Serial link, utilization using txload,rxload

[wilson_1234_2]

I have seen several posts on this subject and there is still something I am not sure about.

My understanding is that tx and rx are mutually exclusive and the serial link is full duplex, so if the bandwidth is available you could see this on a satuared link:

txload 255/255 rxload 255/255

But if the provider is giving you a T1 at 1.5 Mbps, would these two values be added together to get the BW being utilized?

Or, does the provider give a full 1.5Mbps up and 1.5Mbps down, so that the below is possible:

txload 240/255 rxload 240/255

[Richard Burts]

The values are not added to get the BW being utilized. You should have full 1.5 up and 1.5 down and txload 240/255 rxload 240/255 should be possible (but certainly not desirable).

HTH

Rick

[John Blakley]

The values that you are referring to would be able to tell you the percentage of the link being used. 255/255 would be 100% utilization, whereas 125/255 would be 49% of the link. As Rick said, this has no correlation to your bandwidth. You could have a 100Mb circuit and these values would still be the same.

HTH,

John

[wilson_1234_2]

Ok suppose I am using SNMP to poll the interfaces and I have the below:

txload 1/255 rxload 255/255

Would this be considered only 50% utilization of a serial interface?

If so, wouldn't this be a little misleading since no more traffic would be able to be sent outbound causing issue with anyone that needed to communicate.

They would be experiencing latency with only 50% utilized link.

Is that correct, or would it be considered 100% utilization?

[John Blakley]

Technically, if you have a T1, you have 1.5Mb up and 1.5Mb down. If you're seeing rxload 255/255, that means you're router is receiving 100% of it's capacity inbound only (1.5Mb). You would still have 100% available to transmit outbound for 1.5Mb. (In your example of txload 1/255)

HTH,
John

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[wilson_1234_2]

So this is considered only 50% utilization?

txload 1/255 rxload 255/255

[John Blakley]

If you want to look at it as a complete circuit, I would say yes, but it's not entirely correct. You're 100% utilized inbound and 1% utilized outbound. If you want to figure it as a whole circuit, you could add the numbers together and then divide by 510:

txload 1/255 rxload 255/255 (1.5Mb circuit)

1 + 255 = 256
255 + 255 = 510

256 / 510 = 50% (There's your 50%) But again, you would be dropping traffic inbound if the link is 100% saturated on the rxload side, and you'd be able to send files if the txload is still low.....I see 50% utilization as half on both, but there are probably others on the board that see it differently as well.


HTH,
John

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[Richard Burts]

I would advocate that attempting to present circuit utilization as a single number is a mis-representation of circuit utilization. Trying to reduce utilization to a single number is an appealing concept, and may seem reasonable until you look into the details. As this thread has made clear utilization upstream and utilization downstream are completely separate capacities. Attempting to represent them in a single number is likely to mis-represent one or both of them.

HTH

Rick