RFC 2760 (rfc2760) - Page 3 of 46
Ongoing TCP Research Related to Satellites
Alternative Format: Original Text Document
RFC 2760 Ongoing TCP Research Related to Satellites February 2000
some point, the mechanisms discussed in this memo prove to be safe
and appropriate to be recommended for general use, the appropriate
IETF documents will be written.
It should be noted that non-TCP mechanisms that help performance over
satellite links do exist (e.g., application-level changes, queueing
disciplines, etc.). However, outlining these non-TCP mitigations is
beyond the scope of this document and therefore is left as future
work. Additionally, there are a number of mitigations to TCP's
performance problems that involve very active intervention by
gateways along the end-to-end path from the sender to the receiver.
Documenting the pros and cons of such solutions is also left as
future work.
2 Satellite Architectures
Specific characteristics of satellite links and the impact these
characteristics have on TCP are presented in RFC 2488 [AGS99]. This
section discusses several possible topologies where satellite links
may be integrated into the global Internet. The mitigation outlined
in section 3 will include a discussion of which environment the
mechanism is expected to benefit.
2.1 Asymmetric Satellite Networks
Some satellite networks exhibit a bandwidth asymmetry, a larger data
rate in one direction than the reverse direction, because of limits
on the transmission power and the antenna size at one end of the
link. Meanwhile, some other satellite systems are unidirectional and
use a non-satellite return path (such as a dialup modem link). The
nature of most TCP traffic is asymmetric with data flowing in one
direction and acknowledgments in opposite direction. However, the
term asymmetric in this document refers to different physical
capacities in the forward and return links. Asymmetry has been shown
to be a problem for TCP [BPK97,BPK98].
2.2 Satellite Link as Last Hop
Satellite links that provide service directly to end users, as
opposed to satellite links located in the middle of a network, may
allow for specialized design of protocols used over the last hop.
Some satellite providers use the satellite link as a shared high
speed downlink to users with a lower speed, non-shared terrestrial
link that is used as a return link for requests and acknowledgments.
Many times this creates an asymmetric network, as discussed above.
Allman, et al. Informational