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Extending Globus to support Multicast Transmission. Karl Jeacle. [email protected] 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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Presentation Transcript
rationale
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
multicast availability
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?
multicast tcp
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
building multicast tcp
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
tcp ip udp ip
Sending

Application

Receiving

Application

If natively implemented

TCP

TCP

IP

IP

test deployment

UDP

UDP

IP

IP

TCP/IP/UDP/IP
tcp engine
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”
tcp xm overview
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
slide10
TCP

SYN

SYNACK

ACK

Sender

Receiver

DATA

ACK

FIN

ACK

FIN

ACK

tcp xm
TCP-XM

Receiver 1

Sender

Receiver 2

Receiver 3

tcp xm connection
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
tcp xm transmission
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
fall back fall forward
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
tcp xm reception
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)
grid multicast
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…
globus xio
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
xio xm driver specifics
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
xio code example
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);

one to many issues
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”
lan wan tests
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
driver availability
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/
mcp mcpd
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
future
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
escience volunteers
1. In place

Cambridge

Cardiff

Imperial

Manchester

Newcastle

Oxford

Southampton

UCL

2. Firewall issues

Belfast

Daresbury

Glasgow

Rutherford

3. Not possible

Edinburgh

eScience volunteers…
all done
All done!
  • Thanks for listening!
  • Questions?
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