1 Subnets

2 Token Ring Access Methodology = token passing Logical topology = sequential Physical = traditionally ring, currently star –Logical ring, physical star

3 Token Ring Token Ring Overview Token Ring Architecture was developed in the 1980s –Ethernet is the most popular –IEEE Standards IBMs –PCs –Midrange Computers –Systems Network Architecture 1985 – IBM became an ANSI standard

4 Token Ring Token Ring networks can run at 4, 16, or 100 Mbps –High-Speed Token Ring (HSTR) Use token-passing routine and star-ring hybrid physical topology Token passing: 3-byte packet (token) transmitted between nodes in circular fashion around ring –When station has something to send, picks up token, changes it to a frame, adds header, information and trailer fields –All nodes read frame as it traverses ring

5 Token Ring Token-passing control scheme avoids possibility for collisions –More reliable and efficient than Ethernet Active monitor: maintains timing for ring passing, monitors token and frame transmission, detects lost tokens, corrects errors Token Ring connections rely on NIC that taps into network through a MAU Self-shorting feature of Token Ring MAU ports makes Token Ring highly fault tolerant

6 Token Ring Data Frame

7 Free Token.. Control of the Token.. Flagging a Token..

8 Logical Ring

9 Token Ring (continued) Interconnected Token Ring MAUs

10 Monitoring the system First PC to come online –Ensures the delivery of the token –Checks frames Beaconing –Notification of lack of contact –Sends a message with source and the address of the PC that didn’t respond –Repairs –Active monitor Recognising a computer –Checking for duplicate addresses –Notification

11 Hardware Components Hub houses the ring Multiple Hubs –STP; UTP –Patch Cables –Fibre-Optic Cable MAU MSAU SMAU

12 Hub Capacity IBM MSAU –10 Connection ports –8 Computers –Each ring can have up to 33 Hubs –MSAU: 72 Computers; UTP 260; STP –Each connected so part of the logical ring

13 Adding Hubs

14 Built-in Fault Tolerance Token-passing –NIC Failure –Detects and disconnects from the failure point –No affect on the ring

15 Hub to Computer Distance