The Basic Idea

Webcams, like most things, range from simple to complex. If you understand the essence of a simple Webcam setup, increasing the complexity is only a matter of adding functionality through software, custom code and/or equipment connections.
A simple Webcam setup consists of a digital camera attached to your computer, typically through the USB port. The camera part of the Webcam setup is just a digital camera — there’s really nothing special going on there. The “Webcam” nature of the camera comes with the software. Webcam software “grabs a frame” from the digital camera at a preset interval (for example, the software might grab a still image from the camera once every 30 seconds) and transfers it to another location for viewing. If you’re interested in using your Webcam for streaming video, you’ll want a Webcam system with a high frame rate. Frame rate indicates the number of pictures the software can grab and transfer in one second. For streaming video, you need a minimum rate of at least 15 frames per second (fps), and 30 fps is ideal. To achieve high frame rates, you need a high-speed Internet connection.

Once it captures a frame, the software broadcasts the image over your Internet connection. There are several broadcast methods. Using the most common method, the software turns that image into a JPEG file and uploads it to a Web server using File Transfer Protocol (FTP). You can easily place a JPEG image on any Web page (for information on creating Web pages and adding JPEG images, see How Web Pages Work).

If you don’t have your own Web server, lots of companies offer you a free place to upload your images, saving you the trouble of having to set up and maintain a Web server or a hosted Web site.

This is the simplest possible Webcam. Let’s see what you need to make it happen.

What You Need

In order to create a simple Webcam, you need three things:

•A camera of some sort connected to your computer
•A piece of software that can grab a frame from the camera periodically
•A way to broadcast your images on the Web

If you have your own Web server and Web site, you already have a way to post your Webcam images on the Web. At its most basic, a Web server is simply a piece of hardware that has the ability to deliver Web-based content to a Web browser. For some people, their home computer serves as their Web server. If that’s the case, a camera, a piece of software and your PC are all that you need. If you want to use a Web server that’s hosted elsewhere (for example, if you’re paying an ASP to host your Web server), you also need:
•The ability to move frames from your computer to the Web server, typically by File Transfer Protocol (FTP). For most Web servers, this is no problem; but occasionally, a hosting company will have policies in place that make this difficult.

•A relatively consistent connection between your computer and the Internet. A modem connection to an ISP is fine if it is something that you keep connected most of the time, which implies that you have a dedicated phone line for your computer. If you have something like a cable modem that is connected all the time, that’s perfect.
If you don’t have a Web server or a Web site, and you don’t want one, you can simply have someone else maintain your Webcam images. Lots of Webcam software comes complete with Web-based image access. They usually offer different access options, including remote access, which utilizes UDP protocol to transfer your Webcam images directly from your computer to another computer. This can be done:

•via Web browser, in which case the software itself establishes its own HTTP server so anyone using a Web browser can access the Webcam images on your PC
•via traditional FTP upload to a remote Web server
By using this type of service, you avoid having to host and/or maintain your own Web site. If you are using one of these services and you want the image to refresh itself constantly, you need a relatively consistent connection between your computer and the Internet. If your connection is not consistent, it won’t hurt anything. It just means that the image won’t always be up to date.

Setting It Up

In order to experiment with Webcams and go through the process of setting one up, HowStuffWorks got itself a Webcam. To set it up, here is what we did:

1.We went down to the local computer warehouse and bought the Intel Pro Video PC Camera.

2.We installed the software for the camera on a Windows XP machine.
3.We went to the Web site www.webcam32.com and downloaded a program called Webcam32. This is a popular software package for Webcams. You can get a free demo version or pay $39.95 for the full version. We went ahead and paid for a registered copy. (The complete user’s manual for this product is available on the Web site. Check it out to see the wide array of features available on today’s Webcam software.)

4.We installed Webcam32. It was a very easy installation.
5.After entering the address of the FTP site and a couple of other pieces of information, the Webcam showed its first signs of life!

