1. Univ. of TehranComputer Network1 Computer Networks Computer Networks (Graduate level) University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Lecture 1: Introduction

2. Univ. of TehranComputer Network2 Objectives of course Understand the state-of-the-art in network protocols, architectures and applications Understand how networking research is done and prepare student for research in networking. How is class different from undergraduate networking course Training network programmers vs. training network researchers

3. Univ. of TehranComputer Network3 Course Materials Course Web page visit regularly Research papers Printed papers or pdf/ps version on the Web page ~40 papers, Combination of classic and recent work. Some Optional reading! Recommended textbook “Computer Networks, A system approach. Peterson & Davie 2 nd edition

4. Univ. of TehranComputer Network4 Grading Homework assignments, around %20 Paper review Problems and hands-on assignments Severe late penalties! Class discussion, around 1 point. Project, ~ %25 Exam(s), Midterm and final, ~%50.

5. Univ. of TehranComputer Network5 Covered Topics Traditional Layering Interconnecting (LAN) Internet architecture Routing (IP) Switching Transport (TCP) Queue management (FQ, RED) Naming (DNS) Recent Topics Multicast Mobility Active networks QOS Security Network measurement

6. Univ. of TehranComputer Network6 A tour of networking Goal and objective needs design requirement Whirlwind tour of networking

7. Univ. of TehranComputer Network7 Information, Computers and Networks Information: anything that is represented in bits Form (can be represented) vs substance (cannot) Properties: Infinitely replicable Computers can “manipulate” information Networks create “access” to information Potential of networking: move bits everywhere, cheaply, and with desired performance characteristics Break the space barrier for information

8. Univ. of TehranComputer Network8 Objective of Networking ? Direct or indirect access to every other node in the network Connectivity is the magic needed to communicate if you do not have a link. Must understand many connection factors Traffic data rate Traffic pattern (bursty or constant bit rate) Traffic target (multipoint or single destination, mobile or fixed) Application requirements, Delay sensitivity Loss sensitivity.

9. Univ. of TehranComputer Network9 Another view Building a network to support diverse ranges of applications Distributed computing. Multimedia. Telecommunication. E-commerce, etc. What kind of technology do we need? Hardware. Software.

10. Univ. of TehranComputer Network10 What is a Network? What is computer Network? Different views. Differences from other networks, Its generality. What is requirements? Different perspective: Network provider Network designer Application programmer

11. Univ. of TehranComputer Network11 Design goals Connectivity Scalability Simplicity For designers. Most importantly for users. Efficiency cost performance Support for common user services.

12. Univ. of TehranComputer Network12 Levels of Networking Communicating across a link, LANs. Connecting together multiple links (Bridges) Finding and routing data to nodes on Internet. Communicating on the application level, matching application requirements

13. Univ. of TehranComputer Network13 A First Step Creating a link between nodes Link: path followed by bits Wired or wireless Broadcast or point-to-point (or both) Node: any device connected to a link

14. Univ. of TehranComputer Network14 Types of Links Point-to-PointMultiple Access …

15. Univ. of TehranComputer Network15 Packet Transmission Modes Unicast Transmission to single specific receiver Broadcast Transmission to all network nodes Multicast Transmission to specific subset of nodes Anycast Transmission to one of a specific subset of nodes

16. Univ. of TehranComputer Network16 Switched Network What are Switched Networks? Switch: moves bits between links Packet switching Circuit switching

17. Univ. of TehranComputer Network17 Back in the Old Days…

18. Univ. of TehranComputer Network18 Then Came TDM… Multiplex (mux)Demultiplex (demux) Synchronous time division multiplexing

19. Univ. of TehranComputer Network19 TDM Logical Network View

20. Univ. of TehranComputer Network20 Packet Switching (Internet) Packets

21. Univ. of TehranComputer Network21 Packet Switching Interleave packets from different sources Efficient: resources used on demand Statistical multiplexing General Multiple types of applications Accommodates bursty traffic Addition of queues

22. Univ. of TehranComputer Network22 Statistical Multiplexing Gain 1 Mbps link; users require 0.1 Mbps when transmitting; users active only 10% of the time Circuit switching: can support 10 users Packet switching: with 35 users, probability that >=10 are transmitting at the same time < 0.0017

23. Univ. of TehranComputer Network23 Characteristics of Packet Switching Store and forward Packets are self contained units Can use alternate paths - reordering Contention Congestion Delay

24. Univ. of TehranComputer Network24 Internet[work] Second Step: Internet[work] A collection of interconnected networks Host: network endpoints (computer, PDA, light switch, …) Router: node that connects networks Internet vs. internet

25. Univ. of TehranComputer Network25 Challenge Many differences between networks Address formats Performance – bandwidth/latency Packet size Loss rate/pattern handling Routing How to translate between various network technologies

26. Univ. of TehranComputer Network26 Third Step: How To Find Nodes? internet Computer 1Computer 2

27. Univ. of TehranComputer Network27 Naming Humans use readable host names E.g. www.cmu.eduwww.cmu.edu Globally unique (can correspond to multiple hosts) Naming system translates to physical address E.g. DNS translates name to IP Address (e.g. 128.2.11.43) Address reflects location in network

