Data Communications prelims

26 parallel wires

How many wires was proposed to a Scottish magazine running communication line in villages?

1753

A proposal was submitted to a Scottish magazine suggested running a communications line between villages comprised of 26 parallel wires, each wire for one letter of the alphabet.

1832

Samuel F.B. Morse invented the first successful and practical data communications system which he called the Telegraph. With the telegraph, dots and dashes are transmitted across a wire through eletromechanical induction. He also developed the first practical data communications code which we all know as the Morse Code.

1833

Carl Friedrich Gauss developed an unusual system based on a five-by-five matrix representing 25 letters (I and J were combined).

1840

Morse secured an American patent for his telegraph.

1844

The first telegraph line was established between Baltimore and Washington D.C "What hath God wrought!"

1849

the first slow-speed telegraph printer was invented

1860

the first high-speed (15-bps) printers were available.

1874

Emile Baudot invented a telegraph multiplexer which allowed signals up to six different telegraph machines to be transmitted simultaneously over a single wire.

1876

Alexander Graham Bell invented the telephone

1899

Guglielmo Marconi succeeded in sending radio telegraph messages.

1920

First commercial radio stations were installed, allowing the transmission of information across large spans of water.

1940

Bell Laboratories developed the first special-purpose computer using eletromechanical relay.

1951

The Universal Automatic Computer (UNIVAC) was the first mass produced electronic computer, built by the Remington Rand Corporation

1960s

batch processing systems were replaced by on-line processing systems.

1968

The AT&T operating tariff allowed only equipment furnished by AT&T to be connected to AT&T lines.

1969

Internet began to evolve at the Advanced Research Project Agency (ARPA).

1970

Advanced Research Projects Agency Network (ARPANET) was formed to connect sites around the US.

1970s

microprocessor-controlled microcomputers were introduced.

1980s

Personal computers became an essential item.

1991

The World Wide Web became publicly available

Alexander Graham Bell

He invented the telephone

ARPA

Where the internet began to evolve

ARPANET

Was formed to connect sites around the US.

Bell Laboratories

They developed the first special-purpose computer using eletromechanical relay.

Broadcast Network

All stations and devices on the network share a single communication channel

Bus Topology

there is a main cable and all the devices are connected to this main cable through drop lines. there is a limit of drop lines and the distance a main cable can have

Carl Friedrich Gauss

He developed an unusual system based on a five-by-five matrix representing 25 letters (I and J were combined).

Current Networks

include the most modern and sophisticated networks and protocols available.

Data

Information that is stored in digital form

data

refers to information presented in whatever form is agreed upon by the parties creating and using the data.

Data Communication

is the transfer of data or information between a source and a receiver. The source transmits the data and the receiver receives it.

Data Communication Network

is any system of computers used to transmit and/or receive information between two or more locations

Data Communication Protocols

are sets of rules governing the orderly exchange of data within the network or a portion of the network. Can either be Connection Oriented or Connectionless.

Data Communications Standards

are guidelines that have been generally accepted by the data communication industry. (Proprietary or Open)

Emile Baudot

Invented a telegraph multiplexer which allowed signals up to six different telegraph machines to be transmitted simultaneously over a single wire.

Guglielmo Marconi

He succeeded in sending radio telegraph messages.

Hybrid topology

A combination of two or more topology

Information

Is defined as knowledge or intelligence

Internet

a global computer network providing a variety of information and communication facilities, consisting of interconnected networks using standardized communication protocols

Legacy Networks

A network or a protocol becomes it when no one really wants to use it, but for some reason it just won't go away. It is the generic name assigned to any old network, which is rarely used today and not part of the TCP/IP protocol suite. Legacy networks are mostly proprietary to individual vendors

Mesh Topology

each device is connected to every other device on the network through a dedicated point-to-point link. n devices in the network then each device must be connected with (n-1) devices of the network. Number of links in a mesh topology of n devices would be n(n-1)/2

Morse Code

First practical data communications code

Network

Is a set of devices interconnected by media links

Network Architecture

is a set of equipment, transmission media, and procedures that ensures that a specific sequence of events occurs in a network in the proper order to produce the intended results.

PEER-TO-PEER

: Devices share the link equally

Point-to-point Network

It only has two stations. No addresses are needed. All transmissions from one station are Intended for and received by the other station.

PRIMARY-SECONDARY

One device controls traffic and the others must transmit through it

Protocols

are set if customs, rules, regulations dealing with formality or precedence, such as diplomatic protocol or military protocol.

