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Introduction and Foundation

Introduction and Foundation. Outline - About the book - Requirements Statistical Multiplexing Inter-Process Communication Performance Metrics - Network Architecture Layering & Protocols Internet Architecture OSI Architecture. About the Book. Computer Networks: A Systems Approach

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Introduction and Foundation

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  1. IntroductionandFoundation Introduction & Foundation

  2. Outline - About the book - Requirements Statistical Multiplexing Inter-Process Communication Performance Metrics - Network Architecture Layering & Protocols Internet Architecture OSI Architecture Introduction & Foundation

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

  4. 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 Introduction & Foundation

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

  6. 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) Introduction & Foundation

  7. 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 Introduction & Foundation

  8. 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 Introduction & Foundation

  9. 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 Introduction & Foundation

  10. 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) Introduction & Foundation

  11. Expectations • 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 Introduction & Foundation

  12. 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 Introduction & Foundation

  13. Requirements Introduction & Foundation

  14. … Connectivity: Building Blocks • Nodes: PC, special-purpose hardware… • hosts • switches • Data Links: coax cable, optical fiber… • point-to-point • multiple access Introduction & Foundation

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

  16. The Cloud • The Cloud • c • point-to-point • multiple-access link • Switched network • Any other network covered in the book Introduction & Foundation

  17. 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 Introduction & Foundation

  18. 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 Introduction & Foundation

  19. 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 Introduction & Foundation

  20. 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 Introduction & Foundation

  21. L1 R1 L2 R2 Switch 1 Switch 2 L3 R3 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) Introduction & Foundation

  22. 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 … Introduction & Foundation

  23. Host Host Application Host Channel Application Host Host 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. Introduction & Foundation

  24. IPC Abstractions Network supports common process-to-process channels. • Stream-Based • video: sequence of frames • 1/4 NTSC(standard TV image) = 352x240 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 • 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) Introduction & Foundation

  25. The vic Unix video application Chapter 1, Figure 7Introduction & Foundation

  26. 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. Introduction & Foundation

  27. Performance Metrics • Bandwidth (throughput) • data transmitted per time unit • Link(physical) versus end-to-end(logical) • notation • KB = 210Bytes (or 103 =1,000 Bytes) • Mbps = 220bits per second (or 106 =1,000,000bits 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  108m/s (Vacuum) 2.3  108m/s (Cable) 2.0  108m/s (Fiber) Introduction & Foundation

  28. 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 Introduction & Foundation

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

  30. Delay x Bandwidth Product • Amount of data “in flight” or “in the pipe” • Example: 100ms x 45Mbps = 560KB Introduction & Foundation

  31. Network Architecture Introduction & Foundation

  32. 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 Application programs Request/reply Message stream channel channel Host-to-host connectivity Hardware Introduction & Foundation

  33. 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 Introduction & Foundation

  34. Interfaces Host1 Host2 Service High-level High-level interface object object Protocol Protocol Peer-to-peer interface Introduction & Foundation

  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 Host 2 Host 1 Digital Digital Video Video File File library library application application application application application application RRP MSP RRP MSP HHP HHP RRP - Request/Reply Protocol MSP - Message Stream Protocol HHP – Host-to-Host Protocol

  36. Machinery (cont) • Multiplexing and Demultiplexing (demux key) • Encapsulation (header/body) Host 1 Host 2 Application Application program program Data Data RRP RRP RRP Data RRP Data HHP HHP HHP RRP Data

  37. FTP HTTP NV TFTP UDP TCP IP … NET NET NET 2 1 n 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) Application • 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 Network Introduction & Foundation

  38. 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 Introduction & Foundation

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

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