EMS Technologies Canada Ltd. HSD-MK2 User Manual

eNfusion® HSD-440 Mark 2 Terminal

23-15-30

Each of the Aeronautical Telecommunications Network (ATN) subnetworks transmits join 
and leave words to the CMU whenever a path to a specified ground address changes.

The join event notifies the CMU that a new path to a specified ground address is available, 
triggering ATN air-to-ground communications. The leave event notifies the CMU that a 
path to a specified ground address has been closed, ending ATN air-to-ground 
communications.

The Join/Leave word (label 271) is transmitted on the CMU bus at a minimum rate of 
once per second or be event driven based on log on and log off events as specified by 
the 'CMU - SDU JOIN/LEAVE WORD TRANSMISSION' ORT parameter.

Table F-4 shows the definitions of the bits in the join/leave word.

Bits 8–1

Word Label 271:

 •

Uses the A429 convention

 •

Coded as 10011101

Bits 16–9

GES ID: 

 •

0 is an invalid ID

 •

FF is used for all GESs

 •

ID numbers between 1 and FE are valid GES IDs

 •

GES ID is known to the HSD-440 Mark 2 Terminal

 •

Bits are cleared when the HSD-440 Mark 2 Terminal is not logged on

Bits 22–17

Satellite ID

Bits 25–23

Inmarsat Service:

 •

Aero H+ 011

Bits 28–26

Not used; padded with zeros

Bit 29

Data link from the AES to the GES:

 •

Available (a Join message; Bit = 1)

 •

Not Available (a Leave message; Bit = 0)

 •

Identified by the GES ID and Satellite ID fields

 •

CMU uses this information to initiate network layer virtual circuits with 
available ground routers by determining the ground routers’ DTE 
addresses from the provided GES identity

 •

Bits 9–16, (GES) and Bits 17–22 (Satellite ID) uniquely identify a GES

 •

Aero Service Type field may be used by the CMU to make routing decisions

 •

Bit is cleared when the HSD-440 Mark 2 Terminal is not logged on.

Bits 31–30

SSM information (ARINC 429 para 2.1.5.2)