AV Design Reference Manual - InfoComm

Chapter 6: Networking
Switches, continued
Virtual Local Area Network (VLAN) Operations
One advanced feature of a network switch is to provide virtual LAN (VLAN) segmentation
without the need to connect a given station, server, or shared peripheral device to a specific
switch port. Assuming all switches on an organizational network provide the same features,
any device can be connected to any switch port.
The VLAN groups various combinations of ports into a common broadcast domain. Devices
in the same VLAN group operate as if they were connected to the same switch and cabling
system, even though each device may be physically connected to a different switch using any
type of approved cabling. If stations need to be relocated, the switch ports to which they are
transferred can be assigned to the same VLANs as their previous ports, making the relocation
transparent from a network traffic point of view.
On a conventional LAN, a single broadcast domain spans all of the hubs and switches as well
as the devices connected to them. This is described as a flat network. Any broadcast frame
issued by a device is delivered to all other devices, regardless of the speed or type of
connection used. The greater the number of devices on a LAN, the greater the number of
broadcasts transmitted. Excessive broadcasts limit the total number of devices on a LAN,
even when all connections are switched.
In most cases, a broadcast does not have to be sent to every device on the organizational
network. For example, a broadcast request for configuration or management data issued by a
station in one department is usually intended for a server in the same department. However, if
the organizational network is made up entirely of hubs and switches, every station and server
in the organization will receive the broadcast.
AVDRM, 1st edition 6-10 © 2006 BICSI ® /InfoComm International ®