qos simple question about access ports

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Sep 14th, 2006
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Dear all,

I have a question, which is probably very easy to answer. I've setup a network with auto qos enabled. between the switches I have a dot1q trunk. Now I want to connect a switch to an access port (so it works more like a hub), does this effect my qos?

I would like to know, since we are also starting to roll out VoIP.



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mchoo2005 Thu, 09/14/2006 - 22:42
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Your question is rather ambiguous. Connecting a switch to access ports that have auto qos enabled will not affect the QoS configurations themselves. HOWEVER, it can potentially impact the voice traffic if you connect multiple IP phones into the daisy-chained switch.

There are so many variables. How many IP phones are you connected to that daisy-chained switch? Can the switch support VoIP phones properly? How fast is the uplink?

Really, you should avoid this sort of set up. If you have to, a few things you might want to consider, to minimise voice quality issues down the track:

1. Minimise the number of IP Phones connected to the daisy-chained switch

2. Ensure the switch can properly mark and prioritise voice traffic

3. Ensure the switch uplink has at least the same amount of bandwidth as the aggregated bandwidth of all voice traffic from the downstream switch

4. Ensure the switch uplink is configured with the proper QoS config. Auto qos may not be the best one to use on uplinks. You might have to manually configure QoS on these, including reclassify and remarking the packets/frames.

5. If oversubscribing the switch uplinks, you would want to implement proper CAC (Call Admission Control), to deny additional voice calls that can saturate the switch uplinks.


gerard van rij Thu, 09/14/2006 - 23:11
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Dear mchoo2005,

thanks for the reply. just to give an answer. there will be no ip phones connected to this switch which is connected to the access port.

the network running on this is a old decnet system which will only be reached by telnet sessions. so the traffic load will be very low. and only 8 users will use this network.

I've considered to create a separate network, but I don't have enough fibres to be able to make a separate network.

with this extra info, will it effect my qos?



mchoo2005 Sun, 09/17/2006 - 16:56
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Considering you'll only have mostly telnet traffic to the daisy-chained switch, I don't think it'll affect your QoS. Conceptually, QoS is pretty simple really. Just remember the KISS guideline. :)



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