Need Explanation!

Unanswered Question
markmarek Mon, 06/07/2010 - 06:27

"3)what if the line card is 16 Ports,Total 160 GB so how is that?"

It depends on the asics. What kind card is it?

dominic.caron Mon, 06/07/2010 - 06:35


I think you are refering to a WS-X6716-10G-3C linecard in a 6500 or a 7600 chassis. In that case, that card comes with a DFC (distributed forwarding card).  The ports on the WS-X6716-10G-3C are non-blocking with each other. If the trafic need to be switched to a port on another card, you have a 40 Gbps bottleneck going out of your card and in to the other one.

Jon Marshall Mon, 06/07/2010 - 08:25


The 6509 with a supervisor 720 is capable of providing 40Gbps per slot ie.

9 slots x 40 Gbps = 360Gbps. You then double the figure because the connections are full duplex (bit of marketing really) to get 2 x 360Gbps = 720Gbps.

This 720Gbps is often referred to as the backplane speed or switch fabric although switch fabric includes other things.

Each slot can therefore provide 40Gbps to whatever module is in that slot. If you have a WS-X6748-GE-TX module for example this can support up to 48 10/100/1000 connections ie. 48 x 1Gbps = 48Gbps. The connection to the switch backplane is 40Gbps so if all 48 ports were simultaneously running at 1Gbps you would have oversubscription ie. 40Gbps backplane connection but 48Gbps from the module. It is however highly unlikely you would get all 48 ports producing 1Gbps of traffic each simultaneously. Note that if you wanted to make sure you did not get any oversubscription then with the 6748 module you could connect only 40 devices.

As Dominic noted, this only applies to traffic that is not local to the module.

So the most you can get with a supervisor 720 is a maximum of 40Gbps to the switch backplane. If you insert a module than can produce more than that you have to accept that there may be oversubscription between the module and the switch backplane. It is up to you to decide how likely that oversubscription is and whether it is acceptable or not.


jennyjohn Mon, 06/07/2010 - 22:26

A 16port 10Gig card will have an oversubscription of 4:1 as the backplane will still support only 40Gig per slot.

The 16 ports are grouped into 4 port groups, i.e., each group with 4 ports. In performance mode, the first port in each group should be used to get the complete 10Gig per port.

For more details refer:

The same goes for the 8 port 10GE card also, it is oversubscribed by a factor of 2:1


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