User's Manual

Horizon Compact Plus Release 1.0.1 Wireless Ethernet Product User Manual – Volume 2
14.0 Rapid Link Shutdown (RLS)
Networks containing alternate or redundant routing paths will typically rely on protocols such as Rapid
Spanning Tree Protocol (RSTP) to invoke a reroute when communications to the far end unit fail or
experience high data error rates. The protocols are implemented on the Ethernet switch and rely on
polling or messaging to determine that communications to the far end has been disrupted. Although
very effective, these protocols can result in slow reaction times to determine link issues. It is desirable
to inform a switch or router of a network issue in the quickest manner possible. The Horizon Compact
Plus system provides the Rapid Link Shutdown feature for this purpose. Notification to the switch or
router is provided by shutting down the Ethernet ports connecting the Horizon Compact Plus systems to
the network. The Ethernet ports at both ends of the link are shut down. The Ethernet switch
immediately recognizes the loss of Ethernet connection and invokes its alternate path algorithm.
The default setting for RLS is OFF, meaning that the Ethernet port will remain connected during failure
conditions.
Notes:
1. RLS is not compatible with the Horizon Compact Plus redundancy* option and should NOT be
enabled when the redundancy* option is employed.
2. RLS cannot be invoked when the x2 enhanced throughput feature is enabled.
3. RLS cannot be invoked if Hitless Automatic Adaptive Modulation (HAAM) is enabled, or if 1+1
Redundancy* is enabled.
4. RLS should be disabled during link alignment to prevent the condition where a link goes in and
out of synchronization resulting in the RLS being invoked and released causing loss of Ethernet
management to the systems.
5. A disconnected Ethernet cable at one end of the link will trigger an RLS event and will result in
the Ethernet port on the other end being shut down if RLS is enabled.
* The Redundancy feature and any related redundancy commands are not supported in this
release.
14.1 Determination of Error Rates on Horizon Compact Plus Systems
Horizon Compact Plus systems employ forward error correction to compensate for and correct errors
occurring over the RF link. Once these errors are corrected, the user data can flow error-free. The post-
correction data error rate is reported as "Rx Block Receive Errors" within the Horizon Compact Plus,
accessible through traffic statistics in CLI or through the Performance web page. Rx Block Error Rate is
also available and is reported in scientific notation.
The Horizon Compact Plus systems communicate with each other via “Rx Blocks” at all times even if
there is no Ethernet traffic. The Rx Blocks are transmitted at a fixed rate and therefore a Rx Block error
rate is also available. The incoming Ethernet data stream is treated as a bit stream and sub-divided into
Rx Blocks for transmission over the RF link. Rx Blocks are continuously transmitted to the far end
modem regardless of whether or not Ethernet traffic exists. The modems transmit approximately 59,000
blocks per second on a 100 Mbps link. In order to determine a Rx Block error rate of 1x10e-6 there
would have to be a minimum of 1 million Rx Blocks transmitted. At 59,000 blocks per second, it would
take 16.8 seconds to transmit 1 million blocks.
Horizon enhancements to the DragonWave RLS functionality consist of:
The fade monitor (“soft failure” mode) analyzes the Rx Block error rate over time increments.
RLS will trigger when the user-configurable error rate threshold is exceeded. The sample time
parameter for both “break” (“break” relates to the shutting down of the link) and “make” (“make”
relates to the re-establishment of the link) can be configured independently.