Connections +
Feature

40 Gb/S And 100 Gb/S Ethernet

The IEEE 802.3ba Ethernet Task Force is currently working on an amendment that defines MAC, physical layers and management parameters.


January 1, 2009  


Print this page

For this month’s article you will find an update on the next generation standard for 40 Gigabit and 100 Gigabit Ethernet. What I have done is identify what technologies are being considered and what media types are needed to support 40 Gb/s and 100 Gb/s networking speeds.

The IEEE 802.3ba Ethernet Task Force is currently working on an amendment to the IEEE 802.3-2008 standard. This particular standards update defines the parameters for 40 Gb/s and 100 Gb/ s operation, including media access control (MAC) parameters, physical layers and management parameters. The first draft of this amendment was issued this past October.

What are the different IEEE 802.3 physical layer implementations for 40 Gb/s and 100 Gb/s Ethernet? A brief description of these different implementations is listed below: Copper :

40GBASE-CR4: 40 Gb/s over four lanes of twin-ax cabling 100GBASE-CR10: 100 Gb/s over 10 lanes of twin-ax cabling

Multimode fiber:

40GBASE-SR4: 40 Gb/s over four lanes of, short reach, multi mode fiber

100GBASE-SR10: 100 Gb/s over 10 lanes of, short reach, multi mode fiber

Single mode fiber:

40GBASE-LR4: 40 Gb/s over four WDM lanes, long reach, single mode fiber

100GBASE-LR4: 100 Gb/s over four WDM lanes, long reach,

single mode fiber

100GBASE-ER4: 100 Gb/s over four WDM lanes, extended

long reach, single mode fiber

The copper based 40GBASE-CR4 implementation uses a special connectorized cable assembly with eight twinaxial pairs, 4 x 10 Gb/s in each direction, for an aggregate data rate of 40 Gb/s.

The 100GBASE-CR10 implementation uses a cable assembly with 20 twin axial pairs, 10 x 10 Gb/s in each direction, for an aggregate data rate of 100 Gb/s.

The transmission parameters for these cable assemblies are specified up to 6 GHz and are intended for equipment-to-equipment connections for distances up to 10 metres (33 ft). There are no physical layer specifications under development in IEEE 802.3 for 40 Gb/s and 100Gb/s transmission over 4-pair Category cabling, at least not at this time. Such a need may develop over time; however, it is not envisaged before 2013 timeframe.

The 40GBASE-SR4 and 100GBASE-SR10 implementations use four or 10 pairs of multimode fibers respectively, for a distance of at least 100 metres.

The data transmission rate for each multimode fiber is 10 Gb/s, for an aggregate data rate of 40 Gb/s and 100 Gb/s respectively. The connector interface is most likely the MPO connector, although this is not specifically defined in the current draft standard.

The reference is to the performance specifications of IEC 61753-1-1 and IEC 61753-022-2.

Another question to consider is why is the distance limit only 100 meters and not 300 metres?

OM3 fiber is capable of supporting a distance of up 300 metres at 10 Gb/s. After looking into this, it is my understanding that the parallel optics transceivers for SR4 and SR10 are a different specification than 10GBASE-SR.

The 100 metres distance is a minimum objective. It may be possible to do 200 metres or some longer distance yet to be determined.

Table 1 below shows the primary attributes of 40GBASE-SR4 and 100GBASE-SR10

The 40GBASE-LR4, 100GBASE-LR4 and 100GBASE-ER4 implementations use two single mode optical fibers and wavelength division multiplexing (WDM) to achieve an aggregate data rate of 40 Gb/s and 100 Gb/s.

The specified wavelengths and the data rate for each wavelength are shown in Table 2 below.

This is a brief overview of the cabling requirements in support of 40 Gb/s and 100 Gb/s Ethernet over specialized copper cable assemblies and optical fiber. This work is under development in the IEEE 802.3ab task force.

The plan is to complete this work by mid-2010.

Paul Kish is Director, Systems and Standards at Belden. The information presented is the author’s view and is not official TIA correspondence