Telecommunication Networks

Telecommunications Networks HARISH MORWANI [email protected]

Communications Communications may be defined as the transmission of a signal by way of a medium from sender to receiver. Transmission Medium

Sender

Signal

Receiver

Telecommunications ●

Telecommunications - the electronic transmission of signals for communication –

Telephone

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Radio

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Television

Telecommunications Network ●

A telecommunications network is a network of telecommunications links and nodes arranged so that messages may be passed from one part of the network to another over multiple links and through various nodes.

PSTN - The Ist Telecommunication Network ●

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PSTN (public switched telephone network) is the world's collection of interconnected voice-oriented public telephone networks, both commercial and government-owned. It's also referred to as the Plain Old Telephone Service (POTS) Most of the Telephone lines provided by Public Switched Telephone Network had analog connections which transmits data in the form of electrical pulses. Now the trend is towards digital technology

Quality of Service ●

Quality of Service (QoS) refers to control mechanisms that can provide different priority to different users or data flows, or guarantee a certain level of performance to a data flow in accordance with requests from the application program

Local Exchange Carrier ●

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Local Exchange Carrier (LEC) is a regulatory term in telecommunications for the local telephone company. In the United States, wire line telephone companies are divided into two large categories: long distance (inter-exchange carrier, or IXCs) and local (local exchange carrier, or LECs).

Local Exchange Carrier ●

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Local phone calls are defined as calls originating and terminating within a Local Access and Transport Area (LATA) LATA-The geographical areas defining local telephone service. Any call within a LATA is handled by the local telephone company, but calls between LATAs must be handled by long-distance companies, even if the same local telephone company provides service in both LATAs

Local Exchange Carrier LATAs are linked to SLCs by means of copper wires. ●

(Subscriber Loop Carrier) A system that allows one pair of wires, that would normally provide one phone line, to carry multiple conversations.

Long Distance Tx. Media ●

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Guided – wire

Unguided – wireless

– Twisted Pair – Coaxial cable – Optical fiber

Microwave Satellite Infra-red Cellular phone system

For guided, the medium is more important For unguided, the bandwidth produced by the antenna is more important

Standards & Regulations ●

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Standards are used to ensure that there is smooth transmission of calls placed by subscribers of two different companies. Telecommunication standards are governed by ITU (International Telecommunication Union)

Network Access Alternatives ●

There are various alternatives for accessing a Network like – PBX – CELLULAR TELEPHONES – LEASED LINES

PBX

Private branch exchange (PBX) - a common internal phone switching system for medium to large-sized businesses. Provides advanced intelligent features to users, such as: 4-digit, special prefixes for WATS (wide area telephone service) PBX collects dialed digits and intelligently decides how to route this call for fastest speed

PBX

Additional advanced features: Voice mail Routes incoming calls to the best station set (automatic call distribution) Provides recorded messages and responds to touch-tone requests (automated attendant) Access to database storage and retrieval (interactive voice response)

Cellular Telephones

Leased Lines ●

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Many home computer users use POTS lines and conventional modems to connect to other computer systems. What if you need a faster service, or need one that is always on? You can get a leased line service. A basic leased line, or tie line, gives you a 56 Kbps data transfer rate.

Business Applications ● ● ●

Enterprise Collaboration System Electronic Commerce System Internal Business System

Enterprise Collaboration System ●

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When decisions have to be made, you need complete and accurate information wherever you are. (ECS comes in picture) It facilitate communication, coordination and collaboration among the members of an organization by giving them real-time Web conferencing, files at your fingertips, and a single inbox for your email, voicemail, and fax—all with wireless and voice access.

Electronic Commerce System ●

E-commerce (electronic commerce or EC) is the buying and selling of goods and services on the Internet.

Internal Business System ●

Interconnection of different branches/departments of the organization by linking LANs or WANs so that Managers can make inquiries and generate reports from corporate databases stored on distant network servers.

Business Value of Telecommunications ●

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Helps a company overcome geographic, time, cost and structural barriers Helps to provide better customer service Simplifies business processes (e.g. eliminates expensive business trips) Customers, Suppliers and employees can participate in meetings through teleconferencing

Components of Telecommunication Network ● ● ● ● ●

Terminals Telecommunication Processors Telecommunication Channels Computers Telecommunication Control Software

Terminals ●

Any I/O device that uses telecommunication network to transmit or receive data

Telecommunication Processors ●

Devices that are used for data transmission & reception eg. Modem, Switch, Router etc.

Telecommunication Channels ●

The media over which data is transmitted & received

Guess What??????

NOT DOG!!! COMPUTER ANY DESCRITION REQUIRED?

