vlans and subnets 2

[just1moretime]

When setting up a ethernet switch for voip and data.
Why would I need to make seperate vlans for each subnet,
ie-voice and data. Because tcpip will not allow the to
separate subnets to send data each other. With different subnets is there any need to worry about broadcast
collisions? Thank you.

 

[burtsbees]

Voice needs a certain amount of dedicated bandwidth, and if voice and data are in the same vlan, and someone downloads some 4GB movie from a bit torrent, then there goes all the VoIP quality. The best way to handle this is QuS and separate vlans for voice and data. Each subnet would separate broadcast domains, but the broadcasts can be forwarded if you so choose (like DHCP, for example), via the "ip-helper" command, or similar commands. Another purpose of VLANs is for broadcast control.

Burt

 

[jimbopalmer]

VLANs certainly make an easy way to do QoS. 802.1p is simple and 'free' with 802.1Q VLANs. 802.1p is often implemented so that ALL packets of one priority are forwarded, before any packets of a lower priority are even considered.

Jitter or variability in latency is a concern for VoIP, minimizing extraneous traffic helps jitter, a VLAN can help exclude that extraneous traffic as well as prioritizing it lower.

It can simplify your router's rules to know that all traffic on one VLAN (or subnet) has a higher priority, rather than inspecting each packet to recognize it's protocol.

(VoIP quality is only really possible on a full duplex, switched LAN, so no collisions are going to happen)

I tried to remain child-like, all I acheived was childish.