2.1 Description des interactions MAC sublayer LLC sublayer Application layer Figure 2 – Emission de données sans accusé de réception Il est proposé six services pour permettre de transfé
Domaine d'application et objet
La présente section de la CEI 1334-4 décrit pour une entité de sous-couche LLC, Logical Link
Control, les services offerts à la couche application et les services demandés à la sous-couche
In general, the services of a layer (or sub-layer) are defined as the capabilities provided to a user of the upper layer To deliver these services, a layer (or sub-layer) relies on the necessary services from the immediately lower layer (or sub-layer).
Services are defined by the description of the information flow between the application layer and the MAC sublayer, specifically through the characterization of the primitives and parameters that define each service.
Ces primitives sont associées à une transmission du type sans connexion.
This section refers to the three-layer reference model outlined in IEC 1334-4-1, with provisions made for future extensions of the model to include more than three layers.
2 Dans la présente section, une ouverture est aussi ménagée pour de futures extensions au mode de transmission avec connexion.
Dans le présent article, on se référera au modèle de référence OSI selon la norme ISO 7498.
Description des interactions
Trois services de base sont proposés couramment dans le modèle OSI pour les principaux besoins de transmission:
Ces services ne font pas l'objet d'un accusé de réception et sont du mode sans connexion. layer
Figure 2 – Emission de données sans accusé de réception
Six services are proposed to facilitate the transfer of unsolicited L_SDU (Logical Link Control Service Data Units) between a remote application layer entity and a local application layer entity.
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This clause outlines the services that the LLC sublayer must provide to the application layer, enabling local application entities to exchange packets with remote peer entities through DCP LLC operations The description of these services is presented in an abstract manner.
Three ground services are proposed as usual in the OSI model for the main transmission purposes:
These services are non-acknowledged and in connectionless mode.
Figure 2 – Send Data Non-acknowledged
Six services are proposed for providing facilities to transfer unsolicited L_SDU between a remote application layer entity and the local application layer entity:
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Les services DL_Reply sont destinés à demander à l'entité de sous-couche LLC distante d'émettre une L_SDU préalablement préparée.
Les services DL_Update_Reply sont destinés à préparer et demander des services DL_Reply.
Figure 4 – Reply Data on Request
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The DL_Reply.services are designed for asking the remote LLC sublayer entity to send a previously prepared L_SDU.
The DL_Update_Reply services are designed to prepare DL_Reply services.
Figure 4 – Reply Data on Request
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Le service suivant est disponible pour des besoins de gestion:
Ce service utilise les moyens de transmission en diffusion disponible dans l'entité de sous- couche MAC Ce service est utilisé pour transmettre très peu de données à toutes les entités
DL_Data.request
The DL_Data.request primitive is sent to the LLC sublayer entity to request the transmission of an L_SDU to one or more remote LLC sublayer entities using LLC transmission procedures.
La sémantique de la primitive est la suivante:
Les paramètres Destination_LSAP et Source_LSAP spécifient les LSAP, Link Service Access
Point (point d'accès au service livraison) distants et locaux impliqués dans la transmission des unités de données.
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One service is provided for management purposes:
This service uses the broadcast facilities available at the MAC sublayer entity This service is used to transmit very few data to all peer LLC sublayer entities.
The DL_Data.request primitive is utilized by the LLC sublayer entity to initiate the transmission of an L_SDU to one or more remote LLC sublayer entities, following the established LLC transmission procedures.
The semantics of the primitive are as follows:
The Source_LSAP and Destination_LSAP parameters specify the local and remote LSAPs involved in the data unit transmission.
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Le paramètre Destination_address spécifie l'adresse de la station distante impliquée dans la transmission des unités de données.
Le paramètre L_SDU spécifie l'unité de donnée de service devant être transférée par l'entité de sous-couche LLC vers l'entité (ou les entités) de sous-couche LLC homologue(s).
Le paramètre Link_class est réservé pour de futures extensions du service de transmission de
Cette primitive est générée par l'entité de couche application à chaque fois que des données sont émises vers une ou des entités de couche application homologues.
Upon receiving this primitive, the LLC sublayer entity adds all specific LLC fields and forwards the appropriately formatted L_PDU (Logical Protocol Data Unit) to the lower protocol layers for transfer to the corresponding LLC peer entity or entities.
La réception de cette primitive provoque l'émission d'une primitive MA_Data.request afin de transférer la demande vers l'entité de sous-couche MAC.
DL_Data.confirm
La primitive DL_Data.confirm délivre une confirmation locale de la transmission de la L_PDU.
This primitive has a local significance and provides an appropriate response to the application layer entity that initiated a DL_Data.request The response indicates the local success or failure of the request, as specified by the lower layers.
La sémantique de la primitive est la suivante:
Les paramètres Destination_LSAP et Source_LSAP spécifient les LSAP distants et locaux impliqués dans la transmission des unités de données Le paramètre Source_LSAP spécifie le
LSAP qui a délivré une primitive DL_Data.request suite à laquelle la confirmation doit être envoyée.
Le paramètre Destination_address spécifie l'adresse de la station distante impliquée dans la transmission des unités de données.
The Transmission_Status parameter is used to convey the transmission state to the local application layer entity that made the request It indicates whether the previous DL_Data.request primitive was successful or failed.
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The Destination_address parameter specifies the address of the remote station involved in the data unit transmission.
The L_SDU parameter specifies the link data unit to be transferred by the LLC sublayer entity to the peer LLC sublayer entity or entities.
The Link_class parameter is reserved for future DL_Data transfer service extension.
This primitive is generated by the application layer entity whenever data is transmitted to a peer application layer entity or entities.
The receipt of this primitive will cause the LLC sublayer entity to append all LLC specific fields
(given below) and pass the properly formed L_PDU to the lower layers of protocol for transfer to the peer LLC sublayer entity or entities.
