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Peer-to-Peer Communication Systems Protocols and Systems, Reliability, Energy Efficiency and Measurements

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Title: Peer-to-Peer Communication Systems Protocols and Systems, Reliability, Energy Efficiency and Measurements


1
Peer-to-Peer Communication Systems Protocols and
Systems, Reliability, Energy Efficiency and
Measurements
  • Salman Abdul Baset
  • salman_at_cs.columbia.edu
  • Department of Computer Science
  • Columbia University

2
Background and Motivation
3
IP-based communication systems
Client-server
Peer-to-Peer
  • Basic services
  • establish voice, video, IM sessions
  • voicemail
  • Advanced services
  • conferencing, telepresence
  • voicemail to text

4
Client-server IP communication system
SIP registrar / proxy / presence server
SIP registrar / proxy server
IP-PSTN gateway
REGISTER (ip addr)
REGISTER (ip addr)
(1) signaling
(1) signaling
(2) media (voice, video, IM)
User agent
User agent
Utopian Internet No NATs or firewalls
5
Client-server IP communication system
NAT
packet
packet
Src-IP
Dst-IP
Pub-IP
Dst-IP
Network
Src-IP
Pub-IP
Pr-IP
Dst-IP
6
Client-server IP communication system
SIP registrar / proxy / presence / server
media server
IP-PSTN gateway
Peer-to-Peer distribute to user agents
  • What is centralized?
  • directory service
  • call signaling
  • media session and conferencing
  • presence
  • PSTN connectivity


(1) signaling
NAT / firewall
NAT / firewall
(1) signaling
(2) media (voice, video, IM) (UDP or TCP)
User agents
User agents
  • Scaling for millions of users
  • servers
  • b/w
  • management overhead

Why is this a problem?
  • How many calls need media relaying?
  • 30
  • in practice all

7
Peer-to-peer communication system
media relay (or relay)
node A
node E
NAT / firewall
network address of node B?
(3) media (TCP)
(2) signaling
(2)
(4) media
(1)
(3) signaling
P2P / PSTN gateway
(1)
(1)
NAT / firewall
network address of node E?
(2)
(1)
node B
(2) signaling
  • nodes form an overlay
  • share responsibilities for message routing,
    signaling, media relaying
  • super nodes, ordinary nodes

node C
node D
node user agent
8
Challenges Designing, building, and analyzing p2p
communication systems
  • 1 Protocol and system design
  • 2 Reliability
  • 3 Session quality
  • 4 Energy efficiency
  • 5 Measurement

9
Why not just use Skype?
  • Skype works, but
  • Closed and proprietary solution
  • Requires Internet access
  • cannot be used in ad hoc environments
  • Skype network failure for 2-5 days
  • August 2007

10
Motivation
  • Peer-to-peer communication systems
  • Why not client-server?
  • server, b/w, maintenance overhead
  • Why not just use Skype?
  • proprietary solution

11
Outline
Background Motivation
How to design protocols and systems for
p2p. communication?
Other work
Protocol and System Design
Peer-to-Peer Communication Systems
Measurement
Reliability
What is the reliability of a p2p comm. system?
What are the measurement techniques to understand
p2p comm. systems as a black box?
Energy Efficiency
Are p2p VoIP systems more energy efficient than
c/s?
12
Outline
Background Motivation
How to design protocols and systems for
p2p. communication?
Protocol and System Design
Peer-to-Peer Communication Systems
Reliability
13
Protocol and System Design
  • Goal design open, standardized, and
    interoperable protocols for building p2p
    communication systems
  • in ad hoc, office, and Internet environments
  • High-level Requirements
  • Scalability
  • NATs and firewalls
  • churn
  • heterogeneous capabilities
  • overlay routing
  • Security
  • trusted and insecure environments
  • Resources and Services
  • heterogeneity, discovery, addressing
  • Interoperability
  • Reuse existing protocols
  • where possible

Can we meet these requirements?
14
Yes, we can! ?
  • How?
  • Identify common aspects of existing p2p protocols
    and potential deployments and incorporate them in
    the protocol.
  • Support pluggable overlay routing.
  • one overlay protocol may not be suitable for all
    environments
  • Make protocol extensible for future-proofing.

