Week-16

Week-16 Telecommunications and Networks

The Telecommunications Revolution 

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The 1990's mark the beginning of a "Telecommunications Revolution". This can mean a quantum change in the information available to people and organizations. Although the transition will be slow for some, the development seems inevitable. Eventually, all of us will be affected and all of us will be dependent upon the new technology as a basic information resource. The explosive growth of information There has been a recent, explosive growth in the quantity of information that is accessible and useful for individuals and organizations. Text and data are routinely composed on computers. This information can now be organized to allow access through global networks in ways that were difficult or impossible in the past. The quality of information has also changed dramatically. And although new kinds of costs are incurred, the overall cost of information is going down.

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Links between people and organizations over universal networks (LAN with WAN) Communication has also increased. Our social, political and management systems are becoming more sophisticated and dependent upon effective communication. Organizations rely upon a wider variety of supports and relationships. Complex organizations are entering into collaborative relationships requiring extensive communication. These is also greater recognition of the value of links with persons in other communities who share common experiences and challenges.

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A new paradigm: Everyone can read - - Everyone can publish The Telecommunications Revolution has led to a paradigm shift in the creation and distribution of information. In open access systems, everyone can search out and read available material from throughout a community and around the world. More importantly, everyone can contribute - can comment, or create new material for others to read. Distributed processing: Linking personal computers back together Personal computers gave users more control over powerful tools for organizing and analyzing information. Distribution was encouraged within organizations and communities - as the means for working with information was more widely distributed. Networking computers together allows the creation of an information network without reducing local control over the tools to process and use information.

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An emerging "basic" computer - multi-media/ CD/ digital phone/ cable There is a common misperception that the hardware and software requirements of the information highway are many years away and likely to be too expensive for many. Powerful multi-media computers with color graphics, substantial disk storage, "GUI" (graphics) software interfaces, communications cards and even CD players are now standard in $1500 computer systems and are present in every normal home today. Digital phone and cable systems will soon offer inexpensive, very efficient and competitive choices in most communities. Until then, more limited modem connections seem adequate for general purposes. The time required to organize people and information and to adjust to the opportunities Information networks are more about people and organizations than about technology.

Telecommunications System Components

Fig 16.1: Components of a telecommunications system

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There are many, many pieces of equipment between those two computers: look again at Figure 16.1. We'll dissect and examine the equipment and the functions each element serves. Protocols are used to tell the hardware components how to transmit data within a network and between networks. They can also be thought of as a set of rules and procedures for exchanging information between computers in networks. They define how the various communication links are established, how information is transmitted, and how errors are detected and corrected between networks. Most important, the use of protocols allows different makes and types of computers to talk to each other. Examples: HTTP, SMTP, FTP, TCP and IP etc,

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Types of Signals: Analog and Digital Everything going into a computer system must be transformed into digital signals, and operate at shorter distances. In the networking world, however, most of the data are transmitted over telephone lines. These lines don't recognize zeros and ones. They only understand what are called analog signals, and operate at larger distances. To change the signals back and forth between analog and digital transmission methods, you need a modem. The purpose of a modem (modulator/demodulator) is to: Change digital signals from computers to analog signals that telephone lines can carry change analog signals back to digital signals that the computer can understand.

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A channel is the facility through which information is transmitted between physical locations in a network. That's just a fancy way of saying that a channel is the highway on which data travel. Think again about the interstate highway systems.

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Communications Processors and Software In most cases you won't use front-end processors, multiplexers, concentrators, or controllers on your personal computer. These pieces of equipment are used on larger networks and are reserved for the technologies. They are interesting pieces of the puzzle, though, so let's go ahead and look at them. Sometimes the host computer on a large network gets overloaded processing data, monitoring transmissions, controlling the system, etc. That's where front-end processors come in handy. Front-end processors don't store data or application programs. You can't use them for general computing. This type of computer does nothing but process the electronic transmissions between computers on a network system. It's there to relieve the host computer from transmission processing so the host can serve your basic computing needs.

