6/10/2015 Unit-1 : Data Communications 1 CS 1302 Computer Networks — Unit - 1 — — Data Communications — Text Book Behrouz.A. Forouzan, “Data communication and Networking”, Tata McGrawHill, 2004
Overview of Data Communications and Networking 6/10/20152Unit-1 : Data Communications
Overview 6/10/20153Unit-1 : Data Communications
Introduction 6/10/20154Unit-1 : Data Communications
1.1 Data Communication Components Data Representation Direction of Data Flow 6/10/20155Unit-1 : Data Communications
Figure 1.1 Five components of data communication 6/10/20156Unit-1 : Data Communications
Figure 1.2 Simplex 6/10/20157Unit-1 : Data Communications
Figure 1.3 Half-duplex 6/10/20158Unit-1 : Data Communications
Figure 1.4 Full-duplex 6/10/20159Unit-1 : Data Communications
1.2 Networks Distributed Processing Network Criteria Physical Structures Categories of Networks 6/10/201510Unit-1 : Data Communications
Figure 1.5 Point-to-point connection 6/10/201511Unit-1 : Data Communications
Figure 1.6 Multipoint connection 6/10/201512Unit-1 : Data Communications
Figure 1.7 Categories of topology 6/10/201513Unit-1 : Data Communications
Figure 1.8 Fully connected mesh topology (for five devices) 6/10/201514Unit-1 : Data Communications
Figure 1.9 Star topology 6/10/201515Unit-1 : Data Communications
Figure 1.10 Bus topology 6/10/201516Unit-1 : Data Communications
Figure 1.11 Ring topology 6/10/201517Unit-1 : Data Communications
Figure 1.12 Categories of networks 6/10/201518Unit-1 : Data Communications
Figure 1.13 LAN 6/10/201519Unit-1 : Data Communications
Figure 1.13 LAN (Continued) 6/10/201520Unit-1 : Data Communications
Figure 1.14 MAN 6/10/201521Unit-1 : Data Communications
Figure 1.15 WAN 6/10/201522Unit-1 : Data Communications
1.3 The Internet A Brief History The Internet Today 6/10/201523Unit-1 : Data Communications
Figure 1.16 Internet today 6/10/201524Unit-1 : Data Communications
1.4 Protocols and Standards Protocols Standards Standards Organizations Internet Standards 6/10/201525Unit-1 : Data Communications
Network Models 6/10/201526Unit-1 : Data Communications
2.1 Layered Tasks Sender, Receiver, and Carrier Hierarchy Services 6/10/201527Unit-1 : Data Communications
Figure 2.1 Sending a letter 6/10/201528Unit-1 : Data Communications
2.2 Internet Model Peer-to-Peer Processes Functions of Layers Summary of Layers 6/10/201529Unit-1 : Data Communications
Figure 2.2 Internet layers 6/10/201530Unit-1 : Data Communications
Figure 2.3 Peer-to-peer processes 6/10/201531Unit-1 : Data Communications
Figure 2.4 An exchange using the Internet model 6/10/201532Unit-1 : Data Communications
Figure 2.5 Physical layer 6/10/201533Unit-1 : Data Communications
The physical layer is responsible for transmitting individual bits from one node to the next. Note: 6/10/201534Unit-1 : Data Communications
Figure 2.6 Data link layer 6/10/201535Unit-1 : Data Communications
The data link layer is responsible for transmitting frames from one node to the next. Note: 6/10/201536Unit-1 : Data Communications
Figure 2.7 Node-to-node delivery 6/10/201537Unit-1 : Data Communications
Example 1 In Figure 2.8 a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection 6/10/201538Unit-1 : Data Communications
Figure 2.8 Example 1 6/10/201539Unit-1 : Data Communications
Figure 2.9 Network layer 6/10/201540Unit-1 : Data Communications
The network layer is responsible for the delivery of packets from the original source to the final destination. Note: 6/10/201541Unit-1 : Data Communications
Figure 2.10 Source-to-destination delivery 6/10/201542Unit-1 : Data Communications
Example 2 In Figure 2.11 we want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local jurisdiction. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic. 6/10/201543Unit-1 : Data Communications
Figure 2.11 Example 2 6/10/201544Unit-1 : Data Communications
Figure 2.12 Transport layer 6/10/201545Unit-1 : Data Communications
