Cheat Sheet

Cheat Sheet - Circuit Switching-End-end resources reserved...

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Circuit Switching -End-end resources reserved for “call” - link bandwidth, switch capacity - dedicated resources: no sharing - circuit-like (guaranteed) performance - call setup required - resources bandwidth) divided into “pieces” - Frequency and time division - pieces allocated to calls - resource piece idle if not used by call Packet Switching - user A, B packets share network resources - each packet uses full link bandwidth - resources used as needed, no pieces - aggregate resource demand can exceed amount available - congestion: packets queue, wait for link use - store and forward: packets move one hop at a time - no dedicated allocation, resource reservation Nodal Processing delay – examine header and decide where to direct; Queuing delay – wait to transmit into link; transmission delay (length of bits L/transmission rate of link R bits/sec) – to get out; propagation delay – propagates at speed of link = d/s (d = length of physical link; s = propagation speed ~ 2.8 *10^8) Traffic intensity = La/R (a = average packet arrival rate) La/R ~ 0: average queuing delay small; 1 - delays become large; > 1: more “work” arriving than can be serviced, average delay infinite! Total delay = proc + queue + trans + prop delay End-to-end = N (proc + trans + prop) Users share a 1 Mbps link. Each user has periods of activity (when it generates data at 100Kbits/sec) and inactivity. User is active only 10% of the time. With circuit-switching, 100 Kbps must be reserved for each user at all times. Thus, the link can support only ten simultaneous users. With packet switching, if there are 35 users, the prob that there are 10 or more simultaneously active users is less than .0004. If there are 10 or less simultaneously active users (which happens with probability .9996), the aggregate arrival rate of data is less than 1Mbps-the output rate of link Throughput: rate (bits/time unit) at which bits transferred between sender/receiver - instantaneous: rate at given point in time - average: rate over longer period of time if R S < R C , end-end throughput is R S if R C < R S , end-end throughput is R C application-> presentation-> session-> transport-> network-> link-> physical Application Architecture - Client-server, Peer-to-peer (P2P), Hybrid of client-server and P2P Client – server = server: always-on host, permanent IP address, server farms for scaling; clients: communicate with server, may be intermittently connected, may have dynamic IP addresses, do not communicate directly with each other Peer-to-Peer: no always-on server, arbitrary end systems directly communicate, peers are intermittently connected and change IP addresses, Highly
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This note was uploaded on 02/08/2010 for the course CS 118 taught by Professor Chu during the Fall '08 term at UCLA.

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Cheat Sheet - Circuit Switching-End-end resources reserved...

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