1. VoD BitTorrent Framework

2. Background BT is a very popular peer to peer protocol with many implementations: –http://en.wikipedia.org/wiki/Comparison_of_Bit Torrent_clientshttp://en.wikipedia.org/wiki/Comparison_of_Bit Torrent_clients The first one was created in Python by Bram Cohen.

3. Real world motivation BitTorrent is common and Free Most chances there is a swarm for your movie VoD servers are expensive and complicated Its better to use P2P for VoD

4. Some definitions StratUp Delay (D) = How much time I am allowed to hold before starting to play M (Movie). Prefetch Time (P) = How much time before I watch byte B from M, it should arrive. Playback Rate (R) = How many bytes/second I watch B(t) – the index of the bit that must arrive by t. B(t) = R *(P+t-D)

5. Rules and Examples B(t) = R *(P+t-D) If R=5 KB/sec and D=6 seconds and P=2 seconds, than: –At t=6 seconds, I must have 10KB continuous from the start of the movie. –At t=18 seconds I must have 70KB continuous from the start of the movie.

6. What does my server suppose to do Your server suppose to get from the Bittorent clients pieces of data needed to play the video. Each piece needs to arrive by its deadline. If the piece does not arrive by the deadline you “can download it freely” from the server. –In this case you encounter a penalty The number of penalty points you accumulated whole getting/playing the video is your (negative) score.

7. How do I test my server/idea Create my own VoD BitTorrent client. Simulate VoD server – implement a function that copies from a seed directly to my file (Checkpoint 1). Count the bytes your client received from the VoD Server (Checkpoint 1) Aim at minimizing the part of the movie downloaded from VoD Server.

8. Execution example run-all.sh Tracker BT VOD BT

9. How does it work? Run tracker Run the “world” Run your client (if given)

10. How does it work? Both tracker and the “world” run on the same computer we have –pc-hanoch-w3 –Please reserve time in: http://bt-p2p-vod.wikispaces.com/ Or from course www - "Scheduling computers for tests."

11. The main script - run_all.sh Location: –/users/courses/hanochworkshop/bittorrent run_all_vod.sh: –Parameters: Start / stop My client – optional

12. run_all_vod.sh operation Start: –Create download directory –Run the “world” Each world client starts with different “saved” amount. –Run “my client” – if given –All upload rates are restricted (simulate practical world). Stop –Kill all python threads

13. To run client separately: BitTornado-My-Client/btdownloadheadless.py –--saveas /vol/scratch/bt-download/picture.tst.bmp –--max_upload_rate 70 –--security 0 –./picture.pc-hanoch-w3.bmp.torrent (Implement in Checkpoint 1): –-- Rate 60 –-- Delay 6 –-- Prefetch 2 Not necessarily on the same machine as the world.

14. What implementation we use The clients are a modified version based on an up to date version of Bram Python Client. Modifications: –“World” clients do not print as it would only make a mess reincarnate after the finish to make a real world feel. –“My Client” template – kills all clients when finished

15. Python Very common script language Intuitive and readable References: –python.org :http://docs.python.org/reference/python.orghttp://docs.python.org/reference/ –http://wiki.python.org/moin/BeginnersGuide/NonProgrammershttp://wiki.python.org/moin/BeginnersGuide/NonProgrammers –http://wiki.python.org/moin/BeginnersGuide/Programmershttp://wiki.python.org/moin/BeginnersGuide/Programmers The book "Think like a Computer Scientist in Python" has a very good reputation:

16. My Client We supply a default “My Client” In: – BitTornado-My-Client/btdownloadheadless.py and “BitTornado - Your Code” link. It is like the “standard” one.

17. Getting started Run the environment –ssh pc-hanoch-w3 or pc-hanoch-w4 –cd /users/courses/hanochworkshop/bittorrent –run_all_vod.sh start [BitTornado-My-Client/btdownloadheadless.py] –Note tracker prints a message for each GET. You can connect to the tracker, from the CS network, with a browser at: –http://pc-hanoch-w k :6970/http://pc-hanoch-w k :6970/ Do ls -l /home/pc-hanoch-w4/home/hillelav/$USER to see downloaded files

18. What is it doing? Run bttrack. Copy From FreshFiles a set of “downloaded” files to download directory. Run X seeds Run a python client per “downloaded” file. Run my client if given

19. Directory Structure BitTornado-My-Client – –high level application BitTornado-My-Client/BitTornado – –services BitTornado-My-Client/BitTornado/BT1 – –Actual work

20. Client Operation btdownloadheadless.py – First to run. –Performs initializations. get_response – parse the.torrent Infohash – the ID of the.torrent startEngine – Start connection with peers startRerequester - Start connection with tracker –Run rawserver.listen_forever from RawServer.py. –listen_forever is: Polling port executing func() from a task queue.

21. Receiving messages From listen_forever loop it goes to: –BT1/Connecter.py/got_message CHOKE UNCHOKE INTERESTED NOT_INTERESTED BITFIELD REQUEST CANCEL PIECE HAVE

22. Influencing decisions Can be done in in one of the callbacks which spring from Connecter.py / got_message: Downloader.py –HAVE->got_have->send_interested Tune for VoD?

23. BT tracker Send GET request in Rerequester.py / announce Receive GET data in thread in Rerequester.py / _rerequest

24. Influencing decisions In Encrypter.py / start_connection or _start_connection_from_queue For instance try different max_connections. _rerequest_single – check timout for scheduling.

25. Policy Choker.py/_round_robin – decide who to choke / optimistically un choke / send_have to. Downloader.py / _request_more. PiecePicker.py / next - rarest piece, etc. Tune for VoD? got_unchoke->_request_more->next…

26. More about the code Start your project from “BitTornado - Your Code” link. Click “BitTornado - Code Guide” for basic explanations about the code.