Decoding 10 Gigabit Ethernet Transceivers

10Gbps/10GbE/10GBase Transceivers Explained

Background

With components fulfilling the same basic function available in five different form-factors, at first look the world of 10Gbps optical transceiver modules looks a bit cloudy. However, with a bit of historical perspective and a look at today’s marketplace, the picture becomes considerably clearer.

10Gbps transceivers are also commonly referred to as 10GbE or 10GBase transceivers. These transceivers transmit data at a base rate of 10 Gigabits per second typically using Ethernet protocol.  A variety of optical component and systems vendors began working on 10Gbps standards (called Multiple-Source Agreements or MSAs) in about 2000. The following is a list of the MSAs published over the subsequent years:

Multi-Source Agreements

XENPAK Transceivers

The first published form-factor, the XENPAK, was by far the largest in physical size. This standard was driven primarily by large systems vendors and was intended to support essentially any optical application a system vendor may want to deploy. At the time this MSA was published, 10Gbps optical interfaces supporting transmission distances of 80km or more were of a size and heat dissipation that required a relatively large (by today’s standards) package size.

XPAK, X2 and XFP Transceivers

Transceiver Size
Figure 1 10G Transceiver size  comparison (cubic in.)

Many in the industry recognized the size of the XENPAK as very limiting factor and began working on alternative standards. Over the following two years three alternative MSAs were published, called: XPAK, X2 and XFP. When these standards were written they were intended to enable optical interfaces supporting up to about 10 km. While the XPAK standard was not a commercial success, the X2 and XFP form-factors both saw considerable deployment. As optical technology has advanced over the last ten years, X2 and XFP modules have been developed that support all of the high-power, long-distance applications once reserved to the larger XENPAK transceivers.

SFP+ Transceivers

Five years after the first 10Gbps optical transceiver standard was issued, a new MSA was published called the “SFP+”. This agreement has been the basis for the most commercially successful 10Gbps optical transceivers by a large margin. There are several reasons for the success of the SFP+ standard,

  • Flexibility – The SFP+ standard builds on a previous one, the SFP MSA (primarily a 1Gbps standard). SFP+ modules are the same physical size as SFPs and the SFP+ standard allows for either type of module to operate in the new SFP+ slots
  • Small Size – SFP+ modules are one tenth the size of the original XENPAK 10G modules (see Figure 1) and are the same size as the popular 1Gbps SFP modules. This small size allows the design of systems with 10G ports of the same density as previous generations with 1G ports.
  • Low Cost – Since SFP+ modules share many components (bezel, housing, latch/locking mechanism) on the previous SFP standard, the cost of the new 10G modules inherits the low cost of these components. SFP+ units are also lower power, contributing to cost savings.

What 10GBase Form-Factor Do I Need?

Systems (routers, switches, media converters, etc.) designed within the last two or three years have implemented, with very few exceptions, the SFP+ standard for 10Gbps ports. If used – or new equipment of older design – is being considered, users must be careful to identify what type of port is built into their gear. The best guide here is to refer to the equipment manufacturers specifications. This documentation should explicitly list the type of ports that are available and the type of 10GBase modules those ports accept.

When considering new or used equipment for a new network build or expansion, attention should definitely be given to the type of 10Gbase ports in that equipment. One important reason is capital costs. Older gear offering XFP, X2 or XENPAK ports may be attractive due to what seems like very low prices. However, the cost of equivalent 10GBase optics in those older form factors is 2X to 3X the price of SFP+ based modules. Therefore, when the cost of the optics are included, total system costs may end up higher. Other costs to consider are:

  • Power – The older XFP, X2 and especially XENPAK gear, both the host system and the 10GBase optical modules, consume considerably more power than the new SFP+ modules. Power costs include capital outlays for larger power/battery plant as well as operational cost of the electrical power itself.
  • Rack Space – Depending on the location, space in equipment racks can be quite expensive. Equipment utilizing the older 10Gbase interfaces is almost always substantially less dense, consuming more rack space per 10G interface available.

And the Winner is…

Clearly the SFP+! With its substantial advantages in cost, size and power, along with flexibility to support any type of optical interface while maintaining backward compatibility with previous 1Gbps SFPs, the SFP+ is the clear winner in the 10GBase optical transceiver market. New standards work is primarily focused on higher speed, 40Gbps and 100Gbps, interfaces. In FluxLight’s view, SFP+ based optical transceivers are bound to continue to dominate the market for 10Gbps modules for the next 10 years or more.

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