Network Working Group J. Welch
Internet Draft IneoQuest Technologies
Intended Category: Informational J. Clark
Cisco Systems
August, 2004
A Proposed Media Delivery Index
draft-welch-mdi-00.txt
Status of this Memo
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By submitting this Internet-Draft, I accept the provisions of Section
3 of RFC 3667.
Abstract
This memo defines a Media Delivery Index (MDI) measurement which can
be used as a diagnostic tool or a quality indicator for monitoring a
network intended to transport streaming media such as MPEG video or
other arrival time and packet loss sensitive information. It
provides an indication of traffic jitter, a measure of deviation from
nominal flow rates, and data loss at-a-glance. For instance, the MDI
may be used as a reference in characterizing and comparing networks
carrying constant bit rate streaming media. Included is a set of
managed objects for SNMP-based management of IP media streams for
which an MDI measurement is obtained.
The Media Delivery Index measurement and MIB defined in this memo is
intended for Information only.
Conventions used in this document
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 [n14].
Introduction
There has been considerable progress over the last several years in
the development of methods to provide for QOS over packet switched
networks to improve the delivery of streaming media and other time
and packet loss sensitive applications such as [i1], [i5], [i6],
[i7]. QOS is required for 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 properly display the
video 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 easily diagnose issues and monitor the
real time effectiveness of networks employing these QOS methods.
Furthermore, due to the significant installed base of legacy networks
without QOS methods, a delivery system`s transitional solution may be
comprised of both networks with and without these methods thus
increasing the difficulty in characterizing the dynamic behavior of
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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) which indicates
the instantaneous and longer term behavior of networks carrying
streaming media such as MPEG data.
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.
Media Delivery Index Overview
The MDI provides a relative indicator of needed buffer depths at the
consumer node due to packet jitter and network latency as well as an
indication of lost packets. By probing a streaming media network at
various nodes and under varying load conditions, it is possible to
quickly identify devices or locales which 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 MPEG video display
impairments. 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 which 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.
Media Delivery Index Components
- Delay Factor (DF): The maximum difference, observed at the end of
each media stream packet, between the arrival of media data and the
drain of media data, assuming the drain rate is the nominal constant
traffic rate of media stream packet data. 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. This buffered media data in bytes
is expressed in terms of how long it would take to drain (or fill)
this data at the nominal constant traffic rate in milliseconds to
obtain the DF. The DF value MUST be updated and displayed at the end
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of a selected time interval. The selected time interval is chosen to
be long enough to include a number of TS packets and will, therefore,
vary based on the nominal constant traffic rate. The Delay Factor
indicates how long a data stream must be buffered (i.e. delayed) at
its nominal constant bit rate to prevent packet loss. Thus, it is
also proportional to latency. The DF`s max and min over the
measurement period MAY also be displayed to show the worst case
arrival time deviation, or jitter, relative to the nominal constant
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. To arrive at a bounded DF, the long term
flow rate deviation (LFRD) must be 0, where LFRD is a running
deviation of flow rate from expected nominal constant traffic rate
over a measurement period. A large positive or negative LFRD usually
indicates a media stream source failure or misconfiguration and would
cause the DF value to steadily increase from interval to interval.
The Delay Factor gives a hint of the size of the buffer required at
the next downstream node. As a stream progresses, the variation of
the Delay Factor indicates packet bunching (jitter). Greater DF
values also indicate more network latency to deliver a stream due to
the need to prefill a receive buffer before beginning the drain to
guarantee no underflow. The DF is comprised of a fixed part based
on packet size and a variable part based on the various network
component switch elements` buffer utilization that comprise the
switched network infrastructure [i2].
- Media Loss Rate: Lost or out of order Media packets counted over a
selected time interval, where Media packets are packets carrying
media information. There may be 0 or more media packets in a single
layer 2 network packet such as Ethernet. For example, it is common
to carry seven 188 Byte MPEG Transport Stream packets in a 1362 Byte
Ethernet frame. In such a case, a single Ethernet frame loss would
result in 7 lost Media packets counted for the case where the 7 lost
Media packets did not include null packets.
Combining these quantities for presentation results in the MDI:
DF:MLR
Where:
DF is the Delay Factor
MLR is the Media Loss Rate
At a receiving node, knowing its nominal constant drain bit rate, the
DF`s max indicates the size of required buffer 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
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given nominal constant traffic rate, r. In the case where 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 flow. 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.
For a given MDI, if DF is high and/or the DF Max-Min captured over a
significant measurement period 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.
The Internet-Standard Management Framework
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [i10].
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58,
RFC 2578 [n11], STD 58, RFC 2579 [n12] and STD 58, RFC 2580 [n13].
