ALTO Kai Lee
Internet-Draft China Telecom
Intended status: Informational GuangYao.Jian
Expires: Sep 11, 2012 Xunlei network
March 11, 2012
ALTO and DECADE service trial within China Telecom
draft-lee-alto-chinatelecom-trial-04.txt
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Abstract
This document reports the experience of China Telecom in a recent
experiment with the ALTO service and P2P caches deployment. It is
found that the deployment of the ALTO service significantly improves
the capability of a Service Provider to affect the distribution of
P2P traffic. It is also found that a traffic localized ALTO policy
may decrease the download speed of a P2P user. However, the
deployment of some P2P caches can compensate such influence.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. High level description of the trial . . . . . . . . . . . . . . 4
2.1. Difference between standard ALTO protocol . . . . . . . . . 4
2.2. Difference between Comcast's trial . . . . . . . . . . . . 5
3. Trial results . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Trial configuration . . . . . . . . . . . . . . . . . . . . 6
3.2. Xunlei traffic distribution before the trial . . . . . . . 7
3.3. ALTO policy test . . . . . . . . . . . . . . . . . . . . . 8
3.4. P2P cache test . . . . . . . . . . . . . . . . . . . . . . 9
4. Methods of data collection . . . . . . . . . . . . . . . . . . 9
5. Configurations and algorithms in trial . . . . . . . . . . . . 10
5.1. Configuration of PID MAP . . . . . . . . . . . . . . . . . 10
5.2. Algorithms of Xunlei using ALTO information . . . . . . . . 10
5.3. Configuration of cache system . . . . . . . . . . . . . . . 12
6. Next steps . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
Although another trial on P4P, the predecessor of the ALTO, is
available by Comcast, the impact of ALTO on a large scale real
network has never publicly reported. Such real network should post no
limitation on either the number of contents or the number of users.
This draft reports the experience of China Telecom in a recent
experiment with the deployment of the ALTO service and P2P caches.
With over 60 million fixed-line broadband subscribers, China
Telecom is the largest broadband service provider in China. It has
one IP backbone network that cover all of the 31 provinces in China
and about 200 MAN networks are managed by the provinces respectively.
This trial was taken place in one province with 7 million broadband
subscribers and about 11 MAN networks.
Xunlei, the cooperator of this trial, is a leading P2P service
provider in China. Xunlei supports both file downloads and real time
media streaming. In 2009, when was this trail occurring, it serves
over 20 million users each day.
This trial is a joint effort of China Telecom and Xunlei. During
this trial, China Telecom provided the following devices: an alto
server to distribute ALTO information, some P2P caches to improve
Xunlei service experience, and network management systems based on
SNMP and DPI technology to monitor the traffic load within its
backbone. Xunlei provided the P2P client and users. To support this
trial, Xunlei modified its platform to support ALTO, and recorded
operational information on its platform according to the requirement
of China Telecom. Note that the client of Xunlei was not changed.
2. High level description of the trial
2.1. Difference between standard ALTO protocol
Note that ALTO protocol is still on progressing, in this trail,
some modifications were made to the ALTO.
Firstly a server notification mechanism for the ALTO server is
introduced. With this mechanism, the ALTO server notifies its clients
the changes of network maps and cost maps. Thus, ALTO clients can
make timely respond to the change of traffic optimizing
policy(Note:different traffic optimizing policies mean different
network maps and cost maps). This mechanism is mainly used to solve
the problem related to alto effect evaluation. As we know the traffic
within the IP backbone is highly periodical. For example, the traffic
on each weekend is higher than which on the workday.As such, the
evaluation traffic data to compare should be both collected in the
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workday or in the weekend. We need to change the traffic optimizing
policy constantly to collect the traffic data with and without effect
of alto service to evaluate the effect of ALTO service. That's why we
need the server notification in this trial.
In this trail, ALTO clients were embedded in the trackers of
Xunlei, not in the Xunlei clients. The reason for this is mainly for
deployment consideration. There are hundreds of millions of Xunlei
clients in use, To update these clients as the ALTO client in a short
time is not feasible. However, according to the analysis of Xunlei,
although both tracker based and tracker-less technology are adopted,
the traffic does not controlled by the trackers is less than 15% of
its total traffic. Based on this analysis, in this trial, Xunlei
clients are not involved in the ALTO service which has negligible
influence on the final evaluation of this trial. Such design can also
reduce the load on the ALTO server.
Secondly, only map service is provided in this trial. Endpoint
property service and Endpoint cost service were not supplied, as they
are not essential for this trial.
2.2. Difference between Comcast's trial
Comcast has a trial with limited swarms, with the cooperation of
Pando. According to the RFC5632 "Comcast's ISP Experiences in a
Proactive Network Provider Participation for P2P (P4P) Technical
Trial", there are five swarms, and overall 57,000 peers are involved
in that trial.
