Introduction

· A network can be defined as a group of computers and other devices connected in some ways so as to be able to exchange data.

· Each of the devices on the network can be thought of as a node; each node has a unique address.

· Addresses are numeric quantities that are easy for computers to work with, but not for humans to remember.

 Example: 204.160.241.98

· Some networks also provide names that humans can more easily remember than numbers.

Example: www.javasoft.com, corresponding to the above numeric address

Addressing

Internet address

Consists of 4 bytes separated by periods

Example: 136.102.233.49

· The R first bytes (R= 1,2,3) correspond to the network address;

· The remaining H bytes (H = 3,2,1) are used for the host machine.

InterNIC Register: organization in charge of the allocation of the address ranges corresponding to networks.

Criteria considered:

→ Geographical area (country)

→ Organization, enterprise

→ Department

→ Host

Domain Name System (DNS)

· Mnemonic textual addresses are provided to facilitate the manipulation of internet addresses.

· DNS servers are responsible for translating mnemonic textual Internet addresses into hard numeric Internet addresses.

Ports

· An IP address identifies a host machine on the Internet.

· An IP port will identify a specific application running on an Internet host machine.

· A port is identified by a number, the port number.

· The number of ports is not functionally limited, in contrast to serial communications where only 4 ports are allowed.

· There are some port numbers which are dedicated for specific applications.

Data Transmission

· In modern networks, data are transferred using packet switching.

· Messages are broken into units called packets, and sent from one computer to the other.

· At the destination, data are extracted from one or more packets and used to reconstruct the original message.

· Each packet has a maximum size, and consists of a header and a data area.

· The header contains the addresses of the source and destination computers and sequencing information necessary to reassemble the message at the destination.

Types of Networks

There are two principle kinds of networks: Wide Area Networks (WANs) and Local Area Networks (LANs).

WANs

Cover cities, countries, and continents.

Based on packet switching technology

Examples of WAN technology: Asynchronous Transfer Mode (ATM), Integrated Services Digital Network (ISDN)

LANs

· Cover buildings or a set of closely related buildings.

· Examples of LAN technology: Ethernet, Token Ring, and Fibber Distributed Data Interconnect (FDDI).

Ethernet LANs: based on a bus topology and broadcast communication Token ring LANs: based on ring topology

FDDI LANs: use optical fibbers and an improved token ring mechanism based on two rings flowing in opposite directions.

Interconnection

· Networks of low capacity may be connected together via a backbone network which is a network of high capacity such as a FDDI network, a WAN network etc.

· LANs and WANs can be interconnected via T1 or T3 digital leased lines

· According to the protocols involved, networks interconnection is achieved using one or several of the following devices:

→Bridge: a computer or device that links two similar LANs based on the same protocol.

→ Router: a communication computer that connects different types of networks using different protocols.

→ B-router or Bridge/Router: a single device that combines both the functions of bridge and router.

→ Gateway: a network device that connects two different systems, using direct and systematic translation between protocols.

Network Topology Diagram

The specification of the network topology diagram requires the definition of the characteristics and entities underlying the network:

· Geographical locations of the different components or subnets involved in the network.

· Description of the LAN topology

· Description of the WAN topology

· Description of the network connectors such as routers, bridges, repeaters, and gateways.