Networking

Analogy

Networking

A network is two or more computers connected together so that they can exchange information

Networks extend the bus, they convey 0’s and 1’s among computers

Networking

Networks began with the military

Army, Navy, and Air force all had computers, and wanted to communicate with each other

Networks and Protocols were created

The URI Network

Envision Lab

Gateway Gateway

INTERNET

URI Network

What do you need to communicate?

Physical way to send message Smoke signals drum

What do you need to communicate?

What does the message mean?

When will the message start?

When will it end?

Who is it meant for?

What kind of message is it?

Does it require a reply?

What code do you use?

Basic Components of a Data Communication System

Sending Device

Communications Link

Receiving Device

Sending Device - Modem

Modem = modulate/demodulateConverts digital signal to analog and vice versa  User who connects to the computer via telephone servicesspeeds 56k (56,000 bps)directly connected to the internet (unlike LAN)

Sending Device - Modem

US Robotics Internal PCI Faxmodem

$34.99

Sending Device – Cable Modem

Sold by the cable company

Requires Ethernet

Puts home computer on LAN

Speeds > 1 Mbps (1 million bytes per second)

Sending Device – Cable Modem

Linksys Cable Modem

$99.99

Up to 42 Mbps download speeds, 10 Mbps upload

“Always on” connection

Sending Device – Cable Modem

D-Link Fast Ethernet PCI Network Adapter

$19.99

10/100 Mbps Ethernet or Fast Ethernet compatible

Sending Device - DSL

Alternative to cable for faster internet access then dial-up

Offered by phone company (via phone line)

Data transfer of 128,000 – 256,000 bps

(128k – 256k)

Sending Device - DSL

Zoom ADSL Bridge Modem 5515 - DSL modem

~ $60.00

Protocols

To send a message, you need an agreed upon way to pulse the bits (0s and 1s) of the message

Protocol - A set of rules for the exchange of data

Protocols make sure that everything is in order before it is sent

Protocols

How fast to pulse the bits?

How to mark the start and end of a message?

What computer the message is for?

What kind of message is it?

Does the message require a reply?

Is the whole message coming or just part of it?

What part of the message is this?

Terminology

LAN – Local Area NetworkA network of computers directly connected

together by the same network management

URI Dorms, CS Dept, network within a business

Terminology

WAN – Wide Area NetworkA network of computers, usually physically

separated from each other by great distances

Sometimes under the same management, sometimes under different management

ISO’s 7 Layer Model

Physical Layer

The Physical Layer describes the physical properties of the various communications media, as well as the electrical properties and interpretation of the exchanged signals. Ex: this layer defines the size of Ethernet coaxial cable, the type of BNC connector used, and the termination method.

How media gets from one place to another

Speed

10baseT LAN = 10Mbits/sec

100baseT LAN = 100Mbits/sec

ISDN = 64Kbit/sec

Modem = 56Kbits/sec

Cable Modem/DSL = 1.2 Mbits/sec and up

T1 = direct connection at 1.5 Mbits/sec

T3 = 24 parallel T1 lines

Wireless – 11 Mbs

Connection Medium – Wire Pairs

Twisted pair copper (phone lines)

Inexpensive, already installed

Susceptible to noise

Connection Medium – coaxial copper

Faster, less prone to noise

Conductive wires in an enclosure

Laid underground

Carry cable TV

Connection Medium - Fiber

Glass fibers over which light is pulsed

No metal

Faster then coaxial

Materials less expensive and lighter

Connection Medium - Microwave

Fast, cost effective

Line of sight transmission

Connection Medium - Radiowave

Used for long range transmissionsa station on earth sends signal to a satellite orbiting the earth, which has a transponder that receives the signal, amplifies the signal, changes the frequency and sends it back down to another earth station

Hardware – NIC or Modem

NIC – network interface card

Collection of hardware and software resources that allow a computer to communicate to networks

Hardware - NIC

Microsoft Networking 10/100 Ethernet PCI Adapter

$6.99

Hardware - Gateways

Gateways connect two dissimilar networks or two computers with different interface cards

Transfers data from one network to another

Hardware - Bridge

Connects similar networks

Hardware - Router

Hardware that looks at IP addresses and sends data to another router

Finds a path from one computer to another

Hardware - Router

Much of the work to get a message from one computer to another is done by a routerEnsures info doesn’t go where it’s not

neededMakes sure info reaches its destination

Hardware - Router

Linksys Wireless Router

$ 99.99

Hardware - Router

Netgear 4-Port Cable/DSL Router

$59.99

Data Link Layer

The Data Link Layer describes the logical organization of data bits transmitted on a particular medium.

