Networks & Networking

MSI Lecture on 15th February 2003

By Dr.I.Sarafis

Computer Networks Concepts

• Objectives– describe components of telecommunications

system– calculate capacity of telecommunications

channels & evaluate transmission media– compare types of networks & network services– compare alternative network services– identify applications for supporting electronic

commerce, business

Management challenges

– Telecommunications revolution

– Components, functions of telecommunications system

– Communications networks

– Electronic commerce & electronic business technologies

1. MANAGING LOCAL AREA NETWORKS: Must be carefully administered, monitored, vulnerable to interruption, data loss, viruses

2. MANAGING BANDWIDTH:

While costs per unit are dropping and capacity is growing, sudden demand can overwhelm system

Connection Types

• Need for communication

• Communication between 2 devices– Point-to-point

• Multi subscriber communication– 3 -> 6 devices , 3 lines– 4 -> 12 devices , 6 lines

The need for networks

• Ν subscribers– Ν-1 devices– (Ν-1)/2 lines

Communication Network

Communication Node

Terminal Node

Network Uses

Benefits of Networks

• Resource sharing

• Reliability

• Money savings

• Communication

An example

Convergence between I.T. & Telecommunications

– No significant difference between processing of data (computers) and of telecommunication signals (communication equipment)

– Unification between data, voice, video communications

– Hard to distinguish between uni-processor computers, multi-processor systems, local area networks, wide area networks

Network Services

• Voice Networks– Information Transfer– Signaling– Call waiting, Caller ID, call redirection etc.

• Data Networks– File, printer sharing– E-mail, ftp, chat, web– Videoconference, multimedia streaming

• Unification of Services

Communication Categories

• Synchronous

• AsynchronousBit Series

Packets

Network

Network

Bit Errors

Asynchronous communication categories

• Connection oriented

• Connectionless

Connection oriented: packets are transmitted with the right order

Connectionless: packets are transmitted with arbitrary order and without guarantied delivery

Network

Network

Switching

Multiplexing

Using multiplexing multiple sources are transmitted through the same physical medium

Multiplexer De-multiplexer

Circuit Switching

PBX Networks(Public Branch eXchange)

Public Telephone Networks are circuit switched

Switching Node

Public circuit-switching network

Packet Switching

In packet switching information is broken in packets.Each packet is routed independently

Switching techniques comparison

• Circuit switching– Continuous channel occupation– Compatibility of transfer rate– No information processing

• Packet switching – Better bandwidth allocation– Transfer rate conversion– Continuous operation under load– Packet priority techniques

Asynchronous Transfer Mode (ATM)

• New technology– Combines advantages of both techniques– Guarantied packet delivery (circuit switching)– Quality of Service (QoS) (circuit switching)– Effectiveness, flexibility (packet switching)

Autonomous Packets (datagram)

Digital & Analog sources

Digital Source

Digital Source

Analog Source

Analog Source

Digital & Analog signalsA

mp

litu

de

Time Time

Time Time

Digital Signals

Analog Signals

Am

pli

tud

e

Am

pli

tud

eA

mp

litu

de

Advantages of Digital Technologies

• Use of cheap digital circuits• Application of Integrated Circuits techniques• High security with the use of data

cryptography• Integration of a variety of information (data,

voice, video, text)• Easy signal repetition over long distances

– Disadvantages• High bandwidth• Synchronization

Data Coding

Communication Protocols

• What is it?– Specific procedures between devices– Followed with specific order– The “language” of communicating

• Every day protocols example– Waiting for someone to finish talking before we

start talking– Expressing pleasure when seeing someone after

long time

Network Architecture

– Use of independent structural elements– Layered architecture– Layers / levels– Transparent communication– Differences between architectures

• Communication between incompatible devices– Is very complicated to handled by a single

protocol– Use of layered & structured architecture

Layered Architecture

Layers, protocols & interfaces

What Goes Wrong in the Network?

• Bit-level errors (electrical interference)

• Packet-level errors (congestion)

• Link and node failures

• Messages are delayed

• Messages are deliver out-of-order

• Third parties eavesdrop

Advantages of Layered Architecture

• Partitioning the problem– To small ones and– Easier to handle

• Easy upgrade / addition of services– Since the necessary changes concern one layer

only

• General advantages of using modules

The interface

• Defines – The basic operations and services– That a layer offers to the higher one

• Defines– The messages between neighbouring layers

• Should be– Clear & explicit

Architectures standards

• System Network Architecture (SNA), IBM

• Open Systems Interconnection (OSI), ISO

• TCP/IP– Transfer Control Protocol / Internet Protocol

• Architecture is– The collection of protocols, layers & interfaces

OSI Model

OSI LayersApplication LayerProvides access to network services for the users

Presentation LayerCares for the proper data representation

Session LayerControls the communication process. Starts, ends and manages sessions and connections

OSI LayersTransport LayerCares for the reliable data transfer, for data flow control and for error correction

Network LayerIsolates higher layers from transfer and switching technologies. Cares for data transfer through the proper route

Data link LayerEnsures reliable information transfer on the physical media. Transfers frames with synchronization, flow control & error correction

Physical LayerDeals with cabling issues and physical (electrical) bit transfer

Network Categories(geographical)

• Local Area Networks (LANs)

• Wide Area Networks (WANs)

Comparison LAN / WAN

• Different area size

• Different implementation techniques

• Different organizations

• Different transfer rates (speeds)

Standardization & Standards

• What is it?

