287
User Priority
V
VLAN
VLAN ID
Voice VLAN
UDP is an alternative to the Transmission Control Protocol (TCP) that uses the
Internet Protocol (IP). Unlike TCP, UDP does not provide the service of dividing a
message into packet datagrams, and UDP doesn't provide reassembling and
sequencing of the packets. This means that the application program that uses UDP
must be able to make sure that the entire message has arrived and is in the right
order. Network applications that want to save processing time because they have
very small data units to exchange may prefer UDP to TCP.
UDP provides two services not provided by the IP layer. It provides port numbers to
help distinguish different user requests and, optionally, a checksum capability to
verify that the data arrived intact.
Common network applications that use UDP include the Domain Name System
(DNS), streaming media applications such as IPTV, Voice over IP (VoIP), and Trivial
File Transfer Protocol (TFTP).
User Priority is a 3-bit field storing the priority level for the 802.1Q frame. It is also
known as PCP.
Virtual LAN is a method to restrict communication between switch ports. VLANs can
be used for the following applications:
VLAN unaware switching: This is the default configuration. All ports are VLAN
unaware with Port VLAN ID 1 and members of VLAN 1. This means that MAC
addresses are learned in VLAN 1, and the switch does not remove or insert VLAN
tags.
VLAN aware switching: This is based on the IEEE 802.1Q standard. All ports are VLAN
aware. Ports connected to VLAN aware switches are members of multiple VLANs and
transmit tagged frames. Other ports are members of one VLAN, set up with this Port
VLAN ID, and transmit untagged frames.
Provider switching: This is also known as Q-in-Q switching. Ports connected to
subscribers are VLAN unaware, members of one VLAN, and set up with this unique
Port VLAN ID. Ports connected to the service provider are VLAN aware, members of
multiple VLANs, and set up to tag all frames. Untagged frames received on a
subscriber port are forwarded to the provider port with a single VLAN tag. Tagged
frames received on a subscriber port are forwarded to the provider port with a
double VLAN tag.
VLAN ID is a 12-bit field specifying the VLAN to which the frame belongs.
Voice VLAN is VLAN configured specially for voice traffic. By adding the ports with
voice devices attached to voice VLAN, we can perform QoS-related configuration for
voice data, ensuring the transmission priority of voice traffic and voice quality.