Project $7$: Packet information flow in a router

Packet information flow in a router working under TCP$/$IP can be modeled using the

linearized transfer function

$P(s)=\frac{Q(s)}{f(s)}=\frac{\frac{C^2}{2N}{e}^{-sR}}{(s+\frac{2N}{R^{2}C})(s+\frac{1}{R})}$

where

$C=$ link capacity $($packets$/$second$)$

$N=$ load factor $($number of TCP sessions$)$

$Q=$ expected queue length

$R=$ round trip time $($second$)$

$P=$ probability of a packet drop

The objective of an active queue management $($AQM$)$ algorithm is to automatically

choose a packet$-$drop probability, $p,$ so that the queue length is maintained at a

desired level. This system can be represented by the block diagram of Figure $11$ with

the plant model in the $P(s)$ block, the AQM algorithm in the $G(s)$ block, and $F(s)=$

$H(s)=1.$ Several AQM algorithms are available, but one that has received special

attention in the literature is the random early detection $($RED$)$ algorithm. This algorithm

can be approximated with $G(s)=\frac{LK}{s+K},$ where $L$ and $K$ are constants $($Hollot$,2001).$