The receipt of this primitive will generate a MA_Data.request for transfer to the MAC sublayer entity.
The DL_Data.confirm function provides a local acknowledgment of the L_PDU transmission This primitive is significant only within the local context and serves as a response to the application layer entity that initiated the DL_Data.request, indicating whether the request was locally successful or failed, as determined by the lower layers.
The semantics of the primitive are as follows:
The Source_LSAP and Destination_LSAP parameters define the local and remote LSAPs for data unit transmission The Source_LSAP indicates the LSAP that initiated the DL_Data.request, which is the recipient of the confirmation.
The Destination_address parameter specifies the address of the remote station involved in the data unit transmission.
The Transmission_Status parameter conveys status information to the local application layer, indicating whether the preceding DL_Data.request primitive was successful or failed.
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Cette primitive est générée en réponse à une primitive DL_Data.request vers l'entité de couche application locale Cette primitive est générée suite à l'arrivée d'une primitive de service
MA_Data.confirm délivrée par l'entité de sous-couche MAC locale.
Il est supposé que l'entité de couche application dispose de suffisamment d'informations pour associer la réponse à la demande appropriée.
DL_Data.indication
The DL_Data.indication primitive is transmitted from the LLC sublayer to the application layer entity or entities to signal the arrival of an L_PDU It defines the data transfer from the LLC sublayer entity to the application layer entity or entities.
La sémantique de la primitive est la suivante:
The Destination_LSAP and Source_LSAP parameters define the local and remote LSAPs involved in data unit transmission The Destination_LSAP parameter can be specified as either an individual address or a group address, depending on the requirements.
Les paramètres Destination_address et Source_address spécifient l'adresse des stations, locale et distante impliquées dans la transmission des unités de données Le paramètre
Destination_address peut être soit une adresse individuelle, soit une adresse de groupe.
Le paramốtre L_SDU spộcifie l'unitộ de donnộes de service liaison qui a ộtộ reỗue par l'entitộ de sous-couche LLC.
Le paramètre Link_class est réservé pour de futures extensions du service de transmission de
The DL_Data.indication primitive is sent from a LLC sublayer entity to one or more application layer entities to signal the arrival of a MA_Data.indication primitive at the local LLC sublayer entity, triggered by an action from a remote user entity utilizing the data link.
Ces L_PDU ne sont signalées que si le paramètre Destination_address désigne l'un des LSAP locaux par une adresse individuelle ou de groupe.
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The DL_Data.request primitive is generated in response to a request from the local application layer entity, while the incoming MA_Data.confirm service from the local MAC sublayer entity also triggers the generation of this primitive.
It is assumed that sufficient information is available to the application layer entity to associate the response with the appropriate request.
The DL_Data.indication primitive is transmitted from the LLC sublayer to the application layer to signal the arrival of a L_PDU, facilitating the data transfer process.
LLC sublayer entity to the application layer entity or entities.
The semantics of the primitive are as follows:
The Destination_LSAP and Source_LSAP parameters define the local and remote LSAPs used in data unit transmission, with the Destination_LSAP potentially representing either an individual or a group address as indicated by the incoming L_PDU.
The Destination_address and Source_address parameters define the addresses of the local and remote stations participating in data unit transmission The Destination_address can represent either an individual address or a group address.
The L_SDU parameter specifies the link service data unit which has been received by the LLC sublayer entity.
The Link_class parameter is reserved for future DL_Data transfer service extensions.
The DL_Data.indication is transmitted from the LLC sublayer to the application layer to signal the receipt of a MA_Data.indication from a remote data link user to the local LLC sublayer.
Such L_PDU are reported only if the Destination_address designates one of the local LSAPs by a group or unique address.
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DL_Reply.request
La primitive DL_Reply.request est transmise à l'entité de sous-couche LLC pour demander qu'une L_SDU précédemment préparée soit envoyée en retour par une station distante.
La sémantique de la primitive est la suivante:
The Source_LSAP and Destination_LSAP parameters define the local and remote LSAPs involved in the exchange of data units It is important to note that the Destination_LSAP must not be a group address.
Le paramètre Destination_address spécifie l'adresse de la station distante impliquée dans la transmission des unités de données Ce ne doit pas être une adresse de groupe.
Le paramètre Length_allowed (longueur_autorisée) caractérise la longueur maximale de la
L_SDU que l'utilisateur LLC distant a le droit d'envoyer en retour.
When generated, this primitive is sent from the local LLC sublayer entity to the remote LLC sublayer entity to request the transmission of the previously formatted L_SDU The length of this L_SDU must not exceed the specified parameter.
La réception de cette primitive, si elle est valide, générera une primitive MA_Data.request pour le transfert vers l'entité LLC homologue.
DL_Reply.confirm
The DL_Reply.confirm primitive is sent from a LLC sublayer entity to one or more application layer entities to indicate the arrival of a previously requested L_PDU via the DL_Reply.request primitive This primitive signifies the data transfer from the LLC sublayer entity to the application layer entity.
La sémantique de la primitive est la suivante:
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DL_Reply.request primitive is passed to the LLC sublayer entity to request that a previously prepared L_SDU be returned from a remote station.
The semantics of the primitive are as follows:
The Source_LSAP and Destination_LSAP parameters specify the local and remote LSAPs involved in the data unit exchange The Destination_LSAP shall not be a group address.
The Destination_address parameter specifies the address of the remote station involved in the data unit transmission The Destination_address must not be a group address.
The Length_allowed parameter characterizes the maximum length of the L_SDU the remote
LLC user is allowed to send in return.
The primitive is transmitted from the local LLC sublayer entity to the remote LLC sublayer entity to initiate the transmission of the previously created L_SDU.
