1 / 32

TCP-XM: Unicast-enabled Reliable Multicast

TCP-XM: Unicast-enabled Reliable Multicast. Karl Jeacle. karl.jeacle@cl.cam.ac.uk. Rationale. Would like to achieve high-speed bulk data delivery to multiple sites Multicasting would make sense Existing multicast research has focused on sending to a large number of receivers

matty
Download Presentation

TCP-XM: Unicast-enabled Reliable Multicast

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. TCP-XM: Unicast-enabled Reliable Multicast Karl Jeacle karl.jeacle@cl.cam.ac.uk

  2. Rationale • Would like to achieve high-speed bulk data delivery to multiple sites • Multicasting would make sense • Existing multicast research has focused on sending to a large number of receivers • But Grid is an applied example where sending to a moderate number of receivers would be extremely beneficial

  3. Multicast availability • Deployment is a problem! • Protocols have been defined and implemented • Valid concerns about scalability; much FUD • “chicken & egg” means limited coverage • Clouds of native multicast • But can’t reach all destinations via multicast • So applications abandon in favour of unicast • What if we could multicast when possible… • …but fall back to unicast when necessary?

  4. Multicast TCP? • TCP • “single reliable stream between two hosts” • Multicast TCP • “multiple reliable streams from one to n hosts” • May seem a little odd, but there is precedent… • TCP-XMO – Liang & Cheriton • M-TCP – Mysore & Varghese • M/TCP – Visoottiviseth et al • PRMP – Barcellos et al • SCE – Talpade & Ammar

  5. ACK implosion

  6. Building Multicast TCP • Want to test multicast/unicast TCP approach • But new protocol == kernel change • Widespread test deployment difficult • Build new TCP-like engine • Encapsulate packets in UDP • Run in userspace • Performance is sacrificed… • …but widespread testing now possible

  7. Sending Application Receiving Application If natively implemented TCP TCP IP IP test deployment UDP UDP IP IP TCP/IP/UDP/IP

  8. TCP engine • Where does initial TCP come from? • Could use BSD or Linux • Extracting from kernel could be problematic • More compact alternative • lwIP = Lightweight IP • Small but fully RFC-compliant TCP/IP stack • lwIP + multicast extensions = “TCP-XM”

  9. TCP-XM overview • Primarily aimed at push applications • Sender initiated – advance knowledge of receivers • Opens sessions to n destination hosts simultaneously • Unicast is used when multicast not available • Options headers used to exchange multicast info • API changes • Sender incorporates multiple destination and group addresses • Receiver requires no changes • TCP friendly, by definition

  10. TCP SYN SYNACK ACK Sender Receiver DATA ACK FIN ACK FIN ACK

  11. TCP-XM Receiver 1 Sender Receiver 2 Receiver 3

  12. TCP-XM connection • Connection • User connects to multiple unicast destinations • Multiple TCP PCBs created • Independent 3-way handshakes take place • SSM or random ASM group address allocated • (if not specified in advance by user/application) • Group address sent as TCP option • Ability to multicast depends on TCP option

  13. TCP Group Option kind=50 len=6 Multicast Group Address 1 byte 1 byte 4 bytes • New group option sent in all TCP-XM SYN packets • Non TCP-XM hosts will ignore (no option in SYNACK) • Presence implies multicast capability • Sender will automatically revert to unicast

  14. TCP-XM transmission • Data transfer • Data replicated/enqueued on all send queues • PCB variables dictate transmission mode • Data packets are multicast (if possible) • Retransmissions are unicast • Auto fall back/forward to unicast/multicast • Close • Connections closed as per unicast TCP

  15. TCP-XM protocol states

  16. Fall back / fall forward • TCP-XM principle • “Multicast if possible, unicast when necessary” • Initial transmission mode is group unicast • Ensures successful initial data transfer • Fall forward to multicast on positive feedback • Typically after ~75K unicast data • Fall back to unicast on repeated mcast failure

  17. Multicast feedback Option kind=51 len=3 % Multicast Packets Received 1 byte 1 byte 1 byte • New feedback option sent in ACKs from receiver • Only used between TCP-XM hosts • Indicates % of last n packets received via multicast • Used by sender to fall forward to multicast transmission

  18. TCP-XM reception • Receiver • No API-level changes • Normal TCP listen • Auto-IGMP join on TCP-XM connect • Accepts data on both unicast/multicast ports • tcp_input() accepts: • packets addressed to existing unicast destination… • …but now also those addressed to multicast group • Tracks how last n segs received (u/m)

  19. API changes • Only relevant if natively implemented! • Sender API changes • New connection type • Connect to port on array of destinations • Single write sends data to all hosts • TCP-XM in use: conn = netconn_new(NETCONN_TCPXM); netconn_connectxm(conn, remotedest, numdests, group, port); netconn_write(conn, data, len, …);

  20. PCB changes • Every TCP connection has an associated Protocol Control Block (PCB) • TCP-XM adds: struct tcp_pcb { … struct tcp_pcb *firstpcb;/* first of the mpcbs */ struct tcp_pcb *nextm; /* next tcpxm pcb */ enum tx_mode txmode; /* unicasting or multicasting */ u8_t nrtxm; /* number of retransmits for multicast */ u32_t nrtxmtime; /* time since last retransmit */ u32_t mbytessent; /* total bytes sent via multicast */ u32_t mbytesrcvd; /* total bytes received via multicast */ u32_t ubytessent; /* total bytes sent via unicast */ u32_t ubytesrcvd; /* total bytes received via unicast */ struct segrcv msegrcv[128]; /* ismcast boolean for last n segs */ u8_t msegrcvper; /* % of last segs received via mcast */ u8_t msegrcvcnt; /* counter for segs recvd via mcast */ u8_t msegsntper; /* % of last segs delivered via mcast */ }

  21. next next next next next U1 U2 M1 M3 M2 nextm nextm nextm nextm nextm Linking PCBs • *next points to the next TCP session • *nextm points to the next TCP session that’s part of a particular TCP-XM connection • Minimal timer and state machine changes

  22. What happens to the cwin? • Multiple receivers • Multiple PCBs • Multiple congestion windows • Default to min(cwin) • i.e. send at rate of slowest receiver • Is this really so bad? • Compare to time taken for n unicast transfers

  23. LAN speed

  24. LAN efficiency

  25. WAN speed

  26. WAN efficiency

  27. Multiple TCP-XM flows

  28. TCP-XM vs TCP flows

  29. Protocol performance

  30. Protocol efficiency

  31. mcp & mcpd • Multicast file transfer application using TCP-XM • ‘mcpd &’ on servers • ‘mcp file host1 host2… hostN’ on client • http://www.cl.cam.ac.uk/~kj234/mcp/ • Full source code online • FreeBSD, Linux, Solaris

  32. All done! • Thanks for listening! • Questions?

More Related