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HP OpenVMS System Manager's Manual, Volume 2:... |
Managing InfoServer Systems |
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Understanding LASTport Protocols
On OpenVMS systems running the LASTport transport, all Ethernet devices must be terminated either by attaching the devices to an active network or by using an appropriate terminator. Failure to terminate the devices causes a system crash.
LASTport
Transport Protocol
The LASTport protocol is a specialized
LAN transport protocol that allows many clients to access InfoServer
systems and perform reliable transactions. For the InfoServer system,
a transaction is a device read or write operation. The LASTport
protocol allows many client systems concurrently to read information from,
and and write information to, an InfoServer storage device.
Unlike timer-based protocols, the LASTport protocol is a transaction-oriented protocol. Normally, information does not pass between a client and an InfoServer system unless the client initiates a transaction. The client system then runs a timer on the transaction, normally waiting from two to five seconds before assuming that the transaction is lost and retrying the operation.
The LASTport protocol does not provide any routing functions; it runs only in a LAN. The LASTport protocol type is 80-41. If the extended LAN uses any filtering devices, the devices must allow this protocol type to pass unfiltered so that clients can access InfoServer systems across the filtering device.
The InfoServer system uses a multicast address feature of the LASTport protocol to establish connections to devices. The format of the multicast address is 09-00-2B-04-nn-nn , where nn depends on the work group enabled (refer to the InfoServer System Operations Guide ).
LASTport/Disk
Protocol
The LASTport/Disk protocol is a specialized device protocol
that uses the LASTport transport. That is, LASTport/Disk messages
are delivered in LASTport messages. The LASTport/Disk protocol provides
the mechanism for reading and writing logical blocks independent
from any underlying file system. The clients that implement the
LASTport/Disk protocol interpret the file system locally. By using
the LASTport/Disk protocol for access to compact discs and read/write
disks, the InfoServer system can support multiple client operating
systems and on-disk structures concurrently.
The LASTport/Disk protocol also provides the naming facility to access compact discs and read/write disks. The InfoServer system assigns each virtual device a service name and allows clients to query the LAN for these names. When the requested service is found, the client connects to it, and device access can begin. When duplicate virtual devices are available under identical service names, the protocol provides a facility for load balancing among the available devices.
LASTport/Tape
Protocol
Like the LASTport/Disk protocol, the LASTport/Tape protocol
uses the LASTport transport. That is, LASTport/Tape messages are
delivered in LASTport messages. The LASTport/Tape protocol provides
the mechanism for reading and writing tape records. Tape devices
attached to the InfoServer system appear to tape clients as locally
attached devices.
The LASTport/Tape protocol also provides the naming facility to access tapes. The InfoServer system assigns each tape device a service name and allows clients to query the LAN for these names. When the requested service is found, the client connects to it, and tape access can begin.
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