连接缓冲管理和行程安排服务培训讲义(英文版)(pdf 15页)

连接缓冲管理和行程安排服务培训讲义内容摘要：
1、Introduction
        Quality-of-Service (QoS) guarantees in packet networks are often classified according to two criteria. The first criterion is whether guarantees are expressed for individual
end-to-end traffic flows (per-flow QoS) or for groups of flows with the same QoS requirements(per-class QoS). The second criterion is whether guarantees are expressed with reference to guarantees given to other flows/flow classes (relative QoS), or whether guarantees are expressed as absolute bounds (absolute QoS).
        Efforts to provision for QoS in the Internet in the early and mid-1990s, which resulted in the Integrated Services (IntServ) service model [3], focused on per-flow absolute QoS guarantees. However, due to scalability issues and a lagging demand for per-flow absolute QoS, the interest in Internet QoS eventually shifted to relative perclass guarantees. Since late 1997, the Differentiated Services (DiffServ) [2] working group has discussed several proposals for per-class relative QoS guarantees, e.g., [4,17].
        With the exception of the Expedited Forwarding service [11], proposals for relative per-class QoS discussed within the DiffServ context define the service differentiation qualitatively, in the sense that some classes receive lower delays and a lower loss rate

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