软件能力成熟度模型CMM(Capability Maturity Model)描述和分析了软件过程能力的发展与改进的程度，确立了一个软件过程成熟程度的分级标准。在初始级，软件过程定义几乎处于无章可循的状态，软件产品的成功往往依赖于个人的努力和机遇。在(7)，已建立了基本的项目管理过程，可对成本、进度和功能特性进行跟踪。在(8)，用于软件管理与工程两方面的软件过程均已文档化、标准化，并形成了整个软件组织的标准软件过程。在已管理级，对软件过程和产品质量有详细的度量标准。在(9)，通过对来自过程、新概念和新技术等方面的各种有用信息的定量分析，能够不断地、持续地对过程进行改进。

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Frame. Relay is simplified form. of(71), similar in principle to(72), in which synchronous, frames of data are routed to different destinations depending on header information . Packets are routed throught one or more Virtual Circuits known as(73). Most Virtual Circuits are(74),which means that the network provider sets up all DLCI connections at subscription time.(75)are also part of the Frame. Relay specification . They privide a link that only lasts only as long as the session.

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Networks can be interconnected by different devices．In the physical layer，networks can be connected by(66)or Hubs, which just move the bits from one network to an identical net-work. One layer up we find bridgas and swiehes, which operate at data link layer. They can accept(67), examine the MAC address, and forward the frames to a different network while doing minor protocol translation in the process. In the network layer, we have routers that can connect two netwoks. If two networks have(68)network layer, the router may be able to translate between the packet formats. In the transport layer we find transport gateway, which can interface between the two transport connections. Finally, in the application layer, application gateways translate message(69). As an example, gateways between Internet e-mail and X.400 e-mail must(70) the e-mail message and change various header fields.

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