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

2. Lecture 1 What is the Internet? 1-2 Internetworked networks – Internet ! Image courtesy: http://www.seopher.com/images/internet.jpg

3. Lecture 1 What is the Internet?  A vast universe of computer networks growing continuously  Not just computers but also other mobile devices like our smart phones, PDAs etc. are also becoming part of it  Difficult to manage without a proper structure…  Designed as a hierarchical structure  A simple example:  Computers combine to form a Local Area Network (LAN) (e.g., our lab)  LANs combine to form an Autonomous System (AS) (e.g., our college or CUNY)  Autonomous Systems combine to form the Internet! 1-3

4. Lecture 1 What’s the Internet: the “hardware” view 1. Millions of connected computing devices: hosts = end systems  running network apps Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points 2. Communication links  Wired (example: fiber, copper cables)  Wireless (example: radio, satellite) 3. Routers  forward packets (chunks of data) 1-4

5. Lecture 1 What’s the Internet: “operational” view  Internet: “network of networks”  Requires sending, receiving of messages  Requires mechanisms (protocols) to control sending, receiving of messages  Design of protocols is the key for Internet Home network Institutional network Mobile network Global ISP Regional ISP 1-5

6. human protocols: … specific questions asked … specific actions taken when questions asked… … constant learning of protocols Lecture 1 What’s a protocol? A protocol is defined as a code of correct conduct. human protocol Hi Got the time? 2:00 time 1-6

7. Lecture 1 Internet:  computers rather than humans  But the concept of protocol remains same  Code of correct conduct  set of rules which is used by computers to communicate with each other across a network What’s a protocol in the Internet? 1-7  As the Internet grows rapidly so does the necessity of these rules (protocols)…

8. Connection reply Auhtentication req. Lecture 1 A web browsing protocol example a human protocol and a computer network protocol: Internet protocol example Hi Got the time? 2:00 Connection req. Username, password Get http://jjcweb.jjay.cuny.edu/ssengupta/slide.ppt time human protocol 1-8 Time request Slides request

9. Lecture 1 Thus protocols define format, order of messages sent and received among network entities, actions taken on message transmission and receipt address conflicts among network entities What’s the Internet: an operational view 1-9

10. Lecture 1 We have studied a high-level overview of the Internet! Now, A closer look at the Internet structure! 1-10

11. Lecture 1 We already know the components of Internet:  Hosts (end-users)  e.g. computers  Access networks, physical media: wired, wireless communication links  Interconnected routers 1-11 Let’s look at little more detail of each of these components!

12. Lecture 1 The network edge: two communication models  End-users (hosts):  run application programs  e.g. Web, email client/server peer-peer  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 1-12

13. Lecture 1 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 1-13

14. Lecture 1 Residential access: point to point access  Dialup via modem  up to 56Kbps direct access to router (conceptually)  ADSL: asymmetric digital subscriber line  up to 1 Mbps home-to-router  up to 8 Mbps router-to-home  ADSL deployment: happening 1-14

15. Lecture 1 Residential access: cable modems  HFC: hybrid fiber coax  asymmetric: up to 10Mbps upstream, 1 Mbps downstream  network of cable and fiber attaches homes to ISP router  shared access to router among home  issues: congestion  deployment: available via cable companies, e.g., MediaOne, CableVision 1-15

16. Lecture 1 Institutional access: local area networks  company/univ local area network (LAN) connects end system to edge router  Ethernet:  shared or dedicated cable connects end system and router  10 Mbps, 100Mbps, Gigabit Ethernet  deployment: institutions, home LANs happening now 1-16

17. Lecture 1 Wireless access networks  shared wireless access network connects end system to router  wireless LANs:  radio spectrum replaces wire  e.g., 802.11b/g (WiFi): 11 or 54 Mbps  wider-area wireless access  next up (?): WiMAX (10’s Mbps) over wide area base station mobile hosts router 1-17

18. Lecture 1 The Client/Server Model  Client/server model is a basic design for Internet applications  server - is the information provider  client - is the information consumer  example  web server and a client running web browser  a CNN web server simultaneously serves thousands of clients.  In this class, we will also learn how to construct Web pages at the client end! 1-18

19.  What is Internet?  Components…  Operational view…  System (structure) view…  Client-server and peer to peer model…  Access Networks… Lecture 1 Summary: What have we learnt? 1-19

20. Lecture 1 Next Up… 1.1 What is the Internet? 1.2 Network edge  end systems, access networks, links 1.3 Network core: operations in Internet  circuit switching, packet switching 1.4 Delay, loss and throughput in Internet 1.5 Protocol layers, service models 1.6 Networks under attack: security 1-20