Multi-Segment RETHER

Due to electrical signal considerations, multiple Ethernet segments connected by bridges or switches are required to accommodate a large number of PLC nodes. To provide end-to-end network bandwidth guarantees between any pair of nodes in a multi-segment Ethernet environment, RETHER has been extended to operate across switches. Conceptually, a real-time connection applies the single-segment RETHER protocol to reserve on each of the segments on the path from its source to the destination. The per-segment reservations along the way are parts of one logical real-time connection. Consider the network configuration in Figure . Suppose a real-time connection runs from A1 to C1. This connection is broken down into three sub-connections namely A1-Gw1 on Segment 1, Gw1-Gw2 on Segment 2, and Gw2-C1 on Segment 3, where the nodes on the left are the sender and those on the right are the receivers. For a multi-segment real-time connection, each intermediate switch acts as a sender on one segment and a receiver on the other. All Ethernet segments run the single-segment RETHER protocol, with the token cycles on different segments proceeding completely independently of one another. That is, token cycles associated with adjoining segments, although of the same length, are not synchronized at all.

  

Figure: A sample multi-segment RETHER connection from Node A1 to C1, through two intermediate switches Gw1 and Gw2.