IEEE COMSOC MMTC E-Letter
ISP-Friendly P2P Streaming
Nazanin Magharei, Reza Rejaie
University of Oregon
nazanin,reza@cs.uoregon.edu
Mesh-based Peer-to-Peer (P2P) streaming
applications (i.e., IPTV-like applications) have
been widely used for scalable delivery of live
video over the Internet, mainly due to their
ability to gracefully accommodate churn and
bandwidth heterogeneity. In mesh-based P2P
streaming, participating peers typically build a
randomly connected mesh over which they
incorporate a swarm-like content delivery
mechanism.
The popularity and high bandwidth demand of
mesh-based P2P streaming applications can
potentially result in generating a significant
amount of network traffic. As these applications
rely on building underlay-agnostic random
overlays among participating peers, their
generated inter-ISP traffic results in a high cost
on ISPs. Consequently, ISPs try to overcome this
hurdle and reduce the unwanted inter-ISP P2P
traffic by various transparent or non-transparent
means. For instance, some ISPs have limited the
traffic to certain ports associated with P2P
applications, performed packet inspection to
identify P2P traffic, incorporated caching
mechanism for P2P traffic and recently,
redirected local P2P connections to internal peers
[1].
The interference of ISPs on the connectivity of
P2P overlays has resulted in some recent studies
on the localization of overlay connectivity within
edge ISPs. These studies have primarily focused
on the overlay localization for P2P file-sharing
applications (e.g., Bittorrent) and examined the
effect of localization on the performance of such
applications. [1] and [7] propose solutions for
facilitating local peer discovery and further
demonstrate an improvement in the performance
of Bittorrent-like applications over localized
overlays. Clearly, the observed performance
improvement of P2P file-sharing applications
over localized overlays can be affected by the
number of seeds, population of peers in each ISP
and the aggregate amount of resources (e.g.,
bandwidth). Therefore, the reported findings
cannot be easily extended to all scenarios.
Compared to P2P file-sharing applications,
live P2P streaming applications have unique
requirements due to their timing constraint and
the limited availability of future content. Due to
these requirements, the performance of live P2P
http://www.comsoc.org/~mmc/
streaming applications can be adversely affected
by overlay localization. In fact, in a localized
P2P overlay, despite the random connectivity
among ISPs and between peers in each ISP, there
may not be an adequate number of inter-ISP
shortcuts in the overlay. This may affect the flow
of content through the overlay and limit the
diversity of available content in each
neighborhood
which
can
degrade
the
performance of live P2P streaming applications.
Mesh-based P2P Streaming: In a typical
mesh-based live P2P Streaming mechanism such
as [4], [6] and [8], participating peers maintain a
randomly connected overlay mesh over which
they incorporate swarming (i.e., pull) content
delivery. Each peer has multiple parents that
receives content from and multiple children that
provides content to. We assume that the
incoming and outgoing degree of any peer is
proportional to its incoming and outgoing
bandwidth, respectively. This implies that the
average bandwidth of all overlay connections is
roughly equal to a configurable value which we
call BWPC. Each peer as a parent, periodically
reports the availability of new content (i.e.,
blocks) to all of its children. Individual peers
leverage the block availability information
among their parents and determine which block
should be pulled from each of their parents to
maximize the utilization of their aggregate
incoming bandwidth and thus the delivered
quality.
Maximum Overlay Localization: In the
context of live P2P streaming, the aggregate
incoming bandwidth to each ISP should be at
least equal to the stream bandwidth (STRBW).
Otherwise, the delivery rate of the stream to ISPs
will be less than the stream rate and thus, stream
cannot be received and played back continuously
by the participating peers in each ISP.
Consequently, the maximum tolerable level of
localization in live P2P streaming applications is
equal to the stream rate. In such a fully localized
overlay, only a single copy of the stream can be
diffused to each ISP. On the other hand, lower
levels of localization allow for delivery of
redundant content to each ISP. Assuming all
overlay connections have roughly the same
bandwidth, the level of localization can be
controlled by the number of incoming external
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IEEE COMSOC MMTC E-Letter
connections to each ISP. For instance, in the
fully localized overlay, the number of incoming
external connections to each ISP is set to its
minimum value of STRBW .
BWPC
Effect of Localization: To investigate the
effect of localization on the performance of
mesh-based live P2P streaming applications, we
evaluate the performance of a typical meshbased live P2P streaming mechanism (i.e.,
PRIME [2], [4]) over overlays with various
levels of localization through NS-2 simulations.
We consider a homogeneous scenario with 500
peers that are evenly distributed across 10 ISPs.
