cheme is the IEEE 802.1Q on attributes of the packet, such as CoS priority. A ser- standard, which uses four bytes to augment the layer-2 vice quality is then negotiated. Examples of QoS are header. IEEE 802.1Q defines the open standard for CBWFQ (Class-Based Weighted Fair Queuing), RSVP VLAN tagging. Two bytes house twelve bits used to tag (Resource Reservation Protocol-RFC 2205), MPLS each frame with a VLAN identification number. The (Multi Protocol Label Switching-RFC 1117 and IEEE 802. 1p standard uses three of the remaining bits in others). the 802.1Q header to assign one of eight different classes CoS, or tagging, is totally ineffective in the absence of of service. IEEE 802.1Q are OSI layer-2 solutions and QoS because it can only mark data. QoS relies on tags or work on frames. filters to give priority to data streams. VLANs UDP ports VLANs provide limited security and create smaller One prioritization scheme assigns priority based on the broadcast domains through software by creating virtu- UDP (User Datagram Protocol) port numbers used by ally separated subnets. Broadcasts are a natural occur- the voice packets. This scheme allows the use of network rence in data networks from protocols used by PCs, equipment to prioritize all packets from a port range. servers, switches, routers, NOS, etc. Creating a sepa- UDP is used to transport voice through the LAN be- rate VLAN for voice reduces the amount of broadcast cause, unlike TCP, it is not connection based. Because of traffic (and unicast traffic on a shared LAN) the tele- the human ear's sensitivity to delay, it is better to drop phone will receive. Separate VLANs result in more packets rather than retransmit voice in a real-time envi- effective bandwidth utilization and reduce the pro- ronment, SO a connectionless protocol is preferable to cessor burden on the IP telephones and PCs by freeing a connection-based protocol. them from having to analyze irrelevant broadcast VoIP devices and servers can define a port range for packets. VLANs, a layer-2 feature,