Determines speed at which data is pulsed over the medium and adds special bits to indicate the start and stop of transmission

PPP

Point to Point protocol

Used by modems

No collisions

Windows has PPP built into dial-up adapter software

Ethernet

Protocol used on LANs and by cable modems

Collisions all computers use the same cableThe node “listens” to see if the cable is in

useCSMVCD – carrier sense multiple access

w/ collision detection

Internet or Network Layer

The Network Layer describes how a series of exchanges over various data links can deliver data between any two nodes in a network. Allows computers on different networks to talk to each otherAdds bits of data to determine where data is headed

IP Address

Each computer is assigned a unique IP address

ISP gives you a dynamic IP address

LAN gives you a fixed IP

We are currently using IPv4 which was developed 20 years ago

IPv4

IIPv4, IP addresses have 4 bits fields

Each bit field is represented using a binary number and is referred to as an octet

They each have eight positions when viewed in binary form

If you add all the positions together, you get 32, which is why IP addresses are considered 32-bit numbers

IPv4

Since each of the eight positions can have two different states (1 or 0) the total number of possible combinations per octet is 28 or 256

So each octet can contain any value between 0 and 255, Eg. homepage.cs.uri.edu is 131.128.81.37

Classes

The four octets are used to create classes of IP addresses

Classes can be assigned to a particular business, government or other entity based on size and need

Classes

There are 5 classes in IPv4 plus some special addresses

The five IP classes are: A,B,C,D, and E

Net and Host

The five octets are split into two sections: Net and Host

Net always contains the first octetUsed to identify the network that a

computer belongs to

Host always contains the last octetUsed to identify the actual computer on the

network

Default Network

0.0.0.0

Class A

Used for very large networks

IP addresses with a first octet from 1 to 126

The other three octets are used to identify each host

There are 126 class A networks with 16,777,214 possible hosts

2,147,483,648 unique IP addresses

115.24.53.107

Loopback

127.0.0.1

Used as a loopback address

Used by the host computer to send messages back to itself

Commonly used for troubleshooting and network testing

Class B

Used for medium sized networksIP addresses with an octet from 128 to 191 The second octet is also part of the Net IdentifierThe other two octets are used to identify each host16,384 class B networks with 65,534 possible hosts1,073,741,824 unique IP addresses145.24.53.107

Class C

Used for small to mid-sized businessesIP addresses with a first octet from 192 to 223Second and Third octets are also used as part of the Net identifierLast octet is used to identify the host2,097,152 class C networks each with 254 possible hosts536,870,912 unique IP addresses195.24.53.107

Class D

Used for multicasts

The first four bits are 1110

The other 28 bits are used to identify a group of computers the multicast message is intended for

268,435,456 addresses

224.24.53.107

Class E

Used for experimental purposes

They have never been documented or utilized in a standard way

First four bits are 1111

240.24.53.107

Broadcasts

Messages that are intended for all computers on a network are sent as broadcasts

These messages always use the IP address 255.255.255.255

IPv4

Combine the four octets and you get 232 or a possible 4,294,967,296 unique valuesWe are running out of IP addresses!In the next 5 – 15 years we will be switching to IPv6, which uses 128 bit IP addressesUntil then we use NAT

NAT

Network Address Translation

Allows your home network to share a single internet connection over a single IP address

Also, NAT keeps your home network fairly secure

DNS

Domain Name Server

Translates names like homepage.cs.uri.edu to IP addresses

You can use a name or an IP address in a web browser http://homepage.cs.uri.edu/courses/fall2004/csc101s1 http://131.128.81.37/courses/fall2004/csc101s1

Transport Layer

The Transport Layer describes the quality and nature of the data delivery.