The transport layer is responsible for delivery of a message from one process to another. Note: 6/10/201546Unit-1 : Data Communications
Figure 2.12 Reliable process-to-process delivery of a message 6/10/201547Unit-1 : Data Communications
Example 3 Figure 2.14 shows an example of transport layer communication. Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet. 6/10/201548Unit-1 : Data Communications
Figure 2.14 Example 3 6/10/201549Unit-1 : Data Communications
Figure 2.15 Application layer 6/10/201550Unit-1 : Data Communications
The application layer is responsible for providing services to the user. Note: 6/10/201551Unit-1 : Data Communications
Figure 2.16 Summary of duties 6/10/201552Unit-1 : Data Communications
2.3 OSI Model A comparison 6/10/201553Unit-1 : Data Communications
Figure 2.17 OSI model 6/10/201554Unit-1 : Data Communications
Digital Transmission 6/10/201555Unit-1 : Data Communications
4.1 Line Coding Some Characteristics Line Coding Schemes Some Other Schemes 6/10/201556Unit-1 : Data Communications
Figure 4.1 Line coding 6/10/201557Unit-1 : Data Communications
Figure 4.2 Signal level versus data level 6/10/201558Unit-1 : Data Communications
Figure 4.3 DC component 6/10/201559Unit-1 : Data Communications
Example 1 A signal has two data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = 1/ = 1000 pulses/s Bit Rate = Pulse Rate x log 2 L = 1000 x log 2 2 = 1000 bps 6/10/201560Unit-1 : Data Communications
Example 2 A signal has four data levels with a pulse duration of 1 ms. We calculate the pulse rate and bit rate as follows: Pulse Rate = = 1000 pulses/s Bit Rate = PulseRate x log 2 L = 1000 x log 2 4 = 2000 bps 6/10/201561Unit-1 : Data Communications
Figure 4.4 Lack of synchronization 6/10/201562Unit-1 : Data Communications
Example 3 In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps? Solution At 1 Kbps: 1000 bits sent 1001 bits received 1 extra bps At 1 Mbps: 1,000,000 bits sent 1,001,000 bits received 1000 extra bps 6/10/201563Unit-1 : Data Communications
Figure 4.5 Line coding schemes 6/10/201564Unit-1 : Data Communications
Unipolar encoding uses only one voltage level. Note: 6/10/201565Unit-1 : Data Communications
Figure 4.6 Unipolar encoding 6/10/201566Unit-1 : Data Communications
Polar encoding uses two voltage levels (positive and negative). Note: 6/10/201567Unit-1 : Data Communications
Figure 4.7 Types of polar encoding 6/10/201568Unit-1 : Data Communications
In NRZ-L the level of the signal is dependent upon the state of the bit. Note: 6/10/201569Unit-1 : Data Communications
In NRZ-I the signal is inverted if a 1 is encountered. Note: 6/10/201570Unit-1 : Data Communications
Figure 4.8 NRZ-L and NRZ-I encoding 6/10/201571Unit-1 : Data Communications
Figure 4.9 RZ encoding 6/10/201572Unit-1 : Data Communications
A good encoded digital signal must contain a provision for synchronization. Note: 6/10/201573Unit-1 : Data Communications
Figure 4.10 Manchester encoding 6/10/201574Unit-1 : Data Communications
In Manchester encoding, the transition at the middle of the bit is used for both synchronization and bit representation. Note: 6/10/201575Unit-1 : Data Communications
Figure 4.11 Differential Manchester encoding 6/10/201576Unit-1 : Data Communications
In differential Manchester encoding, the transition at the middle of the bit is used only for synchronization. The bit representation is defined by the inversion or noninversion at the beginning of the bit. Note: 6/10/201577Unit-1 : Data Communications
In bipolar encoding, we use three levels: positive, zero, and negative. Note: 6/10/201578Unit-1 : Data Communications
Figure 4.12 Bipolar AMI encoding 6/10/201579Unit-1 : Data Communications
Figure B1Q 6/10/201580Unit-1 : Data Communications
Figure 4.14 MLT-3 signal 6/10/201581Unit-1 : Data Communications
