Subnets

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Subnets
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Token Ring

• Access Methodology token passing
• Logical topology sequential
• Physical traditionally ring, currently star
• Logical ring, physical star

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Token Ring

• Token Ring Overview
• Token Ring Architecture was developed in the
  1980s
• Ethernet is the most popular
• IEEE 802.5 Standards
• IBMs
• PCs
• Midrange Computers
• Systems Network Architecture
• 1985 IBM became an ANSI standard

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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

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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

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Token Ring Data Frame
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Free Token.. Control of the Token.. Flagging a
Token..
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Logical Ring
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Token Ring (continued)
Interconnected Token Ring MAUs
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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 didnt respond
• Repairs
• Active monitor
• Recognising a computer
• Checking for duplicate addresses
• Notification

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Hardware Components

• Hub houses the ring
• Multiple Hubs
• STP UTP
• Patch Cables
• Fibre-Optic Cable
• MAU
• MSAU
• SMAU

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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

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Adding Hubs
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Built-in Fault Tolerance

• Token-passing
• NIC Failure
• Detects and disconnects from the failure point
• No affect on the ring

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Hub to Computer Distance