Data Communications & Networking

attenuation, distortion, and noise

3 causes of transmission impairment

Shielded Twisted Pair Cable

A cable that is made of one or more twisted pairs of wires and is surrounded by a metal shield.

Local Area Networks (LAN)

A category of network that is usually limited to a few kilometers of area. It may be privately owned and could be a network inside an office on one of the floor of a building

Narrowband Channel

A channel whose bandwidth is less than the bandwidth of the signal

Hybrid Topology

A combination of two or more different topologies.

Composite Signal

A combination of two or more simple sine waves with different frequency, phase and amplitude.

Network topology

A description of the layout of the region or area covered by that network.

Receiver

A device that the sender wants to communicate the data (message).

Session Layer

A layer of OSI model that establish, manage and terminate sessions

Datalink Layer

A layer of OSI model that provide hop to hop delivery of frames.

Transport Layer

A layer of OSI model that provide process to process delivery of message

Presentation Layer

A layer of OSI model that provides the functions of translation, encryption and compression.

Application Layer

A layer of OSI model that provides the users access to network resources

Physical Layer

A layer of OSI model that transmit data over a bit stream from one hop to the next

Images

A matrix of pixel elements.

Transmission media

A means by which a communication signal is carried from one system to another

Protocol

A necessity in data communications without which the communicating entities are like two persons trying to talk to each other in a different language without know the other language.

Data Communication

A process of exchanging data or information

Noise

Any unwanted signal that is mixed or combined with the original signal during transmission. Due to this the original signal is altered and signal received is not same as the one sent.

Computer Network

Defined as a collection of nodes, used for data communications

Transmission medium

Defined as anything that can carry information from a source to a destination.

Bandwidth

Defined as the frequency range over which a signal is transmitted.

Bandwidth

Defined as the portion of the electromagnetic spectrum occupied by the signal

Phase of a sine wave

Describes the position of the waveform with respect to time (specifically relative to time O).

Distortion

Distortion changes the shape of the signal as shown below

Radio waves Radio waves are omni-directional when an antenna transmits radio waves they are propagated in all directions.

Electromagnetic wave ranging in frequencies between 3 KHz and 1GHz; omni-directional

Microwaves Microwaves are unidirectional; when an antenna transmits microwaves they can be narrowly focused. This means that the sending and receiving antennas need to be aligned. Microwaves propagation is line-of-sight.

Electromagnetic waves having frequencies between 1 and 300 GHz; unidirectional

Semantics

Element of a protocol that tells the meaning of each section of bits and indicates the interpretation of each section.

Timing

Element of a protocol that tells the sender about the readiness of the receiver to receive the data

Timing

Element of a protocol that tells the sender at what rate the data should be sent to the receiver to avoid overwhelming the receiver.

Semantics

Element of a protocol that tells what action/decision is to be taken based on the interpretation.

Syntax Semantics Timing

Elements of a Protocol

Text

Form of data that includes combination of alphabets in small case as well as upper case. It is stored as a pattern of bits. Prevalent encoding system : ASCII, Unicode

Audio

Form of data which can be recorded and broadcasted.

Packet Switching

In __________________, communication is discrete in form of packets. The packets are handled by the intermediate nodes in a store-and-forward fashion

Circuit Switching

In this method of switching, two communicating stations are connected by a dedicated communication path.

Full Duplex

In this mode of communication, both stations can transmit and receive at the same time.

Half Duplex

In this mode of communication, both the stations can transmit as well as receive but not at the same time. When one device is sending other can only receive and vice-versa

Broad band Transmission

In this type of transmission we use modulation, i.e we change the signal to analog signal before transmitting it.

Baseband Transmission

In this type of transmission, the bandwidth of the signal to be transmitted has to be less than the bandwidth of the channel.

Subnetting

It allows a network to be split into several parts for internal use but still act like a single network to the outside world.

Network

It consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications.

Protocol

It defines what is to be communicated, how it is to be communicated and when it is to be communicated

Phase of a sine wave

It indicates the forward or backward shift of the waveform from the axis

Application Layer

It is a combination of Session, Presentation & Application Layers of OSI models and define high level protocols like File Transfer (FTP), Electronic Mail (SMTP), Virtual Terminal (TELNET), Domain Name Service (DNS), etc.

Open Systems Interconnection (OSI) Model 1. Application Layer 2. Presentation Layer 3. Session Layer 4. Transport Layer 5. Network Layer 6. Data Link Layer 7. Physical Layer

It is a hierarchical model that groups its processes into layers. It has 7 layers as follows:

IGMP- Internet Group Message Protocol

It is a mechanism that allows to send the same message to a group of recipients.

