October 27, 2010
Satellite Optimization and the Space Communications Protocol Standard
By David Sims, TMCnet Contributing Editor
For satellite optimization enhanced communications, TCP is subject to a number of limitations on a WAN that can affect its performance. Officials of Expand’s SCPS recommend some features for a Space Communications Protocol Standard which can help deliver better application performance for satellite users:
Standard TCP stacks on workstations typically support a maximum transmission window of 64 KB. This means that, at any one time, only 64 KB of data maybe transmitted without receiving an acknowledgement. When transferring data over a long-haul WAN connection, the maximum threshold must be increased to avoid severe under-utilization of the expensive link. In order to keep the pipe full, Expand Networks’ (News - Alert) TCP acceleration creates a much larger window to allow the link to be fully used.
With TCP acceleration, a file transfer that used only a fraction of the available bandwidth will now fully use the link and complete the transfer faster.
Error Detection and Proactive Resolution
Standard TCP assumes that all packet loss is caused by network congestion. But, on a dedicated and controlled WAN link packet loss could also be due to a bit error that can occur from noise in the channel or other environmental conditions. TCP Vegas and TCP Reno congestion avoidance mechanisms have been designed to address these network issues and adjust the transmission speed accordingly. By implementing both TCP Vegas and TCP Reno network congestion avoidance mechanisms, Expand Accelerator’s TCP acceleration feature can perform the appropriate corrective measure both when there is network congestion and when there is bit-error packet loss.
Dynamic Bandwidth Adjust
In addition to TCP Vegas and TCP Reno algorithms, Expand Accelerators have also implemented the Dynamic Bandwidth Adjust feature. Through a real-time feedback mechanism, the accelerator can adjust the bandwidth it sends to the WAN when congestion in the network occurs. This feature also provides effective traffic optimization when multiple paths with different bandwidths or delay characteristics exist.
The proxy operation of the Accelerator means that TCP sessions are terminated locally, so that establishing and tearing down TCP connections takes place at LAN speeds.
David Sims is a contributing editor for TMCnet. To read more of David’s articles, please visit his columnist page. He also blogs for TMCnet here.
Edited by Erin Monda