|
Claude E. Shannon, author of "The Mathematical Theory of Communication" defined Shannon capacity, also known as Shannon's Law, which demonstrates the limits of the capacity of a link in relation to the signal to noise ratio of the link (expressed in bits per second). In other words, a finite amount of information can travel any link, which decreases as the amount of noise in the channel increases. Any and all electronics have and produce noise. External interferences can also produce noise. Category 5e came to market and offered better performance, more margin and headroom due greatly to its signal to noise ratio.
In early networks, most connections were shielded. As the telecommunications carriers entered the cabling and network markets, networks were adapted with baluns (Balance to Unbalanced adapters) to allow the balance signal to run over unshielded systems. Electronics were then developed that would utilize unshielded cabling systems eliminating the need for baluns. Shielding is gaining popularity on high bandwidth and noisy environments such as radiology centers and manufacturing facilities. The ability to block out the noise coming from equipment creates a heartier environment for data transmission.
Shielded systems have changed significantly from the earlier iterations. The cable is much smaller, easier to handle, and connectors provide the ability to self terminate the shield. Outside of the US, particularly in France and Germany, most systems are shielded.
Class E (or category 6) systems can be either UTP or ScTP (screened twisted pair which is shielded). Category 7/Class F is a shielded system that includes not only the overall shields, but also each pair is wrapped in foil called a PiMF cable (Pairs in Metal Foil). There is also a new non-RJ45 interface (TERA) that was approved as part of the standard which has shielded quadrants within the interface so that the pairs can either all be used or split out for separate applications within the same footprint as an RJ45. There is also an RJ45 type connector called the GG45.
|
