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Traffic modelling and traffic control ...

Traffic modelling and traffic control. ... are necessary for QoS (or qos) and this is still an issue (over)provisioning... ... and controlled sharing QoS tends to mean "hard" qos (Intserv-like)

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Traffic modelling and traffic control ...

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  1. Traffic modelling and traffic control ... • ... are necessary for QoS (or qos) and this is still an issue • (over)provisioning... • ... and controlled sharing • QoS tends to mean "hard" qos (Intserv-like) • for an announced connection – a priori traffic descriptor, admission control, scheduling and/or traffic conditioning • statistical network calculus is the state of the art in realizing hard QoS guarantees (delay < d, negligible loss) • Diffserv is softer qos • aggregate descriptors, conditioning and per hop behaviours • but how can we meet the SLA's? • some believe even softer qos is sufficient (and necessary?) • a self-managed Internet... • ... or a network with implicit admission control and implicit differentiation • we also need modelling to understand best effort control! • eg, TCP modelling and re-design NeXtworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN NETWORKING

  2. Answering the questions • is standard queueing theory enough? • frequently: model at the appropriate granularity, seek insensitivities • is first course control theory enough? • significant advances: cf. work on stability of TCP • how can we understand time-scale interactions and design for them? • time scale separation is key to successful modelling • but beware of drawing conclusions without regard to all time scales • are time varying averages enough, or do we need to capture higher moments? • insensitivity results suggest time averages are often sufficient • stationarity is a key assumption – is this valid with LRD traffic? NeXtworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN NETWORKING

  3. Answering the questions • what happens to "effective" bandwidth and good old Erlang? • effective bandwidth is useful for sizing • Erlang is still insensitive ... to criticism! • why are we insisting on modelling TCP and RED • evolution to higher rates, ensure stability, improve fairness? improve efficiency? • why did it take us some time to be more careful? • self-similarity vs pseudo ss, limit cycle vs instability, etc • who was not careful? who is now more careful? NeXtworking’03 June 23-25,2003, Chania, Crete, Greece The First COST-IST(EU)-NSF(USA) Workshop on EXCHANGES & TRENDS IN NETWORKING

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