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New Member

e1 full-duplex or half duplex ?

Hi all,

I have a (interesting) problem and maybe some of you experts can help me out with.

At present I have 2 sites connected by 3 * E1 links combined in to 1 multilink.

On my 7200 series router the duplex setting are configured default (which I think is full) (ios Version 12.2(13)T3)

My provider tells me that the e1 links are full duplex. However after analyzing the wan link with a net flow analyzer I see that in and out traffic never go over 50 % utilization.

I have confirmed that the bandwidth settings in my net flow analyzer software are correctly set. And I have confirmed the bandwidth settings on my serial interfaces are correctly set.

4 questions.

1) if any where on the point to point link a device is set to half duplex this will result in the link being half ?duplex (effectively) ?

2) Are there any software based tools that can verify the duplex setting of the complete (ip) path?

3) Is the fact that utilization never goes above 50% (in/out) a good indication that the link might be performing on half duplex?

4) what is the default on a Cisco 7200 serial interface full or half duplex (show interface gives me no information in regards to the duplex)

Thanks for your time


Re: e1 full-duplex or half duplex ?


E1 links are by nature full-duplex. Actually there is no such term for E1 Links..

the E1 link will have separate Tx and Rx pairs of wire from the telco. TX signal and Rx signal have separate path end to end.

In your case if the E1 links are bundled in a multilink, then you have observe the traffic utilisation ( netflow) on the multilink only.

And one more point to add, are you having CSU/DSU devices to have the E1 terminated in the routers serial link. If so you can check the E1 channel configuration in the CSU/DSU device to cross verify that you are not using fractional E1..


Re: e1 full-duplex or half duplex ?

The answer to (3) is no, the fact that the utilization never goes above 50% is not a good indication that the link might be performing in half duplex. A half duplex link can easily go over 50% in any particular direction if there is more traffic in one direction than the other - and that is usually the case if you think about, say, web browsing or FTP.

It may depend on how your analyser is analysing the traffic. What is the overall bandwidth figure it is using to base its calculation.

You can usually get a good indication of the bandwidth used from the show int on your router. But this assumes that you actually have enough traffic to go uver the 50%, sustained over the sampling period. Also that the windowing of your TCP sessions etc. will allow such traffic.

I doubt whether this is a half-duplex full-duplex issue - I think there is a more banale explanation. Could you provide some more details of your analysis precedure and results?

Finally, you should be aware that the bandwidth configured on the interface has no impact at all on the throughput through the interface. It only affects things like routing protocol metrics and % load calculations, but not the actual traffic.

Kevin Dorrell


New Member

Re: e1 full-duplex or half duplex ?

Thanks for the reply

At present this is what the show interface look like

Serial3/2 is up, line protocol is up

Hardware is 4ME1-UNBAL

Description: ***** *****************

MTU 1500 bytes, BW 2048 Kbit, DLY 20000 usec,

reliability 255/255, txload 33/255, rxload 67/255

Encapsulation PPP, LCP Open, multilink Open, crc 16, loopback not set

Restart-Delay is 0 secs

There is no information about duplex setting. Is the BW 2048 kbit the actual bandwidth or is it taken from the bandwidth command?

I am evaluating a net flow analyzer called "net flow analyzer 5" I am sure i configured the bandwidth in this tool correctly (3 * 2048kbit). I know (from user experience / performance) this link is almost fully utilized however the net flow analyzer tells me a different story.

During a 10 hour working day it report an average traffic in utilization of 49,93 % and a average out traffic of 24,15%

I would aspect that if I for example copy a 1000mb file over this link that the utilization will go op to a 100 %?

Or am I mistaken and are protocols like http, SMTP and NetBIOS very wan aware these day?s?

Thanks for any help in this matter.

With kind regards,

J Wouter

Re: e1 full-duplex or half duplex ?


The bandwidth that you see in the show interface output, is just the value taken from the Bandwidth commands, it has nothing to do with the actual bandwidth on the link.

1)You can check the actual traffic flow on the link, using "show interface serial X/Y" command to see the actual input/ouput rate during peak hours and cross check with what is reported by the analyser.

2) I believe that the E1s in your setup is getting terminated via the LL modem and connected to the serial interface via v.35 interface. correct me if i'm wrong.

If modems are involved, check the channel settings on the modem and ensure that it is using all the timeslots of the e1. ( Just to be sure )

3) Moreover in your setup, you have mentioned that the serial link are multilinked.

If so, the traffic from the logical multilink interface will be shared across all the serial interface and this might be one reason that at any point, individual serial links are not utilising the full bandwidth.

For testing if possible, you can shut one serial link and observe the utilisation on the other serial link. ( shutting one link in the bundle will not affect the traffic flow ).



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