Traffic Shaping

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Traffic Shaper

Traffic shapers delay certain packet types, based on their content, to ensure that other packets have higher priority.

• help to ensure that latency is reduced for critical applications
• simpler devices that perform traffic policing do not offer the enhanced traffic management functions of a shaper
  • e.g.,
    • typical traffic policing devices will fail to deliver packets once the configured traffic threshold has been reached
      • called tail drop
    • will be times when:
      • packets are being lost
      • network is relatively idle
    • traffic shaper will store packets until there is free bandwidth available
      • leads to consistent usage of the bandwidth and few lost packets

Info

• essential that the selected device is capable of handling high traffic volumes
  • these have a limited buffer,
    • will be situations when the buffer overflows
• Devices can either
  • drop packets and in essence provide traffic policing
  • else they must implement a dropping algorithm
    • Random Early Detection (RED) is an algorithm that can help manage traffic overflow on the shaper

QoS vs CoS

• Quality of Service (QoS) is distinct from class of service (CoS)
  • CoS
    • categorize protocols into groups requiring different service levels
    • provide a tagging mechanism to identify a frame or packet’s class
    • e.g., DiffServ, 802.1p
  • QoS
    • allows fine-grained control over traffic parameters
    • e.g., if network link is congested,
      • DiffServ and 802.1p cannot address it
      • Multiprotocol Label Switching (MPLS) with QoS can
        • reserve required bandwidth
        • predetermine statistics when setting up the link
          • e.g., acceptable packet loss and maximum latency and jitter
• QoS network functions are divided into 3 planes:
  • control plane
    • makes decisions about how traffic should be prioritized and where it should be switched
  • data plane
    • handles switching of traffic
  • management plane
    • monitors traffic conditions
• Protocols, appliances, and software that can apply these three functions are described as traffic shapers or bandwidth shapers