标签:audio ini isp iso 创建 ethernet control sig today
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https://en.wikipedia.org/wiki/Quality_of_service
Quality of service (QoS) is the overall performance of a telephony or computer network, particularly the performance seen by the users of the network. To quantitatively measure quality of service, several related aspects of the network service are often considered, such as error rates, bit rate, throughput, transmission delay, availability, jitter, etc.
In the field of computer networking and other packet-switched telecommunication networks, quality of service refers to traffic prioritization and resource reservation control mechanisms rather than the achieved service quality. Quality of service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow.
Quality of service is particularly important for the transport of traffic with special requirements. In particular, developers have introduced technology to allow computer networks to become as useful as telephone networks for audio conversations, as well as supporting new applications with even stricter service demands.
https://zh.wikipedia.org/wiki/服务质量
在因特网创建的初期并没有意识到QoS应用的需要,因此整个因特网运作如一个“竭尽全力”的系统。每段信息都有4个“服务类别”位和3个“优先级”位,但是他们完全没有派上用场。依发送和接收者看来,数据包从起点到终点的传输过程中会发生许多事情,并产生如下有问题的结果:
流量约定(SLA, Service Level Agreement服务等级协议)给数据流设定优先级,以此在网络/协议层面上,根据相互商定的尺度,设定有保障的性能、通过量、延迟等界限。一些特定形式的网络数据流需要定义服务质量,例如:
这些类型的服务被称为非弹性,意思是它们需要固定的带宽才能运作--如果得到多余的带宽,它们也无法使用;如果得到较少的带宽,则根本无法工作。相形之下,弹性应用可以从多余的带宽中受益。
实质上有两种方式提供QoS保证。第一种,就是简单地提供大量的资源,用丰富、安全的余量设备应付预期中的“高峰”需求。这样既好又简单,然而有人认为这种方式代价昂贵,而且不能应对高峰需求超越预期的情形,部署额外的资源也很耗费时间。
第二种是要求用户预约带宽,并且仅在能够提供可靠服务的前提下接受预约。自然,可以为预约服务向用户收费。常用的实现方法有两类。
Conventional Internet routers and LAN switches operate on a best effort basis. This equipment is less expensive, less complex and faster and thus more popular than competing more complex technologies that provided QoS mechanisms. There were four “Type of service” bits and three “Precedence” bits provided in each IP packet header, but they were not generally respected. These bits were later re-defined as Differentiated services code points (DSCP).
With the advent of IPTV and IP telephony, QoS mechanisms are increasingly available to the end user.[citation needed]
A number of attempts for layer 2 technologies that add QoS tags to the data have gained popularity in the past. Examples are frame relay, asynchronous transfer mode (ATM) and multiprotocol label switching (MPLS) (a technique between layer 2 and 3). Despite these network technologies remaining in use today, this kind of network lost attention after the advent of Ethernet networks. Today Ethernet is, by far, the most popular layer 2 technology. Ethernet uses 802.1p to signal the priority of a frame.
In packet-switched networks, quality of service is affected by various factors, which can be divided into “human” and “technical” factors. Human factors include: stability of service, availability of service, delays, user information. Technical factors include: reliability, scalability, effectiveness, maintainability, grade of service, etc.[5]
Many things can happen to packets as they travel from origin to destination, resulting in the following problems as seen from the point of view of the sender and receiver:
标签:audio ini isp iso 创建 ethernet control sig today
原文地址:http://www.cnblogs.com/yuanjiangw/p/6710648.html