Introduction cont. Network Core: Circuit Switching Lecture goal: - PDF document

Introduction cont. Network Core: Circuit Switching Lecture goal: Overview: network resources (e.g., bandwidth) divided into ¸ get context, overview, ¸ access net, physical media “pieces” “feel” of networking ¸ performance: loss, delay pieces allocated to calls ¸ more depth, detail later ¸ resource piece idle if not used in course ¸ protocol layers, service models ¸ by owning call (no sharing) ¸ approach: ¸ backbones, NAPs, ISPs dividing link bandwidth into ¸ o descriptive “pieces” o use Internet as frequency division o example time division o 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 1 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 2 Network Core: Packet Switching Network Core: Packet Switching 10 Mbs each end-end data stream divided into resource contention: C A packets statistical multiplexing Ethernet ¸ aggregate resource user A, B packets share network ¸ demand can exceed resources 1.5 Mbs each packet uses full link amount available B ¸ bandwidth queue of packets 45 Mbs ¸ congestion: packets resources used as needed , waiting for output ¸ queue, wait for link use link ¸ store and forward: D E packets move one hop at Bandwidth division into “pieces” a time Dedicated allocation o transmit over link Packet-switching versus circuit switching: human restaurant Resource reservation analogy o wait turn at next link 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 3 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 4 Network Core: Packet Switching Packet switching versus circuit switching Packet-switching: Packet switching allows more users to use network! store and forward 1 Mbit link ¸ behavior each user: ¸ 100Kbps when “active” o active 10% of time o Example N users ¸ 7.5 Mbit message circuit-switching: ¸ 1 Mbps link 10 users ¸ 1.5 Mbps link transmission o rate packet switching: ¸ with 35 users, probability > 10 o ¸ 5000 1.5 Kbit packets active less that .004 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 5 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 6 1

Packet switching versus circuit switching Packet-switched networks: routing Is packet switching a “slam dunk winner?” Goal: move packets among routers from source to destination ¸ ¸ Great for bursty data we’ll study several path selection algorithms (chapter 4) o o resource sharing datagram network: ¸ destination address determines next hop o no call setup o routes may change during session o ¸ Excessive congestion: packet delay and loss analogy: driving, asking directions o o protocols needed for reliable data transfer, virtual circuit network: ¸ congestion control each packet carries tag (virtual circuit ID), tag determines next hop o ¸ Q: How to provide circuit-like behavior? fixed path determined at call setup time , remains fixed thru call o routers maintain per-call state o bandwidth guarantees needed for audio/video o apps still an unsolved problem (chapter 6) 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 7 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 8 Access networks and physical media Residential access: point to point access Q: How to connection end ¸ Dialup via modem systems to edge router? o up to 56Kbps direct access to ¸ residential access nets router (conceptually) ¸ institutional access networks ¸ ISDN: intergrated services (school, company) digital network: 128Kbps all- ¸ mobile access networks digital connect to router Keep in mind: ¸ ADSL: asymmetric digital subscriber line ¸ bandwidth (bits per second) of access network? o up to 1 Mbps home-to-router ¸ shared or dedicated? o up to 8 Mbps router-to-home o Ordinary PSTN 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 9 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 10 Residential access: cable modems Institutional access: local area networks ¸ HFC: hybrid fiber coax ¸ company/univ local area network (LAN) connects o asymmetric: up to 10Mbps upstream, 1 Mbps end system to edge router downstream ¸ Ethernet: ¸ network of cable and o shared or dedicated fiber attaches homes to cable connects end ISP router system and router o shared access to router o 10 Mbs, 100Mbps, among home Gigabit Ethernet o issues: congestion, dimensioning ¸ LANs: chapter 5 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 11 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 12 2

Physical Media Wireless access networks ¸ shared wireless access Twisted Pair (TP) ¸ physical link: network connects end ¸ two insulated copper transmitted data bit system to router router wires propagates across link ¸ wireless LANs: o Category 3: traditional base ¸ guided media: o radio spectrum replaces phone wires, 10 Mbps station wire o signals propagate in ethernet o e.g., Lucent Wavelan 10 solid media: copper, o Category 5 TP: Mbps fiber 100Mbps ethernet ¸ wider-area wireless ¸ unguided media: access mobile o signals propagate freely o GPRS (General Packet hosts e.g., radio Radio Service) 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 13 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 14 Physical Media: coax, fiber Physical media: radio Radio link types: Coaxial cable: Fiber optic cable: ¸ signal carried in electromagnetic ¸ microwave ¸ wire (signal carrier) ¸ glass fiber carrying light spectrum o e.g. up to 45 Mbps channels within a wire (shield) pulses ¸ LAN (e.g., waveLAN) ¸ no physical “wire” o baseband: single channel ¸ high-speed operation: o 2Mbps, 11Mbps on cable ¸ bidirectional o 100Mbps Ethernet ¸ wide-area (e.g., cellular) o broadband: multiple ¸ propagation o high-speed point-to-point o e.g. GPRS, 10’s Kbps channel on cable environment effects: transmission (e.g., 5 Gbps) ¸ satellite ¸ bidirectional ¸ low error rate o reflection o up to 50Mbps channel (or ¸ common use in 10Mbps o obstruction by objects multiple smaller channels) Ethernet o interference o 270 msec end-end delay 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 15 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 16 Delay in packet-switched networks Delay in packet-switched networks ¸ nodal processing: packets experience delay Transmission delay: Propagation delay: check bit errors on end-to-end path o ¸ R=link bandwidth (bps) ¸ d = length of physical link determine output link o ¸ four sources of delay ¸ queuing ¸ L=packet length (bits) ¸ s = propagation speed in at each hop time waiting at output link medium (~2x10 8 m/sec) o ¸ time to send bits into for transmission link = L/R ¸ propagation delay = d/s depends on congestion o level of router Note: s and R are very transmission A different quantities! propagation transmission A propagation B B nodal nodal queuing processing queueing processing 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 17 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 18 3

Protocol “Layers” Queuing delay (revisited) Networks are complex! ¸ R=link bandwidth (bps) ¸ many “pieces”: ¸ L=packet length (bits) o hosts Question: ¸ a=average packet arrival o routers Is there any hope of organizing rate structure of network? o links of various traffic intensity = La/R media Or at least our discussion of o applications networks? ¸ La/R ~ 0: average queuing delay small o protocols ¸ La/R -> 1: delays become large o hardware, software ¸ La/R > 1: more “work” arriving than can be serviced, average delay infinite! 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 19 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 20 Organization of air travel Organization of air travel : a different view ticket (purchase) ticket (complain) ticket (purchase) ticket (complain) baggage (claim) baggage (claim) baggage (check) baggage (check) gates (load) gates (unload) gates (load) gates (unload) runway takeoff runway landing runway takeoff runway landing airplane routing airplane routing airplane routing airplane routing airplane routing airplane routing Layers: each layer implements a service o via its own internal-layer actions ¸ a series of steps o relying on services provided by layer below 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 21 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 22 Layered air travel: services Distributed implementation of layer functionality Counter-to-counter delivery of person+bags Departing airport ticket (purchase) ticket (complain) arriving airport baggage-claim-to-baggage-claim delivery baggage (check) baggage (claim) people transfer: loading gate to arrival gate gates (load) gates (unload) runway-to-runway delivery of plane runway takeoff runway landing airplane routing airplane routing airplane routing from source to destination intermediate air traffic sites airplane routing airplane routing airplane routing 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 23 9/9-02 Datorkommunikation & Internet, Anders broberg, Umu - Introduction 24 4