A Client is a computer application that depends on another application such as a server to retain storage and processing functions. An example of a client is AOL Pictures. Your Server is a system that gives the services to other computers through a network. So AOL would be the server that hosts the website for AOL Pictures.

Your Browser is an application or program that allows you to access sites or information over the World Wide Web, or through a LAN. Your Cache is a set of space that is set aside specifically to hold files that are shown on your browser. So if you visit the site CNN.com, there is a lot of information on this site to process. Your cache will temporarily hold some of this information, and if you visit another page off of CNN.com and some of the page setup is the same like pictures or headlines, then your cache pulls this information from the pre-determined disk space, and shows it on the page for you. This cuts down on load time and will make your webpage appear faster.

Cookies are small files normally made up of text that are sent by a server such as AOL, to your web browser such as Netscape or Internet Explorer, as packets. They are returned every time your browser accesses that server. So if you go to CNN.com on Monday, there is a cookie sent to your computer. When you return on Tuesday to the same site, that cookie is returned to CNN.com and lets that site know that you have previously visited. Cookies can track your every move on the Internet, if they are not erased on a regular basis.

Webmail is your web application that sends and receives messages from an email server and then puts them into an HTML format for display to your website such as Yahoo email. Your messages are stored on an email server before and after you see them, until they are finally manually deleted by you. There is also a kind of email called POP3. This is a client application that is stored on your PC, and uses POP3 to get your email information from a server with your TCP/IP connection. An example of this is Microsoft Office Outlook. Your mail is stored on your hard drive until you click on email, and it is retrieved.

So now if you are having problems with your Internet mail, this information will tell you how to track down your problem. This will cut out time on the phone with your Internet Service Provider's help desk, as well as make you sound as though you really do understand what is going on with your PC. You will not have to feel helpless while they are putting information into laymen's terms for you again.

Your DSL Circuit is completed as follows: Your computer connects to the modem, and then the modem connects to the local DSL remote for your Internet Service Provider, and then directly to the Internet Service Provider's database. For your PC to use the DSL Circuit, your computer has to have a network ready operating system, or a network adapter, or a network interface card known as a NIC. A Network Ready Operating System or an IPv4 example would be all versions of Windows, Macintosh and Linux.

To find your network adapter, find My Computer on your desktop, and right click on it. Open this and then click on Properties. Now you should click on Device Manager, and then Network Adapter. This will bring your network adapter information up, and you can tell the technician you speak to what it says here. If it doesn't say wireless, then it will be a Broadband connection in most cases. In Vista, you should click on the Windows icon, then on Control Panel. From here, click on Classic View and then your Device Manager. You should hit Continue now, and then your Network Adapter. If it is working correctly, there will be a normal icon next to it. If it is yellow, or has an exclamation point next to it, then there is a problem with it that can easily be fixed. If it is red, your network adapter is disabled, and this only takes a few clicks to fix.

LAN and WAN IP Addresses can be confusing. Your Internet Service Provider such as AOL or AT&T assigns your computer a WAN IP address. For instance, your home that has 3 rooms with Internet would have 2 IP Addresses. The WAN IP would be assigned to your house as a whole, and is assigned by your Internet Service Provider. But each one of the rooms in your home that has a different computer hooked up would have different LAN IP addresses assigned to each one. These LAN IP Addresses are used to track all of the movements from your computer to the Internet. Don't worry, no one is really looking at what you do on your computer, this is just a way of showing that your individual computer has accessed the Internet.

Now when you talk to that technician that makes you feel like you don't know what you're talking about, you have a little ammunition on your side. Just refer back to this page, or check out the series on Getting to Know Your Computer for more in depth information. Get back at those technicians; know your computer so they don't have to tell you what you "should" know.

That is inter-connected in such a manner that any computer anywhere in the world can exchange information between each other.

Chatting, e-mail, video conferencing, e-commerce all there terms is based upon the communication technology.

Types of connections

Dial-up networking

A connection to your Internet service Provider (ISP) over your existing telephone line. Your ISP then connects you to Internet after you type in your username and password.

