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Lecture - 4

Protocol and Reference Models

There are two basic types of networking models: protocol models and reference models.

A protocol model provides a model that closely matches the structure of a particular protocol suite. The hierarchical set of related protocols in a suite typically represents all the functionality required to interface the human network with the data network. The TCP/IP model is a protocol model because it describes the functions that occur at each layer of protocols within the TCP/IP suite.

A reference model provides a common reference for maintaining consistency within all types of network protocols and services. A reference model is not intended to be an implementation specification or to provide a sufficient level of detail to define precisely the services of the network architecture. The primary purpose of a reference model is to aid in clearer understanding of the functions and process involved.

The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model. It is used for data network design, operation specifications, and troubleshooting.

Although the TCP/IP and OSI models are the primary models used when discussing network functionality, designers of network protocols, services, or devices can create their own models to represent their products. Ultimately, designers are required to communicate to the industry by relating their product or service to either the OSI model or the TCP/IP model, or to both.

OSI and TCP/IP Model

Although the TCP/IP protocol suite was developed prior to the definition of the OSI model, the functionality of the TCP/IP Application layer protocols fit roughly into the framework of the top three layers of the OSI model: Application, Presentation and Session layers.

Most TCP/IP Application layer protocols were developed before the emergence of personal computers, graphical user interfaces and multimedia objects. As a result, these protocols implement very little of the functionality that is specified in the OSI model Presentation and Session layers.

The Presentation Layer

The Presentation layer has three primary functions:

Coding and conversion of Application layer data to ensure that data from the source device can be interpreted by the appropriate application on the destination device.

Compression of the data in a manner that can be decompressed by the destination device.

Encryption of the data for transmission and the decryption of data upon receipt by the destination.

Presentation layer implementations are not typically associated with a particular protocol stack. The standards for video and graphics are examples. Some well-known standards for video include QuickTime and Motion Picture Experts Group (MPEG). QuickTime is an Apple Computer specification for video and audio, and MPEG is a standard for video compression and coding.

Among the well-known graphic image formats are Graphics Interchange Format (GIF), Joint Photographic Experts Group (JPEG), and Tagged Image File Format (TIFF). GIF and JPEG are compression and coding standards for graphic images, and TIFF is a standard coding format for graphic images.

The Session Layer

As the name of the Session layer implies, functions at this layer create and maintain dialogs between source and destination applications. The Session layer handles the exchange of information to initiate dialogs, keep them active, and to restart sessions that are disrupted or idle for a long period of time.

Most applications, like web browsers or e-mail clients, incorporate functionality of the OSI layers 5, 6 and 7.

The most widely-known TCP/IP Application layer protocols are those that provide for the exchange of user information. These protocols specify the format and control information necessary for many of the common Internet communication functions. Among these TCP/IP protocols are:

Domain Name Service Protocol (DNS) is used to resolve Internet names to IP addresses.

Hypertext Transfer Protocol (HTTP) is used to transfer files that make up the Web pages of the World Wide Web.

Simple Mail Transfer Protocol (SMTP) is used for the transfer of mail messages and attachments.

Telnet, a terminal emulation protocol, is used to provide remote access to servers and networking devices.

File Transfer Protocol (FTP) is used for interactive file transfer between systems.

The protocols in the TCP/IP suite are generally defined by Requests for Comments (RFCs). The Internet Engineering Task Force maintains the RFCs as the standards for the TCP/IP suite.

The Client-Server Model

When people attempt to access information on their device, whether it is a PC, laptop, PDA, cell phone, or some other device connected to a network, the data may not be physically stored on their device. If that is the case, a request to access that information must be made to the device where the data resides.

The Client/Server model

In the client/server model, the device requesting the information is called a client and the device responding to the request is called a server. Client and server processes are considered to be in the Application layer. The client begins the exchange by requesting data from the server, which responds by sending one or more streams of data to the client. Application layer protocols describe the format of the requests and responses between clients and servers. In addition to the actual data transfer, this exchange may also require control information, such as user authentication and the identification of a data file to be transferred.

One example of a client/server network is a corporate environment where employees use a company e-mail server to send, receive and store e-mail. The e-mail client on an employee computer issues a request to the e-mail server for any unread mail. The server responds by sending the requested e-mail to the client.

Although data is typically described as flowing from the server to the client, some data always flows from the client to the server. Data flow may be equal in both directions, or may even be greater in the direction going from the client to the server. For example, a client may transfer a file to the server for storage purposes. Data transfer from a client to a server is referred to as an upload and data from a server to a client as a download.

