1. CS380 Intro. to Comp. Networks Introduction & Foundation1 Introduction and Foundation

2. CS380 Intro. to Comp. Networks Introduction & Foundation2 Outline - About the book - Requirements  Statistical Multiplexing  Inter-Process Communication  Performance Metrics - Network Architecture  Layering & Protocols  Internet Architecture  OSI Architecture

3. CS380 Intro. to Comp. Networks Introduction & Foundation3 About the Book Computer Networks: A Systems Approach - Peterson& Davie (3 rd Edition) Core Concepts and Fundamental Principles - standards change - technology evolves How network works & how packet header are formatted

4. CS380 Intro. to Comp. Networks Introduction & Foundation4 About the Book Each Chapter begins with a problem statement Shaded sidebars - elaborate/introduce related topics(advanced) Highlighted paragraphs - very important info you should know Open Issues / Conclusion - research issues, commercial, or society Recommended Reading

5. CS380 Intro. to Comp. Networks Introduction & Foundation5 Most other Computer Network books Application Presentation Session Transport End host One or more nodes within the network Network Data link Physical Network Data link Physical Network Data link Physical Application Presentation Session Transport End host Network Data link Physical Organized according to layered model given by ISO (International Standards Organization) OSI (Open Systems Interconnection) Architecture - Partitioning of network functionality into 7 layers - Not a Protocol Graph - A reference model for a protocol graph

6. CS380 Intro. to Comp. Networks Introduction & Foundation6 About our Book - Most fundamental issues of networking involve more than one OSI layer. - A book organized strictly according to a layered model has some of the attributes of spaghetti code.Network Requirements and Architecture - This book organize discussion of fundamental concepts in a way that is independent of layering. (layer independent)

7. CS380 Intro. to Comp. Networks Introduction & Foundation7 About our Book Foundation (Chap 1) - Network Requirements and Architecture - Implementation Direct Link Networks (Chap 2) - Hardware, Encoding, Framing, Error Detection - Reliable Transmission, Ethernet, Token Ring, Wireless Network Packet Switching (Chap 3) - Switching and Forwarding - Bridges and Switches

8. CS380 Intro. to Comp. Networks Introduction & Foundation8 About the Book Internetworking (Chap 4) - Simple Internetworking, Routing - Global Internet, Multicast End-to-End Protocols (Chap 5) - UDP, TCP, RPC Congestion Control and Resources Allocation (Chap 6) - Resource Allocation, Queuing Discipline - Congestion Control and Avoidance

9. CS380 Intro. to Comp. Networks Introduction & Foundation9 About the Book End-to-End Data (Chap 7) - Presentation Formatting - Data Compression Network Security (Chap 8) - Cryptography - Security Mechanisms, Firewalls Applications (Chap 9) - DNS, SMTP, HTTP, SNMP

10. CS380 Intro. to Comp. Networks Introduction & Foundation10 Expectations This class IS about... –Principles and Concepts –General-Purpose Computer Networks –Internet Perspective –Network Software –Designing and Building a System –Hands-on experience on Switches and Routers ( CS Network Lab, 3-127)

11. CS380 Intro. to Comp. Networks Introduction & Foundation11 This class IS NOT about... –Survey of existing protocol standards –Specialized networks (e.g., CATV, telephone) –OSI Perspective –Network Hardware (we do survey) –Queuing Theory Expectations

12. CS380 Intro. to Comp. Networks Introduction & Foundation12 Perspective Network users: services that their applications need, e.g., guarantee that each message it sends will be delivered without error within a certain amount of time Network designers: cost-effective design e.g., that network resources are efficiently utilized and fairly allocated to different users Network providers: system that is easy to administer and manage e.g., that faults can be easily isolated and it is easy to account for usage

13. CS380 Intro. to Comp. Networks Introduction & Foundation13 Requirements

14. CS380 Intro. to Comp. Networks Introduction & Foundation14 Connectivity: Building Blocks Nodes: PC, special-purpose hardware… –hosts –switches Data Links: coax cable, optical fiber… –point-to-point –multiple access …

15. CS380 Intro. to Comp. Networks Introduction & Foundation15 Indirect Connectivity: Switched Networks –two or more nodes connected by a link, or –two or more networks connected by two or more nodes A network can be defined recursively as... Nodes forwards data received on one link out on another

