Computer Network – OSI Model Mr. Zeeshan Ali, Asst. Professor

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1 Computer Network – OSI Model Mr. Zeeshan Ali, Asst. Professor
Department: B.E. Electronic & Telecommunication Subject: Internet & Voice Communication Semester: VIII Teaching Aids Service by KRRC Information Section

2 INTRODUCTION 7 Application 6 Presentation 5 Session 4 Transport
3 Network 2 Data Link 1 Physical

3 NETWORK GOALS 7 Application
The two main benefits of networking computers are… Communications Information can be distributed very quickly, such as and video conferencing. Saving Money Resources such as information, software, and hardware can be shared. CPUs and hard disks can be pooled together to create a more powerful machine. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

4 APPLICATIONS 7 Application
A lot of things we take for granted are the result of computer networks. Chat Web sites Sharing of documents and pictures Accessing a centralized database of information Mobile workers 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

5 NETWORK STRUCTURE 7 Application The subnet interconnects hosts.
Carries messages from host to host. It is made up of telecommunication lines (i.e. circuits, channels, trunks) and switching elements (i.e. IMPs, routers). Hosts End user machines or computers. Q: Is the host part of the subnet? 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

6 NETWORK ARCHITECTURES
7 Application NETWORK ARCHITECTURES A set of layers and protocols is called the network architecture. 1. Protocol Hierarchies Networks are organized as layers to reduce design complexity. Each layer offers services to the higher layers. Between adjacent layers is an interface. Services – connection oriented and connectionless. Interface – defines which primitives and services the lower layer will offer to the upper layer. Primitives – operations such as request, indicate, response, confirm. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

7 NETWORK ARCHITECTURES
7 Application NETWORK ARCHITECTURES 2. Design Issues for the Layers Mechanism for connection establishment Rules for data transfer Error control Fast sender swamping a slow receiver Inability of processes to accept long messages Routing in the case of multiple paths 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

8 OSI REFERENCE MODEL 7 Application
The Open Systems Interconnection is the model developed by the International Standards Organization. Benefits Interconnection of different systems (open) Not limited to a single vendor solution Negative Aspect Systems might be less secure Systems might be less stable 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

9 OSI REFERENCE MODEL 7 Application 1. Physical Layer 6 Presentation
a) Convert the logical 1’s and 0’s coming from layer 2 into electrical signals. b) Transmission of the electrical signals over a communication channel. Main topics: Transmission mediums Encoding Modulation RS232 and RS422 standards Repeaters Hubs (multi-port repeater) 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

10 OSI REFERENCE MODEL 7 Application 2. Data Link Layer 6 Presentation
a) Error control to compensate for the imperfections of the physical layer. b) Flow control to keep a fast sender from swamping a slow receiver. Main topics: Framing methods Error detection and correction methods Flow control Frame format IEEE LAN standards Bridges Switches (multi-port bridges) 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

11 OSI REFERENCE MODEL 7 Application 3. Network Layer 6 Presentation
a) Controls the operation of the subnet. b) Routing packets from source to destination. c) Logical addressing. Main topics: Internetworking Routing algorithms Internet Protocol (IP) addressing Routers 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

12 OSI REFERENCE MODEL 7 Application 4. Transport Layer 6 Presentation
a) Provides additional Quality of Service. b) Heart of the OSI model. Main topics: Connection-oriented and connectionless services Transmission Control Protocol (TCP) User Datagram Protocol (UDP) 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

13 OSI REFERENCE MODEL 7 Application 5. Session Layer 6 Presentation
a) Allows users on different machines to establish sessions between them. b) One of the services is managing dialogue control. c) Token management. d) Synchronization. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

14 OSI REFERENCE MODEL 7 Application 6. Presentation Layer 6 Presentation
a) Concerned with the syntax and semantics of the information. b) Preserves the meaning of the information. c) Data compression. d) Data encryption. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

15 OSI REFERENCE MODEL 7 Application 7. Application Layer 6 Presentation
a) Provides protocols that are commonly needed. Main topics: File Transfer Protocol (FTP) HyperText Transfer Protocol (HTTP) Simple Mail Transfer Protocol (SMTP) Simple Network Management Protocol (SNMP) Network File System (NFS) Telnet 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

16 7 Application SERVICES Each layer provides services to the layer above it. 1. Terminologies Entities – active elements in each layer (e.g. process, intelligent I/O chip). Peer Entities – entities in the same layer on different machines. Service Provider – Layer N. Service User – Layer N + 1. Service Access Points – places where layer N + 1 can access services offered by layer N. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

