RSTP協議——第6章(6-6.2)

6    Support of the MAC Service

MAC Bridges interconnect the separate IEEE 802 LANs that compose a Bridged Local Area Network by relaying and filtering frames between the separate MACs of the bridged LANs. The position of the bridging function within the MAC Sublayer is shown in Figure 6-1.

MAC網橋把彼此獨立的IEEE 802 LAN鏈接在一塊兒，構成橋接本地局域網，MAC網橋對於不一樣LAN之間的數據進行轉發和過濾，如Figure 6-1。

 

 

This clause discusses the following aspects of service provision:

 

a) Provision of the MAC Service to end stations.

b) Preservation of the MAC Service.

c) Maintenance of QoS.

d) Provision of the Internal Sublayer Service within the MAC Bridge.

e) Support of the Internal Sublayer Service by specific MAC procedures.

f) Filtering services.

 

本章討論以下方面的規定：

a)   MAC服務到終端工做站的規定。

b)   MAC服務的保存。

c)   維護QoS。

d)   在MAC網橋內的內部子層服務的規定。

e)   使用特定MAC函數支持內部子層服務。

f)   過濾服務。

6.1         Support of the MAC Service

The MAC Service provided to end stations attached to a Bridged Local Area Network is the (unconfirmed) connectionless-mode MAC Service defined in ISO/IEC 15802-1. The MAC Service is defined as an abstraction of the features common to a number of specific MAC Services; it describes the transfer of user data between source and destination end stations, via MA-UNITDATA request primitives and corresponding MA-UNITDATA indication primitives issued at MAC service access points. Each MA-UNITDATA request and indication primitive has four parameters: Destination Address, Source Address, MAC Service data unit (MSDU), and Priority.

提供給終端工做站，鏈接到橋接LAN的MAC服務是ISO/IEC 15802-1所定義的非正式的無鏈接模式MAC服務。MAC服務是對多種具體MAC服務共同特性的抽象，它描述了用戶數據在源和目的終端工做站之間的傳輸，使用MA-UNITDATA請求和對應的MA-UNITDATA指示原語來描述。每一個MA-UNITDATA請求和指示原語都有4個參數：目的地址、源地址、MAC服務數據單元（MSDU）和優先級。

 

To improve the availability of the MAC Service to end stations and support network management, MAC Bridges can be configured:

爲了提高MAC服務到終端工做站和網管的可用性，MAC網橋能夠配置爲：

 

a) To provide redundant paths between end stations to enable the network to continue to provide the MAC Service in the event of component failure (of Bridge or LAN).

a)  支持終端工做站之間冗餘的路徑，以便網絡一部分發生故障時還能繼續提供MAC服務。

 

b) So that the paths supported between end stations are predictable and configurable given the availability of network components.

b)  在給定網絡可用性的條件下，在終端工做站之間的路徑是可預測和可配置的。

 

A MAC Bridge may restrict the provision of the MAC Service to authenticated and authorized devices. Unauthorized devices can be denied access to a bridged LAN, except as necessary for the purpose of conducting protocol exchanges required by an authentication process.

MAC網橋能夠經過對設備進行認證和受權來顯示MAC服務。除了認證協議外，非受權設備被禁止訪問橋接LAN。

 

NOTE—Authentication and authorization to access a LAN may be achieved by administrative or management mechanisms, or by means of an active authorization mechanism, such as is defined in IEEE Std 802.1X.

注意：認證和對LAN訪問的認證參見IEEE Std 802.1X。

6.2         Preservation of the MAC Service

The MAC Service provided by a Bridged Local Area Network is similar to that provided by a single LAN (6.3). In consequence,

橋接LAN提供的MAC服務相似於單個LAN(6.3)所提供的服務。以下：

 

a) A Bridge is not directly addressed by communicating end stations, except as an end station for management purposes—frames transmitted between end stations carry the MAC Address of the peer-end station in their Destination Address field, not a MAC Address of the Bridge.

a)  網橋不能經過與終端工做站直接通信而進行尋址，除非終端工做站處於管理目的，在終端工做站之間傳輸的數據包在目的地址字段帶着對端工做站的MAC地址，不是網橋的MAC地址。

 

b) All MAC Addresses need to be unique within the network.

b) 全部MAC地址在網絡內都是惟一的。

 

c) MAC Addresses of end stations are not restricted by the topology and configuration of the network.

c) 網絡拓撲和配置對終端工做站的MAC地址沒有限制。