Considerations for ALTO with network-deployed P2P caches-00
draft-deng-alto-p2pcache-00
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| Authors | Deng Lingli , Yan Zhang | ||
| Last updated | 2013-07-03 | ||
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draft-deng-alto-p2pcache-00
Application-Layer Traffic Optimization Group L. Deng
Internet-Draft China Mobile
Intended status: Informational Y. Zhang
Expires: January 05, 2014 Chinese Academy of Sciences
July 04, 2013
Considerations for ALTO with network-deployed P2P caches-00
draft-deng-alto-p2pcache-00.txt
Abstract
Transparent forwarding caching effectively localizes the downloading
P2P traffic within the sub-net under its coverage resulting in
reduction of network cost for cross-boundary peer selection, whereas
transparent reverse caching blocks the uploading traffic outside a
wireless sub-net leading to elimination of network cost for wireless
uploading peer selection. In other words, caching between pairs of
endpoints changes the traffic cost along the way.
Therefore, it is proposed to use locations of caches as dividers of
different DIPs to guide intra-ISP network abstraction and mark costs
among them according to the location and type of relevant caches.
Status of This Memo
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This Internet-Draft will expire on January 05, 2014.
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Internet-DraConsiderations for ALTO with network-deployed P2P July 2013
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Architecture . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. T-Cache for Wired subscribers . . . . . . . . . . . . . 4
3.2. B-Cache for WLAN subscribers . . . . . . . . . . . . . . 4
3.3. Generalized cache architecture for intra-ISP networks . . 5
4. Considerations for ALTO deployment with P2P Caches . . . . . 7
4.1. T-Cache: vertical separator from outsiders . . . . . . . 7
4.2. B-Cache: horizontal division within insiders . . . . . . 7
5. Further Discussions . . . . . . . . . . . . . . . . . . . . 7
5.1. 5.1. Selective caching . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
P2P applications like file sharing and multimedia streaming are so
popular that lots of P2P technologies have been increasingly utilized
throughout the world. The goal of Application-Layer Traffic
Optimization (ALTO) [I-D.ietf-alto-protocol] is to provide guidance
to these applications, which have to select one or several hosts from
a set of candidates that are able to provide a desired resource.
Meanwhile, since wireless accesses to Internet have become pervasive
with widely deployed WLANs, more and more people access Internet
services via WLAN and the amount of P2P traffic in WLAN is
explosively growing. In addition to a huge number of individually
setup WLANs at homes, there has been an increasing trend for the
government, organizations, and even traditional network operators to
set up publicly accessible WLAN facilities. Even though the service
may be free of charge, to use the resources effectively in a fair
way, and to avoid congestion for the purpose of service availability
are vital for these public WLANs.
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However, recent statistics reveal that P2P traffic accounts for 80%
in part of China Mobile's WLANs, and traffic congestion at APs
(access points) frequently occurs because of P2P applications. P2P
traffic in WLANs not only causes problems on their own delivery
quality, but also degrades the performance of other Internet
applications in WLANs.
2. Motivation
On one hand, it is well accepted that compared to fixed networks,
mobile networks have some special characters, including small link
bandwidth, high cost, limited radio frequency resource, and terminal
battery. Therefore, it is recommended by [I-D.ietf-alto-deployments]
that in mobile network, the usage of wireless link should be
decreased as far as possible and be high-efficient. For example, in
the case of a P2P service, the clients in the fixed network should
decrease the data transport from the clients in the mobile networks,
as well as the clients in the mobile networks should prefer the data
transmission from the clients in the fixed networks.
On the other hand, Efforts have been put on using transparent caches
to optimize traffic pattern in such scenarios, which demonstrates
great improvement in user experience and considerable traffic
reduction at interworking points. What's more, owing to the
characteristics of the DCF model in 802.11, there is an constant
unfairness between uplink and downlink traffic in competing wireless
channel resources, which leads to downlink congestion in WLAN
resultant from P2P traffic (as it requires of both downloading and
uploading). However, traditional P2P cache (as a forward cache)
cannot help here, since it does nothing to stop a WLAN peer from
uploading. Hence, bidirectional caches are proposed, which contains
a reverse cache as well as a forward cache can be deployed at the AC
of a WLAN. The reverse cache can cache the P2P traffic flowing out
of all the associated APs and provide uploading service for peers
outside the WLAN. As a result, the uplink bandwidth consumption at
each AP can be reduced and the uplink congestion can be alleviated
effectively. Meanwhile, the forward cache can still act as the
traditional P2P cache to reduce the cross domain traffic. Simulation
results in file-sharing scenarios show that, compared with
traditional P2P cache, the bidirectional cache accelerates file
transfer by 42% while improving the throughput of other Internet
applications under the same AP by 28%.
