I am not getting Dial Tone at the Analog Port of the MT128ST with the Firmware Version (2.48). But if I downgrade the same TA with the Firmware Version 2.46, I'm able to get Dial Tone at its Analog Port.

You can use the register S45 so the TA will generate the dialtone. S45=2

S-Register: S45
Usage: S45=n; S45?
Function: Use Dial Tone From Central Office
Unit: Decimal ASCII code
Range: n=0--No Dial Tone,
n=1--Use Central Office Dial Tone,
n=2--TA Generates Dial Tone
Default: 2 (TA Generates Dial Tone)--En-bloc sending
1 (Use Central Office Dial Tone)--Overlap sending

Description: S45 allows the option of having the TA generate a dial tone on the POTS port (default for En-bloc sending), not allowing any dial tone on the POTS port, or allowing the dial tone from the central office to be passed through to the POTS port (default for overlap sending). However, some Central Offices send a "loud" dial tone which if passed through to the POTS port make DTMF-dialing difficult due to the DTMF digits having to overcome the loudness of the dial tone. The range of S45 depends on the dialing method (%A97=n).