RSTP協議——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實體提供給網橋內的MAC轉發實體的內部子層服務，是由每一個LAN端口的MAC提供的。它遵照合適的MAC函數和其所鏈接的LAN的協議。沒有控制幀，即，沒有傳達MAC用戶數據的幀，被轉發到除了其所在的LAN意外的任意LAN。（譯者注：應該是控制幀不能轉發到其他LAN，而普通幀能夠）

 

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.

內部子層服務來自於ISO/IEC 15802-1的MAC服務，並對其充實了必需的轉發性能的元素。在終端工做站內，這些額外的元素被認爲或者是在MAC服務邊界之下、只跟服務提供者的操做有關，或者本地事務沒有造成MAC服務端到端特性的一部分。與ISO/IEC 15802-1相比，MA_UNITDATA.request和MA_UNITDATA.indication原語被增長了兩個參數，分別是frame_type和frame_check_sequence。內部子層服務的定義沒有爲LAN MAC服務定義增長任何新的服務原語。

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

內部子層服務不包括MAC專有特性，也不包括單獨一個LAN內的操做。描述該服務的原語以下：

 

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.

每一個M_UNITDATA指示對應了從LAN接收的沒有錯誤的MAC幀。

 

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：接收包錯誤狀況的詳細定義在相應的MAC標準裏，例如，FCS錯誤，長度錯誤，非整數的字節等。

 

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參數表示幀類別。參數取值爲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參數是單獨的MAC地址或MAC組的地址。

 

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

source_address參數是單獨的源MAC地址。

 

The mac_service_data_unit parameter is the service user data.

mac_service_data_unit參數是用戶數據。

 

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參數是發起請求的原始用戶的優先級。取值範圍爲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的缺省值爲0。其他1-7表示優先級，1最低，7最高。進一步的說明請參見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參數做爲原語的參數提供出來，能夠用做相關請求原語的參數，不須要再從新計算。

 

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.

根據所接收的數據包識別LAN是本地事務，沒有表示爲服務原語的參數。

 

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.

數據請求原語被髮送到單獨的LAN。

 

The frame_type parameter indicates the class of frame.

frame_type參數表示幀類別。

 

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

destination_address參數是單獨的MAC地址或MAC組的地址。

 

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

source_address參數是單獨的源MAC地址。

 

The mac_service_data_unit parameter is the service user data.

mac_service_data_unit參數是用戶數據。

 

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參數是發起請求的原始用戶的優先級。取值範圍爲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參數是本地服務提供者所使用的優先級。只要MAC方法容許，無論是本地仍是鏈接到同一LAN的其它工做站，它都可以用於肯定發送數據包（由本地MAC實體進行排隊）的優先級。

 

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參數做爲原語的參數提供出來，能夠用做相關請求原語的參數，不須要再從新計算。

 

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.

根據所接收的數據包識別LAN是本地事務，沒有表示爲服務原語的參數。

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.

在單元數據服務原語以外，內部子層服務經過MAC轉發實體提供了兩個參數，用來檢查和控制MAC實體的管理和控制狀態。

 

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：若是容許MAC實體工做，則值爲TRUE，不然爲FALSE。本參數的值由6.5節規定的MAC函數所肯定。

 

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：若是MAC實體處於某個工做狀態且MAC_Enabled爲TRUE，即，MAC實體可用於發送和/或接收數據包，而且管理員贊成這樣作，則本參數值爲TRUE。不然爲FALSE。本參數的值由6.5節規定的MAC函數所肯定。

 

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

注意：這些狀態參數爲以下操做提供了跨越不一樣MAC的共同方法：

 

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

a)  MAC是否工做（由MAC_Operational參數指示這一點）

 

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) 若是MAC是可操做的，有時可能出於管理緣由修改其操做狀態，阻止任意用戶使用其所提供的服務（使用MAC_Enabled參數）。

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.

在單元數據服務原語以外，內部子層服務經過MAC轉發實體提供了兩個參數，用來檢查和控制MAC實體點對點狀態的管理和控制狀態。

 

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

operPointToPointMAC：參數取值以下：

 

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鏈接到點對點LAN，即最多有一個其它系統鏈接到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鏈接到非點對點LAN上，便可以有多個其它系統鏈接到LAN上。

 

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

adminPointToPointMAC：參數取值以下：

 

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。管理員強制要求MAC認爲本身鏈接到一個點對點LAN，無論MAC實體本身的判斷如何。

 

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。管理員強制要求MAC認爲本身鏈接到一個非點對點LAN，無論MAC實體本身的判斷如何。

 

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。管理員要求根據6.5節定義的MAC函數肯定MAC點對點狀態。

 

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

若是adminPointToPointMAC設置爲ForceTrue，則operPointToPointMAC應該設置爲TRUE。若是adminPointToPointMAC設置爲ForceFalse，則operPointToPointMAC應該設置爲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.

若是adminPointToPointMAC設置爲Auto，operPointToPointMAC的值根據6.5節定義的MAC函數肯定。若是這些函數肯定MAC實體鏈接到一個點對點LAN，則operPointToPointMAC爲TRUE，不然爲FALSE。在缺少是否MAC鏈接到點對點 LAN的規定時，operPointToPointMAC應該設置爲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的值是動態肯定的，即，一旦adminPointToPointMAC的值發生改變，或者MAC實體指定的函數改變了點對點的狀態，則該值都須要從新設置。