Telecommunication, Internet, and

E-Commerce

Communication hardware

• Communication channel

• Communication devices

Communication Channel Media

• Wire cables: – twisted-pair (voiceband): 2MBPS– coaxial: 550 MBPS– fiber-optic: 30 GBPS

• Wireless channel:– microwave (land-based, satellite-based):100

MBPS– infrared: 4 MBPS

Communication Channel Characteristics

• Data rate: bps, bandwidth (“higher bandwidth” means more data can be transmitted)

• Transmission method– Asynchronous: one character is sent at a time.

• Start bit + Character code + Parity bit + Stop bit

– Synchronous: the codes for several hundred characters are sent together in a block.

• Start bytes + Codes for many characters + Error checking bits + Stop bytes

Communication Devices• Modem• ISDN adapter• Network Interface Card• Router:device that connects two networks• Communication control units:

– multiplexer: allows a single channel to carry simultaneous data transmission from many terminals.

– front-end processor: a dedicated computer to perform communication functions.

Network Organization

• Star network: polling

• Bus network: contention

• Ring network: token

• Local Area Network/Wide Area Network– peer-to-peer: all PCs are equal– client/server network

• Client-Server Computing

Introduction to Internet

• A network of networks that connects computers across the world.

• It is growing rapidly:– Host computers– Users– Information

• It is a network that follows the TCP/IP protocol (packet switch network).

Internet protocol

– Transmission Control Protocol – handles communications between applications.

• A message is divided into pieces called packets.

• Packets are numbered and may be transmitted by different routes.

– Internet Protocol – handles communications between network addresses.

• A computer on the internet is assigned an unique address, IP address, which consists of 4 numbers (each number is less than 256) separated by period. Exanple, 158.104.1.10

• Domain name and Domain Name Service

Major Internet Services

• Email

• FTP - File Transfer

• Web browsing and publishing

• Telnet

World Wide Web

• A service on the Internet that links information so that the user can easily go from one piece of information to another, related piece.

• Web page:Hypertext/Hypermedia– a document that contains hyperlink (link) to

another hypertext.

• Uniform Resource Locator (URL):– http://Web site/Directory/Document

Intranet

• It is a corporate network that functions with Internet technologies, such as browsers, using Internet protocols.

• Major applications:– Corporate/department/individual web pages– Database access– Interactive communication– Document distribution

Extranet

• It is a network that links the intranets of business partners over the Internet by Virtual Private Network.

• Virtual Private Network:– A secure network that uses the Internet as its main

backbone network to connect the intranets of a company’s different locations, or establish extranet links between business partners.

• Improved communications between business partners

E-Commerce• Buying and selling, and marketing and

servicing of products and services, and information via computer networks.

E-Commerce Models

• 1. Storefront model: b2c– Shopping cart, on-line shopping mall

• 2. Auction model: e-Bay• 3. Portal model: yahoo.com• 4. Dynamic pricing: name-your-price,

comparison-pricing, bartering(exchange items), • 5. B2B & EDI (Electronic Data Interchange)• 6. Etc.

Internet Security

• Authenticity: Is the sender of a message who they claim to be?

• Privacy: Are the contents of a message secret and only known to the sender and receiver?

• Integrity: Have the contents of a message been modified during transmission?

• Nonrepudiation: Can the sender of a message deny that they actually sent the message?

Encryption (Cryptography)

• Plain text: the original message in human-readable form.

• Ciphertext:the encrypted message

• Encryption algorithm: the mathematical formula used to encrypt the plain text.

• Key: the secret key used to encrypt and decrypt a message.

Encryption Algorithms

• Private key encryption

• Public key encryption

• Digital signature

• Digital certificate

Private Key Encryption

• The same key is used by a sender (for encryption) and a receiver (for decryption)

• The key must be transmitted to the receiver.

• Example: – DES (Data Encryption Standard) algorithm

with 64-bit key

Public Key Encryption

• Uses two different keys: a public and a private key.• Receiver’s public key must be delivered in advance.• Sender uses receiver’s public key to encrypt the

message and receiver uses private key to decrypt the message (Sender can be sure the receiver is the true receiver)

• Example:– RSA (Rivest, Shamir, and Adelman) algorithm with 512-

bit to 1024-bit key.

Ceritificate

• A certificate is an identification issued by a trusted third-party certificate authority (CA).

• A certificate contains records such as a serial number, user’s name, owner’s public key, name of CA, etc.

• Example of CA: VeriSign, U.S. Postal Service.

Cookies• Designed to hold information about a user.• Created by a web site and saved on the visitor’s

machine.• It contains:

– Web site that sets the cookie.– One or more pieces of data.– Expiration date for this cookie.

• Cookies directory:– Windows: C:\windows\cookies– Netscape: c:\program files\Netscape\users\

• Browser sends cookie with the URL when you visit the site that issued the cookie.