CSCI 491-01 Topics: Internet Programming Fall 2008 Introduction Derek Leonard Hendrix College September 3, 2008 Original slides copyright 1996-2007 J.F Kurose and K.W. Ross 1
Chapter 1: Introduction Our goal today: Understand course structure and terminology More depth, detail later in the course Approach: Use the Internet as example Chapter overview: What s the Internet What s a protocol? Network edge Network core Performance: loss, delay Security Protocol layers, service models History 2
Chapter 1: Roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Delay & loss in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History 3
The Internet: Nuts and Bolts View 1) Millions of connected computing devices: Hosts = end systems Run network apps 2) Communication links: Fiber, copper, radio, satellite Transmission rate = bandwidth 3) Routers: forward packets (chunks of data) router server local ISP workstation mobile regional ISP company network 4
The Internet: Nuts and Bolts View 4) Protocols control sending, receiving of msgs E.g., TCP, IP, HTTP, FTP, PPP Internet: network of networks Loosely hierarchical Public networks / private intranets Internet standards RFC: Request for comments IETF: Internet Engineering Task Force router server local ISP workstation mobile regional ISP company network 5
What s s the Internet: A Service View Internet provides a communication infrastructure Enables distributed applications: Web, email, games, e- commerce, file sharing Communication services: Connectionless/unreliable Connection-oriented/reliable 6
What s s a Protocol? 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 the Internet governed by protocols Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission/receipt 7
What s s a Protocol? A human protocol and a computer network protocol: 2:00 Hi Hi Got the time? time TCP connection response TCP connection request <file> GET index.html 8
Chapter 1: Roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Delay & loss in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History 9
A Closer Look at Network Structure: Network edge: Applications and hosts 400+ million hosts 20 billion+ web pages Network core: Routers Links 10
The Network Edge: End systems (hosts): Run application programs E.g., Web, email At edge of network Client/server model Client host requests, receives service from always-on server Example: web browser/server; email client/server Peer-peer model: Minimal (or no) use of dedicated servers Example: Gnutella, KaZaA, BitTorrent 11
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 12
Residential Access: Point to Point Access Dialup via modem Up to 56 kb/s direct access to router (often less) Can t surf and phone at same time: can t be always on ADSL: asymmetric digital subscriber line Up to 1 Mbps upstream (today typically < 768 kbps) Up to 8 Mbps downstream (today typically < 3 Mbps) Newer DSL based on fiber offers up to 100 Mbps 13
Residential Access: Cable Modems HFC: hybrid fiber coax Asymmetric: up to 30 mb/s downstream, 2 mb/s upstream Network of cable and fiber attaches homes to ISP router Homes share access to router Deployment: available via cable TV companies 14
Residential Access: Cable Modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html 15
Cable Network Architecture: Overview server(s) Typically 500 to 5,000 homes cable headend cable distribution network (simplified) home 16
17 Cable Network Architecture: Overview Cable Network Architecture: Overview Cable Network Architecture: Overview home cable headend cable distribution network Channels 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 D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 FDM:
Company Access: Local Area Networks Company/univ local area network (LAN) connects end system to edge router Ethernet: Shared or dedicated link connects end system and router 10 mb/s, 100 mb/s, Gigabit Ethernet, 10 GE LANs: chapter 5 18
Wireless Access Networks Shared wireless access network connects end system to router Via base station aka access point Wireless LANs: 802.11b: 11 mb/s 802.11a: 54 mb/s Wide-area wireless access Provided by telco operator 3G ~ 384 kb/s router base station mobile hosts 19
Home Networks Typical home network components: ADSL or cable modem Router/firewall/NAT Ethernet Wireless access point to/from cable headend cable modem router/ firewall Ethernet wireless access point wireless laptops 20
Physical Media Physical link: what lies between transmitter & receiver Guided media: Signals propagate in solid media: copper, fiber Unguided media: Signals propagate freely, e.g., radio Twisted Pair (TP) Two insulated copper wires Category 3: traditional phone wires, 10 mb/s Ethernet Category 5: 100 mb/s Ethernet 21
Physical Media: Coax, Fiber Coaxial cable: Two concentric copper conductors Bidirectional Baseband: Single channel on cable Legacy Ethernet Broadband: Multiple channels on cable HFC Fiber optic cable: Glass fiber carrying light pulses, each pulse a bit High-speed operation: high-speed point-to-point transmission (e.g., 200 gb/s) Low error rate: repeaters spaced far apart ; immune to electromagnetic noise 22