DSL

Digital Subscriber Loop (DSL) high-speed digital signals over telephone lines.

ISDN

The telephone line carries conversation as an analogue message. Digital networks are called Integrated Services Digital Network (ISDN).

If you are a businessman then you must choose ISDN or DSL Internet connection.

Types of domain

• .edu -   educational
• .com-   commercial
• .net-     network resources
• .org -    non-profit organization
• .co-      Company
• .int -     international
• .mil-     military

Types of network

• LAN - Local Area Network, DAN - Desk Area Network
• WLAN - Wireless Local Area Network
• WAN - Wide Area Network
• CAN - Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
• SAN - Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
• PAN - Personal Area Network
• MAN - Metropolitan Area Network

 

 

STEP 1: Go to https://secure.logmein.com/products/hamachi/list.asp and press the download button under the "Windows" heading.

STEP 2: A box will pop up asking if you want to "Open" or "Save" Press open.

STEP 3: The following few steps are self explanatory. Wait about a minute or less for it to complete downloading. After it finishes, a box like the one below will pop up. Press "next"

STEP 4: Read the License Agreement and check the box that says I accept the agreement, if you agree. You will have to press it to continue.

STEP 5: Check whichever box you need and press "next"

STEP 6: Read the paragraphs. Then check “Disable vulnerable Windows services over Hamachi” if you will be using this program with people that you don't trust or don't know. This option will block remote access connections and won't allow you to share files with them. Press "next"

STEP 7: Select "Non-Commercial" to use the free version unless you want to try Hamachi premium for 30 days. Then press "next"

STEP 8: Click "Install"

STEP 9: Wait… please be patient

STEP 10: Now it is done installing, press "next"

STEP 11: Click "Finish." Now two possible things might happen. 1) You will be prompted to restart your computer 2) Hamachi tutorial will start

STEP 12: If no restart took place, a Hamachi tutorial should begin. It will ask you to complete certain tasks and after you complete the tasks, you will be able to use Hamachi. If a restart took place, the tutorial will begin after the restart.

STEP 13: Now that Hamachi is successfully installed, let's learn the basic features of Hamachi and how to use them. Please visit http://www.computersight.com/Software/Hamachi-User-Guide.317079 for a complete guide.

Definitions

File Sharing: Creating a drive which can be setup so other people connected to it can access files put in it. They can add their own files, change files, delete files and view files on the drive depending on the permissions you set for them.

Print Sharing: Sharing one printer with more than one computer. This means people who are connected to the printer can use it to print.

Remote access: The act of using another computer from your current computer. You can use their programs; control their cursor, type, and anything else you would be able to do if you were actually at that computer.

Opening Hamachi

To open the Hamachi program, double click on the icon in the taskbar with the three green dots. The box below should show up.

Power on/off

Press the power button once to turn it on and press it again to turn it off. Since Windows automatically starts Hamachi each time you log in, you won't need to turn on Hamachi manually. You might need the power button to restart Hamachi if you have connection problems.

Join an existing network

Press the button with 3 circles forming a triangle. Then select “Join an existing network ..” A box like the one below should show up. Enter the network name and password in the boxes. Note: the network name and password are case-sensitive. Only join an existing network if you know someone who created a network and wants you to join. If you don't know any networks, simply create a network.

Create a new network

To create a new network, click the button with the three dots forming a triangle, then select “Create a new network” A box like the one below should pop up. Enter the preferred network name and password for your new network. Then press create. Now give your network name and password to people who have Hamachi so they can join your network.

Setting your online status

To set your online status, first click on the button with a gear. Then select preferences. A box like the one below should pop up. Select Presence, check Enable and check “Show peer status in the main list.” I don't recommend you check the third box. It means that after 300 seconds of inactivity you will be switched to Away mode. Then press ok.

