Chapter 10

Internet-Based Applications

Electronic Mail Facilities

Message preparationWord processingAnnotation

Message sendingUser directoryTimed deliveryMultiple addressingMessage priorityStatus informationInterface to other facilities

Message receivingMailbox scanningMessage selectionMessage notificationMessage replyMessage rerouting

Internet Mail Architecture

Defined in RFC 5598At its most fundamental level consists of:

User worldIn the form of message user agents (MUA)

Transfer worldIn the form of the message handling service (MHS)

Which is composed of message transfer agents (MTA)

Internet Mail

Architecture

ADMD/DNS

Administrative management domain (ADMD)Internet e-mail providerExamples include:

A department that operates a local mail relay (MTA)An IT department that operates an enterprise mail relayAn ISP that operates a public shared e-mail service

Domain name system (DNS)Directory lookup service that provides a mapping between the name of a host on the Internet and its numerical address

Internet Mail Standards

Simple Mail Transfer Protocol (SMTP)

Standard protocol for transferring mail between hosts in the TCP/IP suiteDefined in RFC 821Standardizes the message character set as 7-bit ASCIIAdds log information to the start of the delivered message that indicates the path the message took

SMTP Mail Flow

RFC 822

RFC 822 Messages

Consist of a sequence of lines of text and use a general “memo” framework

A message consists of some number of header lines, which follow a rigid format, followed by a body portion consisting of arbitrary text

A header line usually consists of a keyword, followed by a colon, followed by the keyword’s argumentsThe most frequently used keywords are From, To, Subject, and DateAlso commonly found in the header is a Message-ID field which contains a unique identifier associated with the message

Limitations of SMTP/822 Scheme

Multipurpose Internet Mail Extensions (MIME)

MIME Header FieldsMIME-Version

Must have the parameter value 1.0Field indicates that the message conforms to the RFCs

Content-TypeDescribes data in sufficient detail for receiver to pick method for representation

Content-Transfer-Encoding Indicates type of transformation used to represent content

Content-IDUsed to uniquely identify MIME entities

Content-DescriptionPlain text description of the object with the body for use when object is not readable

Table 10.2

MIME Content Types

Post Office Protocol (POP)

Internet Message Access Protocol (IMAP)

Defined by RFC 3501Provides more functionality to users than the POP model

Clients can have multiple remote mailboxes from which messages can be retrievedClients can specify criteria for downloading messagesAlways keeps messages on the server and replicates copies to the clientsAllows clients to make changes when connected and when disconnected

Table 10.3

Key Terms Related to

HTTP

Table can be found on page 292 in text

Hypertext Transfer Protocol (HTTP) Overview

Transaction oriented client/server protocolMost typical use is between a Web browser and a Web serverMakes use of TCP to provide reliabilityIs a stateless protocol

Each transaction is treated independentlyFlexible in the formats that it can handle

Examples of HTTP Operation

Intermediate HTTP Systems

Examples of

HTTP Message Format

Web Security Challenges

The Web is vulnerable to attacks on the Web servers over the Internet

Reputations can be damaged and money can be lost if the Web servers are subverted

A Web server can be exploited as a launching pad into the corporation’s or agency’s entire computer complex

Web servers are relatively easy to configure and manage but the underlying software is extraordinarily complex and may hide potential security flaws

Users are not necessarily aware of the security risks that exist and do not have the tools or knowledge to take effective countermeasures

The Role of the

Secure Sockets Layer (SSL)

in the TCP/IP

Architecture

SSL Security Categories

ConfidentialityAll data that pass between the two applications are encrypted so that they cannot be eavesdropped on the Internet

Message integritySSL assures that the message is not altered or substituted for en route

Authentication SSL can validate the identity of one or both partners to the exchange

HTTPS

Multimedia Terminology

MultimediaTaxonomy

Media Types

TextInformation that can be entered via a keyboard and is directly readable and printable

AudioEncompasses two different ranges of sound

GraphicsSupports the communication of individual pictures, charts, or drawings

Video Carries sequences of pictures in time

Table 10.5

Domains of Multimedia Systems and Example Applications

Acceptable Use PoliciesWidespread use of e-mail and the Internet by employees raises a number of concerns for employersPolicy Issues:

Business use onlyPolicy scopeContent ownershipPrivacyStandard of conductReasonable personal useUnlawful activity prohibitedSecurity policyCompany policyCompany rightsDisciplinary action

Table 10.6 Acceptable Use Responsibilities

Summary Electronic mail

Internet mail architecture

SMTP MIME POP and IMAP

Web access and HTTP Web security

Web traffic security approaches

SSL HTTPS

Chapter 10: Internet-Based Applications

Multimedia applications Media types Multimedia

applications Multimedia

technologies Acceptable use

policies Motivation Policy issues Guidelines for

developing a policy