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Token Ring - Computer Networks - Lecture Slides, Slides of Computer Networks

Dr. Bhim Rao Ambedkar UniversityComputer Networks

Some concept of Computer Networks are Aloha Ethernet, Application Layer Protocols, Basic Building Blocks, Computer Networking, Content Free Protocols, Medium Access Sub Layer, Packetised Filetransmission. Main points of this lecture are: Token Ring, Particular Direction, Upstream Neighbour, Downstream Neighbour, Shared Ring, Special Sequence, Circulates Around, Frame Removed, Sender Reinsert Token, Token Circulates

Typology: Slides

2012/2013

Uploaded on 04/27/2013

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IEEE 802.5 Token Ring
• Consists of a set of nodes connected in a
ring.
• Data flows in a particular direction only.
• Data received from upstream neighbour
forwarded to downstream neighbour.
• Token – access to the shared ring
– a special sequence of bits
– circulates around the ring.
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IEEE 802.5 Token Ring

  • Consists of a set of nodes connected in a

ring.

  • Data flows in a particular direction only. • Data received from upstream neighbour

forwarded to downstream neighbour.

  • Token – access to the shared ring
    • a special sequence of bits – circulates around the ring.

IEEE 802.5 Token Ring

  • Each node receives and forwards token. • Frame makes its way back to sender
    • frame removed by sender – sender reinsert token.
      • As token circulates around ring, each station

gets a chance to transmit

  • Service round - robin fashion

Token Ring Issues

Host Host To nexthost Previoushost To nexthost Previoushost relay closedbypass station relay open - stationincluded

Multistation Access Unit (MSAU)

  • Several relays in a box• Add new station
    • Plug into MSAU H 1 H 3 H 2 H 4 To next MSAU From prevMSAU Docsity.com

Differential Manchester

clock Differential Manchester Manchester (^1) NRZ 0 0 0 1 0

Token Ring Access Control

  • Network adapter: receiver, and transmitter,

and one or more bits of data storagebetween them.

  • When no stations have anything to transmit

token circulates

  • Ring has enough storage capacity to hold an

entire token.

  • 1 bit / station

IEEE 802.

  • Token Size: 24 bits
    • Minimum number of stations is 24 – Overcome this by including a monitor which adds the extra bits of delay - Token operation - Token circulates – Station seizes a token

IEEE 802.

  • Modifies a bit in the second byte of token – Station that has token transmits data – Station drains token out of the ring – Station sends data – Each packet has destination address – All stations downhill check destination address – Destination copies packet – Packet finds its way back to sending station

IEEE 802.

  • Issues
    • Size of data that given node is allowed to transmit - Token holding time (THT) =
  • Utilisation is 100% • Unfair to stations to other than the station holding the token - THT affects ring performance

Token Holding Time

  • Token Rotation Time (TRT): •

TRT

Active nodes * THT + Ring

Latency

  • Ring Latency – token circulation time

Priorities in IEEE 802.

  • Supports different levels of priority
    • 3 bits – each station waiting to send, sets priority for packet packet’s priority as high current token - then token can be seized – Intending to send station – sets the priority on currently passing data frame

Priorities in IEEE 802.

  • releasing station sets priority of token to n. – Lower priority packets circulate for long in ring
    • Token Release
      • Early release
        • After transmitting packet
          • Delayed release
            • After removing packet when it returns to the sender

Token Ring Maintenance

  • Role of monitor
    • insert additional delay in ring – ensure always that there is a token somewhere in the ring - regenerate a vanished token – no token seen for TRT => regenerate

Token Ring Maintenance

  • orphaned / corrupted packets – drain them if orphaned - (A and C bits set – parent dies) • A bit set C bit not set – parent dies - bit is initially set to 1 by monitor - monitor notices back when packet passes by monitor a second time