- A node can
send
2 types of
frames in
the Token Bus network:
- A token frame
- A data frame
- Token ring's
token frame format:
Meaning of the fields:
- Start delimiter:
- Signals the
start of a
frame
(Use like a start flag)
- Signals the
start of a
frame
- Access-control byte contains
Description:
- Priority field:
specifies the priority level
of the frame
- Token bit:
when bit is set (= 1),
the frame contains
the token
- Monitor bit:
used by the activity monitor
to monitor
whether some frame
is circling the ring
indefinitely.
- Reserved bits: reserved for future use
- Priority field:
specifies the priority level
of the frame
- End delimiter:
- Signals the end
of a frame
(It's like an "end flag")
- Signals the end
of a frame
- Start delimiter:
- Token passing:
- Nodes in the
token ring
continously pass
the token
(= a frame that
contains token bit = 1)
to
each other:
- Only the node that has received the token is allowed to transmit on the token ring network
- Nodes in the
token ring
continously pass
the token
(= a frame that
contains token bit = 1)
to
each other:
- Token ring's
data frame format:
Meaning of the fields:
- Start delimiter:
- Has been discussed before
- Access control:
- Has been discussed before
- Frame-control byte
- Indicates whether the frame contains data or control information.
- Destination and
source addresses
- Consists of two 6-byte address fields that identify the destination and source station.
- Frame Status
- Is a 1-byte field terminating
a command/data frame.
- The Frame Status field
includes:
- the address-recognized indicator bit
- the frame-copied indicator bit
End delimiter:
- Has been discussed before
- Is a 1-byte field terminating
a command/data frame.
- Start delimiter:
- Note:
- Only the node that has received the token (frame) is allowed to transmit a data frame !!!