GE T1000, Техническое руководство

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GE Reason Switches Chapter 4
– Functions
REASON SWITCHES-TM-EN-3 69
Figure 29: CIST roots an MSTP regions and legacy RSTP LAN
The Common Internal Spanning Tree (CIST) root bridge is the root of the internal
spanning tree, which is limited to each region. The regional root is the main root of all
regions interconnected.
In a macroscopic view, all regions in the MSTP protocol behave as bridges in a
common Spanning Tree LAN. Thus, RSTP convergence will be easier as internal loops
created at the regions will be solved independently. Besides, a change in the
topology inside a region will not affect all bridges, as it will be limited to its own
region. The figure below shows how RSTP and STP bridges will behave when
connected to regions created by the MSTP protocol.
Figure 30: MSTP regions behavior using RSTP protocol
6.5 UltraRSTP
UltraRSTP is a GE approach to improve the standard RSTP fault recovery time
performance and reduce packet loss during faults in the network. With UltraRSTP
fault recovery times of less than 5ms per hop are achieved, while maintaining
compatibility with standard RSTP for interoperability with commercial switches.
To improve the recovery performance, Reason switches implement a hardware
interruption to ensure the highest priority in reconfiguring RSTP. As such, all switches
in the ring must support UltraRSTP in order to attain this recovery time. All Reason
Ethernet Switches support UltraRSTP natively and no extra configuration other than
the standard RSTP is needed.
UltraRSTP Performance Example:
For a network comprised of 20 Reason Ethernet switches (i.e. sw1 – sw20) in a ring
topology we can expect better than 5ms/hop fault recovery performance: Expected
fault recovery time < 100ms
Testing performed with Reason Ethernet switches with UltraRSTP technology using
an industry standard network analyzer revealed:
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