IEC 61334-4-61:1998 pdf download

IEC 61334-4-61:1998 pdf download.Distribution automation using distribution line carrier systems
This part of IEC 61 334 is closely related to IEC 61 334-4-1 that refers to a minimal three-layer architecture as an example of the use of an efficient communication architecture to build a communication system used for low-voltage DLC applications. Nevertheless, the suggested layered architecture is open to support additional features which are to be implemented in the case of several subnetworks, as MV and LV networks, are used for DLC applications. The basic three layer communication architecture provides communication among applications which are hosted by stations on one single line carrier link (e.g. an LV section), as in the example represented in figure 1 : this set of stations is here defined as a “subnetwork”. Furthermore, two subnetworks may be connected through an internetworking unit which hosts an application acting as gateway in case of communication between a client and a server running on stations that belong to different subnetworks (see figure 2). Another approach is to define a network layer entity (N) supporting a routing function which provides the necessary address mapping between the two subnetworks (see figure 3). In the example of figure 3, all the stations have to implement the network layer function: nevertheless, applications running on the same subnetwork may directly use the LLC services using a LSAP different from that assigned to the network layer entity, as defined in the following. In the general case, a mixed approach may be useful and a number of subnetworks could be crossed by a message (see figure 4 for an application example). A protocol at the network layer is to be used and the entity, implementing it, is located between the N-user and the LLC layers, as defined in the following architecture mode.
2 N service definition
The N service primitives allow a connectionless, unacknowledged data transfer at the N-user interface, improving the addressing capabilities of the underlying LLC service. The N data transfer primitive refers to a network address and, in the general case, while in the global network two or more stations belonging to different subnetworks may have the same MAC station address, each of them will be univocally identified by its own unique network address. In details, an N user is identified by its title composed by a network address and a NSAP selector, in a similar way as specified in IEC 61 334-4-1. A message coming from an N user has associated the network destination address and the N- entity should map it in a transmission request to the underlying LLC sublayer, with an associated LLC destination station address of the next station involved in the network path to be traversed by the message. The LLC destination station address is composed of two parts: the LSAP selector (the fixed value 01 Hex assigned to the referenced symbol N-entity_LSAP, identifying the N-entity LSAP) and the MAC address. Therefore, each N-entity has to have a table (routing table) to execute the addressing translation between the network destination address and the next-hop station LLC address. The N-entity recognizes also its own local station network address, so that the messages for its local N-users are not routed to the next-hop station but delivered to them. The services assumed from the LLC sublayer are those related to the LLC connection oriented (LLC-CO) protocol mode, which supports bi-directional full-duplex connectionless LLC service of data transfer. It should be noted that the network layer does not support segmentation nor reassembling of data: that means the NSDUs have to be a maximum size compatible with the size supported by all the involved subnetworks.