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Dialogic® MSP Multi-Services Gateway
MSP 1010 Multi-Services Platform replaces 'fe' or 'fd' by 'fd01' or 'fd02'
Symptom:
At times it may appear that a Dialogic® MSP 1010 Multi-Services Platform (MSP) is manipulating the data being monitored prior to forwarding it to an SS7 Monitoring Application (MA). Specifically, when an 'fe' byte is expected an MA will receive two bytes 'fd 01'. Likewise, when an 'fd' byte is expected an MA will receive 'fd 02'.
For example, an MA may expect to receive the following data from an MSP (note 'fe' enclosed in *):
At times it may appear that a Dialogic® MSP 1010 Multi-Services Platform (MSP) is manipulating the data being monitored prior to forwarding it to an SS7 Monitoring Application (MA). Specifically, when an 'fe' byte is expected an MA will receive two bytes 'fd 01'. Likewise, when an 'fd' byte is expected an MA will receive 'fd 02'.
For example, an MA may expect to receive the following data from an MSP (note 'fe' enclosed in *):
fe 00 76 01 2b 26 f4 03 03 04 67 02 00 01 64 02 15 00 64 02 10 00 64 02 10 07 00 02 e0 21 00 03 03 00 00 e0 00 00 52 00 02 90 0d 00 0b 05 0c d9 46 00 05 00 03 00 0c 01 90 0e 00 3d ed 39 3a 83 74 a5 6e 09 01 3c 03 00 02 02 06 04 43 74 25 *fe* 04 04 43 ba 25 *fe* 0f 20 00 1e 57 05 08 00 12 f4 70 03 2a 76 df 17 0f 05 08 00 12 f4 70 03 55 33 05 f4 14 01 e6 4d 21 81 00 26
In this case, an MA would receive the following data from an MSP (note 'fd 01' enclosed in *):
fe 00 76 01 2b 26 f4 03 03 04 67 02 00 01 64 02 15 00 64 02 10 00 64 02 10 07 00 02 e0 21 00 03 03 00 00 e0 00 00 52 00 02 90 0d 00 0b 05 0c d9 46 00 05 00 03 00 0c 01 90 0e 00 3d ed 39 3a 83 74 a5 6e 09 01 3c 03 00 02 02 06 04 43 74 25 *fd 01* 04 04 43 ba 25 *fd 01* 0f 20 00 1e 57 05 08 00 12 f4 70 03 2a 76 df 17 0f 05 08 00 12 f4 70 03 55 33 05 f4 14 01 e6 4d 21 81 00 26
Technical discussion
MSP uses the value 0xFE in the Frame field to indicate the beginning of a new frame. If 0xFE occurs in a message or response, MSP must not process the data that follows the 0xFE as a new message or response. MSP uses escape sequences to prevent this so that 0xFE cannot appear in the message.
0xFD is used as an escape byte, so both 0xFD and 0xFE are escaped as follows:
Value To Be Sent Escape Sequence Values
0xFD 0xFD 0x02
0xFE 0xFD 0x01
When MSP calculates the length of a message containing one or more escape sequences the length of a message is defined before any escape sequences are inserted and, therefore, the length excludes any bytes added by the escape sequences.
An MA needs to take these escape sequences into account when parsing SS7 monitoring data received from the MSP.
Product List
Dialogic® MSP 1010 Multi-Services Platform
Related Documentation
MSP Developers Information Manual
- Monitoring SS7 section
