RSTP协议――第6章(6.4)

6.4         Internal Sublayer Service provided within the MAC Bridge

The Internal Sublayer Service provided by a MAC entity to the MAC Relay Entity within a Bridge is that provided by the individual MAC for the LAN Port. This observes the appropriate MAC procedures and protocol for the LAN to which it attaches. No control frames, i.e., frames that do not convey MAC user data, are forwarded on any LAN other than that on which they originated.

由MAC实体提供给网桥内的MAC转发实体的内部子层服务，是由每个LAN端口的MAC提供的。它遵守合适的MAC函数和其所连接的LAN的协议。没有控制帧，即，没有传达MAC用户数据的帧，被转发到除了其所在的LAN意外的任意LAN。（译者注：应该是控制帧不能转发到其余LAN，而普通帧可以）

 

The Internal Sublayer Service is derived from the MAC Service defined by ISO/IEC 15802-1 by augmenting that specification with elements necessary to the performance of the relay function. Within an end station, these additional elements are considered to be either below the MAC Service boundary, and pertinent only to the operation of the service provider; or local matters not forming part of the peer-to-peer nature of the MAC Service. Two parameters are added to the list of parameters associated with the MA_UNITDATA.request and MA_UNITDATA.indication primitives defined by ISO/IEC 15802-1. These are frame_type and frame_check_sequence. The definition of the Internal Sublayer Service does not add any new service primitives to those defined by the LAN MAC Service Definition.

内部子层服务来自于ISO/IEC 15802-1的MAC服务，并对其充实了必需的转发性能的元素。在终端工作站内，这些额外的元素被认为或者是在MAC服务边界之下、只跟服务提供者的操作有关，或者本地事务没有形成MAC服务端到端特性的一部分。与ISO/IEC 15802-1相比，MA_UNITDATA.request和MA_UNITDATA.indication原语被增加了两个参数，分别是frame_type和frame_check_sequence。内部子层服务的定义没有为LAN MAC服务定义增加任何新的服务原语。

6.4.1   Service primitives

The Internal Sublayer Service excludes MAC-specific features and procedures whose operation is confined to that of the individual LANs. The unit-data primitives that describe this service are

内部子层服务不包括MAC专有特性，也不包括单独一个LAN内的操作。描述该服务的原语如下：

 

M_UNITDATA.indication

(

frame_type,

destination_address,

source_address,

mac_service_data_unit,

user_ priority,

frame_check_sequence

)

 

Each M_UNITDATA indication corresponds to the receipt of an error-free MAC frame from a LAN.

每个M_UNITDATA指示对应了从LAN接收的没有错误的MAC帧。

 

NOTE—Detailed specifications of error conditions in received frames are contained in the relevant MAC standards; for example, FCS errors, length errors, non-integral number of octets.

注意：接收包错误情况的详细定义在相应的MAC标准里，例如，FCS错误，长度错误，非整数的字节等。

 

The frame_type parameter indicates the class of frame. The value of this parameter is one of user_data_frame, mac_specific_frame, or reserved_frame.

frame_type参数表示帧类别。参数取值为user_data_frame, mac_specific_frame, 或reserved_frame

 

The destination_address parameter is the address of an individual MAC entity or a group of MAC entities.

destination_address参数是单独的MAC地址或MAC组的地址。

 

The source_address parameter is the individual address of the source MAC entity.

source_address参数是单独的源MAC地址。

 

The mac_service_data_unit parameter is the service user data.

mac_service_data_unit参数是用户数据。

 

The user_priority parameter is the priority requested by the originating service user. The value of this parameter is in the range 0 through 7.

user_priority参数是发起请求的原始用户的优先级。取值范围为0-7。

 

NOTE—The default user_priority value is 0. Values 1 through 7 form an ordered sequence of user_priorities, with 1 being the lowest value and 7 the highest. See 7.7.3 and Annex G (informative) for further explanation of the use of user_priority values.

