Basic Computer Network

Bandwidth

Data rate measured in bits (not bytes) per seconds

Kbps (Kilobits per seconds) 125 chars/sec

Mbps (Megabits per seconds) 1,250 chars/sec

Gbps (Gigabits per seconds) 12,500 chars/sec

Connecting to the Internet

Requirement A computer or PDA or cell phone An account with an ISP (Internet Service Provider) A modem (modulator/demodulator) for dial-up

services or a NIC (Network Interface Card) for DSL/Cable services

Home Network (single machine)

USB/Ethernet Cable

DSL/Cable Modem

Wall Jack

Home Network (multiple machines)

USB/Ethernet Cable

DSL/Cable Modem

Wall Jack

Hub/Switch/Router

Home Network (multiple machines)

Ethernet Cable

DSL/Cable Modem

Wall Jack

Hub/Switch/Router

Home Wireless Network

Ethernet Cable

DSL/Cable Modem

Wall Jack

Hub/Switch/Router

Connection Types

LAN WLAN Dial-up Services Broadband Services WAN

LAN (Local Area Network)

A network of computers that are in the same physical location, such as home or building

Usually connected using Ethernet A standard on how computers communicate over

a shared media (cable)

http://en.wikipedia.org/wiki/Image:Ethernet_RJ45_connector_p1160054.jpghttp://en.wikipedia.org/wiki/Image:BNC_connector.jpg

Old: BNC connector for coaxial cable New: RJ45 for twisted pair cable

LAN (Local Area Network)

Ethernet Standard 10BaseT

10Mbps (Mega bits per second) 100BaseT

100Mbps 1000BaseT

1000Mbps or 1Gbps

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Ethernet

First network to provide CSMA/CD Developed in 1976 by Xerox PARC (Palo Alto

Research Center) in cooperation with DEC and Intel Is a fast and reliable network solution One of the most widely implemented LAN standards Can provide speeds in the range of 10Mbps- 10

Gbps Used with a bus or star topology

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Types of Ethernet LANs

10Base-T Operates at 10 Mbps IEEE 802.3 standard

Fast Ethernet (100Base-T) Operates at 100 Mbps

Gigabit Ethernet Operates at 1 Gbps Uses fiber optic cable

10 Gbps Ethernet Latest development of ethernet Uses fiber optic cable Developed to meet the increasing bandwidth needs of the LAN

market Wireless Ethernet

IEEE 802.11 standard Operates at around 2.4 Gbps

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LAN basics

LAN’s can be either wired or wireless. Twisted pair, coax or fiber optic cable can be used in wired LAN’s

Nodes in a LAN are linked together with a certain topology. These topologies include: Bus Ring Star Branching tree

A node is defined to be any device connected to the network. This could be a computer, a printer, a router, etc.

A Hub is a networking device that connects multiple segments of the network together A Network Interface Card (NIC) is the circuit board that has the networking logic

implemented, and provides a plug for the cable into the computer (unless wireless). In most cases, this is an Ethernet card inserted in a slot of the computer’s motherboard

The Network Operating System (NOS) is the software (typically part of the operating system kernel) that communicates with the NIC, and enables users to share files and hardware and communicate with other computers. Examples of NOS include: Windows XP, Windows NT, Sun Solaris, Linux, etc..

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Star Topology Each node is connected to a device in the center of the

network called a hub The hub simply passes the signal arriving from any node to

the other nodes in the network The hub does not route the data

Hub

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Ring Topology The ring network is like a bus network, but the “end” of the

network is connected to the first node Nodes in the network use tokens to communicate with each

other

Backbone

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Access Control Methods

Two primary access control methods exist for computers to communicate with each other over the network Token based access Carrier Sense Multiple Access with Collision

Detection (CSMA/CD)

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Token based access

Used in bus and ring network topologies (token ring) Each computer in the network can only send its data

if it has the token. This prevents collisions that occur when data is sent at the same time over the network

The token is a special pattern of bits/bit in a frame that is directly detectible by each node in the network

A computer may only transmit information if it is in possession of the token

The message is sent to all other computers in the network

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Operation of token ring

As an example, suppose node # 1 wants to send information to node # 4 over the network

Initially, an empty frame (network packet) circulates in the network

1

2

3

45

6

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When node # 1 receives the empty frame, it inserts a token in the token bit part of the frame. This operation may just be an insertion of a “1” bit

The node then inserts the message it wants to send as well as the address of the receiving node in the frame

The frame is then successively received and examined by each node in the network. First it is sent to node #2. Node #2 examines the frame and compares the address in the frame to its own address. Since addresses do not match, it passes the frame onto node #3, which does the same thing

When the frame is received by node #4, the address of the node matches the destination address within the frame. The node copies the message and changes the token bit in the frame to “0”

The frame is then sent over to node #5. This node also compares addresses and sends it to node #6 which does the same procedure

When node #1 receives the frame, it examines the token bit and recognizes that it has been changed to “0”. Node #1 then concludes that the message has been received by the intended node: node #4. Node #1 then empties the frame and releases the empty frame back into the network for circulation

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Let’s see an animation of the token ring

