Networking

WHAT IS A NETWORK ?

• A

network

is simply two or more computers that

are linked together.

• The most common types of networks are:

• Local Area Networks (LANS) and

• Wide Area Networks (WANS).

• The primary difference between the two is that a

LAN

is

generally

confined

to

a

limited

geographical area, whereas a

WAN

covers a

large geographical area. Most WANs are made

up of several connected LANs.

Client/Server Networks

• In a client/server network arrangement, network services are located in a dedicated computer whose only function is to respond to the requests of clients.

• The server contains the file, print, application, security, and other services in a central computer that is continuously available to respond to client requests.

Peer-to-Peer Networks

• In a peer-to-peer network, the networked computers act as equal partners, or peers, to each other.

• As peers, each computer can take on the client function or the server function alternately.

Metropolitan-Area Network (MANs)

A metropolitan area network

(MAN) is a computer network that usually spans a city or a large campus. A MAN usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.

Storage-Area Networks (SANS)

A storage area network (SAN) is a

dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices.

Virtual Private Networks (VPNs)

A virtual private network (VPN) is a private computer network that interconnects remote geographically separate networks through primarily public communication infrastructures such as the Internet. VPNs provide security through tunneling protocols and security procedures such as encryption. For example, a VPN could be used to securely connect the branch offices of an organization to a head office network through the public Internet. A VPN can also be used to interconnect two similar networks over a dissimilar middle network;

BENEFITS OF A NETWORK

• Information sharing: Authorized users can use other computers on the network to access and share information and data. This could include special group projects, databases, etc.

• Hardware sharing: One device connected to a network, such as a printer or scanner, can be shared by many users.

• Software sharing: Instead of purchasing and installing a software program on each computer, it can be installed on the server. All of the users can then access the program from a single location.

• Collaborative environment: Users can work together on group projects by combining the power and capabilities of diverse equipment.

RISKS OF NETWORK COMPUTING

The security of a computer network is challenged

everyday by:

– Equipment malfunctions

– System failures

Note: equipment malfunctions and system failures may be caused by natural disasters such as floods, storms, or fires, and electrical disturbances.

– Computer hackers

– Virus attacks

Concepts of Communication

• Communications

– activity associated with

distributing or exchanging information.

• Telecommunications

–

technology

of

communications at a distance that permits

information to be created any where and

used everywhere with little delay.

• Today it, involves

– Data: digital and analog – Voice: spoken word

Essentials for Communications

Workstation/PC Medium Workstation/PC

1 2 3 4 5 6

Source Transmitter Transmission Receiver Destination

Source System Destination System

1. Text input information

2. Input data digital bit stream 3. Transmitted analog signal 4. Received analog signal

5. Output data digital bit stream 6. Text output information

Simplex Transmission

• Simplex transmission is a single one-way baseband transmission.

• It is also called unidirectional because the signal travels in only one direction.

• An example of simplex transmission is the signal sent from the cable TV station to the home television.

Half-Duplex Transmission

• In Half-Duplex Transmission

only one side can transmit at a time.

• Two-way radios, such as Citizens Band (CB) and police / emergency commu -nications mobile radios, work with half-duplex transmissions.

Full-Duplex Transmission

• In Full-Duplex Transmission

Traffic can travel in both directions at the same time. • A regular telephone

conver-sation is an example of full-duplex communication. Both parties can talk at the same time, and the person talking on the other end can still be heard by the other party while they are talking.

Communication Devices

• Synchronous

communication uses a

clock signal separate from the data

signal- communication can only happen

during the ‘tick’ of the timing cycle.

• Asynchronous

communication does not

use a clock signal- rather, it employs a

start and stop bit to begin and end the

irregular transmission of data.

Network Topologies

The Network Topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.

Networks have both a physical and logical topology:

Physical topology: the layout of the devices and media.

Logical topology : paths that signals travel from one point on the network to another.

Networking Media : Coaxial-cable

• Networking media can be defined simply as the means by which signals (data) are sent from one computer to another (either by cable or wireless means).

• Coaxial cable is a copper-cored cable surrounded by a heavy shielding and is used to connect computers in a network.

• There are several types of coaxial cable, including thicknet, thinnet, RG-59 (standard cable for cable TV), and RG-6 (used in video distribution).

• Twisted-pair is a type of cabling that is used for telephone communi-cations and most modern Ethernet networks.

• A pair of wires forms a circuit that can transmit data. The pairs are twisted to provide protection against crosstalk, the noise generated by adjacent pairs.

• There are two basic types, shielded twisted-pair (STP) and unshielded twisted-pair (UTP).

