Data Communications and Networking

1. Data CommunicationsandNetworking Copy rights: Waleej Haider

4. Chapter 1. Introduction Data communications Networks The Internet Protocols and standards Copy rights: Waleej Haider

5. 1. Data Communications Data Information presented in whatever form, agreed upon by the parties who are creating and using the data Communication Sharing information Sharing can be local or remote Local Communication: usually occurs face to face Remote communication: takes place over distance (prime concern) Data Communication Exchange (sharing) of data between two devices Via some form of transmission medium (wired or wireless) Communication System includes: Hardware : Physical equipments/devices Software : Programs Copy rights: Waleej Haider

6. Cont.. Fundamental characteristics of effective data communication The effectiveness of a data Comm. System depends on 4 fundamental chars.: Delivery: Delivery of data to the correct and only that destination Accuracy: No loss of information/data Timeliness: Without significant delay & in the same order (audio/video) Jitter : Variation in the packet arrival time (uneven delay) Telecommunication: Communication at a distance (‘tele’ in Greek means “far”) using telephony, telegraphy, television, computer.

7. Data Communications The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point - The Mathematical Theory of Communication by Claude Shannon Copy rights: Waleej Haider

8. Five Components of Data Communication Message: Information (data) to be communicated (text, numbers, pics, audio, video) Sender: that sends the data message Receiver: that receives the message Transmission medium: Physical path by which a message travels Protocol: A set of rules that govern data communication. An agreement between the communicating devices. Without a protocol, two devices may be connected but not communicated Copy rights: Waleej Haider

9. A Communication Model (Digital bits to analog signals) (Analog signals to Digital bits)

10. Cont.. Source - generates data to be transmitted Transmitter - converts data into transmittable signals Transmission System - carries data from source to destination Receiver - converts received signals into data Destination - takes incoming data

11. Direction of Data Flow

12. Data Flow Simplex Unidirectional As on a one-way street Half-duplex Both transmit and receive possible, but not at the same time When there is no need for communication in both direction at the same time Like a one-lane road with two-directional traffic but at different times Entire capacity of the channel can be utilized for each direction Walkie-talkie, CB (citizens band) radio Full-duplex Transmit and receive simultaneously Like a two-way street; telephone network Channel capacity must be divided between two directions

13. 2. Networks Network: A set of devices (nodes) connected by communication links Node: Computer, printer, or any device capable of sending and/or receiving data Network Criteria: To be considered effective and efficient, a network must meet a number of criteria

14. Network Criteria Performance can be measured in: Transit time: amount of time required for a message to travel from one device to another Response time: elapsed time between an inquiry and a response More throughput (no. of bits/sec) Less delay Other factors: no. of users, type of medium, connected hardware, and efficiency of the software

15. Cont.. Reliability is measured by: Frequency of link failure Recovery time from a failure Network robustness in a crash Security issues include: Protecting data from unauthorized access Protecting data from damage Implementing policies for recovery from data losses

16. Type of Connection

17. Types of Connection • Point-to-point • Dedicated link between two devices • The entire capacity of the channel is reserved • Wired or wireless • Eg: Microwave or satellite link, link between TV and remote control • Multipoint • More than two devices share a single link • Capacity of the channel is shared either • Spatially shared: Several devices can use the link simultaneously (cable TV channels using diff freq. bandwidths) • Temporally shared: Users must take their turns, also called timeshared (telephone networks)

18. Physical Topology • Two or more devices connect to a link • Two or more links form a topology • A Method of physical (LAN) arrangement of computers/devices • The topology of a network is the geometric representation of the relationship of all the links and linking devices (nodes)

19. Mesh Topology Dedicated point-to-point link to every other nodes Dedicated link carries traffic only b/w the two devices it connects A mesh network with n nodes needs n(n-1)/2 links. As each node requires (n-1) I/O ports (links) Advantages: No traffic problems, robust, security, easy fault identification & isolation because of dedicated links Disadvantages: Difficult installation/reconfiguration, more space, expensive As it is expensive therefore used in limited fashion Mostly as a backbone connecting the main computers of a hybrid network that can include several other topologies