flexibility vs. complexity tradeoff
15
Protocol and System Design
  • Data model
  • addressing, storage, integrity
  • Message reliability
  • hop-by-hop, e2e
  • Non-common aspects
  • Next-hop determination
  • depends on the overlay protocol
  • Chord, Kademla, Gia,
  • Common aspects
  • Connectivity
  • NAT traversal
  • bootstrap
  • Resilience
  • recovery from node churn
  • Request routing
  • recursive vs. iterative
  • parallel vs. sequential
  • Heterogeneity of nodes
  • mobile, desktop
  • super node vs. ordinary node
  • Security
  • identity
  • message confidentiality
  • Methods for implementing the common aspects
  • Overlay protocol implements specific methods

16
Peer-to-Peer Protocol (P2PP)
  • Now part of RELOAD protocol being standardized in
    the IETF
  • Not a new DHT!
  • Geared towards IP telephony but applicable to
    streaming, VoD etc.
  • A request / response binary protocol
  • Common methods
  • Join, Leave, Publish, Lookup etc
  • Overlay specific
  • FindPeer, ExchangeTable
  • Pluggable overlay routing (Chord, Kademlia etc)
  • Application-level API
  • Security
  • enrollment server, shared-secret, X.509
    certificates
  • TLS, DTLS for message confidentiality

SIP
API
P2PP
ICE
TLS / SSL
protocol stack of a node
IETF P2PSIP working group documents
17
Peer-to-Peer Protocol (P2PP)
  • Node heterogeneity
  • peers (super nodes) and clients (ordinary nodes)
  • use of peers as relays
  • NAT traversal built-in
  • a node exchanges its host, NAT, and a relay IP
    address in requests and responses
  • then uses ICE (interactive connectivity
    establishment) for NAT traversal
  • Message reliability
  • hop-by-hop, e2e
  • Data model
  • key / value pairs
  • value single, array, dictionary
  • data integrity
  • Monitoring and diagnostics gathering

18
OpenVoIP architecture
  • Proof-of-concept system based on P2PP

SIGCOMM (demo) 2008
19
OpenVoIP key facts
  • 1000 node network on 500 PlanetLab machines
  • Kademlia, Bamboo, Chord
  • Windows XP / Vista, Linux
  • Integrated with Google, flash-based maps
  • Integrated with open source SIP phone OpenWengo
    (Qutecom)
  • Code used and modified by Ericsson Labs, Nokia
    Labs, Telecom Italia, and many universities

20
OpenVoIP geological interface
21
Outline
Background Motivation
Protocol and System Design
Peer-to-Peer Communication Systems
Reliability
What is the reliability of a p2p comm. system?
22
Reliability of P2P Comm. Systems
  • Goal to reason about the reliability of p2p
    comm. systems
  • ReliabilityProportion of completed calls
  • understand reasons for call failure
  • devise techniques to improve them
  • Reasons for call failure
  • (1) distributed search fails to find online
    callee
  • (2) distributed search fails to find a suitable
    relay
  • (3) relay fails during voice/video session
  • understand and improve reliability for relayed
    calls

media relay (or relay)
NAT / firewall
node A
node E
(3) media (TCP)
(2) signaling
(1)
(1)
network address of node E?
NAT / firewall
node B
(2) signaling
node C
node D
IPTCOMM2010
23
Understanding reliability of relayed calls
  • For desired reliability, minimum relays k per
    call?
  • Model
  • when ith relay fails, call is switched (i1)st
    relay which is instantly selected from the global
    pool of all relays.
  • Ri residual lifetime of a relay candidate
    (i.i.d.)
  • let D denote the call duration.

D
Rk
Rk-1
R1
k
1
2
k-1
99.9
k depends on the relationship b/w node lifetime
and call duration
24
Understanding reliability of relayed calls
Exponential node lifetimes
Skype node lifetimes
95 of Skype relay calls last less than 60 mins
Min of relays k
6 4
3 5
1 10
Min of relays k
Skype 12 hours (mean) 4 hours (med) 3 (mean call holding time one hour)
Mean node lifetime Mean call duration
lifetimes approximated as pareto
95 of Skype call durations minimum of 3 relays
to maintain 99.9 success rate
What if the system does not have enough relays?
25
Outline
Background Motivation
Protocol and System Design
Peer-to-Peer Communication Systems
Reliability
Energy Efficiency
Are p2p VoIP systems energy efficient than c/s?
26
Are p2p comm. systems more energy efficient than
c/s?
  • Two reasons
  • overheads (e.g., cooling) power utilization
    efficiency (PUE)
  • ratio of data center power draw to IT power draw
  • idle power consumption
  • But really?
  • we tried to answer this question

