Welcome to CSC358! Introduction to Computer Networks Amir H. Chinaei, Winter 2016 Today Course Outline . What this course is about Logistics . Course organization, information sheet . Assignments, grading scheme, etc. Introduction to . Principles of computer networks Introduction 1-2 What is this course about? Theory vs practice . CSC358 : Theory . CSC309 and CSC458 : Practice Need to have solid math background . in particular, probability theory Overview . principles of computer networks, layered architecture . connectionless and connection-oriented transports . reliable data transfer, congestion control . routing algorithms, multi-access protocols, . delay models, addressing, and some special topics Introduction 1-3 Overview: internet protocol stack application: supporting network applications . FTP, SMTP, HTTP application transport: process-process data transfer transport . TCP, UDP network network: routing of datagrams from source to destination link . IP, routing protocols link: data transfer between physical neighboring network elements . Ethernet, 802.111 (WiFi), PPP physical: bits “on the wire” Introduction 1-4 Logistics (1/3) Prerequisite knowledge . Probability theory is a must . Mathematical modeling . Data structures & algorithms Course components . Lectures: concepts . Tutorials: problem solving . Assignments: mastering your knowledge . Readings: preparing you for above . Optional assignments: things in practice, bonus Introduction 1-5 Logistics (2/3) Text book . Computer Networking A Top-Down Approach Featuring the Internet 5th Edition, J. F. Kurose and K. W. Ross Lecture slides . Many slides are (adapted) from the above source . © All material copyright . All rights reserved for the authors Introduction 1-6 Logistics (3/3) For important information on . Lecture and tutorial time/location . Contact information of course staff (instructor and TAs) . Office hour and location . Assignments specification and solution . Readings, lectures notes (slides), and tutorial materials . Deadlines and evaluation . Communication and announcements Follow the course web page, regularly http://www.cs.toronto.edu/~ahchinaei/teaching/2016jan/csc358/ Introduction 1-7 Let’s begin with Chapter 1 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 Key terms Internet protocol packet ~ chunk of data network edge, access net, physical media, network core host ~ end system ~ (computing) device/machine/terminal ~ server (or client) ~ sender/transmitter ~ receiver router ~ (packet) switch ~ sender/transmitter ~ receiver packet/circuit switching (wired, wireless) link link capacity ~ link bandwidth ~ transmission rate propagation rate performance: loss, delay, throughput Introduction 1-9 What is the Internet? What’s the Internet: “nuts and bolts” view PC millions of connected mobile network server computing devices: wireless . hosts~end systems global ISP laptop smartphone . running network apps home network communication links regional ISP wireless . fiber, copper, radio, links satellite wired links . transmission rate: bandwidth Packet switches router institutional . routers and switches network . forward packets (chunks of data) Introduction 1-11 “Fun” internet appliances Web-enabled toaster + weather forecaster IP picture frame http://www.ceiva.com/ Tweet-a-watt: monitor energy use Slingbox: watch, control cable TV remotely Internet refrigerator Internet phones Introduction 1-12 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 1-13 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 network provides application regional ISP programming interface . hooks that allow sending and receiving app programs to “connect” to Internet . provides service options, analogous to postal service institutional network Introduction 1-14 What’s a protocol? human protocols: network protocols: “what’s the time?” machines rather than “I have a question” humans introductions all communication activity 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 1-15 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 1-16 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 media: wired, wireless regional ISP communication links network core: . interconnected routers . network of networks institutional self-reading network to Page 28 Introduction 1-17 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 1-18 Access net: digital subscriber line (DSL) central office telephone network DSL splitter modem DSLAM ISP voice, data transmitted 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 < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) < 24 Mbps downstream transmission rate (typically < 10 Mbps) Introduction 1-19 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 1-20 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 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 1-21 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 1-22 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 1-23 Wireless access networks shared wireless access network connects end system to router . via base station aka “access point” wireless LANs: wide-area wireless access . within building (100 ft) . provided by telco (cellular) . 802.11b/g (WiFi): 11, 54 Mbps operator, 10’s km transmission rate . between 1 and 10 Mbps . 3G, 4G: LTE to Internet to Internet Introduction 1-24 Physical media bit: propagates between transmitter/receiver pairs physical link: what lies twisted pair (TP) between transmitter & two insulated copper receiver wires guided media: . Category 5: 100 Mbps, 1 Gpbs Ethernet . signals propagate in solid media: copper, fiber, coax . Category 6: 10Gbps unguided media: . signals propagate freely, e.g., radio Introduction 1-25 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 ’ ’ . multiple channels on cable transmission (e.g., 10 s-100 s Gpbs transmission rate) . HFC low error rate: . repeaters spaced far apart . immune to electromagnetic noise Introduction 1-26 Physical media: radio signal carried in radio link types: electromagnetic spectrum terrestrial microwave no physical “wire” . e.g. up to 45 Mbps channels bidirectional LAN (e.g., WiFi) propagation environment . 11Mbps, 54 Mbps effects: wide-area (e.g., cellular) . reflection . 3G cellular: ~ few Mbps . obstruction by objects satellite . interference . Kbps to 45Mbps channel (or multiple smaller channels) . 270 msec end-end delay . geosynchronous versus low altitude Introduction 1-27 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 2 1 transmission rate R R: link transmission rate . link transmission rate, host aka link capacity, aka link bandwidth packet time