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Thursday
Sep172015

Choosing paths to future Gigabit Ethernet speeds

Industry discussions are being planned in the coming months to determine how Ethernet standards can be accelerated to better serve industry needs, including how existing work can be used to speed up the creation of new Ethernet speeds.

 

The y-axis shows the number of lanes while the x-axis is the speed per lane. Each red dot shows the Ethernet rate at which the signalling (optical or electrical) was introduced. One challenge that John D'Ambrosia highlights is handling overlapping speeds. "What do we do about 100 Gig based on 4x25, 2x50 and 1x100 and ensure interoperability, and do that for every multiple where you have a crossover?" Source: Dell

One catalyst for these discussions has been the progress made in the emerging 400 Gigabit Ethernet (GbE) standard which is now at the first specification draft stage.

“If you look at what is happening at 400 Gig, the decisions that were made there do have potential repercussions for new speeds as well as new signalling rates and technologies,” says John D’Ambrosia, chairman of the Ethernet Alliance.

Before the IEEE P802.3bs 400 Gigabit Ethernet Task Force met in July, two electrical signalling schemes had already been chosen for the emerging standard: 16 channels of 25 gigabit non-return-to-zero (NRZ) and eight lanes of 50 gigabit using PAM-4 signalling. 

For the different reaches, three of the four optical interfaces had also been chosen, with the July meeting resolving the fourth -  2km - interface.  The final optical interfaces for the four different reaches are shown in the Table.

 

 

The adoption of 50 gigabit electrical and optical interfaces at the July meeting has led some industry players to call for a new 50 gigabit Ethernet family to be created, says D’Ambrosia. 

Certain players favour the 50 GbE standard to include a four-lane 200 GbE version, just as 100 GbE uses 4 x 25 Gig channels, while others want 50 GbE to be broader, with one, two, four and eight lane variants to deliver 50, 100, 200 and 400 GbE rates.  

 

If you look at what is happening at 400 Gig, the decisions that were made there do have potential repercussions for new speeds as well as new signalling rates and technologies

 

The 400 GbE standard’s adoption of 100 GbE channels that use PAM-4 signalling has also raised questions as to whether 100 GbE PAM-4 should be added to the existing 100 GbE standard or a new 100 GbE activity be initiated.

“Those decisions have snowballed into a lot of activity and a lot of discussion,” says D’Ambrosia, who is organising an activity to address these issues and to determine where the industry consensus is as to how to proceed. 

“These are all industry debates that are going to happen over the next few months,” he says, with the goal being to better meet industry needs by evolving Ethernet more quickly.

Ethernet continues to change, notes D’Ambrosia. The 40 GbE standard exploited the investment made in 10 gigabit signalling, and the same is happening with 25 gigabit signalling and 100 gigabit. 

 

If you buy into the idea of more lanes based around a single signalling speed, then applying that to the next signalling speed at 100 Gigabit Ethernet, does that mean the next speed with be 800 Gigabit Ethernet? 

 

With 50 Gig electrical signalling now starting as part of the 400 GbE work, some industry voices wonder whether, instead of developing one Ethernet family around a rate, it is not better to develop a family of rates around the signalling speed, such as is being proposed with 50 Gig and the use of 1, 2, 4 and 8 lane configurations.

“If you buy into the idea of more lanes based around a single signalling speed, then applying that to the next signalling speed at 100 Gigabit Ethernet, does that mean the next speed with be 800 Gigabit Ethernet?” says D’Ambrosia.     

The 400 GbE Task Force is having its latest meeting this week. A key goal is to get the first draft of the standard -  Version 1.0 - approved. “To make sure all the baselines have been interpreted correctly,” says D’Ambrosia. What then follows is filling in the detail, turning the draft into a technically-complete document. 

 

Further reading:

LightCounting: 25GbE almost done but more new Ethernet options are coming, click here

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