This is a draft cheat sheet. It is a work in progress and is not finished yet.
Introduction
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 |
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Delay, Loss and Throughput
Delay when arrival rate > output link capacity; Loss when no free buffers |
d(nodal)=d(proc)+d(queue)+d(trans)+d(prop) |
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
application |
no of bytes |
FTP,SMTP,HTTP |
transport |
identify apps |
TCP, UDP |
network |
identify end host |
IP, Routing |
data link |
identify next hop router |
Ethernet, 802.11 |
physical |
identify group of bits |
Wire |
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