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9033630 Product Overview 11
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.
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.
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.
ELS100-48tx2m.book Page 11 Thursday, November 16, 2000 4:59 PM