Notes - MIECT
Redes E Sistemas Autónomos
Notes - MIECT
Redes E Sistemas Autónomos
  • Redes e Sistemas Autónomos
  • Peer-to-Peer Systems and Networks
    • Content Distribution Networks
    • Peer-to-peer networks
      • Types
    • Structured vs Unstructured
    • Fully Decentralized Information System
    • FastTrack/KaZaA
    • OpenNAP/Napster
    • BitTorrent
  • InterPlanetary File System (IPFS)
    • IPFS
      • Bitswap
    • Connecting an IPFS node to the P2P network
    • Searching in DHTs (Structured)
    • File Search
    • Security
  • Ad-Hoc Networks
    • Mobile Ad-hoc networks
    • Application Scenarios
    • Routing
      • AODV - Ad Hoc On-Demand Distance Vector Routing
      • OLSR - Optimized Link State Routing Protocol
      • LAR – Location Aided Routing
      • Batman
    • IP Address Assignment
  • Self-organized systems: Data, learning and decisions
    • Use Cases and Data
    • Machine Learning
      • Supervised Learning
      • Neural Networks
      • Reinforcement Learning
      • Unsupervised Learning: K-means
    • Learning
  • Vehicular Networks
    • Vehicular Ad Hoc Networks
    • How do they work?
    • SPAT: Signal Phase And Timing
    • MAP: MAP
    • Manoeuvre Coordination Message (MCM)
    • Communication Technologies
  • QoS and Security
    • TCP- and UDP-based applications
      • TCP-Cubic
    • QUIC
    • TCP-Vegas
    • Classification of Transport protocols
    • Exploiting Buffering Capabilities
    • QoS in UDP: trade-offs
    • Transmission Quality (Batman v.3)
    • QoS-OLSR
    • Security
      • Key Management
      • RSA (Rivest-Shamir-Adleman) Key
      • Key Management in ad-hoc networks
      • Self-organized public key management (SOPKM)
      • Self-securing ad-hoc wireless networks (SSAWN)
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  • Problem: Evaluate TCP
  • Overview of TCP concepts
  • Wireless networks and ad-hoc
  • 1. Mobility
  • 2. High bit error rate
  • 3. Unpredictability/Variability
  • 4. Contention: packets compete for airtime
  • 5. Long connections have poor performance
  • Why does TCP fail wireless and in ad-hoc networks?
  • TCP misinterprets route failures as congestion
  • TCP misinterprets wireless errors as congestion
  • A delay spike causes TCP to invoke unnecessary retransmissions
  • Inefficiency due to the loss of retransmitted packet
  1. QoS and Security

TCP- and UDP-based applications

PreviousCommunication TechnologiesNextTCP-Cubic

Last updated 1 year ago

Problem: Evaluate TCP

Why does TCP perform poorly in ad-hoc/vehicular networks?

  • Developed for wire-line networks.

  • Assumes all losses are due to congestion.

Many TCP variants have been proposed.

  • How good are they?

  • Are they sufficient?

Are there any other alternatives?

  • Are non-TCP protocols the solution?

Overview of TCP concepts

Conventional TCP: Tahoe, Reno, New-Reno.

Sending rate is controlled by:

  • Congestion window (cwnd): limits the number of packets in flight.

  • Slow-start threshold (ssthresh): when congestion avoidance starts.

Loss detection.

  • 3 duplicate ACKs (faster, more efficient).

  • The retransmission timer expires (slower, less, efficient).

Overview of congestion control mechanisms:

  • Slow-start phase: cwnd starts from 1 and increases exponentially.

  • Congestion avoidance (CA): cwnd increases linearly.

  • Fast retransmit and fast recovery: Triggered by 3 duplicate ACKs.

Wireless networks and ad-hoc

1. Mobility

  • Route stability and availability.

2. High bit error rate

  • Packets can be lost due to “noise”.

3. Unpredictability/Variability

  • Difficult to estimate time-out, RTT, bandwidth.

4. Contention: packets compete for airtime

  • Intra-flow and inter-flow contentions.

5. Long connections have poor performance

  • More than 4 hops throughput drops dramatically.

Why does TCP fail wireless and in ad-hoc networks?

TCP misinterprets route failures as congestion

  • Effects: Reduce sending rate.

  • Buffered packets (Data and ACKs) at intermediate nodes are dropped.

  • Sender encounters timeouts.

    • Under prolonged disconnection, a series of timeouts may be encountered.

TCP misinterprets wireless errors as congestion

  • Effects: Incorrect execution of congestion control -> performance drops.

  • The wireless channel is error-prone compared to the wireline.

    • Fading, interference, noise.

A delay spike causes TCP to invoke unnecessary retransmissions

  • Effects: Performance drops and many unnecessary retransmissions exist.

  • Variability: Spikes are not uncommon here.

  • Spikes throw off parameter estimation and tuning.

    • RTO, window size, slow-start threshold.

Inefficiency due to the loss of retransmitted packet

  • Effects: performance drops significantly under a high-loss environment.

  • Losing a retransmitted packet hurts.

    • TCP can recover from one loss (fast retransmission).

  • Wired networks: packet loss rate is low.

  • Here, high packet loss makes the problem significant.