Phoebe Koszek 00049914

This page was written by a student of Communication Networks (49740)

University of Technology, Sydney


Statement of Originality:
The contents of this web page are the work of the author listed above. All material used to produce this web page are credited in the references section.



1      Key Learning Points. 2

2      Introduction. 3

2.1       What is an intranet?. 3

2.2       What is an extranet?. 4

2.3       How do they compare to other networks?. 4

3      Intranet Architecture. 5

3.1       Network Topology. 6

3.1.1        Ring Topology. 6

3.1.2        Bus and Tree Topologies. 6

3.1.3        Star Topology. 7

3.2       Medium Access Control (MAC) 7

4      Network Hardware. 7

4.1       Network Adapter Card. 7

4.1.1        Ethernet 7

4.1.2        Token Ring. 8

4.2       Network Cabling. 8

4.2.1        Twisted Pair Cabling. 8

4.2.2        Coaxial Cabling. 9

4.2.3        Optical Fibre. 9

5      Network Communications. 9

5.1       Transmission Control Protocol and Internet Protocol (TCP/IP) 9

5.2       Packet Switching. 10

6      Network Security. 10

6.1       Firewalls. 10

6.1.1        Packet Filtering. 15

6.1.2        Circuit Relay. 24

6.1.3        Application Gateway. 32

6.2       Encryption. 39

6.3       Digital Certificates. 47

6.4       Virtual Private Networks. 49

7      Standards pertaining to Intranets and Extranets. 55

8      Applications of Intranets and Extranets. 89

8.1       Why Web Technology is Attractive. 90

8.2       Who is Using Intranets and Extranets. 97

9      The Future of Intranets and Extranets. 105

10        Review Questions. 118

11        Glossary. 186

11.1     Terms. 187

11.2     Acronyms. 208

12        References. 234


In order to view the animations on this page, you will require a Flash plug-in.

Packet Switching Flash Animation

Packet Filtering Flash Animation


1         Key Learning Points

[Return To Index]

2         Introduction

2.1      What is an intranet?

In' tra net - n. 1) A network connecting an affiliated set of clients using standard internet protocols, esp. TCP/IP and HTTP. 2) An IP-based network of nodes behind a firewall, or behind several firewalls connected by secure, possibly virtual, networks [11].

An intranet is a network within an organization that uses internet technologies to enable users to find, use, and share documents and Web pages. Corporations use intranets to communicate with employees.

They usually reside behind firewalls, for security, and are not limited by physical location—anyone around the world can be on the same intranet. Intranets also link users to the outside Internet, and with the proper security in place may use public networks to transfer data [12].

To deploy an Intranet, a company must have: A local/wide area network in place (a core requirement); a web server up and running (this can be a freeware or an expensive solution - depending on a company's needs); and clients using browsing software to access the Intranet [13].

 Simply put, an intranet is a company-wide software and information distribution system that uses internet tools and technology. It could be a simple HTML file linked on a LAN, a full-blown sophisticated system with dedicated server hardware, or anything in between [13].

2.2      What is an extranet?

Ex' tra net - n. 1) "a business-to-business intranet that allows limited, controlled, secure access between a company's intranet and designated, authenticated users from remote locations". 2) "an intranet that allows controlled access by authenticated parties" [11].

Extranets are networks that connect companies with customers and partners. When it comes to extranets, a company has to work with the other organisations on the network, so that it’s available to specific people or groups outside of an organisation. Extranets require more security and technical consideration because they have to send private information securely over public networks [12].

An extranet provides various levels of accessibility to outsiders. You can access an extranet only if you have a valid username and password, and your identity determines which parts of the extranet you can view [14]. This requires firewall server management, the issuance and use of digital certificates or similar means of user authentication, encryption of messages, and the use of virtual private networks (VPN) that tunnel through the public network [15].

2.3      How do they compare to other networks?

The terms “intranet” and “extranet” are roughly web-based analogues of Local Area Network (LAN) and Wide Area Network (WAN). The following tables clarify the similarities and relationships between the networks:

Table 1 - Comparison of LAN and WAN Characteristics








Building or campus

City to global





Very high


Source: [11]

Table 2 - Comparison of Intranet and Extranet Characteristics








Building or campus

City to global





Moderate to high

Low to moderate

Source: [11]

Differences appear with regard to protocol (by definition) and security. Leased lines as used by LANs and WANs have a much higher security level when compared with the security of internet communications.

