What is moving?
The yellow token is permission to transmit. The purple frame is real data that must return to the sender so it can be removed from the ring.
Ring Topology Token Passing
Step through logical ring token passing, bounded access delay, frame return, and single-link fault behavior
animation
ring-topology
token-passing
mac
networking
intermediate
A guided ring topology workbench for seeing how a token controls transmission, why collisions are avoided, and where ring fault tolerance depends on the design.
Animation
Intermediate
Logical ring
Token passing
Ring topology token passing workbench
Watch a free token circulate around a logical ring. When the selected sender receives the token it is allowed to transmit one frame, the destination copies the frame, and the sender removes the returning frame before releasing the token again.
Free token
Current network state
10.4 ms
Worst-case access delay
12.5 ms
Loaded token cycle
Healthy
Fault tolerance result
Why no collisions?
Only the node holding the token may send. Other nodes listen and forward, so two stations do not intentionally transmit at the same time.
Try first
Press Step until the token reaches the sender. Then change node count and token holding time to see why the delay bound changes.
Important caveat
This is a logical ring model. Classic IEEE 802.5 was often cabled as a star through a MAU, and IoT token protocols may use a bus while keeping a logical token order.
Stage 1
Free token circulates Each node gets a predictable chance to transmit when the token arrives.Stage 2
Sender captures token The sender changes the free token into a data frame for one destination.Stage 3
Frame is copied and returns The destination copies the frame, but the frame continues until the source removes it.Stage 4
Fault response depends on design A single ring can stop at a break; a protected dual ring can often wrap around one fault.Interactive workbench
A free token is moving clockwise. The sender must wait until it owns the token.
Single ring
Clockwise path
Token
Data frame
Active path
Broken link
Token holder
Node 0 Only this node has transmit permission right now.Frame progress
Waiting The data frame appears only after the sender captures the token.Access rule
One sender Token ownership serializes access and prevents intentional collisions.Healthy single ring. The sender is waiting for the token; increasing node count or token holding time increases the access delay bound.
Current packet story
The token is free. Every node forwards it until the selected sender receives it.
Event log
Use this like a packet trace. It shows what a learner should notice after each step.
Quick reference
Token
A small control frame that grants send permission to the node that currently holds it.
Logical ring
The order in which nodes pass the token. It may not match the physical cable route.
Bounded delay
With one token and a hold-time limit, a busy node can estimate the latest time it should get access.
Dual ring
A protected design can wrap around a single break. Multiple faults can still partition the network.
Guided practice
Beginner path
- Press Step until the sender captures the token.
- Watch the destination copy the frame, then watch the frame return to the source.
- Raise node count from 6 to 10 and compare the worst-case delay.
Diagnostic path
- Choose Single break and notice where the token stops.
- Switch to Protected dual ring and compare the diagnosis.
- Use the formula trace to explain why this is still not infinite reliability.
Technical accuracy notes
What the model includes
- One free token, one sender with queued data, one destination, and a finite token holding time.
- Frame copying by the destination and frame removal by the source after the frame returns.
- A simple worst-case access delay estimate:
(N - 1) x THT + propagation. - Single logical ring failure versus protected dual ring wrap-around for one break.
What real standards add
- IEEE 802.5 includes monitor functions, priority and reservation bits, timers, error handling, and management details not shown here.
- FDDI used counter-rotating rings with wrapping behavior; this model only shows the concept.
- BACnet MS/TP and PROFIBUS use token passing in building or industrial networks, but their physical media and timing rules are not identical to IEEE token ring.
- Propagation delay in short IoT links is usually small compared with hold time, but the model still includes it so the formula is visible.