WWW Service and HTTP

When a web address (or URL) is typed into a web browser, the web browser establishes a connection to the web service running on the server using the HTTP protocol. URLs (or Uniform Resource Locator) and URIs (Uniform Resource Identifier) are the names most people associate with web addresses.

The URL http://www.cisco.com/index.html is an example of a URL that refers to a specific resource - a web page named index.html on a server identified as cisco.com (click the tabs in the figure to see the steps used by HTTP).

Web browsers are the client applications our computers use to connect to the World Wide Web and access resources stored on a web server. As with most server processes, the web server runs as a background service and makes different types of files available.

In order to access the content, web clients make connections to the server and request the desired resources. The server replies with the resources and, upon receipt, the browser interprets the data and presents it to the user.

Browsers can interpret and present many data types, such as plain text or Hypertext Markup Language (HTML, the language in which web pages are constructed). Other types of data, however, may require another service or program, typically referred to as plug-ins or add-ons. To help the browser determine what type of file it is receiving, the server specifies what kind of data the file contains.

To better understand how the web browser and web client interact, we can examine how a web page is opened in a browser. For this example, we will use the URL: http://www.cisco.com/web-server.htm.

First, the browser interprets the three parts of the URL:

1. http (the protocol or scheme)

2. www.cisco.com (the server name)

3. web-server.htm (the specific file name requested).

The browser then checks with a name server to convert www.cisco.com into a numeric address, which it uses to connect to the server. Using the HTTP protocol requirements, the browser sends a GET request to the server and asks for the file web-server.htm. The server in turn sends the HTML code for this web page to the browser. Finally, the browser deciphers the HTML code and formats the page for the browser window.

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Lecture 3

End Devices and their Role on the Network

The network devices that people are most familiar with are called end devices. These devices form the interface between the human network and the underlying communication network. Some examples of end devices are:

• Computers (work stations, laptops, file servers, web servers)

• Network printers

• VoIP phones

• Security cameras

• Mobile handheld devices (such as wireless barcode scanners, PDAs)

In the context of a network, end devices are referred to as hosts. A host device is either the source or destination of a message transmitted over the network. In order to distinguish one host from another, each host on a network is identified by an address. When a host initiates communication, it uses the address of the destination host to specify where the message should be sent.

In modern networks, a host can act as a client, a server, or both. Software installed on the host determines which role it plays on the network.

Servers are hosts that have software installed that enables them to provide information and services, like e-mail or web pages, to other hosts on the network.

Clients are hosts that have software installed that enables them to request and display the information obtained from the server.

Fig: End devices

Intermediary Devices and their Role on the Network

In addition to the end devices that people are familiar with, networks rely on intermediary devices to provide connectivity and to work behind the scenes to ensure that data flows across the network. These devices connect the individual hosts to the network and can connect multiple individual networks to form an internetwork. Examples of intermediary network devices are:

• Network Access Devices (Hubs, switches, and wireless access points)

• Internetworking Devices (routers)

• Communication Servers and Modems

• Security Devices (firewalls)

The management of data as it flows through the network is also a role of the intermediary devices. These devices use the destination host address, in conjunction with information about the network interconnections, to determine the path that messages should take through the network. Processes running on the intermediary network devices perform these functions:

• Regenerate and retransmit data signals

• Maintain information about what pathways exist through the network and internetwork

• Notify other devices of errors and communication failures

• Direct data along alternate pathways when there is a link failure

• Classify and direct messages according to QoS priorities

• Permit or deny the flow of data, based on security settings

Fig: Intermediary devices

Network Media

Communication across a network is carried on a medium. The medium provides the channel over which the message travels from source to destination.

Modern networks primarily use three types of media to interconnect devices and to provide the pathway over which data can be transmitted. These media are:

• Metallic wires within cables

• Glass or plastic fibers (fiber optic cable)

• Wireless transmission

The signal encoding that must occur for the message to be transmitted is different for each media type. On metallic wires, the data is encoded into electrical impulses that match specific patterns. Fiber optic transmissions rely on pulses of light, within either infrared or visible light ranges. In wireless transmission, patterns of electromagnetic waves depict the various bit values.

Different types of network media have different features and benefits. Not all network media has the same characteristics and is appropriate for the same purpose. Criteria for choosing a network media are:

• The distance the media can successfully carry a signal.

• The environment in which the media is to be installed.

• The amount of data and the speed at which it must be transmitted.