Although intranets and extranets are internet-based technologies, there remain some important differences between intranets and the internet.

Table 3 - Comparison of Internet and Intranet Characteristics



Packets are public

Packets are private

IP protocol suite

IP protocol suite

Cost spread out

Enterprise bears costs

Problematic management

Enterprise management

Weak policies

Strong policies

Source: [16]

[Return To Index]

3         Intranet Architecture

Figure 1 depicts an example of intranet architecture. The important components of this architecture to note are:

Figure 1 - Example Intranet Architecture

Source: [16]

3.1      Network Topology

The topology of a network describes the actual layout of the stations that make up the physical network. The common topologies for Intranets are bus, tree, ring and star.

3.1.1      Ring Topology

The ring topology network is a closed loop that consists of a set of repeaters joined by point-to-point links. The repeater’s role is to receive data on one link and retransmit the data on the other link as fast as it is received. The links are unidirectional, which implies that the data circulates around the ring in one direction [10].

Each station joins onto a repeater and transmits any data through that repeater. Medium access control is needed to determine when each station can transmit data to prevent corruption of data from multiple stations transmitting at one time [9].

Figure 2 - A ring topology in which computers are connected in a closed loop. Each computer connects directly to two others.

Source: [17]

3.1.2       Bus and Tree Topologies

Bus and tree topologies work using a multipoint medium. The bus topology involves attaching all stations directly to a linear transmission medium, known as a bus. The connection is through a device called a tap. Transmissions from stations propagate the length of the bus in both directions and can be received by all other stations.

The tree topology is similar to the bus topology in that the transmission medium is a branching cable with no closed loops. The tree begins at a point called the headend. One or more cables start from this point, and each of these can have branches. The branches can have their own branches and so on. As with the bus topology, a transmission propagates throughout the medium and can be received by all stations [9].

Figure 3 - Illustration of a bus topology in which all computers attach to a single cable.

Source: [17]

3.1.3      Star Topology

A star topology depicts a star in that each station is directly connected to a common central node. This is typically done through two point-to-point links, one each for transmission and reception [9]. Each station on the central node is treated equally.

There are two options for the transfer of data on a star topology. The first is for the central node to broadcast data, with transmission of data from one station to the node being retransmitted on all of the outgoing links. The second is for the central node to act as a switching device, buffering incoming data then retransmitting it on an outgoing link to the destination station [10].

Figure 4 - A star topology showing 6 stations connected to a hub

Source: [17]

3.2      Medium Access Control (MAC)

Due to the fact that networks are made up of collections of devices that share the same transmission capacity, intranets require some means of controlling access to the transmission medium in order to provide orderly and efficient use of the network’s communications capacity.

There are three methods of medium access control, Round Robin, Reservation and Contention. An overview of each method follows:

[Return To Index]

4         Network Hardware

4.1      Network Adapter Card

The device that allows a computer to communicate on a network is known as a network adapter card, or a network interface card (NIC). The network adapter is a circuit board, or card, that is inserted into a slot in the computer. On the back of the card is a receptacle into which a communication cable is plugged [10]. There are several types of cards available, each with its own advantages. Two of the most prevalent types of cards in intranets and extranets are Ethernet and token ring.

4.1.1      Ethernet

The most common type of Ethernet card has a 10Mbps throughput. It operates by sensing if a transmission is taking place on the network and waiting for a break in the transmission before it transmits data. If a data collision occurs, all cards on the network stop sending data until the collision is resolved [10].

Figure 5 - The conceptual flow of bits across an Ethernet. While transmitting a frame, a computer has exclusive use of the cable.

Source: [17]

4.1.2      Token Ring

The most common type of Token Ring card has a 16Mbps throughput. This system uses a token passing method of data transmission. When a station wants to transmit, it attaches the data to the “travelling” token, a special message. The data is then delivered and the token is freed for the next transmission of data. Under this system, other stations must wait until the token is free to perform their transmissions; in this manner, data collisions are totally avoided [2].

Figure 6 - The conceptual flow of bits during a transmission on a token ring network. Except for the sender, computers on the network pass bits of the frame to the next station. The destination makes a copy.

Source: [17]

4.2      Network Cabling

Network cabling is required to physically connect the stations on a network. There is a range of cabling options available, each possessing certain advantages. The two most popular types of cabling used in intranets are twisted pair and coaxial cables [6].

