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Extending Globus to support Multicast Transmission

Extending Globus to support Multicast Transmission. 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

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Extending Globus to support Multicast Transmission

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  1. Extending Globus to support Multicast Transmission 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-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

  14. 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

  15. 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)

  16. Grid multicast? • How can multicast be used in Grid environment? • TCP-XM is new multicast-capable protocol • Globus is de-facto Grid middleware • Would like TCP-XM support in Globus…

  17. Globus XIO • eXtensible Input Output library • Allows “i/o plugins” to Globus • API • Single POSIX-like API / set of semantics • Simple open/close/read/write API • Driver abstraction • Hides protocol details / Allows for extensibility • Stack of 1 transport & n transform drivers • Drivers can be selected at runtime

  18. XIO architecture

  19. XIO implementation

  20. XIO/XM driver specifics • Two important XIO data structures • Handle • Returned to user when XIO framework ready • Used for all open/close/read/write calls • lwIP netconn connection structure used • Attribute • Used to set XIO driver-specific parameters… • … and TCP-XM protocol-specific options • List of destination addresses

  21. XIO code example // init stack globus_xio_stack_init(&stack, NULL); // load drivers onto stack globus_xio_driver_load("tcpxm", &txdriver); globus_xio_stack_push_driver(stack, txdriver); // init attributes globus_xio_attr_init(&attr); globus_xio_attr_cntl(attr, txdriver, GLOBUS_XIO_TCPXM_SET_REMOTE_HOSTS, hosts, numhosts); // create handle globus_xio_handle_create(&handle, stack); // send data globus_xio_open(&handle, NULL, target); globus_xio_write(handle, "hello\n", 6, 1, &nbytes, NULL); globus_xio_close(handle, NULL);

  22. One-to-many issues • Stack assumes one-to-one connections • XIO user interface requires modification • Needs support for one-to-many protocols • Minimal user API changes • Framework changes more significant • GSI is one-to-one • Authentication with peer on connection setup • But cannot authenticate with n peers • Need some form of “GSI-M”

  23. LAN Computer Laboratory Mix of CPU speeds Linux All multicast Throughput to each host is typically at least 10Mb/s, depending on CPU and network load of both sender and receiver. WAN UK eScience Network Mix of CPU speeds FreeBSD/Linux/Solaris Some multicast Throughput varies (Mb/s) Imperial 25 Cardiff 13 Manchester 11 Southampton 10 Belfast 5 LAN/WAN tests

  24. LAN speed

  25. LAN efficiency

  26. WAN efficiency

  27. Driver availability • Multicast transport driver for Globus XIO • Requires Globus 3.2 or later • Source code online • Sample client • Sample server • Driver installation instructions • http://www.cl.cam.ac.uk/~kj234/xio/

  28. 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

  29. Future • Protocol work • Parallel unicast / multicast transmission • Multicast look ahead & multiple groups • Deliverables • Updates to mcp/mcpd • Experimentation • More detailed testing required • Currently limited to LAN and UK eScience • Will extend to global Intel PlanetLab

  30. 1. In place Cambridge Cardiff Imperial Manchester Newcastle Oxford Southampton UCL 2. Firewall issues Belfast Daresbury Glasgow Rutherford 3. Not possible Edinburgh eScience volunteers…

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

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