Now that the online presence is activated, you should see a third button which is a paw icon. The point of setting your status is to let others know if you are busy, wanting to chat or not. To set your online status press the paw icon and then choose available, busy, away or custom. Select custom if you want to type your own status. An example would be, “Away at a doctor's appointment.” Now under your name they will see your status. If you set it to available, there will be nothing under your name. Your online status is automatically set to available if you don't set one.

Chatting

To chat to a specific peer, right click their name and select chat. You can only chat with someone after you are in a network (created, joined) A box like the one below will pop up. Now you can type your message. The typing notification tells you when the person is typing.

     

When someone sends you a message, the Hamachi icon flashes and a balloon pops up telling you who the message is from. (Above) To read the message double click the Hamachi icon.

What if you don't want to chat with a specific peer? Then use group chat. Right click your network and press open chat window.

When a group message is received, the above balloon pops up. To read, double click the Hamachi icon.

Leaving networks and going offline

To leave a network simply right click the network and select leave network. Only choose this option if you don't want to chat permanently for some reason. For example, you are being made fun of. Don't choose this if you are going on vacation or shutting down.

To go offline right click the network and press go offline. Going offline doesn't mean you aren't leaving permanently but means you don't want to be disturbed and is temporary. To go back online simply right click the network and select go online.

Banning and evicting members

Note: Banning and evicting members can only be done if you own the network. (You created the network) To ban a member: Right click their name and then select ban. Banning a member means that member will be temporarily out of the network until you unban him/her.

To evict means removing the member from the network permanently. To evict: Right click the member and select evict.

To unban a member, right click the network and select details. A box like the one below should pop up. On the left hand side select banned. Then select the member that was banned and click unban, then click ok.

  

Hamachi parts

Setting permissions and sending notices

First right click the network and select details. Then select notices on the left hand side. A box similar to the box below should pop up. There should be two spaces. There is one for a welcome message and another for an announcement. The welcome message is a notice sent to every new joiner of your network. The announcement is a notice sent to every member in your network each time it is modified. After typing the messages press ok.

     

To set permissions, also right click the network and select details. Then instead of selecting notices, select administrators. A box like the one below should pop up.

Now you can set the permissions for administrators. Check the permissions you want the administrators to be able to have. Then under that you get to choose who the administrators are in your network. Double click the peer to make him/her an administrator. Choose wisely! Then press ok.

Status Indicators

A status indicator is a small icon (usually a star or circle) in front of each peer that indicates the status of the connection to that peer. Below is a small guide telling you what each indicator means.

 A grey star indicates the peer is offline

 A green star indicates that you have a direct connection to the peer. This happens 95% of the time

 A blinking star indicates that Hamachi is trying to establish a direct connection with the peer. It usually takes under a minute to establish a direct connection

 A cyan down arrow indicates that Hamachi can't establish a direct connection with the peer. A low-speed relay is used to connect instead

A cyan star indicates that Hamachi can't establish a direct connection with the peer.

A high-speed relay is used to connect instead. It is used to connect peers to premium Hamachi users. Premium Hamachi accounts are paid options giving you access to more advanced features

 A yellow star indicates that Hamachi can't connect to the peer directly or with relay. This means you can't chat with this peer or reach him. This peer is unreachable.

 A red indicates that you are blocking the peer. This doesn't mean blocking the peer from sending you a message. It blocks network traffic to and from this peer but still enabling you to chat with him/her. You would use this option if you wish to chat with a non-trustable peer.

To block a peer, right click the peer and select block. Now their status indicator will be a red star.

Often Hamachi will be able to establish a direct connection with your peers. But sometimes a low/high speed relay is used. A direct connection is the best connection type and the fastest. The best way to ensure you have direct connections is having the same version and account type with all your peers. Also make sure that your firewall isn't blocking any connections.

Now that you know the basics of Hamachi, start using it. Think about using it for chatting, gaming, file sharing or remote accessing.

Geographical

WAN stand for Wide Area Network, and is used to refer to those networks that are not limited to a single building, site or location. LAN networks stand for Local Area Networks. Essentially, these are smaller networks, usually limited to a single site or location.