17 SERVICES 7 Application 2. Connection-Oriented and Connectionless
Connection-Oriented – before data is sent, the service from the sending computer must establish a connection with the receiving computer. Connectionless – data can be sent at any time by the service from the sending computer. Q: Is downloading a music file from the Internet connection-oriented or connectionless? Q: Is connection-oriented or connectionless? 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

18 SERVICES 7 Application 3. Service Primitives
Request – entity wants the service to do some work Indicate – entity is to be informed about an event Response – entity responds to an event Confirm – entity is to be informed about its request Sending Computer Receiving Computer 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 4 Transport 4 Transport 1 Physical 1. request 4. confirm 2. indicate 3. response 3 Network 3 Network

19 BANDWIDTH 7 Application The capacity of the medium to transmit data.
Analog Bandwidth Measurement is in Hertz (Hz) or cycles/sec. Digital Bandwidth Measurement is in bits per second (bps). Q: Is 100MHz = 100Mbps? Q: Is 100Mbps = 100MBps? 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

20 7 Application 6 Presentation 5 Session 4 Transport 3 Network
Hello 7 Application AH Hello 6 Presentation PH AH Hello 5 Session SH PH AH Hello 4 Transport TH SH PH AH Hello 3 Network NH TH SH PH AH Hello 2 Data Link DH NH TH SH PH AH Hello DT 1 Physical Bits

21 PHYSICAL LAYER 7 Application 6 Presentation 5 Session 4 Transport
3 Network 2 Data Link 1 Physical

22 OVERVIEW 7 Application Signals 6 Presentation Fourier analysis
Maximum data rate of a channel Transmission Media Guided and Unguided Analog Transmission Modulation Modems RS-232, RS-422 Digital Transmission Encoding schemes Repeaters and hubs Transmission and Switching Multiplexing (FDM and TDM) Circuit vs. packet switching 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

23 SIGNALS 7 Application 1. Fourier Analysis 6 Presentation
a) All signals can be represented mathematically. b) A periodic function can be constructed by adding a number of sine and cosine functions. Fundamental frequency – where f = 1/T Harmonics – integer multiples of the fundamental frequency Baud – number of signal level changes per second Q: Is baud and data rate different terms? Q: Is 1 baud equal to 1bps? 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

24 SIGNALS 7 Application 2. Maximum Data Rate of a Channel 6 Presentation
Nyquist Maximum data rate = 2H log2V (bits/sec) H = line bandwidth V = a signal with V discrete levels Example: A noiseless 3kHz channel cannot transmit binary (2 level) signals at a rate faster than 6000bps 2(3k) log22 = 6000bps 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link logAV = (1 / ln A) ln V 1 Physical

25 SIGNALS 7 Application Shannon 6 Presentation
Maximum data rate (bits/sec) = H log2(1+ PS/PN) H = line bandwidth PS = signal strength in watts PN = noise strength in watts Example: A 3kHz channel with a noise ratio of 30dB (PS/PN = 1000) cannot transmit at a rate faster than 30,000bps (3k) log2(1001) = 30,000bps Note: SNR = 10log10(PS/PN) 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

26 SIGNALS 7 Application 3. Attenuation vs. Amplification 6 Presentation
The signal received is weaker than the signal sent. Attenuation (dB) = 10log10(P1/P2) Amplification The signal received is stronger than the signal sent. Amplification (dB) = 10log10(P2/P1) Note: P1 = transmitted signal power in watts P2 = received signal power in watts Q: If the result of the attenuation formula is negative, what happened to the signal? 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

27 TRANSMISSION MEDIA 7 Application 1. Guided 6 Presentation
Data is sent via a wire or optical cable. Twisted Pair Two copper wires are twisted together to reduce the effect of crosstalk noise. (e.g. Cat5, UTP, STP) Baseband Coaxial Cable A 50-ohm cable used for digital transmission. Used in 10Base2 and 10Base5. Broadband Coaxial Cable A 75-ohm cable used for analog transmission such as Cable TV. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

28 TRANSMISSION MEDIA 7 Application Fiber Optic Cables 6 Presentation
Two general types are multimode and single mode. In multimode, light is reflected internally. Light source is an LED. In single mode, the light propagates in a straight line. Light source come from expensive laser diodes. Faster and longer distances as compared to multimode. * Fiber optic cables are difficult to tap (higher security) and are normally used for backbone cabling. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

29 TRANSMISSION MEDIA 7 Application 2. Unguided 6 Presentation
Data is sent through the air. Line-of-sight Transmitter and receiver must “see” each other, such as a terrestrial microwave system. Communication Satellites A big microwave repeater in the sky. Data is broadcasted, and can be “pirated.” Radio Term used to include all frequency bands, such as FM, UHF, and VHF television. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