We focus on a resource-constrained setting
where the source and peers bandwidth is equal to
the stream bandwidth of 700 Kbps. The
incoming and outgoing degree of each peer is set
to 6 and source has also 6 children. We define
the level of localization as the ratio of stream
bandwidth to aggregate external incoming
bandwidth for each ISP. For instance, in case of
100% localization or fully localized overlay, the
aggregate incoming bandwidth to each ISP is
equal to the stream bandwidth which implies that
the total number of incoming connections to each
ISP is 6. Figure 1 depicts the distribution of the
percentage of delivered quality to peers for
overlays with various levels of localization. The
line labeled as ‘Rand‘ shows the delivered
quality in a random overlay. Interestingly, this
figure illustrates the following important points:
(i) In a typical mesh-based P2P streaming
mechanism over a fully localized overlay, the
delivered quality to all peers significantly
decreases. (ii) Decreasing the level of
localization (i.e., allowing more redundant traffic
to ISPs) gradually improves the overall
performance. In fact, to deliver a good quality to
a large fraction of peers, the level of localization
should be less than 20%. In other words the
external incoming bandwidth to each ISP should
be at least 5 times of the stream bandwidth.
Solution: There are two approaches to tackle
the problem of P2P localization in the context of
live streaming as follows: (i) Identify the
maximum level of localization (minimum
amount of external incoming traffic) that enables
a typical mesh-based P2P streaming mechanism
to provide high quality stream to individual peers
by maintaining adequate level of diversity in the
overlay. Such a maximum level of localization
can be potentially affected by several factors
such as the number of ISPs, peer population in
each ISP and peers bandwidth. Thus, the key
http://www.comsoc.org/~mmc/
Figure 1: Distribution of the delivered quality
to individual peers across overlays with
various levels of localization and a random
overlay.
issue in this approach, is to find the maximum
level of localization in a dynamic and distributed
fashion. (ii) Design an ISP-friendly P2P
streaming mechanism that achieves a good
performance in fully localized overlays. In such
an ISP-friendly mechanism, edge peers of the
ISPs (i.e., those peers with an external incoming
connection) play a more important role in
determining the proper flow of content and
should pull fresh and unique blocks of content to
their corresponding ISPs.
Our research group is investigating both of the
above approaches. Further information about
these projects is available online at
http://mirage.cs.uoregon.edu/PRIME/P2P.html.
REFERENCES
[1] D. R. Choffnes and F. E. Bustamante,
“Taming the torrent: A practical approach to
reducing cross-isp traffic in peer-to-peer
systems,” in ACM SIGCOMM, 2008.
[2] N. Magharei and R. Rejaie, “PRIME: Peerto-Peer
Receiver-drIven
MEsh-based
Streaming,” in IEEE INFOCOM, 2007.
[3] N. Magharei and R. Rejaie, “Overlay
monitoring and repair in swarm-based peer-topeer streaming,” in ACM NOSSDAV, 2009.
[4] N. Magharei and R. Rejaie, “PRIME: Peerto-Peer
Receiver-drIven
MEsh-based
Streaming,” ACM/IEEE Transactions on
Networking, 2009.
[5] N. Magharei, R. Rejaie, V. Hilt, I. Rimac,
and M. Hofmann, “ISP-Friendly Live P2P
Streaming,” Tech. Rep. CIS-TR-09-07, 2009.
[Online].
Available:
http://mirage.cs.uoregon.edu/pub/tr09-07.pdf
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IEEE COMSOC MMTC E-Letter
[6] V. Pai, K. Kumar, K. Tamilmani, V.
Sambamurthy, and A. Mohr, “Chainsaw:
Eliminating Trees from Overlay Multicast,” in
IPTPS, 2005.
[7] H. Xie, R. Yang, A. Krishnamurthy, Y. Liu,
and A. Silberschatz, “P4p: Provider portal for
(p2p) applications,” in ACM SIGCOMM, 2008.
[8] X. Zhang, J. Liu, B. Li, and T. Yum,
“Coolstreaming: A data-driven overlay network
for live media streaming,” in IEEE INFOCOM,
2005.
Nazanin Magharei is currently a Ph.D.
candidate in the Computer Science Department
at the University of Oregon. She received her
B.S. degree in Electrical Engineering from Sharif
University of Technology, Iran in 2002. Her
research interests include P2P streaming, P2P
overlay
characterization
and
network
measurement.
http://www.comsoc.org/~mmc/
Reza Rejaie (SM'06/ACM SM'06) received his
M.S. and Ph.D. degrees from the University of
Southern California in 1996 and 1999, and his
B.S. degree from the Sharif University of
Technology in 1991. He is currently an
Associate Professor at the University of Oregon.
From 1999 to 2002, he was a Senior Technical
Staff member at AT\&T Labs---Research in
Menlo Park, California. His research interests
include P2P networking, network measurement
and multimedia networking. Reza received a
NSF CAREER Award for his work on P2P
streaming in 2005.
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