Telecommunication Control Software ●

Program that control telecommunication activities and manage the functions of the telecommunication network eg. Web browsers

TELECOMMUNICATION MEDIA ●

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Medium is the physical path between transmitter and receiver in a data transmission system Guided Medium: waves are guided along a solid medium path (twisted pair, coaxial cable, and optical fiber). Unguided medium: waves are propagated through the atmosphere and inner/outer space (satellite, laser, and wireless transmissions).

TWISTED PAIR WIRE UTP-cable

STP-cable

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Physical description: – – – – –

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Each wire with copper conductor Separately insulated wires Twisted together to reduce cross talk Often bundled into cables of two or four twisted pairs If enclosed in a sheath then is shielded twisted pair (STP) otherwise often for home usage unshielded twisted pair (UTP). Must be shield from voltage lines

Application: – Common in building for digital signaling used at speed of 10’s Mb/s (CAT3) and 100Mb/s (CAT5) over 100s meters. – Common for telephone interconnection at home and office buildings – Less expensive medium; limited in distance, bandwidth, and data rate.

COAXIAL CABLE ●

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Widely installed for use in business and other types of LANs. Consists of inter copper insulator covered by cladding material, and then covered by an outer jacket  Inner conductor is solid copper metal  Separated by insulating material  Outer conductor is braided shielded (ground)  Covered by sheath material

COAXIAL CABLE ●

Applications: – TV distribution (cable tv); long distance telephone transmission; short run computer system links – Local area networks

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Transmission characteristics: – Can transmit analog and digital signals – Usable spectrum for analog signaling is about 400 Mhz – Amplifier needed for analog signals for less than 1 Km and less distance for higher frequency – Repeater needed for digital signals every Km or less distance for higher data rates – Operation of 100’s Mb/s over 1 Km.

OPTICAL FIBRE ●

Physical Description: – – – –

Glass or plastic core of optical fiber = 2to125 µm Cladding is an insulating material Jacket is a protective cover Laser or light emitting diode provides transmission light source

Applications: ● ● ● ● ●

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Long distance telecommunication Greater capacity; 2 Gb/s over 10’s of Km Smaller size and lighter weight Lower attenuation (reduction in strength of signal) Electromagnetic isolation – not effected by external electromagnetic environment. More privacy Greater repeater spacing – fewer repeaters, reduces line regeneration cost

Terrestrial Microwave ●

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Electromagnetic waves with a very high frequency ranging from 1000-30000 MHz are called microwaves Physical applications: – Terrestrial microwave – long haul telecommunication service (alternative to coaxial or optical fiber) – Few amplifier and repeaters – Propagation via towers located without blockage from trees, etc (towers less than 60 miles apart)

Concept of repeaters

Communication Satelite ● ●

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Satellite is a microwave relay station placed in outer space Placed 36000 kms above the equator with an orbit speed that exactly matches the earth’s rotation speed. This allows a ground station to aim its antenna at a fixed point in the sky Satellite ground stations are aligned to the space satellite, establishes a link, broadcast at a specified frequency. Ground station normally operate at a number of frequencies – full duplex Satellite space antenna is aligned to the ground station establishes a link and transmits at the specified frequency. Satellite are capable of transmitting at multiple frequencies simultaneously, full duplex. The transmission frequency (Ground station) is 4GHz and retransmission frequency (Satellite) is 6GHz to avoid interference with the incoming signal

Characteristics ●

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Each satellite can receive back its own transmission & check whether the tx. was proper or not. Can retransmit in case of error The tx. And reception cost is independent of the location Too expensive Signal is broadcasted so proper security measures are necessary to prevent unauthorized tampering of data

MODEM ● ● ●

It stands for MOdulator-DEModulator Modulation: Digital to Analog Demodulation: Analog to Digital

MOdulator

DEMOdulator

Multiplexing ●

The combining of two or more information channels onto a common transmission medium.

Frequency Division Multiplexing ●

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The deriving of two or more simultaneous, continuous channels from a transmission medium by assigning a separate portion of the available frequency spectrum to each of the individual channels. Transmission is organized in frequency channels, assigned for an exclusive use by a single user at a time

Time Division Multiplexing •

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A single carrier frequency channel is shared by a number of users, one after another. Transmission is organized in repetitive “time-frames”. Each frame consists of groups of pulses - time slots. Each user is assigned a separate time-slot

Inter-networked Processors ●

Switches: Connects different telecomm. circuits in a network so that a message can reach to its intended destination

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Routers: Interconnects networks based on different protocols, so that a message can be routed to its destination

Inter-networked Processors ●

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Hubs: Provides automatic switching among connections called ports for shared access to a network resource Gateways: Interconnects networks that use different communication architectures

Telecommunication Software ●

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These software package provides a variety of communication support services like Access Control Establishes comm. parameters such as tx. Speed, mode & direction. (User specific services such as Automatic Telephone dialing and automatic answering of telephone calls etc.) Tx. Control Tx. in the form of files. Error checking & correction

Telecommunication Software ●

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Network Mgmt. Software such as Network Operating System determine tx. priorities (Waiting queues of Tx. requests) Error Control Errors caused by distortion in the channel can be detected & corrected by the software. Re-Tx. in case of errors Security Mgmt. Protects the network from unauthorized access (Encryption)

Communication Channels (ANALOG V/S DIGITAL) ● ●

Analog: Continuously varying quantities Digital: 2 possible values (on/off; 0/1)

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Voltage

Voltage

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Time

Time

Analog

Digital

(ANALOG V/S DIGITAL) ANALOG

DIGITAL

Voice Tx.

