Introduction and Foundation CS565 Introduction & Foundation 1

Introduction & Foundation About the Book Computer Networks: A Systems Approach - Peterson& Davie (5th Edition) Core Concepts and Fundamental Principles - standards change - technology evolves How network works & how packet header are formatted CS565 Introduction & Foundation 2

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 CS565 Introduction & Foundation 3

Introduction & Foundation Expectations This class IS about... Principles and Concepts General-Purpose Computer Networks Internet Perspective Network Software Designing and Building a System CS565 Introduction & Foundation 4

Introduction & Foundation 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 CS565 Introduction & Foundation 5

Introduction & Foundation Requirements CS565 Introduction & Foundation 6

Connectivity: Building Blocks Nodes: PC, special-purpose hardware… hosts switches Data Links: coax cable, optical fiber… point-to-point multiple access … CS565 Introduction & Foundation 7

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 CS565 Introduction & Foundation 8

Introduction & Foundation The Cloud The Cloud c point-to-point multiple-access link Switched network Any other network covered in the book CS565 Introduction & Foundation 9

Introduction & Foundation LANs, MANs, WANs Local Area Network (LAN) – < 1 km Metropolitan Area Network (MAN) – tens of km Wide Area Network (WAN) – can be worldwide CS565 Introduction & Foundation 10

Introduction & Foundation 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 CS565 Introduction & Foundation 11

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 CS565 Introduction & Foundation 12

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 CS565 Introduction & Foundation 13

Introduction & Foundation 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 1 Switch 2 CS565 Introduction & Foundation 14

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 … CS565 Introduction & Foundation 15

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 Channel CS565 Introduction & Foundation 16

Introduction & Foundation IPC Abstractions Network supports common process-to-process channels. 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) = 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 CS565 Introduction & Foundation 17

Introduction & Foundation The vic Unix video application CS565 Introduction & Foundation

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. CS565 Introduction & Foundation 19

Introduction & Foundation Performance Metrics Bandwidth (throughput) data transmitted per time unit Link(physical) versus end-to-end(logical) notation KB = 210 Bytes (or 103 =1,000 Bytes) Mbps = 220 bits per second (or 106 =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 / c Speed of Light over that wire Transmit = Size / Bandwidth 3.0  108 m/s (Vacuum) 2.3  108 m/s (Cable) 2.0  108 m/s (Fiber) CS565 Introduction & Foundation 20

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 CS565 Introduction & Foundation 21

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) 100 2-KB object, 1.5-Mbps link 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 CS565 Introduction & Foundation

Delay x Bandwidth Product Amount of data “in flight” or “in the pipe” Example: 100ms x 45Mbps = 560KB CS565 Introduction & Foundation 23

Introduction & Foundation Network Architecture CS565 Introduction & Foundation 24

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 CS565 Introduction & Foundation 25

Introduction & Foundation 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 CS565 Introduction & Foundation 26

Introduction & Foundation Interfaces Host 1 Host 2 Service High-level High-level object interface object Protocol Protocol Peer-to-peer interface CS565 Introduction & Foundation 27

Introduction & Foundation 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 1 Host 2 File Digital Video Digital File Video 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 CS565 Introduction & Foundation 28

Introduction & Foundation 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 CS565 Introduction & Foundation 29

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 … FTP HTTP NV TFTP TCP UDP IP NET 1 2 n 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 CS565 Introduction & Foundation 30

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 CS565 Introduction & Foundation 31

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 message rather than a packet or frame Implements process-to-process channel Transport Transport The unit of data exchanged is typically called a packet rather 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 bits over a communication link Physical Physical Physical Physical One or more nodes within the network CS565 Introduction & Foundation 32