Categories of Twisted Pairs

Category Max Data Rate Usual Application

CAT 1 Less than 1 Mbps Analog Voice (plain old telephone

service) Integrated Services Digital Network (ISDN)

CAT 2 4 Mbps Mainly used in the IBM Cabling System

for token ring networks

CAT 3 16 Mbps Voice and data on 10BASE-T Ethernet

CAT 4 20 Mbps Used only in 16Mbps Token Ring

CAT 5 100 Mbps 100 Mbps - 155 Mbps Asynchronous

Transfer Mode

CAT 6 250 Mbps Voice and data using upto 10-Gigabit Ethernet

• Fiber-optic cable is a networking medium capable of conducting modulated light transmissions.

• Fiber-optic refers to cabling that has a core of strands of glass or plastic (instead of copper), through which light pulses carry signals.

• Signals that represent data are converted into beams of light.

• If the cost of running cables is too high or computers need to be movable without being tethered to cables, Wireless

is an alternative method of connecting a LAN.

• Wireless networks use radio frequency (RF), laser, infrared (IR), and satellite /microwaves to carry signals from one computer to another without a permanent cable connection.

Networking Devices : Hub

• A Hub is a device that is used to extend an Ethernet wire to allow more devices to communicate with each other.

• Hubs are most commonly used in Ethernet 10BASE-T or 100BASE-T networks, although there are other network architectures that use them.

• A Switch is a more sophisticated device than a hub, although the basic function of the switch is almost same as of hub.

• Allow different nodes of a network to communicate directly with each other.

• Allow several users to send information over a network at the same time without slowing each other down.

• A Bridge is a product that connects a local area network (LAN) to another local area network that uses the same protocol (for example, Ethernet or token ring).

• The basic functionality of the bridge resides in its ability to make intelligent decisions about whether to pass signals on to the next segment of a network.

Networking Devices : Bridge

Routers connect two or more networks having same or different protocol and forward data packets between them. When data arrives from one of the segments, the router decides, according to it's routing table, to which segment to forward that data.

Networking Devices : Gateways

• A gateway is a network point that acts as an entrance to another network. On the internet, in terms of routing, the network consists of gateway nodes and host nodes.

• Host nodes are computer of network users and the computers that serve contents (such as Web pages).

• Gateway nodes are computers that control traffic within your company’s network or at your local internet service provider (ISP)

Networking Devices : Modem

An illustration of data sent using a modem and a regular telephone line.

A Modem is a device that converts digital data originating from a terminal or computer, to analog signals used by voice communication networks such as the telephone system. At one end, modems convert the digital pulses to audible tones and convert audio tones back to digital pulses at the other.

Networking Devices : Firewalls

Firewalls are systems that establish access control policies among networks. They can block information from entering a network or from getting out of that network, they can permit different users to perform different kinds of operations, according to the user's authorizations.

Networking Protocols

• Protocol are used for communication between computers in different computer networks. Protocol achieves:

• What is communicated between computers? • How it is communicated?

• When it is communicated?

• What conformance (bit sequence) between computers?

• Key elements of a protocol are:

• SYNTAC: Data format and signal levels

• SEMANTICS: Control information for coordination and error handling

• TIMING: Synchronization, speed matching, and sequencing

• Examples of protocols:

• WAN Protocol: TCP/IP

Programmers Do Not Throw Sausage Pizza Away

Networking layers : OSI Model

• Provides connectivity and path selection between two hosts

• Provides Logical address

Encapsulation in layers

TCP/IP Model

Network access: data transfer between neighboring Network access: data transfer between neighboring network elements and Physical: bits “on the wire” -- ppp, ethernet

Internet: routing of datagrams from source to destination -- ip, routing protocols

Application: supporting network applications -- ftp, smtp, http

What is an Address ?

An unique number ID assigned to host or

interface to identify within a network

•

MAC Address

:

Manufacturer allocated permanent and

unique ID, six pair of hexadecimal number,

such as 01-23-45-67-89-ab

•

IP Address :

A temporary 32 bit address (IPv4) divided into

four octate and separated by a dot, such as

192.168.100.12

IP Address Types

IP addresses can be one of three types:

•

Unicast:

This type forwards the packet

to a single target host (one-to-one

forwarding).

•

Multicast:

This type forwards the packet

to all hosts that have joined a multicast

group (one-to-many forwarding).

•

Broadcast:

This type forwards the

packet to all hosts on a subnet or

network (one-to-all forwarding).

IP Address Classes

Class First Octet Used For

A 1–126 Very large networks

B 128–191 Medium to large networks C 192–223 Small networks

D 224–239 Multicasting

Subnet Mask

A 32-bit address used to partion Network

Id and Host Id to determine whether a

given address is local or remote. Two types

of subnet masks are:

•

Default subnet mask:

Partitions IP

addresses into their network ID and host

ID portions

•

Custom subnet mask:

Further partitions

the network ID into a number of

separate subnets by using a process

called subnetting

Subnetting

Subnetting: Partitioning a single network into multiple subnets to reduce network congestion.

