CENG415 – Communication Networks

1. CENG415 – Communication Networks Lectures 1 Introduction

2. Contents of CENG415 • Network communication principles • Network Protocols • Application: HTTP, FTP, SMTP, DNS ... • Transport: TCP/UDP • Network: IP • Data link: Ethernet… • The path from sender to receiver • Access networks • Hubs, Switches and routers • Routing and addressing • Routing algorithms • Congestion and flow control

3. Text book and Handouts • James F. Kurose, Keith W. Ross, “Computer Networking, A Top-Down Approach,”Fourth Edition, Pearson Education International, 2008, ISBN-10: 0-321-51325-8. NOTE: THE BOOK IS A MUST • Some handouts given by the instructor • Power point presentations (not sure!)

4. Course requirements • Test1: 20% Midterm: 30% Final: 40% • Assignments: 10%. Exercises from the book in addition to some challenging ones. • Individual – No late policy • In class participation: is taken into consideration.

5. Syllabus – Rules • SOE rules and regulations • Important dates • Absences and late policy • Email usage • SP courses policy • Labs • Office hours

6. How to fail the course • Be always late to lectures • Do not do assignments or start late • COPY YOUR ASSIGNMENTS • Do not ask questions in class • Do not come to see me during office hours • Cheating is also an option • Other options are available

7. Work envirement • In the LAB we will use: • Packet tracer 5.0 (CISCO) • WireShark 0.99.7 • Windows commands • Each of you should duplicate this environment on his home computer. It is needed for assignments and practices. • A 4GB flash memory is required to exchange data

8. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

9. What is the Internet Backbone: link between IXP IXP (Internet Exchange Point) Long distance connection. Also called NAP (network access point) ISP: Internet Service provider provide everyone with internet access POP: Point of presence

10. What is the Internet • millions of connected computing devices: hosts = end systems • running network apps (email, Web, telephone, banking, time, updates, …) • communication links • fiber, copper, radio, satellite • transmission rate = bandwidth • routers: forward packets (chunks of data) • search engines: "crawl" the Web, sorting Web sites by key words into huge databases (e.g., Google). • security systems: monitor the Web traffic for malicious activities.

11. What is the Internet • Communication is controlled by protocols • Protocols are layered • Each is responsible for a particular service

12. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

13. Network structure • network edge: applications and hosts • network core: • routers • network of networks • access networks, physical media:communication links • end systems (hosts): • run application programs, like Web, email at “edge of network” • 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, KaZaA

14. Network edge Goal: data transfer between end systems Two types of connection: • Connection oriented • Establish a connection during transmission. • set up “state” in two communicating hosts • Uses TCP - Transmission Control Protocol • Reliable • Automatic flow control and congestion control • Connectionless • Connectionless • unreliable data transfer • no flow control • no congestion control

15. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

16. The network core • how is data transferred through the net? • circuit switching:dedicated circuit per call: telephone net • packet-switching: data sent thru net in discrete “chunks”

17. The network core – Circuit switching End-end resources reserved for “call” • link bandwidth, switch capacity • dedicated resources: no sharing • circuit-like (guaranteed) performance • call setup required network resources (e.g., bandwidth) divided into “pieces” • pieces allocated to calls • resource piece idle if not used by owning call (no sharing)

18. Example: 4 users FDM frequency time TDM frequency time The network core – Circuit switching • dividing link bandwidth into “pieces” • frequency division • time division

19. The network core – Packet switching each end-end data stream divided into packets • user A, B packets 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

20. Bandwidth division into “pieces” Dedicated allocation Resource reservation The network core – Packet switching each end-end data stream divided into packets • user A, B packets 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

21. The network core – Packet switching 100 Mb/s Ethernet C A statistical multiplexing • Entire packet must arrive at router before it can be transmitted on next link: store and forward • Packet switching allows more users to use network! 1.5 Mb/s B queue of packets waiting for output link D E

22. Chapter 1 • What is the Internet? • Network edge • Network core • Network access and physical media • Internet structure and ISPs • Delay & loss in packet-switched networks • Protocol layers, service models • Networks under attack: security (covered in CENG410) • History

23. Access networks and physical media Q: How to connect end systems to the Internet? • residential access nets • institutional access networks (school, company) • mobile access networks Keep in mind: • bandwidth (bits per second) of access network? • shared or dedicated?

24. Residential access: point to point Dialup via modem • up to 56Kbps direct access to router (often less) • Can not surf and phone at same time: can’t be “always on” ADSL: asymmetric digital subscriber line • up to 1 Mbps upstream (today typically 256 kbps) • up to 8 Mbps downstream (today typically 1.5 Mbps) • FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone • wireless LANs: • 802.11b/g (WiFi): 11 or 54 Mbps, @2.4 GHZ (range 100 m), • 802.11a 54 Mbps @ 5 GHz

25. Residential access: point to point Dialup via modem • up to 56Kbps direct access to router (often less) • Can not surf and phone at same time: can’t be “always on” ADSL: asymmetric digital subscriber line • up to 1 Mbps upstream (today typically 256 kbps) • up to 8 Mbps downstream (today typically 1.5 Mbps) • FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for ordinary telephone • wireless LANs: • 802.11b/g (WiFi): 11 or 54 Mbps, @2.4 GHZ (range 100 m), • 802.11a 54 Mbps @ 5 GHz

26. Physical media Twisted Pair (TP) • two insulated copper wires • Straight-through Cables: both ends are the same. Used to connect devices of different type • Crossover Cables: one end T568A and the other T568B. Used to connect devices of the same type