1. Introduction to Networks and Distributed Systems

RouterRouter

Network server(such as UNIX, Novell NetWare orWindows NT/2000):• File server.• Print services.• Network login.

Local WWW/Internet server:- HTTP (for WWW)- FTP (for remote file transfer)- Telnet (for remote login)- SMTP (for electronic mail)

Access to remoteInternet access

Internet

1.1 Application of the Internet

Internet (Globalinfrastructurefor information

which uses TCP/IP

communication)

World-wide web (WWW)

Electroniccommerce

Remote filetransfer

Remote login

Digital video/audio/applications download

Videoconferencing

Remotecontrol

Electronicmail

Distributeddatabases

Searchfacilities

+ Purchasing goods

+ Home banking

+ Electronic cash

+ MP3 audio files

+ MPEG movies (DVD/etc)

+ Software applications/updates

+ White pages

+ Key words

+ Yellow pages

Interconnectionof networks(Intranets)

1.2 Application of the Internet

Internet (Globalinfrastructurefor information

which uses TCP/IP

communication)

World-wide web (WWW)

Electroniccommerce

Remote filetransfer

Remote login

Digital video/audio/applications download

Videoconferencing

Remotecontrol

Electronicmail

Searchfacilities

+ Global database

+ Interconnected links

+ Integrated sound/text/images/video

+ Business meetings

+ Family/friends conversations

+ Remote presentations (/lectures)

+ Any size

+ Synchronization

+ Enhanced search

Interconnectionof networks(Intranets)

Distributeddatabases

1.3 Some of the applications of Internet/networks HomeHome

Privatenetworks

Internet/Intranet

IndustryIndustry

+ Distributed Databases

+ Electronic Commerce

+ New markets

+ Electronic mail

+Automated systems (front-office/paperless office)

+ Automated customers +Sharing of electronic information (design/data)

+ Technical information/backup

+ Remote control/logging

+Integrated digital communications (Audio/Video)

+ WWW information

+ Remote working

+ Sales information

CommerceCommerce

+ Video conferencing

Provide by telecommunicationcompanies or privateorganizations

1.4 From cash-based to cashless Electronic commerce

Cash-basedsociety

Cashlesssociety

Credit/debitcards

ATM

Automatedbanking

Share dealings

withencryption

withencryption

Privatenetworks

Internet/Intranet

1.5 Advantages of Internet shopping

1. If the goods are in an electronic format, such as digital audio or video, the customer can typically sample the material before buying it. A good example of this is listening to tracks on a music CD, or viewing chapters from a book. This allows a consumer to make a better choice on their products.

2. Customers do not have transport problems on the Internet (apart from TCP/IP transport problems).

3. The Internet is open 24 hours a day, 365 days per year. It is not affected by holidays, weather, traffic and parking problems and industrial strikes (not directly). The Internet allows for backup systems to be installed over geographically wide areas, so that companies do not have to rely on a single source of supply.

4. Apart from a computer, a modem, and an Internet connection, all that is required is a credit or a debit card. No need to find loose change, or to wait in a queue.

5. The Internet is not affected by the weather (well, not directly, of course), while traditional shopping involves bracing all kinds of weather (although, some weather is pleasurable, most of it is okay, but the rest is pretty bad).

6. It can be based anywhere, in virtually any country, in any town or in any building. Traditional shopping tends to group shops around key shopping areas, such as cities, or shopping centres.

7. Internet-based companies can quickly update their stock provision, at the press of a button, worldwide. Price changes can also be quickly reported.

8. Internet-based companies can typically offer a much greater supply of goods, as they do not necessarily have to have the goods they display actually in stock. They can simply take an order, and then quickly order the goods from the supplier.

1.6 Problems with Internet shopping

1. Internet shopping typically depends on the postal service delivery, which can take days to deliver a single package.

2. Internet shopping is highly dependent on the speed of delivery from the supplier. Problems with suppliers can lead to lengthy time delays.

3. Post and package can considerably add to the cost of goods. Typically goods are cheaper on the Internet, but when post and packaging are added they end up being less of a bargain.

4. Consumers are quickly put-off by bad service, and slow delivery times. Typically, a consumer will only allow delivery times of a few days; once it is greater than this they may become annoyed, and not purchase over the Internet, again.

5. Internet shopping is becoming swamped with too many suppliers. It is often difficult to differentiate the good ones from the bad ones.

6. For non-electronic goods, such as clothes and jewellery, the consumer cannot properly feel, look at, or touch the goods, and will simply waste time in sampling them (similar to buying through a mail-order company).

