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Update 2

High Speed Ethernet in data centers - IEEE standard update

Hans-Jürgen Niethammer, Director Technical Services & Sales Operations for TE Connectivity Enterprise Networks provides an update on latest IEEE high speed ethernet development.

40 Gigabit Ethernet, or 40GbE, and 100 Gigabit Ethernet, or 100GbE, are high-speed computer network standards developed by the Institute of Electrical and Electronics Engineers (IEEE). They support the sending of Ethernet frames at 40 and 100 gigabits per second over multiple 10 Gb/s or 25 Gb/s lanes. Previously, the fastest published Ethernet standard was 10 Gigabit Ethernet. They were first studied in November 2007, proposed as IEEE 802.3ba in 2008, and ratified in June 2010, defining both data rates in the same standard.

Several application types have been defined initially, addressing both WAN and Data Center environments.

40/100 GBE application types defined by IEEE 802.3ba

In March 2011, an additional application type called 40Gbase-FR was ratified with IEEE 802.3bg using singlemode fiber (SMF) up to to a length of 2 km.

Out of these application types, there are 4 applications that are primarily defined for use in data centers:

40GBASE-CR4 resp. 100GBASE-CR10
40GBASE-SR4 resp. 100GBASE-SR10

While the -CR variants use a QSFP-copper cable assembly with limited reach of 7 m, the -SR applications use multimode fiber. The following picture shows a QSFP-cable assembly and transceivers for 40GBE.

QSFP-cable assembly and transceivers for 40GBE

The high speed ethernet application types 40GBASE-SR4 and 100GBASE-SR10 are the first ethernet applications that require more than 2 fibers for the transmission over multimode fiber. Based on multiple 10 Gb/s data streams in full duplex mode, the main applications are: 40GBASE-SR4 (8 fibers) and 100GBASE-SR10 (20 fibers). Hence, these applications require the use of the multi fiber connector MPO. Here is how the applications work and which pin-out is used for the multi fiber connector MPO.

Although 40/100 GBE multimode applications dominate the data center, the following table also includes singlemode applications in order to give a complete overview about all of the 40/100 GBE applications.

Channel length definitions for 10GBE depending on application and fiber type

High Speed Ethernet Outlook

IEEE is currently studying the requirements for additional variants of 40Gbe and 100 GbE for data centers.

A Study Group was formed in July 2011 to investigate the feasibility of 100G optical Ethernet PHYs based on 4 lanes of 25G per lane. A possible name for this application could be 100Gbase-SR4. The intention of this application is to reduce the fiber count from currently 20 fibers for 100Gbase-SR10 to 8 fibers, resulting is much less cabling and easy migration from 40 GBE to 100 GBE because both application then would use 8 fibers.

A second very interesting topic is the work of the 40GBASE-T interest group which is doing study work "in the background" about possible options to achieve 40GBase-T over structured copper cabling. The interest group is growing and very interested to define this application especially for the equipment areas in data centers because this is expected to offer a lower cost solution than fiber.

Cabling recommendations for 40/100 GBE

TE Connectivity recommends the use of pre-terminated 12 fiber MPO cabling systems in data centers. There are basically two major advantages compared to the 24 fiber MPO systems currently available on the market today:

Lower channel attenuation:

A 24 fiber MPO connector is much more complex to manufacture. Fiber protrusion and end-face geometry are more difficult to control than with a 12 fiber MPO. This means that lower attenuation and better return loss can be achieved with a 12 fiber connector, resulting in much higher design flexibility in the data center.

Less complex upgrade:

Irrespective of whether one wants to migrate from 10G to 40G or from 40G to 100G, a 12 fiber solution can be easily upgraded as the following pictures show:

MTP* is an improved version of the MPO connector *MTP is a trademark of USConnec

10 GBE -> 40 GBE

Assuming the current application used in a DC 1GB or 10 GBE. Both applications are, so called, "dual-fiber" applications meaning that they use two fibers and duplex connectors for transmission. In the following example there are 2 MTP trunks with 12 fiber each connected to cassettes with 12 LC-Duplex connectors

Pre-terminated MTP solution with LC-Duplex equipment interface for applications up to 10GBE

The upgrade to 40GBE is achieved easily by just replacing the LC-Duplex cassettes with MTP-to-MTP cassettes.

Pre-terminated MTP solution for 40GBE with MTP equipment interface

The 24 fibers of the 2 trunks are converted by the cassette to 3 x 40GBE allowing the usage of all fibers of the trunks.

40 GBE -> 100 GBE

There are two options for upgrading from 40GBE to 100 GBE:

from 40Gbase-SR4 to 100Gbase-SR10
from 40Gbase-SR4 to possible future 100Gbase-SR4 (see above in the outlook paragraph)

In the same way that it is simple to upgrade from 10GBE to 40GBE, upgrading from 40Gbase-SR4 to 100Gbase-SR10 is achieved simply by replacing the cassette.

When upgrading from 40Gbase-SR4 to 100Gbase-SR4 (in case this will be defined as a standard), it is even easier. As a possible 100Gbase-SR4 will use 8 fibers like 40Gbase-SR4, no upgrade work is required. The cabling remains as it is.

TE Connectivity's MPOptimate fiber solution for data centers offers the ideal migration path within data centers.

Find out more about MPOptimate here

For further information Hans-Jürgen Niethammer can be contacted vie email here: hjniethammer@te.com