L_SDU shall not exceed the Length_allowed parameter.
The receipt of this primitive will generate (if valid) a MA_Data.request for transfer to the peer
The DL_Reply.confirm primitive is transmitted from the LLC sublayer to the application layer to signal the arrival of a previously requested L_PDU via the DL_Reply.request primitive This primitive facilitates the transfer of data from the LLC sublayer to the application layer.
The semantics of the primitive are as follows:
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Les paramètres Destination_LSAP et Source_LSAP spécifient les LSAP distants et locaux impliqués dans la transmission des unités de données Les paramètres Destination_LSAP et
Source_LSAP ne doivent pas être une adresse de groupe.
The Destination_address and Source_address parameters define the remote and local addresses of the stations involved in data unit transmission Both addresses must be unique.
Le paramètre Transmission_Status sert à communiquer l'information concernant l'état de la transmission à l'entité de couche application locale qui a délivré la primitive DL_Reply.request.
Il sert à indiquer le succès ou l'échec de la primitive associée DL_Reply.request précédente.
Le paramốtre L_SDU spộcifie l'unitộ de donnộes de service liaison qui a ộtộ reỗue par l'entitộ de sous-couche LLC.
The DL_Reply.confirm primitive is sent by the LLC sublayer entity to the application layer entity (or entities) to indicate the arrival of a primary MA_Data.indication on the local LLC sublayer, following the action of a remote entity using the data link This occurs after the transmission of a DL_Reply.request primitive, which conveys to the application layer entity the received L_SDU or the reason for failure.
Ces L_PDU ne sont signalées que si le paramètre Destination_address désigne l'un des LSAP locaux.
DL_Reply.indication
The DL_Reply.indication primitive is sent to the application layer to confirm that the local LLC sublayer entity has successfully transmitted a previously prepared L_SDU in response to a request from the remote LLC user This indicates that the remote LLC user initiated a DL_Reply.request and that a response has been successfully delivered.
La sémantique de la primitive est la suivante:
Le paramètre Destination_LSAP spécifie le LSAP qui a préalablement délivré une primitive
DL_Update_Reply.request et auquel l'indication doit être envoyée Ce LSAP ne doit pas être une adresse de groupe.
Le paramètre Source_address spécifie l'adresse de la station qui est à l'origine de la primitive
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The Destination_LSAP and Source_LSAP parameters define the local and remote LSAPs used in data unit transmission It is important to note that neither the Destination_LSAP nor the Source_LSAP can be a group address.
The Destination_address and Source_address parameters define the local and remote addresses of the stations participating in data unit transmission Both addresses must be unique and individual.
The Transmission_Status parameter communicates the status of the DL_Reply.request primitive back to the local application layer, indicating whether the previous request was successful or failed.
The L_SDU parameter specifies the link service data unit which has been received by the LLC sublayer entity.
The DL_Reply.confirm service primitive is transmitted from the LLC sublayer to the application layer to signal the receipt of a MA_Data.indication from a remote data link user This occurs following the transmission of a DL_Reply.request, and it conveys either the received L_SDU or the reason for any failure.
Such L_PDU are reported only if the Destination_address designates one of the local LSAPs.
The DL_Reply.indication primitive is passed to the application layer to indicate that the local
LLC sublayer entity has successfully transmitted a previously prepared L_SDU as requested by the remote LLC user It is both the indication that the remote LLC user has initiated a
DL_Reply.request and that a response has been transmitted.
The semantics of the primitive are as follows:
The Destination_LSAP parameter specifies the LSAP which has previously issued a
DL_Update_Reply.request and to which the indication has to be sent This LSAP shall not be a group address.
The Source_address parameter specifies the address of the station which initiated the
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The Transmission_Status parameter is used to convey information about the transmission state to the local application layer entity from which the request originates It indicates the success or failure of the previously defined L_SDU transmission.
The L_SDU parameter specifies the service data unit that has been sent in response This L_SDU must match the L_SDU previously prepared with the DL_Update_Reply.request primitive.
Upon receiving a DL_Reply.request primitive from the remote LLC sublayer entity, the local LLC sublayer entity initiates the transmission of the requested L_SDU by emitting a MA_Data.request primitive The DL_Reply.indication primitive is generated upon receiving the corresponding MA_Data.confirm, signaling the successful transmission.
On suppose que l'entité de couche application dispose de suffisamment d'informations pour associer la primitive DL_Reply.indication à la primitive DL_Update_Reply.request appropriée.
DL_Update_Reply.request
The DL_Update_Reply.request primitive is sent to the LLC sublayer along with an L_SDU that must be retained by the LLC sublayer entity and issued later upon request from another station.
La sémantique de la primitive est la suivante:
Le paramètre Source_LSAP spécifie le LSAP local à associer à la préparation de l'unité de données Il indique l'adresse d'ó est issue la demande.
NOTE − Aucun paramètre Destination_address n'est précisé Chaque station distante peut demander à la sous- couche LLC Locale de transmettre la L_SDU en attente.
The L_SDU parameter defines the service data unit that the LLC sublayer retains for future transfer, which will occur upon request.
Cette primitive est transmise par l'entité de couche application à l'entité de sous-couche LLC pour associer la L_SDU au LSAP local et indiquer sa présence à l'utilisateur distant.
The presence of a pending L_SDU is indicated at the remote station by setting the Reply subfield of all outgoing L_PDU to a non-zero value This value specifies the length of the pending L_SDU.
The application layer entity must handle the DL_Update_Reply.request primitive and pass it to the LLC sublayer entity to prevent unwanted rewrites The LLC sublayer entity does not verify the existence of a previously sent L_SDU to the local LSAP.
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The Transmission_Status parameter conveys status information to the local requesting application layer, indicating whether the transmission of the previously set L_SDU was successful or failed.
