Introduction to Computer Networks: Understanding the Internet and its Protocols

1. Comp 365 Computer Networks Fall 2014 Chapter 1Introduction These slides derived from Computer Networking: A Top Down Approach ,6th edition. Jim Kurose, Keith RossAddison-Wesley, March 2012. Introduction

2. Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example Overview: 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 security protocol layers, service models history Chapter 1: Introduction Introduction

3. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction

4. millions (>900m) of connected computing devices: hosts = end systems runningnetwork apps PC Mobile network server Global ISP wireless laptop cellular handheld Home network Regional ISP access points wired links Institutional network router What’s the Internet: “nuts and bolts” view • communication links • fiber, copper, radio, satellite • transmission rate = bandwidth • Packet switches: forward packets (chunks of data) • routers and switches Introduction

5. “Cool” 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 phones Internet refrigerator Introduction

6. protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Ethernet Internet: “network of networks” loosely hierarchical Interconnected ISPs public Internet versus private intranet Mobile network Global ISP Home network Regional ISP Institutional network What’s the Internet: “nuts and bolts” view ISP = Internet service provider Introduction

7. Internet standards RFC: Request for comments the standards documents Very technical > 5,000 RFCs Include TCP, IP, HTTP, SMTP IETF: Internet Engineering Task Force the body that creates standards Other bodies: IEEE 803 LAN/MAN, etc. Mobile network Global ISP Home network Regional ISP Institutional network What’s the Internet: “nuts and bolts” view ISP = Internet service provider Introduction

8. communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing What’s the Internet: a service view Introduction

9. communication services provided to apps: reliable data delivery from source to destination “best effort” (unreliable) data delivery What’s the Internet: a service view Introduction

10. Application programming interface (API): Describes how these distributed apps send information back and forth Like the post office: must put name, street, city, etc. on an envelope Different internet services have different APIs. What’s the Internet: a service view Introduction

11. human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols What’s a protocol? protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt Introduction

12. a human protocol and a computer network protocol: TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection request Hi Q: Other human protocols? Introduction

13. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History Introduction

14. network edge: hosts: clients and servers servers often in data centers A closer look at network structure: • access networks, physical media: wired, wireless communication links • network core: • interconnected routers • network of networks Introduction

15. end systems (hosts): run application programs e.g. Web, email at “edge of network” peer-peer client/server The network edge • client/server model • client host requests, receives service from always-on server • e.g. Web browser/server; email client/server • peer-peer model: • minimal (or no) use of dedicated servers • e.g. Skype, BitTorrent Introduction

16. 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? Access networks and physical media Introduction

17. Dial-up Modem central office telephone network Internet homedial-up modem ISPmodem (e.g., AOL) home PC • Uses existing telephony infrastructure • Home is connected to central office • Modem converts digital output of PC to analog format • up to 56Kbps direct access to router (often less) • 8 minutes to download 3 minute MP3; days for a movie • Can’t surf and phone at same time: not “always on”

18. ISP voice, data transmitted at different frequencies over dedicated line to central office DSL access multiplexer Digital Subscriber Line (DSL) DSL: digital subscriber line central office telephone network DSLAM: digital subscriber line access multiplier DSL modem splitter DSLAM • uses 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 (typically < 1 <bps) • < 24 Mbps downstream (typically < 10 Mbps) • Local telco is the ISP asymmetric

19. Does not use telephone infrastructure Instead uses cable TV infrastructure cable modem termination system data, TV transmitted at different frequencies over shared cable distribution network ISP Residential access: cable network cable headend … cable modem splitter CMTS Introduction

20. HFC: hybrid fiber coax Fiber from cable head end to neighborhood level junctions Coaxial cable to house Special cable modems used through ethernet port asymmetric: up to 30Mbps downstream, 2 Mbps upstream cable modem termination system data, TV transmitted at different frequencies over shared cable distribution network ISP Residential access: cable network cable headend … cable modem splitter CMTS Introduction

