End-to-End QoS Levels

Service levels refer to the actual end-to-end QoS capabilities, meaning the ability of a network to deliver service needed by specific network traffic from end to end or edge to edge. The services differ in their level of "QoS strictness," which describes how tightly the service can be bound by specific bandwidth, delay, jitter, and loss characteristics.

Three basic levels of end-to-end QoS can be provided across a heterogeneous network, as shown in Figure below

 

• Best-effort service---Also known as lack of QoS, best-effort service is basic connectivity with no guarantees.
• Differentiated service (also called soft QoS)---Some traffic is treated better than the rest (faster handling, more bandwidth on average, lower loss rate on average). This is a statistical preference, not a hard and fast guarantee.
• Guaranteed service (also called hard QoS)---An absolute reservation of network resources for specific traffic.

Deciding which type of service is appropriate to deploy in the network depends on several factors:

 

• The application or problem the customer is trying to solve. Each of the three types of service is appropriate for certain applications. This does not imply that a customer must migrate to differentiated and then to guaranteed service (although many probably eventually will). A differentiated service---or even best-effort service---may be appropriate depending on the customer application requirements.
• The rate at which customers can realistically upgrade their infrastructures. There is a natural upgrade path from the technology needed to provide differentiated services to that needed to provide guaranteed services, which is a superset of that needed for differentiated services.
• The cost of implementing and deploying guaranteed service is likely to be more than that for a differentiated service.

Figure belwo shows the three levels of end-to-end QoS are best-effort service, differentiated service, and guaranteed service.