Internet DRAFT - draft-ding-tcp-emdi
draft-ding-tcp-emdi
Network Working Group X. Ding
Internet-Draft Q. Wu
Intended status: Standards Track Huawei
Expires: January 4, 2018 R. Gu
China Mobile
July 3, 2017
An Enhanced Media Delivery Index (eMDI) based on TCP
draft-ding-tcp-emdi-00
Abstract
This document introduces an Enhanced Media Delivery Index (eMDI) that
can be used as a diagnostic tool or a quality indicator for
monitoring a network intended to deliver streaming media over TCP
transport. It aims to address the problems that RFC4445 has when
measuring in environments where TCP traffic is dominated as a
transport for streaming media.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Measurement Setup . . . . . . . . . . . . . . . . . . . . . . 3
4. Measurement Method . . . . . . . . . . . . . . . . . . . . . 4
5. Use Examples . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Network Troubleshooting in VoD scenario . . . . . . . . . 5
5.2. WiFi Anomaly Analysis in the Home Network . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
TCP is one major transport protocol in use in most IP networks, and
supports the transfer of over 80 percent of all traffic (e.g.,OTT
traffic, IPTV VOD traffic) across the public Internet today. Packet
loss ratio and latency are two major characteristics in the network
to affect the behavior of TCP. The bad TCP performance might also
indicate the unacceptable end-user-perceived quality level.
Media Delivery Index (MDI)[RFC4445] is a method widely used in the
network as a diagnostic tool to measure both the instantaneous and
longer-term behavior of networks carrying streaming media in the
media layer. However the limitation of MDI measurement is mostly
applicable to streaming media and protocol over UDP, it falls short
when monitoring a network intended to deliver multimedia applications
over TCP Transport, i.e., the traditional MDI metrics especially
Media Loss Rate (MLR) deployed in the network devices is difficult to
infer the packet loss if the missing packets were retransmitted when
the packet loss was detected by the TCP sender. On the other hand,
TCP sender will adjust the sending data rate to reduce the
probability of further packet loss, which means throughput is
declining when extra delay is incurred by retransmitting lost
packets. Therefore, throughput can be regarded as a quality
indication for network monitoring and diagnosis.
This document introduces a new measurement method and associated
metrics,i.e.,downstream/upstream/end to end throughput, to complement
methods defined in [RFC4445]. This new method can quickly identify
the root cause of the QoS related problem, improve efficiency of
network monitoring and troubleshooting.
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2. Terminologies
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].
This document uses the following terms:
Measurement point (MP): A measurement point is the logical or
physical location defined in the TCP that acts as a source of
information gathered for monitoring purposes.
Upstream packet lost ratio (UPLR): UPLR is the ratio of the number
of packets lost to the total number of packets sent from server to
measurement point during predefined measurement interval.
Downstream packet lost ratio (DPLR): DPLR is the ratio of the
number of packets lost to the total number of packets sent from
measurement point to client during a predefined measurement
interval.
Upstream average RTT (URTT): URTT is the average RTT at the path
from server to measurement point during a predefined measurement
interval.
Downstream average RTT (DRTT): DRTT is the average RTT at the path
from measurement point to client during a predefined measurement
interval.
End to end Throughput (E2ET): E2ET is the rate of successful packet
delivery over an end-end network path during a predefined
measurement interval.
Downstream throughput (DT): DT is measured by the number of packets
received per second at the downstream of measurement point during
a predefined measurement interval.
Upstream throughput (UT): UT is measured by the number of packets
received per second at the upstream of measurement point during a
predefined measurement interval.
3. Measurement Setup
A stream of packets sent by streaming media Server passes through MP
(MP can be bridge, router or gateway), and finally reach the client
(destination endpoint). If a node A is placed between the server and
MP in the network , then A is upstream node of MP. Otherwise, A is
downstream node of MP.
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+--------+ MP | +--------+
| Server |------Upstream---->|-----Downstream---->| client |
+--------+ | +--- ----+
4. Measurement Method
The rationale of the measurement is to compare DT/UT/E2ET with data
packet rate. If DT is less than data packet rate and UT is greater
than data packet rate, there is something wrong with the downstream
network. Otherwise, the upstream network has some problems.
When the packet loss occurs in the network, an additional limit(i.e.,
packet loss probability) is imposed on the throughput besides TCP
recieve window. In case of light or moderate packet loss when the
TCP rate is adjusted by the congestion avoidance algorithm, DT can be
calculated according to the following formula:
DT = MSS/(DRTT+URTT)(DPLR)(1/2);
Where MSS is the maximum segment size. Assuming the number of lost
packets at the downstream during a predefined measurement interval is
a, and the number of total packets sent by MP is x, then DPLR is then
calculated as following:
DPLR = a/x.