The L_SDU parameter specifies the link service data unit which has been sent in response.
This L_SDU shall be the same as the L_SDU previously prepared with the
DL_Update_Reply.request primitive (see below).
Upon receiving a DL_Reply.request from the remote LLC sublayer entity, the local LLC sublayer entity begins the transmission of the requested L_SDU through a MA_Data.request.
DL_Reply.indication primitive is generated on receipt of the corresponding MA_Data.confirm It then indicates the transmission of the previously sent L_SDU.
It is assumed that sufficient information is available to the application layer entity to associate the DL_Reply.indication with the appropriate DL_Update_Reply.request.
The DL_Update_Reply.request primitive is transmitted to the LLC sublayer along with an L_SDU, which the LLC sublayer entity retains for future transmission upon request from another station.
The semantics of the primitive are as follows:
The Source_LSAP parameter specifies the local LSAP to be associated with the data unit preparation It is the address indicating which LSAP issues the request.
NOTE − No Destination_address is defined Each of the remote station can request the local LLC sublayer to transmit the waiting L_SDU.
The L_SDU parameter specifies the link service data unit to be held by the LLC, in preparation for transfer at a later time when requested The L_SDU may be empty.
This primitive is transmitted from the application layer to the LLC sublayer, linking the L_SDU with the local LSAP and signaling its availability to the remote user.
The remote station is informed of a waiting L_SDU by assigning a non-zero value to the Reply subfield of all outgoing L_PDU, indicating the length of the pending L_SDU.
The application layer must effectively manage the DL_Update_Reply.request primitive sent to the LLC sublayer to prevent unintended overwriting, as the LLC sublayer does not check for the presence of a previously transmitted L_SDU to the local LSAP.
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DL_Update_Reply.confirm
La primitive de service DL_Update_Reply.confirm est transmise par l'entité de sous-couche
LLC vers l'entité de couche application afin d'indiquer les résultats de la primitive associée
DL_Update_Reply.request précédente.
La sémantique de la primitive est la suivante:
Le paramètre Source_LSAP spécifie le LSAP local associé à la préparation de l'unité de données de service liaison.
Le paramètre Status indique le succès ou l'échec de la demande de préparation antérieure de l'unité de données associée.
The Old_L_SDU parameter defines the service data unit held by the LLC sublayer It informs the application layer that the previously held L_SDU value is ready for subsequent transfer, which will occur upon request.
This primitive is communicated by the LLC sublayer entity to the data link user to indicate the success or failure of the previous data unit preparation request.
Si le paramètre status est à l'état "succès", cette primitive indique à l'entité de couche application que l'entité de sous-couche LLC garde la L_SDU remise dans la primitive
DL_Update_Reply.request associée avec le LSAP local Toutes les L_PDU sortantes, résultantes d'une demande DL_Data request émise par ce LSAP, contiendront un sous-champ
Reply différent de zéro Ce sous-champ indique à l'entité ou aux entités LLC homologues l'existence d'une L_SDU en attente jusqu'à la réception d'une nouvelle demande
DL_Update_Reply.request avec une L_SDU nulle.
Le paramètre status à l'état "échec" indique que la L_SDU associée avec le LSAP local n'a pas pu être gardée, et la raison de cet échec.
NOTE − A un même instant, une seul L_SDU peut attendre la transmission vers un LSAP Une primitive
DL_Update_Reply.request peut écraser une L_SDU définie auparavant.
Pour que la primitive DL_Update_Reply.confirm véhicule une information utile, il faut qu'une information à contexte suffisamment implicite soit transmise avec les primitives
DL_Update_Reply.request et confirm, de manière que l'utilisateur de la liaison de données connaisse l'état de la demande précédente.
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The DL_Update_Reply.confirm service transmits the outcomes of the preceding DL_Update_Reply.request primitive from the LLC sublayer entity to the application layer entities.
The semantics of the primitive are as follows:
The Source_LSAP parameter specifies the local LSAP associated with the link service data unit preparation.
The Status parameter indicates the success or failure of the previously associated data unit preparation request.
The Old_L_SDU parameter specifies the link service data unit that was currently held by the
LLC This parameter indicates to the application layer the previously held value of the L_SDU in preparation for transfer at a later time when requested.
This primitive is passed from the LLC sublayer entity to the data link user to indicate the success or failure of the previous data unit preparation request.
Upon a successful status, the application layer is informed that the LLC sublayer holds the L_SDU submitted with the DL_Update_Reply.request linked to the local LSAP Consequently, all outgoing L_PDUs from a DL_Data.request initiated by this LSAP will feature a non-zero Reply subfield, signaling to the peer.
LLC entity or entities the existence of a waiting L_SDU until the reception of a new
DL_Update_Reply.request with a null L_SDU.
A failure status indicates that the L_SDU associated with the local LSAP could not be held and the reason for the failure.
NOTE − At the same time, only one L_SDU can wait for transmission at one LSAP A DL_Update_Reply.request primitive will overwrite a previously set L_SDU.
To ensure that the DL_Update_Reply.confirm primitive provides valuable information, it is essential to include adequate implicit context with the DL_Update_Reply.request.
.confirm primitives so that the data link user knows the status of the previous request.
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DL_Update_Reply.indication
The DL_Update_Reply.indication primitive is sent by the LLC sublayer entity to the application layer to indicate the presence of an L_PDU in the corresponding link layer This primitive requests the application layer to initiate a DL_Reply service procedure.
La sémantique de la primitive est la suivante:
The Destination_LSAP and Source_LSAP parameters define the local and remote LSAPs involved in data unit transmission The Destination_LSAP parameter must be a unique address as specified in the incoming L_PDU.