Open Systems Interconnection (OSI) Model

It is a network model that defines the protocols for network communications

SCTP - Stream Control Transmission Protocol

It is a relatively new protocol added to the transport layer of TCP/IP protocol suite. It combines the features of TCP and UDP. It is used in applications like voice over Internet and has a much broader range of applications

ICMP- Internet Control Message Protocol

It is a signaling mechanism used to inform the sender about datagram problems that occur during transit. It is used by intermediate devices.

UDP - User Datagram Protocol

It is a simple protocol used for process to process transmission. It is an unreliable, connectionless protocol for applications that do not require flow control or error control. It simply adds port address, checksum and length information to the data it receives from the upper layer.

TCP/IP Model 1. Host to Network Layer 2. Internet/Network or IP Layer 3. Transport Layer 4. Application Layer The Application layer of TCP/IP model corresponds to the Application Layer of Session, Presentation & Application Layer of OSI model. The Transport layer of TCP/IP model corresponds to the Transport Layer of OSI model The Network layer of TCP/IP model corresponds to the Network Layer of OSI model The Host to network layer of TCP/IP model corresponds to the Physical and Datalink Layer of OSI model.

It is also called as the TCP/IP protocol suite. It is a collection of protocols.

Protocol

It is an agreed upon set or rules used by the sender and receiver to communicate data.

Bandwidth of an analog signal

It is defined as the maximum bit rate of the signal to be transmitted. It is measured in bits per second.

Bandwidth of a digital signal

It is defined as the range of frequencies that the composite analog signal carries. It is expressed in terms of its frequencies.

Syntax

It is the arrangement of data in a particular order.

Wavelength

It is the distance a signal travels in one period.

Message

It is the information to be communicated by the sender to the receiver.

Physical Address

It is the lowest level of addressing, also known as link address. It is local to the network to which the device is connected and unique inside it. The physical address is usually included in the frame and is used at the data link layer.

Port Address Ex. TELNET uses port address 23, HTTP uses port address 80

It is the name or label given to a process. It is a 16 bit address.

Transmission Medium

It is the path by which the message travels from sender to receiver. It can be wired or wireless and many subtypes in both.

RARP- Reverse Address Resolution Protocol

It is used by a device on the network to find its Internet address when it knows its physical address.

ARP - Address Resolution Protocol

It is used to resolve the physical address of a device on a network, where its logical address is known.

De jure Standard

It means by law or by regulation. These standards are legislated and approved by an body that is officially recognized.

Syntax

It means the structure or format of the data.

Unguided Media/Wireless There are three types of Unguided Media (i) Radio waves (ii) Micro waves (iii) Infrared.

It uses wireless electromagnetic signals to send data.

Open Systems Interconnection (OSI) Model

It was developed to allow systems with different platforms to communicate with each other. Platform could mean hardware, software or operating system.

Wavelength of a signal

Refers to the relationship between frequency (or period) and propagation speed of the wave through a medium.

Period of a sine wave

Refers to the time taken by the wave to complete one second.

Transport Layer The transport layer contains three protocols: 1. TCP 2. UDP 3. SCTP

Responsible for transmission of data running on a process of one machine to the correct process running on another machine.

Non-Periodic Signals

Signals which do not repeat itself after a fixed time period

Periodic Signals

Signals which repeat itself after a fixed time period

Infrared

Signals with frequencies ranges from 300 GHz to 400 GHz which can be used for short range communication; having high frequencies, cannot penetrate walls.

Examples of Standard Creation Committees : International Organization for Standardization(ISO) International Telecommunications Union - Telecommunications Standard (ITU-T) American National Standards Institute (ANSI) Institute of Electrical & Electronics Engineers (IEEE) Electronic Industries Associates (EIA) Examples of Forums: ATM Forum MPLS Forum Frame Relay Forum Examples of Regulatory Agencies: Federal Communications Committee (FCC)

Standards are created by standards creation committees, forums, and government regulatory agencies.

Specific Address

Such address are user friendly addresses

Metropolitan Area Network (MAN)

This category of network is of size between LAN & WAN. It is larger than LAN but smaller than WAN.

Low pass Channel

This channel has the lowest frequency as '0' and highest frequency as some non-zero frequency 'f1'. This channel can pass all the frequencies in the range 0 to f1.

