Specifications

Watson Ethernet
Operating Manual
Watson-Ethernet-Manual.doc
Version 3.3-01
3-18
Revision: 2010-01-20
 Root port determination: each non-root bridge designates one root port. The
root port is the port through which this non-root bridge communicates with the
root bridge.
The root port is the port on the non-root bridge with the lowest path cost
(measured as sum the costs of all paths traversed to the root) to the root
bridge. The root port is in Forwarding state.
 Designated port determination: for each LAN segment (collision domain) the
RSTP configures one Designated port. The Designated port is the port on
this segment that has the lowest path cost to the root bridge. If more than
one port in the segment have the same path cost, the port of the bridge with
the lowest bridge ID is selected as a Designated port.
Designated ports are set to Forwarding state, all other ports are in Blocking
state.
Edge Ports
Ports which are known to be at the edge of the network i. e. not connected to
any other bridge can be configured as edge ports. Edge ports will immediately
transition into forwarding state since there is no possibility of it participating in a
loop.
Note that configuring a non-edge port as edge port might create loops in the
network. Any port configured as edge port will automatically revert to non-edge
configuration if a BPDU is received on this port.
Point-to-point ports
Ports which connect to exactly one other bridge (no shared media) can be confi-
gured as point-to-point ports. Point-to-point ports can signal to the neighboring
bridge their desire to be Designated and Forwarding. Upon explicit acknowled-
gement from the neighboring bridge these ports can transition directly Into for-
warding state without waiting for a timer expiry.
Path cost
Path cost is the total cost of transmitting a frame on to a LAN through that port to
the root bridge. This is the sum of the costs of each LAN segment or link along
the path.
Cost values are configured according to the bandwidth of the link. The slower the
media, the higher the cost.
Recommended cost values are:
Link Speed
Recommended Cost
Recommended Cost Range
1 Mbps
20'000'000
2'000'000 – 200'000'000
2 Mbps
10'000'000
1'000'000 – 100'000'000
4 Mbps
5'000'000
500'000 – 50'000'000
8 Mbps
2'500'000
250'000 – 25'000'000
10 Mbps
2'000'000
200'000 – 20'000'000
100 Mbps
200'000
20'000 – 2'000'000
Table 3-6: Recommended port cost values