Data Transfer Rate

The data transfer rate is one of the big differences between LAN and WAN networks. LAN networks are faster than WAN, with transfer speeds up to 10 gb.

Network Topology

The network topology of LAN and WAN differ. LAN is a peer to peer network where resources are shared between terminals. WANs are actually more client to server based, with ISPs and central servers.

Cost

LAN networks are cheaper than WAN. They require less hardware, and also do not rely on leased lines.

Access

LAN networks, will more likely be password protected. They will have password validation, and possibly user-rights with a network administrator.  The WAN, will likely not have these.  On a LAN hardware resources are shared, while this is not so much the case with a WAN.

Connections

There are differences between LAN and WAN connections. Ethernet is a common type of LAN, which is used for smaller networks. WANs do not use Ethernet, but rely on other forms of connection.

Those are the main differences you will find between LAN and WAN networks. If there are others I can add, please let me know and I will do so.  

The hardware on a network may include: personal computers, mainframes, supercomputers, printers, fax machines, navigational control systems, and interactive entertainment centers.
The software on a network always includes application software, workstation operating systems, and network operating systems.

Networked computers have a number of advantages. They allow information to be exchanged at high speeds, they allow important devices to be shared, and they allow people to connect to their computers over long distances.

Benefit of Networking

Geographically remote areas can be connected to share information. Without actually transferring the entire file to all people involved, several people can simultaneously share large files. Also within a networked environment the information generated by a single user can be shared worldwide instantaneously. This enables faster, more precise communication which should translate into greater accuracy, productivity and cost savings.

• Networking allows different types of computers to communicate. Mac and PC users can share information and resources over a network.
  
• Users on a network can also share physical resources such as scanner, printer, or other expensive piece of hardware. Sharing hardware significantly reduces the expense of running a system.
  

Local Area Network (LAN)

1. Limited to a small geographical region
   
2. Specifically designed to share hardware and software at high speeds.
   
3. Originally developed to connect mainframes to dumb terminals (keyboard and monitor only-no system unit) over 50 years ago.
   
4. Mainframe LANs are faster, more powerful and have higher storage capabilities, while PC based LANs are more flexible to changing environments
   
5. Many companies used a combined network of mainframes and PCs
   
6. Computers
   

Texas Instruments Inc.

This device extends the battery life in certain types of medical tools, scales, and data acquisition applications.

Rock & Roll Hall of Fame Building- I. M. Pei

The architect tends to design buildings that depict the high-tech movement. He always works on larger scale projects and uses geometric designs to shape his buildings.

The "Butterfly Effect" - Prof. Edward Lorenz

Professor Lorenz realized that small differences in a forceful system such as the atmosphere could trigger unsuspected results. These explanations eventually led him to formulate what became known as the butterfly effect. "This term came from a paper he wrote in 1972 entitled Predictability: Does the Flap of a Butterfly's Wings in Brazil Set off a Tornado in Texas?"

Bose stereo - Professor Amar Bose

These stereo speakers are world-renowned for giving high-end performance despite their reticent size.

Ethernet - Robert Metcalf

Ethernet is a relationship between the unit frame-based computer networking technologies for (LANs). The Ethernet controls our access to certain types of data processing models, i.e. Internet.

The Internet Archive - Brewster Kahle

The Internet Archive (IA) consists of an online library containing the vast information on the Web and other multimedia resources. This information includes certain snapshots from various times from software, WebPages, audio visual and other sources.

Rockman amplifier - Tom Scholz

The Rockman is used in conjunction with headphones and an amplifier used for certain guitars. If any of you are familiar with Boston then you know who invented this.

Spacewar, the first computer game-Steve Russell

Spacewar was the first digital computer game of our time. The idea behind the game involved spaceships attempting to shoot each other while manipulating within the galaxy. I remember this game; I used to play it all the time on my Atari. I wish I still had it.

Hypertext - Prof. Vannevar Bush PhD

Hypertext is defined as words or text that leads the user to information associated with those words.