20. Star Topology Dedicated point-to-point link only from each device to a central controller, called a hub (or switch) Hub acts as an exchange-because no direct traffic between devices Advantages: Less expensive; robust; each device requires only one link that is only one I/O port therefore easy to install/reconfigure; easy fault identification and isolation Disadvantages: dependency of the whole on one single point, the hub; If hub goes down the whole system is dead High-speed LANs often use a star topology

21. Bus Topology Bus topology is multipoint One long cable acts as a backbone to link all nodes Nodes are connected by drop lines and taps to the bus cable Cable ends act as terminators that remove any signal from the bus Advantages: Easy installation; less cabling; cheap Disadvantages: Limited no. of devices and the distance b/w the devices; difficult reconfiguration (for new nodes) ; no fault isolation; a fault or break in the bus stops all transmissions; taps cause degradation in quality Less popular due to above disadvantages Flow of data

22. Ring Topology Each device has a dedicated point-to-point link with only the two devices on either side of it Signal is passed in one direction (clock or counter clockwise) from device to device until it reaches its destination e.g; using token passing access method Each device incorporates a repeater A repeater regenerates the bits and passes signals along if signals are intended for another device Advantages: Easy installation, reconfiguration, fault isolation Disadvantage: Unidirectional traffic, a break in the ring can disable the entire network Today, the need for higher speed LANs has made this topology less popular

23. Hybrid Topology Collection of more than one topology Used to share advantages from various topologies Example: Main star topology with each branch connecting several stations in a bus topology

24. Categories of Networks

25. LAN Usually privately owned A network for a single office, building, or campus  a few Kms (2kms) LANs are designed to share resources b/w PCs Resources can be a printer, a software, data, etc. Beside size, LANs are also distinguished from other networks by their transmission media and topology Common LAN topologies: Bus, Ring, Star, Mesh Data rate: 100 or 1000 Mbps Wired or Wireless LANs E.g; an isolated LAN connecting 12 computers to a hub in a closet

26. MAN A network with a size between LAN and WAN Designed to extend to an entire city or a town Topology: Hybrid Mainly used for Cable TV network; High speed internet (broadband); a company’s connected LANs, high speed DSL line provided by telephone company network Owned by a private or a public company

27. WAN Long distance transmission, e.g., a country, a continent, the world A WAN that is owned and used by one company is called Enterprise network Switched WAN: connects the end systems, which comprise a router that connects to another LAN or WAN (highlighted devices are switches) Router: used for connecting various networks ( LANs/MANs/WANs). It is an internetworking connecting device

28. WAN (cont..) Examples of Packets Switched WANs: X.25, Frame Relay, and ATM (are networks designed to provide connectivity b/w end users) Examples of Circuit Switched WANs: country wide PTCL network Point-to-point WAN: it is normally a line leased from a telephone or cable TV provider that connects a home computer or a small LAN to an internet service provider (ISP)– this type of WAN is mainly used for internet purpose Copy rights: Waleej Haider

29. Comparisons

30. Networking Tasks – phone net. sol’n • Addressing- identify the end user • phone number 1-201-222-2673 = country code + region code + exchange + number • Routing – Find route from source to destination. • determined from phone number by static routing tables • Forwarding– how information is moved • circuit switching::a fixed circuit along path to destination • Information Units - How information is sent • voice samples; no addressing attached • samples sent continuously , 8000/sec • network must prepare source-dest. circuit in advance

31. Networking Tasks – Internet Solution Addressing - identify the end user • IP addresses 132.66.48.37, = network number || host # Routing- How to get from source to destination • routers learn automatically network topology • build routing tables / updated frequently Forwarding – how information is moved • packet switching: move packets 1 by 1 through routers. Information Units - How information is sent. • self-descriptive packet = data + header • header contains destination address

32. Telephone networks support a high end-to-end quality of service, but is expensive Internet supports no quality of service but is flexible and cheap Future networks will have to support a wide range of service qualities at a reasonable cost

33. Internetwork Internetwork (internet) : Interconnection of networks ( LANs/MANs/WANs) The Internet: a specific worldwide network Network of networks two or more networks are connected to one another by internetworking devices Internetworking devices: router, gateway, etc.