6.We pointed the camera out the window.
7.We then tuned the software a bit to reduce the file size of the images and to enable the temporary-file copying feature.

There are many different features you can experiment with in Webcam32: streaming video, chat, captions, AVI files and different resolutions and compression ratios, to name a few. Webcam32 also supports the AutoCam feature, which allows you to create a Web page for your Webcam for free on the company’s server. The software makes it simple.
As you can see, setting up a basic Webcam is extremely easy. If nothing else, the setup described here is a fun, inexpensive and simple way to experiment with a Webcam and see what you can do with one of your own!

Advanced Features

Once you manage the simple system, you can look into other Webcam features and settings like:

•Motion sensing – The Webcam takes a new picture when it detects motion.
•Image archiving – You can create an archive that saves all of your Webcam images or only certain images at pre-set intervals.
•Video messaging – Some instant messenger programs support Webcam video.
•Advanced connections – Use wired or wireless methods to connect your home-theater A/V equipment to your Webcam.
•Automation – Robotic cameras let you set a series of pan/tilt positions and program frame-capture settings based on the position of the camera.
•Streaming media – For professional applications, a Webcam setup can use MPEG4 compression to achieve true streaming audio and video (this is the compression system used in most of the popular PC-based media players).
•Custom coding – Import your own computer code to tell the Webcam what to do.

One example of custom coding is a set of commands that makes a Webcam image automatically refresh. The simple Webcam system we’ve set up in this article produces a static image. Users have to refresh the image manually (by pushing the Refresh button in the browser) if they want to see any changes. There are three different techniques you can use to create automatic refreshing:

•You can add a meta tag to the HTML for the page so that the page refreshes at some frequency. The tag to add is:

<meta http-equiv=”refresh” content=”30″>

The “30″ is the number of seconds between each refresh and can be set to anything you like. The entire page will reload every 30 seconds, so it is beneficial to keep the page short.

•You can add a Java applet to your site. The Webcam32 and Java Applets page explains how to obtain and install the free applet. The applet is a program that automatically fetches the image periodically. The advantage is that only the image refreshes, not the entire page. Most browsers support Java applets, so most of your viewers will have no problem.

•You can use JavaScript, as demonstrated on The JavaScript Source: Refresh (look at the source code on this page). You can also check out How Java Works for a detailed look at Java programming.

Webcam Networking

One problem with using a camera hooked to a computer via a USB cable is the limited cable length. What if the room you want to capture is at the other end of the house, or outside? In that case, you need to purchase a camera with external connections. You have a few options:

•You can place a standard camera anywhere in the house and run a video cable with RCA jacks on it from the camera to the computer. There are all sorts of places on the Web that sell small pinhole video cameras, either on their own or embedded in things like clocks and smoke detectors. You can find small security cameras for less than $100. (Click here to use the HowStuffWorks search engine to search for security cameras.)

•You can avoid the cable by using a radio link (X10: XRay Vision is one example of this type of product), an Ethernet connection or a WiFi setup. If you already have a home network, connecting an external Webcam to your computer probably won’t require any additional networking.

Monitoring your home and sharing images via the Web are only a couple of the things you can do with your Webcam. There are any number of ways to make use of a camera that’s connected to your computer. You can get software that will let you make video phone calls with a friend who also has a Webcam. You can hold a video-conferencing session with business associates on the other side of the world. You can conduct a video interview and broadcast it live on your blog. Some Webcam software will even deliver images directly to your Web-enabled PDA or smartphone. Other products let you connect your camcorder to your Webcam setup so you can let everybody watch your vacation footage via the Internet. The possibilities are endless.

See the original article here>>

It is a default private IP for various NAT/network devices such as routers. In order to resolve the issue of shortage of IP to be used on the Internet, these IP addresses were devised. RFC 1918 defines the ranges of the private IP.

