PPSP Group G.Lu
Internet Draft JC.Zuniga
Intended status: Informational A.Rahman
Expires: March 21, 2011 InterDigital Communications, LLC
September 21, 2010
P2P Streaming for Mobile Nodes: Scenarios and Related Issues
draft-lu-ppsp-mobile-04.txt
Abstract
The scenarios where a Peer-to-Peer Streaming Protocol (PPSP) contains
mobile nodes need special considerations. An analysis of all the
scenarios that involve mobile nodes is necessary to provide the
guidelines to PPSP protocol design and applicability. This document
describes some key issues for a PPSP network with mobile nodes, and
proposes some additional requirements for PPSP to handle these
scenarios.
Status of this Memo
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This Internet-Draft will expire on March 21, 2011.
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Copyright Notice
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Table of Contents
1. Introduction...................................................2
2. Conventions and Terminology....................................3
3. Mobile Node Issues.............................................3
3.1. Uplink vs. Downlink Bandwidth.............................3
3.2. Battery Power.............................................3
3.3. Multiple Interfaces.......................................4
3.4. Geo-Targeting.............................................5
4. Conclusion and Recommendations.................................6
5. Security Considerations........................................6
6. IANA Considerations............................................6
7. References.....................................................7
7.1. Normative References......................................7
7.2. Informative References....................................7
8. Acknowledgments................................................7
9. Appendix A - Other Mobility Considerations.....................7
9.1. Processing Power..........................................8
9.2. Link Layer Mobility.......................................8
9.3. Mobile IP.................................................9
9.4. Proxy Mobile IP..........................................11
9.5. Mobility support with RELOAD.............................11
9.6. Tracker Mobility.........................................11
1. Introduction
The PPSP Working Group is developing protocols for Peer-to-Peer (P2P)
streaming systems [I-D.zong-ppsp-reqs]. In the past P2P solutions
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have mostly targeted wired or fixed connections. Mobile P2P
communications are expected to grow rapidly and the nature of mobile
nodes and mobile environments cause specific challenges to P2P
communications, specifically for streaming scenarios. This draft
discusses some key mobility specific issues.
2. Conventions and Terminology
This document uses the same terminologies as [I-D.zong-ppsp-reqs].
For simplicity, this document illustrates scenarios showing a
centralized Tracker architecture. However, it should be understood
that all the scenarios also apply to the distributed architecture,
e.g. using a Distributed Hash Table (DHT).
3. Mobile Node Issues
Mobile nodes are constrained by nature due to their limited battery,
screen size, computational capability, etc. Also mobile nodes operate
in variable and unpredictable environments. These attributes bring
about the following problems that may adversely affect the P2P
Streaming sessions.
3.1. Uplink vs. Downlink Bandwidth
Often mobile nodes have asymmetrical bandwidth capabilities. For
instance, most mobile nodes are capable of handling higher bit rates
in the downlink (to the mobile) than in the uplink (from the mobile).
In addition, many mobile networks also have policies to assign
bandwidth in this asymmetrical manner regardless of the capabilities
of the mobile node. Since peer-to-peer streaming sessions can be
either generated or terminated on a mobile node, this bandwidth
asymmetry should be considered for the Tracker-Peer protocol (e.g. as
part of Peer status parameters reported to the Tracker), and may also
affect Peer-Peer protocol in the peer information negotiation.
3.2. Battery Power
By definition, a mobile node is often disconnected from the
electrical grid and runs on its own battery power. In this
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scenario, the user of the mobile node may want to restrict the types
of P2P sessions that the mobile node should participate in because of
battery drain issues. For example, the user may be willing to
participate in a P2P session if the user herself is watching the
content. However, the user may not want to participate in uploading
large amounts of content to other peers.
Therefore, battery power (or battery status) of a mobile node should
be considered in both the Peer-Peer and the Tracker-Peer protocols
(e.g. as part of Peer status parameters reported to the Tracker and
other peers).
3.3. Multiple Interfaces
Simple IP refers to the scenario where there is no IP layer mobility
protocol such as Mobile IP or Proxy Mobile IP, and a peer needs to
obtain a new IP address through a standard method like DHCP after
losing the previous IP address.
As illustrated in Figure 1, when Peer 1 moves from AN1 to AN2, its IP
address changes from IP1 to IP2. This will impact both the Peer-Peer
connection and the Tracker-Peer connection. For example, Peer-Peer
communication maybe lost (e.g. Peer 2 incorrectly sends chunks to IP1
even though Peer 1 has now changed address to IP2). Also the
Tracker-Peer communication may be compromised (e.g. Tracker has
corrupted Peer lists containing incorrect IP Address for Peer 1).
