Next-generation Ethernet interfaces

For the first time in its history, the IEEE has released two Ethernet standards simultaneously: 40 Gigabit Ethernet (40GE) and 100 Gigabit Ethernet (100GE), both defined by the 802.3ba Task Force.

40GE is expected to be initially deployed to support cost-sensitive applications such as data center switch aggregation and high-performance server interconnection, while 100GE will be used in for demanding needs such as interconnecting core routers and DWDM transport equipment. 100GE will also be used in the data center once higher performance or higher density is required and its cost decreases as deployed volumes increase.

Evolution of Ethernet

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For the first time in its history, the IEEE has released two Ethernet standards simultaneously: 40 Gigabit Ethernet (40GE) and 100 Gigabit Ethernet (100GE), both defined by the 802.3ba Task Force.

40GE is expected to be initially deployed to support cost-sensitive applications such as data center switch aggregation and high-performance server interconnection, while 100GE will be used in for demanding needs such as interconnecting core routers and DWDM transport equipment. 100GE will also be used in the data center once higher performance or higher density is required and its cost decreases as deployed volumes increase.

Evolution of Ethernet

The optical interfaces for 40GE, also known as optical "Physical Media Dependent" or PMDs, are defined as the following:

* 40GBASE-SR4: Maximum link length of 100 meters on OM3-grade Multimode Fiber (MMF).

* 40GBASE-LR4: Maximum link length of 10 kilometers on Single Mode Fiber (SMF).

The PMDs defined for 100GE are the following:

* 100GBASE-SR10: Maximum link length of 100 meters on OM3-grade Multimode Fiber (MMF).

* 100GBASE-LR4: Maximum link length of 10 kilometers on Single Mode Fiber (SMF).

* 100GBASE-ER4: Maximum link length of 40 kilometers on Single Mode Fiber (SMF).

What follows is a more detailed description of the technical approaches used for these interfaces, as well as descriptions of several optical transceiver module form factors that either already exist or are being defined which can support the various 40GE and 100GE PMDs.

40G Ethernet interfaces

Two types of electrical interfaces have been defined to interconnect the 40GE optical transceiver modules and the host board. Both are based on four independent lanes, each carrying 10.3125Gbps. The first, called "40Gigabit Attachment Unit Interface", or XLAUI, assumes a retiming functionality is present inside the optical transceiver module. The second, called "40 Gigabit Parallel Physical Interface", or XLPPI, assumes no retiming in the module.

Two optical PMD interfaces have been defined for 40GE by IEEE 802.3ba, one for multimode and the other for single mode fiber optics:

* 40GBASE-SR4: This optical interface is based on four independent full-duplex 10.3125Gbps optical links, supporting a maximum distance of 100 meters over OM3-type (i.e., 2000 MHz*km bandwidth) multimode fiber optics. Four independent 850nm lasers are used as transmitters, each connected to four independent optical fibers. Similarly, the receivers consist of four photo-detectors connected to another set of four independent fibers. In a typical implementation, these eight fibers will be part of a single fiber ribbon cable, which connects to the transceiver module through a single MPO/MTP-type optical connector.

* 40GBASE-LR4: This optical interface is based on four different CWDM wavelengths in the 1300nm window, each transmitting at 10.3125Gbps and supporting a maximum distance of 10 kilometers over standard single-mode fiber. Four independent, un-cooled CWDM lasers are used as transmitters, and the four wavelengths are optically multiplexed into a single fiber. The receiver follows a similar configuration, where the four CWDM wavelengths on the incoming fiber are optically demultiplexed into four independent photo-detectors. A duplex set of single mode fibers are used on this PMD, similarly to 10GBASE-LR or 1000BASE-LX interfaces.