gross data rate on a 10GBit fiber

janlausch · ‎07-15-2008

Hi guys,

Just some question that might sound stupid at first:

What would about be the possible gross data rate on a 10GBit fiber link (e.g. 3750 uplink to a 65xx via singlemode fiber)?

As far as I understand, all of the 10gig fiber optic standards do have in common that they introduce an additional sublayer (XGMII) between the MAC-layer and the medium and on the other hand get rid of CSMA/CD as obviously collision detection is no longer necessary. All higher layers are simply passed through. The question is now how this affects the percentage of usable data rate compared to standard 1.000BASE-T

That would imply that all losses on the higher layers would have to be considered with about the same % like in a standard 100/1.000MBit connection.

This would mean that eg. on the IP-layer I could assume a gross data rate of ~80% of the 10GBit net rate?

Are these thoughts correct?

I know that that kind of a calculation is a good guess at best and that there are so many factors to consider that I can't even begin to mention them here, but I hope to get just a feeling for the whole thing.

Any ideas about this?

Giuseppe Larosa · ‎07-16-2008

Hello,

modulation can use more BW but this is done using a line rate greater then the nominal speed rate. This happens also with Gigabit ethernet actual line rate is bigger because it codes 4 bits on 5 line bits.

10 Gbps use to carry 8 bits in 10 line bits on the line providing the same overhead.

In a ethernet network you need to take in account the interframe gap:

even in a full duplex link two frames must be separated by a silence interval that is rouoghly 20.1 or 20.2 bytes

At the beginning of a frame there is a preamble equivalent to 8 bytes in order to allow the receiver to synchronize.

Ethernet header is 6+6+2 = 14 bytes

At the end of the frame there is the 4 byte FCS.

In our calculations usually we add 38 bytes to the IP size to calculate the layer 1 bandwidth.

In this way you can find the maximum frame rate with the shortest frames that are 64 bytes.

Be aware that for 10GE there are a LAN PHY and a WAN PHY that are different at the physical layer.

The values I have suggested above is for LAN PHY, WAN PHY is framed.

Hope to help

Giuseppe