PLANET WGSW-48000 - Manual (Page 292)

User’s Manual of WGSW-48000
292
UDP is an acronym for User Datagram Protocol. It is a communications protocol that uses the Internet Protocol (IP) to
exchange the messages between computers.
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
User Priority is a 3-bit field storing the priority level for the 802.1Q frame.
V
VLAN
Virtual LAN. 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
VLAN ID is a 12-bit field specifying the VLAN to which the frame belongs.