Introduction_Chap1.pdf

Chapter 1 – Introduction Part 1 Computer Networking: A Top-Down Approach 8th edition Jim Kurose, Keith Ross...

Chapter 1 – Introduction Part 1 Computer Networking: A Top-Down Approach 8th edition Jim Kurose, Keith Ross Pearson, 2020 Computer Networks  Chapter 1: introduction Chapter goal: Overview/roadmap: ▪ Get “feel,” “big picture,” ▪ What is the Internet? introduction to terminology ▪ What is a protocol? more depth, detail later in ▪ Network edge: hosts, access network, course physical media ▪ Approach: ▪ Network core: packet/circuit switching, internet structure use Internet as example ▪ Performance: loss, delay, throughput ▪ Security ▪ Protocol layers, service models ▪ History Computer Networks  The Internet: a “nuts and bolts” view Billions of connected mobile network computing devices: national or global ISP ▪ hosts = end systems ▪ running network apps at Internet’s “edge” Packet switches: forward local or packets (chunks of data) Internet regional ISP ▪ routers, switches home network content Communication links provider network datacenter ▪ fiber, copper, radio, satellite network ▪ transmission rate: bandwidth Networks enterprise ▪ collection of devices, routers, network links: managed by an organization Computer Networks  “Fun” Internet-connected devices Pacemaker & Monitor Tweet-a-watt: monitor energy use Amazon Echo IP picture frame Web-enabled toaster + weather forecaster Internet refrigerator Slingbox: remote control cable TV Security Camera AR devices sensorized, bed Internet phones mattress Others? Fitbit Computer Networks  The Internet: a “nuts and bolts” view mobile network 4G ▪ Internet: “network of networks” national or global ISP Interconnected ISPs ▪ protocols are everywhere Skype IP Streaming video control sending, receiving of messages local or regional ISP e.g., HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4G, Ethernet home network content provider ▪ Internet standards HTTP network datacenter network RFC: Request for Comments Ethernet IETF: Internet Engineering Task TCP Force enterprise network WiFi Computer Networks  The Internet: a “service” view ▪ Infrastructure that provides mobile network services to applications: national or global ISP Web, streaming video, multimedia teleconferencing, email, games, e- Streaming commerce, social media, inter- Skype video connected appliances, … local or regional ISP ▪ provides programming interface to distributed applications: home network content provider “hooks” allowing sending/receiving HTTP network datacenter network apps to “connect” to, use Internet transport service provides service options, analogous enterprise to postal service network Computer Networks  What’s a protocol? Human protocols: Network protocols: ▪ “what’s the time?” ▪ computers (devices) rather than humans ▪ “I have a question” ▪ all communication activity in Internet ▪ introductions governed by protocols … specific messages sent Protocols define the format, order of … specific actions taken when message received, messages sent and received among or other events network entities, and actions taken on msg transmission, receipt Computer Networks  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://gaia.cs.umass.edu/kurose_ross 2:00 time Q: other human protocols? Computer Networks  Chapter 1: roadmap ▪ What is the Internet? ▪ What is a protocol? ▪ Network edge: hosts, access network, physical media ▪ Network core: packet/circuit switching, internet structure ▪ Performance: loss, delay, throughput ▪ Security ▪ Protocol layers, service models ▪ History Computer Networks  A closer look at Internet structure mobile network Network edge: national or global ISP ▪ hosts: clients and servers ▪ servers often in data centers local or regional ISP home network content provider network datacenter network enterprise network Computer Networks  A closer look at Internet structure mobile network Network edge: national or global ISP ▪ hosts: clients and servers ▪ servers often in data centers local or Access networks, physical media: regional ISP ▪wired, wireless communication links home network content provider network datacenter network enterprise network Computer Networks  A closer look at Internet structure mobile network Network edge: national or global ISP ▪ hosts: clients and servers ▪ servers often in data centers local or Access networks, physical media: regional ISP ▪wired, wireless communication links home network content provider network datacenter Network core: network ▪ interconnected routers ▪ network of networks enterprise network Computer Networks  Access networks and physical media Q: How to connect end systems mobile network national or global ISP to edge router? ▪ residential access nets ▪ institutional access networks (school, company) local or ▪ mobile access networks (WiFi, 4G/5G) regional ISP What to look for: home network content provider network ▪ transmission rate (bits per second) of access datacenter network network? ▪ shared or dedicated access among users? enterprise network Computer Networks  Access networks: cable-based access 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 (FDM): different channels transmitted in different frequency bands Computer Networks  Access networks: cable-based access cable headend … cable splitter cable modem modem CMTS termination system data, TV transmitted at different frequencies over shared