2003 봄컴퓨터 통신 참고자료 Introduction- 참고 자료 #1 컴퓨터 통신

2003 봄컴퓨터 통신 참고자료 스트리밍 클라이언트로 FM 청취

2003 봄컴퓨터 통신 참고자료 실시간 네트워크 패킷 분석기 인터넷 패킷의 모습은 ?

2003 봄컴퓨터 통신 참고자료 데이터 패킷의 내용 ( 헤더 )

2003 봄컴퓨터 통신 참고자료 이더넷 케이블

2003 봄컴퓨터 통신 참고자료 인터넷 연결 ( 한국 )

2003 봄컴퓨터 통신 참고자료 인터넷 연결 ( 미국 )

2003 봄컴퓨터 통신 참고자료 라우팅 ( 길찾기 ): 라우터가 결정 – 라우터는 클라이언트 - 서버간 연결에 대해 알지 못함 – 같은 클라이언트 - 서버간 데이터 패킷들이 서로 다른 경로로 갈수도 있음 application transport network data link physical application transport network data link physical 데이터 패킷

2003 봄컴퓨터 통신 참고자료 링크 공유 ( 통계적 다중화 ) 전화선과 비교 A B C 10 Mbs 이더넷 1.5 Mbs 45 Mbs D E 통계적 다중화 패킷 대기 큐

2003 봄컴퓨터 통신 참고자료 패킷 다중화의 잇점 1 Mbps link 각 사용자 : –100Kbps ( 전송시 ) – 10% 의 시간만 전송 서키트 스위칭 : –10 사용자 패킷 다중화 : –35 사용자 –10 명 이상이 사용하고자 할 확률.004 더 많은 사용자가 공유 가능 N 사용자 1 Mbps link

2003 봄컴퓨터 통신 참고자료 Packet switching versus circuit switching Great for bursty data –resource sharing –simpler, no call setup Excessive congestion: packet delay and loss –protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? –bandwidth guarantees needed for audio/video apps –still an unsolved problem (chapter 6) Is packet switching a “ slam dunk winner? ”

2003 봄컴퓨터 통신 참고자료 Circuit Switching: TDMA and TDMA FDMA frequency time TDMA frequency time 4 users Example:

2003 봄컴퓨터 통신 참고자료 Packet-switching: store-and-forward Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps Entire packet must arrive at router before it can be transmitted on next link: store and forward delay = 3L/R Example: L = 7.5 Mbits R = 1.5 Mbps delay = 15 sec R R R L

2003 봄컴퓨터 통신 참고자료 Packet Switching: Message Segmenting Now break up the message into 5000 packets Each packet 1,500 bits 1 msec to transmit packet on one link pipelining: each link works in parallel Delay reduced from 15 sec to sec

2003 봄컴퓨터 통신 참고자료 Packet-switched networks: forwarding Goal: move packets through routers from source to destination –we ’ ll study several path selection (i.e. routing)algorithms (chapter 4) datagram network: –destination address in packet determines next hop –routes may change during session –analogy: driving, asking directions virtual circuit network: –each packet carries tag (virtual circuit ID), tag determines next hop –fixed path determined at call setup time, remains fixed thru call –routers maintain per-call state

2003 봄컴퓨터 통신 참고자료 Four sources of packet delay 1. nodal processing: –check bit errors –determine output link A B propagation transmission nodal processing queueing 2. queueing –time waiting at output link for transmission –depends on congestion level of router

2003 봄컴퓨터 통신 참고자료 Delay in packet-switched networks 3. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R 4. Propagation delay: d = length of physical link s = propagation speed in medium (~2x10 8 m/sec) propagation delay = d/s A B propagation transmission nodal processing queueing Note: s and R are very different quantities!

