ZyXEL Communications ZyAIR G-3000, User Manual

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ZyAIR G-3000 User’s Guide
Chapter 5 Wireless Configuration and Roaming 60
A large Fragmentation Threshold is recommended for networks not prone to interference
while you should set a smaller threshold for busy networks or networks that are prone to
interference.
If the Fragmentation Threshold value is smaller than the RTS/CTS value (see previously)
you set then the RTS (Request To Send)/CTS (Clear to Send) handshake will never occur as
data frames will be fragmented before they reach
RTS/CTS size.
5.3 Spanning Tree Protocol (STP)
STP detects and breaks network loops and provides backup links between switches, bridges or
routers. It allows a bridge to interact with other STP-compliant bridges in your network to
ensure that only one route exists between any two stations on the network.
5.3.1 Rapid STP
The ZyAIR uses IEEE 802.1w RSTP (Rapid Spanning Tree Protocol) that allow faster
convergence of the spanning tree (while also being backwards compatible with STP-only
aware bridges). Using RSTP topology change information does not have to propagate to the
root bridge and unwanted learned addresses are flushed from the filtering database. In RSTP,
the port states are Discarding, Learning, and Forwarding.
5.3.2 STP Terminology
The root bridge is the base of the spanning tree; it is the bridge with the lowest identifier value
(MAC address).
Path cost is the cost of transmitting a frame onto a LAN through that port. It is assigned
according to the speed of the link to which a port is attached. The slower the media, the higher
the cost - see the next table.
On each bridge, the root port is the port through which this bridge communicates with the root.
It is the port on this switch with the lowest path cost to the root (the root path cost). If there is
no root port, then this bridge has been accepted as the root bridge of the spanning tree network.
Table 10 STP Path Costs
LINK SPEED
RECOMMENDED
VALUE RECOMMENDED
RANGE ALLOWED
RANGE
Path Cost 4Mbps 250 100 to 1000 1 to 65535
Path Cost 10Mbps 100 50 to 600 1 to 65535
Path Cost 16Mbps 62 40 to 400 1 to 65535
Path Cost 100Mbps 19 10 to 60 1 to 65535
Path Cost 1Gbps 4 3 to 10 1 to 65535
Path Cost 10Gbps 2 1 to 5 1 to 65535