• The cost of the media and installation

Fig: Network media

Local Area Networks

Networks infrastructures can vary greatly in terms of:

• The size of the area covered

• The number of users connected

• The number and types of services available

An individual network usually spans a single geographical area, providing services and applications to people within a common organizational structure, such as a single business, campus or region. This type of network is called a Local Area Network (LAN). A LAN is usually administered by a single organization. The administrative control that governs the security and access control policies are enforced on the network level.

Wide Area Networks

When a company or organization has locations that are separated by large geographical distances, it may be necessary to use a telecommunications service provider (TSP) to interconnect the LANs at the different locations. Telecommunications service providers operate large regional networks that can span long distances. Traditionally, TSPs transported voice and data communications on separate networks. Increasingly, these providers are offering converged information network services to their subscribers.

Individual organizations usually lease connections through a telecommunications service provider network. These networks that connect LANs in geographically separated locations are referred to as Wide Area Networks (WANs). Although the organization maintains all of the policies and administration of the LANs at both ends of the connection, the policies within the communications service provider network are controlled by the TSP.

WANs use specifically designed network devices to make the interconnections between LANs. Because of the importance of these devices to the network, configuring, installing and maintaining these devices are skills that are integral to the function of an organization's network.

LANs and WANs are very useful to individual organizations. They connect the users within the organization. They allow many forms of communication including exchange e-mails, corporate training, and other resource sharing.

The Internet - A Network of Networks

Although there are benefits to using a LAN or WAN, most of us need to communicate with a resource on another network, outside of our local organization.

Examples of this type of communication include:

Sending an e-mail to a friend in another country

Accessing news or products on a website

Getting a file from a neighbor's computer

Instant messaging with a relative in another city

Following a favorite sporting team's performance on a cell phone

Internetwork

A global mesh of interconnected networks (internetworks) meets these human communication needs. Some of these interconnected networks are owned by large public and private organizations, such as government agencies or industrial enterprises, and are reserved for their exclusive use. The most well-known and widely used publicly-accessible internetwork is the Internet.

The Internet is created by the interconnection of networks belonging to Internet Service Providers (ISPs). These ISP networks connect to each other to provide access for millions of users all over the world. Ensuring effective communication across this diverse infrastructure requires the application of consistent and commonly recognized technologies and protocols as well as the cooperation of many network administration agencies.

Intranet

The term intranet is often used to refer to a private connection of LANs and WANs that belongs to an organization, and is designed to be accessible only by the organization's members, employees, or others with authorization.

Note: The following terms may be interchangeable: internetwork, data network, and network. A connection of two or more data networks forms an internetwork - a network of networks. It is also common to refer to an internetwork as a data network - or simply as a network - when considering communications at a high level. The usage of terms depends on the context at the time and terms may often be interchanged.

Fig: Internet

Network Protocols

At the human level, some communication rules are formal and others are simply understood, or implicit, based on custom and practice. For devices to successfully communicate, a network protocol suite must describe precise requirements and interactions.

Networking protocol suites describe processes such as:

The format or structure of the message

The method by which networking devices share information about pathways with other networks

How and when error and system messages are passed between devices

The setup and termination of data transfer sessions

Individual protocols in a protocol suite may be vendor-specific and proprietary. Proprietary, in this context, means that one company or vendor controls the definition of the protocol and how it functions. Some proprietary protocols can be used by different organizations with permission from the owner. Others can only be implemented on equipment manufactured by the proprietary vendor.

The Interaction of Protocols

An example of the use of a protocol suite in network communications is the interaction between a web server and a web browser. This interaction uses a number of protocols and standards in the process of exchanging information between them. The different protocols work together to ensure that the messages are received and understood by both parties. Examples of these protocols are:

Application Protocol:

Hypertext Transfer Protocol (HTTP) is a common protocol that governs the way that a web server and a web client interact. HTTP defines the content and formatting of the requests and responses exchanged between the client and server. Both the client and the web server software implement HTTP as part of the application. The HTTP protocol relies on other protocols to govern how the messages are transported between client and server

Transport Protocol:

Transmission Control Protocol (TCP) is the transport protocol that manages the individual conversations between web servers and web clients. TCP divides the HTTP messages into smaller pieces, called segments, to be sent to the destination client. It is also responsible for controlling the size and rate at which messages are exchanged between the server and the client.

Internetwork Protocol:

The most common internetwork protocol is Internet Protocol (IP). IP is responsible for taking the formatted segments from TCP, encapsulating them into packets, assigning the appropriate addresses, and selecting the best path to the destination host.

