Some doubts about ip telephony..

[ciscolover]

Hi all ¡¡

I'm studing about ip telephony and i have some doubts.

"The voice packets must be carried over a unique voice VLAN (known as the voice VLAN ID or VVID) or over the regular data VLAN (known as the native VLAN or the port VLAN ID, PVID)."

The regular data know as the native VLAN-->For me the native vlan is the vlan used by all the switch ports by default(normally vlan1). Also is the vlan they belong the untagged paquets carrieds in the trunk 802.1q links.

Suppose i want to use one vlan to data traffic and one vlan to telephony and i configure a trunk port between switch and ip phone.

What happens If i not use de native vlan for data vlan??? if i  use another vlan, for example vlan 2...¿Why it names it native vlan? I'm obliged to use native vlan to data vlan?? I can't use another vlan?

This is my first question...

Best regards and thanks

[dijohn]

In the VOIP world currently, we use the "minitrunk" a trunk which carries just two vlans (DATA and VOICE) on a switchport connected to a phone

You can configure an access port with an attached Cisco IP Phone to use  one VLAN for voice traffic and another VLAN for data traffic from a  device attached to the phone. You can configure access ports on the  switch to send Cisco Discovery Protocol (CDP) packets that instruct an  attached Cisco IP Phone to send voice traffic to the switch in any of  these ways:

•In the voice VLAN tagged with a Layer 2 CoS priority value

•In the access VLAN tagged with a Layer 2 CoS priority value

•In the access VLAN, untagged (no Layer 2 CoS priority value)

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface gigabitethernet0/1 

Switch(config-if)# switchport voice vlan 100
Switch(config-if)# swithcport access vlan 200

Switch(config-if)# end 

This config will instruct the phone to tag all the voice RTP packets with VLAN Tag 100. All the data packets from the PC will go to the DATA VLAN.

Hope this clears things out for you. 

Here's a doc 
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_20_se/configuration/guide/swvoip.html#wp1050913

[ciscolover]

Hi im not sure... I have read the doc.. I have doubts.

I have a doubts about the modes to configure the link between the switch and the ip phone:I put the questions :For example:

dot1p—Configure the Cisco IP  Phone to use 802.1p priority tagging for voice traffic and to use the  default native VLAN (VLAN 0) to carry all traffic.

• To use the default native vlan (vlan 0) ?¿¿?¿? native vlan its vlan 1 Why it talks about vlan 0???This is not native vlan...

[cadet alain · Accepted solution]

hi,

if your switch is a fairly recent one, 2950 or newer then just do what dijohn explained.

configure your switchport as access and put one vlan for data and another for voice.

All this stuff about native vs data is just lingo stuff.

what is important is that dat traffic is untagged and voice traffic is tagged doing this way.

But if you have older switch you'll have to trunk to your phone and use 2 VLANs: one for data and put it as native and the other for voice.

Regards.

Alain.

[ciscolover]

Hi ¡¡¡

Ok i understand this but.. I dont understand why it talks about native vlan 0 '¿?¿

[dijohn · Accepted solution]

From my understanding,

A value of 0 means that the frame does not belong to any VLAN; in this

case the 802.1Q tag specifies only a priority and is referred to as a

priority tag.

When using dot1p, you are just using dot1q tag for dot1p priority bits.

That's marking the Voice packets from the IP Phone with COS 5.

So, When you use dot1p, PC frames go untagged, whereas the IP Phone

frames go tagged with VLAN 0 with the correct QOS Tag on Layer 2 COS.

I hope this clears things up for you

PS: Rate if the posts are helpful

[ciscolover]

Thaks all... I understand better now the types of links between ip phones and switches.