1.7 Internet infrastructure

Internet infrastructure– any link may fail, butall nodes will still be ableto communicate, using a different route

Connection toanother node

1.8 Connection to the Internet(ANYTHING IS POSSIBLE!)

Internet

Kitchen appliances- status- configuration- servicing

Cookers- automatic control- remote monitoring of cooking

Cameras- security systems- long-distance monitoring- ‘virtual’ holidays

Central heating- automatic control- monitoring- automated billing- fault diagnosis

Cars- real-time diagnostics- servicing monitoring- efficiency calculations- tracking systems

1.9 Networks

Client Service

Network Protocol

Network interface

Communications protocol: – TCP/IP – SPX/IPX – NetBEUI – IBM DLC – DEC PATHWORKS

Interface to network: – NDIS2 – ODI – Manufacturer driver

Enables computers to share resources: – NetWare 3 – NetWare Directory Services

Connection to other computers: – NetWare network – Microsoft network

Ethernet/FDDI/ISDN/etc

NETWORKING OPERATING SYSTEMSNovell NetWare. This is the network created using Novell NetWare, typically NetWare 3 or NetWare 4. NetWare 4 has many great advantages over NetWare 3. NetWare 4 uses NetWare Directory Services (NDS) to create global networks. Windows NT/95/98/2000. Windows 95/98 and Windows 2000 (Workstation) create peer-to-peer networks where computers share resources, such as disk drives and printers. Windows NT/2000 (Server) can create a network with a network server, which allows the creation of network logins, file sharing, and so on.UNIX. A well-proven operating system which is typically used with high-powered workstations. It has always supported networking and is robust and extremely reliable.

NETWORKING OPERATING SYSTEMSNovell NetWare. This is the network created using Novell NetWare, typically NetWare 3 or NetWare 4. NetWare 4 has many great advantages over NetWare 3. NetWare 4 uses NetWare Directory Services (NDS) to create global networks. Windows NT/95/98/2000. Windows 95/98 and Windows 2000 (Workstation) create peer-to-peer networks where computers share resources, such as disk drives and printers. Windows NT/2000 (Server) can create a network with a network server, which allows the creation of network logins, file sharing, and so on.UNIX. A well-proven operating system which is typically used with high-powered workstations. It has always supported networking and is robust and extremely reliable.NETWORKING PROTOCOLS

TCP/IP. This is the standard protocol which computers use to connect to the Internet and over UNIX-based networks. Each node on the network is granted an IP address which it uses for the time of its connection, or it can have a permanently assigned address.SPX/IPX. This protocol is used by computers over a NetWare-based network.NetBEUI. This protocol is used in a Microsoft Windows network.

NETWORKING PROTOCOLSTCP/IP. This is the standard protocol which computers use to connect to the Internet and over UNIX-based networks. Each node on the network is granted an IP address which it uses for the time of its connection, or it can have a permanently assigned address.SPX/IPX. This protocol is used by computers over a NetWare-based network.NetBEUI. This protocol is used in a Microsoft Windows network.

NETWORKING TECHNOLOGYEthernet. The most widely used networking technology where computers either connect to a network hub or a common bus.FDDI. A ring-based network, where computers connect either to a network hub or onto a fibre ring.ISDN. Used to connect computers over a telephone connection.Other: ATM/Token Ring/etc.

NETWORKING TECHNOLOGYEthernet. The most widely used networking technology where computers either connect to a network hub or a common bus.FDDI. A ring-based network, where computers connect either to a network hub or onto a fibre ring.ISDN. Used to connect computers over a telephone connection.Other: ATM/Token Ring/etc.

1.10 Overview

Java, HTMLJava. Programming language that can be used in WWW browsers and is hardware-independent.HTML. Standard programming language which is interpreted by a WWW browser.

Java, HTMLJava. Programming language that can be used in WWW browsers and is hardware-independent.HTML. Standard programming language which is interpreted by a WWW browser.

TCP/IPStandard protocol for the Internet and UNIXIP Addresses. 146.176.151.130DNS (Domain Name Services). www.pi.comApplications: TELNET/SMTP (Email)/HTTP

(WWW)/FTP/etc

TCP/IPStandard protocol for the Internet and UNIXIP Addresses. 146.176.151.130DNS (Domain Name Services). www.pi.comApplications: TELNET/SMTP (Email)/HTTP

(WWW)/FTP/etc

LANs, WANs and MANsWide area networks (WANs), which normally connect networks over a large physical area, such as between different buildings, towns or even countries.Local area networks (LANs), which connect computers within a single office or building. They typically connect to a common electronic connection – commonly known as a network backbone. LANs can connect to other networks either directly or through a WAN.Metropolitan area networks (MANs), which normally connect networks around a town or city. An example of a MAN is the EaStMAN network that connects universities and

colleges in Edinburgh and Stirling, UK.

LANs, WANs and MANsWide area networks (WANs), which normally connect networks over a large physical area, such as between different buildings, towns or even countries.Local area networks (LANs), which connect computers within a single office or building. They typically connect to a common electronic connection – commonly known as a network backbone. LANs can connect to other networks either directly or through a WAN.Metropolitan area networks (MANs), which normally connect networks around a town or city. An example of a MAN is the EaStMAN network that connects universities and

colleges in Edinburgh and Stirling, UK.

