Help with GBIC selection LH vs ZX

[aoshea]

Dear Support,

I now have the estimated Attenuation values from our fibre provider, and wondering if anyone could help with determining if I can utilise the cheaper (LH modules) across the 20 & 15 KM streches.

Thanks in advance (many thanks to Josh for helping out with my previous post - below)

HQ to DC1 = 1310nm: 2.5dB, 1550nm: 2.2dB.

DC1 to DC2 = 1310nm: 14.5dB , 1550nm: 13.1dB

DC2 to HQ = 1310nm: 10.1dB, 1550nm: 9dB

=========================================

Dear Support,

Sorry but new to optical networking, but need some assistance on an upgrade that we are performing.

We currently have two data centres that hold our servers and are planning to upgrade from LES circuits to Gigabit links, and triangulate our topology. (effectively a ring topology)

I have already spoken to our proposed fibre provider and they have provide me with rough distances, but due to one of the data centres being more than 10 km away we need to use ZX based GBICs. Summary of distances below;

HQ -> dc1 (1 – 2 km)

HQ -> dc2 (15 km)

Dc1 -> dc2 (20 km)

From our HQ to dc1 we will use LH (via a GLC-LH-SM= in a 2970G) and a to dc2 we will use ZX (via a GLC-ZX-SM= in another 2970G)

From DC1 to HQ we will use LH (via a WS-G5486 in a 7204VXR) and a to dc2 we will use ZX (via a WS-G5487 in another 7204VXR)

From DC2 to HQ we will use ZX (via a WS-G5487 in a 7204VXR) and a to dc1 we will use ZX (via a WS-G5487 in another 7204VXR)

Hope this doesn’t confuse things more.

Now to the question.

From the Cisco web site it mentions the following;

When shorter distances of single-mode fiber are used, it might be necessary to insert an in-line optical attenuator in the link to avoid overloading the receiver:

• A 5-dB or 10-dB inline optical attenuator should be inserted between the fiber-optic cable plant and the receiving port on the Cisco 1000BASE-ZX GBIC at each end of the link whenever the fiber-optic cable span is less than 15.5 miles (25 km).

We haven’t yet had the fibre survey performed, but once they have advised me of the attenuation on the link, how should I calculate what level of “in-line optical attenuator” I should need or should all reputable fibre providers advise me of this detail.

Thanks in advance.

Regards, Adrian

[pkhatri]

Summary of Optical Levels:

GLC-ZX-SM:

Transmit: 0 to +5

Receive: -23 to 0

GLC-LH-SM:

Transmit: -9.5 to -3

Receive: -20 to -3

G5486:

Transmit: -9.5 to -3

Receive: -20 to -3

G5487:

Transmit: 0 to 5.2

Receive: -24 to -3

Given the above:

HQ -> DC2: maximum receive level will be 5-10.1 = -5.1 dB, which is OK for the G5487

HQ <- DC2: maximum receive level will be 5.2-10.1 = -4.9 dB, which is OK for the GLC-ZX-SM

HQ -> DC1: maximum receive level will be -3-2.5 = -5.5 dB, which is OK for the G5486

HQ <- DC1: maximum receive level will be -3-2.5 = -5.5 dB, which is OK for the GLC-LH-SM

DC1 -> DC2:maximum receive level will be 5.2-14.5 = -9.3 dB, which is OK for the G5487

DC1 <- DC2:maximum receive level will be 5.2-14.5 = -9.3 dB, which is OK for the G5487

Therefore, you do not need attenuators anywhere.

Now, to your next queston. If you used the LH modules, you the minimum possible receive levels now become:

HQ -> DC2: minimum possible receive level will be -9.5-10.1 = -19.6 dB, which is only just OK for the G5486

HQ <- DC2: minimum possible receive level will be -9.5-10.1 = -19.6 dB, which is only just OK for the G5486

DC1 -> DC2: minimum possible receive level will be -9.5-14.2 = -24 dB, which is too low for the G5486

DC1 <- DC2: minimum possible receive level will be -9.5-14.2 = -24 dB, which is too low for the G5486

Therefore, my recommendation is to stick with the ZX modules for these links.

Hope that helps - pls rate the post if it does.

Paresh

[konigl]

If these attenuation values were actually measured, I would tell you that you could not use the LX/LH GBICs and SFPs on the 15km and 20km stretches.

The WS-G5486 1000BASE-LX/LH GBIC provides a minimum optical power budget of 9.5 dB; the GLC-LH-SM 1000BASE-LX/LH SFP can do 10.5dB.

On the 20km stretch you are 5.0dB over the limit for GBIC-to-GBIC. On the 15km stretch, since you are mixing SBIC and SFP, you have to use the lesser value of 9.5dB; in which case you are 0.6dB over the limit.

Now, you did say that these were "estimated" attenuation values. It is possible that actual measured values on the 15km stretch would fall just under the limit, allowing you to use the LX/LH ones. But I wouldn't recommend it: you will have little to no safety margin in the optical budget to allow for future repair splices to the cable, which will push you into needing ZX optics sooner or later anyway. In my opinion, you're better off spending the money and getting the ZX now. (It will cost you less than the downtime you would incur later.)

As for the attenuation you would need for ZX operation: Cisco's guidelines specify 10dB attenuators for 0-25km stretches. Those will work for the estimated attenuation value you have on the 15km run. However, they would be just a bit excessive on the 20km run, putting you 0.1dB over the limit. On your 20km run, with 13.1dB of loss at 1550nm, you should be fine with just 5dB attenuators.

[JoshGH]

If you need a bit more flexibility with attenuators, I would suggest Corning's. Most of their attenuators are available in 1db increments from 1db - 20db. Here is the datasheet for those: http://www.corningcablesystems.com/web/library/litindex.nsf/$ALL/EVO-61-EN/$FILE/EVO-61-EN.pdf

[aoshea]

Dear All,

Many thanks for everyone's help with this, I appreciate all the help and effort everyone has contributed in helping me out.

Thanks again.

Regards, Adrian.