Why Latency Matters to Mobile Backhaul - O3b Networks

Why Latency Matters to Mobile Backhaul
For instance, the receiver advertised a maximum window size of 10
segments. The transmitter will send the 10 segments (at a variable rate
described in the congestion avoidance) and will then stop until ACK is
received. For each ACK (if window size stays constant) received, the
transmitter may send another segment. The algorithm may advertise
a variable window size depending on the actual state of the receiver
(i.e. buffers filling or emptying), allowing it to transmit more or fewer
segments and vary the actual throughput.
Congestion Control
Flow control enables the two end devices to regulate the transmission
throughput, but it does not take into account the status of the network links
between them. Congestion control mechanisms are required to regulate
the speed of the data transmission and the quality of the network link.
Using a slow start mechanism, the sender begins to transmit TCP segments
at a low rate, gradually increasing the number of segments simultaneously
transmitted until the full window size is reached or congestion is detected.
In case of congestion, an avoidance mechanism will drastically decrease
the rate and initiate the step increase again, creating a saw-tooth effect.
Various TCP flavors (Reno, Vegas, Cubic, Compound) have variations in the
algorithm used to define the increasing and decreasing rate, based on a
maximum segment size and/or queuing delay.
Other optimizations include retransmission of selected segments and fast
recovery to increase the transmission rate more quickly.
TCP maximum throughput estimation
TCP maximum throughput can be estimated using a formula based on TCP
RENO (RFC2001) as described by Padhye et. al. in "Modeling TCP
Throughput: a Simple Model and its Empirical Validation"
The model used is the following one:
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0
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32 p ⎟⎟ 8
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