Average RTT of some packets (d1..dm) at the downstream direction are
used to compute DRTT:
DRTT= sum (RTTdi)/m, i= 1..m
Where RTTdi indicates the RTT of packet di at downstream.
Similarly, average RTT of some packets (u1..un) at the upstream
direction are used to compute URTT:
URTT= sum (RTTui)/n, i= 1..n
Where RTTui indicates the RTT of packet ui at the upstream.
And, UT can be calculated according to the formula:
UT = MSS/(DRTT+URTT)(UPLR)(1/2);
Assuming the number of lost packets at the upstream during a
predefined measurement interval is b, and the number of total packets
sent by Server is y, then UPLR is then calculated as following:
UPLR = b/y.
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And E2ET can be calculated according to the formula:
E2ET = MSS/(DRTT+URTT)(UPLR+DPLR)(1/2).
5. Use Examples
5.1. Network Troubleshooting in VoD scenario
+--------+
IPTV Platform +--------+----------^--------------
/OTT/CDN +--------+ |
+----+---+ |
| |
//----+---\\ |
|/// \\\| |
| | |URTT
|\\\ ///| |
\\----+---// |
| |
| |
+--------+ |
CR +--------+ |
| |
---------------V------------------
| ^
BRAS +-----+---+ |
+---/---\-+ | Downstream
// \\ | Fixed
// \ | Network
OLT +---------+ +-\------+ | Latency
+---------+ +--------+ DRTT |
|
---- ---- ---- ---- --------------
/----\ /----\ /----\ /----\ |
| | | | | | | | |Home Network
Home | | | | | | | | | Latency
Network | | | | | | | |
+----+ +----+ +----+ +----+----V------
Figure 1: Figure 1
The proposed measurement method can be applied when VoD streaming
media running over TCP is delivered as unicast stream from VoD server
in the operator network to end users in home network. In some cases,
the fault occurs in the home network which cause user experience
downgrading, in some other cases, fault occurs in the operator
network.
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To pinpoint the location of the fault , MP can be deployed on ONT
device of the home network. The home network is refer to the
downstream of the MP and the operator network is refer to the
upstream of the MP. Suppose the rate of the media rate is v, we can
compare DT/UT/E2ET with v. If DT<v and UT>v, the home network is the
root cause for streaming media quality downgrading. If DT>v and
UT<v, the operator network is the root cause. If DT>v, UT>v, and
E2E<v, both home network and operator network should be responsible
for streaming media quality downgrading.
5.2. WiFi Anomaly Analysis in the Home Network
WiFi latency is a key factor impacting the user experience of home
network application. [WIFI] shows WiFi latency follows a long tail
distribution: its 50th, 90th and 99th percentile are around 3ms, 20ms
and 250ms. If the WiFi network get congested, the quality degrades
proportionally with WiFi lantency. To analyse WIFi Anomaly degree in
the home network, See figure 1, we can calculate cumulative
distribution of WiFi latency based on measured values:
WiFi Latency = DRTT - Downstream Fixed Network Latency
and determine threshold value for WiFi Latency based on periodically
collected dataset,e.g.,
Threshold = UBV + coef *(UBV-LBV)
Where UBV is the 75th percentile value, LBV is the 25th Percentile
value, coef is coefficiency value which can be set to 1.5.
By Comparing WiFi latency measured value with the threshold value, we
can decide if WiFi Anomaly is the root cause of network quality
degrading.
6. Security Considerations
This document does not introduce security issues beyond those
discussed in [[RFC4445].
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC4445] Welch, J. and J. Clark, "A Proposed Media Delivery Index
(MDI)", RFC 4445, DOI 10.17487/RFC4445, April 2006,
<http://www.rfc-editor.org/info/rfc4445>.
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[WIFI] MobiSys'16, 2016, Singapore, ACM ISBN
978-1-4503-4269-8/16/06, "Characterizing and Improving
WiFi Latency in Large-Scale Operational Networks", 2016.
Authors' Addresses
Xiaojian Ding
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: dingxiaojian1@huawei.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: bill.wu@huawei.com
Rong Gu
China Mobile
32 Xuanwumen West Ave, Xicheng District
Beijing 100053
China
Email: gurong_cmcc@outlook.com
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