GPS (Global Positioning System) - Ivan Getting

The GPS uses satellites that transmit microwave signals. These signals enable receivers to determine certain types of pertinent information such as direction, time, speed and location.

Introducing Wide Area Networks (WANs)

A Wide Area Network (WAN) is generally considered to be a type of computer network that covers a broad area where communications links cross regional, metropolitan or national boundaries. Today, it is probably better to think of a WAN as a network that uses routers and publicly accessible communications links. Without doubt the largest and most well-known WAN is the Internet.

Wide Area Networks (WANs) are used to connect Local Area Networks (LANs) and other types of networks, including Metropolitan Area Networks (MANs), Local Area Networks (LANs), wireless and private networks. The purpose of a WAN is to enable users and computers in one location to communicate with users and computers in other, often very geographically dispersed and separated locations.

Typically a WAN will consist of a number of interconnected switching nodes that allows transmissions from any one device to be routed through these interconnected nodes to the specified destination device(s). These nodes are not concerned with the contents of data rather their interest is focused on the provision of a switching facility to move the data from node-to-node until they arrive at their intended destination.

Wide Area Network (WAN) Models

In essence there are two basic design models upon which all WAN connectivity structures and organization are based. They are:

The Centralized WAN Model - Consists of a server or group of servers in a central location and client computers or dumb terminals that connect to the server(s) which provide the bulk of the network's functionality. Figure 1 above is a logical construct of a typical centralized WAN. Note that all points lead to the centrally located servers.

Today's typical physical Point of Sale (POS) functionality such as that implemented by chain organizations such as banks and supermarkets etc is a classic example of a centralized WAN. Software-as-a-Service (SaaS) and web based applications are other examples of a centralized WAN computing model.

The Distributed WAN Model - Consists of client and server computers distributed throughout the network (see Fig.2 below). The Internet is a distributed WAN.

The three tiered network design hierarchy consisting of a core layer, a distribution layer and an access layer is implemented on top of which ever WAN connectivity and organizational structures are chosen. For more about the three tiered network design hierarchy check this article out Network Design: Hierarchies.

Building Wide Area Networks (WANs)

In order to facilitate the efficient and effective transfer of information between a WAN's end systems a number of protocols (rules that govern the transmission and reception of information between computers and network end-points) needed to be developed and implemented.

Generically speaking; a networking protocol is the formal description of a set of rules that describe, enable, govern and regulate the various characteristics, aspects, attributes and properties of an internetwork. One of the more important early WAN protocols was X.25. Although it is not used today, many of X.25's underlying protocols and functions (with modifications and improvements) are still in use by current iterations of Frame Relay.

Initially, most WANs were built using expensive leased lines. The most common production implementations of leased line based WANs involved the use of a router at each end of the leased line to connect to the LAN on one side to a hub within the WAN on the other.

Wide Area Networks (WANs) Reducing Implementation Costs

If ever the use of Wide Area Networks (WANs), including the Internet was to become widespread and accessible to the bulk of humanity (be it as individuals or collectives) something needed to be done to reduce the startup and running costs of planning, implementing and maintaining WANs. Fortunately solutions did exist.

Less costly alternatives to using expensive leased lines when building a WAN include the use of circuit switching or packet switching technologies. Here, network protocols including TCP/IP serve to deliver transport and addressing functions. While protocols such as Packet over SONET/SDH, Multiprotocol Layer Switching (MPLS), Asynchronous Transfer Mode (ATM) and Frame Relay are commonly used by Internet Service Providers (ISPs) to deliver the links that are used in WANs.

Wide Area Network (WAN) Connectivity Options

Leased Line - Provide secure but comparatively expensive Point-to-Point connectivity between two computers or Local Area Networks (LANs) using protocols such as Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC) and Synchronous Data Link Control (SDLC).

Circuit Switching - A less expensive dedicated circuit path offering bandwidth data transfer rates ranging from 28K-bit/sec to 144K-bit/sec is created between end points. On the downside call setup and connection establishment needs to be renegotiated every time access is desired because the link is not necessarily permanent. The most well known example of circuit switching WAN connectivity is dial-up connections. Point-to-Point Protocol (PPP) and Integrated Service Digital Network (ISDN) are two of the most widely used protocols for circuit switching WAN connectivity.

