1. Introduction Computer Networking: A Top Down Approach th 6 edition Jim Kurose, Keith Ross Addison-Wesley March 2012 All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights Reserved Introduction 1-1 1. Introduction Goals: v get “feel” and terminology v defer depth and detail to later in course v understand concepts using the Internet as example Introduction 1-2 1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge § end systems, access networks, links 1.3 network core § packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers 1.6 networks under attack: security 1.7 history Introduction 1-3 What’s the Internet: “nuts and bolts” view PC v hosts or end-systems mobile network server § millions of connected wireless computing devices global ISP laptop smartphone running network apps home network v communication links regional ISP wireless § fiber, copper, radio, links satellite with different wired links transmission rates or bandwidth v packet switches router v forward packets or institutional chunks of data network Introduction 1-4 “Fun” internet appliances Web-enabled toaster + weather forecaster IP picture frame Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely Internet refrigerator InternetInternet phones phones Introduction 1-5 What’s the Internet: “nuts and bolts” view mobile network v Internet: “network of networks” § Interconnected ISPs global ISP v protocols control sending, receiving of msgs § e.g., TCP, IP, HTTP, Skype, 802.11 home network v Internet standards regional ISP § RFC: Request for comments § IETF: Internet Engineering Task Force institutional network Introduction 1-6 What’s the Internet: a service view mobile network v Infrastructure that provides services to applications: global ISP § Web, VoIP, email, games, e- commerce, social nets, … home network v provides programming regional ISP interface to apps § hooks that allow sending and receiving app programs to “connect” to Internet § provides service options, analogous to postal service institutional network Introduction 1-7 What’s a protocol? human protocols: network protocols: v “what’s the time?” v machines rather than v “I have a question” humans v introductions v all communication activity in Internet governed by … specific msgs sent protocols … specific actions taken when msgs received, or protocols define format, order other events of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction 1-8 What’s a protocol? a human protocol and a computer network protocol: Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 <file> time Q: other human protocols? Introduction 1-9 1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge § end systems, access networks, links 1.3 network core § packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history Introduction 1-10 A closer look at network structure: v network edge: mobile network § hosts: clients and servers global ISP § servers often in data centers home v network access networks, physical regional ISP media: wired, wireless communication links v network core: § interconnected routers § network of networks institutional network Introduction 1-11 Access networks and physical media Q: How to connect end systems to edge router? v residential access nets v institutional access networks (school, company) v mobile access networks keep in mind: v bandwidth (bits per second) of access network? v shared or dedicated? Introduction 1-12 Access net: digital subscriber line (DSL) central office The telephone image cannot be displayed network DSL splitter modem DSLAM ISP voice, data transmitted at different frequencies over DSL access dedicated line to central office multiplexer v use existing telephone line to central office DSLAM § data over DSL phone line goes to Internet § voice over DSL phone line goes to telephone net v < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) v < 24 Mbps downstream transmission rate (typically < 10 Mbps) Introduction 1-13 Access net: cable network cable headend … cable splitter modem 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 1 2 3 4 5 6 7 8 9 Channels frequency division multiplexing: different channels transmitted in different frequency bands Introduction 1-14 Access net: cable network cable headend … cable splitter cable modem modem CMTS termination system data, TV transmitted at different frequencies over shared cable ISP distribution network v HFC: hybrid fiber coax § asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate v network of cable, fiber attaches homes to ISP router § homes share access network to cable headend § unlike DSL, which has dedicated access to central office Introduction 1-15 Fiber to the home (FTTH) v Fully optical fiber path all the way to the home § e.g., Verizon FIOS, Google § ~30 Mbps to 1Gbps v Active (like switched Ethernet) or passive optical networking as shown below Introduction 1-16 Access net: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem wireless access router, firewall, NAT point (54 Mbps) wired Ethernet (100 Mbps) Introduction 1-17 Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers v typically used in companies, universities, etc v 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates v end systems typically connect into Ethernet switch possibly through a wireless access point Introduction 1-18 Wireless access networks v shared wireless access network connects end system to router § via base station aka “access point” wireless LANs: wide-area mobile access § within building (100 ft) § provided by telco (cellular) § 802.11b/g/n (WiFi): 11, 54,256 operator, 10’s km Mbps transmission rate § between 1 and 20 Mbps § 3G, 4G/LTE to Internet to Internet Introduction 1-19 Host: sends packets of data sending host: v breaks app message into smaller chunks, known as two packets, packets, of length L bits L bits each v transmits packet into access network at transmission rate R 2 1 § aka link capacity or link R: link transmission rate bandwidth host packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) 1-20 Physical media v bit: propagates between transmitter/receiver pairs v physical link: what lies between transmitter & receiver v guided media: § signals propagate in solid media: copper, fiber, coax v unguided media: § signals propagate freely, e.g., radio Introduction 1-21 Physical media: twisted pair, coax, fiber twisted pair (TP) fiber optic cable: v two insulated copper v glass fiber carrying light wires pulses, each pulse a bit § Category 5: 100 Mbps, 1 Gpbs Ethernet v high-speed operation: § Category 6: 10Gbps § high-speed point-to-point transmission (e.g., 10’s-100’s Gpbs transmission rate) v low error rate: § repeaters spaced far apart § immune to electromagnetic coaxial cable: noise v two concentric copper conductors v broadband: § multiple channels on cable § HFC Introduction 1-22 Physical media: radio v signal carried in radio link types: electromagnetic spectrum, v terrestrial microwave i.e., no physical “wire” § e.g. up to 45 Mbps channels v LAN (e.g., WiFi) v propagation environment § 11Mbps, 54 Mbps effects: v wide-area (e.g., cellular) § reflection § 3G cellular: ~ few Mbps § obstruction by objects v satellite § interference § Kbps to 45Mbps channel (or multiple smaller channels) § 270 msec end-end delay § geosynchronous versus low earth-orbitting (LEO) Introduction 1-23 1. Introduction: roadmap 1.1 what is the Internet? 1.2 network edge § end systems, access networks, links 1.3 network core § packet switching, circuit switching, network structure 1.4 delay, loss, throughput in networks 1.5 protocol layers, service models 1.6 networks under attack: security 1.7 history Introduction 1-24 The network core v mesh of interconnected routers v packet-switching: hosts break application-layer messages into packets § forward packets from one router to the next across links on path from source to destination § each packet transmitted at full link capacity Introduction 1-25 Packet-switching: store-and-forward end-end transmission delay = 2L/R L bits per packet 3 2 1 source des+naon R bps R bps v takes L/R seconds to transmit (push out) L-bit Example packet into link at R bps • L=1500B v store and forward: entire • R=1.5Mbps packet must arrive at router • Transmission delay = ? before it can be transmitted on next link Introduction 1-26 Packet Switching: queueing delay, loss C A R = 100 Mb/s D R = 1.5 Mb/s B queue of packets E waiting for output link queuing and loss: v If arrival rate (in bits) to link exceeds transmission rate of link for a period of time: § packets will queue, wait to be transmitted on link § packets can be dropped (lost) if memory (buffer) fills up Introduction 1-27 Two key network-core functions routing: determines source- forwarding: move packets from destination route taken by router’s input to appropriate packets router output § routing algorithms routing algorithm local forwarding table header value output link 0100 3 1 0101 2 0111 2 3 2 1001 1 dest address in arriving packet’s header Network Layer 4-28 Alternative core: circuit switching end-end resources allocated to, reserved for “call” between source & dest: v In diagram, each link has four circuits. § call gets 2nd circuit in top link and 1st circuit in right link.