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Computer Network Cheat Sheet (DRAFT) by

This is a draft cheat sheet. It is a work in progress and is not finished yet.


Internet: interc­onn­ection of networks - Interr­con­nected ISPs
Commun­ication links:fiber­,co­ppe­r,r­adio...
Trans rate R=bandw­idt­h[b­its­/s]­=ca­pacity
Hosts=end systems: break app data into packets of length L bits, transmit packet into access network at transm­ission rate R
Packet trans delay = time to transmit L-bit packet into link = L(bits)/R(bits/s)
Protocols: Rules for data commun­ication includes Syntax, Semant­ics­(me­aning of each section of bits), Timing
Internet standards define protocols: developed by IETF(I­nternet Engine­ering Task Force), IETF standards documents are called: RFCs(R­equest for comments);
Circuit Switching: dedicated circuit for every connec­tion. FDM vs TDM(Fr­eq/time Division Multip­lexing)
Packet Switching: break msgs to smaller chunks­/pa­ckets. Store-­and­-fo­rwa­rd:­entire packet must arrive at router before sending. + It allows more users,good for bursty data,r­esource sharing, no call setup, but excessive congestion possible: packet delay&loss

Delay, Loss and Throughput

Delay when arrival rate > output link capacity; Loss when no free buffers
d(proc)=nodal proces­sin­g:check bit errors­&d­ete­rmine output link, typically < msec
d(queue):time waiting to be transm­itted . a:average packet arrival rate. Queuing delay larger when traffic intensity La/R goes to 1
d(trans) = L/R; d(prop­aga­tion) = length of physical link/prop speed(2 x 10^8)
End-to-End Delay (PSw) = Time to deliver all for hop + 1 packet for each hop...
End-to-End Delay (CSw) = Call setup time + Trans time + Prop time
Throughput: rate at which bits transf­erred btw sender and receiver (bottl­eneck)

Internet protocol stack

no of bytes
identify apps
identify end host
IP, Routing
data link
identify next hop router
Ethernet, 802.11
identify group of bits