Packet Switching - Variable length packets are transported over a shared single point-to-point or point-to-multipoint link across a carrier internetwork using Permanent Virtual Circuits (PVC) or Switched Virtual Circuits (SVC). X.25 and Frame Relayare two examples of packet switching protocols used for WAN connectivity.

Cell Relay - Cell Relay is very similar to packet switching, but uses fixed length cells instead of variable length packets. Data is divided into fixed-length cells and then transported across virtual circuits. Unfortunately the overhead can constitute a significant proportion of the total bandwidth. Cell relay protocols such as Asynchronous Transfer Mode (ATM) (up to 155M-bit/sec) are best for simultaneous use of Voice and data.

Virtual Private Network (VPN) - With the recent reductions in Internet connectivity and concurrent increases in bandwidth and transmission rates now offered by ISPs many organizations have opted to use VPN technologies such as those on offer from the likes of Cisco Systems, New Edge Networks, Juniper, Check Point and Vyatta to interconnect their networks. One of VPN's strong points is encryption and considering the prevalence of cyber-crime today it is no surprise to find that this form of WAN is currently very popular.

Wide Area Network (WAN) Transmission Media and Links

Any given WAN may use one, more or even all of the following technologies for the transmission and transport of information:

Copper-Based Media - Telephone lines, coaxial cable, CAT cable etc

Fiber Optic-Based Cables - Single-Mode and Multi-Mode (see Fiber Optic Cableand Optical Networkingfor more).

Wireless - Radio frequency channels, microwave links, satellite channels and publically accessible wireless “hot spots”

Wide Area Network (WAN) Transmission Rates

Typically, WAN transmission rates usually have ranged from 1.2K-bits/sec to 6 M-bit/sec, although some connections such as ATM and Leased lines can reach speeds greater than 156 M-bit/sec. The advent of ADSL 2+ has upped the ante even further.

Now with transmission rates up to 30 Mbps, DSL and cable modem are two high data-transmission rate consumer Internet connections that transmit considerably faster than a dial-up modem (56 kbps). Add to this the fact that they are also generally cheaper than both ISDN and dial-up and you get a very cost-effective solution.

Wide Area Network (WAN) Access

Wide Area Networks (WANs) may be public (usually built by Internet Service Providers (ISPs) to provide Internet connectivity) while others are private (built for a specific organization). That is to say that public access to an organization's “private” network component is regulated by that organization. In contrast, access to public networks and user privileges remains largely unregulated beyond the criteria as defined by the agreement between the consumer and your Internet Service Provider (ISP).

Hence, the general public, anonymous and guest visitors, colleagues, business partners, and associates etcetera may be permitted limited privilege access to various sectors of an organization's private network but not to all of it. Functionalities, services, assets and user capabilities will vary greatly on a case-by-case network-by-network basis.

Demilitarized Zones (DMZs)

A classic example of this regulated limited access is commonly implemented in the form of Demilitarized Zones (DMZs) that allow public access to a very restricted and confined portion of an organization's private network. Here they may be able to access a web server for e-commerce, technical support or even just for casual browsing. You cannot make a sale if you cannot communicate with your customers. Even auto responders and automated shopping carts require some degree of two-way participation from both the customer and your software.

Metropolitan Area Network (MAN)

Another increasingly more common type of WAN is the Metropolitan Area Network (MAN) which is basically the same as a WAN except that its boundaries are contained within a single metropolitan area (city).

In Australia, a MAN can be viewed as a network for which standard landline telephone communications are charged at the local call rate (not STD) as all endpoints have the same area code. With broadband configured as a permanently connected service the customer only pays the local call fee for the initial setup connection or reconnection if the service is interrupted for any reason.