Band pass channel

This channel has the lowest frequency as some non-zero frequency 'f1' and highest frequency as some non-zero frequency 'f2'. This channel can pass all the frequencies in the range f1 to f2.

Physical topology

Refers to the configuration of cables, computers, and other peripherals.

Transmission mode

Refers to the mode used for transmitting the data

Frequency of a sine wave

Refers to the number of cycles completed by the wave in one second.

Data

Refers to the raw facts that are collected

TCP - Transmission Control Protocol

A reliable connection-oriented, reliable protocol. i.e. a connection is established between the sender and receiver before the data can be transmitted. It divides the data it receives from the upper layer into segments and tags a sequence number to each segment which is used at the receiving end for reordering of data.

Protocol

A set of rules that governs data communication.

1. Peak Amplitude 2. Frequency 3. Phase

A sine wave is characterized by three parameters

Simple Analog Signal

A sine wave that cannot be further decomposed into simpler signals.

Ground-wave propagation

A way in which wireless signals travel i. Follows contour of the earth ii. Can Propagate considerable distances iii. Frequencies up to 2 MHz iv. Example a. AM radio

Sky-wave propagation

A way in which wireless signals travel i. Signal reflected from ionized layer of atmosphere back down to earth ii. Signal can travel a number of hops, back and forth between ionosphere and earth's surface iii. Reflection effect caused by refraction iv. Examples a. Amateur radio b. CB radio

Line-of-sight propagation

A way in which wireless signals travel i. Transmitting and receiving antennas must be within line of sight a. Satellite communication - signal above 30 MHz not reflected by ionosphere b. Ground communication - antennas within effective line of site due to refraction

Network Layer or IP IP is a combination of four protocols: 1. ARP - Address Resolution Protocol 2. RARP - Reverse Address Resolution Protocol 3. ICMP- Internet Control Message Protocol 4. IGMP- Internet Group Message Protocol

Also called as the Internetwork Layer (IP). It holds the IP protocol which is a network layer protocol and is responsible for source to destination transmission of data.

Node

Any device capable of transmitting or receiving data.

Sender

Any device that is capable of sending the data

Co-Axial Cable

Cable that consists of 2 conductors used as transmission lines for radio frequency, video and data signals. They have traditionally been used as feed lines to connect radio transmitters and receivers with antennas, internet connections, digital audio and cable television signals.

Unshielded Twisted Pair Cable

Cables without a shield used for networks, composed of four pairs of wires twisted around each other to reduce electrical interference

Timeliness Real Time Transmission of Data.

Characteristics of Data Communication Audio and Video data has to be delivered in a timely manner without any delay; such a data delivery is called ___________

Jitter

Characteristics of Data Communication It is the variation in the packet arrival time. Uneven ________ may affect the timeliness of data being transmitted.

Accuracy

Characteristics of Data Communication The communication system should deliver the data accurately, without introducing any errors. The data may get corrupted during transmission affecting the _________ of the delivered data.

Delivery

Characteristics of Data Communication The data should be delivered to the correct destination and correct user.

Data

Collection of raw facts which is processed to deduce information.

Money. Length of cable needed. Future growth. Cable type.

Considerations When Choosing a Topology

Fiber Optic Cable

Consists of thin glass fiber that can carry information at frequencies in the visible light spectrum Advantages: 1. Small size and light weight 2. Easy availability and low cost 3. No electrical or electromagnetic interference 4. Large Bandwidth

Attenuation

Loss of power in a signal as it travels from the sending device to the receiving device A type of transmission impairment that results in loss of energy. When a signal travels through a medium, it loses some of its energy in overcoming the resistance of the medium.

Standards

Necessary in networking to ensure inter-connectivity and interoperability between various networking hardware and software components.

Numbers

Numbers include combination of digits from 0 to 9. It is stored as a pattern of bits. Prevalent encoding system : ASCII, Unicode

Point-to-point connections

Provide a direct link between two devices; for example, a computer connected directly to a printer, or a modem to a mainframe.

Multi-point connections

Provide a link between three or more devices on a network.

Standards

Provide guidelines to product manufacturers and vendors to ensure national and international interconnectivity.

Data

Refers to any information which is presented in a form that is agreed and accepted upon by is creators and users.

Video

Refers to broadcasting of data in form of picture or movie

Logical topology

Refers to how data is actually transferred in a network as opposed to its physical design

Digital data

Refers to information that has discrete states.

Analog data

Refers to information that is continuous; ex. sounds made by a human voice

Network Layer

The OSI layer that addresses data packets, routes the packets from a source to a destination through the network, and ensures the delivery of those packets. The OSI layer that is responsible for providing source to destination delivery of packets.