Les paramètres Destination_address et Source_address spécifient les adresses des stations locale et distante impliquées dans la transmission de l'unité de données Le paramètre
Destination_address doit être une adresse individuelle.
Le paramètre Length_requested indique l'existence et la longueur d'une L_SDU en attente de transmission dans la station distante.
The DL_Data.indication is sent from the LLC sublayer entity to the application layer to signal the arrival of a MA_Data.indication from the remote link entity The first bit of the "qualifier" field in this incoming frame indicates that an L_PDU is pending in the remote link entity.
Une telle L_PDU est rapportée seulement si la Destination_address désigne un des LSAP locaux au travers d'une adresse individuelle.
DL_Broadcast.request
This primitive facilitates the transfer of data from a local system management application to all corresponding system management applications The only available addressing mode is broadcasting This service is designed for management tasks.
La sémantique de la primitive est la suivante:
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The DL_Update_Reply.indication primitive is transmitted from the LLC sublayer to the application layer to signal that a waiting L_PDU exists at the peer data link layer This primitive prompts the application layer to initiate the DL_Reply.service procedure.
The semantics of the primitive are as follows:
The Destination_LSAP and Source_LSAP parameters define the local and remote LSAPs for data unit transmission, with the Destination_LSAP being a specific address indicated by the incoming L_PDU.
The Destination_address and Source_address parameters define the addresses of the local and remote stations participating in data unit transmission, with the Destination_address required to be an individual address.
The Length_requested parameter indicates the existence and the length of a L_SDU waiting for transmission at the remote station.
The DL_Data.indication is transmitted from the LLC sublayer to the application layer to signal the receipt of a MA_Data.indication from a remote data link user The first bit of the qualifier field in this incoming frame signifies the presence of a waiting L_PDU at the remote data link entity.
Such L_PDU are reported only if the Destination_address designates one of the local LSAPs by an individual address.
This primitive facilitates the transfer of data from a local system management application to all peer system management applications, utilizing broadcasting as the sole addressing mode It is specifically designed for management purposes.
The semantics of the primitive are as follows:
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Le paramètre Source_LSAP spécifie le LSAP local impliqué dans la transmission de l'unité de données Ce LSAP doit désigner une entité d'application.
Le paramètre L_SDU spécifie l'unité de données qui doit être transférée par l'entité de sous- couche LLC vers les entités de sous-couche homologues.
The Service_class parameter defines the type of frame that the MAC sublayer entity must use to transmit the L_PDU This parameter's value must be greater than or equal to zero, indicating a broadcast transmission mode.
Cette primitive est générée par l'entité d'application super utilisateur chaque fois qu'une commande de gestion doit être transmise à toutes les entités d'application en mode diffusion.
La rộception de cette primitive entraợnera de la part de l'entitộ LLC l'ajout de tous les champs
LLC spécifiés et le passage de la L_PDU correctement formée vers la couche inférieure du protocole de manière à la transférer vers les sous-couches LLC homologues.
3 Interface entre les sous-couches MAC et LLC
Le présent article décrit les services demandés à la sous-couche MAC (Medium Access
Control) par la sous-couche LLC (Logical Link Control) pour permettre à l'entité de sous- couche LLC locale d'échanger des unités de données LLC avec des entités de sous-couche
LLC homologues Ces services sont décrits de manière abstraite.
Description des interactions
Trois services de base sont proposés, comme généralement dans le modèle OSI:
Service MA_Data.request
This primitive outlines the data transfer from a local LLC sublayer entity to a unique peer LLC entity or to multiple peer LLC entities in the case of a group address.
La sémantique de la primitive est la suivante:
The Destination_address parameter can specify either an individual or a group MAC address It must contain sufficient information to create the destination address (DA) and the repetition credit fields included in the header of the frame by the local MAC sublayer entity.
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The Source_LSAP parameter specifies the local LSAP involved in the data unit transmission.
This LSAP shall designate an application entity.
The L_SDU parameter specifies the link data unit to be transferred by the LLC sublayer entity to the peer LLC sublayer entities.
The Service_class parameter defines the frame type required by the MAC sublayer entity for transmitting the L_PDU, with its value being 0 or greater.
This primitive is generated by the super user application entity whenever management command shall be transmitted to all application entities in broadcast mode.
The receipt of this primitive prompts the LLC entity to add all specified fields and transmit the correctly formatted L_PDU to the lower protocol layer for delivery to the corresponding peer LLC sublayers.
3 LLC to MAC sublayer interface
This clause outlines the services that the Medium Access Control (MAC) sublayer must provide to facilitate the operation of the Logical Link Control (LLC) sublayer It enables the local LLC entity to exchange data units with peer LLC entities, with the services being described in an abstract manner.
Three ground services are proposed, as usual in the OSI model:
This primitive defines the transfer of data from a local LLC sublayer entity to a single peer LLC entity or multiple peer LLC entities in the case of group address.
The semantics of the primitive are as follows:
The Destination_address parameter can indicate either a single MAC entity address or a group MAC entity address It must provide enough information to generate the Destination Address (DA) that is incorporated in the frame header by the local MAC sublayer entity.
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NOTE − L'adresse source n'est pas spécifiée car c'est un paramètre local que la sous-couche MAC remplit elle- même.
The M_SDU (MAC Service Data Unit) parameter defines the data unit of the MAC service that must be transmitted by the MAC sublayer entity It contains sufficient information for the MAC sublayer entity to determine the length of the data unit.
Le paramètre Service_class spécifie le type de classe de service que l'entité de sous-couche
MAC doit utiliser pour transmettre la M_SDU.
This primitive is generated by the LLC sublayer entity whenever data needs to be transmitted to one or more corresponding LLC entities This process can occur in response to a request from the higher layers of the protocol.