Examples of private Metropolitan Area Networks (MANs) would be the corporate links between various branches of the same organization (chain stores, banks) in the Perth metropolitan area. The key here is that regardless of the protocols or other technologies being used, part of the transit will be via publically accessible networks such as the Internet. The remainder will of course be contained within the boundaries of their “private LAN”.

WANs, MANs and Interoperability

Internetworking and interoperability are key factors critical to the realization of effective and readily available e-commerce portals as well as other external network resources and services. Regulatory and other compliance issues also need to be taken into consideration.

The seamless, secure interoperability of multiple systems and networks is essential in order for the general public to have free and ready access to those components of the enterprise LAN/MAN/WAN deemed desirable by that organization/enterprise.

For example; it is usually deemed to be highly desirable that the general public have rapid seamless access and interactivity with an organization's e-commerce facilities such as the shopping cart, support services if appropriate and resources such as online documentation.

The expansion of Web 2.0 functionality and the upsurge of social networking applications all rely heavily on the effective and efficient seamless integration of internetworking and interoperability technologies at all levels.

The Advantages of Fiber Optical Networking

First of all, we must note that the biggest advantage of using fiber optic networking and hence the use of fiber optic cable as a transmission medium is the high degree of immunity to noise, cross-talk and Electromagnetic Interference (EMI) that this medium provides.

Spanning Large Distances - With the fiber optic technologies currently available today signal degradation and regeneration issues are not what they once were and so the distance factor that so limits copper-based media is of negligible consequence where fiber optic transmission is concerned.

Environmental Damage - Environment factors such as moisture and Radio Frequency Interference (RFI) are also not of the same criticality as they are for copper-based media. The reasons for fiber optic cable as a transmission medium providing a high degree of immunization to noise (EMI) as opposed to other transmission media all stem from the use of light to convey the information (signals) and the construction of the medium (the fiber optic cable).

Security - Due to the degree of difficulty in “tapping” fiber optic transmission lines without being detected, fiber optic transmission media offer a more secure medium than copper-based or wireless technologies.

The result is that fiber optic transmission media are the media of choice when it comes to “long haul” applications such as intercontinental, cross-continental and oceanic (marine) backbone links. It is also the preferred medium for tier one ISP backbone links. This means that new WAN implementations and applications are now predominantly fiber optic cable based. Wireless rollouts being the major exception.

Additional information regarding fiber optic cable construction, signal propagation, signal regeneration, connectors, cable rollout and modes (single-mode and multi-mode fibers) can be found at Fiber Optic Cable.

I will now discuss the major standards and implementations of fiber optic networking starting with the Fiber Distributed Data Interface (FDDI) standard and then the Synchronous Optical Networking (SONET) and the Synchronous Digital Hierarchy (SDH).

Fiber Distributed Data Interface (FDDI)

FDDI which evolved from the IEEE 802.4 token bus timed token protocol is a fault tolerant 100Mbit/sec token passing counter-rotating dual ring LAN standard that permits data transmission between two end-point devices that can be many tens of kilometers apart.

As its name indicates, fiber optic cable is the main form of physical transmission medium used in FDDI. Although a copper-based implementation called, Copper Distributed Data Interface (CDDI) does exist. Although conceived as a LAN standard FDDI has also been used for MAN and WAN implementations.

FDDI Topology - In essence FDDI is a ring network similar to IBM's Token Ring network but with a number of critical differences. The most noticeable of which is that a FDDI uses a dual-attached, counter-rotating token ring topology (see Figure 1: FDDI).

Fault Tolerance - One ring acts as the primary transmission ring and in the original implementations was capable of delivering transmission speeds of up to 100Mbit/sec. The other or secondary ring was originally intended solely to act as a backup.

This meant that the secondary ring was inactive and remained so for as long as the primary ring was functional. In the event of failure of the primary ring the secondary ring would become active. Now all traffic goes to the secondary ring for transmission. It is this built-in redundancy that makes FDDI is a fault tolerant technology.

Higher Effective Sustained Data Throughput - Another factor in FDDI's favor was that it used a much larger frame size than Ethernet which meant that it was capable of much higher effective sustained throughput rates than standard 100Mbit/sec Ethernet. Administrators also had the option of using the secondary ring for data transport rather than having it stand idly by thereby doubling transmission capacity to 200Mbit/sec.

