Nagarjuna College of Engineering and Technology Information Science and Engineering
MODULE – I Introduction, Network model, Physical Layer & media Lecture 01 Data Communications, Networks What is data communication?
Electronic transmission of information that has been encoded digitally with some standard from one network (systems) to other network (systems) via certain medium, knows as Data Communication. Elements of Data Communication; Information / Data Digital encoded Transfer of data / sender and receiver Specific medium What is network?
A computer network often simply referred to as a network, is a collection of hardware components, which are interconnected by communication channels that allow sharing of resources and information with respect to certain set of rules / protocols via OS / software. Elements of Network; Hardware equipments Network OS / software Communication channel Information / Data / Recourse Protocols Terminologies
Data transmission process between sender and receiver is refer to data communication, and deployed physical environment (hardware / software / protocols / channel ) is network.
Data: digital information over computer / network, which may define with certain type of file extension; like .doc, .ppt,.pdf, .exe, and etc. File extension dominate nature of data file Resource: all sharable / accessible items over network, which may physical / virtual, knows as resource. physical resource - may be hard drive, printer, servers and etc. virtual resource - may be data files, online application, web site, internet and etc. Share Resource: a shared resource or network share is a device / piece of information means file / software or application, on a computer that can be remotely accessed from another computer. Channel: communication channel is a medium on which resource can be access over network and establish connectivity between sender and receiver. Channel speed / network speed is depends upon bandwidth. bandwidth - channel capacity known as bandwidth. There are two types of channels: Physical channel like network cable, fiberoptic, wire, and etc. Logical or virtual channel like wireless, radio frequency, Wi-Fi, Wi-Max, and Bluetooth Protocols and standards
Protocols: a communications protocol is a system of digital message formats and rules for exchanging those messages in or between computer systems and in network / telecommunications. Protocols regulate the following characteristics of a network: access method, allowed physical topologies, types of cabling, and speed of data transfer. Protocols may include signaling, authentication, error detection method, and network policies. A protocol can be implement at hardware or software or both, and with respect to assignment these are implemented like; for web http, for security SSL, for email POP3 / SMTP, for LAN network Ethernet, for routing BGP / RIP,etc.
8 Lecture 02 Layered Tasks, The OSI model Layered tasks
In layered architecture of Network Model, one whole network process is divided into small tasks. Each small task is then assigned to a particular layer which works dedicatedly to process the task only. Every layer does only specific task. one layer of a host deals with the task done by or to be done by its peer layer at the same level on the remote host. The task is either initiated by layer at the lowest level or at the top most level. If the task is initiated by the-top most layer, it is passed on to the layer below it for further processing. The lower layer does the same thing, it processes the task and passes on to lower layer. If the task is initiated by lower most layer, then the reverse path is taken.er does only specific work. Every layer clubs together all procedures, protocols, and methods which it requires to execute its piece of task. All layers identify their counterparts by means of encapsulation header and tail. OSI model
Open System Interconnect is an open standard for all communication systems. OSI model is established by International Standard Organization (ISO). This model has seven layers: Lecture 03 Layers in OSI model Application Layer: This layer is responsible for providing interface to the application user. This layer encompasses protocols which directly interact with the user. Presentation Layer: This layer defines how data in the native format of remote host should be presented in the native format of host. Session Layer: This layer maintains sessions between remote hosts. For example, once user/password authentication is done, the remote host maintains this session for a while and does not ask for authentication again in that time span. Transport Layer: This layer is responsible for end-to-end delivery between hosts. Network Layer: This layer is responsible for address assignment and uniquely addressing hosts in a network. Data Link Layer: This layer is responsible for reading and writing data from and onto the line. Link errors are detected at this layer. Physical Layer: This layer defines the hardware, cabling wiring, power output, pulse rate etc. Lecture 04 TCP/IP Protocol suite TCP/IP protocol suite
Internet uses TCP/IP protocol suite, also known as Internet suite. This defines Internet Model which contains four layered architecture. OSI Model is general communication model but Internet Model is what the internet uses for all its communication. The internet is independent of its underlying network architecture so is its Model. This model has the following layers: Application Layer: This layer defines the protocol which enables user to interact with the network. For example, FTP, HTTP etc. Transport Layer: This layer defines how data should flow between hosts. Major protocol at this layer is Transmission Control Protocol (TCP). This layer ensures data delivered between hosts is in-order and is responsible for end-to-end delivery. Internet Layer: Internet Protocol (IP) works on this layer. This layer facilitates host addressing and recognition. This layer defines routing. Link Layer: This layer provides mechanism of sending and receiving actual data. Unlike its OSI Model counterpart, this layer is independent of underlying network architecture and hardware. Lecture 05 Addressing, Transmission Impairment Addressing
A network address is any logical or physical address that uniquely distinguishes a network node or device over a computer or telecommunications network. It is a numeric/symbolic number or address that is assigned to any device that seeks access to or is part of a network. A network address is a key networking technology component that facilitates identifying a network node/device and reaching a device over a network. It has several forms, including the Internet Protocol (IP) address, media access control (MAC) address and host address. Transmission impairment
Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This means that the signal at the beginning of the medium is not the same as the signal at the end of the medium. What is sent is not what is received. The three different causes of impairment are attenuation distortion noise Attenuation
Attenuation means a loss of energy. When a signal, simple or composite, travels through a medium, it loses some of its energy in overcoming the resistance of the medium. That is why a wire carrying electric signals gets warm, if not hot, after a while. Some of the electrical energy in the signal is converted to heat. To compensate for this loss, amplifiers are used to amplify the signal. The following figure shows the effect of attenuation and amplification. Distortion
Distortion means that the signal changes its form or shape. Distortion can occur in a composite signal made of different frequencies. Each signal component has its own propagation speed (see the next section) through a medium and, therefore, its own delay in arriving at the final destination. Differences in delay may create a difference in phase if the delay is not exactly the same as the period duration. In other words, signal components at the receiver have phases different from what they had at the sender. The shape of the composite signal is therefore not the same. The following figure shows the effect of distortion on a composite signal. Noise
Noise is another cause of impairment. Several types of noise, such as thermal noise, induced noise, crosstalk, and impulse noise, may corrupt the signal. Thermal noise is the random motion of electrons in a wire which creates an extra signal not originally sent by the transmitter. Induced noise comes from sources such as motors and appliances. Lecture 06 Data Rate limits Data rate limits
A very important consideration in data communications is how fast we can send data, in bits per second. over a channel. Data rate depends on three factors: The bandwidth available The level of the signals we use The quality of the channel (the level of noise) • Two theoretical formulas were developed to calculate the data rate: Nyquist for a noiseless channel Shannon for a noisy channel Lecture 07 Performance Performance measures
Bandwidth commonly measured in bits/second is the maximum rate that information can be transferred Throughput is the actual rate that information is transferred Latency the delay between the sender and the receiver decoding it, this is mainly a function of the signals travel time, and processing time at any nodes the information traverses Jitter variation in packet delay at the receiver of the information Error rate the number of corrupted bits expressed as a percentage or fraction of the total sent Lecture 08 Digital-digital conversion –Polar line coding DIGITAL-DIGITAL CONVERSION (only line coding: polar, bipolar and manchester coding)
Data as well as signals that represents data can either be digital or analog. Line coding is the process of converting digital data to digital signals. By this technique we converts a sequence of bits to a digital signal. At the sender side digital data are encoded into a digital signal and at the receiver side the digital data are recreated by decoding the digital signal. Unipolar scheme
In this scheme, all the signal levels are either above or below the axis. Non return to zero (NRZ) – It is unipolar line coding scheme in which positive voltage defines bit 1 and the zero voltage defines bit 0. Signal does not return to zero at the middle of the bit thus it is called NRZ. For example: Data = 10110. But this scheme uses more power as compared to polar scheme to send one bit per unit line resistance. Moreover for continuous set of zeros or ones there will be self-synchronization and base line wandering problem. Polar schemes
In polar schemes, the voltages are on the both sides of the axis. NRZ-L and NRZ-I – These are somewhat similar to unipolar NRZ scheme but here we use two levels of amplitude (voltages). For NRZ-L(NRZ-Level), the level of the voltage determines the value of the bit, typically binary 1 maps to logic-level high, and binary 0 maps to logic-level low, For NRZ-I(NRZ-Invert), two-level signal has a transition at a boundary if the next bit that we are going to transmit is a logical 1, and does not have a transition if the next bit that we are going to transmit is a logical 0. Note – For NRZ-I we are assuming in the example that previous signal before starting of data set “01001110” was positive. Therefore, there is no transition at the beginning and first bit “0” in current data set “01001110” is starting from +V. Example: Data = 01001110. Comparison between NRZ-L and NRZ-I: Baseline wandering is a problem for both of them, but for NRZ-L it is twice as bad as compared to NRZ-I. This is because of transition at the boundary for NRZ-I (if the next bit that we are going to transmit is a logical 1). Similarly self-synchronization problem is similar in both for long sequence of 0’s, but for long sequence of 1’s it is more severe in NRZ-L. Return to zero (RZ) – One solution to NRZ problem is the RZ scheme, which uses three values positive,negative,and zero. In this scheme signal goes to 0 in the middle of each bit. Note – The logic we are using here to represent data is that for bit 1 half of the signal is represented by +V and half by zero voltage and for bit 0 half of the signal is represented by -V and half by zero voltage. Example: Data = 01001. Manchester encoding
Manchester encoding is somewhat combination of the RZ (transition at the middle of the bit) and NRZ-L schemes. The duration of the bit is divided into two halves. The voltage remains at one level during the first half and moves to the other level in the second half. The transition at the middle of the bit provides synchronization. Lecture 09 Bipolar and Manchester coding Bipolar schemes
There are three voltage levels positive, negative, and zero. The voltage level for one data element is at zero, while the voltage level for the other element alternates between positive and negative. Alternate Mark Inversion (AMI)– neutral zero voltage represents binary 0. Binary 1’s are represented by alternating positive and negative voltages. Pseudoternary – Bit 1 is encoded as a zero voltage and the bit 0 is encoded as alternating positive and negative voltages i.e., opposite of AMI scheme. Example: Data = 010010. The bipolar scheme is an alternative to NRZ.This scheme has the same signal rate as NRZ,but there is no DC component as one bit is represented by voltage zero and other alternates every time.