Networking. What is a Network? A group of Computers and devices connected together for the purpose...

Networking

What is a Network? A group of Computers and devices

connected together for the purpose of sharing resources and services.

It may be as simple as two computers or as complex as the Internet.

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Why Networking?Why Networking?• Sharing information — eg. data communication

• Do you prefer these?

• Or this?

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• Sharing hardware or software

• Centralize administration and support

• eg. print document

• eg. Internet-based, so everyone can access the same administrative or support application from their PCs

What is a LAN? Local Area Network A group of computers in a single location Limited by no. of computers and distance covered Example: Our school network

What is a WAN? Wide Area Network Two or more LANs connected together using a telecommunication service Example: NYC Dept. of Education

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• Example of WAN: Broadband Cable Network

• Cable TV services have been extensively developed in most modern cities

• Cable TV companies try to make use of their coaxial cable installed (that are supposed to carry TV signals) to deliver broadband data services

• Many cable network wiring has been replaced with hybrid fiber-coax (HFC) ― i.e. use of fiber-optic cable to connect to the subscribers’ buildings, and then the original coaxial cable to connect to each household

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The connection is shared by a number of subscribers, hence may raise performance and security problems

Fiber-optic cable

Cable companyCoaxial Cable

TV

PC

Cable Drop

What is a WLAN Wireless LAN This is a LAN that uses Radio Frequency

technology to allow for communication among computers and devices

Example: wireless home network

Role of Computers in a Network Client- computer or device that specializes in

knowing how to ask for services in a network. Example: Workstation in a network

Server- Computer or device that specializes in knowing how to provide services in network. Example: Print Server in a network

Peer- Computer or device that may be able to be both a server or a client at the same time. Example: Workstation in a simple network (peer-to-peer network …. P2P Network)

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How many kinds of How many kinds of Networks?Networks?

• We can classify networks in different ways

• Based on network medium: Wired (twisted pair, coaxial cables, fiber-optic cables) and Wireless

• Based on network size: LAN and WAN

• Based on management method: Peer-to-peer and Client/Server

• Based on topology (connectivity): Bus, Star, Ring, Mesh

What is the Network Medium?

Cabled/Wired STP – shielded twisted pair UTP – unshielded twisted pair(cat 5, 5E, 6, 7) Coaxial Fiber Optic (single mode, Multi mode)

Wireless Microwave - Microwaves are electromagnetic waves

with wavelengths ranging from as long as one meter to as short as one millimeter

Infrared - Infrared radiation (IR) is electromagnetic radiation with a wavelength between 0.7 and 300 micrometers

Radio - Radio waves transmit music, conversations, pictures and data invisibly through the air, often over millions of miles - wavelengths in the electromagnetic spectrum longer than infrared light

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If the pair of wires are not twisted, electromagnetic noises from, e.g., motors, will affect the closer wire more than the further one, thereby causing errors

Twisted-Pair CablesTwisted-Pair Cables

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Unshielded Twisted-Pair (UTP)

Typically wrapped inside a plastic cover (for mechanical protection)

A sample UTP cable with 5 unshielded twisted pairs of wires

MetalInsulator

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Categories of UTP CablesUTP cables are classified according to the quality: Category 1 ― the lowest quality, only good for voice, mainly found in

very old buildings, not recommended now Category 2 ― good for voice and low data rates (up to 4Mbps for low-

speed token ring networks) Category 3 ― at least 3 twists per foot, for up to 10 Mbps (common in

phone networks in residential buildings) Category 4 ― up to 16 Mbps (mainly for token rings) Category 5 (or 5e) ― up to 100 Mbps (common for networks targeted for

high-speed data communications) Category 6 ― more twists than Cat 5, up to 1 Gbps

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Shielded Twisted-Pair (STP) STP cables are similar to UTP cables, except

there is a metal foil or braided-metal-mesh cover that encases each pair of insulated wires

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Coaxial CablesIn general, coaxial cables, or coax, carry signals of

higher frequency than UTP cablesOuter metallic wrapping serves both as a shield

against noise and as the second conductor that completes the circuit

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Fiber-Optic CablesLight travels at 3108 ms-1 in free space and is the

fastest possible speed in the UniverseAn optical fiber consists of a core (denser material)

and a cladding (less dense material)Simplest one is a multimode step-index optical fiberMultimode = multiple paths, step-index = refractive

index follows a step-function profile (i.e. an abrupt change of refractive index between the core and the cladding)

Common light sources: LEDs and lasers

Network Types Peer to peer

Client/server

Advantages of Peer-to-Peer Easy to install and configure

Most Client OS already have the components required to set the computer as part of a peer to peer network

Individual machines do not depend on the presence of a dedicated server

Individual users control their own shared resources Inexpensive to purchase and operate Need no additional equipment or software beyond a

suitable operating system. Best for networks with less than 10 users

Disadvantages of Peer-to-Peer

Security applies to a single resource at a time Users may be required to use as many passwords

as there are shared resources. Each machine must be backed up individually to

protect all shared data. The machine that shares resources suffers

reduced performance There is no centralized organizational scheme to

locate or control access to data

Advantages of Client/Server Centralized User Accounts, Security, and access

controls simplify network administration More powerful equipment means more efficient

access to network resources A single password for network logon delivers

access to all resources Server based networking makes the most sense

for networks with 10 or more users or any network where resources are used heavily.