注意：user_priority的缺省值为0。其余1-7表示优先级，1最低，7最高。进一步的说明请参见7.7.3和附件G。

 

The frame_check_sequence parameter is explicitly provided as a parameter of the primitive so that it can be used as a parameter to a related request primitive without recalculation.

frame_check_sequence参数作为原语的参数提供出来，可以用作相关请求原语的参数，不需要再重新计算。

 

The identification of the LAN from which particular frames are received is a local matter and is not expressed as a parameter of the service primitive.

根据所接收的数据包识别LAN是本地事务，没有表示为服务原语的参数。

 

M_UNITDATA.request

(

frame_type,

destination_address,

source_address,

mac_service_data_unit,

user_priority,

access_priority,

frame_check_sequence

)

 

A data request primitive is invoked to transmit a frame to an individual LAN.

数据请求原语被发送到单独的LAN。

 

The frame_type parameter indicates the class of frame.

frame_type参数表示帧类别。

 

The destination_address parameter is the address of an individual MAC entity or a group of MAC entities.

destination_address参数是单独的MAC地址或MAC组的地址。

 

The source_address parameter is the individual address of the source MAC entity.

source_address参数是单独的源MAC地址。

 

The mac_service_data_unit parameter is the service user data.

mac_service_data_unit参数是用户数据。

 

The user_priority parameter is the priority requested by the originating service user. The value of this parameter is in the range 0 (lowest) through 7 (highest).

user_priority参数是发起请求的原始用户的优先级。取值范围为0-7，0最低，7最高。

 

The access_priority parameter is the priority used by the local service provider to convey the request. It can be used to determine the priority attached to the transmission of frames queued by the local MAC Entity, both locally and among other stations attached to the same individual LAN, if the MAC method permits. The value of this parameter, if specified, is in the range 0 (lowest) through 7 (highest).

access_priority参数是本地服务提供者所使用的优先级。只要MAC方法允许，不管是本地还是连接到同一LAN的其它工作站，它都能够用于确定发送数据包（由本地MAC实体进行排队）的优先级。

 

The frame_check_sequence parameter is explicitly provided as a parameter of the primitive so that it can be used without recalculation.

frame_check_sequence参数作为原语的参数提供出来，可以用作相关请求原语的参数，不需要再重新计算。

 

The identification of the LAN to which a frame is to be transmitted is a local matter and is not expressed as a parameter of the service primitive.

根据所接收的数据包识别LAN是本地事务，没有表示为服务原语的参数。

6.4.2   MAC status parameters

In addition to the unit-data service primitives, the Internal Sublayer Service makes available a pair of status parameters that permit inspection of, and control over, the administrative and operational state of the MAC entity by the MAC Relay Entity.

在单元数据服务原语之外，内部子层服务通过MAC转发实体提供了两个参数，用来检查和控制MAC实体的管理和控制状态。

 

MAC_Enabled: The value of this parameter is TRUE if use of the MAC entity is permitted; and is otherwise FALSE. The value of this parameter is determined by the specific MAC procedures, as specified in 6.5.

MAC_Enabled：如果允许MAC实体工作，则值为TRUE，否则为FALSE。本参数的值由6.5节规定的MAC函数所确定。

 

MAC_Operational: The value of this parameter is TRUE if the MAC entity is in a functioning state and MAC_Enabled is also TRUE; i.e., the MAC entity can be used to transmit and/or receive frames, and its use is permitted by management. Its value is otherwise FALSE. The value of this parameter is determined by the specific MAC procedures, as specified in 6.5.