4.2 Block Coding Steps in Transformation Some Common Block Codes 6/10/201582Unit-1 : Data Communications
Figure 4.15 Block coding 6/10/201583Unit-1 : Data Communications
Figure 4.16 Substitution in block coding 6/10/201584Unit-1 : Data Communications
Table 4.1 4B/5B encoding DataCodeDataCode /10/201585Unit-1 : Data Communications
Table 4.1 4B/5B encoding (Continued) DataCode Q (Quiet)00000 I (Idle)11111 H (Halt)00100 J (start delimiter)11000 K (start delimiter)10001 T (end delimiter)01101 S (Set)11001 R (Reset) /10/201586Unit-1 : Data Communications
Figure 4.17 Example of 8B/6T encoding 6/10/201587Unit-1 : Data Communications
4.3 Sampling Pulse Amplitude Modulation Pulse Code Modulation Sampling Rate: Nyquist Theorem How Many Bits per Sample? Bit Rate 6/10/201588Unit-1 : Data Communications
Figure 4.18 PAM 6/10/201589Unit-1 : Data Communications
Pulse amplitude modulation has some applications, but it is not used by itself in data communication. However, it is the first step in another very popular conversion method called pulse code modulation. Note: 6/10/201590Unit-1 : Data Communications
Figure 4.19 Quantized PAM signal 6/10/201591Unit-1 : Data Communications
Figure 4.20 Quantizing by using sign and magnitude 6/10/201592Unit-1 : Data Communications
Figure 4.21 PCM 6/10/201593Unit-1 : Data Communications
Figure 4.22 From analog signal to PCM digital code 6/10/201594Unit-1 : Data Communications
According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency. Note: 6/10/201595Unit-1 : Data Communications
Figure 4.23 Nyquist theorem 6/10/201596Unit-1 : Data Communications
Example 4 What sampling rate is needed for a signal with a bandwidth of 10,000 Hz (1000 to 11,000 Hz)? Solution The sampling rate must be twice the highest frequency in the signal: Sampling rate = 2 x (11,000) = 22,000 samples/s 6/10/201597Unit-1 : Data Communications
Example 5 A signal is sampled. Each sample requires at least 12 levels of precision (+0 to +5 and -0 to -5). How many bits should be sent for each sample? Solution We need 4 bits; 1 bit for the sign and 3 bits for the value. A 3-bit value can represent 2 3 = 8 levels (000 to 111), which is more than what we need. A 2-bit value is not enough since 2 2 = 4. A 4-bit value is too much because 2 4 = 16. 6/10/201598Unit-1 : Data Communications
Example 6 We want to digitize the human voice. What is the bit rate, assuming 8 bits per sample? Solution The human voice normally contains frequencies from 0 to 4000 Hz. Sampling rate = 4000 x 2 = 8000 samples/s Bit rate = sampling rate x number of bits per sample = 8000 x 8 = 64,000 bps = 64 Kbps 6/10/201599Unit-1 : Data Communications
Note that we can always change a band-pass signal to a low-pass signal before sampling. In this case, the sampling rate is twice the bandwidth. Note: 6/10/ Unit-1 : Data Communications
4.4 Transmission Mode Parallel Transmission Serial Transmission 6/10/ Unit-1 : Data Communications
Figure 4.24 Data transmission 6/10/ Unit-1 : Data Communications
Figure 4.25 Parallel transmission 6/10/ Unit-1 : Data Communications
Figure 4.26 Serial transmission 6/10/ Unit-1 : Data Communications
In asynchronous transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits (1s) at the end of each byte. There may be a gap between each byte. Note: 6/10/ Unit-1 : Data Communications
Asynchronous here means “asynchronous at the byte level,” but the bits are still synchronized; their durations are the same. Note: 6/10/ Unit-1 : Data Communications
Figure 4.27 Asynchronous transmission 6/10/ Unit-1 : Data Communications
In synchronous transmission, we send bits one after another without start/stop bits or gaps. It is the responsibility of the receiver to group the bits. Note: 6/10/ Unit-1 : Data Communications
Figure 4.28 Synchronous transmission 6/10/ Unit-1 : Data Communications
5.2 Telephone Modems Modem Standards 6/10/ Unit-1 : Data Communications
