Computer Networks Laboratory Electrical Engineering Department Technion, Haifa, Israel REAL TIME ET

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     Computer Networks Laboratory
    Electrical Engineering Department         
Technion, Haifa, IsraelREAL TIME ETHERNET

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PROJECT GOAL

• Design, implementation and evaluation of a
  software-based protocol that provides real-time
  performance guarantees to multimedia applications
  without requiring any modifications to existing
  half-duplex Ethernet (LAN) hardware.

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PROJECT OBJECTIVES

• Examine the present Ethernet protocol (CSMA/CD)
  and requirements for real time network traffic.
• Designing and implementing (opnet) a hybrid mode
  protocol that allows real time and non- real time
  network traffic.
• Simulating (opnet) the new protocol and
  evaluating the simulation results.

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Real time data
(what is real time data?)

• Multimedia application incorporate continuous
  media
• data, such as video and audio, therefore a time
• constrain on network traffic is demanded.

• In order to preserve the characteristics of
  continuous
• media data, it is essential to guarantee
  resources (QoS)
• on these three domains network, I/O and
  processor.

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Half-duplex Ethernet

• 1 persistent CSMA/CD
• Carrier Sense Multiple Access / Collision
  Detection.

• T/R rate of 10Mb/s (100M/1G/10G b/s on fast
  Ethernet)

• Binary exponential backoff

• Single/multi segment

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So why does the existing Ethernet protocol is
unsuitable for real time applications ?

• The probabilistic nature (backoff mechanism) of
  the
• protocol cannot provide bondable and
  deterministic
• access to the network.

• Ethernet packets do no have priorities,
  therefore it
• cannot distinguish between real time and
• non-real time data.

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Which protocols does support real time traffic ?

• ATM and FDDI based networks.

• MAC level protocols for LANs with Token-based
• protocols (such as token-ring and token-bus
  protocols).

• Some internet protocols.
• (reservation based / adaptive or best-effort
  protocols)

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Token passing protocols
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Single-Segment RETHER
Overview

• Hybrid protocol that switches between CSMA/CD
• and token bus protocols.

• Fixed number of nodes

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Protocol description

• The CSMA Mode
• Switch to RETHER Mode
• The RETHER Mode
• Switch to CSMA Mode

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The CSMA Mode When there no real time session,
all node compete for the channel using the
generic CSMA/CD. When a process in a node make a
reservation request, the switch to RETHER mode is
initiate.
Switch to RETHER Mode When an application on a
node generates an RT request, and the node is in
CSMA mode, it becomes an initiator by
broadcasting a Switch-to-RETHER message on the
link.
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Problems while switching to RETHER
I) Multiple Initiators the smallest ID get
the higher priority.
II) Node failures
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The RETHER Mode
Much of the protocol state is maintained in the
token, therefore it must contain

• Residual time in the token cycle.
• Network State Information about all the nodes in
  RETHER-mode.
• RT Stream Information about all active RT
  streams
• and their reservation.
• First NRT node in next token cycle.

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TRT - Token Rotation Time THT - Token Holding Time
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Example for RETHER Mode
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Switch to CSMA Mode The last node to terminate
its RT session destroys the token and sends out a
Switch-to-CSMA broadcast message.
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• Fault Tolerance
• Node reboot.
• Node failure.
• Token loss.
• Token corruption.
• Multiple tokens.

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Summary The design of RETHER centers around a
timed token passing Mechanism that prevents any
collisions in the network. The protocol id
designed to be implemented in software within the
device driver of the Ethernet.

• Still to do
• Studying the OPNET system.
• RETHER implementation on OPNET.
• Results evaluation and conclusions.