34. What’s the Internet: “nuts and bolts” view A world-wide computer network, i.e., a network that interconnects millions of computing devices throughout the world. Mobile network PC access points router server Global ISP wired links wireless laptop cellular handheld Home network Regional ISP Institutional network • e.g. desktop PCs, Unix-based workstations, PDAs, TVs, mobile computers, cell phones, automobiles etc.

35. What’s the Internet: “nuts and bolts” view hosts = end systems are computers connected to the internet running network apps • End systems are connected by communication links • Fiber optics, coaxial cable, copper, radio, satellite • Different links can transmit data at different rates known as transmission rate(bits/sec) = bandwidth

36. What’s the Internet: “nuts and bolts” view protocolscontrol sending, receiving of msgs e.g., TCP, IP, HTTP, Skype, Ethernet Internet: “network of networks” loosely hierarchical public Internet versus private intranet Internet standards RFC: Request for comments IETF: Internet Engineering Task Force Mobile network Global ISP Home network Regional ISP Institutional network

37. What’s the Internet: a service view communication infrastructure enables distributed applications: Web, VoIP, email, games, e-commerce, file sharing communication services provided to apps: reliable data delivery from source to destination “best effort” (unreliable) data delivery

38. Internetwork Example There are 3 entities (2 LANs and 1 president office) For this heterogeneous network following are required: One switched WAN has been leased (country wide telephone network) 3 point-to-point WANs required to connect LANs to switched WAN

39. Internet Today • ISPs (Internet service providers) are local ISPs to provide direct service to the end users • RISPs (Regional ISPs) are mostly city wide ISPs • NISP (National ISP) is mostly country wide ISP • NAP (network access point) is a third party to connect all NISPs

40. What’s a protocol? human protocols: “what’s the time?” “I have a question” Introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

41. 4. Protocols Key elements of a protocol Syntax: Structure or format of data Semantics: meaning of each section of bits in the structure Timing: when data should be sent and how fast they can be sent

42. What’s a protocol? a human protocol and a computer network protocol: Got the time? 2:00 TCP connection response Get http://www.awl.com/kurose-ross <file> time Hi TCP connection request Hi

43. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge • end systems, access networks, links 1.3 Network core • circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History

44. 1.2 Network edge Computers and other devices connected to the Internet are often referred to as end systems (because they sit at the edge of the Internet). • desktop computers (e.g., desktop PCs, Macs, and Linux boxes), • servers (e.g., Web and e-mail servers), and • mobile computers (e.g., portable computers, PDAs, and phones with wireless Internet connections).

45. Continued… • End systems are also referred to as hosts because they host (that is, run) application programs : • Web browser program, a Web server program, an e-mail reader program, or an e-mail server program. • Two categories: clients (desktop and mobile PCs, PDAs, and so on ) and servers (machines that store and distribute Web pages, stream video, relay e-mail, and so on)

46. Client and Server Programs • A client program is a program running on one end system that requests and receives a service from a server program running on another end system. • The Web, e-mail, file transfer, remote login, newsgroups, and many other popular applications adopt the client- server model.

47. peer-to-peer (P2P) applications • Increasingly, many applications are peer-to-peer (P2P) applications, in which end systems interact and run programs that perform both client and server functions. • For example, in P2P file-sharing applications (such as BitTorrent and eMule), the program in the user's end system acts as a client when it requests a file from another peer; and the program acts as a server when it sends a file to another peer.

48. mesh of packet switches and links that interconnects the Internet's end systems. The fundamental question: how is data transferred through net? circuit switching packet-switching The Network Core

49. In circuit-switched networks, the resources needed along a path (buffers, link transmission rate) to provide communication between the end systems are reserved for the duration of the communication session between the end-systems. E.g. telephone net • In packet-switched networks, these resources are not reserved; a session's messages use the resources on demand, and as a consequence, may have to wait (that is, queue) for access to a communication link. E.g. Internet

50. Circuit Switching • In this network, the four circuit switches are interconnected by four links. • Each of these links has n circuits, so that each link can support n simultaneous connections. • The hosts are each directly connected to one of the switches. • When two hosts want to communicate, the network establishes a dedicated end-to-end connection between the two hosts. E.g. Conference calls between A and B.