Optical Ethernet vs Electrical Ethernet

Venkat

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Feb 14, 2016, 2:01:55 PM2/14/16

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Hi Hubb,

I have few basic questions on Ethernet..

What's the difference between Optical Ethernet and Electrical Ethernet?

Given that the optical Ethernet is also transmitted over a DWDM wavelength , why do we need OTN to transmit Optical Ethernet over longer distances ( I see optical Ethernet is limited to 80km only ..why ? what is limiting the distance?)

Thanks
venkat

Huub van Helvoort

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Feb 19, 2016, 6:16:04 PM2/19/16

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Hello Venkat,

You wrote:

> I have few basic questions on Ethernet..

OK.

> What's the difference between Optical Ethernet and Electrical
> Ethernet?

The difference is only the line signal. The characteristics of
electrical signals and optical signals are different.
Electrical are normally short distance, e.g between equipment
in the same building.
Optical are normally longer distance, outside the building.

> Given that the optical Ethernet is also transmitted over a DWDM
> wavelength , why do we need OTN to transmit Optical Ethernet over
> longer distances ( I see optical Ethernet is limited to 80km only
> ..why ? what is limiting the distance?)

It depends on the optical components that are used.
The IEEE standard for the Ethernet optical interface limits it
to about 80km.

Best regards, Huub.

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Stephen

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Feb 20, 2016, 5:46:20 PM2/20/16

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On Sat, 20 Feb 2016 00:16:13 +0100, Huub van Helvoort
<hhelv...@chello.nl> wrote:

>Hello Venkat,
>
>You wrote:
>
>> I have few basic questions on Ethernet..
>
>OK.
>
>> What's the difference between Optical Ethernet and Electrical
>> Ethernet?
>
>The difference is only the line signal. The characteristics of
>electrical signals and optical signals are different.
>Electrical are normally short distance, e.g between equipment
>in the same building.
>Optical are normally longer distance, outside the building.
>
>> Given that the optical Ethernet is also transmitted over a DWDM
>> wavelength , why do we need OTN to transmit Optical Ethernet over
>> longer distances ( I see optical Ethernet is limited to 80km only
>> ..why ? what is limiting the distance?)
>
>It depends on the optical components that are used.
>The IEEE standard for the Ethernet optical interface limits it
>to about 80km.

But the 80 Km limit comes down to assumptions around fibre quality,
optics power, no of splices and Ethernet speed / version....

Some optics suppliers will provide parts with a longer reach.
>
>
>Best regards, Huub.
Stephen Hope stephe...@xyzworld.com
Replace xyz with ntl to reply

Michelot

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Feb 21, 2016, 1:00:52 PM2/21/16

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Hi Venkat and Stephen,

> Some optics suppliers will provide parts with a longer reach.

I would add a statement from Huub "Unfortunately there are several vendors/operators who use the term WDM but actually mean OTN..."

Best regards,
Michelot

krishna

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Feb 28, 2016, 12:37:25 AM2/28/16

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Hi,

Thanks for the replies.

I still don't understand why do we need transport technologies like OTN and SONET , when we have transport Ethernet ( I assume transport Ethernet is sending Ethernet signals on DWDM wavelengths directly) ?

Why cant transport Ethernet travel same distance as OTN ? Hub you said , "It depends on the optical components that are used" . Does that mean optical components used in Transport Ethernet are cheaper than components used for OTN ?

Thanks
Krishna

Michelot

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Feb 28, 2016, 9:01:07 AM2/28/16

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Hi Krishna,

> I assume transport Ethernet is sending Ethernet signals on DWDM
> wavelengths directly) ?

No, in 802.3 Ethernet architectures, that is MAC 802.3 over RS/PHY 802.3, you don't have PHY 802.3 signals that are DWDM.

Best regards,
MIchelot

krishna

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Mar 1, 2016, 11:30:38 PM3/1/16

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On Sunday, February 28, 2016 at 10:01:07 PM UTC+8, Michelot wrote:

Hi Michelot,

>>I assume transport Ethernet is sending Ethernet signals on DWDM
>>wavelengths directly) ?
>
> No, in 802.3 Ethernet architectures, that is MAC 802.3 over RS/PHY 802.3, you don't have PHY 802.3 signals that are DWDM.

