Siera Wireless MP555, Руководство по установке программного обеспечения

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Rev 1.2 49
MTP message types
...
MTP message
Jan.05
The table on the next page lists the six message types used in
the MTP protocol. The Message ID is the “tag” of the MTP
packet. Message types with ID numbers in the 0 to 127 range
are messages types sent from the MP 555 GPS to the host
application. Those with Message ID numbers in the 128 to 255
Tag
1 byte
Length
2 bytes
Message payload
(variable length)
(Message ID)
Using the Monitoring and Tracking Protocol
• Application ID (8 bits)—code identifying the application
protocol. The only currently supported ID is ‘01’ for the
MTP protocol.
• Unique Mobile Device ID (32 bits)—binary code identi­
fying each individual MP 555 GPS modem.This is not a
user-defined ID.
For packets originating from the MP 555 GPS, this identi­
fies the source. For packets originating from the server, this
identifies the destination. When the packet arrives at the
MP 555 GPS, this ID is validated. If the ID fails validation,
the packet is silently discarded.
The host application must be able to recognize each vehicle
by this ID. See “Retrieving the Unique Mobile Device ID”
on page 45.
The MTP Protocol
An MTP packet consists of a one-byte tag identifying the
message type, two bytes that identify the length of the
message, and the message payload.The message payload
contains the fields that correspond to the message type. Each
field is preceded by a one-byte field tag, and two bytes that
identify the length of the field.
Field ID
1 byte
Length
2 bytes
Field
(variable
length)
Field ID
1 byte
Length
2 bytes
Field
(variable
length)