These effects may be somewhat mitigated by having the mobile node
update the tracker and corresponding peers with its new IP address.
The key question then is the trade-off between signaling required to
provide notification of the IP address change and the load this
causes on the system. Also race conditions must be carefully
considered.
Therefore, reporting of change of the IP address of a mobile node
should be considered in both the Peer-Peer and the Tracker-Peer
protocols.
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+---------+
---------- >| Tracker |< ----------
| +---------+ |
X 3) Tracker-Peer communication |
| may be corrupted |
| |
| |
v 2) P2P communication v
+------+ may be lost +------+
|Peer 1|< ------------X------------ >|Peer 2| ^
+------+ +------+ |
IP1 ^ ^ IP2 1)IP address of ^ IP3 |
| | Peer 1 changes | Logical P2P
X --------- | Overlay Network
| | | ----------------
| | | Physical
| | | Network
v v v |
****** ****** ****** |
* AN1 * * AN2 * * AN3 * v
* * * * * *
****** ****** ******
| | |
| | |
************************************************
* Internet *
* *
************************************************
Figure 1 P2P Streaming with Device with Multiple Interfaces
3.4. Geo-Targeting
Geo-targeting is a technique used to determine the physical location
(i.e. geo-location) of a user. The geo-location is based on
geographical and other personal information provided by the requester
peer or a third party. Techniques to determine geo-location of a user
can rely on civic location, GPS geographical coordinates, cellular
base station ID, or most commonly IP address. The primary source for
IP address geographical data is the regional Internet registries.
Depending on the location, different regulations and rules may apply.
For instance, some content may not be distributed on certain
locations or can only be distributed on some other locations.
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Current content distribution policies can apply certain rules to
fixed P2P Streaming clients. However, device mobility may hide the
peer movement from one region to another where possibly different
content distribution rules may apply hence rendering the set forth
policies un-enforceable. This may also be the case where the peer is
connecting through a Virtual Private Network (VPN).
Therefore, geo-location reporting of a mobile node should be
considered in both the Peer-Peer and the Tracker-Peer protocols.
4. Conclusion and Recommendations
The PPSP Working Group should consider the impacts of various aspects
of mobility discussed in this draft. In particular, PPSP should
consider how these issues can be mitigated in a mobile P2P streaming
environment when designing both the PPSP Peer-Peer and the Tracker-
Peer protocols. Therefore, it is recommended that the following
requirements be added to the "Basic Requirements to PPSP Node"
section of [I-D.zong-ppsp-reqs]:
PPSP.REQ-1: Change in IP address of a Peer device MUST immediately be
reported via the Tracker Protocol and Peer Protocol
PPSP.REQ-2: Available uplink and downlink bandwidth of a Peer device
MAY be reported via the Tracker Protocol and Peer Protocol
PPSP.REQ-3: Battery status of a Peer device SHOULD be reported via
the Tracker Protocol and Peer Protocol
PPSP.REQ-4: Location of a Peer device SHOULD be reported via the
Tracker Protocol and Peer Protocol
5. Security Considerations
This draft does not introduce new threats to security.
6. IANA Considerations
This document makes no request of IANA.
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7. References
7.1. Normative References
[RFC3775] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in Ipv6", RFC 3775, June 2004.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
7.2. Informative References
[I-D.zong-ppsp-reqs]
Zong, N., Zhang, Y., Pascual, V., and C. Williams, "P2P
Streaming Protocol (PPSP) Requirements", draft-zong-ppsp-
reqs-04 (Work in progress), July 7, 2010.
[I-D.ietf-p2psip-base]
Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and H.
Schulzrinne, "REsource LOcation And Discovery (RELOAD) Base
Protocol", draft-ietf-p2psip-base-10 (Work in progress),
August 3, 2010.
8. Acknowledgments
The authors would like to thank Serhad Doken and Milan Patel for
their thorough review and valuable inputs to this draft.
9. Appendix A - Other Mobility Considerations
This Appendix summarizes some other mobility considerations that were
analyzed. However, these considerations are outside the scope of the
current PPSP Working Group scope and thus are recorded here for
purely informational purposes.
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9.1. Processing Power
Some devices are more capable than others in terms of computational
performance or processing power. Similarly, devices can have
different performance for generating a session (e.g. video recording)
or terminating it (e.g. video display). Taking these differences into
account is important for maintaining a good quality of the P2P
streaming session.
9.2. Link Layer Mobility
PPSP uses a P2P based overlay network on top of the transport
network. Mobility or link quality at link layers is not visible to
the peers.
