Page 846 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

loss in potential throughput.

Token Passing This is the LAN media access technology that
performs communications using a digital token. Possession of the

token allows a host to transmit data. Once its transmission is
complete, it releases the token to the next system. Token passing is
used by Token Ring networks, such as FDDI. Token Ring prevents
collisions since only the system possessing the token is allowed to
transmit data.

Polling This is the LAN media access technology that performs
communications using a master-slave configuration. One system is

labeled as the primary system. All other systems are labeled as
secondary. The primary system polls or inquires of each secondary
system in turn whether they have a need to transmit data. If a
secondary system indicates a need, it is granted permission to
transmit. Once its transmission is complete, the primary system

moves on to poll the next secondary system. Synchronous Data Link
Control (SDLC) uses polling.

Polling addresses collisions by attempting to prevent them from using
a permission system. Polling is an inverse of the CSMA/CA method.
Both use masters and slaves (or primary and secondary), but while
CSMA/CA allows the slaves to request permissions, polling has the
master offer permission. Polling can be configured to grant one (or

more) system priority over other systems. For example, if the standard
polling pattern was 1, 2, 3, 4, then to give system 1 priority, the polling
pattern could be changed to 1, 2, 1, 3, 1, 4.