Physical Media: Radio Radio Signal carried in electromagnetic spectrum No physical wire Bidirectional Propagation environment effects: Reflection Obstruction by objects Interference Radio link types: Terrestrial microwave e.g. up to 45 mb/s channels WLAN 2, 11, 54 mb/s Wide-area (e.g., cellular) e.g. 3G: hundreds of kb/s Satellite Up to 50 mb/s (or multiple smaller channels) 270 msec end-end delay 23
Chapter 1: Roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Delay & loss in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History 24
The Network Core Mesh of interconnected routers Fundamental question: how is data transferred through the network? Circuit switching: dedicated circuit per call: telephone network Packet-switching: data sent thru net in discrete chunks Notation reminder Call = connection 25
Network Core: Circuit Switching End-end resources reserved for each call Link bandwidth, switch capacity Dedicated resources: no sharing Circuit-like (guaranteed) performance Call setup required 26
Network Core: Circuit Switching Network resources (e.g., bandwidth) divided into pieces Pieces allocated to calls Resource piece idle if not used by owning call (no sharing) Dividing link bandwidth into pieces Frequency division multiplexing (FDM) Time division multiplexing (TDM) 27
Circuit Switching: FDM and TDM FDM Example: 4 users frequency TDM time frequency time 28
Numerical Example How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 mb/s Each link uses TDM with 24 slots (1536/24 = 64000) 500 msec to establish end-to-end circuit Work it out! 29
Network Core: Packet Switching Each end-end data stream divided into packets Packets of users A and B share network resources Each packet uses full link bandwidth Resources used as needed Resource contention: Aggregate resource demand can exceed amount available Congestion: packets queue, wait for link use Store and forward: Packets move one hop at a time Node receives complete packet before forwarding 30
Packet Switching: Statistical Multiplexing A 10 Mb/s Ethernet statistical multiplexing C B queue of packets waiting for output link 1.5 mb/s D E Sequence of A s and B s packets does not have a fixed pattern statistical multiplexing In TDM, each host gets the same slot in a revolving TDM frame 31
Packet Switching: Store-and-Forward L R R R Takes L/R seconds to transmit (push out) packet of L bits on to link of R bps Entire packet must arrive at router before it can be transmitted on next link: store and forward Path delay = 3L/R Example: L = 7.5 mbits R = 1.5 mb/s End-to-end delay = 15 sec 32
Packet Switching vs. Circuit Switching Packet switching allows more users to use network! 1 mb/s link Each user: 100 kb/s when active Active 10% of time Circuit-switching: Supports 10 users Packet switching: With 35 users, probability that N users more than 10 users are active is 0.0424%; with 50 users 0.94% Max 100 users (if perfectly unsynchronized) 1 mb/s link 33
Packet Switching vs. Circuit Switching Packet switching: Great for bursty data Resource sharing Simpler, no call setup But suffers from excessive congestion (packet delay and loss) Protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? Bandwidth guarantees needed for audio/video apps Still an unsolved problem (chapter 7) 34
Internet Structure: Network of Networks Roughly hierarchical In the center: tier-1 ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage Treat each other as equals Form the backbone of the Internet Tier-1 providers interconnect (peer) privately Tier 1 ISP NAP Tier 1 ISP Tier 1 ISP Tier-1 providers also interconnect at public network access points (NAPs) 35
Tier-1 1 ISP: XO Communications (2001) 36
Internet Structure: Network of Networks Tier-2 ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet Tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier 1 ISP NAP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISPs also peer privately with each other, or interconnect at NAP Tier-2 ISP 37
Internet Structure: Network of Networks Tier-3 ISPs and local ISPs Last hop ( access ) network (closest to end systems) Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet local ISP local ISP Tier 3 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP Tier 1 ISP local ISP Tier-2 ISP NAP Tier 1 ISP Tier-2 ISP local ISP local ISP Tier-2 ISP local ISP 38
Internet Structure: Network of Networks A packet passes through many networks! local ISP Tier 3 ISP Tier-2 ISP local ISP Tier 1 ISP local ISP Tier-2 ISP NAP local ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP Tier-2 ISP local ISP local ISP 39
Network Taxonomy Telecommunication networks Circuit-switched networks Packet-switched networks FDM TDM Networks with VCs Datagram Networks Internet is a datagram network It provides both connection-oriented (TCP) and connectionless services (UDP) to applications 40
Next Time Finish chapter 1 Reminder: Quiz on Sep 12 based on problems at the end of chapter 1 (pp. 69-75 problems P1-P26) 41