voice and data vlan

Answered Question
Oct 25th, 2007
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hi

i was wondering if there is any differance between voice and data vlan for a switch on the frame stracture perhaps or anything else.

is it nessesary to create voice vlan for an ip phone to play or just a data vlan?


thanks

Correct Answer by AJAZ NAWAZ about 9 years 8 months ago

Bkoum,


The answer to your qtn is 'Yes'. There is a difference in the frame structure between the traffic carried on data and voice vlan's. The first of those differences is that frames sent to/from the switch/phone on the data vlan are dot1q tagged. Frames sent to/from the switch/phone on the voice vlan are untagged. Contrary to common belief the connection between the switch <> phone is not a 'Trunk'. As such, only one set of frames require tagging and in this case that happens to be data. This makes sense since dot1q tagged frames are larger than untagged, therefore, less processing required before forwarding takes place. Shifting voice packets is most cases No.1 priority.


The other difference, and one why using the voice vlan is recommended is to do with QoS (or CoS) at layer2. For more information pertaining to this I would suggest you take 5min to go through the following document:


<http://www.cisco.com/en/US/docs/switches/metro/catalyst3750m/software/release/12.2_25_ey/configuration/guide/swvoip.html>


Once you have digested the information set out in the document following the link, you will appreciate I'm sure that using data vlan for voice traffic is highly discouraged.


hth,

Ajaz


pls rate this post if it helped.

Correct Answer by knudsen-s about 9 years 8 months ago

The link between the phone and the switch is using a trunk, and the voice vlan is tagged and the data vlan i native vlan (not tagged). It is best practice to separate voice and data in 2 vlans, but is not a requrement. Is you do not have a PC behind the phone is it not a requrement to have this vlan , but for the quality of the conversation is is always best to separate this in 2 vlans.


If you realy do not whant to have a voice vlan and a data vlan you can run both on the data vlan. If you have the ip address og the ccm in the dhcp og static in the phone on the data vlan it wil work. Jusk config the switchport as an access port and have the dhcp option 150 to the ccm.


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Correct Answer
knudsen-s Thu, 10/25/2007 - 13:03
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The link between the phone and the switch is using a trunk, and the voice vlan is tagged and the data vlan i native vlan (not tagged). It is best practice to separate voice and data in 2 vlans, but is not a requrement. Is you do not have a PC behind the phone is it not a requrement to have this vlan , but for the quality of the conversation is is always best to separate this in 2 vlans.


If you realy do not whant to have a voice vlan and a data vlan you can run both on the data vlan. If you have the ip address og the ccm in the dhcp og static in the phone on the data vlan it wil work. Jusk config the switchport as an access port and have the dhcp option 150 to the ccm.


Correct Answer
AJAZ NAWAZ Fri, 10/26/2007 - 01:05
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Bkoum,


The answer to your qtn is 'Yes'. There is a difference in the frame structure between the traffic carried on data and voice vlan's. The first of those differences is that frames sent to/from the switch/phone on the data vlan are dot1q tagged. Frames sent to/from the switch/phone on the voice vlan are untagged. Contrary to common belief the connection between the switch <> phone is not a 'Trunk'. As such, only one set of frames require tagging and in this case that happens to be data. This makes sense since dot1q tagged frames are larger than untagged, therefore, less processing required before forwarding takes place. Shifting voice packets is most cases No.1 priority.


The other difference, and one why using the voice vlan is recommended is to do with QoS (or CoS) at layer2. For more information pertaining to this I would suggest you take 5min to go through the following document:


<http://www.cisco.com/en/US/docs/switches/metro/catalyst3750m/software/release/12.2_25_ey/configuration/guide/swvoip.html>


Once you have digested the information set out in the document following the link, you will appreciate I'm sure that using data vlan for voice traffic is highly discouraged.


hth,

Ajaz


pls rate this post if it helped.

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