Bithoc bittorrent for wireless ad hoc networks
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28/02/2008. MAESTRO/PLANETE INFORMEL SEMINARY. BitHoc: BitTorrent for wireless ad hoc networks. Mohamed Karim Sbaï. Jointly with: Chadi Barakat Jayeoung Choi Anwar Al Hamra Thierry Turletti. EPI PLANETE. Wireless ad hoc networks.

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Bithoc bittorrent for wireless ad hoc networks

28/02/2008

MAESTRO/PLANETE

INFORMEL SEMINARY

BitHoc: BitTorrent for wireless ad hoc networks

Mohamed Karim Sbaï

Jointly with:

Chadi Barakat

Jayeoung Choi

Anwar Al Hamra

Thierry Turletti

EPI PLANETE


Wireless ad hoc networks

Wireless ad hoc networks

  • No central administration

  • No base station

  • Nodes are both hosts and routers

  • Need for multi-hop routing approaches

  • The connectivity is ensured thanks to the collaboration of nodes in forwarding and routing messages of each others

  • It is the P2P paradigm in the network layer.


P2p file sharing applications

P2P file sharing applications

  • No central server

  • Users are both clients and servers : They download content and share some of their upload capacity to serve other users.

  • The global capacity of the system grows thanks to their collaboration.

  • This is the P2P paradigm in the overlay.


P2p file sharing in wireless ad hoc networks constraints

P2P file sharing in wireless ad hoc networks : constraints

  • Routing overhead

  • Transport protocols performance drops seriously in wireless multi-hop paths

  • P2P file sharing solutions are topology unaware : Overlay neighbors are selected independently of their locations.

 How will such applications perform in wireless ad hoc networks ? What are the modifications (namely in overlay construction) to be made to ameliorate both download time and sharing ratios ?


Outline

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Outline1

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Bittorrent 1 2

BitTorrent (1/2)

  • a P2P efficient content distribution protocol

  • Peer lookup:

    • A Client contacts a central rendezvous node named Tracker to get addresses of other clients

  • Sharing content:

    • A file is cut into pieces (multi-sourcing)

    • Each client shares some of its upload bandwidth with other clients

    • Torrent : peers cooperating to download the same content

    • Seed : a peer who finished downloading the content and still serving other peers

    • leecher : peer who is downloading the file


Bittorrent 2 2

BitTorrent (2/2)

  • Choking algorithm: A peer chooses periodically a set of peers with whom it opens TCP connections to upload pieces.

    Only 4 simultaneous connections:

    3 best uploaders + 1 a random peer (discovering new upload capacities )

     Enforce cooperation and reciprocity among peers

  • Piece selection strategy:When a peer receives a piece offer message from a neighbor, it selects the rarest piece in the peer list.

     This increases the entropy of pieces in the network and then the chance to replicate pieces after downloading them.


Outline2

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Framework scenario and assumptions

Framework, scenario and assumptions

Assumptions

  • All nodes are peers

  • No mobility in the network

  • Trackerless BitTorrent : a flooding of HELLO messages to discover all peers in the network.

Framework

  • We added a module to NS-2 implementing BitTorrent functionalities.


Framework scenario and assumptions1

Framework, scenario and assumptions

Ad hoc scenario

  • A grid topology of N nodes (10 per row) (distance = 40 m between nodes)

  • No mobility of nodes

  • DSDV proactive routing protocol

  • 802.11 MAC Layer with RTS/CTS-DATA/ACK

  • Data rate = 1 MB/s, range = 50 m

BitTorrent Scenario

  • 1 file = 10 Mbit

  • 1 original seed

  • Choking period = 40 s

  • Flooding TTL = variable

  • Number of pieces = variable, number of blocks = variable

  • Block size = 1 KB


Outline3

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Performance metrics of bittorrent in ad hoc networks

Performance metrics of BitTorrent in ad hoc networks

  • Rij : sharing ratio between i and j

  • Ri: sharing ratio of node iRi = average on j of Rij( Uij<>0 or Dij<>0)

  • Rh: average on nodes i located at h hops from the original seed of Ri

  • Fi : finish time of peer i.