An IP, where IP stands for Internet Protocol, is a numeric identification that is assigned to all the devices or machines, which are a part of any computer network. All the devices, which are connected to a network, have a unique IP. As we have said earlier, these addresses are numeric representations, which are divided into four parts, and each part is separated by a period (dot) between them. For instance, an IP normally looks like 192.168.1.1.

One series of these numbers is classified as private IP. Generally, this set of numbers range from 192.168.0.0 to 192.168.255.255. Each of these numbers is retained and unique as compared to other IP addresses. The word unique here is used in the sense that these numbers are unique within the network they belong. To make this clear let us take an example of your college or office computer, which is assigned an IP 192.168.1.1 in network and you, will have the same IP address in your home network as well and it won’t create any conflicting issue.

NAT (Network Address Translation) and Private Address Space

With the evolution of Internet, there started to be a shortage of IP addresses simply due to the way through which these are allocated. For a quick fix of this problem, NAT devices are used. For instance, if you have more than one computer in your home and all of them are connected to a NAT device say router, that router assigned a unique private Ip to each computer.

The NAT devices, such as router or firewall, modify the information that your computer send to the Internet, hence in turn they get a normal address that can be used on the web. Another important feature of the NAT device is that they are accountable to route the information entering the network to the right computer in your network.

Default IP

192.168.1.1 is a default IP address used by various NAT devices in private networks such as routers. Some other default IP addresses include 192.168.2.1 and 192.168.0.1. As we have said in the beginning that the ranges of these IP is defined by RFC 1918. The Internet Assigned Numbers Authority (IANA) is responsible for keeping these and other numbers reserved within their particular ranges for private network use.

There are so many Nat devices or network devices, which use 192.168.1.1 as default private IP. But the two most popular NAT devices brands, Linksys and Speedtouch use this and other numbers as their default IP.

source: http://ezinearticles.com/?What-Is-an-IP-Address?&id=5235745

The Promiscuous mode is a specific receive mode for network-technology devices such as wireless network cards. It is normally used for packet sniffing and bridged network for hardware virtualization. The frames include the MAC (Media Access Control) address of the hardware.

In this mode the device submits all incoming traffic to the network interface and transmits the data for processing to the operating system. Devices that use this mode can be combinations of switches and routers, network tester or even a normal computer with a connection to a network.

For Wireless LANs in promiscuous mode it will only forward the packets of the network (access points) to which the client is currently connected. The Promiscuous Mode is unsuitable to receive packages from a network which you do not own because you need to authenticate yourself with the network.

The opposite of this mode is the non-promiscuous mode. In this mode the unit handles only the packets addressed to it and this happens for example in Ethernet networks, the evaluation of the MAC address plus broadcast packets.

Another method of usage is to detect network connectivity issues. Some programs use this feature to show everything that is transferred by the network and some of them can transfer passwords and data in clear text. So a normal user should stay away of this mode to prevent that someone else could steal this data while the transferring process.

As you can see the Promiscuous Mode should only be used by advanced users to avoid any damage to your system or to open the door for hackers. But when you know what you are doing this mode is quite powerful and you can repair your network without any problem.

Of course not every wireless card drivers support this mode because of it’s not a secure mode. If you need this mode you should watch out for another driver that supports the Promiscuous Mode. You can contact your device’s manufacturer and ask for a new driver.

source: http://ezinearticles.com/?Wireless-Network-Monitor—The-Promiscuous-Mode&id=5160653

Many people are not aware that when they are surfing the internet, they run the risk of inviting malware and virus into their computer system. It is not difficult to create these harmful software to destroy people’s computer system and there is nothing you can do to stop them. However, what you can do is to protect your system and ensure that it does not get attacked by virus by applying the following 4 tips.

1. Install updated virus protection software
The first thing you can do to protect your system is to install updated virus protection software. This will ensure that the bad software in your system gets eliminated as the protection software will carry out constant scans. Once you have installed the protection software, make sure it is turned on all the time, especially when you are surfing the internet to prevent virus invasion.