cable ISP distribution network ▪ HFC: hybrid fiber coax asymmetric: up to 40 Mbps – 1.2 Gbs downstream transmission rate, 30-100 Mbps upstream transmission rate ▪ network of cable, fiber attaches homes to ISP router homes share access network to cable headend Computer Networks  Access networks: digital subscriber line (DSL) central office telephone network DSL splitter modem DSLAM voice, data transmitted ISP at different frequencies over DSL access dedicated line to central office multiplexer ▪ 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 ▪ 24-52 Mbps dedicated downstream transmission rate ▪ 3.5-16 Mbps dedicated upstream transmission rate Computer Networks  Access networks: home networks wireless devices to/from headend or central office often combined in single box cable or DSL modem WiFi wireless access router, firewall, NAT point (54, 450 Mbps) wired Ethernet (1 Gbps) Computer Networks  Wireless access networks Shared wireless access network connects end system to router ▪ via base station aka “access point” Wireless local area networks Wide-area cellular access networks (WLANs) ▪ provided by mobile, cellular network ▪ typically within or around operator (10’s km) building (~100 ft) ▪ 10’s Mbps ▪ 802.11b/g/n (WiFi): 11, 54, 450 ▪ 4G cellular networks (5G coming) Mbps transmission rate to Internet to Internet Computer Networks  Access networks: enterprise networks Enterprise link to ISP (Internet) institutional router Ethernet institutional mail, switch web servers ▪ companies, universities, etc. ▪ mix of wired, wireless link technologies, connecting a mix of switches and routers (we’ll cover differences shortly) ▪ Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps ▪ WiFi: wireless access points at 11, 54, 450 Mbps Computer Networks  Host: sends packets of data host sending function: ▪ takes application message ▪ breaks into smaller chunks, two packets, known as packets, of length L bits L bits each ▪ transmits packet into access 2 1 network at transmission rate R link transmission rate, aka link host capacity, aka link bandwidth R: link transmission rate packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec) Computer Networks  Links: physical media ▪ bit: propagates between Twisted pair (TP) transmitter/receiver pairs ▪ two insulated copper wires ▪ physical link: what lies Category 5: 100 Mbps, 1 Gbps Ethernet between transmitter & Category 6: 10Gbps Ethernet receiver ▪ guided media: signals propagate in solid media: copper, fiber, coax ▪ unguided media: signals propagate freely, e.g., radio Computer Networks  Links: physical media Coaxial cable: Fiber optic cable: ▪ two concentric copper conductors ▪ glass fiber carrying light pulses, each pulse a bit ▪ bidirectional ▪ high-speed operation: ▪ broadband: high-speed point-to-point multiple frequency channels on cable transmission (10’s-100’s Gbps) 100’s Mbps per channel ▪ low error rate: repeaters spaced far apart immune to electromagnetic noise Computer Networks  Links: physical media Wireless radio Radio link types: ▪ signal carried in ▪ terrestrial microwave electromagnetic spectrum up to 45 Mbps channels ▪ no physical “wire” ▪ Wireless LAN (WiFi) ▪ broadcast and “half-duplex” Up to 100’s Mbps (sender to receiver) ▪ wide-area (e.g., cellular) ▪ propagation environment 4G cellular: ~ 10’s Mbps effects: ▪ satellite reflection up to 45 Mbps per channel obstruction by objects 270 msec end-end delay interference geosynchronous versus low- earth-orbit Computer Networks  Chapter 1: roadmap ▪ What is the Internet? ▪ What is a protocol? ▪ Network edge: hosts, access network, physical media ▪ Network core: packet/circuit switching, internet structure ▪ Performance: loss, delay, throughput ▪ Security ▪ Protocol layers, service models ▪ History Computer Networks  The network core ▪mesh of interconnected mobile network national or global ISP routers ▪packet-switching: hosts break application-layer messages into packets local or regional ISP forward packets from one router home network content to the next, across links on path provider network datacenter from source to destination network each packet transmitted at full link capacity enterprise network Computer Networks  Packet-switching: store-and-forward L bits per packet 3 2 1 source destination R bps R bps ▪ Transmission delay: takes L/R seconds to transmit (push out) L-bit packet into link at R One-hop numerical example: bps ▪ L = 10 Kbits ▪ Store and forward: entire packet must arrive at ▪ R = 100 Mbps router before it can be transmitted on next link ▪ one-hop transmission delay ▪ End-end delay: 2L/R (above), assuming zero = 0.1 msec propagation delay (more on delay shortly) Computer Networks  Packet-switching: queueing delay, loss R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for output link Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for a period of time: ▪ packets will queue, waiting to be transmitted on output link ▪ packets can be dropped (lost) if memory (buffer) in router fills up Demo : https://computerscience.unicam.it/marcantoni/reti/applet/QueuingAndLossInteractive/1.html Computer Networks  Two key network-core functions routing algorithm Routing: Forwarding: local local forwarding forwarding table table ▪ global action: header value output link determine source- ▪ local action: 0100 3 destination paths 0101 2 move arriving 0111 2 taken by packets 1001 1 packets from