2003 봄컴퓨터 통신 참고자료 Caravan analogy Cars “ propagate ” at 100 km/hr Toll booth takes 12 sec to service a car (transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? Time to “ push ” entire caravan through toll booth onto highway = 12*10 = 120 sec Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr A: 62 minutes toll booth toll booth ten-car caravan 100 km

2003 봄컴퓨터 통신 참고자료 Caravan analogy (more) Cars now “ propagate ” at 1000 km/hr Toll booth now takes 1 min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth? Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth. 1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router! –See Ethernet applet at AWL Web site toll booth toll booth ten-car caravan 100 km

2003 봄컴퓨터 통신 참고자료 Nodal delay d proc = processing delay –typically a few microsecs or less d queue = queuing delay –depends on congestion d trans = transmission delay –= L/R, significant for low-speed links d prop = propagation delay –a few microsecs to hundreds of msecs

2003 봄컴퓨터 통신 참고자료 Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R La/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R > 1: more “ work ” arriving than can be serviced, average delay infinite!

2003 봄컴퓨터 통신 참고자료 Delay Box : Multiplexer Switch Network Message, Packet, Cell Arrivals Message, Packet, Cell Departures T seconds Lost or Blocked Network Delay Analysis

2003 봄컴퓨터 통신 참고자료 A(t) t n-1 n n+1 Time of nth arrival =  1 +   n Arrival Rate n arrivals  1 +   n seconds = 1 = 1 (  1 +   n )/n E[]E[] 11 22 33 nn  n+1 Arrival Rate = 1 / mean interarrival time Arrival Rates and Interarrival Times

2003 봄컴퓨터 통신 참고자료 A(t) D(t) Delay Box N(t) T Little’s Theorem

2003 봄컴퓨터 통신 참고자료 Little ’ s Theorem N = T N = Average Number of packets in the system = Packet Arrival rate T = Average Service Delay per packet Larger the service delay (queuing delay +service time), larger the number of waiting (or buffered) packets Higher the arrival rate, larger the number of buffered packets

2003 봄컴퓨터 통신 참고자료 A(t) D(t) T1T1 T2T2 T3T3 T4T4 T5T5 T6T6 T7T7 Assumes first-in first-out C1C1 C2C2 C3C3 C4C4 C5C5 C6C6 C7C7 C1C1 C2C2 C3C3 C4C4 C5C5 C6C6 C7C7 Arrivals Departures Arrivals and Departures in a FIFO System

2003 봄컴퓨터 통신 참고자료 0 Probability density e - t t Exponentail interarrival

2003 봄컴퓨터 통신 참고자료 Service times X M = exponential D = deterministic G = general Service Rate:  E[X] Arrival Process / Service Time / Servers / Max Occupancy Interarrival times  M = exponential D = deterministic G = general Arrival Rate:  E[  ] 1 server c servers infinite K customers unspecified if unlimited Multiplexer Models: M/M/1/K, M/M/1, M/G/1, M/D/1 Trunking Models: M/M/c/c, M/G/c/c User Activity: M/M/ , M/G/  Queuing Model Classification

2003 봄컴퓨터 통신 참고자료 1 2 c X N q (t) N s (t) N(t) = N q (t) + N s (t) T = W + X W  P b  P b ) N(t) = number in system N q (t) = number in queue N s (t) = number in service T = total delay W = waiting time X = service time  Queuing System Variables

2003 봄컴퓨터 통신 참고자료 Poisson arrivals rate K-1 buffer Exponential service time with rate  M/M/1K Queue

2003 봄컴퓨터 통신 참고자료 01 2n-1 n n (  t 1 -  t  t  t A Markov State transition diagram

2003 봄컴퓨터 통신 참고자료 A necessary condition for a steady-state solution is that p n '(t) vanish identically, leaving us with a time-independent system of infinitely many equations: p 0 =  p 1 ; ( +  ) p n =  p n+1 + p n-1, for n ≥ 1. We recall that  is what we called utilization. We can now proceed with, essentially, and induction: p 1 =  p 0 ; p 2 = (  + 1)p 1 -  p 0 =  2 p 0 ; …. p n =  n p 0, for all n ≥ 0. Since, we must have  < 1. Summing the geometric series: p 0 = (1 -  ), p n = (1 -  )  n. From  = 1 - p 0, we can conclude that  is the probability the system is not empty.

