Network Cables for Ethernet

Computers can be linked together with cables or the connection can be wireless (through radio communication).

Common cable types are:

• "Category 5" (CAT5 - usually blue, and looks like telephone cable). CAT5 is a type of unshielded twisted pair cable (UTP) and is often used for the last connection between a PC and the network.  Maximum length of a single cable can be up to 100m.  Its Ethernet code name is 10Base-T.
  

• Coaxial: black, about as thick as a pencil, has an inner cable surrounded by insulation and then a grounded shield of braided wire. Cable TV comes through one of these. The shield minimizes electrical and radio frequency interference. Although more expensive than standard telephone wire, it is much less susceptible to interference and can carry much more data. Commonly called "coax" (pronounced "co-ax")
• Thin coaxial cable (10Base-2) can carry signals about 185 metres before the signals degrade to rubbish.
  Coaxial cable is often used as a backbone - a high-speed "data freeway" that gets a lot of data from a central place to another place quickly.

  Coaxial cables are split and joined using metal connectors known as T-Pieces and I-Pieces (T-Pieces let a device join onto a passing cable; I-pieces join separate pieces of cable into a single cable).  The cables and connectors have matching bayonet-type ("BNC") fittings that twist and lock together.

  

  Above: A coaxial cable and T-piece, used to connect separate cables.  The white knob is a terminator, which must appear at the end of a coaxial cable.

• Thick coaxial cable (10Base-5) can carry network signals up to 500m.
• Broadband coaxial cable (10Base-35), which may bring cable TV into your house, can carry multiple channels, and can reach 3600m.

FIBRE OPTIC

One drawback of standard CAT5 and coaxial network cabling is the maximum distance a signal can travel. If the distance is too large, repeaters are needed to boost the signal and keep it travelling. CAT5 cable, being metallic, is also subject to interference from strong electromagnetic fields (such as the motors in lift shafts).

The core of fibre optic cable is made of glass and signals are sent along the cable optically (via laser) rather than electrically.

The cables can be far longer than CAT5 and they are not subject to electrical distortion.

Fibre optic cable does tend to be fragile, however, and needs to be treated carefully.

Fibre is very thin and can carry far more "channels" in the same diameter of a CAT5 cable.

At one end of the cable is a converter that changes normal electrical network signals into laser pulses (and vice versa) much like a modem converts digital to analogue signals and back again

The downside of fibre is its cost, and that the strong jacket, which protects the glass core, is stiff and hard to bend around corners.

By using different frequencies of light, many signals can be pushed along a single fibre optic cable at once, allowing to carry massive amounts of data.

Its Ethernet code name is 10Base-F.

Example of a fibre optic connector

Fibre optic cable is a very high-bandwidth, very high speed, very long length form of cable. It has allowed LANs to greatly expand beyond the length limits of traditional UTP and coaxial cables without the need for signal boosting by repeaters. Many fibre optic threads can be bound into a slim, single cable without their signals interfering with each other, giving massive data throughput. 'FO' cables as thick as your thumb are being increasingly used to cross oceans and continents in the place of heavy and expensive copper cables as fat as an elephant's trunk.

The Benefits of Fiber Optic Technology

Adapted from http://www.novastars.com/optics/optic-benefit.htm

Long Distance Signal Transmission
Large Bandwidth, Light Weight, and Small Diameter
Long Lengths
Easy Installation and Upgrades
Non-Conductivity
Security
Designed for Future Applications Needs

Optical fiber systems have many advantages over metallic-based communication systems. These advantages include:

Long Distance Signal Transmission

The low attenuation and superior signal integrity found in optical systems allow much longer intervals of signal transmission than metallic-based systems. While single-line, voice-grade copper systems longer than a couple of kilometers (1.2 miles) require in-line signal repeaters for satisfactory performance, it is not unusual for optical systems to go over 100 kilometers (km), or about 62 miles, with no active or passive processing.  Emerging technologies promise even greater distances in the future.

The optical fiber cable in the foreground has the equivalent information-carrying capacity of the copper cable in the background.

Large Bandwidth , Light Weight, and Small Diameter

While today's applications require an ever-increasing amount of bandwidth, it is important to consider the space constraints of many end-users. It is commonplace to install new cabling within existing duct systems. The relatively small diameter and light weight of optical cables makes such installations easy and practical, and saves valuable conduit space in these environments.

Long Lengths

Long, continuous lengths also provide advantages for installers and end-users. Small diameters make it practical to manufacture and install much longer lengths than for metallic cables: twelve-kilometer (12 km) continuous optical cable lengths are common.

Multimode cable lengths can be 4 km or more, although most standards require a maximum length of 2 km or less.  Multimode cable lengths are based on industry demand. (Single-mode and multimode fibers will be covered in detail later in this text.)

Easy Installation and Upgrades

Long lengths make optical cable installation much easier and less expensive. Optical fiber cables can be installed with the same equipment that is used to install copper and coaxial cables, with some modifications due to the small size and limited pull tension and bend radius of optical cables.

Optical cables can typically be installed in duct systems in spans of 6000 meters or more depending on the duct's condition, layout of the duct system, and installation technique. The longer cables can be coiled at an intermediate point and pulled farther into the duct system as necessary.

System designers typically plan optical systems that will meet growth needs for a 15- to 20-year span. Although sometimes difficult to predict, growth can be accommodated by installing spare fibers for future requirements. Installation of spare fibers today is more economical than installing additional cables later. The dielectric nature of optical fiber can eliminate the dangers found in areas of high lightning-strike incidence.

Non-Conductivity

Another advantage of optical fibers is their dielectric nature. Since optical fiber has no metallic components, it can be installed in areas with electromagnetic interference (EMI), including radio frequency interference (RFI).  Areas with high EMI include utility lines, power-carrying lines, and railroad tracks. Another advantage of optical fibers is their All-dielectric cables are also ideal for areas of high lightning-strike incidence.

Security

Unlike metallic-based systems, the dielectric nature of optical fiber makes it impossible to remotely detect the signal being transmitted within the cable. The only way to do so is by actually accessing the optical fiber itself.  Accessing the fiber requires intervention that is easily detectable by security surveillance. These circumstances make fiber extremely attractive to governmental bodies, banks, and others with major security concerns.

Designed for Future Applications Needs

Fiber optics is affordable today, as electronics prices fall and optical cable pricing remains low. In many cases, fiber solutions are less costly than copper.

As bandwidth demands increase rapidly with technological advances, fiber will continue to play a vital role in the long-term success of telecommunications.

So, if even fibre optic has a length limit, how can it cross oceans?

Traditional tTransoceanic and regional cables have large numbers of optical amplifiers which contain active optical amplifiers requiring power. These systems also require high investments not only in physical plant, but also in fleets of ships to provide restoration and maintenance in case of cable cuts and failures.

Another submarine market exists for unrepeatered submarine fiber optic systems which have no active components under water. Only a passive cable is laid underwater with the active components on dry land or on off-shore platforms such as oil rigs. The unrepeatered cable does not require power.

As the technology improves and drives down the cost of optoelectronics, the market for unrepeatered links expands dramatically. Unrepeatered links require less investment in electronics, installation and maintenance. Typical applications include along a shore (festoons), or drilling rigs, shore-to-islands, island-to-island, along canals and other waterways, and across rivers and harbors.

From www.telecombriefings.com/pastbrief/brief13.html

• -T = UTP cable
• -2 = thin coaxial
• -5 = thick coaxial
• -F = fibre optic
• -35 = broadband coaxial