ltd., 2003.   [i10] Demichelis, C. and P. Chimento, "IP Packet Delay Variation         Metric for IP Performance Metrics (IPPM)",RFC 3393, November         2002.Welch & Clark                Informational                      [Page 8]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 2006   [i11] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol         Extended Reports (RTCP XR)",RFC 3611, November 2003.   [i12] Schulzrinne, H.,  Casner, S., Frederick, R., and V. Jacobson,         "RTP: A Transport Protocol for Real-Time Applications", STD 64,RFC 3550, July 2003.7.  Acknowledgements   The authors gratefully acknowledge the contributions of Marc Todd and   Jesse Beeson of IneoQuest Technologies, Inc., Bill Trubey and John   Carlucci of Time Warner Cable, Nishith Sinha of Cox Communications,   Ken Chiquoine of SeaChange International, Phil Proulx of Bell Canada,   Dr Paul Stallard of TANDBERG Television, Gary Hughes of Broadbus   Technologies, Brad Medford of SBC Laboratories, John Roy of Adelphia   Communications, Cliff Mercer, PhD of Kasenna, Mathew Ho of Rogers   Cable, and Irl Duling of Optinel Systems for reviewing and evaluating   early versions of this document and implementations for MDI.Authors' Addresses   James Welch   IneoQuest Technologies, Inc   170 Forbes Blvd   Mansfield, Massachusetts 02048   Phone: 508 618 0312   EMail: Jim.Welch@ineoquest.com   James Clark   Cisco Systems, Inc   500 Northridge Road   Suite 800   Atlanta, Georgia 30350   Phone: 678 352 2726   EMail: jiclark@cisco.comWelch & Clark                Informational                      [Page 9]

RFC 4445         A Proposed Media Delivery Index (MDI)        April 2006Full Copyright Statement   Copyright (C) The Internet Society (2006).   This document is subject to the rights, licenses and restrictions   contained inBCP 78 and at www.rfc-editor.org/copyright.html, and   except as set forth therein, the authors 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.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at   ietf-ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is provided by the IETF   Administrative Support Activity (IASA).Welch & Clark                Informational                     [Page 10]