2003 봄컴퓨터 통신 참고자료 The expected number of customers in the system is given by An easy derivation of the closed form of the sum follows from observing that

2003 봄컴퓨터 통신 참고자료 “ Real ” Internet delays and routes What do “ real ” Internet delay & loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: –sends three packets that will reach router i on path towards destination –router i will return packets to sender –sender times interval between transmission and reply. 3 probes

2003 봄컴퓨터 통신 참고자료 “ Real ” Internet delays and routes 1 cs-gw ( ) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu ( ) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu ( ) 6 ms 5 ms 5 ms 4 jn1-at wor.vbns.net ( ) 16 ms 11 ms 13 ms 5 jn1-so wae.vbns.net ( ) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu ( ) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu ( ) 22 ms 22 ms 22 ms ( ) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net ( ) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net ( ) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net ( ) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr ( ) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr ( ) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr ( ) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net ( ) 135 ms 128 ms 133 ms ( ) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr ( ) 132 ms 128 ms 136 ms traceroute: gaia.cs.umass.edu to Three delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no reponse (probe lost, router not replying) trans-oceanic link

2003 봄컴퓨터 통신 참고자료 Packet loss queue (aka buffer) preceding link in buffer has finite capacity when packet arrives to full queue, packet is dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all

2003 봄컴퓨터 통신 참고자료 편지 (Everything over Anything!)

2003 봄컴퓨터 통신 참고자료 IP 데이타그램 ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier Internet checksum 32 bit source IP address head. len type of service flgs fragment offset upper layer 32 bit destination IP address Options (if any) ttl

2003 봄컴퓨터 통신 참고자료 제비 ( 물리적 통신매체 )

2003 봄컴퓨터 통신 참고자료 보장성 없음 (No Guarantee!)

2003 봄컴퓨터 통신 참고자료 논리적 통신 (Transport) application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data ( 예 ) transport 응용 프로그램들에 서 메시지를 받아 신뢰성, 다중화를 위 한 헤더 추가 수신자의 같은 계층 으로 데이터를 보내 고 “ 수신 확인 ” 을 기다 린다. 등기 우편 data transport ack

2003 봄컴퓨터 통신 참고자료 물리적 통신 ( 실제 데이터의 흐름 ) application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

2003 봄컴퓨터 통신 참고자료 프로토콜 계층과 헤더 ( 송신자측 ) 각 계층은 위로 부터 데이터를 받아 : 자신의 헤더를 붙여 아래 계층으로 보낸다 application transport network link physical application transport network link physical 송신자 수신자 M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l 메시지 세그먼트 데이타그램 프레임

2003 봄컴퓨터 통신 참고자료 시뮬레이션 프로그램 (ns-2,UC-Berkeley 대학 )

2003 봄컴퓨터 통신 참고자료 네트워크 애니메이션 (nam,USC 대학 )

2003 봄컴퓨터 통신 참고자료 성능 예측 ( 전송율,congwin)

2003 봄컴퓨터 통신 참고자료 네트워크 설계 장비 (OPNET)

2003 봄컴퓨터 통신 참고자료 Network Core: Packet Switching each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed resource contention: aggregate resource demand can exceed amount available congestion: packets queue, wait for link use store and forward: packets move one hop at a time –transmit over link –wait turn at next link Bandwidth division into “ pieces ” Dedicated allocation Resource reservation

2003 봄컴퓨터 통신 참고자료 Packet Switching: Statistical Multiplexing Sequence of A & B packets does not have fixed pattern  statistical multiplexing. In TDM each host gets same slot in revolving TDM frame. A B C 10 Mbs Ethernet 1.5 Mbs D E statistical multiplexing queue of packets waiting for output link

2003 봄컴퓨터 통신 참고자료 Packet switching versus circuit switching 1 Mbit link each user: –100 kbps when “ active ” –active 10% of time circuit-switching: –10 users packet switching: –with 35 users, probability > 10 active less than.0004 Packet switching allows more users to use network! N users 1 Mbps link