Flow Control
Flow control allows you to manage network traffic during congestion periods and to prevent the loss of packets when port buffer thresholds are exceeded. Flow control also serves to deny access to additional traffic that could add to a congestion condition. The VH-4802 switch supports flow control per the IEEE 802.3x standard. Note that flow control is disabled on all ports by default but can be enabled on a per-port basis by using the console interface menus, the on-board Web agent, or via SNMP. See Appendix B, “Flow Control,” for more information on this feature.
If flow control is desired for one port, it is recommended that it be enabled on all ports. However, note that flow control should not be used if a port is connected to a hub. Also, be aware that when interconnecting high-speed LANs (such as Gigabit Ethernet) and low-speed LANs, flow control can cause traffic from the high-speed LAN to be blocked for all other ports on the switch.
Virtual LANs (VLANs)
VLANs allow you to connect users to a specific LAN segment regardless of their physical location. The VH-4802 switch supports tagged VLANs per the IEEE 802.1Q draft standard. With frame tagging, a short tag is appended to every frame that crosses the network backbone. The tag identifies which VLAN the frame belongs to. See Appendix B, “Virtual LANs,” in the Management Guide for more information.
Class of Service
Class of Service support allows you to assign a higher priority to selected traffic passing through the switch. The VH-4802 switch supports Class of Service attributes per the IEEE 802.1p standard using a priority queuing mechanism. This feature ensures that traffic during congestion periods will not interfere with traffic assigned a higher priority. Traffic assigned a lower priority is subject to discard when memory is in short supply. See Appendix C, “Class of Service,” in the Management Guide for more information.
Port Trunking
Port trunking allows you to combine ports into an aggregate connection between VH-4802 switches. Besides balancing the load across each port in the trunk, the additional ports provide redundancy by taking over the load if a port in the trunk should fail. The VH-4802 allows up to four ports of the same media type to be joined together as a trunk. RJ-45 ports must be selected from pre-determined port groups, and 100Mbps fiber ports must be on the same module, but both 1000Mbps module ports can be combined together. Up to eight port trunks on a single VH-4802 switch can be configured.