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A Concentrator is a telecommunications computer that collects data signals and holds them. When enough signals are collected, the computer sends them on to the host as a batch. A Controller computer simply processes signals between the CPU and terminals, printers, or other peripheral devices attached to the network. Multiplexers are the equipment, that combines many channel (signals) into single channel (signal). i.e. Many to one. What the New York bank will do is install a multiplexer component in the branch to which each of the 10 terminals will be connected. The multiplexer gathers the signals from each terminal and transmits them to the New York bank over a single transmission line. Now you're talking efficiency

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Routers How does your Internet Service Provider manage to send your email to the right place? We're talking millions and millions of people sending email every day. How in the world do you keep from getting Mary's email intended for Billy in Atlanta? If you ever noticed, each computer user connected to a network has a separate, individual address. No two addresses are exactly the same. All of these addresses are stored on various computers placed around the networks. Software stored on routers uses these addresses to route the data to the right location. Routers use protocols to help route data around the many networks to get them to their correct destination.

Communications Networks and Standards 

The topology, which is the shape or configuration of a network, or physical layout of the network.

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Network Topologies

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One way of describing a network is by its shape:

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Star, Bus, or Ring.

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The star network is usually used in larger companies with lots of communications traffic. All nodes are connected to centralized location, which is a hub or switch. The distinct drawback is that if the hub or switch goes down (malfunction), the whole network goes down. You've experienced this type of situation if you've tried to access a Web site and you get a message that says the host computer is down.

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There is no centralized node with the bus network. Rather, all the computers in the network are linked with cables. This type of network is usually used in smaller companies with few computers and a much lower volume of traffic. Like the bus network, the ring network doesn't have a centralized node either. However, with this topology, if one computer goes down, the other computers can still process data and transactions.

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Types of Networks

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PAN, LAN, MAN, WAN

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You are already familiar with these types of networks according to geographical area.

Routing to another LAN • walkthrough: routing from host A to host B via Router R

Routing to another LAN ❒ A creates IP packet with source A, destination B ❒ A uses ARP (or table) to get R’s MAC address for 111.111.111.110 (Router with IP address) ❒ A creates Ethernet frame with R's MAC address as destination, Ethernet frame contains A-to-B IP datagram ❒ A’s data link layer sends Ethernet frame ❒ R’s data link layer receives Ethernet frame ❒ R removes IP datagram from Ethernet frame, sees that it is destined to B ❒ R uses ARP (or table) to get B’s MAC address ❒ R creates frame containing A-to-B IP datagram and sends it to B

The Network Core ❒ Mesh of interconnected routers ❒ the fundamental question: how is data transferred through network? ❍ circuit switching: dedicated circuit per call: telephone net

❍ packet-switching: data sent through network in discrete “chunks”.

Ethernet 

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A local-area network (LAN) protocol developed by Xerox Corporation in cooperation with DEC and Intel in 1976. It is one of the most widely implemented LAN standards. Originally transmission rates were 3 Megabits per second (Mb/s) over thick coaxial cable. Media today include fiber, twisted-pair (copper), and several coaxial cable types. Rates are upto 10 Gigabits per second or 10,000 Mb/s. One of the most common local area network (LAN) wiring schemes, Ethernet has a transmission rate of 10 megabits per second; a newer standard called Fast Ethernet will carry 100 megabits per second.

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Carrier Sense Multiple Access Collision Detection is a network access method in which devices that are ready to transmit data first check the channel for a carrier. If no carrier is sensed, a device can transmit. If two devices transmit at once, a collision occurs and each computer backs off and waits a random amount of time before attempting to retransmit. This is the access method used by Ethernet. Differential Manchester Encoding scheme is used by Ethernet.

Token Ring 

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LAN technology in which packets are conveyed between network end stations by a token moving continuously around a closed ring between all the stations. Runs at 4 or 16 Mbps. A LAN architecture with transmission speeds of 4 or 16 Mbits/sec. Though less popular than Ethernet, it performs better under heavy load. It conforms to international standards and is supported by all major network software suppliers.

ATM 

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Asynchronous Transfer Mode A high bandwidth, High speed (up to 155 Mbps), controlled-delay fixed-size packet switching and transmission system integrating multiple data types (voice, video, and data). Uses fixed-size packets also known as "cells" (ATM is often referred to as "cell relay"). Communication technology that uses high-bandwidth, low-delay transport technology, and multiplexing techniques. Through dedicated media connections it provides simultaneous transport of voice, video, and data signals more than 50 times faster than current technology. May be used in phone and computer networks of the future.

