CWDM Questions

[Joseph Lombardo]

I am trying to determine the best way to link 7 sites to our central site over a fiber ring.  The county I work for is installing a fiber ring to connect various offices and they will bring fiber to 7 of my 16 sites.  Eventually all 16 sites will be connected to this ring but current funding will only allow 7.  The sites are relatively close to the central site the furthest at 50km.  The sites are currently linked to the central site via point to point carrier Ethernet circuits.

The county only gave me 6 pairs of SM fiber at my central site.  I figure if I used CWDM I can use one pair of SMF to go clockwise around the ring and another pair of SMF to go counter clockwise.  So my setup would look something like this...

Central Site

Switch connected to

CWDM-SFP-1470 through 1590 connected to

CWDM-MUX8A connected to

SMF pair to first site

First Site

SMF pair from central

CWDM-OADM1-1470

CWDM-SFP-1470

Switch

CWDM-SFP-1470

CWDM-OADM1-1470

SMF pair to next site

And so on through site 7.  Then the SMF pair would come back to the central site to another CWDM-MUX8a and back into the switch stack via the SWDM SFPs.

Does this architecture sound like it would work?

The remote site switches are 2960.  Will the CWDM SFP work with this switch?

I have never built a long range optical network before so any help or suggestions would be appreciated.

Thank you

Joe

[Tom Randstrom · Accepted solution]

Joe,

This would be a nice solution; the actual fiber route length(s) will determine if this is feasible.  The CWDM optics may not have the optical budget, without regeneration, to reach around a 50km ring network. 

SWAG Estimate (assuming protected path)

CWDM SFP Optical Reach = ~29 dB

minus

50km fiber = 12.5db/loss (assuming 0.25dB per km)

MUX8A (drop loss) = 2.2dB

1 CH OADM (thru Loss) = 2.5dB x 6sites = 15dB

1 CH OADM – Drop Loss = 1.8dB

End-of-Life margin = 3dB

29db – (2.2 + 12.5 + 15 + 1.8 + 3) = -5.5dB… The network would not have enough optical signal for the furthest sites.

There are ways to work around this issue. 

1) You could use a 2^nd pair of fibers and split the sites, having fewer OADMs per fiber pair; reducing your filter loss per ring. 

2) If you don’t need 1Gbps to each site, you could share a wavelength across 2/3/4/sites: allowing the optical signals to be regenerated at intermediate sites.

3) I am sure there are plenty of other possible solutions.

The remote site switches are 2960.  Will the CWDM SFP work with this switch?

Yes, the CWDM SFPs are compatible with the 2960. 

I have never built a long range optical network before so any help or suggestions would be appreciated.

You may want to discuss your network plans with an optical networking specialist to nail down your exact requirements (today and looking to higher speed upgrades in the future).

Hope this helps!

Tom

[Joseph Lombardo]

I forgot to calculate the loss for the OADMs.  So my numbers were off a bit.  I am still in the design phase so my next step is to talk to a consultant.  I wanted to get my head around the technology so that I at least have some idea what I am talking about.

Thanks for the help

Joe

[taelon_x7]

If you have the funding, since you are going to be connecting all 16 sites eventually, I would go with a DWDM solution