Envoy Application Programming Manual

BISYNC Multipoint Tributary Protocol
Envoy Application Programming Manual—427159-001
5-17
Normal Text
Normal Text
Normal text is indicated by messages having the following form:
message = STX—text—ETB
message = STX—text—ETX
(message length = 2 + text length)
Transparent Text
Transparent text is indicated by messages having the following form:
message = DLE STX—text—ETB
message = DLE STX—text—ETX
(message length = 3 + text length)
Transparent mode is initiated by inserting a DLE control character before the STX.
Transparent text, including data-link control characters continue to be sent until an ETB
or an ETX is sent followed by nothing else.
The transmission of DLE text characters is handled entirely by Envoy hardware. Envoy
automatically inserts a DLE character in front of a DLE text character upon transmission
and deletes a DLE character from the front of a DLE text character upon reception. The
application process deals only with the original binary text.
Headings
Headings use the formats shown in Table 5-6.
Intermediate Text Blocking
The BISYNC protocol allows a message to be divided into segments called intermediate
text blocks (ITBs). This division causes a single message to be transmitted as a series of
intermediate messages, each of which has its own block-check character. Each block is
checked for errors when received (that is, after each ITB) and the entire message is
acknowledged only when the last intermediate block is received (that is, after an ETB or
an ETX).
Table 5-6. Formats for Headings
Headings Format Message Length
Heading only SOH-heading-ETB 2 + heading length
Heading and normal
text
SOH-heading-STX-text-ETB
SOH-heading-STX-text-ETX
3 + heading length +
text length
Heading and transpar-
ent text
SOH-heading-DLE STX-text-ETB
SOH-heading-DLE STX-text-ETX
4 + heading length +
text length