Datacom module 3: Data Communications Circuits, Arrangements, and Networks

Module 3Datacom Circuits, Circuit

Arrangements, and Networks

Chapter 21

Electronic Communications Sytems , Fifth Editon

By: Wayne Tomasi

ECE @Saint Louis University, Baguio City1

Prepared by: Engr. Jeffrey Des B. Binwag

Datacom Circuit Components

• Source

• Transmitter

• Transmission Medium

• Receiver

• Destination

ECE @Saint Louis University, Baguio City 2

Serial and Parallel Data Transmission

• Parallel Transmission. Involves sending data bits simultaneously on a set of transmission lines on a single clock pulse. Also called parallel by bit or serial by charactertransmission.

• Serial Transmission. Involves sending data bits on a single transmission line involving several clock cycles. Also called serial by bit transmission.


Datacom Circuit Arrangements• Circuit Configurations.

– Point-to-point. Involves only two stations on a circuit.

– Multipoint. Involves more than two stations in a datacomcircuit.

• Transmission Modes.

– Simplex (SX). Transmit only or receive only or one-way-only lines

– Half duplex (HDX). Two way alternate or either-way lines.

– Full duplex (FDX). Two-way simultaneous or both-way lines

– Full/full duplex (F/FDX). Transmission in both directions at the same time but not between the same two stations.


Datacom Network Components, Functions and Features

• Servers. Computers that hold shared files, programs, and the network operating system.

• Clients. Computers that access and use the network and other shared resources.

• Transmission Media. Facilities used to interconnect computers in a network.

• Shared Data. Data that file servers provide to clients such as data files, printer access programs, and e-mail.


Datacom Network Components, Functions and Features

• Shared Peripherals. Hardware resources provided to users by the network servers.

• Network Interface Card (NIC). Prepares, and sends data, receives data, and controls data flow between the computer and the network.

• Local Operating System (LOS). A software that allows personal computers to access files, print to a local printer, and connect to other local memory and peripheral devices.

• Network Operating System (NOS). A program that runs on computers and servers that allows the computers to communicate over the network.


Datacom Network Models

• Peer-to-Peer Client/Server. A network in which all computers share their resources, such as hard drives, printers, and so on, with all the other computers in the network.

– No dedicated servers or hierarchy among computers

– Used for networks with 10 users or less, when computers are located in the same general area, when security is not an issue, or when limited growth is projected for the network in the immediate future.


Datacom Network Models

• Dedicated Client/Server. A network where one computer is designated as the server, and the rest of the computers are clients.

– Features highly centralized network control

– There could be a dedicated server to serve each network function.

– Preferred model for general purpose data networks.


Datacom Network Topologies

• Network Topology. Describes the layout or appearance of a network. A physical topology describes how a network is actually laid out while the logical topology describes how data actually flow through the network.

– Star. A multipoint datacom network where remote stations are connected by cable segments directly to a centrally located computer called a hub which acts as a multipoint connector.

– Bus. A multipoint datacom circuit where remote stations are physically or logically connected to a single transmission line called a bus. Also called a multidrop, horizontal bus, or linear bus, it is the simplest and most common method of interconnecting computers.


Datacom Network Topologies

– Ring. A network where all stations are interconnected in tandem (series) to form a closed loop or circle. In this type of topology that is also called a loop, transmissions are unidirectional and must propagate through all stations in the loop such that each computer acts like a repeater.

– Mesh. A network where every station has a direct two-point communication link with the rest of the computers in the network. Also known as a fully connected network, this topology offers reduced traffic problems, increased reliability, and enhanced security although requires a much greater number of transmission paths and input/output ports.

– Hybrid. A network that combines two or more of the traditional topologies to form a larger, more complex topology.


Datacom Network Classifications• Network Classification. Generally classified by size, which

includes geographic area, distance between stations, number of computers, transmission speed, transmission media, and the network’s physical architecture.

– LAN (Local Area Network). Typically privately owned data communications networks in which 10 to 40 computer users share data resources with one another. Most LANs are owned by the company or organization that uses it and have a connection to a building backbone for access to other LANs, MANs, WANs, and GANs.

– MAN (Metropolitan Area Network). A high speed network similar to a LAN except it is designed to encompass larger areas, usually an entire city/metropolis. A MAN can be owned and operated entirely by a single company, or could lease services and facilities on a monthly basis from the local cable or telephone company.


Datacom Network Classifications– WAN (Wide Area Network). The oldest type of data communications

network that provides relatively slow-speed, long-distance transmission of data, voice, and video information over relatively large and widely dispersed geographical areas, such as a country or an entire continent.

– GAN (Global Area Network). A network that provides connections between countries around the entire globe.

– Building Backbone. A network connection that normally carries traffic between departmental LANs within a single company.

– Campus Backbone. A network connection used to carry traffic to and from LANs located in various buildings on a campus or similar settings like corporate headquarters, universities, airports, and research parks.

– Enterprise Network. A network connection that includes some or all of the previously mentioned networks and components connected in a cohesive and manageable fashion.


Datacom Networks Comparison


Network Classification

Geographic Area Distance Between Stations

TransmissionSpeed

Examples

LAN Same room, building, or building complex

A few miles 10 – 100 Mbps PAN, Ad-hoc wireless, SoHo

MAN City, Metropolis A few hundred miles

1.5 – 10 Mbps SMDS, FDDI, ATM

WAN Country, Continent

100 to 1000 miles

1.5 Mbps –2.4 Gbps

ISDN, X.25, ATM, T1 and T3 Digital Carrier Systems

GAN Global Thousands of miles

1.5 Mbps –100 Gbps

Internet, WWW

Engineering

Datacom module 3: Data Communications Circuits, Arrangements, and Networks