Network Access Protocols:

Network access protocols describe two primary functions, data link management and the physical transmission of data on the media. Data-link management protocols take the packets from IP and format them to be transmitted over the media. The standards and protocols for the physical media govern how the signals are sent over the media and how they are interpreted by the receiving clients. Transceivers on the network interface cards implement the appropriate standards for the media that is being used.

Technology Independent Protocols

Networking protocols describe the functions that occur during network communications. In the face-to-face conversation example, a protocol for communicating might state that in order to signal that the conversation is complete, the sender must remain silent for two full seconds. However, this protocol does not specify how the sender is to remain silent for the two seconds.

Protocols generally do not describe how to accomplish a particular function. By describing only what functions are required of a particular communication rule but not how they are to be carried out, the implementation of a particular protocol can be technology-independent.

Looking at the web server example, HTTP does not specify what programming language is used to create the browser, which web server software should be used to serve the web pages, what operating system the software runs on, or the hardware requirements necessary to display the browser. It also does not describe how the server should detect errors, although it does describe what the server should do if an error occurs.

This means that a computer - and other devices, like mobile phones or PDAs - can access a web page stored on any type of web server that uses any form of operating system from anywhere on the Internet.

The Benefits of Using a Layered M odel

To visualize the interaction between various protocols, it is common to use a layered model. A layered model depicts the operation of the protocols occurring within each layer, as well as the interaction with the layers above and below it.

There are benefits to using a layered model to describe network protocols and operations. Using a layered model:

• Assists in protocol design, because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below.

• Fosters competition because products from different vendors can work together.

• Prevents technology or capability changes in one layer from affecting other layers above and below.

• Provides a common language to describe networking functions and capabilities.

Protocol and Reference M odels

There are two basic types of networking models: protocol models and reference models.

A protocol model provides a model that closely matches the structure of a particular protocol suite. The hierarchical set of related protocols in a suite typically represents all the functionality required to interface the human network with the data network. The TCP/IP model is a protocol model because it describes the functions that occur at each layer of protocols within the TCP/IP suite.

A reference model provides a common reference for maintaining consistency within all types of network protocols and services. A reference model is not intended to be an implementation specification or to provide a sufficient level of detail to define precisely the services of the network architecture. The primary purpose of a reference model is to aid in clearer understanding of the functions and process involved.

The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model. It is used for data network design, operation specifications, and troubleshooting.

Although the TCP/IP and OSI models are the primary models used when discussing network functionality, designers of network protocols, services, or devices can create their own models to represent their products. Ultimately, designers are required to communicate to the industry by relating their product or service to either the OSI model or the TCP/IP model, or to both.

The TCP/IP Model

The first layered protocol model for internetwork communications was created in the early 1970s and is referred to as the Internet model. It defines four categories of functions that must occur for communications to be successful. The architecture of the TCP/IP protocol suite follows the structure of this model. Because of this, the Internet model is commonly referred to as the TCP/IP model.

Most protocol models describe a vendor-specific protocol stack. However, since the TCP/IP model is an open standard, one company does not control the definition of the model. The definitions of the standard and the TCP/IP protocols are discussed in a public forum and defined in a publicly-available set of documents. These documents are called Requests for Comments (RFCs). They contain both the formal specification of data communications protocols and resources that describe the use of the protocols.

The RFCs also contain technical and organizational documents about the Internet, including the technical specifications and policy documents produced by the Internet Engineering Task Force (IETF).

The Communication Process

The TCP/IP model describes the functionality of the protocols that make up the TCP/IP protocol suite. These protocols, which are implemented on both the sending and receiving hosts, interact to provide end-to-end delivery of applications over a network.

A complete communication process includes these steps:

1. Creation of data at the Application layer of the originating source end device

2. Segmentation and encapsulation of data as it passes down the protocol stack in the source end device

3. Generation of the data onto the media at the Network Access layer of the stack

4. Transportation of the data through the internetwork, which consists of media and any intermediary devices

5. Reception of the data at the Network Access layer of the destination end device

6. Decapsulation and reassembly of the data as it passes up the stack in the destination device

7. Passing this data to the destination application at the Application layer of the destination end device

Protocol Data Units and Encapsulation

As application data is passed down the protocol stack on its way to be transmitted across the network media, various protocols add information to it at each level. This is commonly known as the encapsulation process.

