Connection Setup and Admission Control

In single-segment RETHER , connections are set up by modifying the information on the token when it arrives. It is not necessary to contact any other node, including the receiver. Multi-segment RETHER , however, needs an explicit connection setup protocol to establish end-to-end real-time connections across bridges/switches. RETHER connection messages are initiated by the senders and routed via the static routing tables in the switches. As a multi-segment RETHER connection is established, resources, namely buffers and network bandwidth, on the nodes along the way are reserved accordingly. More concretely, as each intermediate switch receives a connection request, it creates a single-segment RETHER connection on the network link through which the message is forwarded. In addition, the switch maintains the following information:

• The multi-segment RETHER connection ID, in the form of the sender's IP address and source port number, and the local single-segment RETHER connection ID.
• The next-hop interface and the Ethernet address of the next-hop node.
• The previous-hop interface and the Ethernet address of the previous-hop node.

When the last-hop switch successfully reserves a single-segment RETHER connection to the destination node, it sends back an acknowledgment through the same path to commit the resource reservations made by intermediate switches and the sender. Only when the sender receives a success acknowledgment for connection establishment will it start to send real-time data out.

In multi-segment RETHER , admission control is performed independently on each of the segments on a hop-by-hop basis. Each intermediate switch applies the same admission control criterion as single-segment RETHER . If the admission test fails in any of the segments, a connection termination message is sent on the same path back to the sender node, to cancel all resource reservations. Note that each single-segment RETHER connection is only aware of its other end-point in the same segment. The information about the final source and destination of the multi-segment RETHER connection is hidden from non-periphery switches.