2. Take precaution when downloading documents
The second tip is to be extra careful when you are downloading any documents from others on the internet, especially when the documents are of a free nature. Very often the malware and virus are hidden within these free documents which will be allowed a chance to enter your system when you download them. If you are downloading some materials which you have purchased, make sure you have bought it from reputable sites to prevent unnecessary problems. Once the virus enters your computer system, it will not be an easy task removing.

3. Guard your particulars
By guarding you particulars, I am referring to your username and password to important sites such as Paypal account, Ebay account or your personal bank accounts. Either make sure the internet transaction is carried out over secured networking or refrain from using links provided to you from someone else. You can always get to site yourself by tying the URL directly in the browser.

4. Beware of free software
As mentioned earlier, free software might pose as a problem to many because of the dangers they hold. Nevertheless, you can prevent falling a victim to such online viruses by being extra careful when you are downloading something. Check the instructions or policy carefully to prevent unnecessary problems. Who knows, besides virus, you might even invite unwanted spyware to your computer system.

The internet makes it easy for people to find out information but at the same time, you also have to exercise vigilance when you are surfing the internet because you do not want to fall prey to unscrupulous others out there who might harm your system by sending you computer virus. Remember, a slight mistake can destroy all the hard work you have done on your computer.

source: http://ezinearticles.com/?How-to-Ensure-the-Safety-of-Your-Computer-System-When-Surfing-the-Internet&id=4588520

Connection to the Internet these days has become so easy and user-friendly that we tend to forget the technical aspects of things like page loads and file downloads. Such operations still take place, even though the average user doesn’t give them a second thought.

One such overlooked set of operations is TCP/IP. This often used but little understood set of operations stands for Transmission Control Protocol/Internet Protocol. TCP/IP is the combination of the two and describes the set of protocols that allows hosts to connect to the Internet. In actuality, TCP/IP is a combination of more than those two protocols, but the TCP and IP parts of TCP/IP are the main ones and the only ones to become part of the acronym that describes the operations involved.

TCP/IP doesn’t just happen. It is an active process; a set of constant communications between private computers and Internet servers. When a computer attempts to log on to the Internet, that computer’s TCP/IP operations send a series of signals to Internet servers looking for a connection. In nearly all cases, access is successful. Some exceptions would keep access from being granted, but these exceptions are rare.

The two layers of TCP/IP are defined by the separate spelled-out versions. Transmission Control Protocol is the top layer; the one that converts messages or files into data packets that are transmitted over the network connection to the destination computer and then reassembled into messages or files that can be read by the destination user. The lower layer of TCP/IP, Internet Protocol, provides the transmitting operation, configuring the connection’s address so that the information gets to the right place. IP could function without TCP, although it would be idle, but the reverse is not possible.

Despite the very evident presence of the word Internet in the spelled-out version of TCP/IP, the set of protocols can be used for internal use as well. Company intranets utilize TCP/IP protocols in order to set up a network within the company’s computer framework. No outside connection develops, but connections are made between the company’s servers and/or mainframes and individual computers. This sort of connectivity mimics the connection functionality of TCP/IP as used for Internet connections.

source: http://www.wisegeek.com/what-is-tcpip.htm

The SSID (Service Set IDentifier) is a token which identifies a 802.11 (Wi-Fi) network. The SSID is a secret key which is set by the wireless network administrator. You must know the SSID to connect to a 802.11 wireless network. However, the SSID can be discovered by network sniffing/scanning. By default, the SSID is part of the packet header for every packet sent over the WLAN.

SSID access points continuously broadcast radio signals which are received by client machines if enabled. Based on the automatic or manual configuration, the client can connect to the access point. A SSID is generally 32 bit long, but when displayed to the user, it is projected into a human readable ASCII format. Multiple access points can possibly share same SSID if they are for the same wireless network. Many wireless access points support broadcasting multiple SSIDs, permitting the formation of Virtual Access Points. Such Virtual Access Points partition a single physical access point into many logical access points, each of which can have a special set of security and network settings.

