NetWare 4.1/9000 Concepts

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NetWare Glossary

Semaphore

A ﬂag that coordinates activities of both programs and processes to prevent

data corruption in multiprocess or multiuser environments.

Semaphores are similar to logical locks in that they lock a certain string.

However, unlike logical locks, semaphores allow more than one user to

control the lock at one time.

For example, semaphores can allow a speciﬁed number of users access to a

resource, such as to network applications with limited-user licenses. When

the speciﬁed number is reached, the semaphore denies access to additional

users.

See also “File locking”; “Record locking”; “Synchronization services.”

Sequenced Packet Exchange (SPX)

A NetWare DOS Requester module that enhances the IPX protocol by

supervising data sent out across the network.

Se also: “Sequenced Packet eXchange II (SPXII).”

Sequenced Packet eXchange II (SPXII)

An update to the SPX protocol.

Two characteristics differentiate SPXII from SPX:

• Larger packet sizes

Applications that used SPX were responsible for determining the size of the

packet that could be used. In contrast, when an application uses SPXII, the

SPXII driver is responsible for packet size negotiation.

• A windowing protocol.

The SPXII windowing protocol uses the existing header ﬁelds and allows the

transmitter to send multiple packets before requesting an acknowledgment.

The receiver determines and maintains the window size for its half of the

session.

The receiving endpoint is passive, that is, it only sends acknowledgments when

the transmitting endpoint sets the ACK bit in the header.