Disadvantages of Client/Server Server failure renders the network

unusable, or it results in loss of network resources.

Special purpose server software requires allocation of expert staff, which increases expenses.

Dedicate hardware and software add to the cost.

What are ProtocolsSet of rules that allow computer to communicate with each other

Network Protocols TCP/IP (Transmission Control Protocol/

Internet Protocol) Nwlink or IPX/SPX NetBEUI

Network Software NOS (Network Operating System)

Windows Server 2008 Windows 2003 Server Novell Netware 6.5 Unix Linux

Network ServicesThe reason for setting up a network in the first place: File and Print DHCP (Dynamic Host Configuration Protocol) DNS (Domain Naming Service) Security E-mail Application or Database Web / Proxy Mail/FTP/IM/Chat RAS (Remote Access Service)

What are Topologies?The physical shape computers and devices create

when connected together

The different topologies are: BUS STAR RING MESH HYBRIDS

Bus (not commonly found in LANs anymore) Needs termination Adding devices

disrupts the network Cable failure hard to

find

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Bus Topology

BNC T-Connector

Coaxial cable

Network Card

Star (Most common topology) Requires a

hub/switch Easy to troubleshoot Requires more

wiring

Star Topology

Topologies Ring

No beginning and no end Uses token passing

to communicate

Mesh All computers are

connected to each other More Fault tolerant

Variation of Major Topologies(Hybrids)

Star-Bus Backbone interconnect two

or more hubs

Star-Ring Physical Star, but logical ring The way the IBM token ring Works.

What are Networking Models?

A model describes the different stages data needs to go through in order to go from one computer to another.

When you send an e-mail how does it reach the destination?

Examples are TCP/IP and the OSI models

OSI Networking Model 7 Layers

Application Presentation Session Transport Network Data link Physical

TCPI/IP Networking model 4 layers

Application Layer Transport Internet Layer Network Interface Layer

Networking standards

IEEE 802.x Standards 802.3 Ethernet Networks 802.11 Wireless Networks

11a, 11b, 11g, 11n

Bluetooth an alternative wireless network technology

standard supports a very short range (approximately

10 meters) relatively low bandwidth (1-3 Mbps)

Computer/device ID/AddressingEvery computer or device which is part of a network includes a network card.Every network card needs to have:

Physical address (MAC address) Logical address (IP address)

MAC address Media Access Control address a unique identifier assigned to most

network adapters or NIC by the manufacturer for identification

a series of 6 groups of two digits, letters and numbers, separated by dashes Example: 00-1E-4F-A0-61-69

IP Addressing Supports 4.3 billion addresses 32 bit address (Dotted decimal) 4 numbers (0 to 255) separated by dots The addresses are divided into Class

A, B, C, D, E according to network size.

Subnet MaskThe subnet mask is used to identify the network address. The sending computer needs to know this in order to decide whether the packet is meant for the local network or for another network.

Default Subnet masks are:

Class A 255.0.0.0Class B 255.255.0.0Class C 255.255.255.0

Private vs. Public Addresses.

Private addresses are only valid in a private network

Public are valid in the Internet Ex. Private address. 10.0.0.0/8 ,

172.16.0.0 to 172.31.0.0, and 192.168.0.0/24

IP addressing

Network Class Number of Hosts

Class A approximately 16,000,000

Class B approximately 65,000

Class C 254

IP address Class A Class A addresses range from 1.0.0.0 to 126.0.0.0 The Class A range has the possibility of 126

networks Each network has the capability of 16,777,214

unique hosts The default subnet mask is 255.0.0.0

IP address Class B Class B addresses range from 128.0.0.0 to

191.255.0.0 The Class B range has the possibility of

16,384 networks Each network has the capability of 65,534

unique hosts The default subnet mask is 255.255.0.0

IP address Class C Class C addresses range from 192.0.1.0 to

223.255.255.0 The Class C range has the possibility of

2,097,152 networks Each network has the capability of 254

unique hosts The default subnet mask is 255.255.255.0

IP Address Class D Class D addresses are used for multicasting

to a number of different hosts. Class D addresses range from 224.0.0.0 to

239.255.255.255 Has the potential for 268,435,456 unique

multicast groups.

IP address Class E Class E is an experimental address block

that is reserved for future use Class E addresses range from 240.0.0.0 to

254.255.255.255

Communication types Unicast (One to one) Broadcast (One to all) Multicast (One to a group)

TCP/IP Protocols Application layer

Telnet, FTP, HTTP, SMTP DHCP, DNS, TFTP, SNMP

Transport Layer TCP, UDP

Internet Layer ICMP, ARP, RARP, IP

Binary to decimal conversion

Binary= 01001011 This is equivalent to Decimal=64+8+2+1=75

128 64 32 16 8 4 2 1

0 1 0 0 1 0 1 1

Binary ConversionBinary Decimal

_____________________________________10000000 12811000000 19211100000 22411110000 24011111000 24811111100 25211111110 25411111111 255