router’s input link ▪ routing algorithms to appropriate 1 router output link 3 2 destination address in arriving packet’s header Computer Networks  Alternative to packet switching: circuit switching end-end resources allocated to, reserved for “call” between source and destination ▪ in diagram, each link has four circuits. call gets 2nd circuit in top link and 1st circuit in right link. ▪ dedicated resources: no sharing circuit-like (guaranteed) performance ▪ circuit segment idle if not used by call (no sharing) ▪ commonly used in traditional telephone networks Computer Networks  Circuit switching: FDM and TDM Frequency Division Multiplexing (FDM) 4 users ▪ optical, electromagnetic frequencies frequency divided into (narrow) frequency bands ▪ each call allocated its own band, can transmit at max rate of that narrow band time Time Division Multiplexing (TDM) frequency ▪ time divided into slots ▪ each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band, but only during its time time slot(s) Computer Networks  Packet switching versus circuit switching packet switching allows more users to use network! Example: ▪ 1 Gb/s link ▪ each user: N 100 Mb/s when “active” users 1 Gbps link active 10% of time ▪ circuit-switching: 10 users Q: how did we get value 0.0004? ▪ packet switching: with 35 users, probability > 10 active at same time Q: what happens if > 35 users ? is less than.0004 * Computer Networks  Packet switching versus circuit switching Is packet switching a “slam dunk winner”? ▪ great for “bursty” data – sometimes has data to send, but at other times not resource sharing simpler, no call setup ▪ excessive congestion possible: packet delay and loss due to buffer overflow protocols needed for reliable data transfer, congestion control ▪ Q: How to provide circuit-like behavior? bandwidth guarantees traditionally used for audio/video applications Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet switching)? Computer Networks  Internet structure: a “network of networks” ▪ Hosts connect to Internet via access Internet Service Providers (ISPs) residential, enterprise (company, university, commercial) ISPs ▪ Access ISPs in turn must be interconnected so that any two hosts can send packets to each other ▪ Resulting network of networks is very complex evolution was driven by economics and national policies ▪ Let’s take a stepwise approach to describe current Internet structure Computer Networks  Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access access net net access net access access net net access access net net access access net net access net access net access net access net access access net access net net Computer Networks  Internet structure: a “network of networks” Question: given millions of access ISPs, how to connect them together? access access net net access net access access net net access access net net connecting each access ISP to each other directly doesn’t scale: access access net O(N2) connections. net access net access net access net access net access access net access net net Computer Networks  Internet structure: a “network of networks” Option: connect each access ISP to one global transit ISP? Customer and provider ISPs have economic agreement. access access net net access net access access net net access access net net global access net ISP access net access net access net access net access net access access net access net net Computer Networks  Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. access access net net access net access access net net access access net net ISP A access net ISP B access net access ISP C net access net access net access net access access net access net net Computer Networks  Internet structure: a “network of networks” But if one global ISP is viable business, there will be competitors …. who will want to be connected Internet exchange point access access net net access net access access net net IXP access access net net ISP A access net IXP ISP B access net access ISP C net access net access net peering link access net access access net access net net Computer Networks  Internet structure: a “network of networks” … and regional networks may arise to connect access nets to ISPs access access net net access net access access net net IXP access access net net ISP A access net IXP ISP B access net access ISP C net access net access net regional ISP access net access access net access net net Computer Networks  Internet structure: a “network of networks” … and content provider networks (e.g., Google, Microsoft, Akamai) may run their own network, to bring services, content close to end users access access net net access net access access net net IXP access access net net ISP A Content provider network access net IXP ISP B access net access ISP C net access net access net regional ISP access net access access net access net net Computer Networks  Internet structure: a “network of networks” Tier 1 ISP Tier 1 ISP Google IXP IXP IXP Regional ISP Regional ISP access access access access access access access access ISP ISP ISP ISP ISP ISP ISP ISP At “center”: small # of well-connected large networks ▪ “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage ▪ content provider networks (e.g., Google, Facebook): private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs Computer Networks  ISP Network map: Pakistan Computer Networks  QUESTIONS Computer Networks