The form that a piece of data takes at any layer is called a Protocol Data Unit (PDU). During encapsulation, each succeeding layer encapsulates the PDU that it receives from the layer above in accordance with the protocol being used. At each stage of the process, a PDU has a different name to reflect its new appearance. Although there is no universal naming convention for PDUs, in this course, the PDUs are named according to the protocols of the TCP/IP suite.

• Data - The general term for the PDU used at the Application layer

• Segment - Transport Layer PDU

• Packet - Internetwork Layer PDU

• Frame - Network Access Layer PDU

• Bits - A PDU used when physically transmitting data over the medium

Lecture 2

The Elements of a Network

The diagram shows elements of a typical network, including devices, media, and services, tied together by rules, that work together to send messages. We use the word messages as a term that encompasses web pages, e-mail, instant messages, telephone calls, and other forms of communication enabled by the Internet. In this lecture, we will learn about a variety of messages, devices, media, and services that allow the communication of those messages. We will also learn about the rules, or protocols, that tie these network elements together.

Networking is a very graphically oriented subject, and icons are commonly used to represent networking devices. On the left side of the diagram are shown some common devices which often originate messages that comprise our communication. These include various types of computers (a PC and laptop icon are shown), servers, and IP phones. On local area networks these devices are typically connected by LAN media (wired or wireless).

The right side of the figure shows some of the most common intermediate devices, used to direct and manage messages across the network, as well as other common networking symbols. Generic symbols are shown for:

• Switch - the most common device for interconnecting local area networks

• Firewall - provides security to networks

• Router - helps direct messages as they travel across a network

• Wireless Router - a specific type of router often found in home networks

• Cloud - used to summarize a group of networking devices, the details of which may be unimportant to the discussion at hand

• Serial Link - one form of WAN interconnection, represented by the lightning bolt-shaped line

For a network to function, the devices must be interconnected. Network connections can be wired or wireless. In wired connections, the medium is either copper, which carries electrical signals, or optical fiber, which carries light signals. In wireless connections, the medium is the Earth's atmosphere, or space, and the signals are microwaves. Copper medium includes cables, such as twisted pair telephone wire, coaxial cable, or most commonly, what is known as Category 5 Unshielded Twisted Pair (UTP) cable. Optical fibers, thin strands of glass or plastic that carry light signals, are another form of networking media. Wireless media may include the home wireless connection between a wireless router and a computer with a wireless network card, the terrestrial wireless connection between two ground stations, or the communication between devices on earth and satellites. In a typical journey across the Internet, a message may travel across a variety of media.

Human beings often seek to send and receive a variety of messages using computer applications; these applications require services to be provided by the network. Some of these services include the World Wide Web, e-mail, instant messaging, and IP Telephony. Devices interconnected by medium to provide services must be governed by rules, or protocols. In the chart, some common services and a protocol most directly associated with that service are listed.

Protocols are the rules that the networked devices use to communicate with each other. The industry standard in networking today is a set of protocols called TCP/IP (Transmission Control Protocol/Internet Protocol). TCP/IP is used in home and business networks, as well as being the primary protocol of the Internet. It is TCP/IP protocols that specify the formatting, addressing and routing mechanisms that ensure our messages are delivered to the correct recipient.

We close this section with an example to tie together how the elements of networks - devices, media, and services - are connected by rules to deliver a message. People often only picture networks in the abstract sense. We create and send a text message and it almost immediately shows up on the destination device. Although we know that between our sending device and the receiving device there is a network over which our message travels, we rarely think about all the parts and pieces that make up that infrastructure.

The Messages

In the first step of its journey from the computer to its destination, our instant message gets converted into a format that can be transmitted on the network. All types of messages must be converted to bits, binary coded digital signals, before being sent to their destinations. This is true no matter what the original message format was: text, video, voice, or computer data. Once our instant message is converted to bits, it is ready to be sent onto the network for delivery.

The Devices

To begin to understand the robustness and complexity of the interconnected networks that make up the Internet, it is necessary to start with the basics. Take the example of sending the text message using an instant messaging program on a computer. When we think of using network services, we usually think of using a computer to access them. But, a computer is only one type of device that can send and receive messages over a network. Many other types of devices can also be connected to the network to participate in network services. Among these devices are telephones, cameras, music systems, printers and game consoles.

In addition to the computer, there are numerous other components that make it possible for our instant message to be directed across the miles of wires, underground cables, airwaves and satellite stations that might exist between the source and destination devices. One of the critical components in any size network is the router. A router joins two or more networks, like a home network and the Internet, and passes information from one network to another. Routers in a network work to ensure that the message gets to its destination in the most efficient and quickest manner.

