Jumpers are twisted pairs of cable, each one corresponding to an individual telephone line. MDFs are single-sided so that the workers can install, remove or change jumpers. However, old manual jumpering systems are now mostly automated using automated main distribution frames.
Computer systems that control MDF operations assign terminals close to one another so that jumpers need not be long and shelves are not congested with wires as the jumpers are shorter. MDFs in private branch exchanges perform functions that are similar to those performed by those in central offices but on a smaller scale. By: Justin Stoltzfus Contributor, Reviewer. By: Satish Balakrishnan. Dictionary Dictionary Term of the Day. Gorilla Glass. Techopedia Terms. Connect with us. Thin coaxial cable has been popular in school networks, especially linear bus networks.
Thick coaxial cable is also referred to as thicknet. The 5 refers to the maximum segment length being meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network.
One disadvantage of thick coaxial is that it does not bend easily and is difficult to install. Different types of adapters are available for BNC connectors, including a T-connector, barrel connector, and terminator. Connectors on the cable are the weakest points in any network. To help avoid problems with your network, always use the BNC connectors that crimp, rather screw, onto the cable. Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials See fig.
It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting. Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair.
It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify.
The center core of fiber cables is made from glass or plastic fibers see fig 5. A plastic coating then cushions the fiber center, and kevlar fibers help to strengthen the cables and prevent breakage.
The outer insulating jacket made of teflon or PVC. There are two common types of fiber cables -- single mode and multimode. Multimode cable has a larger diameter; however, both cables provide high bandwidth at high speeds. Single mode can provide more distance, but it is more expensive.
More and more networks are operating without cables, in the wireless mode. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations, servers, or hubs. Information is relayed between transceivers as if they were physically connected.
For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite. Wireless networks are great for allowing laptop computers, portable devices, or remote computers to connect to the LAN. Wireless networks are also beneficial in older buildings where it may be difficult or impossible to install cables. The two most common types of infrared communications used in schools are line-of-sight and scattered broadcast.
Advances were also made in design of insulators and wire transpositions. Interest grew in the development of telephone cables. Many telephone wires were contained in one telephone cable. Better insulation, both electromagnestic and water resistance, were required.
Early telephone cables relied upon the technology used in the manufacture of telegraph cables. Gutta percha and various rubber compounds were used for insulating and water proofing the telegraph and early telephone cables. Telephone cables were employed for aerial, underwater and underground use around Early cables were single grounded wires followed by metallic circuits lines after their development.
By all of the newly manufactured cables were metallic circuit cables. There were numerous cable manufacturers. The cables made by the different manufacturers were very similar but not identical. The cables contained up to copper wires. They were insulated with cotton, cotton impregnated with paraffin, gutta percha or a rubber compound, and then in wrapped in lead.
There was a large demand for telephone cables. Telephone cables were needed to replace the large number of aerial wires present in the cities. In the 's the major telephone cable concerns were noise elimination, waterproofing and fitting more wires in each cable.
The technique of wrapping the conducting wires in lead was developed to eliminate electromagnetic noise in the lines. Other insulating techniques, such as covering the insulated wires with tin foil and using additional insulating layers, were employed. Techniques for impregnating the lead tubes after the conducting wires were drawn through with melted paraffin, resin, a mixture of paraffin and resin or high test illuminating oil were used to protect the insulation from moisture.
Then vitrified clay conduits were developed. The multiple duct vitrified clay conduit became the main type of underground construction used.
A separate square hole was provided for each cable, and when more ducts were required sections of conduit could be added. The general complaints of the poor voice transmission over the telephone cables, unrecognizable voices, and muffled and hollow sounds were still present. There were two major improvements made to telephone cable in the late 's. The first was the issuance of a specification for a standard type of telephone cable in
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