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Occasional Contributor
Posts: 16
Registered: ‎02-25-2011

BB credits on ISL

Ihave two questions regarding ISL and BB credits:

1. Can I manually set BB credits for E_port?

AFAIK It's possible for F_ports.

2.  The following scenario: Few ISL's set on 2Gbps (DWDM limitation). Length of fiber is approx. 7km.

On the Web Tools Port in L0 mode shows 5km and 26/26 buffers Needed/Allocated. I changed it to LE mode and got 10km and 16/16 buffers Needed /Allocated!

I don't care about the distance since it is probably not real (measured) value. I worry about number of buffers - Why in LE mode number of buffers is smaller? Rule of thumb says you need more buffers on longer line.

Should I use L0 mode or LE mode???

Hint: I don't have Extended Fabrics license, so I cannot use other modes.

Regards

--

Radoslaw Skorupka

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: BB credits on ISL

1-Set the distance mode to LS with portcfglongdistance .

2-

an L0 mode port has buffers by default for 20 full size frames.

an LE mode port assigns 10 buffer credits for a 2G ISL.

Those buffer credits assume full size frames, thus an payload of 2112 bytes per frame.

If your payload is, say half of the maximum, you'll need twice as much credits.

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: BB credits on ISL

Oh in addition to my previous post.

You're using *WDM. If you're wdm solution actively negotiate credits for the wdm link, you only need enough credit configured to span the distance to your wdm equipment.

Occasional Contributor
Posts: 16
Registered: ‎02-25-2011

Re: BB credits on ISL

Well, I don't know My DWDM is Adva FSP 2000, 2Gbps cards named "WCM-PLR". I thought that such device is completely transparent to the protocol and does not make any negotiations, including BB credits.

In addition to you previous response - I cannot use neither LS, nor LD mode, because I don't have license. My only choice is L0 or LE. For distance below 10km it should be sufficient, but I'm worrying about number of BB_credits which is smaller in case of LE mode - IT DOESN'T MAKE ANY SENSE.

Regards

Radoslaw Skorupka

Valued Contributor
Posts: 931
Registered: ‎12-30-2009

Re: BB credits on ISL

Well, I don't know My DWDM is Adva FSP 2000, 2Gbps cards named  "WCM-PLR". I thought that such device is completely transparent to the  protocol and does not make any negotiations, including BB credits.

In don't know either and I'm not saying you wdm equip. actively participates. I'm only saying should it participate you only need the credits te reach your wdm equipment and not the whole distance.

With regards to the credits thats just how it works.

Default ports get 20 credits for being in L0, it doesn't matter wheter they are F,E, or L ports.

When in LE (or LD/LS) mode you get/set enough credits to have enough performance for the desired distance with maximum payload per frame.

Having just enough to make the distance allows the rest of the credits to be used elsewhere if desired/needed.

As far as I know of the portcfglongdistance command only effects how and howmuch credits are being reserved.

So when LE modes gives you less performance over L0 mode, go for the latter.

On a side note, ask your wdm supplier if the equipment is active or passive.

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