The Medium

To send our instant message to its destination, the computer must be connected to a wired or wireless local network. Local networks can be installed in homes or businesses, where they enable computers and other devices to share information with each other and to use a common connection to the Internet.

Wireless networks allow the use of networked devices anywhere in an office or home, even outdoors. Outside the office or home, wireless networking is available in public hotspots, such as coffee shops, businesses, hotel rooms, and airports.

Many installed networks use wires to provide connectivity. Ethernet is the most common wired networking technology found today. The wires, called cables, connect the computers and other devices that make up the networks. Wired networks are best for moving large amounts of data at high speeds, such as are required to support professional-quality multimedia.

The Services

Network services are computer programs that support the human network. Distributed on devices throughout the network, these services facilitate online communication tools such as e-mail, bulletin/discussion boards, chat rooms, and instant messaging. In the case of instant messaging, for example, an instant messaging service, provided by devices in the cloud, must be accessible to both the sender and recipient.

The Rules

Important aspects of networks that are neither devices nor media are rules, or protocols. These rules are the standards and protocols that specify how the messages are sent, how they are directed through the network, and how they are interpreted at the destination devices. For example, in the case of Jabber instant messaging, the XMPP, TCP, and IP protocols are all important sets of rules that enable our communication to occur.

Lecture 1

Communication - An Essential Part of Our Lives

What is Communication?

Communication in our daily lives takes many forms and occurs in many environments. We have different expectations depending on whether we are chatting via the Internet or participating in a job interview . Each situation has its corresponding expected behaviors and styles.

Establishing the Rules

Before beginning to communicate with each other, we establish rules or agreements to govern the

conversation. These rules, or protocols, must be followed in order for the message to be successfully

delivered and understood. Among the protocols that govern successful human communication are:

• An identified sender and receiver

• Agreed upon method of communicating (face-to-face, telephone, letter, photograph)

• Common language and grammar

• Speed and timing of delivery

• Confirmation or acknowledgment requirements

Communication rules may vary according to the context. If a message conveys an important fact or

concept, a confirmation that the message has been received and understood is necessary. Less

important messages may not require an acknowledgment from the recipient.

The techniques that are used in network communications share these fundamentals with human conversations. Because many of our human communication protocols are implicit or are ingrained in our cultures, some rules can be assumed. In establishing data networks, it is necessary to be much more explicit about how communication takes place and how it is judged successful.

Quality of Communications

Communication between individuals is determined to be successful when the meaning of the message

understood by the recipient matches the meaning intended by the sender.

For data networks, we use the same basic criteria to judge success. However, as a message moves

through the network, many factors can prevent the message from reaching the recipient or distort its

intended meaning. These factors can be either external or internal.

External Factors

The external factors affecting communication are related to the complexity of the network and the number of devices a message must pass through on its route to its final destination.

External factors affecting the success of communication include:

• The quality of the pathway between the sender and the recipient

• The number of times the message has to change form

• The number of times the message has to be redirected or readdressed

• The number of other messages being transmitted simultaneously on the communication network

• The amount of time allotted for successful communication

Internal Factors

Internal factors that interfere with network communication are related to the nature of the message itself.

Different types of messages may vary in complexity and importance. Clear and concise messages are

usually easier to understand than complex messages. Important communications require more care to

ensure that they are delivered and understood by the recipient.

Internal factors affecting the successful communication across the network include:.

• The size of the message

• The complexity of the message

• The importance of the message

Large messages may be interrupted or delayed at different points within the network. A message with a low importance or priority could be dropped if the network becomes overloaded.

Both the internal and external factors that affect the receipt of a message must be anticipated and

controlled for network communications to be successful. New innovations in network hardware and

software are being implemented to ensure the quality and reliability of network communications.

Communicating over Networks

Being able to reliably communicate to anyone, anywhere, is becoming increasingly important to our

personal and business lives. In order to support the immediate delivery of the millions of messages being exchanged between people all over the world, we rely on a web of interconnected networks. These data or information networks vary in size and capabilities, but all networks have four basic elements in common:

• Rules or agreements to govern how the messages are sent, directed, received and interpreted

• The messages or units of information that travel from one device to another

• A means of interconnecting these devices - a medium that can transport the messages from one device to another

• Devices on the network that exchange messages with each other

The standardization of the various elements of the network enables equipment and devices created by different companies to work together. Experts in various technologies can contribute their best ideas on how to develop an efficient network, without regard to the brand or manufacturer of the equipment.