SSID Security Issues

The fact that the SSID is a secret key instead of a public key creates a key management problem for the network administrator. Every user of the network must configure the SSID into their system. If the network administrator seeks to lock a user out of the network, the administrator must change the SSID of the network, which will require reconfiguration of the SSID on every network node. Some 802.11 NICs allow you to configure several SSIDs at one time.

Default SSID’s

Most 802.11 access point vendors allow the use of an SSID of “any” to enable an 802.11 NIC to connect to any 802.11 network. This is known to work with wireless equipment from Buffalo Technologies, Cisco, D-Link, Enterasys, Intermec, Lucent, and Proxim. Other default SSID’s include “tsunami”, “101″, “RoamAbout Default Network Name”, “Default SSID”, and “Compaq”.

Every time a client connects to the wireless network, the SSID is communicated in plain text format, which can easily be sniffed by eavesdropper using sniffing applications like Kismet. Hence, additional security techniques are required to be implemented in order to enhance the wireless security.

Disabling SSID Broadcasting

Many Wireless Access Point (WAP) vendors have added a configuration option which lets you disable broadcasting of the SSID. This adds little security because it is only able to prevent the SSID from being broadcast with Probe Request and Beacon frames. The SSID must be broadcast with Probe Response frames. In addition, the wireless access cards will broadcast the SSID in their Association and Reassociation frames. Because of this, the SSID cannot be considered a valid security tool.

An SSID by any other name

The SSID is also referred to as the ESSID (Extended Service Set IDentifier).

Some vendors refer to the SSID as the “network name.”

source: http://www.topbits.com/ssid.html

Network access control or NAC is one of the strategies that is employed to enhance the security protocols associated with a private or proprietary network. This is accomplished by setting restrictions on the ability to access various programs and functions that are available on the network. The creation of the authorizations required to allow access to any given database, software, or function on the network remains in the control of a network administrator or other persons who are granted that level of management by the administrator.

There are several common ways that network access control is achieved. The most common approach is to set up a process for authenticating each valid user for the network. This may be accomplished by employing a simplistic user name and password combination, or involve additional clearances that are necessary, such as a test question or proper identification of an image that is associated with the login credentials.

Typically, the administrator sets the structure for the credentials, although users may or may not be granted the privilege of changing passwords from time to time. This level of network admission control (which is also identified as NAC) is usually the foundational tool in making sure a network is secure. However, it rarely is the only security measure utilized.

Along with setting login credentials and procedures, network access control also usually involves setting rights and privileges associated with each user. For example, salespersons are likely to have access rights to a general sales database, but be limited to the type of information that may be accessed and viewed from the accounting software program that also resides on the network access server or NAS. Privileges are usually determined based on the perimeters of the job or position held by each user. However, administrators can grant users additional rights and privileges if the need arises.

Other tools help to provide general enhancement to these basic network access control protocols. The addition of a firewall can help to minimize attacks from outside the network. In like manner, the presence of spyware detection programs and antivirus protection software can also be a great help if users make regular use of Internet access.

While a network administrator can purchase and load individual tools to assist in network access control, several vendors now offer software packages that include a wide range of different network access control features and options. Several of the packages allow the administrator to pick and choose from available options, making it possible to customize the type and level of network security that is required.

source: http://www.wisegeek.com/what-is-network-access-control.htm

Understanding Firewalls

When anyone or anything can access your computer at any time, your computer is more susceptible to being attacked. You can restrict outside access to your computer and the information on it with a firewall.

What do firewalls do?

Firewalls provide protection against outside attackers by shielding your computer or network from malicious or unnecessary Internet traffic. Firewalls can be configured to block data from certain locations while allowing the relevant and necessary data through (see Understanding Denial-of-Service Attacks and Understanding Hidden Threats: Rootkits and Botnets for more information). They are especially important for users who rely on “always on” connections such as cable or DSL modems.
What type of firewall is best?
Firewalls are offered in two forms: hardware (external) and software (internal). While both have their advantages and disadvantages, the decision to use a firewall is far more important than deciding which type you use.