Ring Topology

each device is connected with the two devices on either side of it. There are two dedicated point to point links a device has with the devices on the either side of it. If a device wants to send data to another device then it sends the data in one direction, each device has a repeater.

Samuel F.B. Morse

invented the first successful and practical data communications system which he called the Telegraph.

Semantics

refers to the meaning of each section of data.

Star Topology

each device in the network is connected to a central device called hub. y doesn't allow direct communication between devices, a device must have to communicate through hub.

Syntax

refers to the structure or format of the data within the message, which includes sequence in which the data are sent.

Topology

is the geometric representation of the relationship of the links and the linking devices (Nodes) in a Network" or "Topology defines the physical or the Logical Agreement of Links in a Network"

Universal Automatic Computer (UNIVAC)

Was the first mass produced electronic computer, built by the Remington Rand Corporation

International Standard Organization (ISO)

is the international organization for standardization on a wide range of subjects. It is comprised mainly of members from the standards committee of various governments throughout the world. I

International Telecommunications Union-Telecommunication Sector (ITU-T)

is one of the four permanent parts of the International Telecommunications Union based in Geneva, Switzerland. Its membership consists of government authorities and representatives from many countries, and it is the present standards organization for the United Nations. It has developed three sets of specifications: the V series for modem interfacing and data transmission over telephone lines, the X series for data transmission over public digital networks, email and directory services; the I and Q series for ISDN and its extension Broadband ISDN.

integrated Services Digital Network

ISDN

Institute of Electrical and Electronics Engineers (IEEE)

is an international professional organization founded in United States and is comprised of electronics, computer and communications engineers. It is currently the world's largest professional society with over 200,000 members. It develops communication and information processing standards with the underlying goal of advancing theory, creativity, and product quality in any field related to electrical engineering.

American National Standards Institute (ANSI)

is the official standards agency for the United States and is the U.S voting representative for the ISO. It I is a completely private, non-profit organization comprised of equipment manufacturers and users of data processing equipment and services. Its membership is comprised of people form professional societies, industry associations, governmental and regulatory bodies, and consumer goods.

Electronics Industry Association (EIA)

A is a non-profit U.S. trade association that establishes and recommends industrial standards. Its activities include standards development, increasing public awareness, and lobbying and it is responsible for developing the RS (recommended standard) series of standards for data and communications.

Telecommunications Industry Association (TIA)

It is the leading trade association in the communications and information technology industry. It facilitates business development opportunities through market development, trade promotion, trade shows, and standards development. It represents manufacturers of communications and information technology products and also facilitates the convergence of new communications networks.

Internet Architecture Board (IAB)

Earlier known as Internet Activities Board is a committee created by ARPA (Advanced Research Projects Agency) so as to analyze the activities of ARPANET whose purpose is to accelerate the advancement of technologies useful for U.S military. It is a technical advisory group of the Internet Society.

Internet Engineering Task Force (IETF)

is a large international community of network designers, operators, vendors and researchers concerned with the evolution of the Internet architecture and smooth operation of the Internet.

Internet Research Task Force (IRTF)

promotes research of importance to the evolution of the future Internet by creating focused, long-term and small research groups working on topics related to Internet protocols, applications, architecture and technology.

Transmission Mode

means transferring of data between two devices. It is also known as communication mode. Buses and networks are designed to allow communication to occur between individual devices that are interconnected

Simplex Mode

the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit, the other can only receive. It can use the entire capacity of the channel to send data in one direction.

Half-Duplex Mode

each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. It e is used in cases where there is no need for communication in both direction at the same time. The entire capacity of the channel can be utilized for each direction

Full-Duplex Mode

both stations can transmit and receive simultaneously. signals going in one direction share the capacity of the link with signals going in other direction, this sharing can occur in two ways.

full/full duplex mode

transmission is possible in both directions at the same time but not between the same two stations (i.e. station 1 transmitting to station 2, while receiving from station 3). It is possible only on multipoint circuits. Postal system can be given as a person can be sending a letter to one address and receive a letter from another address at the same time.

Circuit

Is the physical path that runs between two or more points. It terminates on a port (that is, a point of electrical or optical interface), and that port can be in a host computer (that is, a switching device used to establish connections), on a multiplexer, or in another device.

Two-Wire Circuits

has two insulated electrical conductors. One wire is used for transmission of the information. The other wire acts as the return path to complete the electrical circuit. Two-wire circuits are generally deployed in the analog local loop, which is the last mile between the subscriber and the subscriber's first point of access into the network.