With deployed P2P caches on the internal network, especially at a
position as low as the AC-level, it could be sub-optimal to simply
use the accessing network type as the divider for different PIDs and
assign sufficient high cost within the wireless PID to prefer
accessing remote peers over local peers blindly.
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To this end, this draft discusses the optimal ALTO deployment
recommendations for a P2P application in terms of a wireless
accessing network with network-deployed application-agnostic caches.
In summary, the goal here is to illuminate applications through ALTO
about these existing network capabilities and full use of them, in
order to maximize intra-network localization for P2P traffic between
wireless subscribers for both application performance improvement and
network cost reduction.
3. Architecture
3.1. T-Cache for Wired subscribers
Fig. 1 illustrates the proposed architecture of a traditional uni-
directional P2P cache (or T-Cache for short) system for wired
subscribers, deployed mainly for the purpose of reducing interworking
P2P traffic. T-Caches are assumed to be deployed at the interworking
gateways to maximize their coverage for local subscribers. They
buffer downloading content from outside ISP networks, intercept the
upcoming outgoing P2P requests from local subscribers and serve them
with cached content instead.
+--------------+ +------+
| ISP 1 network+----------------+Peer 1|
+-----+--------+ +------+
|
+--------+------------------------------------------------------+
| ISP 2 network |
| +----------------+ +----------+ |
| |Interworking GW |----------------| T-Cache | |
| +-----+----------+ +----------+ |
| | |
+--------+------------------------------------------------------+
+---------------------------+
| |
+-----+-+ +--+---+
|Peer 2 | |Peer 3|
+-------+ +------+
Figure 1: Architecture of T-cache at interworking gateway
3.2. B-Cache for WLAN subscribers
Fig. 2 illustrates the proposed architecture of a bidirectional cache
(or B-Cache for short) system in WLAN. In a WLAN, all AP will
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connect to a device named AC, and the AC can be seen as the gateway
to Internet of the WLAN. For most settings, both the traffic flowing
into the WLAN and the traffic flowing out of the WLAN pass through
the AC, hence B-Caches are assumed to be deployed at AC to exploit
the traffic locality. Besides the normal functions of a T-Cache, A
B-Cache buffers uploading content from inside the WLAN network,
intercepts the upcoming outgoing P2P responses from local WLAN
subscribers and serve the correspondent requester (be it another
local WLAN subscriber or an outsider) with cached content instead.
+--------------+ +------+
| ISP 1 network+----------------+Peer 1|
+-----+--------+ +------+
|
+--------+------------------------------------------------------+
| | ISP 2 network |
| +----------------+ +----------+ |
| |Interworking GW |----------------| T-Cache | |
| +-----+----------+ +----------+ |
| | |
| | |
| +-----+------+ +---------+ |
| | AC +----------------+ B-Cache | |
| +-----+------+ +---------+ |
| | |
| +-------------------------------+ |
| +----+------+ +-----+-----+ |
| | AP_1 | . . . . | AP_n | |
| +----+------+ +-----+-----+ |
| | | |
+--------+-------------------------------+----------------------+
| |
+--+----------+ |
| | |
+--+--+ +--+--+ +--+--+
|Peer2| |Peer3| |Peer4|
+-----+ +-----+ +-----+
Figure 2: Architecture of B-cache in WLAN
3.3. Generalized cache architecture for intra-ISP networks
Fig. 3 generalized the overall architecture of the potential P2P
cache deployments inside an ISP with various access network types.
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As it shows, P2P caches may be deployed at various levels, including:
the interworking gateway linking with other ISPs, internal access
network gateways linking with different types of accessing networks
(e.g. WLAN, cellular and wired), and even within an accessing network
at the entries of individual WLAN sub-networks. Moreover, depending
on the network context and the operator's policy, each cache can be a
T-Cache or a B-Cache.
