Cisco ONS 15454 SDH - E-Series Spanning Tree (IEEE 802.1 D)

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Cisco ONS 15454 and Cisco ONS 15454 SDH Ethernet Card Software Feature and Configuration Guide, R8.0
Chapter 23 E-Series and G-Series Ethernet Operation
E-Series Spanning Tree (IEEE 802.1D)
Figure 23-16 Priority Queuing Process
The ONS node uses a “leaky bucket” algorithm to establish a weighted priority. A weighted priority, as
opposed to a strict priority, gives high-priority packets greater access to bandwidth, but does not totally
preempt low-priority packets. During periods of network congestion, about 70 percent of bandwidth
goes to the high-priority queue and the remaining 30 percent goes to the low-priority queue. A network
that is too congested will drop packets.
Note IEEE 802.1Q was formerly known as IEEE 802.1P.
Note E-Series cards in port-mapped mode and G-Series cards do not support priority queing (IEEE 802.1Q).
E-Series Spanning Tree (IEEE 802.1D)
The E-Series operates IEEE 802.1D Spanning Tree Protocol (STP). The E-Series card supports common
STPs on a per-circuit basis up to a total of eight STP instances. It does not support per-VLAN STP. In
single-card mode, STP can be disabled or enabled on a per-circuit basis during circuit creation. Disabling
STP will preserve the number of available STP instances.
Data Flow
No priority
ONS node maps a frame
with port-based priority using
a Q-tag.
The receiving ONS node
removes the Q-tag and
forwards the frame.
ONS node uses a Q-tag to
map a frame with priority and
forwards it on.
The receiving ONS node
receives the frame with a
Q-tag and forwards it.
Priority tag
removed
Priority
Priority
Priority
Same
priority
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