Two-Wire Transmission

both directions are carried on the same pair of wires

1970s

Using actual wires to circuit switch a telephone call became obsolete when the crossbar switch (a mechanical system) was replaced by 4ESS electronic switches by the Bell System in the US.

Four-Wire Circuits

has two pairs of conductors. That is, it has two sets of one-way transmission paths: one path for each direction and a complementary path to complete the electrical circuit. They are used where there is distance between the termination points which requires that the signal be strengthened periodically. It is a two-way circuit using two paths so arranged that the respective signals are transmitted in one direction only by one path and in the other direction by the other path.

physical four-wire

you can actually count four wires.

logical four-wire

physically there are only two wires, but you derive the four individual paths by splitting the frequency. Half of the frequency band carries the transmit signal, and the other half carries the receive signal. So you can't always tell just by looking what kind of circuit you're dealing with; the application dictates the type of circuit it is. (with operator)

amplifier

boosts an attenuated signal back up to its original power level so it can continue to make its way across the network.

6,000 feet (1,800 meters)

distance requirement between amplifiers is on copper wires

Synchronization

means that the receiver must be able to determine, when to expect a new transmission and when to send acknowledgements. In other words transmitter and receiver should have an agreement on the nature as well as timing of the signals. In the context of .NET, is a process that involves coordinating the execution of multiple threads to ensure a desired outcome without corrupting the shared data and preventing any occurrence of deadlocks and race conditions. also occurs between network nodes to ensure that data streams are received and transmitted correctly, and to prevent data collision. It usually uses a clock signal transmitted in sequence with a data stream to maintain proper signal timing.

Timing

refers to the method used by the data communication system so that the destination station recognizes the start of a data stream and reliably reads the information sent.

Asynchronous communications or transmission

sends data from the source to the destination without synchronizing the two clock systems. The source and destination clocks are free running and not locked to each other. Short characters of 7 to 8 bit data are sent one at a time framed by a start bit and 1 or 2 stop bits. is used for low data transfer rates usually 128 kbps or less and short bursts of data. Faster data rates and longer data lengths cause the data errors at the receiver

Stop bits

is to indicate the end of data. There could be 1 or 2 bits with 1 being the typical number of bits used today.

Synchronous transmission

is a method of data communication that requires the source and destination to synchronize their clocks together. This synchronization of the clocks can occur externally to the data information or be incorporated with the data information.

Synchronous Transmission

sends blocks of characters at a time. Each block of data is preceded by a Start Field which is used to tell the receiving station that a new packet of characters is arriving. The blocks of data also have End Fields to indicate the end of the data block.

64,000

The packet can contain up to \____ bytes depending on the protocol

Internally clocked synchronous transmission

is more difficult and expensive to implement than externally clocked synchronous transmission. The timing signal for synchronization between the source and destination is encoded within the data stream. Manchester encoding is an example of an internally clocked synchronous transmission code. It is often called self clocking as no external timing lines are required.

Manchester Encoding

has no DC component and there is always a transition available for synchronizing receive and transmit clocks. Because of the continuous presence of these transitions. It is also called a self clocking code.

Externally clocked synchronous transmission

has separate lines from the data lines for synchronizing the clock.

The Transmit Timing balanced pair

is used to send out a timing clock to the destination, the Receive Timing balanced pair is a separate clock timing received from the destination.

Generic Packet X

is used as an introduction to Synchronous Data Transmission.

Preamble

At the beginning of each frame (packet), there will be a sequence of bytes (8 bit words), used to Inform the receiving station that a new packet is arriving. It is a series of bytes with a specific bit pattern that is used only by the Preamble.

Address Field

consists of a Source Address and/or a Destination Address. s are hexadecimal numbers that identify the sender - Source and receiver - Destination. The Network Addresses reside in either the Network Interface Card's firmware or can be either assigned during the initialization of the NIC.

Source Address

is to identify to the network who is sending data.

Destination Address

is to identify to the network who should be receiving the data.

Control Field

is used to indicate the Type of Information being sent as Data. The Type of Information can be Control information used when establishing a connection (handshaking) or it can be Data such as file transfers between clients and servers. It is to identify what the purpose of the packet or frame is

Data Field or Message

is the actual information that is being transmitted. It can contain Control Information for handshaking or actual Data used by applications. The Control Field would indicate the Data Field size. It is also called the Info field by some protocols.

Cyclic Redundancy Checking (CRC) / Frame Check Sequence (FCS)

contains an error checking number that the Destination can use to verify that the packet is okay and error-free.

End Frame Delimiter

is a series of bytes that have a specific bit pattern that identifies the end of the packet to the Destination.