Chapter 11: Local Area Network Solutions
In this section, learn why high bandwidth does not mean high frequency in an SAP infrastructure. Discover why copper cables are easier to install and more cost-effective than optical fibers, and how deformation or mechanical stress during installation can cause cable failures. Also, find out why sporadic disturbances and breakdowns take place in data networks without a clear reason.
Adaptive hardware infrastructures for SAP, Ch. 11
Table of contents:
How to attain high availability for SAP and local networks
Configuring wires and fibers in adaptive SAP hardware infrastructures
WLAN standards and integrating WLAN into SAP hardware infrastructures
Chapter 11: Local Area Network Solutions
11.2 Wires and Fibers
Today, basically two cable types are used for local networks: lines with twisted pairs of copper wires and fiber optics cables. Both have types have advantages and disadvantages, because of their physical characteristics.
11.2.1 Copper Cables
The area of end device connections is generally based on twisted pair copper wires. This type of cable has existed since the first telephone signals were transferred. Throughout the years, on the one hand, the transfer frequencies have become much higher; on the other hand, there are essentially more sources of disturbance. Fortunately, twisted pair cables were also developed to the same extent. Therefore, we can say with assurance that twisted copper cables actually do meet the requirements of high-speed data transfers. Compared with optical fibers, copper cables are much easier to install and, consequently, are more cost-effective.
Twisted pair cable consists of two copper wires. Each wire is encased in its own color-coded insulation, twisted around one another. Multiple pairs are packaged in an outer sheath, or jacket, to form a twisted-pair cable. The twist of the cable is essential for electrical noise immunity and must go as near as possible to the connectors of the wall receptacles and patch-panels. By varying the length of the twists in nearby pairs, the crosstalk between pairs in the same cable sheath can be minimized. The typical nominal impedance is 100 ohms.
The decisive quality attribute for top quality data cables is the symmetry of the cable. Different twist lengths of pairs that are placed next to each other avoid crosstalk. In this context, it is important that the cables are not only symmetrically stranded but also precisely finished.
|There only appears to be a connection between the transfer frequency and the achievable bandwidth. By using highly developed signal encoding processes, all high-speed technologies such as Fast Ethernet and Giga Ethernet, as well as ATM, don't exceed 310 MHz as the transfer frequency. Technologies with higher bandwidth are based on fibre optic cables.|
|Another factor to consider when choosing a cabling system relates to electromagnetic compatibility (EMC). In the U.S. and Germany, EMC regulations have existed for years. However, the implementation of the European EMC Directive 89/336/EEC in 1989 has refocused attention on EMC. With the increased amount of electronic equipment in the average workspace, EMC becomes increasingly more important. Excess radiation from one piece of equipment can adversely affect performance of another piece of equipment. EMC refers to the ability of an electronic system to function properly in an environment where several pieces of equipment radiate electromagnetic emissions. This means that every electronic system, which includes all copper based cabling systems, must meet this directive.|
|In a company, a complete administration building was suddenly without network based IT services. The reason behind this was a fiber optics cable that had been gnawed through in a cable conduit. Rodents like to build their houses in cable conduits, and their offspring like to test their teeth on the cables. Since fiber optics cables can only be spliced by using special tools, this led to a downtime lasting several days. Even rodent-safe cables and mousetraps are therefore investments that increase availability of enterprise service architectures and IT services in general.|
| The insulation of data cables generally consists of flammable synthetic materials, mainly polyethylene and PVC. To reduce the threat to people and material, Building Codes generally require cables that does not generate toxic fumes when burning, such as FEP (fluoro-ethylene polymer) in air ducts, air plenums, and other environmental air spaces.|
In the event of a fire, these cables also don't generate corrosive gases and the smoke gas density is considerably lower. Therefore, PVC cables are banned in building installations in an increasing number of countries.
It is for good reason that building insurers in recent years placed major emphasis on the issue of fire protection. According to the insurers, all cable conduits in ceilings that run at a right angle to an emergency route must have a full fire protection. This also applies to all later changes. You should therefore always ensure that the cable installations are in accordance with the regulations of the property insurers.