MAC_Operational：如果MAC实体处于某个工作状态且MAC_Enabled为TRUE，即，MAC实体可用于发送和/或接收数据包，并且管理员同意这样做，则本参数值为TRUE。否则为FALSE。本参数的值由6.5节规定的MAC函数所确定。

 

NOTE—These status parameters provide a common approach across MACs for handling the fact that:

注意：这些状态参数为如下操作提供了跨越不同MAC的共同方法：

 

a) A MAC can inherently be working or not (as indicated by MAC_Operational).

a)  MAC是否工作（由MAC_Operational参数指示这一点）

 

b) If the MAC is operational, there may be the need to override its operational state for administrative reasons, preventing any users from making use of its services (by means of MAC_Enabled).

b) 如果MAC是可操作的，有时可能出于管理原因修改其操作状态，阻止任意用户使用其所提供的服务（使用MAC_Enabled参数）。

6.4.3   Point-to-Point MAC parameters

In addition to the unit-data service primitives, the Internal Sublayer Service makes available a pair of parameters that permit inspection of, and control over, the administrative and operational state of the point- to-point status of the MAC entity by the MAC Relay Entity.

在单元数据服务原语之外，内部子层服务通过MAC转发实体提供了两个参数，用来检查和控制MAC实体点对点状态的管理和控制状态。

 

operPointToPointMAC: This parameter can take two values, as follows:

operPointToPointMAC：参数取值如下：

 

a) True. The MAC is connected to a point-to-point LAN; i.e., there is at most one other system attached to the LAN.

a) True。MAC连接到点对点LAN，即最多有一个其它系统连接到LAN上。

 

b) False. The MAC is connected to a non-point-to-point LAN; i.e., there can be more than one other system attached to the LAN.

b) False。MAC连接到非点对点LAN上，即可以有多个其它系统连接到LAN上。

 

adminPointToPointMAC: This parameter can take three values, as follows:

adminPointToPointMAC：参数取值如下：

 

a) ForceTrue. The administrator requires the MAC to be treated as if it is connected to a point-to-point LAN, regardless of any indications to the contrary that are generated by the MAC entity.

a) ForceTrue。管理员强制要求MAC认为自己连接到一个点对点LAN，不管MAC实体自己的判断如何。

 

b) ForceFalse. The administrator requires the MAC to be treated as connected to a non-point-to-point LAN, regardless of any indications to the contrary that are generated by the MAC entity.

b) ForceFalse。管理员强制要求MAC认为自己连接到一个非点对点LAN，不管MAC实体自己的判断如何。

 

c) Auto. The administrator requires the point-to-point status of the MAC to be determined in accordance with the specific MAC procedures defined in 6.5.

c) Auto。管理员要求根据6.5节定义的MAC函数确定MAC点对点状态。

 

If adminPointToPointMAC is set to ForceTrue, then operPointToPointMAC shall be set True. If adminPointToPointMAC is set to ForceFalse, then operPointToPointMAC shall be set False.

如果adminPointToPointMAC设置为ForceTrue，则operPointToPointMAC应该设置为TRUE。如果adminPointToPointMAC设置为ForceFalse，则operPointToPointMAC应该设置为FALSE。

 

If adminPointToPointMAC is set to Auto, then the value of operPointToPointMAC is determined in accordance with the specific procedures defined for the MAC entity concerned, as defined in 6.5. If these procedures determine that the MAC entity is connected to a point-to-point LAN, then operPointToPointMAC is set TRUE; otherwise it is set FALSE. In the absence of a specific definition of how to determine whether the MAC is connected to a point-to-point LAN or not, the value of operPointToPointMAC shall be FALSE.

如果adminPointToPointMAC设置为Auto，operPointToPointMAC的值根据6.5节定义的MAC函数确定。如果这些函数确定MAC实体连接到一个点对点LAN，则operPointToPointMAC为TRUE，否则为FALSE。在缺乏是否MAC连接到点对点 LAN的规定时，operPointToPointMAC应该设置为FALSE。

 

The value of operPointToPointMAC is determined dynamically; i.e., it is re-evaluated whenever the value of adminPointToPointMAC changes, and whenever the specific procedures defined for the MAC entity evaluate a change in its point-to-point status.

operPointToPointMAC的值是动态确定的，即，一旦adminPointToPointMAC的值发生改变，或者MAC实体指定的函数改变了点对点的状态，则该值都需要重新设置。