ALTO Kai.Lee
Internet-Draft China Telecom
Intended status: Informational GuangYao.Jian
Expires: April 22, 2011 Xunlei network
October 22, 2010
ALTO and DECADE service trial within China Telecom
draft-lee-alto-chinatelecom-trial-01.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 ................................................. 3
2. High level description of the trial .......................... 4
2.1. Difference between standard ALTO protocol ............... 4
2.2. Difference with Comcast's trial ......................... 5
3. Trial results ................................................ 6
3.1. ALTO server policy test...................................7
3.2. P2P cache test .......................................... 8
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...................................... 14
8. IANA Considerations ......................................... 14
9. References .................................................. 14
Author's Addresses ............................................. 14
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 and
about 200 MAN networks 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 for distribute ALTO information, some P2P caches to test its
influence on traffic localization and user experience. China Telecom
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also monitored 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.
First, a 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
respond fast to the change of traffic optimizing policy.
One problem that this trail met is to find the effect of ALTO&Cache
deployment. The traffic within the IP backbone is highly periodical
For example, the traffic on each weekend is higher than the workday.
As such, data should be collected in the same workday in different
week. This can facilitate the comparison of the effects on p2p
traffic under different ALTO configuration and different policy, and
to evaluate the effect of ALTO service
In this trail, ALTO clients were just embedded in the trackers of
Xunlei, not in the Xunlei clients. The reason for this is mainly for
deployment consideraton. 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. Other services
of ALTO service were not deployed, as they are not essential for
this trial.
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2.2. Difference with Comcast's trial
Comcast has a trial with limited swarms, with the cooperation of
Pando. According to (ref), there are five swarms, and overall 57,000
peers are involved in that trial.
There are several differences between our trial and Comcast's trial:
1. The scope of the trail: This 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. Thus, this
trial is more realistic than the previous trial from Comcast.
2. The usage of P2P cache: This trail differs from the previous
trail by the utilization of P2P cache. In this trail, the average
download speed of a Xunlei client decreases with the increase of
the level of traffic localization. Thus the usage of 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
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 20% of backbone traffic flow. This
traffic flow will all be affected by our alto policy and it is big
enough to be observed by network operator'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 from DHT mechanism is less than 15%.
An alto server dedicated for Xunlei tracker can control
majority of Xunlei traffic flow.
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3. Trial results
This trial used all Xunlei p2p client in the province and all
contents that are requested or served by Xunlei P2P client in the
province. 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 normal
p2p activity.
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 their relationship with the scale
of cache and.
Our trial starts at 2009.6.12 and ends at 2009.10.18, lasting nearly
four months. We do this trial by applying different ALTO policy to
Xunlei tracker. There are two kinds of ALTO policy: One is optimized
policy and the other is normal policy. The optimized policy will try to
localize the traffic as much as possible by utilizing the information
from ALTO server. The normal policy will just use the original Xunlei
peer selection and traffic control rules and no alto policy are
involved. 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)
Before we do the trial , we collect the information about Xunlei'S
peer and traffic distribution
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+------------------------------------------+--------------------+
| 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|intra-province traffic |peers to report |
| | |23.1% is |their traffic flow |
| | |inter-province traffic | |
+----+------------+------------------------+--------------------+
3.1. ALTO server 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:
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+------------------------------------------+-----------------------+
| 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 |
+----+------------+------------------------+-----------------------+
User's average download speed will decreased if traffic localization
policy is applied
3.2. 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.
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+------------------------------------------+-----------------------+
| 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
include
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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
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
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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.
+-------------------+
| 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;
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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
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.
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+-----------+---------+----------+-------------+
|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.
6. Next steps
The alto mechanism is very effective to optimize the traffic flow.
But when the traffic is localized, the user average download speed
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is slowed down simultaneously. 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
[RFC 5693]
Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 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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