The merger of the ISO and IEC information technology standardisation activities proved an important milestone back in 1987. Development of generic cabling standards for residential, office and industrial premises was the focus of the work from the beginning. In this context ?generic? refers to a cabling system defined by its physical transmission parameters such as signal attenuation, crosstalk, return loss. It also implies that any transmission protocol is supported within the limits of the frequency range.

The work accomplished in the last five years has dealt with both vertical developments, particularly higher transmission frequencies, and horizontal developments related to industrial building and the ?intelligent home?.

The current standards for generic cabling and industrial buildings was developed from earlier and parallel work in Europe by CENELEC, and in the US by TIA. The document which emerged ? ISO/IEC 24702 ? supports both philosophies for using shielded cable (STP), popular and most used in Europe; and unshielded cable (UTP) for the US market. We as a company participated actively in the development of these standards because generic cabling ends per definition in a TO (Telecommunication Outlet). In other words, the connector to which an industrial automation device, computer or telephone is connected.

Technical enhancements in ISO/IEC 24702

The transmission requirements and general structure of industrial cabling are based on ISO/IEC 11801, but the following enhancements are noteworthy:

• The maximum distance over which communications services can be distributed is 10km instead of 2km in ISO/IEC 11801;
• Modified hierarchical cabling structures;
• Implementation options;
• Environmental classes for industrial buildings were defined and specified in the MICE table.

The three MICE

• M1 I1 C1 E1 classifies the typical office environment, as is assumed in ISO/IEC 11801.
• M2 I2 C2 E2 classifies the industrial environment of an ordinary factory floor.
• M3 I3 C3 E3 classifies harsh environmental conditions, such as in heavy industries.

MICE stands for: Mechanical, Ingress, Climatic, Chemical and Electromagnetic. To get the idea behind the MICE philosophy, it might be helpful to understand what MICE is not!

The classification does not claim to take all possible industrial environments into consideration. As a result, the planning engineer is still obliged to define the appropriate specifications for the project. The values in the MICE tables given in ISO/IEC 24702 are not qualification testing requirements for cables or connectors. They are also not system requirements for the installed cabling.

For example, a transmission link can begin in an air-conditioned area and end at a machine with strong vibrations and electromagnetic interference fields. However the MICE tables give network architects guide values to assist technical design, while keeping in mind that actual conditions encountered may not be strictly class 1, 2 or 3, areas. For instance, high mechanical loading in combination with low climatic and electromagnetic loads are very common, for example M3 I1 C1 E 1. The planning engineer is encouraged to use local mitigation or isolation techniques to protect exposed areas of the cabling by either protecting/covering the critical areas of cable and/or connector or;

Isolating the source of the environmental impact be it heat, vibration, electromagnetic load, or use a less critical installation path. In other words use common sense!

Higher requirements for components such as connectors and cables should be considered in conjunction with all the above to achieve the best installation practice. In other words, more common sense! International standardisation depends on consensus between all stakeholders, but due to diverging interests this is sometimes hard to achieve. In the development of ISO/IEC24702 there were various opinions regarding the MICE requirements and the selection of the generic TO connector. The decision between four connector candidates was finally achieved by an international consultation process at the level of the participating national committees. The result of this selection was that the final draft was approved unanimously.

Higher frequency and PoE

Generic cabling should support the highest technical requirements. IEEE 802.3an (10GBaseT) released in June 2006 is actually the most prominent and challenging topic of ISO/IEC working group. It states that the cabling must be specified for up to 500MHz. For existing buildings with lower performance cabling, recommendations are under preparation to provide information about the conditions under which 10GBaseT can still be reliably supported. The work will be published as a Technical Report, ISO/IEC TR 24750.

For new installations, an annex to ISO/IEC 11801 is under preparation, specifying new classes EA for 500MHz, and FA for 1000 MHz. This annex will also probably assume that a transmission channel with cables and connectors according to category 6A will meet the transmission requirements of class EA.

The connector requirements for the 250 to 500MHz frequency range are still under discussion. Critical transmission characteristics for connectors include return loss, crosstalk and alien crosstalk, which is the electromagnetic interference caused by external sources. It is currently up for discussion whether the limiting values for crosstalk should be extrapolated between 250 and 500MHz, or whether the requirements for the connectors must be reduced in this range. The following values are being discussed for 500MHz:

Power over Ethernet
Until now, a maximum power of 15.4W was specified by IEEE 802.3af at 48V, but IEEE 802.3at (PoE plus) specifies power up to 30W with even higher power levels being discussed.

Temperature increase of installed cable bundles is a particular risk. So far, ISO/IEC 11801 specifies an upper temperature of 60�C for the cable, including current heating. The experts of ISO/IEC JTC1 SC25/WG3 worry about transgression of the upper temperature limit in existing installations resulting in possible damage, breakdown or even fire. Thus relaxing the requirements for old installations is unacceptable. To support the IEEE work a PoE cabling guide is under preparation in SC25/WG3 to provide information about the conditions under which PoE plus can be supported by existing cabling.

Increasing the PoE current to 420mA could also cause damage to connectors if connections are routinely disconnected under load. Therefore the working group recommends that the IEEE PoEplus Task Force clearly points out in its document that disconnection under load is not permitted. IEC SC 48B connector experts are working on a technical report to provide recommendations for disconnection under load.

Summary

The development of generic cable systems for the IT infrastructure in modern buildings is still progressing. Up until now, the copper cabling industry has always managed to push the limits further upwards, i.e. to higher frequencies. As a result, the optical cabling segment has remained relatively small. The clear trend to wireless will take over parts of today?s IT infrastructure in the foreseeable future, but will not replace it. For industrial applications, the published ISO/IEC 24702 standard will be approved and published as EN50173 1 and EN50173 3 for Europe and ANSI/TIA/ EIA 1005 in the US.

Gerd Weking is general manager Intellectual Property and international standardisation, Harting Technology Group