There are several differences between CT's trial and Comcast's
trial:
1. The scope of trail: CT's trial covers the whole province with over
700 million broadband users. It lasted for over 4 months. There
are countless swarms with all kinds of contents. from this point
of view, our trial is more realistic than the previous trial from
Comcast.
2. The usage of P2P cache: CT's trail differs from the Comcast's
trail by the utilization of P2P cache. In this trail, the average
download speed of a Xunlei client decreases a little with the
degree of traffic localization increased. Thus P2P cache was
introduced to compensate the decrease of download speed.
3. The evaluation method: In contrast to that all test data was
collected by Pando client in Comcast's trial, we collect test data
from two ways. Besides the data from Xunlei P2P client, we
simultaneously collect the data from network operator's NMS
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system.(such as data from SNMP reports and DPI(deep package
inspection) device deployed on backbone). We can do this because
Xunlei's p2p traffic occupy about 20% of whole backbone traffic
flow in that province. This traffic flow will almost all be
affected by alto service and it is big enough to be observed by
CT's NMS system.
4. The implementation of ALTO: In this trial, only the P2P trackers
are ALTO clients, but not those Xunlei clients. There are some
reasons to do this:
a) To avoid the update all Xunlei clients and simplify the
deployment of trial.
b) To lessen the alto server load.
c) Above 85% of Xunlei traffic flow is controlled by Xunlei
tracker, the traffic flow affected by DHT mechanism is less
than 15%. An alto server dedicated for Xunlei tracker can
affect majority of Xunlei traffic flow.
3. Trial results
3.1. Trial configuration
All Xunlei p2p client in the province and all contents that are
requested or served by Xunlei P2P client in the province are involved
in this trial. The trial environment is more realistic than
Comcast's. A primary objective of this trial is to measure the
effects of traffic localization and change of users download speed in
comparison to those without alto service.
The test process is divided into two parts: first part is just
applied the ALTO server to measure the effects of traffic
localization and change of P2P user experience. The second part is to
introduce the P2P cache to the trial, to measure the improvement of
user download speed, the bandwidth consumption and relationship with
the scale of p2p cache and average download speed.
Our trial starts at 2009.6.12 and ends at 2009.10.18, lasting
nearly four months. We do this trial by applying different traffic
control policy to Xunlei tracker through ALTO service. There are two
kinds of traffic control policy: One is optimized policy and the
other is un-optimized policy. corresponding to the different traffic
control policy there are two kinds of network map and cost map the
ALTO server need to create.The optimized policy tries to localize the
traffic by utilizing the information from ALTO server. Here is the
network map and cost map corresponding to the optimized policy below.
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----------
-------- --------
//- PID12 -\\
/// \\\
// --------- \\
/// --+--- ------ \\\
/ /// | \\\ \
// /// |2 \\\ \\
/ // | \\ \
/ / ---+- \ \
| / /// \\\ \ |
| // || | ----- \\ |
| | | PID1 | ---1- // \\ | |
| | || | ---+ | | |
| | \\\ /// | PID2 |----+ |
| | --\-- | | 2 | |
| | \ | | | |
| | \ \\- -// | |
| | 1 // --- | |
| | \ 1/ | |
| | \ // | |
| | /-\-----\/ | |
| | //// \\\\ | |
| | | PID.. | | |
| \\ | | // |
| \ \\\\ //// / |
\ \ \----+--/ / /
\ \\ | // /
\\ \\\ |2 /// //
\ \\\ | /// /
\\\ ------ | ------ ///
\\ ----+---- //
\\\ ///
\\- -//
-------- --------
----------
The normal policy will just use the original Xunlei peer selection
and traffic control rules though . The corresponding network map just
has one PID with all IPs.
