LX-LH Cable lengths

[kalyanccie]

Dear all

Can u please guide me on the following distance problems.

i want gigabit ethernet, what distances will the following modules support

1. LX/LH Module in Single Mode Fiber

2. LX/LH Module on MultiMode Fiber

3. SX Module in Multimode Fiber

4. ZX Module on single mode fiber

have i missed some other modules,i have a lot of confusions in this, i wanted to settle this once and for all in this forum

regards and thanks in advance to all

[lgijssel]

Please check the following URL for info on cabling & distances for different types of GBICs:

http://www.cisco.com/en/US/products/hw/switches/ps679/products_installation_and_configuration_guide09186a008007d1cd.html

Regards,

Leo

[konigl]

The distances for multimode in the link Leo provided are from the Gigabit Ethernet standards. Actual testing has shown LX optical transceivers work out to 700m over worst-case multimode, but the IEEE 802.3z specified distance was reduced to 550m to agree with ISO/IEC 11801 structured cabling model.

Here's a Cisco link that quotes the 700m distance of LX over multimode; search for the number "700" to find it:

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/ethernet.htm

This link also quotes the "standard" distance for LX over single mode, which is 5km. Cisco and other manufacturers have tested their LX transceivers and found that they can reach to distances of 10km consistently, which is why they list that distance instead. That's where the "LH" in their LX/LH GBICs and SFPs comes from: it's to distinguish it as a "Long Haul" LX vs. regular LX.

It's also worth noting that there are fiber optic cable manufacturers out there making high-quality 62.5/125 and 50/125 multimode cable these days. Extends the distances beyond the specs; which cable you should install depends on how far you want to be able to go, and with what wavelengths. Here's a link to a document at Corning's web site that discusses different kinds of multimode that they have, that can take Gig Ethernet out to 1000m(!)

http://www.corningcablesystems.com/web/pubnet/ftppub.nsf/download/dgch3.pdf/$FILE/dgch3.pdf

It all boils down to what kind of cable you have, what kind of optics you connect to it, and is there a usable signal reaching the other end. If you stay within the standard distances, you should never have a problem. There are plenty of examples where people exceed the standards every day, though; and their networks still work. Why? Because they took the time to scan the cable with an optical time domain reflectometer, and verify optical power levels at the wavelengths used (850, 1300, and 1550nm for ZX GBICs/SFPs).

Anything beyond 5km exceeds the IEEE standard; at that point, you're working with the manufacturer's standards/recommendations.

Hope this helps.

[kalyanccie]

thanks a lot

i have become somewhat clear on this, does cisco have modules that fit into switches, of 100 FX , and not gigabit .

regards

[konigl]

No pluggable 100FX modules for the 3500XL/3550/3750 series of switches.

There are some 2950 models and older 2900XL series with two fixed 100FX MMF ports in each. And there's a 2924M XL modullar switch that had two slots for modules, you could put a two-port 100FX module in each slot; but that's scheduled for End-Of-Sale in April 2004, which means End-Of-Life for the product follows.

Really your best bet these days if you need 100FX is to get media converters to take you from fiber to copper, and plug the copper connection into an everyday 10/100 switchport. If you need medium- to high-density, you can buy either fixed-configuration media converter boxes with a set number of ports; or you can buy media conversion housings/shelves, and add modular converters (just as many as you need). Check out Transition Networks, they make a wide variety of solutions along these lines; something they have is bound to fit your needs. Here's a link:

http://www.transition.com

Their MMF fiber to copper media converters can carry 100FX out to 2km in full duplex mode, between two switches, or a router and a switch, or a computer and a switch; 412m in half duplex (for a shared media or dual-speed hub -- some people still use these). SMF media converters from Transition come in a wide variety, and can go to 20km, 40km, 60km, or 80km in full duplex with no problem.

I have a customer with a pair of diverse-routed ISP connections running Fast Ethernet full duplex from Cisco 7206VXR routers to the carrier hotel in downtown Philadelphia over SMF. Distances on those runs are 80+ to 110km; the fiber's been OTDR'd and power-metered, still within the optical specifications for Transition's LW media converters, they're working flawlessly. They're a great solution if 100-meg over fiber is something you want or need.