30 ANALOG TRANSMISSION 7 Application 1. Modulation 6 Presentation
Modulating a sine wave carrier to convey data. Amplitude Modulation (AM) Amplitude is increased/decreased while frequency remains constant. Frequency Modulation (FM) Frequency is increased/decreased while amplitude remains constant. Phase Modulation Wave is shifted, while amplitude and frequency remains constant. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

31 ANALOG TRANSMISSION 7 Application 2. Modems 6 Presentation
A device that accepts digital signals and outputs a modulated carrier wave, and vice versa. It is used to interconnect the digital computer to the analog telephone network. * Modems for PC’s can be external or internal. * Nokia makes modems for leased line connections. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

32 ANALOG TRANSMISSION 7 Application 3. RS-232 and RS-449 6 Presentation
Two well known physical layer standards. RS-232 20 kbps Cables up to 15 meters Unbalanced transmission (common ground) RS-422 2 Mbps at 60 meters 1 Mbps at 100 meters Balanced transmission (a pair of wires for Tx, Rx) 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

33 DIGITAL TRANSMISSION 7 Application 1. Encoding Schemes 6 Presentation
Converting logical data into electrical signals suitable for transmission. Manchester Mid bit transition for clock synchronization and data Logic 0 = high to low transition Logic 1 = low to high transition Differential Manchester Mid bit transition for clock synchronization only Logic 0 = transition at the beginning of each bit period Logic 1 = no transition at the beginning of each bit period 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

34 DIGITAL TRANSMISSION 7 Application 2. Repeaters and Hubs
These are physical layer devices. Repeaters Restores the strength of an attenuated signal. Used to increase the transmission distance. Does not filter data traffic. Hubs Multi-port repeater. Interconnects several computers. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

35 NETWORK LAYER 7 Application 6 Presentation 5 Session 4 Transport
2 Data Link 1 Physical

36 OVERVIEW 7 Application Routing Algorithms 6 Presentation Shortest Path
Flooding Flow-based Distance Vector Link State Hierarchical Broadcast Multicast Routing for Mobile Hosts Congestion control IP Addressing Routers 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

37 ROUTING ALGORITHMS B 1 C 2 2 3 3 2 A D 1 F 1 2 2 E 7 Application
1. Shortest Path 6 Presentation C(B,3) B(A,2) 5 Session B 1 C 2 4 Transport 2 3 3 A(-,-) D(E,3) 2 A D F(E,4) 3 Network 1 F 1 E(A,2) 2 2 Data Link 2 E 1 Physical A – E – D – F A – E – F is the answer.

38 IMP B ROUTING ALGORITHMS 7 Application 2. Flooding 6 Presentation
Packet to IMP C 5 Session IMP B Packet Packet to IMP D 4 Transport Packet to IMP E To prevent packets from circulating indefinitely, a packet has a hop counter. Every time a packet arrives at an IMP, the hop counter is decrease by 1. Once the hop counter of a packet reaches 0, the packet is discarded. 3 Network 2 Data Link 1 Physical

39 IP ADDRESSING 7 Application Format 6 Presentation 5 Session
x x x x x x x x . x x x x x x x x . x x x x x x x x . x x x x x x x x where x is either 0 or 1 Example 1: Example 2: 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

40 IP ADDRESSING 7 Application Network Address 6 Presentation Example 1:
IP address of computer Mask Network address Example 2: Mask Network address Example 3: IP address of computer Mask 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

41 IP ADDRESSING 7 Application Mask 6 Presentation
Valid mask are contiguous 1’s from left to right. Examples: Valid Invalid 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

42 IP ADDRESSING 7 Application Subnets 6 Presentation
The Internet is running out of IP address. One solution is to subnet a network address. This is done by borrowing host bits to be used as network bits. Example: Class B mask Borrowing 1 bit gives a subnet mask of Borrowing 2 bits gives a subnet mask of Borrowing 3 bits gives a subnet mask of Borrowing 4 bits gives a subnet mask of 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

43 IP ADDRESSING 7 Application Example: 6 Presentation
Given an IP address of , subnet by borrowing 4 bits. Subnet mask = The 4 bits borrowed are value 128, 64, 32, 16. This will create 16 sub networks, where the first and last will be unusable. Sub network address: etc… 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

44 IP ADDRESSING 7 Application The first 3 usable sub networks are:
For sub network , the valid IP address are: to Directed broadcast address is: 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical

45 7 Application ROUTERS A layer 3 device that is used to interconnect 2 or more logical networks. Can filter broadcast traffic, preventing broadcast traffic from one network from reaching another network. 6 Presentation 5 Session 4 Transport 3 Network 2 Data Link 1 Physical