Following the receipt of this primitive, the MAC entity adds all the specific fields related to the MAC sublayer and transmits the correctly formed frame to the lower layers of the protocol for transfer to the corresponding peer MAC sublayer entity or entities.
Service MA_Data.confirm
This primitive has a local significance and provides an appropriate response to the LLC sub-layer entity that issued the MA_Data.request primitive The MA_Data.confirm primitive informs the LLC sub-layer entity whether the M_PDU from the previous MA_Data.request was transmitted incorrectly by the physical layer.
La sémantique de la primitive est la suivante:
MA_Data.confirm (Transmission_Status)
The Transmission_Status parameter conveys the transmission state information to the local LLC sublayer entity that made the request It indicates whether the previous MA_Data.request primitive was successful or failed.
Cette primitive est générée en réponse à une primitive MA_Data.request émanant de l'entité de sous-couche LLC locale.
Il est supposé que la sous-couche LLC dispose d'informations suffisantes pour associer la confirmation à la demande correspondante.
MA_Data.indication
Cette primitive définit le transfert de données depuis l'entité de sous-couche MAC vers l'entité de sous-couche LLC.
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NOTE − The source address is not specified because it is a local parameter that the MAC sublayer will fill itself.
The M_SDU (MAC service data unit) parameter defines the data unit that the MAC sublayer entity will transmit, providing essential information for determining its length.
The Service_class parameter specifies the type of class of service that the MAC sublayer entity has to use to transmit the M_SDU.
This primitive is generated by the LLC sublayer entity whenever data is transmitted to a peer
LLC entity or entities This can be in response to a request from higher layers of protocol.
The receipt of this primitive will cause the MAC entity to append all MAC specific fields (state in
DCP MAC description) and pass the properly formed frame to the lower layers of protocol for transfer to the peer MAC sublayer entity or entities.
The MA_Data.confirm primitive informs the LLC sublayer entity about the success or failure of the M_PDU transmission initiated by the MA_Data.request primitive, highlighting its local significance in the communication process.
The semantics of this primitive are as follows:
MA_Data.confirm (Transmission_Status)
The Transmission_Status parameter conveys status information to the local requesting LLC sublayer entity, indicating the success or failure of the preceding MA_Data.request.
This primitive is generated in response to an MA_Data.request from the local LLC sublayer entity.
It is assumed that sufficient information is available to the LLC sublayer to associate the confirm with the appropriate request.
This primitive defines the transfer of data from the MAC sublayer entity to the LLC sublayer entity.
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La sémantique de la primitive est la suivante:
Le paramètre Destination_address peut être soit une adresse individuelle ou soit une adresse de groupe, selon la spécification donnée par le champ DA de la trame entrante.
Le paramètre Source_address est une adresse individuelle, telle que spécifiée par le champ SA de la trame entrante.
Le paramốtre M_SDU spộcifie l'unitộ de donnộes de service MAC telle que reỗue par l'entitộ de sous-couche MAC locale.
The MA_Data.indication primitive is transmitted from the MAC sublayer entity to the LLC sublayer entity or entities to signal the arrival of a frame at the sublayer entity.
4 Structure des unités de données LLC (LLC_PDU)
Structure générale
This article provides a detailed definition of the Protocol Data Unit (PDU) structure of the Logical Link Control (LLC) sublayer for data communication systems utilizing LLC procedures of DCP LLC_PDUs, also referred to as L_PDUs, are examined in terms of the relative positions of their various components Additionally, the article outlines the method for representing the addresses of access points to services at the link layer.
Format des LLC_PDU
Toutes les LLC_PDU doivent présenter le format suivant:
– Destination Service Access Point (DSAP) (point d'accès aux services destinataire)
– Source Service Access Point (SSAP) (point d'accès aux services source)
The control and address fields each consist of one byte The data field length is an integer number of bytes ranging from 0 to the Max_LPDU_length parameter.
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The semantics of this primitive are as follows:
The Destination_address parameter may be either an individual or a group address as specified by the DA field of the incoming frame.
The Source_address parameter is an individual address as specified by the SA field of the incoming frame.
The M_SDU parameter specifies the MAC service data unit as received by the local MAC sublayer entity.
The MA_Data.indication is transmitted from the MAC sublayer to the LLC sublayer to signal the arrival of a frame at the local MAC sublayer entity.
4 LLC protocol data unit structure (LLC_PDU)
This clause defines in detail the Logical Link Control (LLC) Protocol Data Unit (PDU) structure for data communication system using the DCP LLC procedures LLC_PDU are also called
L_PDU This clause defines the relative positions of the various components of the PDU It defines the method for representing the data link layer service access point addresses.
All LLC_PDUs shall conform to the following format:
– Destination Service Access Point (DSAP)
– Source Service Access Point (SSAP)
The control field and the address fields consist of one byte each The data field length is an integer number of bytes between 0 and Max_LPDU_Length.
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Figure 6 – Format de la LLC_PDU
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Figure 6 – LLC_PDU format Qualifier
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Champ de contrôle
The control field consists of an octet that defines the type of the received L_PDU It specifies the command or response to be processed, along with any necessary qualifiers.
Le champ de contrôle contient les bits suivants:
– le sous-champ commande, sur deux bits;
– un bit de commande/réponse (C/R);
– le sous-champ qualificatif, sur quatre bits.
1 Sous-champ Command C/R Sous-champ
In the control field, the C/R bit is used to identify the type of L_PDU, which can either be a command or a response This bit, known as the command/response bit, indicates that if its value is "1," the L_PDU is a command.
"0", la L_PDU est une réponse.
Le sous-champ de commande permet de spécifier le type de primitive de service qui est demandé (sur deux bits).
A DL_Data.request primitive initiates a command without acknowledgment (NA), utilized by the local LLC sublayer entity to transmit an L_PDU to one or more remote stations without requiring any response or acknowledgment In the command subfield, the NA command is encoded with the value "00".
