Posts Tagged ‘ccie qos’


This blog post reviews and compares two most common types of traffic contracts – single rate and dual-rate agreements and their respective implementations using single-rate and dual-rate (two-rate) policing. We are also going to briefly discuss effects of packet remarking on end-to-end throughput and finally look at some examples of IOS configuration.

What is Traffic Contract

Service-providers network topology typically follows core/aggregation model, where network core has meshed topology and aggregation layers use some variation of tree topology. This design results in bandwidth aggregation when flows converge toward the core. Therefore, to avoid network resource oversubscription, accurate admission control is necessary at the network edge. The admission operation was trivial with circuit-switched TDM-based networks, but became significantly more complicated in packet switched networks. In a packet network, there is no such thing as a constant traffic flow rate, as flows only exist “temporarily” when packets are transmitted. In packet networks, it is common for service providers to connect customer using a sub-rate connection. Sub-rate a connection that provides only a fraction of the maximum possible link bandwidth, e.g. 1Mbps on a 100Mbps connection.

Implementing sub-rate access requires special agreement between service provider and customer – a specification known as “traffic contract”. Traffic contracts are enforced both at customer and SP sides by using traffic shaping and policing respectively. Traffic contracts may vary and include multiple QoS parameters, but there are two most common types that we are going to look at today: single-rate and dual-rate traffic contracts.
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