As illustrated in Figure 1, if Peer 1 is connected to a poor quality
link via mobile Access Network 1 (AN1), then the overall P2P
streaming session quality can suffer from high error rate and low
throughput due to poor link layer conditions. This will impact both
the Peer-Peer connection and the Tracker-Peer connection. For
example, on the Peer-Peer connection frame loss, audio/video synch
loss, or streaming stalls are likely to be seen on the media transfer
protocols.
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+---------+
---------- >| Tracker |< ----------
| +---------+ |
| 3)Tracker-Peer communication |
X is poor |
| |
| |
| 2)P2P streaming session |
v quality is poor v
+------+ +------+ ^
|Peer 1|< ------------X------------ >|Peer 2| |
+------+ +------+ |
IP1 ^ ^ IP2 Logical P2P
| | Overlay Network
X 1)Poor quality link layer | ------------------
| | Physical
| | Network
v v |
****** ****** |
* AN1 * * AN2 * v
* * * *
****** ******
| |
| |
************************************************
* Internet *
* *
************************************************
Figure 2 P2P Streaming with Link Layer Mobility
9.3. Mobile IP
Mobile IP (MIP) provides IP mobility and hides the mobile's movement
from the Correspondent Node (CN) [RFC3775].
Figure 3 illustrates the case when Peer 1 moves from AN1 to AN1'.
Because of Mobile IP, neither the Tracker nor Peer 2 are aware of the
change of network for peer 1. However, due to the inherent tunneling
and triangular routing of the Mobile IP protocol (through the Home
Agent) the P2P session may in some scenarios experience extra
latency. This may adversely affect the user experience of the P2P
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streaming session. As seen above, Mobile IP will impact primarily the
Peer-Peer connection (and the Tracker-Peer connection is not
significantly affected).
+---------+
---------- >| Tracker |< ----------
| +---------+ |
| |
| |
| 3) P2P chunk transfer (content) |
| may experience extra latency |
| due to extra MIP tunneling |
v v
+------+ +------+
|Peer 1|< -----------X------------- >|Peer 2| ^
+------+ +------+ |
^ ^ IP-HA 1) Peer 1 moves ^ IP2 |
| | between networks | Logical P2P
X --------- | Overlay Network
| | | ----------------
| | | Physical
| | | Network
| | | |
v v v |
****** ****** ****** v
* AN1 * * AN2 * * AN3 *
* * * * * *
****** ****** ******
| | |
| | |
+---------------+ 2) IP traffic of |
| MIP Home Agent| Peer 1 is always |
+---------------+ tunneled to the |
| Home Agent |
| |
************************************************
* Internet *
* *
************************************************
Figure 3 P2P Streaming with Mobile IP
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9.4. Proxy Mobile IP
The use of Proxy Mobile IP [RFC5213] causes similar issues as the
ones mentioned for Mobile IP in the above section. On top of these,
Proxy Mobile IP also introduces a new issue for P2P streaming
sessions. Since Proxy Mobile IP is a network based solution, the
mobile node (peer) is not aware of its IP mobility so it cannot
inform the Tracker, P2P Cache, CDNs or other peers of the IP level
mobility. Therefore IP mobility is totally invisible to the P2P
Streaming session entities and harder to detect and respond
accordingly. Thus Proxy Mobile IP will impact both the Peer-Peer
connection and the Tracker-Peer connection.
9.5. Mobility support with RELOAD
It has already been identified in the proposed WG charter that any
PPSP developed protocol should be analyzed for interactions with the
RELOAD protocol. The RELOAD protocol provides a signaling and routing
mechanism for P2P overlay networks over the general Internet. The
latest RELOAD draft [I-D.ietf-p2psip-base] also has a future
consideration section for support of HIP (section 5.6.1.1). HIP is
an experimental mobility protocol with good security properties.
In addition to HIP, the following mobility protocols should also be
considered for PPSP-RELOAD interactions:
. Mobile IP
. Proxy Mobile IP
9.6. Tracker Mobility
Normally Trackers are assumed to be fixed nodes. However, in a mobile
environment mobile nodes can also become Trackers. In this sense,
similar considerations to the ones described above for mobile peers
should be applied to mobile Trackers.
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Authors' Addresses
Guang Lu
InterDigital Communications, LLC
Email: Guang.Lu@InterDigital.com
Juan Carlos Zuniga
InterDigital Communications, LLC
Email: JuanCarlos.Zuniga@InterDigital.com
Akbar Rahman
InterDigital Communications, LLC
Email: Akbar.Rahman@InterDigital.com
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