How far can I go with an Ethernet segment?

One of the best-known numbers in the Ethernet world is the maximum length of a cable channel, 100 meters (328 feet). Every book on Ethernet configuration or structured cabling takes pains to reinforce this limit in the reader’s mind. The 100-meter horizontal cable is the basic building block of a structured cabling plant.

Frequently a client will ask us if it is possible to use a channel longer than 100 meters. The answer is, “It depends”. All twisted-pair Ethernet technologies (10Base-T, 100Base-T, and 1000Base-T) were designed for a 100-meter horizontal cable length. 10Base-T, the original 10Mbps standard over twisted-pair cabling, was actually designed to operate on a 100M segment of uncategorized telephone wire. The attenuation of this wire was the determining factor for maximum length. Cat5 and Cat5e cabling have much better attenuation characteristics, and a 10Base-T link should operate 100% reliably up to 150 meters, provided that:

o All segments connect to a good quality 10/100 switch (hubs will not work)
o Cat5 or better cable is used
o The network is used exclusively for Pathport communications

NOTE:  These limits are for isolated segments only, where building geography precludes a 100-meter segment.

There are many other parameters beyond just cable attenuation that come into play at higher speeds. As a result, you cannot run 100/1000Base-T on cable channels longer than 100 meters. In most cases this limitation is not unreasonable, however, since distributed entertainment lighting devices, which may require longer channel lengths (such as Pathport DMX nodes), are well suited to a 10Base-T link due to their modest bandwidth requirements. From a reliability perspective, the more robust 10Base-T will probably remain the best choice for these kinds of devices. The 100-meter limit must still be observed for any 100/1000Base-T network segments, such as switch-to-switch connections, otherwise they will not operate reliably.

It can also be argued that the best course of action for new network installations is to stick with the 100-meter limit for all cable channels, if for no other reason than to ensure that future upgrades are possible. Having stated that, we need to acknowledge that this limit can impose an unnecessary burden on users who want to replace existing DMX networks with Ethernet, or those with existing DMX-over-CAT5 systems who now want to run Ethernet on the installed cabling.

Pathway encourages clients who face the channel length dilemma to call us and discuss their project with one of our engineers. We’ll be able to give you a go/no-go based on your specific situation, and recommend switchgear that we have tested and approved for use with longer network segments.

So how far can you go? Your actual limit for 10Base-T networks is 150 meters, or 500 feet, provided that you use a good 10/100 switch and your cable is CAT5 or better. To those people who when given an inch demand a foot, and after getting the foot want a yard, and when offered a yard ask for a swimming pool in it, all we can say is, if you exceed 150 meters, don’t call us -- you’re on your own!