Ensures that messages are received error free and in the right order

Packets

Data is broken up into fixed sized packets

Each packet is marked with a sequence number

TCP

Transmission Control Protocol TCP enables two hosts to establish a connection and exchange streams of dataTCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent

UDP

Uniform Data Protocol

UDP provides very few error recovery services, offering instead a direct way to send and receive data over an IP network

It's used primarily for broadcasting messages over a network

Session Layer

The Session Layer describes the organization of data sequences larger than the packets handled by lower layers. Ex: this layer describes how request and reply packets are paired in a remote procedure call.

Presentation Layer

The Presentation Layer describes the syntax of data being transferred. Ex: this layer describes how floating point numbers can be exchanged between hosts with different math formats.

Application Layer

The Application Layer describes how real work actually gets done. Ex: this layer would implement file system operations.

HTTP

HyperText Transfer Protocol

HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands

For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page

SMTP

Simple Mail Transfer Protocol

a protocol for sending e-mail messages between servers

Adds the date, and header (to from) to message

POP and IMAP

POPPost office protocolDownload messages to local serverStores e-mail messages in a text file

IMAP Internet Message Access Protocol Your e-mail stays on the server

FTP

File Transfer Protocol

The protocol for exchanging files over the Internet

FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server

Telnet

Terminal Emulation program

For logging into remote servers

To start a Telnet session, you must log in to a server by entering a valid username and password

Your computer acts as a terminal by remotely logging into another computer

Telnet

Telnet is not very secure, it sends your password unencrypted

Many system administrators block the use of Telnet

SSH

Developed by SSH Communications Security Ltd., Secure Shell is a program to log into another computer over a network, to execute commands in a remote machine, and to move files from one machine to another

It provides strong authentication and secure communications over insecure channels.

SSL

Secure Sockets Layer

Encrypts the data before it goes to TCP/IP and decrypts upon receiving

Allows secure transmission of data, used when you buy stuff online, and when you transmit passwords

OSCAR

Used for AOL instant messanger

• A business manager writes a long report and wants to send it by US Mail.

• Data being e-mailed from one computer to another.

• The manager hands the report to a secretary who generates mailing labels using standard addressing conventions of to address and from address.

• The computer adds bits to the e-mail message which represent the “from”, “for”, and “subject” fields. The structure and placement of this data is determined by SMTP.

• The secretary hands the labels and the reports to a mail clerk.

• The e-mail application sends the data to the TCP/IP stack in the computer’s operating system.

• The clerk adds the zip code to the mailing labels.

• The operating system adds does a DNS lookup of the e-mail’s host name address to get the IP address. It adds bits representing the IP address to the data.

• The clerk knows the weight limit of the US postal service, so he breaks the report into several envelopes and puts an address label on each one. He also puts a sequence number (1,2,3…) on each letter.

• The operating system breaks the e-mail message into TCP packets.

• The clerk puts the envelopes in the outbox of the company.

• The computer sends the data to the network card or modem.

• The US postal service comes by and picks up the envelopes at certain times.

• The network card broadcasts the data over the data link layer. The data link layer dictates when the packets can be broadcast.

• The US postal service uses hand carriers, trucks, and airplanes to get the envelopes to their destination.

• The data travels over many types of network media, such as wire pairs, microwave, and satelite.

• The envelopes go to the local post office, then the regional post office, then the central post office, then the local post office of the receiver. Each post office has a set of rules as to where to send certain zip codes.

• The data goes through various gateways and routers. Each router has rules as to where to send certain IP addresses.

• A clerk on the receiving end watched the mail truck go by and continually asks, “Anything for out company?”

• The network card in the receiving computer constantly watched traffic on the network looking for packets with their IP address.

• The receiving clerk collects envelopes off the local mail trucks until he has all the envelopes that make up the report. If any envelopes are missing, he calls the sending clerk and asks him to resend that envelope.

• The receiving computer’s TCP stack collects all packets and puts them into order. If any are missing, it signals the sending computer to re-send the missing packet.

• When all the envelopes have arrived, the clerk gives them to the secretary. The secretary takes out the pieces, puts a nice “to” “from” cover letter on the report, and hands it to the manager.

• The receiving computer uses an e-mail program that understands SMTP to display the e-mail header and the text on the e-mail.