Paper review: TCP Vegas
Reviewer: Kevin Hofstra
- Is there a more effective TCP
protocol then TCP Reno? Is it
possible to reduce the sending rate before actually dropping packets? What would be the ideal number of
buffers taken up by a host in equilibrium?
- An evaluation of the advances
in efficiency of the new proposed standard Vegas. An attempt to maximize the bandwidth
usage of TCP when in an uncongested environment
without packets being lost. The
ideas are even more important today as internet users demand more
bandwidth even though some links over their RT are still inadequate.
- A. By sampling the RTT and comparing that
to an average over time, the sender can determine if they are getting
closer or further to congesting the network without actually having to
experience packet loss.
Each sending host in equilibrium should occupy 1 buffer
within the routers so that in the event the amount of traffic decreases, they
will have a packet to send. They do not
want to occupy more than 3 buffers because then routers with limited buffer
space would be crowded out by only a few hosts.
The slow start with
congestion avoidance algorithm that Vegas uses is a Vegas* modification that
uses the delay between ACKs to actively probe for the
congestion limit without actually having to lose packets, much like its linear
increase algorithm is able to do.
When testing on the actual internet, Vegas outperforms Reno
92% of the time. It does not interfere
with the legacy congestion avoidance protocols.
Vegas is also considered just as fair as Reno
- Critique the main
System researchers and builders
should recognize that it is often possible to improve on the convergence
and decrease the deviation of an algorithm that approaches a
constant. In the case of network
congestion the host is able to see signs of congestion approaching in the
form of a slower RTT. This allows
congestion to be avoided without having to reach congestion and back
off. This leads to much less packet
loss, and reduces the importance of the convergence algorithms because
hosts do not have to recover from large deviation. The increase in responsiveness is
achieved by the magnitude value sensing of congestion instead of an all or
nothing packet loss.
- Significance- 2
The article is very effective in showing how Vegas leads to greater
throughput, less packet loss, and fewer occurrences of congestion, but it
is a modification of Reno and should not be considered groundbreaking.
- Convincing- 3 They offer multiple examples and graphs to prove the
superiority of Vegas over Reno. Test cases in theory,
lab simulations, and on the actual internet seems to back their