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A Guide to 40 Gigabit Ethernet

Dec 8th 2015 at 11:34 PM

The 802.3ba Ethernet standard introduced by the IEEE in June 2010 was in response to the increasing bandwidth demands facing data centers, paving the way for the introduction of 40Gb/s and 100Gb/s Ethernet operations. As you begin to think about the future of your network, understanding all the 40 Gigabit Ethernet (40GbE) and 100 Gigabit Ethernet (100GbE) optical components can be confusing. In this post, a brief overview of the current 40 Gigabit Ethernet to aid in planning for future high-performance Ethernet needs will be given.

What Is 40 Gigabit Ethernet?

40GbE is a standard that enables the transfer of Ethernet frames at speeds of up to 40 gigabits per second (Gbit/s). The 40GbE standard is intended for local server connectivity. One of the most attractive characteristics of 40 Gigabit Ethernet is broad applications and design flexibility. 40 Gigabit Ethernet runs on quad small form factor pluggable (QSFFP) cabling, a high-density fiber connector with 12 strands of fiber. According to the task force, 40GbE fulfills the following requirements and objectives:

  • Preserve existing 802.3 frame format, minimum size, and maximum size.
  • Support high-bandwidth applications such as video on demand (VoD) and high-performance computing (HPC).
  • Support high-speed switching, routing, and application functions in data centers.
  • Exhibit a bit error rate (BER) of 10-12 or better.
  • Provide support for optical transport network (OTN).
  • Provide specifications for operation over single-mode optical fiber, laser optimized multi-mode optical fiber, copper cables, and backplanes.
How Does 40 Gigabit Ethernet Work?

40 Gigabit Ethernet can be deployed using the same cabling systems in use today. Multi-mode will employ parallel optics using MPO interconnects and require additional cable infrastructure depending on the system deployed while single mode fiber will employ serial transmission and use LC or SC connectors. The approach used for the higher speed data rates is based on advanced transceiver technologies engineered to take advantage of the full bandwidth of laser optimized fibers. The 40 Gigabit Ethernet specification calls for a 12-fiber cabling solution, implemented using eight of the twelve fibers in an MPO connector, with each channel featuring four dedicated transmit fibers and four dedicated receive fibers. The middle four fibers remain unused, or dark. Each Tx/Rx pair is operating at 10G.

40 Gigabit Ethernet Cables

Cabling for 40 Gigabit Ethernet can be optical fiber or copper. The supportable channel length depends on the cable and the transceiver type. With regard to connectors, the only significant change outlined in the 802.3ba standard is the use of MPO (Multi-Fiber Push On) type connectors at the multi-mode transceivers to support the multi-fiber parallel optics channels. For data center environments operating at 40Gbps, OM3 and OM4 multi-mode cabling is generally recommended because its reach supports a wider range of deployment configurations compared to copper solutions, and the cost is lower compared to single-mode solutions.

40 Gigabit Ethernet Transceivers

40 Gigabit Ethernet transceivers are being developed along several standard form factors. The C form-factor pluggable (CFP) transceiver features 12 transmit and 12 receive 10Gbps lanes to support up to three 40 Gigabit Ethernet ports. Its larger size is suitable for the needs of single-mode optics and can easily serve multi-mode optics or copper as well. The CXP transceiver form factor also provides 12 lanes in each direction, but is much smaller than the CFP and serves the needs of multi-mode optics and copper. The quad small form-factor pluggable (QSFP) is similar in size to the CXP and provides four transmit and four receive lanes to support 40 Gigabit Ethernet applications for multi-mode fiber and copper. And quad small form-factor pluggable plus (QSFP+) gradually replaces QSFP and is widely used by people as it can provide higher bandwidth. The picture below shows a Cisco WSP-Q40GLR4L compatible QSFP+ transceiver.

Cisco WSP-Q40GLR4L Compatible 40GBASE-LR4L QSFP+ Transceiver

Migrating to 40 Gigabit Ethernet will prove very cost-effective for those who do it right. One critical step is to choose appropriate cables and transceivers. Fiberstore is a professional manufacturer and supplier, which offers a large amount of cables and transceivers for your 40GbE applications. For example, HP 805755-B21 compatible QSFP+ transceiver, and Juniper JNP-QSFP-4X10GE-IR compatible QSFP+ transceiver offered by Fiberstore are cost-effective and high-performance transceiver modules fully compatible with major brands.

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