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Lecture 5: Data Communications Server = End Systems Mobile and Internet Technology ‰ Running Network Apps Local ISP ‰ Communication Links Dr

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Lecture 5: Data Communications Server = End Systems Mobile and Internet Technology ‰ Running Network Apps Local ISP ‰ Communication Links Dr What’s the Internet: “nuts and bolts” view millions of connected router computing devices: hosts workstation Lecture 5: Data Communications server = end systems mobile and Internet Technology running network apps local ISP communication links Dr. Hui Xiong fiber, copper, radio, Rutgers University satellite regional ISP transmission rate = bandwidth routers: forward packets (chunks of data) company network Introduction 1-1 Introduction 1-2 What’s the Internet: “nuts and bolts” view What’s the Internet: a service view router communication protocols control sending, workstation receiving of msgs infrastructure enables server distributed applications: e.g., TCP, IP, HTTP, FTP, PPP mobile local ISP Web, email, games, e- Internet: “network of commerce, file sharing networks” communication services llloosely hhlhierarchical provided to apps: public Internet versus regional ISP Connectionless unreliable private intranet connection-oriented Internet standards reliable RFC: Request for comments IETF: Internet Engineering Task Force company network Introduction 1-3 Introduction 1-4 What’s a protocol? What’s a protocol? human protocols: network protocols: a human protocol and a computer network protocol: “what’s the time?” machines rather than “I have a question” humans Hi introductions all communication TCP connection activity in Internet req Hi … specific msgs sent governed by protocols TCP connection Got the response … specific actions taken protocols define format, time? Get http://www.awl.com/kurose-ross when msgs received, order of msgs sent and 2:00 or other events received among network <file> entities, and actions time taken on msg transmission, receipt Q: Other human protocols? Introduction 1-5 Introduction 1-6 1 A closer look at network structure: The network edge: end systems (hosts): network edge: run application programs applications and e.g. Web, email hosts at “edge of network” network core: client/server model routers client host requests, receives service from always-on server network of e.g. Web browser/server; networks email client/server access networks, peer-peer model: physical media: minimal (or no) use of communication links dedicated servers e.g. Gnutella, KaZaA Introduction 1-7 Introduction 1-8 The Network Core Network Core: Circuit Switching mesh of interconnected End-end resources routers reserved for “call” the fundamental link bandwidth, switch question: how is data capacity transferred through net? dedicated resources: circuit switching: no sharing dedicated circuit per circuit-like call: telephone net (guaranteed) packet-switching: data performance sent thru net in call setup required discrete “chunks” Introduction 1-9 Introduction 1-10 Network Core: Circuit Switching Circuit Switching: FDM and TDM Example: network resources dividing link bandwidth FDM (e.g., bandwidth) into “pieces” 4 users divided into “pieces” frequency division pieces allocated to calls time division frequency resource piece idle if not used by owning call time (no sharing) TDM frequency time Introduction 1-11 Introduction 1-12 2 Network Core: Packet Switching Packet Switching: Statistical Multiplexing each end-end data stream resource contention: 10 Mb/s A Ethernet statistical multiplexing C divided into packets aggregate resource user A, B packets share demand can exceed 1.5 Mb/s network resources amount available B each packet uses full link congestion: packets queue of packets waiting for output bandwidth queue, wait for link use link resources used as needed store and forward: packets move one hop D E at a time Bandwidth division into “pieces” Node receives complete Sequence of A & B packets does not have fixed Dedicated allocation packet before forwarding pattern Î statistical multiplexing. Resource reservation In TDM each host gets same slot in revolving TDM frame. Introduction 1-13 Introduction 1-14 Packet switching versus circuit switching Packet switching versus circuit switching Packet switching allows more users to use network! Is packet switching a “slam dunk winner?” 