Chapter 1 Introduction Adapted from Computer Networking: A Top Down - PowerPoint PPT Presentation

Chapter 1 Introduction  Adapted from Computer Networking: A Top Down Approach, 6th edition, Jim Kurose, Keith Ross Addison-Wesley, March 2012 Introduction 1-1

Chapter 1: introduction Review :  what ’ s the Internet?  what ’ s a protocol?  network edge; hosts, access net, physical media  network core: packet/circuit switching, Internet structure  performance: loss, delay, throughput  protocol layers, service models  history Introduction 1-2

What ’ s the Internet: “ nuts and bolts ” view  millions of connected PC mobile network computing devices: server  hosts = end systems global ISP wireless laptop  running network apps smartphone home  communication links network regional ISP  fiber, copper, radio, wireless satellite links  transmission rate: wired links bandwidth  Packet switches: forward packets (chunks of data) institutional router network  routers and switches Introduction 1-3

What ’ s the Internet: “ nuts and bolts ” view mobile network  Internet: “ network of networks ”  Interconnected ISPs global ISP  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, Skype, 802.11 home network  Internet standards regional ISP  RFC: Request for comments  IETF: Internet Engineering Task Force institutional network Introduction 1-4

What ’ s the Internet: a service view mobile network  Infrastructure that provides services to applications: global ISP  Web, VoIP, email, games, e- commerce, social nets, … home  provides programming network 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 1-5

What ’ s a protocol? human protocols: network protocols:  “ what ’ s the time? ”  machines rather than humans  “ I have a question ”  all communication activity  introductions in Internet governed by protocols … specific msgs sent … 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 1-6

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 1-7

Chapter 1: 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 1-8

A closer look at network structure:  network edge: mobile network  hosts: clients and servers global ISP  servers often in data centers home  access networks, physical network regional ISP media: wired, wireless communication links  network core:  interconnected routers  network of networks institutional network Introduction 1-9

Access networks and physical media Q: How to connect end systems to edge router?  residential access nets  institutional access networks (school, company)  mobile access networks keep in mind:  bandwidth (bits per second) of access network?  shared or dedicated? Introduction 1-10

Access net: digital subscriber line (DSL) central office telephone network DSL splitter modem DSLAM ISP voice, data transmitted DSL access at different frequencies over multiplexer dedicated line to central office  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  < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)  < 24 Mbps downstream transmission rate (typically < 10 Mbps) Introduction 1-11

Access net: cable network cable headend … cable splitter modem C O N V V V V V V D D T I I I I I I A A R D D D D D D T T O E E E E E E A A L O O O O O O 5 6 7 8 9 1 2 3 4 Channels frequency division multiplexing: different channels transmitted in different frequency bands Introduction 1-12

Access net: cable network cable headend … cable splitter cable modem CMTS modem termination system data, TV transmitted at different frequencies over shared cable ISP distribution network  HFC: hybrid fiber coax  asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate  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 1-13

Access net: home network wireless devices to/from headend or central office often combined in single box cable or DSL modem router, firewall, NAT wireless access point (54 Mbps) wired Ethernet (100 Mbps) Introduction 1-14

Enterprise access networks (Ethernet) institutional link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers  typically used in companies, universities, etc  10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates  today, end systems typically connect into Ethernet switch Introduction 1-15

Wireless access networks  shared wireless access network connects end system to router  via base station aka “ access point ” wide-area wireless access wireless LANs:  provided by telco (cellular)  within building (100 ft) operator, 10 ’ s km  802.11b/g (WiFi): 11, 54 Mbps transmission rate  between 1 and 10 Mbps  3G, 4G: LTE to Internet to Internet Introduction 1-16

Host: sends packets of data host sending function:  takes application message  breaks into smaller two packets, chunks, known as packets , L bits each of length L bits  transmits packet into access network at 1 2 transmission rate R R: link transmission rate  link transmission rate, host aka link capacity, aka link bandwidth packet time needed to L (bits) = = transmission transmit L -bit R (bits/sec) delay packet into link 1-17

Physical media  bit: propagates between transmitter/receiver pairs twisted pair (TP)  physical link: what lies between transmitter &  two insulated copper receiver wires  guided media:  Category 5: 100 Mbps, 1 Gpbs Ethernet  signals propagate in solid  Category 6: 10Gbps media: copper, fiber, coax  unguided media:  signals propagate freely, e.g., radio Introduction 1-18

Physical media: coax, fiber coaxial cable: fiber optic cable:  two concentric copper  glass fiber carrying light conductors pulses, each pulse a bit  bidirectional  high-speed operation:  broadband:  high-speed point-to-point transmission (e.g., 10 ’ s-100 ’ s  multiple channels on cable Gpbs transmission rate) HFC   low error rate:  repeaters spaced far apart  immune to electromagnetic noise Introduction 1-19

Physical media: radio radio link types:  signal carried in electromagnetic spectrum  terrestrial microwave  no physical “ wire ”  e.g. up to 45 Mbps channels  LAN (e.g., WiFi)  bidirectional  11Mbps, 54 Mbps  propagation environment effects:  wide-area (e.g., cellular)  reflection  3G cellular: ~ few Mbps  satellite  obstruction by objects  Kbps to 45Mbps channel (or  interference multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude Introduction 1-20

Chapter 1: 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 1-21

The network core  mesh of interconnected routers  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 1-22

Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps  takes L / R seconds to one-hop numerical example: transmit (push out) L -bit  L = 7.5 Mbits packet into link at R bps  R = 1.5 Mbps  store and forward: entire packet must arrive at router  one-hop transmission before it can be transmitted delay = 5 sec on next link  end-end delay = 2 L / R (assuming zero propagation delay) more on delay shortly … Introduction 1-23

Packet Switching: queueing delay, loss C R = 100 Mb/s A D R = 1.5 Mb/s B E queue of packets waiting for output link queuing and loss:  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 1-24