28. Univ. of TehranComputer Network28 Domain Name System What’s the IP address for www.cmu.edu? It is 128.2.11.43 DNS server address manually configured into OS Local DNS ServerComputer 1

29. Univ. of TehranComputer Network29 Packet Routing/Delivery Each network technology has different local delivery methods Address resolution provides delivery information within network E.g., ARP maps IP addresses to Ethernet addresses Local, works only on a particular network Routing protocol provides path through an internetwork

30. Univ. of TehranComputer Network30 Network:Address Resolution Protocol Ethernet Broadcast: who knows the Ethernet address for 128.2.11.43? Ethernet Broadcast: Yes, it is 08-00-2c-19-dc-45

31. Univ. of TehranComputer Network31 Internetwork: Datagram Routing R R R R R H H H H R R H R Routers send packet to next closest point H: Hosts R: Routers

32. Univ. of TehranComputer Network32 Routing Forwarding tables at each router populated by routing protocols. Original Internet: manually updated Routing protocols update tables based on “cost” Exchange tables with neighbors or everyone Use neighbor leading to shortest path

33. Univ. of TehranComputer Network33 Fourth Step: Application Demands Reliability Corruption Lost packets Flow and congestion control Fragmentation In-order delivery Etc…

34. Univ. of TehranComputer Network34 What if the Data gets Corrupted? Internet GET windex.htmlGET index.html Solution: Add a checksum Problem: Data Corruption 0,996,7,8214,571,2,36 X

35. Univ. of TehranComputer Network35 What if the Data gets Lost? Internet GET index.html Problem: Lost Data Internet GET index.html Solution: Timeout and Retransmit GET index.html

36. Univ. of TehranComputer Network36 What if Network is Overloaded? Problem: Network Overload Short bursts: buffer What if buffer overflows? Packets dropped and retransmitted Sender adjusts rate until load = resources Called “Congestion control” Solution: Buffering and Congestion Control

37. Univ. of TehranComputer Network37 Problem: Packet size Solution: Fragment data across packets What if the Data Doesn’t Fit? On Ethernet, max IP packet is 1.5kbytes Typical web page is 10kbytes GETindex.html GET index.html

38. Univ. of TehranComputer Network38 Solution: Add Sequence Numbers Problem: Out of Order What if the Data is Out of Order? GETx.thindeml GET x.thindeml GET index.html ml4inde2x.th3GET1

39. Univ. of TehranComputer Network39 Network Functionality Summary Link Multiplexing Routing Addressing/naming (locating peers) Reliability Flow control Fragmentation Etc….

40. Univ. of TehranComputer Network40 What is Layering? Modular approach to network functionality The idea of divide and conquer Use abstraction to hide complexity. Example: Link hardware Host-to-host connectivity Application-to-application channels Application

41. Univ. of TehranComputer Network41 Protocols Module in layered structure Set of rules governing communication between network elements (applications, hosts, routers) Protocols define: Interface to higher layers (API) Interface to peer Format and order of messages Actions taken on receipt of a message

42. Univ. of TehranComputer Network42 Protocols Building blocks of a network architecture Each protocol object has two different interfaces service interface: operations on this protocol peer-to-peer interface: messages exchanged with peer Term “protocol” is overloaded specification of peer-to-peer interface module that implements this interface

43. Univ. of TehranComputer Network43 Layering Characteristics Each layer relies on services from layer below and exports services to layer above Interface defines interaction Hides implementation - layers can change without disturbing other layers (black box)

44. Univ. of TehranComputer Network44 Layering Host Application Transport Network Link User AUser B Layering: technique to simplify complex systems

45. Univ. of TehranComputer Network45 Layer Encapsulation Get index.html Connection ID Source/Destination Link Address User AUser B

46. Univ. of TehranComputer Network46 Protocol Demultiplexing Multiple choices at each layer FTPHTTPTFTPNV TCPUDP IP NET 1 NET 2 NET n … TCP/UDPIP IPX Port Number Network Protocol Field Type Field

47. Univ. of TehranComputer Network47 E.g.: OSI Model: 7 Protocol Layers Physical: how to transmit bits Data link: how to transmit frames Network: how to route packets Transport: how to send packets end2end Session: how to tie flows together Presentation: byte ordering, security Application: everything else

48. Univ. of TehranComputer Network48 OSI Layers and Locations Switch Router Host Application Transport Network Data Link Presentation Session Physical

49. Univ. of TehranComputer Network49 Example: Transport Layer First end-to-end layer End-to-end state May provide reliability, flow and congestion control

50. Univ. of TehranComputer Network50 Example: Network Layer Point-to-point communication Network and host addressing Routing

51. Univ. of TehranComputer Network51 Is Layering Harmful? Sometimes.. Layer N may duplicate lower level functionality (e.g., error recovery) Layers may need same info (timestamp, MTU) Strict adherence to layering may hurt performance

52. Univ. of TehranComputer Network52 Class Coverage Brief coverage of physical and data link layer Focus on network to application layer We will deal with: Protocol rules and algorithms Investigate protocol trade-offs Why this way and not another?

53. Univ. of TehranComputer Network53 Next Lecture: Links How to make computers talk across a wire Assigned reading Chap. 2 of book (Recommended!)