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CSMA/CD

Usually used in a bus topology Used in Ethernet LAN’s Unlike the token ring, all nodes can send whenever they have

data to transmit When a node wants to transmit information, it first “listens” to

the network. If no one is transmitting over the network, the node begins transmission

It is however possible for two nodes to transmit simultaneously thinking that the network is clear

When two nodes transmit at the same time, a collision occurs The first station to detect the collision sends a jam signal into

the network Both nodes back off, wait for a random period of time and then

re-transmit

WLAN (Wireless LAN)

Wi-Fi (Wireless Fidelity) A wireless technology that connects computers without

cables Access Point (AP)

A device (base station) that connects wireless devices together

Usually connected to a wired-network ESSID (Extended Service Set ID)

A “name” for the AP, eg. mobilenet Hotspot

The area covered by wireless access points

WLAN (Wireless LAN)

Standard 802.11b - 11Mbps 802.11g - 54Mbps 802.11a - 54Mbps

Security WEP (Wired Equivalen Privacy) WPA (Wi-Fi Protected Access)

2.4G

5G

Dial-up Services

Modem Modulator/demodulator A device that converts analog signal to digital

(modulation) and vice versa (demodulation) Speed

1200/2400/9600 bps 14.4/28.8/33.6 Kbps 56 Kbps

Dial-up Services

ISDN Integrated Services Digital Network 2 data channel (56K each) 1 voice channel

Broadband Services

xDSL (Digital Subscriber Line) A technology that provides digital data transmission over

unused frequencies on traditional telephone lines For example, ADSL (Asymmetric DSL): DL > UL Speed

Downlink 128Kbps - 4Mbps

Uplink 64Kbps - 800Kbps

Need a DSL modem Splitters are needed to separate the voice and data

signal

Broadband Services

Cable A technology that provides digital data transmission over cable

TV infrastructure Speed

Downlink 128Kbps - 3~5Mbps

Uplink 64Kbps - 128Kbps~1Mbps

Need a cable modem

Broadband Services

Satellite A technology that provide digital data transmission over

satellites Speed

Downlink 500Kbps - 1Mbps

Uplink 50Kbps - 100Kbps

Need a satellite dish

WAN (Wide Area Network)

A LAN spans a large geographic area, such as connections between cities

Usually connected using leased line T1 (1.5Mbps) T3 (45Mbps) OC3 (155Mbps) OC12 (622Mbps) OC48 (2.4Gbps)

Fiber optic lines

Telecommunication lines

Hub/Switch/Router

To connect multiple segments of networks into a larger one

Hub A multiport repeater to enhance signal within the

same LAN Switch

Like hub but with intelligent Better performance

Router Forward packets from one LAN to another

Intranet vs. Internet

Intranet A private network that is contained within an

enterprise Could be LANs and WANs

Internet A public network of networks

Both are using TCP/IP

TCP/IP

A family of protocols that makes the Internet works

The Robustness Principle “Be liberal in what you accept, and conservative in

what you send” - Jon Postel

TCP/IP (cont)Application Layer

Eg. WWW, FTP, IRC, Email, telnet, …

Transport LayerEg. TCP, UDP

Network LayerEg. IP

Link LayerEg. Ethernet, WiFi

Physical LayerEg. Ethernet Cable, fiber-optics

Segments

Packets

Frames

Bits

Data

Packets

A small chunk of data transmitted over the Internet

Alice

The Internet

The Internet

Bob

VPN (Virtual Private Network) A secure tunnel to a private network through

a public network Once established, local node appears to be a

node in the private network in a secure manner

Host & IP Address

“A host is a computer connected directly to the Internet”

Each host needs an IP address IP address

A 32-bit number, arranged in 4 numbers seperated by “.”

Eg. 74.125.19.147 10. 168. and 192. ranges of IP address’s are

reserved for LANs

DNS (Domain Name System)

Domain name to IP address conversion Eg. www.google.com → ??.???.??.??

Domain name or IP address lookup http://cqcounter.com/whois/

Top-level Domains

gTLDs (generic TLDs) .com, .edu, .net, .org, .gov, .mil .aero, .biz, .coop, .info, .museum, .name, .pro

ccTLDs (country code TLDs) .au, .ca, .br, .de, .fi, .fr, .jp, .hk, .cn, .tw, .my, … .us

Second-level Domains

Domains that are directly below a TLD Eg.

ucr.edu google.com sony.co.jp

Must apply to a registrar for the appropriate TLD

Domain Names & Registrars

Profitable domain names CreditCards.com - $2.75M Loans.com – $3M Business.com - $7.5M

Network Solutions, Inc used to monopolize the name registration

Now, ~500 registrars

How To Register A Domain Name? Come up a new name 2 name servers’ IP addresses 1 administrative contact 1 technical contact Register the name to an Internet domain

registrar Eg. www.netsol.com, www.godaddy.com

Used to be done via email or fax, now all web-based!

Policies

AUP (Acceptable Use Policies) A legal document, written to protect the ISP from

unlawful use of its service, and outlines prohibited uses of the service and possible consequences of misuse

Privacy Policies A document describes an ISP’s policy for

protecting users’ information

Conclusion

Described how to get connected to the Internet

Talked about the related network technologies and components