To subnet an IP network, you take the assigned network ID and borrow bits from the host ID to establish a group of subnet IDs (subnetted network IDs), one for each subnet.

If a class B network 172.16.0.0 needs to be subnetted into 6 subnets, a subnet mask of 255.255.224.0 can be used. Each subnet can be shown to support a maximum of 8190 hosts. The IP address blocks for these six subnets can be selected from the eight possible subnets: ● 172.16.0.1 to 172.16.31.254 ● 172.16.32.1 to 172.16.63.254 ● 172.16.64.1 to 172.16.95.254 ● 172.16.96.1 to 172.16.127.254 ● 172.16.128.1 to 172.16.159.254 ● 172.16.160.1 to 172.16.191.254 ● 172.16.192.1 to 172.16.223.254 ● 172.16.224.1 to 172.16.255.254

Supernetting

By using Supernetting, contiguous blocks of class C addresses can be combined and used for networks larger than a single class C block can satisfy.

Supernetting is the opposite procedure—instead of borrowing bits from the host ID to increase the bits for the network ID (thus increasing the number of networks), supernetting borrows bits from the network ID to increase bits for the host ID, thus combining smaller networks to create larger networks.

For example, a supernetted subnet mask of 255.254.0.0 identifies each class B address as having 15 network ID bits and 17 host ID bits, thus creating fewer networks, each with more hosts, than when using the default subnet mask.

Setting of IP Addresses

IP addresses for hosts on a LAN can be assigned in two ways: 1. Manually assigned by the network administrator

2. Assigned by a Dynamic Host Configuration Protocol (DHCP) server

What is DHCP?

• The most common and efficient way for computers on a large network to obtain an IP address is through a Dynamic Host Configuration Protocol (DHCP) server.

• DHCP is a software utility that runs on a computer and is designed to assign IP addresses to PCs.

• When the DHCP server receives a request from a host, it selects IP address information from a set of predefined addresses that are stored in its database.

What is Default Gateway?

• A computer located on one network segment that is

trying to talk to another computer on a different segment sends the data through a default gateway.

• The default gateway is the “near side” interface of the router, the interface on the router to which the network segment or wire of the local computer is attached.

What is DNS?

• Most hosts are identified on the Internet by friendly computer names known as domain names.

• The Domain Name System (DNS) is used to translate computer names such as cisco.com to their

corresponding unique IP address.

• The DNS server keeps records that map computer (host) names and their corresponding IP address.

What is Domain Names?

• To remember IP addresses of all our favorite Websites is very difficult.

• It’s easy to remember words rather individual IP addresses and that is where domain names come in.

www.google.co.in

Top-level domain Sub-domain

Host name

Some Common Top-Level Domains:

COM -- commercial Web sites, though open to everyone

NET -- network Web sites, though open to everyone

ORG -- non-profit organization Web sites, though open to everyone

EDU -- restricted to schools and educational organizations

MIL -- restricted to the U.S. military

GOV -- restricted to the U.S. government

US, UK, RU, BD, IN and other two-letter country codes -- each is assigned to a domain name authority in the respective country.

What is HTML ?

Hypertext Markup Language (HTML) is the standard formatting language used to publish information on Web servers for delivery to Web browsers over the Internet. HTML allows linked sets of documents (that is, hypertext) to be created, stored, and accessed from Web servers using Uniform Resource Locators (URLs).

An example of classic ‘Hello world’ in HTML:

<!DOCTYPE html> <html> <head> <title>Hello HTML</title> </head> <body> <p>Hello World!</p> </body> </html>

Web page: A file of text information formatted using Hypertext Markup Language (HTML).

What is HTTP?

Hypertext Transfer Protocol (HTTP): A protocol that defines how Web browsers download information from Web servers. HTTP clients: The most common example of an HTTP client is the Web browser, such as Internet Explorer or Firefox.

HTTP servers: It can communicate or serve web pages by means of HTTP with a client such as a Web browser. Microsoft IIS and Apache are the example of HTTP/Web server.

What is URL ?

In computing, a uniform resource locator (URL) is a specific character string that constitutes a reference to an Internet resource.

How email works

1. The sender uses a Mail User Agent (MUA) to compose an email.

2. The mail is sent to a Mail Transfer Agent (MTA)

which is responsible for sending the email to the receipient’s MTA.

3. An MTA transfers mail messages between computers via the SMTP protocol.

4. The recipient’s MTA receives the email and passes it on to a Mail Delivery Agent (MDA).

5. An MDA manages the user’s mailbox and handles mails for delivery to the MUA using either the