Application of T9000 to CPLEAR

5 T805 to T9000 Interface


The T805 system is connected to the T9000 farm by the C100, an OS to DS link converter chip
[10]. There is only minimal support available for the integration of T805 and T9000 systems, in the form of the low-level link protocol conversion offered by the C100. All communication protocols above this physical level had to be implemented in software.

The protocol used by T9000 DS links is based on the exchange of packets, whilst the OS link protocol of the T805 is based on the exchange of bytes. The DS link packet protocol has been emulated in software on the T805 in combination with the low-level DS to OS link conversion performed by the C100.

Each of the T9000 farm workers has seven virtual links to the T805 system. One virtual link corresponds to the raw data source and six to the individual Exabyte drives. Figure 5 shows how these virtual links are mapped onto the corresponding virtual links of the T805s. For each T9000, three virtual links map across to the T805 system. This is less than the seven used in the actual implementation, but demonstrates the principles involved. The tables for each T9000, in Fig. 5, show two pieces of information: the virtual link number (VL #), and the description of the use of that link. In this example virtual link 0 of each T9000 will be used to request raw data from the T805 network, and two other virtual links will be used to send back reconstructed event data. The virtual links `Send A' and `Send B' correspond to different destination Exabytes.

Packets leaving the T805 must have headers to guide them through the C104 network to the correct virtual link on the destination T9000. These headers must be hard-coded into the T805 receive and send process, and need to be pre-calculated for each T9000 network configuration.

When a T805 link receives a packet the header allows the identification of the virtual link on which the packet was received. This virtual link uniquely identifies which T9000 has sent the packet and which one of the three T9000 virtual links the packet was sent from. The receiving T805 process can then acknowledge and provide raw data to the correct virtual link on the appropriate T9000.


Application of T9000 to CPLEAR - 09 NOV 95

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