16. CS380 Intro. to Comp. Networks Introduction & Foundation16 The Cloud –c–c –point-to-point –multiple-access link –Switched network –Any other network covered in the book The Cloud

17. CS380 Intro. to Comp. Networks Introduction & Foundation17 SANs, LANs, MANs, WANs Local Area Network (LAN) – < 1 km Metropolitan Area Network (MAN) – tens of km Wide Area Network (WAN) – can be worldwide System Area Network (SAN) – same room - SAN sometimes defined as storage area network

18. CS380 Intro. to Comp. Networks Introduction & Foundation18 Switching Strategies Circuit switching: dedicated circuit; dedicated circuit; send/receive a bit stream –Original telephone network Packet switching: store-and-forward messages, send/receive messages (packets) –Computer networks, Internet

19. CS380 Intro. to Comp. Networks Introduction & Foundation19 Packet-Switched Networks Nodes in such a network send discrete blocks to each other. We call each block of data either a packet or a message. These blocks of data corresponds to application data such as –A file –A piece of email –An image

20. CS380 Intro. to Comp. Networks Introduction & Foundation20 Addressing and Routing Address: byte-string that identifies a node –usually unique Routing: process of forwarding messages to the destination node based on its address Types of addresses –unicast: node-specific –broadcast: all nodes on the network –multicast: some subset of nodes on the network

21. CS380 Intro. to Comp. Networks Introduction & Foundation21 Multiplexing Cost-Effective Resource Sharing: –Must share (multiplex) network resources (nodes and links) among multiple users. Two Common Multiplexing Strategies: –Time-Division Multiplexing (TDM) –Frequency-Division Multiplexing (FDM) L1 L2 L3 R1 R2 R3 Switch 1Switch 2

22. CS380 Intro. to Comp. Networks Introduction & Foundation22 Statistical Multiplexing On-demand time-division rather than fixed Schedule link on a per-packet basis Packets from different sources interleaved on link Buffer packets that are contending for the link Buffer (queue) overflow is called congestion …

23. CS380 Intro. to Comp. Networks Introduction & Foundation23 Inter-Process Communication Application programs running on the hosts connected to the network must be able to communicate in a meaningful way. Turn host-to-host connectivity into process-to-process communication. Fill gap between what applications expect and what the underlying technology provides. Host Application Host Application Host Channel

24. CS380 Intro. to Comp. Networks Introduction & Foundation24 IPC Abstractions Request/Reply –distributed file systems –digital libraries (web) –Client: process requests access (read/write) to a file –Server: process that supports access to the file –Examples: FTP (File Transfer Protocol) NFS (Network File System) Stream-Based –video: sequence of frames 1/4 NTSC(standard TV image) = 352 x 240 pixels (resolution) 24-bits color for each pixel for each frame: (352 x 240 x 24)/8,= 247.5KB frame rate: 30 fps total  7500KBps = 60Mbps –video applications on-demand video video conferencing Network supports common process-to-process channels.

25. CS380 Intro. to Comp. Networks Chapter 1, Figure 7Introduction & Foundation The vic Unix video application

26. CS380 Intro. to Comp. Networks Introduction & Foundation26 What Goes Wrong in the Network? Bit-level errors (electrical interference) Packet-level errors (congestion) Link and node failures Messages are delayed Messages are out-of-order Third parties eavesdrop The key problem is to fill in the gap between what applications expect and what the underlying technology provides.

27. CS380 Intro. to Comp. Networks Introduction & Foundation27 Performance Metrics Bandwidth (throughput) –data transmitted per time unit –Link(physical) versus end-to-end(logical) –notation KB = 2 10 Bytes (or 10 3 =1,000 Bytes) Mbps = 2 20 bits per second (or 10 6 =1,000,000 bits per seconds) Latency (delay) –time to send message from point A to point B –one-way versus round-trip time (RTT) –components Latency = Propagation + Transmit + Queue Propagation = Distance / cSpeed of Light over that wire Transmit = Size / Bandwidth 3.0  10 8 m/s (Vacuum) 2.3  10 8 m/s (Cable) 2.0  10 8 m/s (Fiber)

