- Transmission order:
- After a
node has
transmitted
a data frame:
- The node will pass the token (frame) to its successor node
- After a
node has
transmitted
a data frame:
- Token bus Operation:
(frame transmission)
Explanation:
- Node 0 is the
current token holder
- Successor of node 0 = node 4
- Node 0 sends
a token message
to
it successor (node 4)
- Token = the red dot in the figure
- When node 4 receives the
token message:
- Node 4
can
transmit a
message
(message = the blue dot)
- Node 4
can
transmit a
message
- After transmitting the message, the node 4 will send a token message (red dot) to its successor
- Node 0 is the
current token holder
- Advantage of
Ethernet (over
Token bus):
- Ethernet performs
much better in
low traffic
conditions
- Low traffic will have few simultaneous transmitters
- Fewer simultaneous transmitters will result in low probability of collision
- Most transmissions will be received correctly on the first try !!!
- Ethernet performs
much better in
low traffic
conditions
- Short-coming of
Ethernet:
- Ethernet performs
terribly in
high traffic
conditions
- High traffic will have many simultaneous transmitters
- More simultaneous transmitters will result in high probability of collision
- Most transmissions will be lost on the first try !!!
- Ethernet performs
terribly in
high traffic
conditions
- Advantage of
Token bus:
- Token bus performs
much better in
a high traffic load
condition:
- There are no collisions in Token bus !!
- Token bus performs
much better in
a high traffic load
condition:
- Short-coming of
Token bus:
- Token bus performs
terribly in
a low traffic load
condition:
- A node must
pass the
token
after the node has
transmitted
its frame
(This is done for fairness sake !!!)
- The node
must
pass the
token
even if its the
only node
that is transmitting !!!
- The node will waste time waiting for the token to come back....
- A node must
pass the
token
after the node has
transmitted
its frame
- Token bus performs
terribly in
a low traffic load
condition:
- Analogy:
- Ethernet is
like a stop sign
- In low traffic condition, intersections with a stop sign performs much better than intersections with a stop light
- Token bus is
like a stop light
- In high traffic condition,
intersections with
a stop light performs
much better than
intersections with
a stop sign
- In low traffic condition, you will have to wait for the stop light to turn green (= receive the token) before you can cross the intersection
- In high traffic condition,
intersections with
a stop light performs
much better than
intersections with
a stop sign
- Ethernet is
like a stop sign
- Advantages of
Token bus over
token ring:
- Token bus network is
easier to
maintain:
- Bus network is easier to connect
- Token bus is
more flexible:
- Nodes can be
added to the
network
more
easily:
(Just connect the node to the bus network.
No need to split the ring network opne !!!)
- Nodes can be
added to the
network
more
easily:
- Token bus network is
easier to
maintain:
- Disadvantages of the
Token bus network:
- Complicated maintenance protocols to insert/delete nods from token bus
- The token bus standard
include
protocols for:
- Token bus membership maintenance
- How to
add a
node to the
token bus
network:
- Connect the
node to the
(token) bus network
- The node will be inserted itself into the token bus network (i.e.: become a member of the token bus) using the node insertion protcol
We will study these protocols: token bus:
- (Automatic) node deletion (this is the easiest)
- (Automatic) node insertion
- (Automatic) ring initialization
- Connect the
node to the
(token) bus network