Une primitive DL_Broadcast.request invoque une commande sans accusé de réception (NA).
The local LLC sublayer entity utilizes a L_PDU to transmit data to remote stations without requiring any response or acknowledgment In the command subfield, the NA command is encoded with the value "01."
A DL_Reply.request primitive invokes a command with acknowledgment (AC), utilized by the local LLC sublayer entity to request data from a remote station In the command subfield, the AC command is encoded with the value "10".
Une primitive DL_Reply.response invoque la réponse à la primitive DL_Reply.request Dans le sous-champ commande, la réponse est codée avec la valeur "11".
The qualifier subfield is designed to provide additional information required by a command or response The structure of this subfield varies depending on the type of L_PDU.
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The control field consists of one byte which is used to define the type of the received L_PDU.
The control field specifies the command or the response which has to be processed and, if necessary, the required qualifiers.
The control field contains the following bits:
– the command subfield of two bits;
– the qualifier subfield of four bits. msb lsb
In the control field, the Command/Response bit (C/R bit) is crucial for identifying the type of L_PDU, distinguishing between commands and responses A C/R bit value of "1" signifies that the L_PDU is a command, while a value of "0" indicates it is a response.
The command subfield (two bits) specifies the service primitive that is requested.
The DL_Data.request primitive initiates a non-acknowledged (NA) command, allowing the local LLC sublayer entity to send a L_PDU to one or more remote stations without needing a response or acknowledgment The NA command is represented in the command subfield with the value "00".
The DL_Broadcast.request primitive initiates a non-acknowledged (NA) command, allowing the local LLC sublayer entity to send a L_PDU to remote stations without needing a response or acknowledgment The NA command is represented by the value "01" in the command subfield.
The DL_Reply.request primitive triggers the acknowledged (AC) command, enabling the local LLC sublayer entity to request data from a remote station The AC command is represented by the value "10" in the command subfield.
A DL_Reply.response primitive invokes the response to the DL_Reply.request In the command subfield, the response is coded with the value "11".
The qualifier subfield is designed to provide additional information as required by the command or the response The qualifier subfield structure depends on the type of the L_PDU.
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Trois types de sous-champ qualificatif sont définis Ces trois types dépendent des valeurs des bits C/R et du champ de commande.
If the L_PDU contains a command without an acknowledgment, the qualifier subfield is referred to as the reply subfield The purpose of the reply subfield is to indicate that unsolicited data is pending transmission at the remote station.
The first bit (most significant bit) of the reply subfield indicates whether the pending L_SDU has already been transmitted A "1" signifies that there is a pending L_SDU that has not yet been sent, while a "0" indicates that the request has already been transmitted.
Les trois derniers bits (poids faibles) du sous-champ précisent la longueur de la L_SDU en attente Une longueur nulle signifie qu'aucune L_SDU n'est en attente de transmission.
L'objet du sous-champ qualificatif dans une commande AC est de préciser à la station distante la longueur de la L_SDU qui peut être transmise en retour.
Les trois derniers bits (poids faibles) du sous-champ précisent la longueur de la L_SDU.
Le premier bit (poids fort) du sous-champ qualificatif est un "0".
L'objet du sous-champ qualificatif dans une réponse AC est de préciser au récepteur le succès ou la cause de l'échec d'une commande AC précédemment émise.
Les valeurs possibles de ce résultat sont définies comme suit:
– 0 Hex = OK Aucune erreur n'a été rencontrée;
– 1 Hex = Longueur insuffisante Une erreur a été détectée La longueur réservée dans la
L_PDU AC response était insuffisante pour contenir la L_SDU en attente L'entité LLC qui a initiée le RDR doit réessayer;
– 2 Hex = Pas de L_SDU en attente Il n'y a pas de L_SDU en attente de transmission sur le Lsap précisé dans la station qui a émise la AC Response.
Pour de plus amples informations, voir l'article 5.
Champ adresse
Each L_PDU contains the DSAP (Destination L_SAP) and SSAP (Source L_SAP) parameters, each occupying one byte The address field contains a single address, with the DSAP field identifying the access point for the services intended for the LLC data field Multiple L_SAPs can be addressed using group addresses, while the SSAP field specifies the particular access point where the data field content was generated.
Chaque adresse contient 8 bits d'adresse proprement dits.
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Three types of qualifier subfield are defined, depending on the values of the C/R and command bits.
In the L_PDU, when a non-acknowledged command is present, the qualifier subfield is referred to as the reply subfield This subfield serves to signal that there is unsolicited data ready for transmission at the remote station.
The most significant bit (msb) of the reply subfield indicates the transmission status of the L_SDU A value of "1" signifies that the L_SDU is waiting to be transmitted, while a "0" indicates that it has already been sent.
The three last bits (lsb) of the subfield define the length of the waiting L_SDU A length of zero expresses that no L_SDU is currently waiting for transmission.
In an AC command, the purpose of the qualifier subfield is to define to the remote station the length of the L_SDU it is allowed to transmit in return.
The three last bits (lsb) of the subfield specify the allowed length of the L_SDU.
The first bit (msb) of the qualifier subfield is set to "0".
In an AC response, the purpose of the qualifier subfield is to define to the receiver the success or the reason for failure of the previously issued AC command.
The possible values are defined as follows:
– 0 Hex = OK No error has been encountered;
The error message indicates that the length reserved in the AC response L_PDU is insufficient to accommodate the waiting L_SDU Consequently, the LLC entity that initiated the RDR must attempt the operation again.
– 2 Hex = No waiting L_SDU There is no L_SDU waiting for transmission at the Lsap in the station that has issued the AC Response.
For more information, refer to clause 5.
