Telecommunications and Networking

What is Telecommunications

• The transportation of information via electronic means– Could include telephone & telegraph

• Data Communications is the part of telecommunications that relates to computer systems or the electronic transmission of data

Importance of Telecommunications

• Provides the foundation for the Internet

• Dramatic cost reductions in the areas of applications development deployment

Importance of Telecommunications

• Transportation of different types of data– Voice, Video, Data, Fax, etc.

• Collaboration

Components of Telecommunications Systems

• Hardware and Telecommunications Software

• Communications Channels– Links required for data and voice to be

transmitted and received

• Communications Processors– Support functions for transmission and reception

• Protocols

Types of Signals• Analog

– Used in everyday telephone conversations

• Digital– Electrical impulses representing a high signal (1) or a low

signal (0)

• Digital has several advantages– Lower error rates– Higher transmission speeds– Inherently less noise

• Noise is filtered out

– No conversion required

Purpose of the Modem

• Modulator/Demodulator

• Converts analog to digital

• Converts digital to analog

• Handshaking or “Interfacing”– Ensures correct protocols are used

• Filters the signal to reduce errors

• Clocking– Timing the rates to sparse data correctly

Communications Channels

• Twisted Pair

• Coaxial Cable

• Fiber Optic

• Microwave

• Satellite

Characteristics of Communications Channels

• Buad Rate– The number of discrete signals over a period of time

• Bandwidth– Determines how much data can be pushed through

– Difference between lowest frequency and highest frequency as measured in Hertz

– Telephone lines transmit between 300hz and 3300hz• Bandwidth is 3000 hz

Sources of Error• White Noise

– Gaussian Noise

– Hissing noise due to movement of electrons

• Impulse Noise– External spikes, ex. Lightning

• Crosstalk– Signals from one channel interferring with another

• Echo– The reflection or reverse of the signal transmitted

• Attenuation– Decrease in signal strength dues to distance

Error Detection• Parity Checking

• Cyclical Redundancy Check

• Error Prevention– Telephone line conditioning

• Service performed by Telephone Company

– Lower transmission speeds for digital

– Shielding

Media Selection Criteria

• Cost• Speed• Availability• Expandability• Error Rates• Security• Distance• Environment• Application• Maintenance

Network Topologies• Star

– All are connected to a central computer– If the central node goes down, all are down

• Bus– Entire network on a single circuit– Popular in LANS– Message is sent over the network and each station is checked to see if the

addresses match• Token Ring

– Each node is sequentially checked to determine if they have a message to send– You must wait for the token before you can send your message

• You can combine networks

LAN and WAN Components

• File Server– Stores programs and/or data for users to access

via a network

• Bridges– Connects similar networks together to facilitate

communications

• Gateways– Connects dissimilar networks together to

facilitate communications

Protocols

• TCP/IP– Extremely popular– Used to establish connections on the Internet

• IPX– Protocol used with Novell Communications

software

• SNA– Used by many mainframes and other IBM

systems

TCP/IP• Transmission Control Protocol / Internet

Protocol

• Developed for the sole purpose of communicating over large geographic areas

• Well suited to allow connectivity between dissimilar operating systems

• Standard used on the Internet since 1983

• To understand TCP/IP is to understand the Internet……. So let’s try

TCP/IP

• TCP/IP Protocol Stacks– Provides standards for network

communications

• Consists of 4 layers– Network Interface Layer– Internet Layer– Transport Layer– Application Layer

Network Interface Layer

• Consists of the Network Interface Card and the Network Interface Card Driver

• Responsible for putting packets on and off the wire

• Packet Switched Technologies supported:– X.25– Frame Relay– ATM

Internet Layer

• Encapsulates packets into internet datagrams and runs the routing algorithms

• Controls the messages as they are sent and received

• Resolves addresses

Transport Layer

• Provides communications sessions between computers

• Establishes sessions by polling destination computer’s port address

• TCP tells host computer how much data the destination computer can receive

• Establishes a connection

Applications Layer

• Area where applications gain access to the network– How applications talk to the network

• Microsoft provides two API’s (Application Programming Interfaces) for use with TCP/IP– Windows Sockets– NetBios over TCP/IP

IP Addresses• Looks like 223.107.2.200

• Acts as your mail address on the Internet

• Provided by a local ISP– Internet Service Provider

• 223.107.2 portion– Defines the network id

• 200– Defines the node on the network

• Subnet Addresses are used when a network has a sub-network

Controlling TCP/IP

• Dynamic Host Configuration Protocol (DHCP) is a program that centrally manages the allocation of TCP/IP information

• DHCP is a server program which runs on a Windows NT Server

• DHCP must have a static IP address

Network Communications• Telnet

– Remote terminal emulation protocol

– You must be known to the host and have an account on the host

• FTP– File Transfer Protocol

– Must have an account or the server allows anonymous accounts

– Program that transfers text and binary files between TCP/IP computers

Network Communications

• Web Browsers– Netscape, Internet Explorer

• Access documents and multimedia files using HTTP– Hypertext Transfer Protocol

• After the data is sent the connection is closed

Competitive Advantages using Telecommunications

• Groupware– Users share common databases– Able to collaborate on a variety of issues– Disparate forms of information can be

contained in a central database• Word Documents, Excel spreadsheets, Email• RDBMS’ required standardized data

– Easily facilitates mobile computing– Virtual meetings

Knowledge Sharing Editorial

• Leading-edge firms create and maintain a culture which promote knowledge creation by encouraging information sharing, openness and trust, cooperation and collaboration, continual search for knowledge and truth, risk taking, experimentation, and a respect other’s knowledge and expertise

Telecommunications and Teamwork

• Team– A well-defined group of individuals sharing a common

goal who must interact among themselves to perform their work

• Today’s teams must often transcend time and space

• Communication speed and convenience often make or break a team’s efforts

• Teams need the right information at the right time– Pulled rather than pushed

Telecommunications and Teamwork

• Teams need to rely on repositories of information from previous experiences rather than “re-invent the wheel”

• Telecommunications provide the tools to allow teams to quickly communicate, store and share results and cross time and space boundaries to maximize efforts

Competitive Advantages using Telecommunications

• The Internet• Cost reductions through teleconferencing and

videoconferencing• Voice Mail and electronic mail

– Cost reductions– Information can be pulled when needed

• EDI– Lower cost– Lock in customers and/or suppliers