4.2.1      Twisted Pair Cabling

Twisted pair cabling consists of paired copper wires within the cable that are twisted around each other. The purpose of the twisting is to reduce line static and noise that interferes with data transmission [10]. The major benefit of twisted pair cabling is that it is inexpensive. It is by far the most common transmission medium for both analogue and digital signals. However, when compared with other transmission media, twisted pair cabling is limited in distance, bandwidth and data rate [9].

Twisted pair cabling is one of the mediums that are used for bus, star and ring topology LANs and intranets, especially star topologies. The reason for this is that virtually all office buildings are equipped with spare twisted pairs running from wiring closets to each office, as unshielded twisted pair cabling is the cabling used for telephone systems.

4.2.2      Coaxial Cabling

Coaxial cable consists of two conductors as is twisted pair cable, but is constructed differently to permit it to operate over a wider range of frequencies. It is used to transmit both analogue and digital signals and can be used effectively at higher frequencies and data rates than twisted pair [9].

A baseband coaxial cable is one that makes use of digital signalling. The original Ethernet scheme, a bus topology, makes use of baseband coaxial cable. Baseband coaxial cable can also be used for repeater-to-repeater links in a ring topology.

4.2.3      Optical Fibre

Optical fibre is a thin, flexible medium capable of guiding an optical ray. It is more expensive to manufacture than both twisted pair and coaxial cable. However, it boasts a number of advantages over the latter two cabling alternatives. Optical cable has a greater capacity, smaller size and weight, lower attenuation and greater repeater spacing than coaxial and twisted pair cables. Additionally, optical fibre cables have electromagnetic isolation [9].

Due to the expense of optical fibre, intranets have not utilised optical fibre to a great extent. However, optical fibre has been used to provide point-to-point links in ring network topologies. Optical fibre is also often used as an alternative to twisted pair cables in star topologies, as unshielded twisted pair cable limits transmission quality at a high data rate and is limited to a link length of approximately 100m. This compares with a maximum optical fibre link length of approximately 500m.

[Return To Index]

5         Network Communications

A Network Protocol is needed in order to control the communication between network stations, whether they are situated on the same or separate networks. Protocols define how the computers on the system will actually exchange information and handle the activity on the network in specific ways, such data addressing, sending data packets over network cabling, and reassembling packets at their destinations.

5.1      Transmission Control Protocol and Internet Protocol (TCP/IP)

The protocols used for network communications on the Internet, on many LANS and on intranets and extranets, are TCP/IP. The TCP/IP suite of protocols includes Transmission Control Protocol (TCP), Internet Protocol (IP), Address Resolution Protocol (ARP), Internet Control Message Protocol (ICMP), User Datagram Protocol (UDP), and others.

Figure 7 - A single protocol network using TCP/IP. The TCP/IP protocol can be used on a multi-platform network to streamline communications and reduce overheads.

Source: Cimino [3]

TCP is a part of the transport layer of the TCP/IP protocol. TCP assembles files into smaller packets that are transmitted over the internet and received by another transport layer that reassembles them. IP is used on the Internet layer of the TCP/IP protocol that specifies the format of packets and the addressing scheme [7].

5.2      Packet Switching

Packet switching is the method of network communications underlying the TCP/IP protocol. With packet switching, a station transmits data in small blocks, called packets. Each packet contains some portion of the user data plus control information needed for proper functioning of the network. Two of the layers that may have added the control information are the transport and internet layers, as discussed above.

A packet usually contains the following information:

Packet switching consists of two different approaches to handling streams of packets as they travel through a network: datagram and virtual circuit. The TCP/IP Protocol utilises the datagram approach.

Datagram – Each packet is treated individually. Packets don’t necessarily follow the same path through the network to get to their destination.  Thus, it is also possible for the packets to arrive out of sequence or for packets to be destroyed in the network. To view an animation of datagram packet switching technology, follow the link.

Virtual Circuit – A pre-planned route for each of the packets to be transmitted is established before any packets are sent. Each packet contains a virtual circuit identifier, instead of a destination address, as well as data [3].

One of the most complex and crucial aspects of packet switching network design is routing. Routing is the function that determines the path that each packet will take through the network to get to its destination. For further information on network routing, read Stallings [9].

[Return To Index]

6         Network Security

6.1      Firewalls

A firewall is defined as a software and/or hardware system that isolates a company's computer network from outsiders. When used for the implementation of intranets and extranets, the most important aspect of a firewall is that it is at the entry point of the network. In the case of packet filtering, it is at the lowest level of the network processes, at the network or internet layer. The firewall is the first program or process that receives and handles incoming intranet traffic, and it is the last to handle outgoing traffic [8].