We usually change the alto policy in midnight of a day and send a
notification to Xunlei tracker with notification
mechanism.(http://tools.ietf.org/id/draft-sun-alto-notification-
02.txt)
3.2. Xunlei traffic distribution before the trial
Before we do the trial , we collect the information about Xunlei'S
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peer and traffic distribution
+------------------------------------------+--------------------+
| No |Data Item |Description |The way of |
| | | |collection |
+----+---------- -+------------------------+--------------------+
| 1 |Peer |24.6% is within |Random sampling by |
| |distribution|the province,75.4% |Xunlei tracker 24 |
| | |is out of the |times one day |
| | |province | |
+----+------------+------------------------+--------------------+
| |Traffic |76.9% is |Random selecting |
| 2 |distribution|inter-province traffic |peers to report |
| | |23.1% is |their traffic flow |
| | |intra-province traffic | |
+----+------------+------------------------+--------------------+
3.3. ALTO policy test
After we applied the alto optimized policy about 60% inter-province
traffic has became The intra-province traffic. Below is the result
that we observed on china telecom's network NMS system:
+------------------------------------------+-----------------------+
| No |Data Item |Description |The way of |
| | | |collection |
+----+---------- -+------------------------+-----------------------+
| 1 |Outbound |Decreased 42.77Gbps, Collecting max average |
| |bandwidth |about 50.61% of total outbound traffic of |
| | |Xunlei outbound |a day from the DPI |
| | |traffic |system |
+----+------------+------------------------+-----------------------+
| |Inbound/ |outbound bandwidth |Collecting max average |
| 2 |outbound |decreased 31.58Gbps |inbound/outbound |
| |bandwidth |inbound bandwidth traffic of a day from |
| | |decreased 10.46Gbps |the snmp system |
+----+------------+------------------------+-----------------------+
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3.4. P2P cache test
In this trial we deployed 16 cache devices, each with 1.8TB SAS
hard disks. The P2P cache system has 15Gbps links connected to the
Internet. We cached the content according to its popularity.
+------------------------------------------+-----------------------+
| No |Data Item |Description |The way of |
| | | |collection |
+----+---------- -+------------------------+-----------------------+
| 1 |Outbound |Decreased 40Gbps, Collecting max average |
| |bandwidth |about 54.47% of total outbound traffic of |
| | |Xunlei outbound traffic |a day from the DPI |
| | | |system |
+----+------------+------------------------+-----------------------+
| |Inbound/ |outbound bandwidth |Collecting max average |
| 2 |outbound |decreased 39.18Gbps |inbound/outbound |
| |bandwidth |inbound bandwidth traffic of a day from |
| | |decreased 28.3 Gbps |the snmp system |
+----+------------+------------------------+-----------------------+
| 3 |Average |From 279KBps up to |Collection from Xunlei |
| |download |294.5KBps |OAM system |
| |speed | | |
+----+------------+------------------------+-----------------------+
The P2P cache system occupancy ratio is about 80%. Bandwidth
consumed is about 4-5Gbps.After deployed the P2P cache system, the
traffic flow in the the province has decreased a lot. Meanwhile the
average download speed of Xunlei client has been increased.
4. Methods of data collection
In this trial we have two ways for information collection; one is
to collect from p2p service provider such as Pando and Xunlei just
like Comcast's trial. The other is to collect from ISP's network OAM
system. Because the Xunlei's inter-province traffic flow is about
80Gbps that is large enough to be observed by ISP's network OAM
system
1. Information from ISP's network OAM system and DPI system
a) Inbound/outbound traffic flow statistic
b) Xunlei traffic flow detected by DPI system. The DPI system just
monitored the uplink of the province to China telecom's
backbone.
2. Information from Xunlei
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a) Inter-province/intra-province traffic flow.
b) User average download speed.
5. Configurations and algorithms in trial
5.1. Configuration of PID MAP
a) PID Map: We define 11 PIDs PID1-PID11 represent the 11 MANs of
the trial network PID12 represents rest of the
Internet
b) Cost Map: Bidirectional cost between any PIDs from PID1 to
PID11 has the same value 1 Bidirectional cost between
PID12 and PIDi (1<=i<=11) has the same value 2
5.2. Algorithms of Xunlei using ALTO information
Xunlei is a hybrid application utilizing both trackers and DHT,
About 85% of Xunlei traffic controlled by Xunlei trackers. In this
trail ALTO clients just include the Xunlei trackers not include the
Xunlei client. Just the traffic controlled by Xunlei tracker has been
affected.
Before the trial Xunlei tracker peer selection algorithm is:Xunlei
Peer selection algorithm depends on two properties: ISP ID and UC
(upload capability), the peer selection priority is :
Same ISP ID > different ISP ID
Higher UC > lower UC
The peers with same ISP ID with the requesting peer have higher
priority than those with different ISP ID. If peers have same ISP ID
then the peers with higher UC have higher priority than those with
lower UC.
After applying the ALTO information into the Xunlei peer selection
algorithm. Xunlei changed his Peers select mechanism. All Xunlei
peers are organized in a tree structure which is indexed by
CID(content ID), in the second level ALTO_ISP and normal_ISP
represent the network of ISP with and without alto information. In
this trial 11 MANs in trial province became 11 ALTO_ISPs.The third
level is defined by different upload capability(UC) of peers. The
fourth level of normal_ISP branch is the different
provinces(PRO1,PRO2) of ISP, the fifth level of the normal_ISP is
different city of ISP.
