Ethernet automatic protection switching (EAPS)
The Ethernet Automatic Protection Switching (EAPS) redundancy method described in RFC 3619 was developed by Extreme Networks and supports the availability of Ethernet ring topologies in city networks( MAN) or in campus areas.
EAPS technology is a fault-tolerant topology that minimizes ring topology recovery time in the event of a fault. EAPS is a layer-2 redundancy protocol, similar to the spanning tree protocol, but with a much shorter interaction time. If the ring is interrupted, an error reaction takes place in a maximum of 250 ms and initialization with automatic switchover to the replacement path in a further 100 ms. Other comparable concepts are Ethernet Protection Switching Ring( EPSR) from Allied Telesis, Rapid Ring Protection Protocol( RRPP) from Huawei, Resilient Ethernet Protocol (REP) from Cisco and the ZTE Ethernet Switch Ring (ZESR).
Conceptually, EAPS works with EAPS domains, where each EAPS domain consists of a master node, which must be EAPS-capable, and additional nodes, the transit nodes, which do not have to be EAPS-capable. Each node is connected to the ring with two ports. One port is the primary port, the other is the secondary port. In normal operation, the master node blocks its secondary port for all data packetsexcept EAPS check packets. This prevents looping in the ring. If the master node detects a ring interruption, the secondary port is released and the data packets reach the ring via both ports.
The master detects ring interruptions by no longer receiving a response to the check packets or by a trap message from a transit node.
The EAPS header is inserted in the Ethernet frame after the MAC header.