Figure 8 - The location of a firewall within an Intranet

Source: [18]

 There are three main types of firewalls; Packet Filtering firewalls, Circuit Relay firewalls and Application Level Gateway firewalls.

6.1.1      Packet Filtering

In packet filtering, only the protocol and the address information of each packet is examined. Its contents and context (its relation to other packets and to the intended application) are ignored. The firewall pays no attention to applications on the host or local network and it "knows" nothing about the sources of incoming data.

Filtering consists of examining incoming or outgoing packets and allowing or disallowing their transmission or acceptance on the basis of a set of configurable rules, called policies. Packet filtering policies may be based upon the source IP address, destination port or the packet’s protocol.

The weaknesses of packet filtering are:

The following link shows an animated example deployment of a packet-filtering rule as a Flash animation. The rule has been designed to allow outgoing telnet sessions from any address internal to the network to any external server, and to disallow any incoming telnet sessions.

6.1.2      Circuit Relay

Also called a "Circuit Level Gateway," this is a firewall approach that validates connections before allowing data to be exchanged. Circuit Level Filtering takes control a step further than a Packet Filter. The firewall determines whether the connection between both ends is valid according to configurable rules, then opens a session and permits traffic only from the allowed source and possibly only for a limited period of time. Whether a connection is valid may for examples be based upon:

6.1.3      Application Gateway

In this approach, the firewall goes still further in its regulation of traffic. The Application Level Gateway acts as a proxy for applications, performing all data exchanges with the remote system in their behalf.

This can render a computer behind the firewall all but invisible to the remote system.

It can allow or disallow traffic according to very specific rules, for instance permitting some commands to a server but not others, limiting file access to certain types, varying rules according to authenticated users and so forth. This type of firewall may also perform very detailed logging of traffic and monitoring of events on the host system, and can often be instructed to sound alarms or notify an operator under defined conditions [8].

A disadvantage is that set up may be very complex, requiring detailed attention to the individual applications that use the gateway. An application gateway is normally implemented on a separate computer on the network whose primary function is to provide proxy service.

6.2      Encryption

Encryption is the conversion of data into a form, called a ciphertext, which cannot be easily understood by unauthorized people. Decryption is the process of converting encrypted data back into its original form, so it can be understood. These functions are performed using keys.

Figure 9 – Encryption using public and private keys

Source: Baker [1]

 In the current public key or asymmetric encryption systems, keys come in pairs: one for encoding and one for decoding. All sets of keys are unique. One of the keys, called the public key, is widely distributed and used for encoding messages. The other key, the private key, is held secret and used to decode incoming messages. The sender encrypts the message with the receiver’s public key, ensuring that only the receiver is able to decrypt the message [3]. This concept is illustrated in Figure 9 above.

6.3      Digital Certificates

A digital certificate is an electronic "credit card" that establishes your credentials when doing business or other transactions on the Web. It is issued by a certification authority (CA). It contains your name, a serial number, expiration dates, a copy of the certificate holder's public key (used for encrypting messages and digital signatures), and the digital signature of the certificate-issuing authority so that a recipient can verify that the certificate is real. Some digital certificates conform to a standard, X.509. Digital certificates can be kept in registries so that authenticating users can look up other users' public keys [1].

6.4      Virtual Private Networks

A VPN (virtual private network) is a way to use a public telecommunication infrastructure, such as the Internet, to provide remote offices or individual users with secure access to their organization's network. A virtual private network can be contrasted with an expensive system of owned or leased lines that can only be used by one organization. The goal of a VPN is to provide the organization with the same capabilities, but at a much lower cost.

A VPN works by using the shared public infrastructure while maintaining privacy through security procedures and tunnelling protocols such as the Layer Two Tunnelling Protocol (L2TP). In effect, the protocols, by encrypting data at the sending end and decrypting it at the receiving end, send the data through a "tunnel" that cannot be "entered" by data that is not properly encrypted. An additional level of security involves encrypting not only the data, but also the originating and receiving network addresses [20].

