Basic Concepts We will define basic telecommunication terms, such as: –analog –digital –bandwidth –compression –protocols –codes and bits

The architecture or protocol suite is the umbrella under which the devices communicate with each other

Congestion All networks are limited in how many peripherals they can support without experiencing too much degradation Today more and more peripherals are being added to networks New ways to eliminate congestion on a network have been developed

Eliminating Congestion Multiplex: –to transmit two or more signals over a single channel Compression: –reducing the representation of the information, but not the information itself –reducing the bandwidth or number of bits needed to encode information or a signal

Multiplexing Several devices can share a telephone line T-1 telephone line will carry 24 communication paths on one high-speed link T-3 provides 672 communication paths on one link

Compression Applications such as: graphics, x-ray images, video are bit intensive Thus require high bandwidth when transmitting Compression reduces the number of bits needed to transfer

Analog and Digital Telephone system developed to transmit speech Spoken words are transmitted as analog sound waves People speak in an analog format, in waves Telephone system was completely analog until 1960

Analog Components Telephones plugged into your home jacks Most TV signals and telephone lines from home to provider Most cable drops

Digital Components ISDN lines Fiber optic lines between telephone company offices

Analog Signals Move down telephone lines as electromagnetic waves The way it travels is expressed in frequency Frequency refers to the number of times per second that a wave oscillates or swings back and forth in a complete cycle from its starting point to its ending point

Analog Signals A complete cycle occurs when a wave starts at a zero point of voltage, goes to the highest positive point of the wave, down to the negative voltage portion, and then back to zero voltage

Analog Signals The higher the speed or frequency, the more complete cycles of a wave are completed in a period of time This speed or frequency is measured in Hertz Hertz: a measurement of frequency in cycles per second, 1 hertz is 1 cycle p/sec

Hertz A wave that oscillates or swings back and forth 10 times per second has a speed of 10 hertz or cycles per second Bandwidth or range of frequencies a service occupies is determined by subtracting the lower range from the higher range Hz (voice)= = 3000Hz

Analog Services Voice ( Hz) Microwave Radio (2-12 GHz) Analog cable TV signals ( MHz) Oscillate between a specific range of of frequencies

Analog versus Digital Analog system can no longer handle the increase in the number of calls that are being generated, was designed for lower volume Digital networks are faster, have more capacity, and are more reliable

Impairments on Analog Services Analog signals loose their power the longer they travel Signal meets resistance in the media (copper, coaxial cable, air), causes fading of the signal or attenuation of the signal Analog signals also pick up noise or electrical energy while travelling from power lines, light sources, and electrical machinery Requires: amplification to inhibit attenuation

Amplification To overcome resistance in a signal, analog signals are amplified while they travel over a medium Drawbacks amplification: –also increases level of noise in signal

Digital Signals Advantages digital signals: –higher speeds –clearer voice quality –fewer errors –less complex peripheral equipment required

Digital Signals No waves are transmitted Digital signals are transmitted in the form of binary bits Binary = being composed of two parts In telecommunications this means only on or off, one or zero piece(s) of information transmitted

Digital Signals Less error, because on-off easier to recreate than an analog signal or sine wave Easier to repair than analog signals When digital signals fade, are easy to REGENERATE (not amplify) over distance Noise is discarded along the digital path

Digital TV Great example of how digital transmission enhances clarity, because: –noise in signal eliminated –error detection high in digital systems, so distance from signal not a factor –signal lost altogether if it is not in range –provides studio quality voice and image –began in 1998, 100% in 2006

Digital Phone Services Digital technology first implemented in 1962 in the long distance network 1975: Northern Telecom introduces the first digital telephone switch (PBX) 1976: ATT #4ESS toll office switch 1977: NT installs first digital switch 1982: #5ESS calls digitally switched to end- users

Channel Banks Introduction of digital transmission between central offices in 1960’s Analog to digital conversions necessary Channel banks served this purpose Expensive to maintain, cumbersome, and expensive Led to development of digital switches

Basics Computers exchange bits to communicate with each other Bits are arranged in a predefined format to make them readable –ASCII: American Standard Code for Information Interchange –EBSDIC: Extended Binary Coded Decimal Interexchange

Basics Baud rate: is a measure of transmission speed over an analog phone line Baud rate measured differently than bit rate Bits are measured in seconds Baud rate measures the number of changes per second in an analog sine wave signal

Baud and Bit Rates A baud is one analog electrical signal One wave or cycle equals one baud 1200 baud line means that the analog wave completes 1200 cycles in one second 56,000 bits per second lines, carry 56,000 bits in one second, or 56Kbps

Codes ASCII code is limited to 128 characters –upper case –lower case –numbers –punctuation Does not include: –bold, underlining, font changes, tables, etc.