WWW and the InternetWWW. One of the applications of the Internet, and supports the hypertext principle (mixed text/images with embedded hyperlinks)Internet.. Infrastructure that supports TCP/IP communications.Connection. Direct connect or through an ISP (Internet Service Provider)

WWW and the InternetWWW. One of the applications of the Internet, and supports the hypertext principle (mixed text/images with embedded hyperlinks)Internet.. Infrastructure that supports TCP/IP communications.Connection. Direct connect or through an ISP (Internet Service Provider)

Application

Presentation

Session

Transport

Network

Data link

Physical

Application

Presentation

Session

Transport

Network

Data link

Physical

D N T S P A D

N T S P A

T S P A

S P A

P A

A

Sender Receiver

Virtualdata flow

Actualdata flow

1.11 OSI 7-layered Model OSI 7-layer Model (International Standards Organisation)Allow manufacturers of different systems to interconnect their equipment through standard interfaces. Allow software and hardware to integrate well and be portable on differing systems.Create a model which all the countries of the world use.

OSI 7-layer Model (International Standards Organisation)Allow manufacturers of different systems to interconnect their equipment through standard interfaces. Allow software and hardware to integrate well and be portable on differing systems.Create a model which all the countries of the world use.

Example layersPhysical/Data Link: Ethernet/FDDI/ISDN/etcNetwork: IP (Internet) or IPX (NetWare)Transport: TCP (Internet) or SPX (NetWare)Session: HTTP/FTP/TELNET/SMTP/etc

Example layersPhysical/Data Link: Ethernet/FDDI/ISDN/etcNetwork: IP (Internet) or IPX (NetWare)Transport: TCP (Internet) or SPX (NetWare)Session: HTTP/FTP/TELNET/SMTP/etc

1.12 OSI Layers

Physical. Defines the electrical characteristics of the communications channel and the transmitted signals, such as voltage levels, connector types, cabling, and so on.Data link. Ensures that the transmitted bits are received in a reliable way, such as adding extra bits to define the start and end of a data frame, adding extra error detection/correction bits and ensuring that multiple nodes do not try to access a common communication channel at the same time.Network. Routes data frames through a network. If data packets require to go out of a network then the transport layer routes them through interconnected networks. Its task may involve, for example, splitting data for transmission and reassembling it upon reception. The IP part of TCP/IP is involved with the network layer.Transport. Network transparent data transfer and transmission protocol. It supports the transmission of multiple streams from a single computer. The TCP part of TCP/IP is involved with the transport layer.

Physical. Defines the electrical characteristics of the communications channel and the transmitted signals, such as voltage levels, connector types, cabling, and so on.Data link. Ensures that the transmitted bits are received in a reliable way, such as adding extra bits to define the start and end of a data frame, adding extra error detection/correction bits and ensuring that multiple nodes do not try to access a common communication channel at the same time.Network. Routes data frames through a network. If data packets require to go out of a network then the transport layer routes them through interconnected networks. Its task may involve, for example, splitting data for transmission and reassembling it upon reception. The IP part of TCP/IP is involved with the network layer.Transport. Network transparent data transfer and transmission protocol. It supports the transmission of multiple streams from a single computer. The TCP part of TCP/IP is involved with the transport layer.

Application

Presentation

Session

Transport

Network

Data link

Physical

TCP or SPX

IP or IPX

Ethernet/ Token Ring/ISDN/FDDI/ATM

Session. Provides an open communications path with the other system. It involves the setting up, maintaining and closing down of a session. The communication channel and the internetworking of the data should be transparent to the session layer. A typical session protocol is telnet, which allows for the remote login over a network.Presentation. Uses a set of translations that allows the data to be interpreted properly. It may have to translate between two systems if they use different presentation standards, such as different character sets or differing character codes. The presentation layer can also add data encryption for security purposes.Application. Provides network services to application programs, such as file transfer and electronic mail.

Session. Provides an open communications path with the other system. It involves the setting up, maintaining and closing down of a session. The communication channel and the internetworking of the data should be transparent to the session layer. A typical session protocol is telnet, which allows for the remote login over a network.Presentation. Uses a set of translations that allows the data to be interpreted properly. It may have to translate between two systems if they use different presentation standards, such as different character sets or differing character codes. The presentation layer can also add data encryption for security purposes.Application. Provides network services to application programs, such as file transfer and electronic mail.

RouterRouter

RouterRouter

Data linklayer

Networklayer

Data stream

Transportlayer

ApplicationApplicationApplicationApplication

ApplicationApplication

ApplicationApplicationApplicationApplication

ApplicationApplication

MACaddressin NIC Network

address

Socket

Physicallayer

1.13 OSI Layers

1.14 OSI Layers

Physical layer:• Cables.• Electrical voltages and currents.• Connectors.• Encoding.

Data link layer:• Error control.• Flow control.• Line discipline.• Network topology.• Ordered delivery of frames.• Physical addressing (e.g. FA-D1-AA-FF-32-20).

Network layer:• Network addresses (e.g. 146.176.151.130).• Routing.

Transport layer:• Connection type.• Name resolution.

Session layer:• Setting-up, maintaining and closing a session

Presentation layer:• Transforms between session and application.

Do you want toconnect?

Yes. Here’s the details of my connection

Here’s the details of my connection

Data transfer

Acknowledgementof data received

Source

Destination

Closeconnection

Connection creation

Connection details sent:• Unique connection

number (socket).• Starting number of data

packets to be sent.• Number of packets to be

received before an acknowledgement is required.

1.15 Transport layer