1. 100BASE-TX: uses 2-pair UTP or STP that can handle 125 MHz signals and beyond.
It uses a binary coding scheme called 4B5B, every 5 clock pulses are used to send 4 bits  100 Mbps.
100BASE-FX: uses two strands of multimode fiber one for each direction and the distance can be up to 2 km.
To solve the collision problem, 100BASE-FX cables must be connected to buffered, switched, hubs, so each is in a collision domain itself.

2. TOKEN BUS IEEE 802.4
Due to the unpredictable collisions and delays in sending data from a control center to computers along an assembly line, IEEE is not suitable for real time applications.
Token Ring (IEEE 802.5) is also not suitable because an assembly line resembles a bus topology and not a ring.
In a token bus, stations are logically organized into a ring. It is limited to factory automation and process control.
A token is passed among stations, and only a station who wants to transmit and has the token can transmit.

3. TOKEN RING (IEEE 802.5) Station takes turns in sending data
A station may send data only when it has possession of the token.
The Token is a three-byte frame that is passed from one station to another in sequence until it encountered a station with data to send.
The station captures the token, sets a bit in its NIC card as a reminder, and sends its data frame.
Each station copies the data frame and checks if the destination address matches its.

4. If the frame is intended for another station, it is regenerated and passed to the next station.
If the frame is intended for the station, it marks the frame as being recognized and copied.
The sender receives the frame and recognizes itself as the source and checks if the frame was recognized and copied.
The sender discards the frame and releases the token back to the ring.

5. Token Passing

6. Token Passing

7. Token Passing

8. Token Passing

9. A station waiting to transmit may reserve the next open token by entering its priority code in the Access Control (AC) field of the token or data frame.
A station with a higher priority may remove a lower priority reservation and replace it with its own.
Regardless of physical location of the station in the ring, a station which sets the reservation gets the opportunity to transmit as soon as the token is free.

10. Each station expects to receive a token within regular time intervals.
Potential problems:
- A token may be destroyed by noise
- A station may neglect to transmit a token
- A sending station may neglect to remove its data from the ring.
Solution: One station is designated as a monitor.
The monitor sets a timer as each token passes. If the token did not appear before timeout, the monitor generates a new token.
The monitor sets a bit in the AC field for each data frame. If it sees a frame with monitor bit set, it destroys the frame and generates a new token.

11. Token Ring Frame
- It runs at 16 Mbps, using differential Manchester encoding,

12. Starting Delimiter (SD): used to alert receiving station of the arrival of a frame and to allow for synchronization (flag).
To ensure data transparency, two types of violations are introduced: J (both transitions are canceled) and K (the middle transition is canceled).
Access Control (AC): 3-bit priority, 3-bit reservation, 1-bit Token, 1-bit monitor.
Frame Control (FC): 1-bit type of PDU (control or data). The remaining 7-bit is used by the ring logic.
Frame Status (FS): 1-bit address recognized, 1-bit frame copied. It is repeated for reliability.

13. Data Frame Fields

14. Data Frame Fields

15. Token Ring
150  STP.

16. Token Ring Switch
The NIC controls the switch via 5-wires to include or bypass the station

17. MAU

18. Fiber Distributed Data Interface (FDDI)
A LAN protocol developed by ANSI and ITU-U.
100 Mbps using dual ring fiber optic or copper (CDDI).
Access is based on token passing and is limited by time. A station may transmit within its allotted time.
Two types of frames: Synchronous (time sensitive) and Asynchronous (time insensitive). S-frames and A-frames.
A station must send out its S-frames first whether or not its time allotment has run out.

19. FDDI defines three time registers:
- Synchronous Allocation (SA) register indicates the amount of time allowed for each station for sending synchronous data.
- Target Token Rotation Time (TTRT) register indicates the average time required for a token to circulate around the ring exactly once.
- Absolute Maximum Time (AMT) register holds a value equal to twice the TTRT. A token may not take longer than the allotted time to traverse the ring. If it does, the ring must be reinitialized.

20. Each station contains a set of timers of which FDDI utilizes two:
- Token Rotation Timer (TRT): When a token is received, the TRT is transferred to THT and it resets based on the TTRT value and starts counting down. When the token completes a rotation, the TRT indicates the amount of time remaining for the station to send data.
- Token Holding Timer (THT) indicates the amount of time remaining for A-frames once the S-frames have been sent. It starts counting down as soon as a token arrives and the value of the TRT is copied. If negative, the station must release the token.

21. FDDI

22. FDDI Example SA = 2, TTRT=30assume many A-frames, frame =1 time unit
AT= 0
TRT =0
AT=1
TRT=0
AT=2
AT=3 1
AT=4,TRT=4
THT=26,TRT=0
S=2,A=24
AT=31,TRT=30
THT=0,TRT= 0
S=2,A=0
AT=34,TRT=32
THT=-2,TRT= 0
S=2.A=0
AT=37,TRT=34
THT=-4,TRT=0 2
AT=40,TRT=36
THT=-6,TRT=0
AT=43,TRT=12
THT=18,TRT= 0
S=2,A=16
AT=62,TRT=28
AT=65,TRT=28
THT=2,TRT=0 3
AT=68,TRT=28
AT=71,TRT=28
THT=2,TRT= 0
AT=74,TRT=12
S=2.A=16
AT=93,TRT=28 4
AT=96,TRT=28
AT=99,TRT=28
AT=102,TRT=28
AT=105,TRT=12
THT=18,TRT=0

23. FDDI Encoding
- Encoding 5-bit/4-bit 5B/4B (each 4-bit is replaced by 5-bit) NRZ-I

24. FDDI Layers Logical link control LLC Media access control MAC
Data Link
Physical
PHY
Physical medium
dependent PMD
Physical

25. FDDI Frames

26. FDDI Rings

27. FDDI Ring Failure

28. Nodes
Three Types:
-Dual Attachment Station (DAS) has two Media Interface Connector (MIC) to allow connection to both rings.
-Single Attachment Station (SAS) has only one MIC. It connects to intermediate node (DAC).
-Dual Attachment Concentrator (DAC) connects SAS to the dual ring.

29. FDDI Nodes