MIB Overview
This MIB provides a set of objects required for the export of MDI
metrics of IP streaming media streams.
MIB Definitions
--
-- Media Stream Monitor MIB
--
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MEDIA-MONITOR-MIB DEFINITIONS ::= BEGIN
IMPORTS
MODULE-IDENTITY,
OBJECT-TYPE,
Integer32,
Unsigned32,
mib-2,
NOTIFICATION-TYPE,
OBJECT-IDENTITY,
IpAddress
FROM SNMPv2-SMI -- RFC2578
DisplayString
FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP,
NOTIFICATION-GROUP
FROM SNMPv2-CONF; -- RFC2580
mediaMonitorMIB MODULE-IDENTITY
LAST-UPDATED "200404040000Z" -- 04 April 2004
ORGANIZATION " xx "
CONTACT-INFO
"IneoQuest Technologies, Inc.
Postal: 170 Forbes Boulevard
Mansfield, MA, 02048
Tel: +1 508 618 0312
E-mail: jim.welch@ineoquest.com"
DESCRIPTION
"The media Monitor MIB (MEDIA-MONITOR-MIB) provides
Metrics for Monitoring IP streaming Media Flows."
-- Revision history
REVISION "200404040000Z" -- 04 April 2004
DESCRIPTION
"Initial version, published as RFC xxxx. (this RFC)"
::= { xxxx }
-- Top level structure of the MIB
mediaMonitorObjects OBJECT IDENTIFIER ::= { mediaMonitorMIB 1 }
ipMediaStreamMonitorTable OBJECT-TYPE
SYNTAX SEQUENCE OF IpMediaStreamMonitorEntry
MAX-ACCESS not-accessible
STATUS current
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DESCRIPTION
"IP Stream Monitor Table. This table is indexed by the
Stream Handle. This Table only shows the currently ACTIVE
video Streams."
::= { mediaMonitorObjects 1 }
ipMediaStreamMonitorEntry OBJECT-TYPE
SYNTAX IpMediaStreamMonitorEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"IP Stream Monitor Table Entry."
INDEX { ipMediaStreamMonitorHandle }
::= { ipMediaStreamMonitorTable 1 }
IpMediaStreamMonitorEntry ::= SEQUENCE {
ipMediaStreamHandle
Unsigned32,
ipMediaStreamSourceIpAddress
IpAddress,
ipMediaStreamSourcePort
Unsigned32,
ipMediaStreamDestinationIpAddress
IpAddress,
ipMediaStreamDestinationPort
Unsigned32,
ipMediaStreamBitRate
Unsigned32,
ipMediaStreamInterval
Unsigned32,
ipMediaStreamStartTime
DisplayString,
ipMediaStreamMDIDelayFactor
Unsigned32,
ipMediaStreamMDILossRate
Unsigned32,
ipMediaStreamMDIDFThreshold
Unsigned32,
ipMediaStreamMDILRThreshold
Unsigned32,
ipMediaStreamMDIDFErrorIntervals
Unsigned32
ipMediaStreamMonitorMDIMLRErrorIntervals
Unsigned32
}
ipMediaStreamHandle OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
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STATUS current
DESCRIPTION
"Table is indexed by stream Handle. The table has one row
for each Media Stream detected from the Ip Interface. The
Stream Handle shall be a unique value for the life of the
stream."
::= { ipMediaStreamMonitorEntry 1 }
ipMediaStreamSourceIpAddress OBJECT-TYPE
SYNTAX IpAddress
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Source IpAddress for the Stream indexed by the Stream
Handle."
::= { ipMediaStreamMonitorEntry 2 }
ipMediaStreamSourcePort OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The Source port for the Stream indexed by the Stream
Handle."
::= { ipMediaStreamMonitorEntry 3 }
ipMediaStreamDestinationIpAddress OBJECT-TYPE
SYNTAX IpAddress
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Destination IpAddress for the Stream indexed by the
Stream Handle."
::= { ipMediaStreamMonitorEntry 4 }
ipMediaStreamDestinationPort OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The Destination port for the Stream indexed by the
Stream Handle."
::= { ipMediaStreamMonitorEntry 5 }
ipMediaStreamBitRate OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
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"The nominal Bit Rate of the Media Stream in bits/second."
::= { ipMediaStreamMonitorEntry 6 }
ipMediaStreamInterval OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number indicates the minimum Interval in seconds for
a good MDI Measurement. The Interval is based on the
current Bit Rate of the Stream. The minimum interval
should be chosen such that at least 10 IP packets occur
per interval. This value defaults to 1 second and the
Interval is typically configured to 1 second unless the
above criteria is not met."