Attachments Word processors add their own codes to perform fancy word processing Easier to send the entire documents as attachment than to come up with coding schemes for all such specialized documents MIME: (multipurpose mail extension) mail protocol used send attachments

Bandwidth Refers to capacity Carrying capacity expressed differently for analog and digital transmissions –analog capacity measured in Hertz –digital capacity measured in bytes

Hertz Measure of frequency of analog services Example: –Co-axial cable with bandwidth of 400 MHz –means 400 million cycles per second –difference between lowest and highest frequency, within which the medium carries traffic

Hertz Cabling which carries between 200MHz and 300 MHz has a bandwidth or frequency of 100 MHz The greater the difference between highest and lowest frequency the greater the bandwidth or capacity of the medium

Bits ISDN, T-1, T-2, ATM are digital services speed is stated in the number of bits transmitted per second –T-1: 1.54 million bits p/s (Mbps) –ISDN: 64Kbps –ATM: 622 Mbps, or Gbps

Narrow/Wideband Narrowband T-1 at 1.54Mbps Analog phone lines at 3,000 Hz BRI ISDN at 64Kbps Wideband Broadcast TV 6MHz per channel Cable TV 700MHz ATM at Gbps SONET up to 13.22G T-3 at 44.7Mbps

Applications Wideband: –TV –Cable –Connections between telephone offices Narrowband: –phone connection to end users

Protocols Enable computers to communicate with each other Spell out the rules of interaction between two or more computers Handle error detection and correction and file transmission

Examples of Protocols Who transmits first? What is the structure of the addresses of devices such as computers? How are errors fixed? How long to wait before disconnecting? How to package data to be sent?

Architecture Ties computers and peripherals together into a coherent whole Forms the network which connects all devices together Layers within architectures have protocols to define functions such as routing, error checking and addressing

Examples of Architectures SNA: developed by IBM to tie together all their devices OSI: Open Standards Interconnection, developed by International Standards Organization, to allow devices from various vendors to communicate with each other

OSI Not widely implemented Laid foundation for the concept of open communications among vendors Basic concept of layering of groups of functions into 7 layers Each layer can be changed and developed independently

Layers 1: physical layer 2: data link layer 3: network layer 4: transport layer 5: session layer 6: presentation layer 7: application layer

Compression White spaces & redundant images removed Letter abbreviation Only changed part of image transmitted Many types of compression methods Based on mathematical algorithms Codec (coder/decoder) devices used to perform the algorithm

Streaming Media Software used to speed up transmission of video and audio over the Internet When graphics and text sent to your screen, text immediately available, graphs later Important feature of browsers to make material available as it downloads MPEG standards are used for streaming

Streaming Media ITU formed the Moving Picture Experts Group (MPEG) in 1991 to develop compression standards Made standard that more processing power needed to encode than to decode material RealNetworks Inc. Microsoft Corporation

Multiplexing Combines traffic from multiple telephones or data devices into one stream Allows many devices to share the same communication path Makes more efficient use of telephone lines Does not alter actual data sent Consists of special equipment, hardware

Networks LAN (local area network) WAN (wide area network) MAN (metropolitan area network)

Network Terminology Hub: wiring center to which all devices are connected within a segment of a LAN, connections with twisted pair cabling Switching Hub: allows multiple transmissions on a LAN segment Backbone: connects hubs together Bridge: connects multiple LAN’s together

Network Terminology Layer 2 switch: bridges with multiple ports, switch data between LAN segments Router: connects multiple LAN’s together, more complex than bridges, handle more protocols Routing Switches: fast router Server: centrally located computer which houses set of files, documents, data, etc.

Bridges Used to connect a small number of LAN’s Provide one common path to connect several LAN’s Easy to configure, all data sent to all devices on a network, appropriate device picks it up, broadcast feature Lack routing and congestion control

Routers Used to connect multiple LAN’s over large distances (differing buildings, cities) More sophisticated than bridges Can handle differing protocols from various LAN’s

Routers Capabilities: –flow control: if path congested holds data until capacity is available –path optimization: selects best available path with use of tables –sequencing: sends data in orderly packets –receipt acknowledgement: receiver send a message back to verify receipt of file

Routers Disadvantages: –Complex to install and maintain –Must have up-to-date address labels –Slower than bridges due to their complexity –Layer 3 device

Switching Routers Faster than non-switching routers Do not look up in tables where to send data Address placed in the pack sent