Coverage and Scalability - Not only can FDDI traverse large distances it also scales much better than 100Mbit/sec Ethernet. This means it provides superior support for expanding enterprise networks consisting of hundreds or thousands of users.

Fiber Distributed Data Interface II (FDDI-II) - FDDI-II is a more recent development of FDDI that has added support for circuit-switched services thereby enabling FDDI to carry both voice and video signals as well. For more on FDDI including applicable standards please see About Fiber Distributed Data Interface (FDDI).

Synchronous Optical Networking - SONET

Synchronous Optical Networking (SONET) is an established high-speed WAN alternative for communicating digital information using lasers or Light-Emitting Diodes (LEDs) over optical cable offered by several telecommunications companies.

SONET was originally developed to replace the Plesiochronous Digital Hierarchy (PDH) system for transporting large amounts of telephone and data traffic as well as providing the mechanisms that allow for interoperability between equipment from different vendors. The result is that there are multiple, very closely related standards that describe synchronous optical networking including:

Synchronous Digital Hierarchy (SDH) - The SDH standard was developed by the International Telecommunication Union (ITU) and is documented in standard G.707 and its extension G.708. SDH is used throughout the world but not in North America

Synchronous Optical Networking (SONET) - The SONET standard as defined by GR-253-CORE from Telcordia™. Primarily used exclusively in Canada and the USA where SDH has not been implemented, although it can be found in other countries.

Synchronization is Key - Through the use of atomic clocks synchronous networking data transport rates are very tightly regulated which allows for entire inter-country networks to operate synchronously while greatly reducing the amount of buffering required between elements in the network. This reduction in overhead (buffering) translates into greater effective net data throughput rates.

Encapsulation - Both SONET and SDH can be used to encapsulate earlier digital transmission standards, such as the PDH standard, or used directly to support either ATM or so-called Packet over SONET/SDH (POS) networking.

Generic Transport Containers - SDH and SONET are generic all-purpose transport containers for moving voice and data rather than just communications protocols per sec.

SDH and SONET Frame Structures

Standard packet or frame oriented data transmission frames usually consist of a header and a payload with the header of the frame being transmitted first, followed by the payload and a trailer (e.g. CRC). With synchronous optical networking both the header, which is referred to as the overhead and the payload still exist but the big difference is that the overhead is not all transmitted before the payload, rather the transmission is interleaved.

Interleaved Transmission - With interleaved transmissions the transmission of the conversation goes like this:

First of all, a portion of the overhead (header) is transmitted. This is followed by part of the payload. After which the next part of the overhead is transmitted. This is followed by the next part of the payload and so on until the entire frame has been transmitted. Figure 2: Interleaving above shows this.

SONET Frame Size and Transmission Sequence - SONET frames are 810 octets in size, transmitted as 3 octets of overhead, followed by 87 octets of payload, nine times over until 810 octets have been transmitted. The total frame transmission time is 125 microseconds.

SDH Frame Size and Transmission Sequence - SDH frames are 2430 octets in size transmitted as 9 octets of overhead, followed by 261 octets of payload, also nine times over until 2430 octets have been transmitted. Again the total frame transmission time is also 125 microseconds.

It doesn't take much brain power to see that SDH is capable of an effective data throughput rate three times that which the North American implementation of SONET can achieve.

Ethernet over Fiber Optic Cable

Today we see the Gigabit Ethernet over fiber optic cable and 10G Ethernet over fiber optic cable standards being the most common implementations of optical local area networks (LANs) currently being rolled out. They are also used extensively as the network core layer's transport medium of choice particularly Ethernet networks.

The majority of the big players in the networking hardware arena like Cisco, Juniper, and Redback etc all produce numerous products with fiber optic support including Ethernet over Fiber Optic modules. Note see Network Design: Hierarchiesfor more about network design and the functions and features of a network's core layer.