* Hardware – Typically called network firewalls, these external devices are positioned between your computer or network and your cable or DSL modem. Many vendors and some Internet service providers (ISPs) offer devices called “routers” that also include firewall features. Hardware-based firewalls are particularly useful for protecting multiple computers but also offer a high degree of protection for a single computer. If you only have one computer behind the firewall, or if you are certain that all of the other computers on the network are up to date on patches and are free from viruses, worms, or other malicious code, you may not need the extra protection of a software firewall. Hardware-based firewalls have the advantage of being separate devices running their own operating systems, so they provide an additional line of defense against attacks. Their major drawback is cost, but many products are available for less than $100 (and there are even some for less than $50).

* Software – Some operating systems include a built-in firewall; if yours does, consider enabling it to add another layer of protection even if you have an external firewall. If you don’t have a built-in firewall, you can obtain a software firewall for relatively little or no cost from your local computer store, software vendors, or ISP. Because of the risks associated with downloading software from the Internet onto an unprotected computer, it is best to install the firewall from a CD or DVD. If you do download software from the Internet, make sure it is a reputable, secure website (see Understanding Web Site Certificates for more information). Although relying on a software firewall alone does provide some protection, realize that having the firewall on the same computer as the information you’re trying to protect may hinder the firewall’s ability to catch malicious traffic before it enters your system.

How do you know what configuration settings to apply?

Most commercially available firewall products, both hardware- and software-based, come configured in a manner that is acceptably secure for most users. Since each firewall is different, you’ll need to read and understand the documentation that comes with it to determine whether or not the default settings on your firewall are sufficient for your needs. Additional assistance may be available from your firewall vendor or your ISP (either from tech support or a website). Also, alerts about current viruses or worms (such as US-CERT’s Cyber Security Alerts) sometimes include information about restrictions you can implement through your firewall.

Unfortunately, while properly configured firewalls may be effective at blocking some attacks, don’t be lulled into a false sense of security. Although they do offer a certain amount of protection, firewalls do not guarantee that your computer will not be attacked. In particular, a firewall offers little to no protection against viruses that work by having you run the infected program on your computer, as many email-borne viruses do. However, using a firewall in conjunction with other protective measures (such as anti-virus software and “safe” computing practices) will strengthen your resistance to attacks.

source: http://www.us-cert.gov/cas/tips/ST04-004.html

What are the network setting required for a computer to join a domain?

In order to be able to join a Windows 2000 or Windows Server 2003 domain you must properly configure your XP/W2K computer.

Note: XP Home Edition is not designed to join domains; only workgroups. To join domains, use XP Professional version or above.
Required Settings

A network Interface Card (NIC) – Duh, but unless you have one (or a wireless connection) how do you expect to connect to the server?

Physically be connected to the LAN – Windows XP (and 2000) has an LAN auto sensing feature. Whenever you disconnect from the network, a balloon appears in the task bar area notifying you of the disconnection status. Without a physically connected network the NIC looses it’s IP settings, thus preventing you from connecting to the network (which was disconnected in the first place) or viewing your IP configuration.

A valid IP address – Valid for the network you’re connected to. You can either configure one manually, receive one from a local DHCP Server, or leave it as is and receive an APIPA address. If it’s an APIPA address you’re asking for potential problems, as APIPA and AD do not go together hand-in-hand.

All-time connectivity to the Domain Controller – Or at least one of them. The IP address you’ve configured (or leased) should be good enough to enable you to connect to one of the Domain Controllers on your Domain. Test your connectivity with PING.

A properly configured DNS server – Without a properly configured DNS server your workstation will not be able to connect to the domain. Even if it did (for example you had a working DNS server but you somehow messed it up or shut it down) it will take a lot of time to actually log-on, and many AD related administration tasks will not work.