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+-------------------+
| CID |
+-------------------+
/ \
+----------+ +----------+
|NORMAL_ISP| | ALTO_ISP |
+----------+ +----------+
/ | \ / | \
UC_BIG UC_MID UC_SMALL UC_BIG UC_MID UC_SMALL
/ | | \
PRO1 PRO2 PEER1 PEER2
/ |
CITY1 CITY2
| \
PEER1 PEER2
The algorithms of cost between origination peer(peer_o) and
destination peer(peer_d) is :
If (peer_o and peer_d both from ALTO_ISP)
If (peer_o and peer_d in the same ALTO_ISP) then cost = 0;
Else cost = 100000;
Else if (peer_o from ALTO_ISP and peer_d from normal_ISP) cost =
100000;
Else if (peer_o from normal_ISP and peer_d from ALTO_ISP) cost =
1000;
Else if (peer_o and peer_d both from normal_ISP){
If (peer_o and peer_d from different normal_ISP) cost =1000;
Else if (peer_o and peer_d from different province) cost = 100;
Else if (peer_o and peer_d from different city) cost = 10;
Else cost =0;
}
The peer select mechanism is lower cost peers will have higher
priority
The updated peer selection mechanism is not the best mechanism.
For example a peer in MAN2 is supposed to be better choice than the
peers which not located in china telecom's network when a peer in
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MAN1 send a content request to tracker. But this mechanism will
select the peer out of china telecom's network first then select the
peer in the MAN2. Before we defined the network map with 12 PIDs. We
first defined a network map with just 2 PIDs. PID1 represent the
trial province and PID2 represent the other network to test the
backbone traffic saving effect of ALTO service. The test result show
that the network map with 12PIDs has almost same backbone traffic
saving effect compared to the network map with 2 PIDs. So in the
trial we deployed this mechanism.
The other change is the number of returned peers from Xunlei
tracker . If a listing request is from the trial province, the
maximum # of returned peers from Xunlei tracker is set to 120, not
the normal case of 500.
5.3. Configuration of cache system
Before we deploy the cache system we have made some statistics
about relationship of content popularity and network traffic caused
by content with different popularity in trial province.
+-----------+---------+----------+-------------+
|content | total |total | proportion |
| popularity| size(GB)|traffic | of total |
| | |(Gbps) |traffic(%) |
+-----------+---------+----------+-------------+
| top 10 | 18.9 | 1.34 | 9.3 |
| top 20 | 29.3 | 1.68 | 11.7 |
| top 50 | 51.8 | 2.28 | 15.9 |
| top 100 | 93.6 | 2.89 | 20.1 |
| top 500 | 418.7 | 4.74 | 33 |
| top 1000 | 812.4 | 5.88 | 40.9 |
| top 2000 | 1518.6 | 7.16 | 49.8 |
| top 5000 | 3551 | 8.89 | 61.9 |
+-----------+---------+----------+-------------+
Our cache system has limited storage and access bandwidth so we
need to know which content is most "valuable" to be cached. According
the statistics from Xunlei if a downloading task is fed over 100
peers , this task always can get the maximum download speed(this
speed depends on the peer's access network, in the trial the average
access speed of user is about 2Mbps). The top 2000 popular content
almost all have over 100 seeds in trial province. That means the top
2000 popular contents don't need be cached. Our cache policy is just
cache the content which's popularity rank behind 2000.
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6. Next steps
The alto mechanism is very effective to optimize the traffic
flow.If alto can cooperate with p2p cache or other service
performance enhancement mechanism, it will be more practical. The
ALTO service's effect depends on the SP such as Xunlei,pando how to
use it. The mechanism such as peer selection mechanism and content
cache mechanism need to be studied.
7. Security Considerations
High-level security considerations can be found in the [draft-ietf-
alto-problem-statement].
8. IANA Considerations
This document requests the registration of a new media type:
"application/alto"
9. References
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693, October
2009.
[RFC5632] Griffiths, C., Livingood, J., Popkin, L., Woundy, R., and
Y. Yang, "Comcast's ISP Experiences in a Proactive Network
Provider Participation for P2P (P4P) Technical Trial",
RFC 5632, September 2009.
[I-D.ietf-alto-reqs] Kiesel, S., Popkin, L., Previdi, S., Woundy, R.,
and Y.Yang,"Application-Layer Traffic Optimization (ALTO)
Requirements",draft-ietf-alto-reqs-01 (work in progress),July 2009.
[I-D.penno-alto-protocol] Penno, R. and Y. Yang, "ALTO
Protocol",draft-ietf-alto-protocol-01 (work in progress),July 2009.
Author's Addresses
Kai Lee
China Telecom Beijing Research Institute
Email: leekai@ctbri.com.cn
GuangYao Jian
Xunlei Network
Email: jianguangyao@xunlei.com
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