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Venture 3 Outline

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  1. Project 3 Overview 15-441 Spring 2010 Recitation #9

  2. So Far .. • IRC Server (Project 1) • Focus: IRC protocol, select() • IRC Routing (Project 2) • Focus: Routing (OSPF) • Working as a team

  3. Now what? • Project 3 • A bit of BitTorrent • Flow Control • Congestion Control • Again, work in teams • Choose fast and mail your andrew ids (id1 id2) it to with the subject ``15441 GROUP”

  4. BitTorrent Peer 4 Peer 2 • Get the torrent file (has tracker and metadata for the file) • Contact the tracker • Tracker tells the peer which peers to contact for the different chunks • Use TCP to get the chunks, use checksum to see if error-free and merge Tracker A1 TCP Peer 1 A2 Peer 3 A1 A2 TCP

  5. Chunking and hashing • Original file • Chunks • Hashing • Torrent Hash

  6. This project • Open chunks file, read the list of chunk hashes • All file data accessed from a single master data file • Peers are configured to tell them what chunks they own • Send WHOHAS <list> • Instead of the tracker, flood the network • Receive IHAVE <list> from different peers • GET <chunk-hash> for each chunk from some peer • Instead of TCP, use UDP • Implement congestion control • Check the hash(chunk_recvd) with chunk_hash • Merge all the received chunks

  7. Packet formats Basic packet header WHOHAS request DATA packet

  8. Terminology • Master-data-file • All the data in the network is present here • A peer can only access the chunk that it owns • A peer owns a chunk if chunk-id and hash present in the has-chunk-file • Master-chunk-file • File that lists chunk IDs and hashes for the chunks in the master-data-file • Has-chunk-file • Per-node file containing list of hashes a node owns • Chunk IDs in this file match with those in the master-chunk-file • Get-chunk-file • Provided by user; contains the chunk ids and hashes to be downloaded • Chunk IDs in this file do not match with those in the master-chunk file; they represent the position of the chunk in the file • See Section 5 of the project description for an example

  9. More terminology • Peer-list-file • Contains list of all the peers in the network • In this project, each peer knows the identity of every other peer • Peer-identity • Used by the peer to get its IP address and port • Max-downloads • Maximum number of simultaneous connections allowed in each direction

  10. Provided files • • Emulates a network topology using • spiffy.[c|h] • Interfaces with the simulator to send and receive packets (spiffy_sendto(), spiffy_recvfrom()) • sha.[c|h] • Generates SHA-1 hash • input_buffer.[c|h] • Handles user input • debug.[c|h] • Helps in debugging • bt_parse.[c|h] • Parses command-line arguments • peer.c • Skeleton peer file (handles some setup and processing) • • Peer-list-file • • Network topology used by (your code should not read this file) • make-chunks • Creates chunk-file given an input file

  11. Flow Control and Congestion Control • Implement sliding window • Only sender window (receiver window size need not be communicated in the header) • Packet-based sliding window (unlike TCP) • Implement congestion control (on top of UDP) • Only for data packets (chunks) • Slow start, congestion avoidance, fast retransmit • More on these in the next recitation

  12. Checkpoints • Checkpoint 1 (Due: April 9th) – Start now! • Simple configuration of 2 hosts • Generate WHOHAS queries based on the input • Correctly respond with IHAVE • Assume no loss in the network • Checkpoint 2 (Due: April 13th) • Send GET request and download entire chunk (2-host configuration) • Use simple stop-and-wait (no loss) • Checkpoint 3 (Due: April 19th) • Sliding window • Reliability (timeouts and retransmissions) • Spiffy router to test your network (with loss) • Checkpoint 4 (Due: April 23rd) • Simple congestion avoidance

  13. Project advice • Stay ahead of the checkpoints • Be an early bird (10 extra points) • Submit by April 27th • Don’t be late • Submit by April 30th • Project 3 contest! (More extra credit) • Optimize your system and make it robust • Be efficient while working as a team • Read the project write-up more than once! • See FAQ (coming soon) • See bboard for related questions • Post on bboard if nothing above helps