28. CS380 Intro. to Comp. Networks Introduction & Foundation28 Bandwidth versus Latency Relative importance –1-byte message: latency dominates bandwidth 1ms  100ms (RTT) is important & 1Mbps  100Mbps (Bandwidth) is not –25MB image: bandwidth dominates latency 1Mbps  100Mbps (Bandwidth) is important & 1ms  100ms(RTT) is not

29. CS380 Intro. to Comp. Networks Introduction & Foundation 10,000 5000 2000 1000 500 200 100 50 20 10 5 2 1 10010 RTT (ms) 1-MB object, 1.5-Mbps link 1-MB object, 10-Mbps link 2-KB object, 1.5-Mbps link 2-KB object, 10-Mbps link 1-byte object, 1.5-Mbps link 1-byte object, 10-Mbps link Perceived latency (ms) Perceived Latency (Response Time) Versus RTT Chapter 1, Figure 9

30. CS380 Intro. to Comp. Networks Introduction & Foundation30 Delay x Bandwidth Product Amount of data “in flight” or “in the pipe” Example: 100ms x 45Mbps = 560KB

31. CS380 Intro. to Comp. Networks Introduction & Foundation31 Network Architecture

32. CS380 Intro. to Comp. Networks Introduction & Foundation32 Layering Use abstractions to hide complexity Abstraction naturally lead to layering Can have alternative abstractions at each layer e.g. at Process-to-process channels layer Request/reply channel Message stream channel Application programs Hardware Host-to-host connectivity

33. CS380 Intro. to Comp. Networks Introduction & Foundation33 Protocols Building blocks of a network architecture Each protocol object has two different interfaces –service interface: defines operations on this protocol –peer-to-peer interface: defines messages exchanged with peer Term “protocol” is overloaded –specification of peer-to-peer interface –module that implements this interface

34. CS380 Intro. to Comp. Networks Introduction & Foundation34 Host 1 Protocol Host 2 Protocol High-level object High-level object Service interface Peer-to-peer interface Interfaces

35. CS380 Intro. to Comp. Networks 35 Protocol Machinery Protocol Graph –collection of protocols and their dependencies –most peer-to-peer communication is indirect –peer-to-peer is direct only at hardware level File application Digital library application Video application RRPMSP HHP Host 1 File application Digital library application Video application RRPMSP HHP Host 2 RRP - Request/Reply Protocol MSP - Message Stream Protocol HHP – Host-to-Host Protocol

36. CS380 Intro. to Comp. Networks 36 Machinery (cont) Multiplexing and Demultiplexing (demux key) Encapsulation (header/body) RRPDataHHP Application program Application program Host 1Host 2 Data RRP Data HHP Data RRP Data HHP

37. CS380 Intro. to Comp. Networks Introduction & Foundation37 Internet Architecture Evolved out of experiences with ARPANET (Advanced Research Projects Agency) Defined by IETF (Internet Engineering Task Force) Hourglass Design Application vs Application Protocol (FTP, HTTP) … FTPHTTPNV TFTP TCP UDP IP NET 1 2 n Application Network Application Protocol HTTP – Hypertext Transport Protocol TFTP – Trivial File Transfer Protocol End-to-end Protocol or Transport Protocol TCP- Transmission Control Protocol UDP – User Datagram Protocol Offers channel abstraction to application programs Supports the interconnection of multiple network technologies into a single logical internetwork

38. CS380 Intro. to Comp. Networks Introduction & Foundation38 Standard Architectures Open Systems Interconnect (OSI) Architecture –International Standards Organization (ISO) –International Telecommunications Union (ITU) –ISO, usually in conjunction with ITU, publishes a series of protocol specification based on the OSI architecture –a “Reference Model” for a protocol graph

39. CS380 Intro. to Comp. Networks Introduction & Foundation39 OSI Architecture (Open Systems Interconnection) Application Presentation Session Transport End host One or more nodes within the network Network Data link Physical Network Data link Physical Network Data link Physical Application Presentation Session Transport End host Network Data link Physical Handles raw bits over a communication link Collects a stream of bits into a larger aggregate called a frame The unit of data exchanged is typically called a packet rather than a frame The unit of data exchanged is commonly called message rather than a packet or frame Handles routing among nodes within a packet- switched network Implements process- to-process channel The transport layer and higher layers typically run only on the end hosts but not on the intermediate switches or routes - - Partitioning of network functionality into 7 layers - Not a Protocol Graph -A reference model for a protocol graph