The DNS server must hold a zone with the exact name of the AD domain you’re trying to join. It also must hold 4 SRV folders (you can tell by the “_” in their name). If it doesn’t, you either misspelled the domain name or DNS zone, or the zone is not configured to accept dynamic registrations, or it’s not a Windows 2000 DNS server, or the Domain Controller does not have a working connection with the DNS server (firewall problems, improper IP configuration, IPSec etc.)

All-time connectivity to the DNS server – Test your connection to the DNS server by PINGing it and performing an NSLOOKUP query.

Local Administrative power – A simple user won’t do. You must be the local Administrator.

Correct domain name, Administrator’s name and password – Misspelled your domain name? You won’t get to the Username and Password prompt!

Got your domain name right? You’ll be asked for a valid username and password. To be safe, enter one that has Domain Admins rights, although you could get away with less, depending on your AD configuration.

No Internet Connection Sharing please – ICS will mess up your network. Do not use it. Use RRAS and NAT instead. It will work if it has to, but ICS and AD do not go together hand-in-hand. You are warned.

source:
http://www.petri.co.il/requirements_when_joining_a_domain.htm

Introduction

For many medium and large sized networks the choice of cabling is the single most important, long-term investment made in the network. The choice of cabling must be a balance between cost and performance, all the while trying to predict future performance requirements. If the network cabling cannot support future requirements you may be forced to re-cable your entire network, which of course can be quite expensive.

In this article I will give you a high level overview of twisted pair cables, Coax cables, and Fibre optic cables. These are the most common types of network cables used in Ethernets. I will explain the advantages, disadvantages and limitations of each.
UTP and STP

By far the most common type of cabling for Ethernets are the twisted pair categories. An Unshielded Twisted Pair (UTP) cable, as shown in Figure A, consists of four pairs of 22 or 24 American Wire Gauge (AWG) copper wire. (The AWG number indicates the thickness of the wire, with higher numbers indicating a smaller diameter.) Each wire has a layer of plastic insulation around it, and the entire cable is wrapped in a protective plastic sheath. Each pair is twisted to provide protection against electromagnetic interference (EMI). To protect against crosstalk between the pairs, there are a different number of twists per metre in each pair. As a general rule, the more twists per metre the pair has, the more protection it has against these types of interference.

Figure A: A UTP cable from www.belkin.com

Shielded Twisted Pair (STP) cabling is the same as UTP cabling except that each pair is wrapped in a metallic foil, and the four pairs together are wrapped in a metallic foil. This metallic foil acts as a shield to electromagnetic fields, thus providing additional protection from interference.

Some of you might be wondering how this metallic foil protects against electromagnetic fields. I thought electromagnetic fields induced electric current in metals? Well, yes. They do. This is precisely why both ends of this metallic foil need to be properly grounded. If this grounding is not done properly you will have nothing more than a glorified radio antenna; but I suppose that would be one way to download free music!

For those that are interested, Figure B shows a very simple way to receive radio signals. Stay tuned for future articles on antennas of all sorts.

Figure B: Radio tuning circuit from http://micro.magnet.fsu.edu

All categories of twisted pair cabling have a maximum data transmission range of 100m but have varying maximum data transfer rates.

Cat1 and Cat2 cables are obsolete. They were once used for telephones, and very early networks.

Cat3 cables became popular in the late 1980s, as they were inexpensive and provided a maximum data transfer rate of 10Mbps.

Cat4 are not seen very often. They were used in earlier token ring network topologies and have a maximum data transfer rate of 16Mbps.

Cat5 cables are currently the most common type of cabling you will see in Ethernets. The maximum data transfer rate of Cat5 cables is 100Mbps.

Cat5e cables are also quite common. They have slightly more enhanced specifications which allow a maximum data transfer rate of 1Gbps.

Cat6, Cat7, and Cat8, cables are not yet very common. However, as gigabyte Ethernets become more popular you will likely see these categories of cables become more popular as they offer even better performance.