ISDN 

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Integrated Services Digital Network (ISDN) is a set of CCITT/ITU standards for digital transmission over ordinary telephone copper wire as well as over other media. Home and business users who install an ISDN adapter (in place of a modem) can see highly-graphic Web pages arriving very quickly (up to 128 Kbps). ISDN requires adapters at both ends of the transmission so your access provider also needs an ISDN adapter. Integrated Services Digital Network is a telephone network facility for transmitting digital and analog information over a digital network connection. Integrated Services Digital Network is a way to move data over existing regular phone lines but at a fast rate. In theory, ISDN can provide speeds of roughly 128,000 bits-per-second over a regular phone line, though in practice, most people will be limited to 56,000 or 64,000 bits-per-second

Frame relay 

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Frame relay is a telecommunication service designed for costefficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). A packet-switching protocol for connecting devices on a Wide Area Network (WAN). Frame relay networks in the United States support data transfer rates at T-1 (1.544 Mbps) and T-3 (45 Mbps) speeds. Most telephone companies now provide frame relay service for customers who want connections from 56 Kbps to T-1 speeds. A fast packet switching protocol. Used mainly in Wide Area Networks. It differs from ATM in that packets can have variable length. Is an efficient data transmission technique used to send digital information quickly and cheaply to one or many destinations from one or many end-points. Commonly implemented for voice and data as an encapsulation technique, used between local area networks (LANs) over a wide area network (WAN). Each end-user gets a private line (or leased line) to a frame relay node.

Network Standards 

OSI Layers Model

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TCP/IP Layers Model

OSI Layers Model Physical layer: how to transfer bits correctly − conversion of bits into signals, what is 0, 1? How long does a bit lasts? − Concerned with the physical characteristics of interfaces and media. − Concerned with Physical topology, Transmission rate and transmission mode. edit] Evolution of graphic user interfaces  Data link layer: how to transfer frames correctly reliably transfer frames over a link, how to identify a frame, error control, Physical addressing, Access control, Flow control − Divided into Media Access Control (MAC) and Logical Link Control (LLC) layers  Network layer: how to send a packet to the destination (hop by hop)? − Forwarding, routing, congestion control, segmentation & reassembly, Logical addressing 

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Transport: end to end communication or process to process communication. − That layer that runs at end points but not at intermediate hops. − Connection establishment/management/termination, error control/flow control/multiplexing, Service-point addressing. − Reliability Session layer: allows users to establish session, enhanced services or Provides mechanism for managing a dialogue between end-user application processes. − Supports duplex or half- duplex operations. − Dialogue control and Synchronization. Presentation layer: provides general solutions to users. − Compression/Decompression, syntax translation conversion, Encryption/Decryption Application layer: Interfaces directly to and performs common application services for application processes. − Variety of protocols/services that are commonly used like − File transfer (FTP) − Network virtual terminal. (Telnet). − Mail services (Email). − Directory services (Domain/DNS).

TCP/IP Layers Model 

TCP/IP reference model:

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Application layer (Telnet, FTP SMPT, DNS, NNTP, HTTP)

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Transport layer (TCP, UDP)

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Internet layer (IP)

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Host to Network layer (Ethernet, FDDI, X.25)

TCP/IP reference model 

Application layer (Telnet, FTP, SMPT, DNS, HTTP)

– Interfaces directly to and performs common application services for application processes. 

Transport layer (TCP, UDP)

– Allow entities at end hosts to communicate – TCP (transmission control protocol): reliable connection-oriented – UDP (user datagram protocol): unreliable connectionless 

Internet layer (IP)

– A packet switching network based on connectionless communication. Hosts send packets into the network and then the packets travel independently to their destinations. – Format conversion: for different networks. – Packet format and protocol: IP

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Host to Network layer (Ethernet, FDDI, X.25)

– Undefined, rely on the existing technology - must be able to send IP packets over this layer.

OSI and TCP/IP Models