In the first two parts of this series we looked at the development of twisted pair structured cabling systems over the last 20 or so years and the local area network (LAN) protocols they were primarily designed to support.

In part three, we shall take a stab at what the future may hold in terms of where twisted pair copper cabling and fibre are going and what the ultimate limitations might be.

Back to basics

Structured cabling systems were devised about 20 years ago in the United States as a standards-based replacement to the plethora of vendor-specific building cabling systems.

Since that time, computer system architecture has evolved from mainframe-based systems, typically using coaxial cable reticulation, to LANs running Ethernet over twisted pair. In addition, Ethernet LAN technology, initially used in office environments only, has grown to the point where it is now found in every home.

The current applicable cabling standards are EIA-568-C (US) and ISO 11801 (Europe and Australia). Transmission performance is guaranteed for various categories (EIA) or classes (ISO) of links and channels up to 100m in length. The performance criteria stipulated in these standards has been specifically engineered to guarantee support for particular types of Ethernet LAN protocols.

In addition, the IEEE 802.3 series of standards defines the media access control (MAC) layer and the physical layer of Ethernet. It too has evolved over the years thanks to ever-increasing LAN speeds, from the early days of 10Mbps systems to today’s 100Gbps fibre-based links.

Present day cabling

Today, most of the existing structured cabling infrastructure found in the office or home is Category 5e-compliant. It is generally used to run either 100BaseT or Gigabit Ethernet LAN services, plus legacy 10BaseT and analogue and digital telephony services. Cat 5e and Class D cabling specifications have been designed to guarantee support for Ethernet over twisted pair up to Gigabit speed. However, new installations tend to be Cat 6, since pricing for these has radically dropped in recent times.

In terms of advantages, Cat 6 offers performance headroom over Cat 5e, but for 100m links and channels it still only supports the same LAN protocols as Cat 5e (up to and including Gigabit Ethernet).

Cat 6A and 10G

Cabling compliant with Cat 6A requirements must be used if support for 10G LANs with horizontal run lengths of up to 100m is to be guaranteed. This is equivalent to the ISO Class EA, with transmission performance parameters specified to 500MHz.

The latest ratified Cat 6A standards are the EIA-568-C series and Amendment 1 to ISO/IEC 11801, Second Edition, 2008.

Existing Cat 6 installations can be re-worked to support 10 Gigabit Ethernet over shorter distances (limited to about 50m). This is done by requalifying the installation according to the procedures outlined in the TIA document TSB-155. The procedures involve retesting the installation to Cat 6A specifications and, subject to the test results, some rework may be necessary. This may involve implementing alien crosstalk mitigation techniques and/or replacing some key components (e.g. jacks) with higher performing counterparts, thereby raising the link/channel performance.

Although Cat 6A cabling hardware and terminal electronics have been available for some years now the cost is still prohibitive, to the point where it has held back commercial deployment on a large scale.

Terminating electronics also presents issues. Even the modern PC fitted with the now popular GBE card has difficulty keeping up with the rate at which data is delivered, particularly during large file transfers. Consequently, the computer architecture required to support a bit stream 10 times faster than this is not trivial (or cheap!).

Another issue holding back Cat 6A proliferation is the generally perceived absence of the need for speed. After all, most offices still run 100Mbps Ethernet.

We are presently being promised up to 100Mbps through the National Broadband Network (NBN), with most users probably ending up with something much less than this. And this will certainly provide us with high definition TV and a host of other goodies.

So where then are we going to use the 10G links that Cat 6A was designed to support? What office or home applications require such prodigious speeds? Apart from server to server links in a large computer room, I certainly can’t think of any.

Other applications

The EIA standard is targeted specifically at Ethernet applications running over twisted pair, with the RJ45 as the connector of choice. It focuses heavily on unshielded solutions, although shielded twisted pair cabling is accommodated in the specifications.

ISO, on the other hand, have tended to focus more on shielded cabling, and have opted to not limit the cabling performance specifications to that required by Ethernet applications.

Thus ISO have defined two additional classes of cabling beyond Class EA (Cat 6A equivalent).

