System information

Troubleshooting Token Ring 6-83
Data/Command Frames
Data/Command Frames
Data/command frames vary in size, depending on the size of the information field. Data frames carry
information for upper-layer protocols; command frames contain control information and have no
data for upper-layer protocols.
In data/command frames, a frame control byte follows the access control byte. The frame control
byte indicates whether the frame contains data or control information. In control frames, this byte
specifies the type of control information.
Following the frame control byte are the two address fields, which identify the destination and source
stations. As with IEEE 802.3, addresses are 6 bytes in length.
The data field follows the address fields. The length of this field is limited by the ring token holding
time, which defines the maximum time a station may hold the token.
Following the data field is the frame check sequence (FCS) field. This field is filled by the source
station with a calculated value dependent on the frame contents. The destination station recalculates
the value to determine whether the frame may have been damaged in transit. If damage did occur,
the frame is discarded.
As with the token, the end delimiter completes the data/command frame.
Troubleshooting Token Ring
This section provides troubleshooting procedures for common Token Ring media problems. It
describes a specific Token Ring symptom, the problems that are likely to cause this symptom, and
the solutions to those problems.
Media Problems: Token Ring
Table 6-1 outlines problems commonly encountered on Token Ring networks and offers general
guidelines for solving those problems.
Table 6-1 Media Problems: Token Ring
Media Problem Suggested Actions
Nonfunctional
Token Ring
Step 1 Use the show interfaces token command to determine the status of the router’s
Token Ring interfaces.
Step 2 If the status line indicates that the interface and line protocol are not up, check the
cable from the router to the MAU.
1
Make sure that the cable is in good condition. If it
is not, replace it.
Step 3 If you are performing a new installation, make sure that the MAU has been properly
initialized. For information on initializing your MAU, refer to the manufacturer’s
documentation.