User's Manual

the distance between the DECT Messenger and the external-paging system is relatively small,
so no extra hardware is needed.
Once a link is established between eESPA and the paging system, the eESPA handles further
communications and informs eKERNEL when relevant information is to be exchanged.
For a detailed description of the ESPA4.4.4 protocol, refer to the proposal for serial data
interface for paging equipment (Nov. 1984), reference JMJ182/NB/12B, and ISO1745
Information processing, basic mode control procedures for data communication systems.
Functional description
In general, eESPA is designed to provide eKERNEL with paging information. This is carried
out using a <msgrqs> message request. For some interfaces eKERNEL must send feedback
to the paging system, a process that is handled through <msgrpy> message reply request.
Figure 72: msgrqs message request
Every <msgrqs> message belongs to a group and has a specific group ID. A group contains
one or more requests. For every message request in a group, a data block is created. A data
block consists of a header, record separators, unit separators, and data that is retrieved from
the message request. Every data block also contains a specifically calculated checksum (block
check character ISO 1155). After sending the data over the serial line, the receiving side uses
the block check character (BCC) to determine whether data has arrived properly or not. In the
event of a successful delivery, the receiving side answers with an ACK.
Figure 73: msgrpy message ACK
If an incorrect BCC is found, delivery fails, and the receiving side sends a NACK, which is
prefixed with error code 1 (Transmission error, corrupt characters or corrupt BCC received by
the station).
Functional description
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