The ISO Class F cabling specification (released back in 2002) is specified to 600MHz and defines its own performance parameters for the constituent components as “Category 7”. Note that EIA has no such definition. Class F cabling uses individually shielded twisted pairs, and thus achieves exceptional crosstalk performance in the cable. In addition, an allowance has been made for using connecting hardware other than the standard RJ45, thus achieving superior crosstalk performance in the connecting hardware as well.

In terms of applications, Class F cabling will support 10G, but at a significant cost penalty when compared to a UTP Cat 6A solution. Properly terminating all those individual shields involves a lot of work.

ISO have also defined a Class FA cabling system, with a corresponding component classification known as “Category 7A”. The system is specified for transmission performance to 1,000MHz (1GHz). Again, this is a fully shielded system with individually shielded pairs, utilising a non-RJ45 connector.

As with Class F, the system was not designed to support any particular new application. Class FA is certainly capable of supporting 10G, but again at a significant cost penalty when compared to UTP. It will also support Broadband CATV to 1GHZ, but this is hardly a killer application, since dedicated coax based reticulation schemes will outperform it at a fraction of the cost.

Beyond 10G Ethernet

The standards have been developed for Ethernet running at both 40GBPS (40G) and 100GBPS (100G) speeds. Copper and fibre-based solutions have been devised for both, but the copper implementations are limited to very short proposed distances (less than 10m).

Both multimode and single mode fibre based implementations are supported by the standards for both 40G and 100G, with a range of at least 100m for multimode and 10km/40km for single mode fibre, depending on the implementation.

This year, a number of companies have announced commercially available 100G systems single mode fibre systems. These are all still very new and as far as I know, none are in commercial service yet (as at October, 2011). All utilise wavelength division multiplexing (WDM) to achieve these prodigious rates of throughput.

Beyond 100G

The IEEE has started a new group to study what should come after 100G Ethernet, once it becomes commonplace. The group, known as the IEEE 802.3 Industry Connections Ethernet Bandwidth Assessment Ad Hoc Group, was formed at the beginning of this year. The aim of the group is simply to gather information about the subject matter for collation and future use b a standards setting body.

They are gathering information on the way the world Ethernet networks are developing, the so-called Ethernet eco-system. This will enable an evaluation of the future bandwidth needs for Ethernet wireline applications. Of particular interest is the rate of high speed Ethernet penetration into corporate networks and the projected traffic growth rates for 1G and 10G networks.

Once gathered, it is proposed to use this information for generating white papers which will then form a reference for use by future standards generating bodies.

The two possible suggested future target speeds for high speed Ethernet are 400 Gigabit (400G) and 1T (1 Terabit) Ethernet.

The key applications for links running at such mind-boggling speeds are to be found in the huge data centres run by organizations such as Google and Facebook, places like the New York Stock Exchange (NYSE), and internet exchanges – the places where the world internet traffic is switched.

To enlarge on this a little, the NYSE has some 200,000 Ethernet ports running at 1G or below, 10,000 ports running at 10G, fed by 10,000 servers with 10 petabytes (that is 10,000 terabytes) of storage(!).

Clearly, technology is racing ahead and with it the ever-increasing need for speed on the links that support the large corporate data centres.

However, the speed requirements for the typical office horizontal cabling system is another matter entirely. The need for high-speed links is simply not there.

Wireless vs Copper

Wireless technology has been touted by some to become the replacement for fixed cabling. Well, in my view the history of data communications does not support this assertion.

Over the last 20 years, structured cabling systems have moved from supporting 10MBPS to 10G, a factor of 1000 increase in speed. Over a similar period, wireless has come from 11MBPS to 54MBPS, and just recently to 300MBPS, a factor of ~30 increase in speed.

In addition, physics plays a role here. By its very nature, RF spectrum is limited. This alone will limit the maximum possible throughput of wireless technology. Furthermore, other wireless technologies such as DECT cordless telephony are beginning to compete for the same RF spectrum space. And finally, adjacent wireless LAN’s can and do interfere with each other, limiting the density of such networks. Fixed cabling has no such restrictions.

In my view, all these issues mean that wireless will never be able to supply the bandwidth currently available on twisted pair copper. Good old copper cabling will be with us for a long time yet, and 10G should serve us well for most commercial and domestic applications the foreseeable future.