Data, Voice & Video Tx,

Electrical pulses

Discrete pulses

Useful for long distance tx. Short distance Tx. Digital-to-analog Problems like attenuation, conversion is done for long Higher power requirements distance Tx. etc. may arise

Switching Alternatives (Circuit Switching) ●

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Circuit switching is a dedicated communications path established between two stations or multiple end points through nodes of the WAN Transmission path is a connected sequence of physical link between nodes. On each link, a logical channel is dedicated to the connection. Data generated by the source station are transmitted along dedicated path as rapidly as possible. At each node, incoming data are routed or switched to the appropriate outgoing channel without excessive delay. However, if data processing is required, some delay is experienced. Example of circuit switching above is the telephone networks.

Circuit Switching ●

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It’s the method used by the telephone network Caller A call has three phases: 1. Establish circuit from end-to-end (“dialing”), 2. Communicate, 3. Close circuit (“tear down”). If circuit not available: “busy signal”

Boston Switch

Callee processing delay at switch propagation delay between caller and and Boston switch

(1)

(2)

DATA (3)

LA Switch

Packet Switching Technologies ●

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It is not necessary (as in circuit switching) to dedicate transmission capacity along a path through the WAN rather data are sent out in a sequence of small chucks, called packets. Each packet, consisting of several bits is passed through the network from node to node along some path leading from the source to the destination At each node along the path, the entire packet is received, stored briefly, and then transmitted to the next node. At destination all individual packets are assembled together to form the complete text and message from the source. Each packet is identified as to its place in the overall text for reassembly. Packet switching networks are commonly used for computer-tocomputer communications. If packet errors occur, the packet is retransmitted.

Packet Switching  

Used in the Internet Data is sent in Packets (header contains control info, e.g., source and destination addresses)

Header

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Host 1

Host 2 Node 1

Data

transmiss ion time of Packet 1 at Host 1

Per-packet routing At each node the entire packet is received, stored, and then forwarded (storeand-forward networks) No capacity is allocated

Packet 1 Packet 2 Packet 3

Node 2

propagation delay between Host 1 & Node 2 Packet 1 Packet 2 Packet 3

processing delay of Packet 1 at Node 2 Packet 1 Packet 2 Packet 3

Packet switching also show reordering Packets in a flow may not follow the same path (depends on routing as we will see later)  packets may be reordered Host C Host D

Host A Node 1

Node 2 Node 3 Node 5

Host B Node 6 Node 4

Node 7

Host E

Differences Between Circuit & Packet Switching Circuit-switching Guaranteed capacity

Packet-Switching No guarantees

Capacity is wasted if data More efficient is bursty (variable tx. rate) Before sending data establishes a path All data in a single flow follow one path No reordering; constant delay; no pkt drops

Send data immediately Different packets might follow different paths Packets may be reordered, delayed, or dropped

ATM ● ●

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Asynchronous Transfer Mode A low-layer networking technology based on fast packet-switching of small fixed size packets called cells All slots are the same size (53 bytes = 1 ATM cell  48 bytes data+5 bytes control information) ATM provides a single transport mechanism for integrated services traffic: data, voice, video, image, graphics...

Bandwidth Alternatives ●

Bandwidth –

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Voice-band Low speed Analog channels(300 to 6600 bps) Medium-band Medium speed channels (9600 bps to 100 mbps) Broad-band High speed digital channels (256000 bps to several billion bps)

Telecommunication Equipment for WAN ●

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Point of Presence (POP): It usually means a city or a location where a network can be connected to another one. POP allows customers to access WAN by means of a local analog telephone Backbone: It carries the most traffic on a communication network. LANs are connected to the backbone via bridges and routers. Backbone serves as a communication highway for LAN-toLAN traffic

Applications of WAN ●

LAN-to-LAN Connections

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Transaction Acquisition: Information about a transaction can be instantly relayed. The POS terminal is linked to the network and the acquired data is collected for accounting. Electronic Data Interchange (EDI): Electronic Data Interchange is the electronic transmission of business documents between vendor and customer computer systems. The use of EDI guarantees optimal efficiency and accuracy of the purchasing cycle.

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