alex中关于PFC的解释，本人英语水平有限，自己看看着翻译吧
4.5Quality of Service
The purpose of QoS is to differentiate resources, that is to differentiate access and bandwidth proportionally to the priority of the different user subscriptions. This is achieved with a QoS reservation and scheduling algorithm.

In the R99 standard, new procedures are introduced to let BSS negotiate the QoS with SGSN. At activation of the PDP-Context between the MS and SGSN, a QoS level is negotiated between BSS and the SGSN.

The QoS level is valid per Packet Flow Context (PFC) for an MS in BSS.
In downlink the MS can have several PFCs activated in BSS, that is an MS can have more than one application running at the same time.
In uplink there can only be one active PFC for an MS.
The inputs for the negotiation of a QoS level, are the QoS attributes and network capability. There are four main traffic classes, Background, Interactive, Streaming and Conversational where the Ericsson BSS supports Background, Interactive and Streaming:

BackgroundThe Background class is intended to be used by applications where the data is not required to arrive within a certain time, for example e-mail and file transfers.

InteractiveThe Interactive class is intended to be used by applications where the end-user is requesting data on line and thus is expecting data to arrive quite quickly, for example web-browsing. It is possible to differentiate between users in the Interactive class, 3 levels of priority are available.

StreamingThe Streaming class is intended to be used by applications where the end-user is requesting real time data such as video or audio clips. Introducing the support of the QoS traffic class Streaming makes it possible to fulfill Guaranteed Bit Rate (GBR) requirements for Streaming applications also in cells with high traffic load. Within traffic class Streaming there are two different priorities, Media Streaming and EIT Streaming.
Media Streaming has the highest priority and is used by audio-video applications with high requirements on bandwidth.

EIT Streaming is used for delay sensitive application that does not require that high bandwidth, for example applications like Push to Talk.



If Conversational is requested, it will be treated as Interactive

Ericsson BSS also supports Quality of Service for MSs and SGSNs supporting only 3GPP R97/R98 by mapping the R97/R98 specific QoS attributes onto the classes specified in R99 version of QoS.

For more information about QoS, see Reference [12].