Congestion Control in Computer Networks - ATM and TCP
Upcoming SlideShare
Loading in...5
×
 

Congestion Control in Computer Networks - ATM and TCP

on

  • 7,593 views

 

Statistics

Views

Total Views
7,593
Views on SlideShare
7,452
Embed Views
141

Actions

Likes
1
Downloads
202
Comments
0

9 Embeds 141

http://hype-free.blogspot.com 98
http://www.slideshare.net 17
http://hype-free.blogspot.in 15
http://www.brijj.com 6
http://203.208.33.101 1
http://webcache.googleusercontent.com 1
http://translate.googleusercontent.com 1
http://hype-free.blogspot.ca 1
http://www.agent31.eu 1
More...

Accessibility

Categories

Upload Details

Uploaded via as OpenOffice

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

Congestion Control in Computer Networks - ATM and TCP Congestion Control in Computer Networks - ATM and TCP Presentation Transcript

  • Congestion Control in Networks ATM and TCP Balazs Attila-Mihaly
  • Outline
    • What is congestion?
    • Myths about congestion
    • Congestion control possibilities
    • ATM – Vocabulary
    • ATM – Congestion Control
    • ATM – CC evaluation
    • TCP
    • TCP – Congestion Control
    • TCP – CC evaluation
    • Bibliography
  • What is congestion?
    • ”network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates” - Wikipedia
    • QoS
      • Packet loss
      • Queuing delay
      • Jitter
      • Low troughput
  • Congestion control possibilities
    • Admission control
    • Traffic access control
    • Packet scheduling (prioritization)
    • Buffer management
    • Flow control (speed matching)
    • QoS routing
  • Congestion control possibilities
    • Admission control
    • Traffic access control
    • Packet scheduling (prioritization)
    • Buffer management
    • Flow control (speed matching)
    • QoS routing
    Congestion
    • prevention
    • avoidance
    • recovery
  • CC Objectives
    • Scalability
    • Fairness
      • Max-Min
      • Min + Equal share
      • Maximum of the previous too
      • Allocation proportional with Min
      • Weighted allocation
    • Robustness
    • Implementability
  • ATM
    • Protocol implemented over different media
    • Fixed sized cells (53 bytes – 48 byte of data)
    • Vocabulary:
      • VCI – Virtual Circuit Identifier
      • PCR – Peak Cell Rate
      • SCR – Sustained Cell Rate
      • MBR – Maximum Burst Size
      • MCR – Minimum Cell Rate
  • ATM
    • Vocabulary
      • CTD – Cell Transfer Delay (maximum / mean)
      • CDV – Cell Delay Variation (peak-to-peak / instant.)
      • CLR – Cell Loss Ratio
    • Service categories
      • CBR – Constant Bit Rate
      • rt-VBR – Real-Time Variable Bit Rate
      • nrt-VBR – Non-Real-Time Variable Bit Rate
      • UBR – Unspecified Bit Rate
      • ABR – Available Bit Rate
  • ATM – Congestion Control
    • Admission control – CAC (Call Access Control)
      • Hard or soft (statistical) limits
    • Traffic access control – GCRA (Generic Cell Rate Algorith)
      • TAT – Theoretical Arrival Time
      • I – Increment
      • L - Limit
    Cell arrival at t t <= TAT TAT = t t+L < TAT Conforming cell TAT = TAT + I Non-conforming cell
  • ATM – Congestion Recovery
    • Mainly for ABR traffic
    • Closed loop, Rate based, Binary & Explicit feedback and Queue growth rate based CC
    • Resource Management (RM) Cells
      • DIR – Direction (forward / backward)
      • BN – Backward Notification
      • CI – Congestion Indication
      • NI – No Increase
      • ER – Explicit Rate
    • CLP – Cell Loss Priority bit
  • ATM – Congestion Recovery
    • RM Cells sent every N cells (for example 32)
    • Considered out of band cells
    • Can be sent by the intermediate switches
    • Tagged packets (CLP) can be dropped at intermediate switches if a treshold is hit
  • ATM – CC evaluation
    • Explicit rather than implicit
    • Each switch can control the flow
    • Can provide guarantess (QoS)
    • Complex system with many parameters
    • Needs ”smart-network”
  • TCP
    • Possibly the most well-known communication protocol
    • Three-way handshake
    • Flow multiplexing with source/destination ports
    • Positive acknowledgement
    • Windowing
  • TCP – Congestion Control
    • Not well known, but fascinating
    • Not part of the original spec
    • As a result in 1986 NSFnet capacity dropped more than 800 (!!!) times
    • Only reactive – needs to respect the ”smart endpoints – dumb network” principle
    • There are alternatives (SACK, RVSP, etc)
  • TCP – Congestion Control
    • Additive increase (+1) / multiplicative decrease (*0.5)
    • Slow start
    • Fast retransmit and recovery
  • TCP – CC evaluation
    • Simple (no parameters to tweak)
    • Doesn't need cooperation from intermediate routers
    • No guarantees by itself
    • It's reactive
    • It actually relies on congestion happening to detect the link speed (for slow start)
    • It assumes that all packed loss is due to congestion
  • Bibliography
    • William Stallings – Data and Computer Communications – Fifth edition
    • Jagannathan Sarangapani – Wireless, Ad Hoc and Senso Networks – Protocol, Performance and Control
    • Steve Sjoquist, Andrew Tucker – Comparison of ATM and TCP Congestion Control
    • http://www.cis.ohio-state.edu/~jain/cis788-95/atm_cong/index.html
  • Thank you