PHY 802.3 can be an optical signal. It is up to the Line module to decide on what wavelength to transmit the signal.

For example you can take this transceiver,

Finisar 80 km DWDM XFP Transceiver | FTLX6811MCC

and below are its specifications. It can send different protocols like 10G Ethernet , 10G fiber channel , SONET/SDH on DWDM wavelengths and it is tunable.

The Finisar FTLX6811MCC 10GBASE-ZR/ZW Ethernet transceiver is a DWDM XFP transceiver for optical communications, rated for distances up to 80 km and a maximum bandwidth of 10Gbps. The FTLX6811MCC transceiver operates at 50GHz wavelength. DWDM, FULL BAND-TUNABLE (C-BAND), 50GHZ SPACING, APD.

Technical Specifications:
*Finisar 10GBASE-ZR/ZW Ethernet XFP
*Up-to 80 km over SMF @ 10Gbps
*50GHz DWDM XFP Transceiver
*0º - 70º Operating Case Temperature
*SFF-8724 Digital optical monitoring
*Hot-swappable for XFP LC ports
*Finisar Standard 1 Year Warranty
*Metal enclosure, for lower EMI
*XFP MSA & IEEE 802.3ae
*Finisar FTLX6811MCC is RoHS compliant

Applications:
*10GBASE-ZR/ZW Ethernet
*10G Fibre Channel
*SONET OC-192

>
> Best regards,
> MIchelot

arstpt....@gmail.com

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Mar 4, 2016, 4:45:06 AM3/4/16

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Hi Krishna,

Many points. I just focalise on some of them.

> PHY 802.3 can be an optical signal.

You're right, either a single wavelength, either several optical lanes for one specific signal.

> It is up to the Line module to decide on what wavelength to transmit
> the signal.

This is not an IEEE 802.3 operation. This line module does not take part of a PHY 802.3 layer.

> *Finisar 10GBASE-ZR/ZW Ethernet XFP

By using the word Ethernet, the vendor wants to underline that MAC 802.3 frames (or ETH frames if you prefer ITU-T terminology) are carried on a 10GBASE-ZR/ZW physical layer.

These 10GBASE-ZR/ZW interfaces are not specified by IEEE 802.3. They are proprietary long haul interfaces.

> *Up-to 80 km over SMF @ 10Gbps

You don't have PHY 802.3 signals specified up to 80 km. The maximum value that you can find is 40 km at least. The philosophy is different.

> *XFP MSA & IEEE 802.3ae

This document doesn't specify 10GBASE-ZR/ZW.

You are neither sured that 2 of these interfaces from different vendors can operate together. Some vendors use 10GBASE-ZR/ZW on STM-64, others in OTU2 and OTUe (which OTU2e is not compliant to G.709 OTN.

Don't confuse a specific proprietary interface between 2 equipments, and a complete operator network that provide multiplexing, routing, management, supervision and survivability of optical channels (as noted in G.870).

Best regards,
Michelot

Michelot

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Mar 5, 2016, 2:40:59 PM3/5/16

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Hi Krishna,

> You are neither sured that 2 of these interfaces from different vendors can operate together. Some vendors use 10GBASE-ZR/ZW on STM-64, others in OTU2 and OTUe (which OTU2e is not compliant to G.709 OTN.

Sorry, not OTU2 or OTU2e for 10GBase-ZW. It's for other proprietary interfaces.

Best regards,
Michelot

Ramakrishna Pratapa

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Jun 21, 2016, 8:35:07 AM6/21/16

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Just wanted to add my two cents:
One of the advantages of OTN is the support for FEC mechanism. FEC mechanism is able to not just detect but also correct lot many errors, which means tolerance to more number of bit errors and thereby increasing the reach.

For point to point link of <=80Km, OTN and native Ethernet link could potentially mean similar performance.

As highlighted by Huub, when the reach is more, the optical components in case of Ethernet are unable to provide the performance achievable with FEC enabled OTN transport. Many other OAM bytes in OTN overhead catalyze the fault diagnosis/isolation/mitigation.

Regards
RK