SIGCOMM Green networking workshop 2010
27
Are p2p comm. systems more energy efficient than
c/s?
  • Issues in comparison
  • under same load
  • centralized vs. distributed aspects
  • do not compare components that are centralized in
    p2p and c/s
  • PSTN replacement
  • Skype vs. Vonage
  • endpoint energy consumption
  • negligible 5W per device,
  • but millions of them
  • workload characteristics
  • impacted by NATs and firewalls
  • Our approach
  • gather peak data from VoIP providers
  • build energy models for c/s and p2p VoIP systems
  • perform measurements
  • C/S VoIP provider
  • 100 K users
  • mostly business
  • 15 calls per second (CPS)
  • 5K calls in system
  • NAT keep-alive traffic
  • all calls are relayed

28
Energy Models for C/S and P2P
  • N users or nodes
  • C/S model
  • C/S power consumption servers x watt/server x
    redundancy factor x PUE
  • P2P model
  • S supernodes
  • ps denotes power consumption by super node
    functions

P2P energy efficient when of super nodes
(S) x power consump. of a super node (ps) lt C/S
power consumption
  • 1 million users
  • servers (50 utilization)
  • 2 kW
  • Estimating super node population
  • one per relayed call

ps 0.266W
P2P may not be energy efficient than c/s for VoIP
29
Energy Efficiency of VoIP Systems
  • End-points dominate energy consumption in c/s
    systems replacing PSTN
  • 1 million users
  • servers 2 kW, endpoints 5000 kW (at 5W)
  • 0.04 (voice)
  • NATs are responsible for energy inefficiency of
    c/s systems
  • problems will not go away with IPv6 firewalls
  • VoIP and PSTN?
  • trying to figure it out

30
Outline
Background Motivation
Protocol and System Design
Peer-to-Peer Communication Systems
Measurement
Reliability
What are the measurement techniques to understand
p2p comm. systems as a black box?
Energy Efficiency
31
Measurement Skype
  • Super node, ordinary node, login server
  • Actively prevent against reverse engineering
  • LD_PRELOAD
  • forcing Skype to use a modified shared library
  • Voice and video calls
  • relaying
  • over TCP
  • Ports no default listening port
  • opens port 80 (HTTP) and 443 (TLS)
  • Contact list
  • stored centrally, initially distributed
  • Video conferencing
  • using central servers ?

INFOCOM06
32
Is Skype free-riding on universities bandwidth?
  • Two Skype clients in Columbia University forced
    to use a relay
  • 6,000 relay calls
  • Median latency 95ms
  • 46 calls through relays with a .edu suffix
  • 8 of calls through Columbia Skype users
  • Is it deliberate?
  • probably not
  • relay selection biased towards high-capacity
    nodes which happen to be in universities

our lab
NAT
NAT
GI08
33
Outline
Background Motivation
Other work
Protocol and System Design
Peer-to-Peer Communication Systems
Measurement
Reliability
Energy Efficiency
34
Other work
  • Research
  • TCP feasibility for real-time traffic
    (SIGMETRICS)
  • Can software routers scale? (PRESTO)
  • Hacking and building
  • vazool.com

35
Directions for future research
  • A holistic framework for reliability,
    performance, and energy tradeoffs in data centers
  • virtualization, consolidation
  • nano data centers?
  • Preventing data lock-in for social networks and
    cloud-based services
  • enabling seamless data migration across different
    cloud providers
  • holy grail one click data migration

36
Conclusions
Background Motivation
  • Open P2PSIP protocol
  • OpenVoIP

Other work
Protocol and System Design
Peer-to-Peer Communication Systems
Measurement
Reliability
3 relays are sufficient to achieve 99.9 call
reliability
Skype is free-riding on universities bandwidth
Energy Efficiency
  • p2p may not be energy efficient than c/s
  • endpoints dominate
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