All information looks like noise until you break the code.
—Hiro in Neal Stephenson's (1959–present) Snow Crash (1992)




Ben Hacker posts occasionally to the Server Room located elsewhere in land. Here is a classic Ben posting, helping you to break the 10 Gigabit link types code.  It has been updated by yours truly to reflect the current state of the art and add in links to help provide illumination and diversion.


Ethernet (IEEE 802.x) has evolved over the years from a new standard linking computers together at slow rates and has moved from 10 Megabit per second (Mbps), to 100Mbps, to 1 Gigabit per second (Gbps), and a few years ago to 10GbE unidirectional throughput. Over time there have been several physical connection types for Ethernet. The most common is copper (Cat 3/4/5/6/7 cabling is used as the physical medium) but Fiber has also been prevalent as well as some other more esoteric (such as BNC Coax) physical media types. The most common 10GbE adapter (until very recently) has been Optical only due the difficulty of making 10GbE function properly over copper cabling.

But this post isn't meant to discuss the past, but more to decode the present and future as it relates to 10Gig Ethernet and the variety of flavors that are available. Below I'll cover a number of acronyms for 10GbE IEEE standards that are often lumped together as '10 Gigabit' and discuss some of the differences and usages for each. After that, I'll also try to clear up some of the confusion about ‘form factor' standards for optical modules (which are separate from IEEE) and some of terms and technologies in that realm:




10GBase-T (aka: IEEE 802.3an):

This is a 10GbE standard for copper-based networking deployments. Networking silicon and adapters that follow this specification are designed to communicate over CAT6 (or 6a/7) copper cabling up to 100 meters in length. To enable this capability, a 10GbE MAC (media access controller) and a PHY (Physical Layer) designed for copper connections work in tandem.


10GBase-T is viewed as the holy grail for 10GbE because it will work within the most prevalent Cat 6/7 based infrastructure that is already in place. For this flexibility, 10GBase-T trades off higher power, and higher latency.


10Gbase-KX4 (aka: IEEE 802.3ap):

This is a pair of standards that are targeted toward the use of 10GbE silicon in backplane applications (such as a blade design). The specifically is designed for an environment where lower power is required and shorter distances (up to only 40 inches) are sufficient.


10GBase-SR (aka: IEEE 802.3ae):

This specification is for 10GbE with optical cabling over short ranges (SR = Short Range) with multi-mode fiber. Depending on the kinds of fiber, SR in this instance can mean anything between 26 - 82 meters on older fiber (50-62um fiber). On the latest fiber technology, SR can reach distances of 300m. To be able to physically support a connection of the cable, any network silicon or adapter that support 10GBase-SR would need to have a 10GbE MAC connected to an Optics module designed for multi-mode fiber. (Optics modules are a whole ‘nother post!)


10GBase-SR is often the standard of choice to use inside the datacenters where fiber is already deployed and widely used.


10GBase-LR (aka: IEEE 802.3ae, Clause 49):

LR is very similar to the SR specification except that it is for Long Range connections over single-mode fiber. Long Range in this spec is defined as 10km, but distances above that (as much as 25km) can often be obtained. 


10GBase-LR is used sparsely and really only deployed where ultra long distances are absolutely required.


10GBase-LRM (aka: IEEE 802.3aq):

LRM stands for Long Range over Multimode and allows distances of up to 220 meters on older standard (50-62um) multi-mode fiber. 


10GBase-LRM is targeted for those customers who have older fiber already in place but need extra reach for their network.


10GBase-CX4 +(aka: IEEE 802.3ak):+

This standard of 10GbE connection uses the CX4 connector/cabling that is used in Inifinband ™* networks. CX4 is a lower power standard that can be supported without a standalone PHY or optics module (the signals can be routed directly from a CX4 capable 10GbE MAC to the CX4 connector). Due to the physical specification for CX4 based 10 Gigabit, it provides a lower latency than comparable 10GBase-T copper PHY solutions. With the use of CX4 passive (copper) cables, the nominal distance you can expect between your 10GbE links is ~10-15m. There are also amplified 'active' (but still copper) cables with nominal distances up near 30m.


Below is an image of a standard CX4 based socket that would be on a 10GBase-CX4 NIC:



There are also what referred to as ‘active optical' cables are for CX4, which actually have an optics module in the termination of the cable, and the cable body is fiber. This kind of active design increases cable reach and improves flexibility (fiber is smaller than copper pairs) but also increases cost. These active cables can increase reach up to 100m.



Intel has recently released our own series of active optical CX4 cables.



For short distances (such as inside the rack in a datacenter), CX4 offers one of the lowest cost ways to deploy 10GbE from switch to server. Because of its design, CX4 also achieves very low latencies as well.

Time for the big review:

1)     Ben Hacker has a great blog

2)     Intel® 10 Gigabit products support a wide variety of 10 Gigabit link types.

3)     Thanks of using Intel networking products!