• Benefits :– Independence from companies– Independence from architectures– Competitiveness

Example:TCP/IP is a de facto standard and is documented with a large number of RFCs (Request for Comments). Despite the fact that it is not approved by any specific organization, TCP/IP is been used in the largest implemented network in the world, the Internet, instead of OSI which is official.

Standardization Organizations

– ISO (International Standards Organization)

– ITU (International Telecommunication Union )

– IETF (Internet Engineering Task Force)– IAB (Internet Architecture Board)– ETSI (European Telecommunications

Standards Institute)– ΕΛΟΤ (Greek Standards Organization)

Note:Official standards firstly are been developed and then companies are trying to comply. On the other hand, de-facto standards are not becoming standards until they are recognized for their usability and efficiency.

Integrated Services Networks

• Integrated Services Digital Network, ISDN

• narrowband ISDN• broadband ISDN ή B-ISDN• ΑΤΜ

Integrated Services Networks

Note:A Wide Area Integrated Network should provide high-speed integrated services (voice, data, video, images). It is expected that there will be a variety of applications that will take advantage of such networks. Applications like video-on-demand, video-conference and other bandwidth-intensive applications.To realize the consequences of high speed transfer rates, here is a simple example:a high resolution image (109 bits) would need over 4 hrs to be transferred through a 64 kbps line, 11 minutes through a 1.5 Mbps line and only 7 seconds through a 150 Mbps ATM line.

Data Rate Requirements

Network Topologies

• Linear Bus - Ethernet/IEEE 802.3 10Base2 and 10Base5

• Star Wired Ring - Token Ring/IEEE 802.5• Star Wired Bus - Ethernet/IEEE 802.3i 10BaseT• Dual Counter Rotating Ring - FDDI/ANSI

X3T9.5• Wireless - Product Specific

Star topology

Node Node

Node Node

Central Hub

Ring Topology

Node

NodeNode

Node

Data direction

ReceiverTransmitter

Repeater

Bus Topology

Node Node

Node

Star-wired Bus Topology

Node

Concentrator Hub

Node

Node

Node

Node

Node

Physical Media

• Physical media provide the connections between network devices that make internetworking possible.

• There are four main types of physical media in widespread use today:– Coaxial Cable

– Twisted Pair

– Fiber Optic Cable

– Wireless Media

Wired media

• Copper wires on posts– Too few cables

• Twisted pairs– Δέσμες καλωδίων– Twisted to avoid co-hearing– Inside tubes fro protection

• Coaxial cables– Used in long installations and underwater

Copper wires

• Twisted so that the pairs are marked

• Thousands of kilometers installed

• Low-pass filters– Difficulty for Data

Twisted Pair Characteristics

• Advantages– Ease of use and installation– Low cost– Wide available

• Disadvantages– Noise sensitive– Lower capacity than coaxial

Coaxial cable

Coaxial cable characteristics

• Advantages – Low noise sensitivity– Increased bandwidth & security– Longer distances

• Disadvantages – More expensive and bulky– Mechanical stiffness and difficult to connect

Fiber optics

Fiber optics characteristics

• Advantages – Very large bandwidth

• Up to 9.9 Gbps

– Long transmission distances– Insensitive to noise– More secure to eavesdropping

• Disadvantages – Expensive, especially in small scale

installations– Termination & connection difficulties (special

equipment and expert personnel needed )

Wireless transmission media

• Advantages – Independent of physical media

• Disadvantages – Noise sensitivity– Data security– High transmitter power– Limited available frequencies

Land microwave connections

• Directed transmission

• Very high frequencies (2-40 GHz)

• Parabolic antennas (dishes)

• Every 40-50 kms

• Up to 100s Mbps

• Example - > ΟΤΕ antennas

Satellite microwave connections

• Uplink– For sending data from earth stations

• & Downlink– For broadcasting (e.g. TV) but also for unicast

(satellite Internet)

Geostatic satellites

Earth curvature

Satellite coverage

Cellular telephony

• Spatial cells (1.5 – 13 kms)

• Low power transmitter

• Frequencies 900 & 1800 MHz

• Different for adjacent cells

• Data transmission capability (GPRS)