Choice of cable for very short distance

[aenagy]

This is a follow-up to my earlier post: https://community.cisco.com/t5/small-business-switches/need-cabling-advice-to-connect-c3750g48ts-and-sg300-20-using-sfp/td-p/3902730

After reading this:

10GBASE-LRM and EDC: Enabling 10GB Deployment in the Enterprise

https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/transceiver-modules/prod_white_paper0900aecd806b8bcb.html

... I'm beginning to re-think my choice of SFP modules. Because this is a home lab cost and distance are major consideration. The limitation is the SG300-20 and available SFP modules which can be summarized as:

MGBBX1	1000BASE-BX-20U SFP transceiver, for single-mode fiber, 1310 nm wavelength, support up to 40 km
MGBLH1	1000BASE-LH SFP transceiver, for single-mode fiber, 1310 nm wavelength, support up to 40 km
MGBLX1	1000BASE-LX SFP transceiver, for single-mode fiber, 1310 nm wavelength, support up to 10 km
MGBSX1	1000BASE-SX SFP transceiver, for multimode fiber, 850 nm wavelength, support up to 550 m

(https://www.cisco.com/c/en/us/products/collateral/switches/small-business-smart-switches/data_sheet_c78-610061.html)

(Q1) I made the assumption that shorter maximum distance meant lower cost for both SFP modules and cabling. Is this correct in the case of SFP + cabling for the SG300?

(Q2) Will a MGBSX1 and SFP-10G-SR (https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/transceiver-modules/data_sheet_c78-455693.html) work together?

(Q3) If the answer to Q2 is yes, is OM3 or OM4 my best choice for re-usability in 10G and lower cost?

(Q4) If the answer to Q2 is no, what do you recommend?

[Joseph W. Doherty]

#1 Generally lower distance optical modules cost less, sometimes much, much, much less. As to the cost of the cabling, the big expense there is often the installation. The latter being so, it's often a good idea to install the best media for your current and possible future needs.

Sorry, didn't find the MGBSX1 listed on you referenced link's datasheet.(?)

[aenagy]

Joseph W. Doherty:

For very short distance (no more than 3m/10ft, this is a home lab) I should be focusing on the minimizing the cost of the modules vs. cabling to keep the total cost down?

The link for the "MGBSX1" is below the table in round brackets.

[Joseph W. Doherty]

Oops, I missed you had two references and that the MGBSX1 was in the first while I had only looked at the second.

In any case, the MGBSX1 is gig while the SFP-10G-SR is 10g, so they won't work together (regardless of cable).

[aenagy]

Joseph W. Doherty:

So then there is no way to mix 1G and 10G, i.e. 10G is not backwards compatible like with the older 10/100/1000M? I just want to make sure I'm crystal clear on that point.

Assuming that the answer to the above question is 'correct' it now becomes a question of will the MGBSX1 work with the GLC-T (https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/gigabit-ethernet-gbic-sfp-modules/datasheet-c78-366584.html)?

[Seb Rupik]

Hi there,

You can connect a 1G SFP to a 10G SFP+ module, providing the speed has been set to 1000. You cannot put a SFP module in a SFP+ slot and vice versa.

As for whether a MGBSX1 will work with a GLC-T, they will not. They use different transmission media, ie fibre and UTP.

If you want a really short 10G run, have you considered Twinax cables? This only go to a maximum of 10 metres and a comparatively extremely cheap!

cheers,

Seb.

[Joseph W. Doherty]

"So then there is no way to mix 1G and 10G, i.e. 10G is not backwards compatible like with the older 10/100/1000M? I just want to make sure I'm crystal clear on that point."

SFP+ ports will support SFPs, gig, or 10g. As far as I know, the 10g fiber modules will not operate at gig, so you cannot mix a gig and 10g module on the same fiber link. (NB: this, I think, is contrary to what Seb writes. So, I may be mistaken. Again, the SFP+ port will support either the gig or 10g SFP, but I don't recall 10g fiber SFPs allowing themselves to be configured to run at gig. Perhaps Seb will confirm he's run a 10g fiber SFP at gig.)

The 3x speed you mention is copper ports. BTW, there's now mgig copper ports that support gig, 2.5, 5 and 10 gig.

As Seb also described, the GLC-T is for copper while the MGBSX1 is for fiber, and you cannot intermix the two on the same link.

[Seb Rupik]

Not sure what I was on this morning! You can put a SFP module in a SFP+ slot providing you set the speed to 1000. SFP modules can be used in SFP+ slots but not vice versa. geez! 

^^^ what @Joseph W. Doherty said :)

[aenagy]

Quoting from my first post in this thread:

"Because this is a home lab cost and distance are major consideration. The limitation is the SG300-20 and available SFP modules which can be summarized as..."

(Q1) Of the four, actually eight, SFP modules available for the SG300 I had assumed that the "MGBSX1" would be the cheapest. Is this a correct assumption?

(Q2) On the C3750G48TS side I could use a "GLC-SX-MMD" (https://www.cisco.com/c/en/us/products/collateral/interfaces-modules/gigabit-ethernet-gbic-sfp-modules/datasheet-c78-366584.html) to match the "MGBSX1". Is this a correct assumption?

Don't ask me where the idea to use the "GLC-T" came from. Even I know you can't mix copper and optical. Sheesh.

(Q3) The real question is: is there a 10 Gbps module that I can use on the C3750G48TS that will play nice with the MGBSX1 at the other end? The reason for asking is if/when I get rid of the C3750G48TS and replace it with 10G hardware it would be nice to re-use the module.

[Joseph W. Doherty]

Ah, there was only one 3750G model that provided a (single) 10g port. Unless you have that model, which is rather rare, the 3750G only supports up to gig interfaces. (NB: the 3750E and 3750-X models better supported 10g.)