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Sandman to Sandman

Consider first the case where two neighbouring Sandman domains want to interoperate, for example to set up a connection from endpoint 1 to endpoint 3 in Figure [*]. As usual, endpoints register callback operations with their respective Sandman MCAs. The only difference with the sequence of operations described in section [*] is that when we set up a connection from endpoint 1 to endpoint 3 (assuming the request originated in Sandman-1), we treat the entire Sandman-2 domain as a single endpoint. For this purpose, we register a pseudo-endpoint corresponding with the link L1 connecting the two domains with both Sandman MCAs. The pseudo-endpoint represents Sandman-1 to Sandman-2 and vice versa. The pseudo-domain also contains its own implementation for the callback operation.

actions [*] and [*] in section [*] (i.e. reservation of endpoint SAP, and callback operation respectively).

Figure: Pseudo-endpoints as control gateways
\includegraphics[height=3in]{translation.eps}

Consider Figure [*]. If the Sandman-1 MCA wants to setup a connection to a destination in Sandman-2, it knows that the pseudo-endpoint of L1 is the via parameter for this connection and hence that this where the appropriate callback operations reside. It will set up the connection in its own domain and (if successful) call the callback operations in both endpoint 1 and the pseudo-endpoint. The pseudo-endpoint now replicates the connection setup request and sends it to the Sandman-2 MCA, specifying itself as the source endpoint and specifying the vpi-vci value it received from Sandman-1 as the starting vci-vpi for link L1 for this connection. The Sandman-2 MCA tries to set up the connection with the specified vpi-vci value and if successful, returns the boolean value true to the pseudo-endpoint, which in turn returns true to the Sandman-1 MCA. We have now established and end-to-end connection between two endpoints in different Sandman domains. In this case the pseudo-endpoints works as a signalling bridge between the two MCA. The tear down of connections proceeds in roughly the same way. Observe that all this takes place on the control path. The datapath is untouched. For this reason, such pseudo-endpoints are sometimes called control gateways.


next up previous
Next: Sandman to MCA-X Up: Simple interoperability between domains Previous: Simple interoperability between domains
Herbert Bos
2001-12-11