A telephone line has a bandwidth of almost 2400 Hz for data transmission. Note: 6/10/ Unit-1 : Data Communications
Figure 5.18 Telephone line bandwidth 6/10/ Unit-1 : Data Communications
Modem stands for modulator/demodulator. Note: 6/10/ Unit-1 : Data Communications
Figure 5.19 Modulation/demodulation 6/10/ Unit-1 : Data Communications
Figure 5.20 The V.32 constellation and bandwidth 6/10/ Unit-1 : Data Communications
Figure 5.21 The V.32bis constellation and bandwidth 6/10/ Unit-1 : Data Communications
Figure 5.22 Traditional modems 6/10/ Unit-1 : Data Communications
Figure K modems 6/10/ Unit-1 : Data Communications
Transmission Media 6/10/ Unit-1 : Data Communications
Figure 7.1 Transmission medium and physical layer 6/10/ Unit-1 : Data Communications
Figure 7.2 Classes of transmission media 6/10/ Unit-1 : Data Communications
7.1 Guided Media Twisted-Pair Cable Coaxial Cable Fiber-Optic Cable 6/10/ Unit-1 : Data Communications
Figure 7.3 Twisted-pair cable 6/10/ Unit-1 : Data Communications
Figure 7.4 UTP and STP 6/10/ Unit-1 : Data Communications
Table 7.1 Categories of unshielded twisted-pair cables CategoryBandwidthData RateDigital/AnalogUse 1very low< 100 kbpsAnalogTelephone 2 < 2 MHz2 MbpsAnalog/digitalT-1 lines 3 16 MHz 10 MbpsDigitalLANs 4 20 MHz 20 MbpsDigitalLANs MHz 100 MbpsDigitalLANs 6 (draft) 200 MHz 200 MbpsDigitalLANs 7 (draft) 600 MHz 600 MbpsDigitalLANs 6/10/ Unit-1 : Data Communications
Figure 7.5 UTP connector 6/10/ Unit-1 : Data Communications
Figure 7.6 UTP performance 6/10/ Unit-1 : Data Communications
Figure 7.7 Coaxial cable 6/10/ Unit-1 : Data Communications
Table 7.2 Categories of coaxial cables CategoryImpedanceUse RG Cable TV RG Thin Ethernet RG Thick Ethernet 6/10/ Unit-1 : Data Communications
Figure 7.8 BNC connectors 6/10/ Unit-1 : Data Communications
Figure 7.9 Coaxial cable performance 6/10/ Unit-1 : Data Communications
Figure 7.10 Bending of light ray 6/10/ Unit-1 : Data Communications
Figure 7.11 Optical fiber 6/10/ Unit-1 : Data Communications
Figure 7.12 Propagation modes 6/10/ Unit-1 : Data Communications
Figure 7.13 Modes 6/10/ Unit-1 : Data Communications
Table 7.3 Fiber types TypeCoreCladdingMode 50/ Multimode, graded-index 62.5/ Multimode, graded-index 100/ Multimode, graded-index 7/ Single-mode 6/10/ Unit-1 : Data Communications
Figure 7.14 Fiber construction 6/10/ Unit-1 : Data Communications
Figure 7.15 Fiber-optic cable connectors 6/10/ Unit-1 : Data Communications
Figure 7.16 Optical fiber performance 6/10/ Unit-1 : Data Communications
7.2 Unguided Media: Wireless Radio Waves Microwaves Infrared 6/10/ Unit-1 : Data Communications
Figure 7.17 Electromagnetic spectrum for wireless communication 6/10/ Unit-1 : Data Communications
Figure 7.18 Propagation methods 6/10/ Unit-1 : Data Communications
Table 7.4 Bands BandRangePropagationApplication VLF3–30 KHzGroundLong-range radio navigation LF30–300 KHzGround Radio beacons and navigational locators MF300 KHz–3 MHzSkyAM radio HF3–30 MHzSky Citizens band (CB), ship/aircraft communication VHF30–300 MHz Sky and line-of-sight VHF TV, FM radio UHF300 MHz–3 GHzLine-of-sight UHF TV, cellular phones, paging, satellite SHF3–30 GHzLine-of-sightSatellite communication EHF30–300 GHzLine-of-sightLong-range radio navigation 6/10/ Unit-1 : Data Communications
Figure 7.19 Wireless transmission waves 6/10/ Unit-1 : Data Communications
Figure 7.20 Omnidirectional antennas 6/10/ Unit-1 : Data Communications
Radio waves are used for multicast communications, such as radio and television, and paging systems. Note: 6/10/ Unit-1 : Data Communications
Figure 7.21 Unidirectional antennas 6/10/ Unit-1 : Data Communications
Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Note: 6/10/ Unit-1 : Data Communications
Infrared signals can be used for short- range communication in a closed area using line-of-sight propagation. Note: 6/10/ Unit-1 : Data Communications