The future is coming, and it's bringing the 10GBASE-T standard with it

Luc W. Adriaenssens

There seems to be a never-ending need for increased speed and bandwidth, and, as companies try to keep up, many are realizing that their existing infrastructures are not adequate to support growth in the months and years to come. As it grows in popularity, Ethernet, in particular, continues its relentless pace toward tenfold data rate increases. Just as Gigabit Ethernet deployments on UTP start to pick up increased momentum and 1000BASE-T interfaces become commonplace in switches, servers and even laptop PCs, a 10 Gigabit Ethernet standard for twisted pair cabling (named 10GBASE-T) is in development already.

Just as in previous Ethernet data rate leaps, there is uncertainty regarding the media requirements and cabling categories that will be involved in 10GBASE-T standards. These elements have become the subject of industry debate, and, if the industry isn't careful to explain standards, the market could become confused. As has been the case in the past, a task force is helping to establish parameters. The IEEE 802.3an 10GBASE-T Task Force devoted to this project is

focused on making the widest possible use of UTP cabling, both with current and enhanced technology. The end result should be a standard that makes possible cost-effective, high-performance Ethernet solutions.

Channel Requirements for a UTP Solution Designed to Enable 10GBASE-T Performance

With the formation of the IEEE Task Force, a 10 Gigabit Ethernet standard

will be possible over twisted pair copper cabling. This new standard will bring

a whole new world of speed, throughput and opportunity to all areas of the

network.

To achieve "Broad Market Potential" (a key aim of the IEEE Task

Force), the main challenge for the IEEE Task Force is to set the requirements

for the complete solution, both electronics and cabling, that ensure 10 Gb/s

capability. While it is anticipated that Category 6 cabling will support

10GBASE-T (albeit to a limited 55 meter distance), the IEEE Task Force has set a

challenge to cabling vendors to develop solutions capable of supporting

10GBASE-T over 100 meters, with support for 4-connector channels and guaranteed

performance out to 625 MHz. If vendors are able to meet these challenges, the

costs and efficiencies involved in the use of 10GBASE-T could be even more

beneficial than initially believed.

The key targets for this new cabling channel specification are listed below:

• IEEE Model No. 1 for Insertion Loss and ANEXT for 100-meter 4-connector
  
  channel performance
• Extrapolation of all Category 6/Class E channel performance requirements
  
  to 625 MHz
• Complete 100-meter 4-connector channel solution tested with sophisticated
  
  system-level tools that allow the modeling of worst-case configurations for
  
  all parameters
• Evolutionary improvements in component design and performance
• Complete cabling system design and installation instructions
• Installation-friendly components (including minimal increase in diameter
  
  and traditional round shape)
• Channel performance verification by laboratory and field-testing
  
  instruments

 

Standards Update on 10GBASE-T: Formation of the IEEE Task Force

The March 2004 formation of the IEEE Task Force marked the culmination of a

one-year IEEE Study Group period to determine the objectives for 10GBASE-T.

While an original objective of the Study Group was to support 10 Gb/s

transmission over Category 5e cabling, it became clear early in the process that

a minimum of Category 6/Class E performance would be required. However, the

maximum distance over which 10 Gb/s transmission can be supported over Category

6/Class E cabling is still uncertain (with a minimum objective of 55 meters). It

also is clear to the IEEE Task Force that there is a strong global preference

for UTP cabling systems that avoid the shielding and grounding complexities of

screened alternatives. At the formation of the IEEE Task Force, the target

performance objectives for 100-meter 4-connector channels were based on Category

6/Class E channel performance parameters extrapolated to 625 MHz, with the

addition of alien crosstalk (the noise from adjacent channels) specifications.

Over the last few months, there has been much progress toward

"locking-in" cabling requirements (in ISO/IEC and EIA/TIA) so that the

work on transceiver designs can be based on viable cabling performance models.

Transmitting 2.5 Gb/s on each of the four pairs is no easy task. It requires

multi-level coding that transmits multiple bits per Hertz of bandwidth. Even

with the planned sophisticated coding schemes, the minimum bandwidth exceeds 250

MHz and likely will approach 625 MHz. Sophisticated Digital Signal Processing (DSP)

techniques also will be required to reduce the effects of within-cable

impairments such as return loss and crosstalk (NEXT and FEXT). The effects of

alien crosstalk cannot be reduced effectively by the electronics and must be

reduced to tolerable levels within the cabling.

The IEEE Task Force has been exploring these issues and interfacing with the

ISO and TIA cabling standards to converge on its cabling channel requirements.

The IEEE Task Force has progressed steadily on improving the specificity of the

cabling channel requirements. At the January meeting, the IEEE committee

unanimously approved minimum channel requirements based on Category 6

extrapolated to 625 MHz. At the March IEEE meeting, the channel requirements

were reaffirmed and appended with a set of alien NEXT requirements.

The powersum Alien NEXT requirements depend on the insertion loss of the

channel as shown in the set of models below:

 

Agreement on some initial models is a significant milestone in the

development of 10GBASE-T. There is general industry agreement regarding the

application of Model No. 1 to the development of new UTP cabling for 10GBASE-T

(sometimes called "augmented" Category 6/Class E).

Model Nos. 2, 3 and 4 are based on existing Category 6/Class E channel

performance requirements extrapolated to 625 MHz, with ANEXT requirements based

on the insertion loss at specific or calculated lengths. Model Nos. 2 and 4 are

designed to accommodate as much of the embedded base as practical. The current

belief is that embedded Category 6/Class E cabling will support 10GBASE-T

transmission for at least 55 meters. Longer distances should be achievable on

existing cabling exhibiting higher performance. Simple techniques such as cord

upgrades also should extend distances. Model No. 3 is an alternative to Model

No. 1 but may not be achievable on Category 6/Class E UTP, even with additional

mitigation.

IEEE liaison letters have been sent to both TIA and ISO cabling committees

with the request to further develop and standardize these requirements. Both

committees have indicated that they are eager to complete this work and plan to

provide more detailed specifications, measurement procedures, field-testing

guidelines, etc.

Implications for Customers

Much progress has been made toward defining the cabling channel requirements

to support 10GBASE-T over new as well as existing cabling. Although clarity has

improved with the agreed-upon models above, many remaining questions must be

answered before "guarantees" can be made with confidence and

credibility. Some companies have developed solution prototypes. However, testing

has detected unexpected phenomena in the channel due to complex interactions

among components. This insight highlights the challenge of achieving robust 10

Gb/s performance using conventional design techniques. In addition, solving

component challenges in isolation does not translate to a guarantee of

end-to-end channel performance. Refinements and system tuning optimizations will

continue, and companies will eventually deliver a UTP solution that meets all

10GBASE-T requirements. When selecting such a solution, end users should assess

claims of 10 Gb/s support critically.

Ultimately, those able to take advantage of a 10GBASE-T solution will enjoy

installation and operations savings over comparable fiber solutions. In

addition, 10Gbps switches cost less than SONET equipment. Expected early

adopters of 10GBASE-T solutions include data centers, educational institutions,

storage area network (SAN) providers and financial institutions.

 

Questions to Ask Vendors Claiming to Meet 10GBASE-T Requirements:

It is clear that users need to assess 10 Gb/s claims critically. The ability

to guarantee the end-to-end channel performance required for 10GBASE-T is

achieved by state-of-the-art R&D as well as rigorous testing and modeling to

identify all possible noise sources and interactions. Many groundbreaking

developments are required to provide a solid assurance of end-to-end performance

over worst-case channels. Many questions, including the following, should be

asked of any potential supplier of 10 Gb/s solutions:

Alternatively:

 

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