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These algorithms (e.g., ERICA, ERICA+) are designed for the ATM Available Bit Rate (ABR) service and require all network switches to compute fair allocations of bandwidth among competing connections. However, these algorithms are not easily tailor able to the current Internet, because they violate the Internet design philosophy of keeping router implementations simple and pushing complexity to the edges of the network. Fig: 2, The Core-Stateless Internet Architecture
Rangarajan and Acharya proposed a network
Assumed By NBP
border-based approach, which aims to prevent
1.1 TCP congestion control has mainly two
congestion collapse through early regulation of
phases:
unresponsive flows (ERUF)12. ERUF border
Slow Start and Congestion avoidance. A
routers rate control the input traffic, while core
new connection begins in Slow-start, setting its
routers generate source quenches on packet drops
initial cwnd to 1 packet, and increasing it by 1 for
to advise sources and border routers to reduce their
every received Acknowledgement (ACK). After
sending rates. While
this
approach
may
cwnd reaches ssthresh, the connection switches to
prevent
congestion-avoidance where cwnd grows linearly.
congestion collapse, it does so after packets have
A variety of methods have been suggested in the
been dropped and the network is congested. It also
literature recently aiming to avoid multiple losses
lacks mechanisms to provide fair bandwidth
and achieve higher utilization during the startup
allocations to flows. That is responsive and
phase. A larger initial cwnd, roughly 4K bytes, is
unresponsive to congestion. Floyd and fall have
proposed in.
approached the problem of congestion collapse by
This could greatly speed up transfers with
proposing low-complexity router mechanisms that
only a few packets. However, the improvement is
promote the use of adaptive or “TCP-friendly”
still inadequate when BDP is very large and the
end-to-end congestion control10. Their suggested
file to transfer is bigger than just a few packets.
approach requires selected gateway routers to monitor determine
high-bandwidth whether
they
flows are
in
order
to
responsive
to
Fast start uses cached cwnd and ssthresh in recent connections to reduce the transfer latency. The cached parameters may be too aggressive or too
congestion. Flows determined to be unresponsive
conservative when network conditions change
to congestion are penalized by a higher packet
Smooth start has been proposed to slow down
discarding rate at the gateway router. A limitation
cwnd increase when it is close to ssthresh. The
of this approach is that the procedures currently
assumption here is that default value of ssthresh is
available to identify unresponsive flows are not
often larger than the BDP, which is no longer true
always successful5.
in large bandwidth delay networks. Proposes to set the initial ssthresh to the BDP estimated (Packet Network Discovery) has been proposed to derive 46