1. Concurrent Multipath Transfer (CMT)
Transport Layer
Concurrent Multipath Transfer (CMT)
Janardhan Iyengar
Protocol · Engineering · Laboratory
University of Delaware

2. What is CMT ? As per current SCTP:
Network
Host A
Host B B1 B2 A1 A2
ISP 2
ISP 1
As per current SCTP:
if peer is multihomed, sender can transmit only to one destination (primary destination)
new data not sent to multiple destinations concurrently
Proposal: Enable sending concurrently to multiple destinations over multiple paths

3. What is CMT ?
Definition of Concurrent Multipath Transfer (CMT): Simultaneous transfer of new data from source to destination via two or more separate paths
Why use CMT at transport layer ?
Exploit all network resources visible at transport layer
Avoid replication of work and coarse-grain load balancing in applications

4. Experiment: Send new data concurrently between a dual-homed sender and a dual-homed receiver:
- Available bandwidth: Path1= 0.3Mbps; Path2 = 1Mbps
- End-to-end delay: Path1= Path2 = 35ms
- Loss in network = zero

5. Expected

6. Research on CMT at PEL CMT should increase net throughput, but …
not clear if it will
side-effects unknown
… more research needed
Identified three negative side-effects of CMT with SCTP
Unnecessary fast retransmissions
Reduced cwnd growth due to fewer cwnd updates
Increased ack traffic due to fewer delayed acks
three algorithms proposed to eliminate them *
Currently investigating other performance hurdles
due to shared receiver buffer, shared bottleneck, etc.
* J. Iyengar, K. Shah, P. Amer, R. Stewart. Concurrent Multipath Transfer Using SCTP Multihoming. Technical Report, CIS Department, June 2003.

7. Expected