+--------------+ +------+
| ISP 1 network+----------------+Peer 1|
+-----+--------+ +------+
|
+--------+------------------------------------------------------+
| | ISP 2 network |
| +---------+ |
| |L1 Cache | |
| +-----+---+ |
| +--------------------+----------------------+ |
| | | | |
| +------+------+ +------+-------+ +------+-------+ |
| | AN1 | | AN2 | | AN3 | |
| | +---------+ | | +----------+ | | | |
| | |L2 Cache | | | |L2 Cache | | | | |
| | +---------+ | | +----------+ | | | |
| +------+------+ +------+-------+ +------+-------+ |
| | | |
| +--------------------+ | |
| | | | |
| +------+------+ +------+-------+ +------+-------+ |
| | SUB-AN11 | | SUB-AN12 | | SUB-AN31 | |
| | +---------+ | | | | | |
| | |L3 Cache | | | | | | |
| | +---------+ | | | | | |
| +------+------+ +------+-------+ +------+-------+ |
| | | | |
+--------+--------------------+----------------------+----------+
| | |
+---+---+ +---+---+ |
| | | | |
+--+--+ +--+--+ +--+--+ +--+--+ +--+--+
|Peer2| |Peer3| |Peer4| |Peer5| |Peer6|
+-----+ +-----+ +-----+ +-----+ +-----+
Figure 3: Generalized Architecture of intra-ISP Caches
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4. Considerations for ALTO deployment with P2P Caches
All in all, transparent forwarding caching effectively localizes the
downloading P2P traffic within the sub-net under its coverage
resulting in reduction of network cost for cross-boundary peer
selection, whereas transparent reverse caching blocks the uploading
traffic outside a wireless sub-net leading to elimination of network
cost for wireless uploading peer selection. In other words, caching
between pairs of endpoints changes the traffic cost along the way.
Therefore, it is proposed to use locations of caches as dividers of
different DIPs to guide intra-ISP network abstraction and mark costs
among them according to the location and type of relevant caches.
4.1. T-Cache: vertical separator from outsiders
It is reasonable to use T-Caches as separators for different DIPs,
since it accelerates P2P traffic in a particular direction,
indicating varied costs among these adjacent partitions. For
instance as shown in Fig.3, assuming the L2 Cache in AN1 of ISP 2
network is a T-Cache, the downloading traffic from other local peers
outside to AN1 can be buffered once and served AN1 network
subsequently. The cost from AN2 or AN3 to AN1 is reduced as result,
but not vise visa. In other words, the ISP 2 network should be sub-
divided into {AN1} and {AN2, AN3}, and the incoming P2P cost for
{AN1} is reduced, for the sake of the L2 T-Cache located at the entry
of AN1.
4.2. B-Cache: horizontal division within insiders
Since B-Cache are deployed in wireless accessing networks to further
reduce the outgoing and local-in-local-out traffic costs in both
directions, it seems straightforward to join the adjacent partitions
together and modify the cost between insiders to zero. However,
there is hidden layering within the B-Cache coverage, as the blocking
of uploading traffic only works for traffic traverse pass the
B-Cache. If the cache is located too high as to be outside a local
routing subnet, the local traffic flows within the subnet cannot
benefit from the B-Cache.
5. Further Discussions
5.1. 5.1. Selective caching
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As there is both CAPEX and OPEX expenditures for dedicated P2P Cache
devices, it may be cost-efficient for transparent caches to make
buffering/serving decisions based on the popularity of the specific
content. How to expose this application-relevant information to ALTO
under such context is an open issue.
6. Security Considerations
TBA
7. IANA Considerations
None.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
8.2. Informative References
[I-D.ietf-alto-deployments]
Stimerling, M., Kiesel, S., and S. Previdi, "ALTO
Deployment Considerations", draft-ietf-alto-deployments-06
(work in progress), February 2013.
[I-D.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol", draft-
ietf-alto-protocol-13 (work in progress), September 2012.
Authors' Addresses
Lingli Deng
China Mobile
Email: denglingli@chinamobile.com
Yan Zhang
Chinese Academy of Sciences
Email: zhangy@hpnl.ac.cn
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