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.
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。
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
destination_address,
mac_service_data_unit,
Each M_UNITDATA indication corresponds to the receipt of an error-free MAC frame from a LAN.
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.
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.
The source_address parameter is the individual address of the source MAC entity.
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.
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.
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.
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.
destination_address,
mac_service_data_unit,
A data request primitive is invoked to transmit a frame to an individual LAN.
The destination_address parameter is the address of an individual MAC entity or a group of MAC entities.
The source_address parameter is the individual address of the source MAC entity.
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).
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).
The frame_check_sequence parameter is explicitly provided as a parameter of the primitive so that it can be used without recalculation.
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.
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.
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_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.
NOTE—These status parameters provide a common approach across MACs for handling the fact that:
a) A MAC can inherently be working or not (as indicated by MAC_Operational).
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).
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.
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.
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.
adminPointToPointMAC: This parameter can take three values, as follows:
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.
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.
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.
If adminPointToPointMAC is set to ForceTrue, then operPointToPointMAC shall be set True. If adminPointToPointMAC is set to ForceFalse, then operPointToPointMAC shall be set 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.
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.