1 Mb/s link Great for bursty data each user: resource sharing 100 kb/s when “active” simpler, no call setup active 10% of time EiExcessive congestion: packet dldelay and loss N users protocols needed for reliable data transfer, circuit-switching: 1 Mbps link congestion control 10 users Q: How to provide circuit-like behavior? packet switching: bandwidth guarantees needed for audio/video with 35 users, probability > 10 active apps less than .0004 still an unsolved problem (chapter 6) Introduction 1-15 Introduction 1-16 Network Taxonomy Packet-switching: store-and-forward L Telecommunication networks R R R Takes L/R seconds to Example: Circuit-switched Packet-switched transmit (push out) L = 7.5 Mbits networks networks packet of L bits on to R = 1.5 Mbps link or R bps delay = 15 sec Networks Datagram Entire packet must FDM TDM arrive at router before with VCs Networks it can be transmitted on next link: store and • Datagram network is not either connection-oriented forward or connectionless. • Internet provides both connection-oriented (TCP) and delay = 3L/R connectionless services (UDP) to apps. Introduction 1-17 Introduction 1-18 3 Access networks and physical media Residential access: point to point access Q: How to connect end systems to edge router? Dialup via modem residential access nets up to 56Kbps direct access to router (often less) institutional access networks (school, Can’t surf and phone at same company) time: can’t be “always on” mobile access networks ADSL: asymmetric digital subscriber line Keep in mind: up to 1 Mbps upstream (today typically < 256 kbps) bandwidth (bits per up to 8 Mbps downstream (today typically < 1 Mbps) second) of access FDM: 50 kHz - 1 MHz for downstream network? 4 kHz - 50 kHz for upstream shared or dedicated? 0 kHz - 4 kHz for ordinary telephone Introduction 1-19 Introduction 1-20 Residential access: cable modems Residential access: cable modems HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router homes share access to router deployment: available via cable TV companies Introduction 1-21 Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction 1-22 Cable Network Architecture: Overview Cable Network Architecture: Overview Typically 500 to 5, 000 homes cable headend cable headend home home cable distribution cable distribution network (simplified) network (simplified) Introduction 1-23 Introduction 1-24 4 Cable Network Architecture: Overview Cable Network Architecture: Overview server(s) FDM: C O V V V V V V N I I I I I I D D T D D D D D D A A R E E E E E E T T O O O O O O O A A L 12 34 56789 Channels cable headend cable headend home home cable distribution cable distribution network network Introduction 1-25 Introduction 1-26 Company access: local area networks Wireless access networks company/univ local area shared wireless access network (LAN) connects network connects end system end system to edge router to router router Ethernet: via base station aka “access point” shared or dedicated link base wireless LANs: connects end system station 802.11b (WiFi): 11 Mbps and router wider-area wireless access 10 Mbs, 100Mbps, provided by telco operator Gigabit Ethernet 3G ~ 384 kbps LANs: chapter 5 mobile • Will it happen?? hosts WAP/GPRS in Europe Introduction 1-27 Introduction 1-28 Home networks Physical Media Typical home network components: Twisted Pair (TP) ADSL or cable modem Bit: propagates between two insulated copper transmitter/rcvr pairs router/firewall/NAT wires physical link: what lies Ethernet Category 3: traditional between transmitter & phone wires, 10 Mbps wireless access receiver Ethernet point guided media: Category 5: 100Mbps Ethernet wireless signals propagate in solid to/from laptops media: copper, fiber, coax cable router/ cable modem firewall unguided media: headend wireless signals propagate freely, access e.g., radio Ethernet point Introduction 1-29 Introduction 1-30 5 Figure 5-7 NIC Interface Card Physical Media: coax, fiber Coaxial cable: Fiber optic cable: glass fiber carrying light two concentric copper pulses, each pulse a bit conductors high-speed operation: bidirectional high-speed point-to-point baseband: transmission (e. g., 5 Gps) single channel on cable low error rate: repeaters legacy Ethernet spaced far apart ; immune broadband: to electromagnetic noise multiple channel on cable HFC Introduction 1-31 Introduction 1-32 Figure 5-8 Unshielded Twisted Pair (UTP) Cable Figure 5-9 Optical Fiber Cable Introduction 1-33 Introduction 1-34 Physical media: radio Internet structure: network of networks signal carried in Radio link types: roughly hierarchical electromagnetic terrestrial microwave at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, spectrum e.g. up to 45 Mbps channels Sprint, AT&T), national/international coverage no physical “wire” LAN (e.g., Wifi) treat each other as equals bidirectional 2Mbps, 11Mbps wide-area (e.g., cellular) Tier-1 prov ider s propagation also interconnect environment effects: e.g. 3G: hundreds of kbps Tier-1 Tier 1 ISP at public network providers access points reflection satellite NAP interconnect (NAPs) obstruction by objects up to 50Mbps channel (or (peer) multiple smaller channels) privately interference Tier 1 ISP Tier 1 ISP 270 msec end-end delay geosynchronous versus low altitude Introduction 1-35 Introduction
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