[Return To Index]

7         Standards pertaining to Intranets and Extranets

There are a wide variety of standards in existence pertaining to intranets and extranets. A large number of these are focused on standardising the technologies underpinning internetworking. Some of these standards include:


Table 4 - Standardised Medium Access Control Techniques


Bus Topology

Ring Topology

Switched Topology

Round Robin

Token Bus (IEEE 802.4)

Polling (IEEE 802.11)

Token Ring (IEEE 802.5; FDDI)

Request/priority (IEEE 802.12)


DQDB (IEEE 802.6)




CSMA/CD (IEEE 802.3)

CSMA (IEEE 802.11)


CSMA/CD (IEEE 802.3)

Source: Stallings [9]

Numerous standards also exist that attempt to standardise the provision of intranet and extranet content. One such standard is the IEEE “Recommended Practice for Internet Practices: Web Page Engineering, Intranet/Extranet Application” (IEEE Std 2001-1999) [5].

Additionally, Netscape, Oracle, and Sun Microsystems have announced an alliance to ensure that their extranet products can work together by standardizing on JavaScript and the Common Object Request Broker Architecture (CORBA). Microsoft supports the Point-to-Point Tunnelling Protocol (PPTP) and is working with American Express and other companies on an Open Buying on the Internet (OBI) standard. The Lotus Corporation is promoting its groupware product, Notes, as well suited for extranet use.

Work of this type includes the maturing of Sun Microsystems' Java language; object technology standards such as CORBA from the OMG [Object Management Group] and UML from Rational Software; the XML protocol suite; Microsoft DNA [Distributed iNternet Architecture]; DEN [Directory-Enabled Networking] from Cisco and Microsoft; the Open Source movement, spearheaded by Linux and Perl; and many more [21].

A brief list of some of the organisations publishing networking related standards follows:

·        International Telecommunications Union (ITU)

·        International Federation for Information Processing, Technical Committee 6 on Networking

·        Federation on Computing in the United States (FOCUS)

·        IEEE Standards

·        The Internet Society (ISOC)

·        The Internet Engineering Task Force (IETF)

·        APPN Implementer's Workshop

[Return To Index]

8         Applications of Intranets and Extranets

8.1      Why Web Technology is Attractive

The number of companies deploying intranets and extranets for intra- and extra-company communication is growing at a rapid rate [6]. There are numerous benefits offered to businesses by intranets and extranets. A few of these are listed below:

  1. Intranets solve the problem of information overload. Information overload is not caused by too much information, but by having little control over the information available. Intranets and extranets can provide structure to the information.
  2. Intranets are cheap. Networked PCs are all perfectly capable intranet clients, and browsers are cheap or free. Furthermore, rollout can be gradual, modular and minimally disruptive.
  3. Intranets are cross-platform. Many organisations have heterogeneous computer systems, and intranets provide a means of communicating across platforms.
  4. Intranets are robust. Much of the underlying intranet and extranet technology has been in use on the Internet for a decade or two, and it's robust and reliable. 
  5. Intranets are fast. Due to the fact that communications are taking place over a local network rather than the public communication network, much higher bandwidths and data rates are possible. [1]

8.2      Who is Using Intranets and Extranets

Intranets have been around for a while and their importance and functionality has grown steadily over the years, as the Internet and the technologies it uses become a more integral part of business [12].

At Ford Motor Co., more than 175,000 employees in 950 locations worldwide have access to the company’s intranet, which is called The intranet gives employees information about benefits, demographics, salary history, general company news and human resources forms. Each business unit posts employee-specific job information on the intranet and each user can create a personalised view of the intranet. Read “Calling All Workers” for more information about Ford’s intranet.

In a more unusual example recently reported on, Hewlett-Packard used its corporate intranet to ask employees to take a voluntary pay cut. Employees went to the site and saw the announcement and a record of how many of their colleagues had signed on. There are 90,000 employees in 150 countries on the HP intranet and in the end 90 percent of their employees signed up for pay cuts [12].

[Return To Index]

9         The Future of Intranets and Extranets

Most of the original internet standards are evolving to meet unprecedented business needs, including the advancement of intranet and extranet technologies. A few active areas are highlighted in Intranet Journal's Emerging Standards series [11]:

In addition to initiatives like these that address infrastructure issues, software engineering standards are evolving to facilitate development of distributed applications.

