Re: [c-nsp] Optical module transmit power
Michael Robson wrote: The circuit supplier quoted dB values for the links on handover which should have meant that most of the links would have been within acceptable values: perhaps the 6500-quoted values aren't very accurate? If you haven't done so, meticulously clean the optics, cables, ferrules. It can make quite a difference, and should really be standard procedure when doing anything with singlemode imho. Also worth testing with a lightmeter as part of the installation process. plug We are hopefully going to have a presentation on this at a future UKNOF later this year - see www.uknof.org.uk /plug Will ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] Optical module transmit power
Michael -- Michael Robson | Tel: +44 (0) 161 275 6113 Senior Network Engineer | Fax: +44 (0) 161 275 6120 Net North West | Email: michael.rob...@manchester.ac.uk On 30 Apr 2009, at 16:08, Dale W. Carder wrote: On Apr 30, 2009, at 9:37 AM, Michael Robson wrote: We have a selection of ZR modules (XENPAK-10GB-ZR) For these modules, none of them are transmitting at anything like their maximum of +4.0dBm (Cisco's figures for the maximum transmit power), they are in fact transmitting between +1.9dBm and +2.3dBm. This is to be expected. Vendors just publish a tolerable range somewhere in which the optics will operate. What determines what they will transmit at i.e. is it simply that better manufactured ones achieve a transmit value closer to the +4.0dBm power level Maybe it's luck. As I suspected, ah well. Anyway, how long are your fiber spans? If they are really long, and you're living on the edge now, you may end up in a sticky situation as these optics degrade over time. They are very long distances; however these links are just stop gaps until we procure our DWDM equipment. If they are not extremely long, you may have some horrible jumpers or splices that are eating some dB. Do you have an OTDR? Dale The circuit supplier quoted dB values for the links on handover which should have meant that most of the links would have been within acceptable values: perhaps the 6500-quoted values aren't very accurate? p.s. My fiance did her postgraduate work at Manchester. Quite a nice place! Manchester is a great place! Thanks, Michael. ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] Optical module transmit power
On Fri, 1 May 2009 15:05:35 +0100, Michael Robson wrote The circuit supplier quoted dB values for the links on handover which should have meant that most of the links would have been within acceptable values: perhaps the 6500-quoted values aren't very accurate? Values reported by ZR XENPAKs are quite precise, so if they report RX level which is much worse than expected, you have to look for dirty connectors, faulty patchcord or the like problems. Our installation team tried to blame XENPAKs for inacurrate measurements several times, but after closer investigation it always turned out that the fault was somewhere else. It's nothing uncommon to see 3 dB extra loss on just one dirty connector. M. ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] Optical module transmit power
On Thu, Apr 30, 2009 at 03:37:44PM +0100, Michael Robson wrote: We have a selection of ZR modules (XENPAK-10GB-ZR) in 6500s that we are using to drive some links at 10Gbps and I have recently noticed that all receive values (as reported via the sh int te x/y trans command) are lower than what Cisco specify as the minimum allowed values for those modules (i.e. the minimum quoted is -24dBm whereas we are seeing value reported as low as -28.8 dBm), and also a link that is receiving at -28.9dB and flapping. This is normal, it is very common for optics to work a bit below their min rx spec. Like how elevator cables don't snap and let you plummet to your death as soon as you hit +1 lbs over the maximum weight specified, there is a built in safety margin in the specs to make sure the min spec is achieved under all circumstances. Of course you're taking your life into your own hands if you run it like this, as someone walking past and bumping or bending the SMF cable could easily add enough loss to kill the circuit completely. When you do cross that magic line where the signal is no longer strong enough to work, flapping constantly is a common behavior on Cisco 6500s with XENPAKs (particularly on WAN PHY optics, which flap on any kind of error). On most other platforms you'll just start to see CRC errors and then eventually lose the link. Of course DOM on these things has been known to be wrong too (both due to hardware and software issues), but the behavior you're describing is normal so this probably isn't the case. For these modules, none of them are transmitting at anything like their maximum of +4.0dBm (Cisco's figures for the maximum transmit power), they are in fact transmitting between +1.9dBm and +2.3dBm. What determines what they will transmit at i.e. is it simply that better manufactured ones achieve a transmit value closer to the +4.0dBm power level, or is there some sort for decision/negotiation that determines the transmit value at connection; if the the latter, how can these modules be convinced to transmit at a higher power value? You can't adjust the transmit power (well not on these things, on some of the latest newfangled optics you can but thats a completely different discussion), what it does it what it does. The transmit power spec is basically telling you to expect your optic to put out a signal level somewhere in the range between specified min and max, so you can plan an optical budget that is both strong enough to work properly, but not so strong that it blows up your amps or rx optics on the other side. -- Richard A Steenbergen r...@e-gerbil.net http://www.e-gerbil.net/ras GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC) ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] Optical module transmit power
On Apr 30, 2009, at 9:37 AM, Michael Robson wrote: We have a selection of ZR modules (XENPAK-10GB-ZR) For these modules, none of them are transmitting at anything like their maximum of +4.0dBm (Cisco's figures for the maximum transmit power), they are in fact transmitting between +1.9dBm and +2.3dBm. This is to be expected. Vendors just publish a tolerable range somewhere in which the optics will operate. What determines what they will transmit at i.e. is it simply that better manufactured ones achieve a transmit value closer to the +4.0dBm power level Maybe it's luck. Anyway, how long are your fiber spans? If they are really long, and you're living on the edge now, you may end up in a sticky situation as these optics degrade over time. If they are not extremely long, you may have some horrible jumpers or splices that are eating some dB. Do you have an OTDR? Dale p.s. My fiance did her postgraduate work at Manchester. Quite a nice place! ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