  • Fh: average on nodes i located at h hops from the original seed of Fi


Outline4

Outline

  • Overview of BitTorrent

  • Performance metrics

  • Framework, scenario and assumptions

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Impact of the size of pieces

Impact of the size of pieces

  • Flooding TTL = MAX

  • Small piece size = 100 blocksBig piece size = 1000 blocks

  • Finish time as a function of number of hops to the seed (Fh):


Impact of the size of pieces1

Impact of the size of pieces

  • Average sharing ratio as a function of number of hops to the seed (Rh):


Impact of the size of pieces2

Impact of the size of pieces

  • Average sharing ratio per couple of nodes for big size of pieces

  • Average sharing ratio per couple of nodes for small size of pieces


Outline5

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Impact of the scope of the neighborhood

Impact of the scope of the neighborhood

  • Flooding TTL = variable

  • piece size = 100 blocks = small

  • Finish time as a function of number of hops to the seed (Fh) for different TTLs:


Impact of the scope of the neighborhood1

Impact of the scope of the neighborhood

  • Average sharing ratio as a function of number of hops to the seed (Rh):


Outline6

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Bithoc our solution

BitHoc: Our solution

  • Reduced neighborhood + a few connections to far peers  good TCP performance in near neighborhood and more entropy of pieces for better sharing.

  • Peers are classified into 2 tables :NNT : Nearby Neighbors Table (hops <=2)FNT : Far Neighbors Table (hops > 2)

  • We redefine the choking algorithm and the piece selection strategy


Outline7

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Bithoc choking algorithm

BitHoc: Choking algorithm

  • 3 best uploaders from NNT and FNT

  • 1 randomly: q times from NNT and 1 time from FNT- uniformly from NNT- probability p to choose a node at h hops in FNT (hm : max hops)ifthenelse 0


Outline8

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Bithoc piece selection strategy

BitHoc: Piece selection strategy

  • Offer from NNT Rarest first in near neighborhood

  • Offer from FNT Absent piece strategy = accept only pieces that do not exist in near neighborhood

  • PIECE UPDATE messages need only to be sent to peers in NNT.


Outline9

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Bithoc some first results

BitHoc: Some first results

  • Finish time as a function of number of hops to the seed (Fh):


Bithoc some first results1

BitHoc: Some first results

  • Average sharing ratio as a function of number of hops to the seed (Rh):


Outline10

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Bithoc static choice of q

BitHoc: Static choice of q

  • We establish an empiric formula for q:

    q = number of slots near / number of slots far

    Goal: send a copy of each piece to the end of the network and wait for it to return to the middle of the network.

αi : average number of pieces sent at i hops in a choking slot.


Bithoc static choice of q1

BitHoc: Static choice of q

  • Finding optimal q by simulations:

q = 1 for 40 nodes

q = 3 for 80 nodes


Bithoc static choice of q2

BitHoc: Static choice of q

  • Validation of the empiric formula:


Bithoc dynamic choice of q

BitHoc: dynamic choice of q

  • Topology, network conditions, etc can change  each node adapts its q dynamically following its observations.


Bithoc dynamic choice of q1

Comparing static to dynamic choice of q: average finish time

BitHoc: dynamic choice of q


Bithoc dynamic choice of q2

Comparing static to dynamic choice of q: average sharing ratio

BitHoc: dynamic choice of q


Outline11

Outline

  • Overview of BitTorrent

  • Framework, scenario and assumptions

  • Performance metrics

  • Impact of the size of pieces

  • Impact of the scope of the neighborhood

  • BitHoc: Our solution

    • Choking algorithm

    • Piece selection strategy

    • Some first results

    • Choice of parameters and new results.

  • Conclusions and future work


Conclusions and future work

Conclusions and future work

  • BitHoc gives better finish times and better sharing ratios than other solutions even those limiting the scope of the neighborhood

  • BitHoc finds a good management of neighbor and piece selection strategies

    • Good performance in near neighborhood

    • Better entropy by adding some few connections to far nodes

    • Only absent pieces are sent to far nodes

  • Future work:

    • Impact of mobility of nodes

    • Studying the case of sparse overlays

    • Optimizing lookup in wireless ad hoc networks

    • Real implementation and testing of the protocol


Thank you

THANK YOU

?

E-mail:[email protected]


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