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What you need to know about 10Gb Ethernet

Discussions about 10Gbit/s Ethernet have been taking place for some time. Indeed, standards for 10Gbit/s Ethernet over fibre optic cabling has existed for several years and has had some success, but has limitations for the enterprise market (such as the predominant use of the Fibre Channel (FC) protocol instead of Ethernet, and the fact that it can only operate for certain distances). 10Gbit/s Ethernet has some distinct advantages for office and other general business applications. For instance, it is expected that the active equipment for the copper links will be about half the price of that for fibre links when the standard is first launched.

Although the main application for 10GBASE-T is storage and server applications, it is potentially appropriate for backbone network applications too. By the way, it should not be confused with another standard– 10G BASE-CX4 – which aims to be a lowercost alternative to optical fibre for rack-to-rack links, switch clustering and certain data centre applications, across distances of no more than 15 metres.

How long before we can expect to see the standard finalised?

The cabling for 10G BASE-T is likely to be standardised by the middle of 2006 and the standards are already fairly stable from a technical point of view. But it is important to remember that it is risky investing in 10G BASE-T products until the ink is dry on the standards, because there is always the chance that matters will change. In addition, the ISO 11801 standard will not be specifying components for 10GBASE-T until 2007. Warranties from manufacturers who promise product compliance based on a draft standard may yet prove to be invalid in the future.

So who is doing what? The Institute of Electrical and Electronics Engineers (IEEE) 802.3 committee is the governing body behind defining the application requirements of 10GBASE-T. The standard is currently expected to be published around July 2006 and will be called IEEE 802.3an. Based on supporting four pair copper cabling, with links of at least 100 metres of 4 pair Class F balanced copper cabling and at least 55-100 metres on 4 pair Class E (Category 6) balanced copper cabling. The chosen connector is the RJ-45, thereby excluding all proprietary connector formats.

Two standards bodies, TIA/EIA and ISO/IEC, are currently working on cabling for 10GBASE-T. Both are creating cabling standards that give the parameters required for 10GBASE-T transmission. For TIA/EIA, the standard is called TIA/EIA-586-B.2-10 and for ISO/IEC, a draft amendment to ISO11801 (called ISO/IEC AM1.1 to ISO11801:2002) has been proposed. It is likely that these two standards will eventually contain different parameters, since they are based on slightly different cabling system ‘philosophies’. ISO/IEC has left category 6 and 7 in the standard but has created two new categories: category 6A and category 7A. Cat 6A is specified to 500MHz and Cat 7A to 1000MHz.

The two standards bodies are also creating ‘reports’ or ‘bulletins’ which guide the user on the assessment (and mitigation if required) of installed cabling. The TIA/EIA document is called TSB-155 and the ISO/IEC document is ISO/IEC 24750. The latter contains helpful advice on the re-qualification of Category 6 cabling to run 10GBASE-T, involving testing to new limits at a higher frequency and including extensive recommendations on alien crosstalk mitigation.

All of these standards are likely to be issued in 2006, although the final version of ISO11801, including the component specifications, is not due until 2007.

Standards aren’t the only issue

Standards are just part of the challenge and it is important to know that with10GB BASE-T, copper will be running closer to its physical limit than ever before. The impact is that this is likely to make a system more difficult to install and maintain. Bend radius – the degree to which the cable can be curved before performance is affected – will be highly challenged. The cable also is likely to be heavier and more expensive than standard copper cabling. Furthermore, until the standards are issued and components can be fully qualified, interoperability between manufacturers cannot be guaranteed.

Another major issue is Alien Cross Talk (AXT), namely signal coupling from one channel to another. In 10GBASE-T, the signal will be carried equally over all four copper pairs, with each pair supporting transmission in both directions. Since the loss of the cable rises steeply with frequency, the signal to noise ratio (SNR) must be kept as low as possible. Although the standards bodies are looking at how they can address alien cross-talk, there are still unknown factors about this complex topic and even after extensive modelling by the standards bodies, as yet there is no finalised method of measurement.

Cables are traditionally bundled closely together, meaning that the noise from one cable can couple into other cables. Although this is has been a problem in the past, it has been manageable, but due to the sensitivity of 10G BASE-T, it has become a bigger problem.

There are some mitigation techniques that can be employed. For example, installers can ‘mess up’ cables and space them out, rather than bundling them in neat parallel lines. Another is to separate the channels altogether, especially where long and short channels run together. Of course, this does create some potential issues: the installer and the user of the system will need to understand the system and maintain it in the‘as installed’ state. The cabling will take up far more space too.

However, by using fully shielded cables, jacks and patch-leads that are compliant with the new standard, these complicated mitigation techniques can be avoided altogether, providing full support for up to 100metre channels.

Of course, if anyone is looking at the 10G BASE-T, which is more expensive than existing Category 5e or Category 6 copper cabling, then it is worth thinking about making the move to fibre optic cabling. Although still currently more expensive than copper, it is light, small in size and immune to electrical magnetic interference (EMI) and RFI (radio frequency interference). Market dynamics could also lead to future price drops.

But the ultimate question has to be: does anyone really need 10G/bits today? Probably not right now, but given the dramatic increase of data bandwidth demands in recent years, it would be foolish to dismiss it altogether. And since users expect their structured cabling systems to last for a few years, it is worth at least considering 10GBASE-T, although not forgetting the alternatives. Above all, everyone needs to be armed with the facts about where 10G BASE-T is today in terms of standardisation,because until this is finalised, any investment in 10G BASE-T is a risk.

Written by Rosemary McGlashon, European Technical Manager, Telecom Enterprise Department, 3M United Kingdom plc. Rosemary has been involved in the cablingindustry for many years and has worked closely with international standards bodies.

3M provides structured cabling connectors for both fibre and copper cabling. For further information, please call + 44 (0) 1234 229 618. or visit www.3MTelecommunications.com.

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