21. network of cable and fiber attaches homes to ISP router homes share access to router Every packet sent by head end travels to every link to every home unlike DSL, which has dedicated access to central office Need shared distributed multiple-access protocol to coordinate upstream transmissions and avoid collisions Residential access: cable networks Introduction

22. Residential access: cable networks Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Introduction

23. Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified) Introduction

24. server(s) Cable Network Architecture: Overview cable headend home cable distribution network Introduction

25. Cable Network Architecture: Overview cable headend home cable distribution network (simplified) Introduction

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

27. C O N T R O L D A T A D A T A V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O 5 6 7 8 9 1 2 3 4 Channels Cable Network Architecture: Overview FDM (more shortly): Frequency-division multiplexing different channels transmitted in different frequency bands cable headend … cable modem splitter Introduction

28. ONT ONT ONT Fiber to the HomeFTTH Verizon PON (passive optical network) opticalfibers Internet • Optical links from central office to the home • Two competing optical technologies: • Passive Optical network (PON) • Active Optical Network (PAN) (like ethernet: see chap 5) • Much higher Internet rates; fiber also carries television and phone services (10-20Mbps download; 2-10 up) opticalfiber OLT Splitter replicates every packet on every line optical splitter OLT: optical line terminator central office (CO) ONT: optical network terminator

29. Ethernet Internet access Typically use twisted-pair copper wire • Typically used in companies, universities, etc • 10 Mbs, 100Mbps, 1Gbps, 10Gbps, 100Gbps Ethernet • Today, end systems typically connect into Ethernet switch institutional link to ISP (Internet) institutional router Ethernet switch institutional mail, web servers

30. shared wireless access network connects end system to router via base station aka “access point” wireless LANs: 802.11b/g (WiFi): 11 or 54 Mbps within building (100 ft) Wireless access networks (chap 6) router base station mobile hosts Introduction

31. wider-area wireless access provided by telco operator 1-10Mbps over cellular system (EVDO, HSDPA) 3G (third generation) wireless: packet-switched wide-area wireless. 4G (various technologies): 100Mbps up to 1Gbps LTE Wireless access networks (chap 6) router base station mobile hosts Introduction

32. Typical home network components: DSL or cable modem router/firewall/NAT* Ethernet wireless access point Home networks wireless laptops to/from cable headend cable modem router/ firewall wireless access point Ethernet *Network Address Translator Introduction

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

34. Bit: propagates betweentransmitter/rcvr pairs physical link: what lies between transmitter & receiver Physical propagation is by electromagnetic waves or optical pulses Can use various types of physical medium in one network guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., Physical Media Introduction

35. Labor cost: (installing physical medium) orders of magnitude higher than medium itself. Medium cost: varies by medium. Several types often installed in case needed in future. Physical Media costs Introduction

36. Twisted Pair (TP) Least expensive physical medium Also used for phone lines (shielded) Internet access over telephone wires use twisted pair UTP: unshielded twisted pair; often used in LANs Physical Media • two insulated twisted copper wires • Category 3: traditional phone wires, 10 Mbps Ethernet • Category 5 UTP: 1Gbps Ethernet up to 100 meters • Category 6 UTP: 10Gbps • Rates depend on thickness of the wire and distance between transmitter and receiver Introduction

37. Coaxial cable: two concentric copper conductors two conductors: the central wire and the tubular shield bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channels on cable HFC Physical Media: coax Coax is concentric, twisted pair is parallel RG-59 flexible coaxial cable composed of: A: outer plastic sheath B: woven copper shield C: inner dielectric insulator D: copper-plated core (image from wikipedia: http://en.wikipedia.org/wiki/Coaxial_cable) Introduction

38. Physical Media: fiber Fiber optic cable: • glass fiber carrying light pulses, each pulse a bit • high-speed operation: • high-speed point-to-point transmission (e.g., 10’s-100’s Gps) • low error rate: repeaters spaced far apart ; immune to electromagnetic noise • Used in Internet backbone, long-distance telephone networks, overseas links. • Expensive. Introduction

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