Sun Microsystems SunLink SNA 9.1 PU2.1, Configuration Manual

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IBM Token Ring Concepts D-3
D
The IBM Token Ring is a compatible superset of the standard established by
the IEEE standards board and the American National Standards Institute
(ANSI) standard for a ring utilizing token passing as the access method: IEEE
Standard 802.5-1989. Data rates for the IBM Token Ring are 4 million bits per
second (4 Mb/s) and 16 Mb/s. Logic to improve throughput, known as early
token release, is covered by the latest version of the standard.
D.2 Frame Formats
The IBM Token Ring has two basic formats, or frames, for transmitted
information. These formats are shown in the following figure.
Figure D-1 IBM Token Ring Frame Format
The first format, known as the token format, consists of the following three
bytes of data and represents the free token:
•
Starting delimiter (SD) byte.
•
Access Control (AC) byte, which is used to differentiate between a free
token and a data frame.
•
Ending delimiter (ED) byte.
The second format, known as the frame format, is used to transmit network
management and user information and consists of the following:
•
Starting delimiter (SD) byte.
•
Access Control (AC) byte, which is used to differentiate between a free
token and a data frame.