Each L_PDU consists of a one-byte Destination LSAP (DSAP) and a one-byte Source LSAP (SSAP) selector field The DSAP field specifies the service access point intended for the LLC data field, allowing for targeted addressing.
L_SAPs is also possible with group addresses The SSAP address field identifies the specific service access point from which the Data field was initiated.
Each address contains 8 bits of actual address.
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Poids forts Poids faibles Poids forts Poids faibles
8 bits Adresse (groupe/individuelle) 8 bits Adresse (individuelle)
Champ LSAP Destination Champ LSAP Source
4.4.1 Adresse de destination Lsap individuelle ou de groupe
In the DSAP address field, the two most significant bits are used to identify whether the DSAP address is an individual or group address, known as address type designation bits When these bits are set to "00", "01", or "10", they indicate an individual address Conversely, if the bits are set to "11", it signifies a group DSAP address that can identify none, one, or multiple service access points managed by the sublayer entity.
An individual address can be used as either a SSAP or DSAP address, while a group address is only applicable as a DSAP address In the SSAP address field, the two most significant bits are always set to indicate an individual address.
Un champ d'adresse DSAP ne contenant que des "1" est prédéfini comme constituant l'adresse
DSAP globale Cette adresse DSAP globale désigne un groupe constitué de tous les DSAP actuellement desservis par l'adresse MAC sous-jacente.
De nombreuses autres adresses sont prédéfinies; se reporter à la CEI 1334-4-1.
LLC_ PDU invalides
Une L_PDU invalide est une L_PDU qui remplit au moins l'une des conditions suivantes:
– sa longueur n'est pas un nombre entier d'octets;
– elle ne contient pas deux champs d'adresse correctement formatés, un champ de commande et optionnellement un champ de données, dans l'ordre correct;
– sa longueur est inférieure à trois octets.
Le contenu des L_PDU invalides n'est pas transmis à la couche supérieure La présence de
L_PDU invalides peut être communiquée à l'application de gestion de réseau.
Description générale
Le champ d'adresse est utilisé pour indiquer la source (SSAP) et la destination (DSAP) du
There is an implicit coupling of access points between the sender and receiver, as the sender must retain temporary state information about the receiver's access point to enable local confirmation This coupling involves a logical concatenation of MAC addresses (Destination_address/Source_address) and LLC addresses (Destination_LSAP/Source_LSAP) This coupling is detailed in Article 4.
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8 bits Address (group/individual) 8 bits Address (individual)
Destination LSAP field Source LSAP field
4.4.1 Individual and group destination Lsap
In the DSAP address field, the two most significant bits serve to distinguish between individual and group addresses, known as address type designation bits Specifically, when these bits are set to "00", "01", or "10", they signify that the address is an individual address.
"11", it indicates that the address is a group DSAP address that identifies none, one or more of the service access points that are serviced by the LLC sublayer entity.
An individual address can function as both an SSAP and a DSAP address, while a group address is limited to being a DSAP address Consequently, the two most significant bits in the SSAP address field are consistently set to indicate an individual address.
The DSAP address field is predefined to contain all "1"s, representing the global DSAP address This address identifies the group of all DSAPs that are currently being serviced by the underlying system.
Many other addresses are predefined; refer to IEC 1334-4-1.
An invalid L_PDU is defined as an L_PDU which meets at least one of the following conditions:
– its length in bytes is not an integral number;
– it does not contain two properly formatted address fields, one control field and, optionally, a Data field in their proper order;
– its length is less than 3 bytes.
The contents of invalid L_PDUs are not passed to the upper layer The occurrence of invalid
L_PDUs may be communicated to the management application.
The address fields are used to indicate the source (SSAP) and the destination (DSAP) of the
The sender must retain temporary state information about the receiving service access point to enable local confirmation, creating an implied pairing between them This pairing is formed by logically concatenating the MAC address (Destination_address/Source_address) with the LLC address (Destination_LSAP).
Source_LSAP) This pairing is described in clause 4 of IEC 1334-4-1.
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La transmission d'information d'une station initiatrice vers une station répondante s'effectue par l'émission de la commande NA ou AC dans le champ de commande.
When a DL_Data.request primitive is issued by the data link user, the LLC sublayer sends a NA command PDU that includes the specified L_SDU, with a NA command subfield where the bits are set to "00".
The DL_Reply.request is generated by the data link user, where the LLC sublayer sends an AC command PDU containing the specified L_SDU (NULL) along with an AC command subfield whose bits are set to "10".
Quand elle initialise une réponse à la commande AC (service Reply), le bit C/R du champ
SSAP est positionné sur "0" (réponse) et le sous-champ commande sur "11" (AC).
A la réception d'une L_PDU avec le bit C/R du champ SSAP positionné sur "1" (commande), la sous-couche LLC vérifie le sous-champ commande pour déterminer s'il s'agit d'une commande
If the command subfield indicates an AC command (Reply service), the LLC sublayer entity checks the accessibility of the appropriate L_SDU If access is granted, a response to the AC command is initiated Upon receiving the corresponding local confirmation, the DL_Reply.indication primitive is delivered to the local user of the data link to signify the transmission of the pending L_SDU.
Si le sous-champ commande désigne une instruction NA (service Data), l'entité de sous-couche
LLC délivre la primitive DL_Data indication appropriée pour le LSAP destinataire.
A number of logical link parameters are defined, and their range of values is determined by the user during the network implementation process.
Les longueurs maximale et minimale d'une L_PDU sont des informations contenues dans la
MIB, Management Information Base (base d'informations de gestion réseau) La longueur maximale est fixée par les limites de la trame MAC.
A valid L_PDU of minimal length must include exactly one command field followed by two address fields, in that specific order Consequently, the minimum number of bytes in a valid L_PDU is 3.