::= { ipMediaStreamMonitorEntry 7 }
ipMediaStreamStartTime OBJECT-TYPE
SYNTAX DisplayString
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The Timestamp shows the Real time at which the stream was
detected. The Timestamp format is YYYY/MM/DD/HH/MM/SS."
::= { ipMediaStreamMonitorEntry 8 }
ipMediaStreamMDIDelayFactor OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This object displays the Media Delivery Index Delay
Factor parameter in units of milliseconds. This parameter
indicates the burstiness of the stream."
::= { ipMediaStreamMonitorEntry 9 }
ipMediaStreamMDILossRate OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This object displays the Media Delivery Index Media Loss
Rate in packets/sec. This parameter indicates rate of
lost media packets of the of the stream."
::= { ipMediaStreamMonitorEntry 10 }
ipMediaStreamMDIDFThreshold OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-write
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STATUS current
DESCRIPTION
"The Threshold for Media Delivery Index Delay Factor in
milliSeconds. The default value is set to 0 indicating
that it is invalid until configured."
::= { ipMediaStreamMonitorEntry 11 }
ipMediaStreamMDILRThreshold OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"The Threshold for Media Delivery Loss Rate
in Packets/second. The default value is set to 0xffffffff
indicating that it is invalid until configured."
::= { ipMediaStreamMonitorEntry 12 }
ipMediaStreamMDIDFErrorIntervals OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number indicates the number of MDI DF Threshold
(ipMediaStreamMonitorMDIDFThreshold) Crossed Intervals
during the life of a stream. This shall be 0 and invalid
until the MDI DF Thresholds are configured."
::= { ipMediaStreamMonitorEntry 13 }
ipMediaStreamMDIMLRErrorIntervals OBJECT-TYPE
SYNTAX Unsigned32
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The number indicates the number of MDI MLR Threshold
(ipMediaStreamMDILRThreshold)Crossed Intervals
during the life of a stream. This shall be 0 and invalid
until the MDI MLR Thresholds are configured."
::= { ipMediaStreamMonitorEntry 14 }
END
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
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network, traffic congestion or device impairments may be detected and
isolated for a network carrying streaming media content. The
included MIB provides a set of objects required for the export of MDI
metrics of IP streaming media streams.
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 which may affect the available bandwidth of the
network or availability of a service is out of scope for this
document.
Normative References
n1. K. McCloghrie, D. Perkins, J. Schoenwaelder, J. Case, J. Rose, M.
and S. Waldbusser, 'Structure of Management Information Version 2
(SMIv2)', STD 58, RFC 2578, April 1999.
n2. K. McCloghrie, D. Perkins, J. Schoenwaelder, J. Case, J. Rose, M.
and S. Waldbusser, 'Textual Conventions for SMIv2', STD 58, RFC
2579, April 1999.
n3. K. McCloghrie, D. Perkins, J. Schoenwaelder, J. Case, J. Rose, M.
and S. Waldbusser, 'Conformance Statements for SMIv2', STD 58, RFC
2580, April 1999.
n4. S. Bradner, 'Key words for use in RFCs to Indicate Requirement
Levels', BCP 14, RFC 2119, March 1997.
Informative References
i1. R. Braden et al., `Resource Reservation Protocol ` Version 1
Functional Specification`, RFC 2205, 1997.
i2. C. Partridge, `A Proposed Flow Specification`, RFC 1363, 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. S. Shenker, C. Partridge, R. Guerin, `Specification of Guaranteed
Quality of Service`, RFC 2212, 1997.
i6. J. Wroclawski, `Specification of the Controlled-Load Network
Element Service`, RFC 2211, 1997.
i7. R. Braden, D. Clark, S. Shenker, `Integrated Services in the
Internet Architecture: an Overview` RFC 1633, 1994.
i8. ISO/IEC 13818-1 (MPEG-2 Systems)
i9. V. Raisanen, `Implementing Service Quality in IP Networks`, John
Wiley & Sons Ltd., 2003.
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i10. J. Case, R. Mundy, D. Partain, B. Stewart, 'Introduction and
Applicability Statements for Internet Standard Management
Framework', RFC 3410, 2002.
Acknowledgments
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 drafts of this document and implementations for MDI.
Authors' Address
James Welch
IneoQuest Technologies, Inc
170 Forbes Blvd
Mansfield, Massachusetts 02048
508 618 0312
Jim.Welch@ineoquest.com
James Clark
Cisco Systems, Inc
500 Northridge Road
Suite 800
Atlanta, Georgia 30350
678 352 2726
jiclark@cisco.com
Copyright Notice
Copyright (C) The Internet Society 2004. This document is subject to
the rights, licenses and restrictions contained in BCP 78, and except
as set forth therein, the authors retain all their rights.
Disclaimer
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.'
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Intellectual Property
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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
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