[Return To Index]

10   Review Questions

  1. Intranets and extranets are based on:
    1. Packet switching
    2. Virtual circuit packet switching
    3. Datagram packet switching
    4. Circuit switching
  1. Which of the following is incorrect:
    1. Intranets have a higher bandwidth than extranets
    2. Extranets are more secure than intranets
    3. The scope of an extranet is greater than the scope of an intranet
    4. Intranets are faster than WANs
  1. Which of the following is not a common feature of intranets and extranets:
    1. Firewalls
    2. DMZ
    3. AMZ
    4. DNS
  1. A DMZ:
    1. Prevents external access to an intranet
    2. Provides services such as email
    3. Is a backup for a firewall
    4. Sets an alarm if unauthorised users attempt to access an intranet
  1. A bus topology is:
    1. When the network components form a closed loop
    2. When all stations are connected at a common node
    3. When all stations have their own ring
    4. When all stations are connected at a linear transmission medium
  1. Which is not a style of medium access control:
    1. Switching
    2. Round Robin
    3. Reservation
    4. Contention
  1. NIC stands for:
    1. Network Interface Cache
    2. New Internet Connection
    3. Network Interface Card
    4. Network Internet Connection
  1. The following cable(s) are constructed of two conductors:
    1. Coaxial
    2. Optical fibre
    3. Twisted Pair
    4. All of the above
    5. A & B
    6. A & C
    7. B& C
  1. The TCP protocol applies to:
    1. The application layer
    2. The internet layer
    3. The physical layer
    4. The transport layer
  1. Which of the following is not a technology based on network security:
    1. Token Ring
    2. Encryption
    3. Circuit Relay
    4. Virtual Private Networks

Answers: 1. c, 2. b, 3. c, 4. b, 5. d, 6. a, 7. c, 8. d, 9. d,10. a.

[Return To Index]

11   Glossary



ARP – Address Resolution Protocol

ADSL – Asymmetric Digital Subscriber Line

DNS – Domain Name Server

DMZ – A Demilitarised Zone

FTP – File Transfer Protocol

HTTP – Hyper Text Transfer Protocol

HP – Hewlett Packard

ICMP – Internet Control Message Protocol

IEEE – Institute of Electrical and Electronics Engineers

IMAP – Internet Message Access Protocol

IP – Internet Protocol

IPv6 – Internet Protocol Version Six

L2TP – Layer Two Tunnelling Protocol

LAN – Local Area Network

LDAP – Lightweight Directory Access Protocol

MAC – Medium Access Control

NIC – Network Interface Card

PC – Personal Computer

SMTP – Simple Mail Transfer Protocol

TCP – Transfer Control Protocol

UDP – User Datagram Protocol

VPN – Virtual Private Network

WAN – Wide Area Network

XML – eXtensible Markup Language

[Return To Index]

12   References

  1. Baker, Richard H., 1997, Extranets: the complete sourcebook, McGraw-Hill, New York.
  1. Buchanan, B., 1999, Handbook of data communications and networks, Kluwer Academic, Boston.
  1. Cimino, J., 1997, Intranets: the surf within, Charles River Media, 1997.
  1. Hackos, JoAnn T., 1997, Standards for online communication: publishing information for the internet/World Wide Web, help systems/corporate intranets, John Wiley, New York.
  1. IEEE Computer Society, 1999, IEEE recommended practice for internet practices: web page engineering, intranet/extranet applications, Institute of Electrical and Electronics Engineers, New York, NY.
  1. Norris, Mark, 1999, Designing the total area network: Intranets, VPN's and enterprise networks explained, Chichester, New York.
  1. Minoli, Daniel, 1997, Internet and intranet engineering, McGraw-Hill, New York.
  1. Oppliger, R., 1998, Internet and Intranet security, Artech House, Boston.
  1. Stallings, W., 2000, Data and Computer Communications – 6th Ed, Prentice Hall, New Jersey.
  1. Starnes, Graves and Justice, 1997, The Complete Intranet Source For Information Professionals, Kent Information Services, Kent.
  1. Intranet Journal - Building Corporate Expertise,, Accessed 25/8/02.
  1. Darwin Mag,, Accessed 25/8/02.

  13.   Netxs,, Accessed 25/8/02.

  1. Webopedia,, Accessed 26/8/02.
  1.,, Accessed 26/8/02.
  1. CIO Webbusiness,, Accessed 26/8/02.
  1. Computer Networks and Internets - 3rd Ed,, Accessed 25/8/02.
  1. Ashley Laurent Broadband and Networking Software,, Accessed 27/8/02.
  1. Personalised PC Help,, Accessed 27/8/02.
  1.,, Accessed 27/8/02.
  1.,, Accessed 27/8/02.

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