Introduction To Computer Networks

1. Introduction To Computer Networks Presented By Md. Asadul Islam Lecturer,Dept. Of CSE,KUET

2. Referances • Computer Networking • By F.Kuross & W.Ross • Computer Networks • By Tanenbaum • Data Communication and Networking • By A.Forouzan • And WWW.

3. Network • A network can be defined as a number of autonomus device connected together in such a way that they can share resources. • The purpose of a network is to share resources • A resource may be: • A file • A folder • A printer • A disk drive • Or just about anything else that exists on a computer.

4. Network(More defination) • A network is simply a collection of computers or other hardware devices that are connected together, either physically or logically, using special hardware and software, to allow them to exchange information and cooperate. • Networking is the term that describes the processes involved in designing, implementing, upgrading, managing and otherwise working with networks and network technologies.

5. Applications of Networks • Resource Sharing • Hardware (computing resources, disks, printers) • Software (application software) • Information Sharing • Easy accessibility from anywhere (files, databases) • Search Capability (WWW) • Connectivity and Communication • Email • Message broadcast • Remote computing • Distributed processing (GRID Computing) or Performance Enhancement and Balancing • Internet Access • Data Security and Management • Entertainment

6. Fundamental Network Classifications Local Area Networks (LANs): • A local area network (LAN) is a computer network covering a small geographic area, like a home, office, or group of buildings Metropolitan Area Network (MAN): • Network in a City is call MAN (Metropolitan Area Network) • Covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). • It is also used to mean the interconnection of several local area networks by bridging them with backbone lines. Wide Area Networks (WANs): • Network spread geographically (Country or across Globe) is called WAN (Wide Area Network) • A network that uses routers and public communications links • The largest and most well-known example of a WAN is the Internet. • WANs are used to connect LANs and other types of networks together.

7. 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

8. Network Topology • Defines the way in which computers, printers, and other devices are connected. • Describes the layout of the wire and devices as well as the paths used by data transmissions.

9. Bus Topology • A bus is the simplest physical topology. It consists of a single cable that runs to every workstation • This topology uses the least amount of cabling, but also covers the shortest amount of distance. • Each computer shares the same data and address path. With a logical bus topology, messages pass through the trunk, and each workstation checks to see if the message is addressed to itself. If the address of the message matches the workstation’s address, the network adapter copies the message.

10. Star & Tree Topology • The star topology is the most commonly used architecture in Ethernet LANs. • When installed, the star topology resembles spokes in a bicycle wheel. • Larger networks use the extended star topology also called tree topology. When used with network devices that filter frames or packets, like bridges, switches, and routers, this topology significantly reduces the traffic on the wires by sending packets only to the wires of the destination host. Star Topology Tree Topology

11. Ring Topology • A frame travels around the ring, stopping at each node. If a node wants to transmit data, it adds the data as well as the destination address to the frame. • The frame then continues around the ring until it finds the destination node, which takes the data out of the frame. • Single ring – All the devices on the network share a single cable • Dual ring – The dual ring topology allows data to be sent in both directions. Ring Topology Dual Ring Topology

12. Mesh Topology • The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. • It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. • Implementing the mesh topology is expensive and difficult. Mesh Topology

13. Topology(cont.) Advantages and Disadvantages of Network Topologies

14. Intranet, Internet & Extranet • Internet: • Is a worldwide system of computer networks • The Internet is an open, public space. • Intranet: • An intranet is a private network • that is contained within an enterprise. • It may consist of many interlinked local area networks and also use leased lines in the wide area network. • An intranet may be accessible from the Internet, but as a rule it's protected by a password and accessible only to employees or other authorized users. • Extranet: • Is a portion of an organization's Intranet • accessible to authorized outside users without full access to an entire organization's intranet.

15. millions of connected computing devices: hosts = end systems running network apps PC Mobile network server Global ISP wireless laptop cellular handheld Home network Regional ISP access points wired links Institutional network router What’s the Internet: “nuts and bolts” view • communication links • fiber, copper, radio, satellite • transmission rate = bandwidth • routers: forward packets (chunks of data)

16. 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 What’s the Internet: “nuts and bolts” view Introduction

17. 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 What’s the Internet: a service view Introduction

18. Protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt a human protocol and a computer network protocol: TCP connection response Get http://www.awl.com/kurose-ross Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection request Hi Q: Other human protocols? Introduction

19. network edge: applications and hosts A closer look at network structure • access networks, physical media: wired, wireless communication links • network core: • interconnected routers • network of networks Introduction

20. end systems (hosts): run application programs e.g. Web, email at “edge of network” peer-peer client/server The network edge: • client/server model • client host requests, receives service from always-on server • e.g. Web browser/server; email client/server • peer-peer model: • minimal (or no) use of dedicated servers • e.g. Skype, BitTorrent Introduction

21. Bit: propagates betweentransmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5: 100Mbps Ethernet Physical Media Introduction

22. Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channels on cable HFC Physical Media: coax, fiber Fiber optic cable: • glass fiber carrying light pulses, each pulse a bit • high-speed operation: • high-speed point-to-point transmission (e.g., 10’s-100’s Gps) • low error rate: repeaters spaced far apart ; immune to electromagnetic noise Introduction

23. signal carried in electromagnetic spectrum no physical “wire” bidirectional propagation environment effects: reflection obstruction by objects interference Physical media: radio Radio link types: • terrestrial microwave • e.g. up to 45 Mbps channels • LAN (e.g., Wifi) • 11Mbps, 54 Mbps • wide-area (e.g., cellular) • 3G cellular: ~ 1 Mbps • satellite • Kbps to 45Mbps channel (or multiple smaller channels) • 270 msec end-end delay • geosynchronous versus low altitude Introduction

24. mesh of interconnected routers the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks” The Network Core Introduction

25. End-end resources reserved for “call” link bandwidth, switch capacity dedicated resources: no sharing circuit-like (guaranteed) performance call setup required Network Core: Circuit Switching Introduction

26. network resources (e.g., bandwidth) divided into “pieces” pieces allocated to calls resource piece idle if not used by owning call (no sharing) dividing link bandwidth into “pieces” frequency division: total frequency bands are divided into several users eg : television broad casting time division: total available time is divided into several user eg: telephone system wdm: Total wave lengnth is divided in to number of users eg: optical networking Network Core: Circuit Switching Introduction

27. Example: 4 users FDM frequency time TDM frequency time Circuit Switching: FDM and TDM Introduction

28. Numerical example • How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? • All links are 1.536 Mbps • Each link uses TDM with 24 slots/sec • 500 msec to establish end-to-end circuit Let’s work it out! Introduction

29. each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed Bandwidth division into “pieces” Dedicated allocation Resource reservation Network Core: Packet Switching resource contention: • aggregate resource demand can exceed amount available • congestion: packets queue, wait for link use • store and forward: packets move one hop at a time • Node receives complete packet before forwarding Introduction

30. Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand  statistical multiplexing. TDM: each host gets same slot in revolving TDM frame. D E Packet Switching: Statistical Multiplexing 100 Mb/s Ethernet C A statistical multiplexing 1.5 Mb/s B queue of packets waiting for output link Introduction

31. takes L/R seconds to transmit (push out) packet of L bits on to link at R bps store and forward: entire packet must arrive at router before it can be transmitted on next link delay = 3L/R (assuming zero propagation delay) Example: L = 7.5 Mbits R = 1.5 Mbps transmission delay = 15 sec Packet-switching: store-and-forward L R R R more on delay shortly … Introduction

32. 1 Mb/s link each user: 100 kb/s when “active” active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active at same time is less than .0004 Packet switching allows more users to use network! Packet switching versus circuit switching N users 1 Mbps link Q: how did we get value 0.0004? Introduction

33. Packet-switching: Pipelining Discard error packet Carry packet header Network Core: Packet Switching

34. Differences Between Circuit & Packet Switching

35. Types of ISPs Tier3 • Tier-1 ISPs: Backbone networks • Tier-2 ISPs: National coverage • Tier-3 ISPs: Directly attached to customers Tier2 P P Tier1 P P P P P P P P P ISP Interconnection of ISP

36. packets experience delay on end-to-end path four sources of delay at each hop nodal processing: check bit errors determine output link queueing time waiting at output link for transmission depends on congestion level of router transmission A propagation B nodal processing queueing Delay in packet-switched networks

37. Transmission delay: R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) propagation delay = d/s transmission A propagation B nodal processing queueing Delay in packet-switched networks Note: s and R are very different quantitites!

38. R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate Queueing delay (revisited) traffic intensity = La/R • La/R ~ 0: average queueing delay small • La/R -> 1: delays become large • La/R > 1: more “work” arriving than can be serviced, average delay infinite!

39. Why layering? Dealing with complex systems: • explicit structure allows identification, relationship of complex system’s pieces • layered reference model for discussion • modularization eases maintenance, updating of system • change of implementation of layer’s service transparent to rest of system • e.g., change in gate procedure doesn’t affect rest of system • layering considered harmful? Introduction

40. application: supporting network applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP network: routing of datagrams from source to destination IP, routing protocols link: data transfer between neighboring network elements PPP, Ethernet physical: bits “on the wire” application transport network link physical Internet protocol stack Introduction

41. presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventions session: synchronization, checkpointing, recovery of data exchange Internet stack “missing” these layers! these services, if needed, must be implemented in application needed? Application Presentation session Transport Network link physical ISO/OSI reference model Introduction

42. TCP/IP Referances Model

43. network link physical link physical M M M Ht M Hn Hn Hn Hn Ht Ht Ht Ht M M M M Ht Ht Hn Hl Hl Hl Hn Hn Hn Ht Ht Ht M M M source Encapsulation message application transport network link physical segment datagram frame switch destination application transport network link physical router Introduction