QoS 101

This tip offers the basics in quality of service (QoS) and what to look for in vendor products.

What is quality of service (QoS)?

Two major components make up QoS :

  • Metrics to indicate network AND application performance
  • Mechanisms to differentiate and manage network traffic through classification, traffic management, monitoring and reporting.

    Queuing
    Most network equipment vendors like Cisco and Nortel utilize very simple static queuing mechanisms under their claims to offer QoS. In the TCP/IP world, routers offer:

    • No rich monitoring or reporting
    • Limited traffic queues, e.g. four, eight or 16
    • Only queuing to avoid traffic starvation or hard bandwidth allocation BUT never the two together.

    The same can be said of Layer 3 LAN switches.

    Older queuing techniques like WFQ (weighted fair queuing) exist in switches, routers (Cisco, Nortel), CSU/DSUs (Adtran) and even firewalls (Check Point Floodgate). These are being supplanted by newer, dynamic mechanisms like CBQ (class-based queuing -- not Cisco CBWFQ). The newer mechanisms are faster, more accurate, build queues as needed and allow you to create "soft, flexible" rules (policies) to burst and borrow between different traffic flows.

    That said, look for products from Lucent (Xedia routers) and Sitara Networks (traffic management appliance) that use CBQ, just to name a few.

    These mechanisms become vital when you try to deploy converged IP networks that are VoIP and video enabled.

  • This was first published in August 2002

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