1. Physical Address 2. Logical Address 3. Port Address 4. Specific Address

The TCP/IP protocol suited involves 4 different types of addressing:

Peak Amplitude

The _________ of a signal is the absolute value of the highest intensity

Routing

The act of moving information across an internetwork from a source to a destination.

Switching

The generic method for establishing a path for point-to-point communication in a network. It involves the nodes in the network utilizing their direct communication lines to other nodes so that a path is established in a piecewise fashion.

Channel

The medium through which the signal carrying information will be passed.

Logical topology

The method used to pass information between workstations.

Network topology

The pattern or layout of interconnections of different elements or nodes of a computer network

Physical topology

The physical design of a network including the devices, location and cable installation.

Baseband Transmission

The signal is transmitted without making any change to it (ie. Without modulation)

Pixel

The smallest element of an image. It is represented in the form of bits.

Topology

The virtual shape or structure of a network

Logical topology

The way a computer in a given network transmits information, not the way it looks or connected, along with the varying speeds of cables used from one network to another.

Twisted-pair cable

The wires is twisted twisted together in pairs. These cable are most effectively used in a system that uses a balanced line method of transmission.

De facto Standard

These are the standards that have been traditionally used and mean by fact or by convention

De facto Standard

These standards are not approved by any organized body but are adopted by widespread use.

Wide Area Network (WAN)

This category of network is made of all the networks in a (geographically) large area.

Host to Network Layer

This layer is a combination of protocols at the physical and data link layers. It supports all standard protocols used at these layers.

A variation of packet switching: Datagram (also known as connectionless)

This method does not rely on a pre-established route, instead each packet is treated independently.

A variation of packet switching: virtual circuit (also known as connectionoriented)

This method is closer to circuit switching. Here a complete route is worked out prior to sending data packets. The route is established by sending a connection request packet along the route to the intended destination.

Simplex

This mode of communication is unidirectional. Only one of the devices sends the data and the other one only receives the data.

Time-domain plot

This shows changes in signal amplitude with respect to time. It indicates time and amplitude relation of a signal.

Frequency-domain plot

This shows signal frequency and peak amplitude.

Analog Signal

This signal has infinitely many levels of intensity over a period of time.

Guided Transmission media Types: 1. Twisted-Pair Cable 2. Coaxial Cable 3. Fiber-OpticCable

Transmission media that uses a cabling system that guides the data signals along a specific path. It is also known as Bounded media, which are those that provide a conduit from one device to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.

Unguided Media/Wireless There are three types of Unguided Media (i) Radio waves (ii) Micro waves (iii) Infrared.

Transport data without using a physical conductor. This type of communication is often referred to as wireless communication.

Synchronous Transmission

Type of serial transmission where the sender and receiver are highly synchronized. No start, stop bits are used. The sender simply send stream of data bits in group of 8 bits to the receiver without any start or stop bit. Advantage 1. There are no start bits, stop bits or gaps between data units 2. Since the above are absent data transmission is faster. 3. Due to synchronization there are no timing errors.

Asynchronous Transmission

Type of serial transmission where the sender and receiver are not synchronized. The data is sent in group of 8 bits i.e. in bytes. The sender can start data transmission at any time instant without informing the receiver. To avoid confusing the receiver while receiving the data, start and stop bits are inserted before and after every group of 8 bits Advantages 1. Cheap and Effective implementation 2. Can be used for low speed communication Disadvantages Insertion of start bits, stop bits and gaps make asynchronous transmission slow. Application Keyboard

Analog Signal

Type of signal that have infinite values in a range

Digital Signal

Type of signal that have limited number of defined values

Logical Address There are two versions of IP addresses being used: a. IPv4: 32 bit address, capable of supporting 2^32 nodes b. IPv6: 128 bit address, capable of supporting 2^128 nodes

Used for universal communication. It is also called as IP Address (Internet Protocol address).

Radio waves Radio waves are omni-directional when an antenna transmits radio waves they are propagated in all directions.

Waves that propagate in sky mode, can travel long distances; omni-directional

1. Ground-wave propagation 2. Sky-wave propagation 3. Line-of-sight propagation

Ways in which wireless signals travel

Serial Transmission

When a single bit is transmitted in unit time (bit by bit, one bit at a time) the transmission mode used is _________

Parallel transmission Example of Parallel Transmission is the communication between CPU and the Projector.

When multiple bits are sent in unit time the transmission mode used is called _____ It can be used for short distance communication only