You will notice that as the category number increases so does the maximum data transfer rate. This is accomplished, in large part, by the copper wire pairs within the cables having more twists per metre. As said earlier, more twists per metre provide more protection against interference and therefore allows a greater spectral bandwidth to be transmitted over the cable.

Straight through and Crossover cables

There are two general configurations for twisted pair cables. A straight through configuration means that both ends of the cable have the same pin configuration. That is, whatever pin number a wire is connected to at one end of the cable it will be connected to that same pin number at the other end of the cable. This configuration is used to connect two different kinds of equipment.

A crossover configuration means that the two ends of the cable have opposite pin configurations. Crossover configurations are used to connect two of the same kinds of equipment. You should be aware that a lot of newer devices are smart enough to know whether you are using a straight through or a crossover cable. So before you go out and buy a new cable, you should check to see if your device is one of these smart devices.

Plenum cables

It should be noted here that all of the cables mentioned in this article are available in a plenum version. It is required to use plenum cables when running cable through ducts, suspended ceilings, or any other area which acts as an air passage. This is because normal cabling can be toxic in the event of a fire; plenum cables have a special coating which makes the cable non-toxic.

Coax cables

Coax cables can also be found in many networks. There are two types of coax cables commonly used in Ethernets. They are 10Base2 and 10Base5, or alternatively thinnet and thicknet. Coax cable consists of a solid copper wire surrounded with insulation. Around this insulation is a copper shield and an outer plastic insulator. Just as in STP cables the copper shield must be grounded at both ends in order to protect against EMI. The difference between thinnet and thicknet is that the solid copper wire has a diameter of 0.35cm in thinnet and a diameter of 1cm in thicknet.

Both types provide a maximum data transfer rate of 100Mbps. The advantages of using coax cabling can be found in the maximum data transmission range. Thinnet has a maximum data transmission range of 185m, while thicknet has a maximum data transmission range of 500m. This is the reason that coax cables are often used as a backbone in network bus topologies.

A typical coax cable is shown here in Figure C.

Figure C: A coax cable from www.belkin.com

A major disadvantage of coax cabling is that the thickness of coax cables, especially thicknet cables, makes them very difficult to install and therefore they are more costly than the twisted pair cables. However, if your network is large the extra money spent on coax cabling may be offset by the money saved by not having to purchase repeaters needed to span long distances.

Fibre optic cables

Fibre optic cables are definitely cool. They provide a transmission length of 10km or more for single mode fibre, or 2km or more for multi mode fibre. Fibre optic cables can also provide maximum data transfer rates of more than 100Gbps.

Fibre optic cable, as shown in Figure D, consists of a glass core with a surrounding cladding. There is also a protective coating, strengthening fibres, and an outer coating. Data is transmitted via light through the glass core. Since data is not transferred with electric signals, fibre optic cables are not affected by EMI. Another advantage of fibre optic cables is that the cable is not affected by water. The performance of coax cables and twisted pair cables can be significantly degraded if water penetrates the cable. This makes fibre optic cables ideal for spanning long distances outside.

Figure D: Fibre optic cables from www.fibrepulse.com

The major disadvantage of fibre optic cables is the cost. It is far more expensive to use fibre optic cable than any other cable discussed in this article. Fibre optic cables can also be quite fragile. The inner glass core can be broken if the cable is pulled too hard, or bent around a sharp corner. In many networks that use fibre optic cabling, cables are often replaced because they have been broken, thus adding additional costs.

Conclusion

As I mentioned in the introduction of this article, the choice of cabling in a network is a balance of cost and performance. The biggest reason twisted pair cabling has become so pervasive is because of the very low cost and relatively high maximum data transfer rates.

As the cost of fibre optic cable decreases, you will no doubt see this as the cabling of choice in more and more networks. In future articles I will give examples of the different types of fibre optic cables, and some of the more unique challenges that come along with this technology.

source:
http://www.windowsnetworking.com/articles_tutorials/Copper-Glass-Guide-Network-Cables.html