This took me a while, so I hope this info helps. I connected a Mitle SX-2000 with an NSU to an Asterisk server with a Sangoma A101 t-1 card. I used PRI signalling so that I could get caller id to pass. I get no echo and great sound quality.

Here is the Asterisk config settings:

zaptel.conf

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span=1,1,0,esf,b8zs
bchan=1-23
dchan=24

loadzone=us
defaultzone=us

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zapata.conf

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trunkgroups

channels

context=from-internal
switchtype=qsig
rxwink=300
callerid=asreceived
usecallerid=yes
hidecallerid=no
echocancel=yes
echocancelwhenbridged=yes
rxgain=0.0
txgain=0.0
faxdetect=incoming

signalling=pri_cpe
group=1
channel => 1-23

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Here is the Mitel forms with settings:

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| LINK DESCRIPTOR ASSIGNMENT
|
|Digital Link Descriptor Number: 15
|
| Description | Value
|------------------------------------------------------------------------------
|Address for Message Control (A/B). . . . . . . . . . . . . A
|BER - Maintenance Limit, 10**-n, n=(3,4,5,6) . . . . . . . 4
|BER - Service Limit, 10**-n, n=(3,4,5,6) . . . . . . . . . 3
|Data Call Alternate Digit Inversion (Yes/No) . . . . . . . Yes
|Framing Losses in 24 hrs - Maintenance Limit (0-9000). . . 255
|Framing Losses in 24 hrs - Service Limit (0-9000). . . . . 9000
|Integrated Digital Access . . . . . . . . . . . . . . . . ISDN NODE
|QSIG Private Network Access (Yes/No) . . . . . . . . . . . Yes
|Vendor Inter-working Type . . . . . . . . . . . . . . . . .
|Satellite Link Delay (Yes/No). . . . . . . . . . . . . . . No
|Slip Rate - Maintenance Limit (0-9000) . . . . . . . . . . 5000
|Slip Rate - Service Limit (0-9000) . . . . . . . . . . . . 7000
|Termination Mode (NT/LT). . . . . . . . . . . . . . . . . . NT
|Send Malicious Call Indication to PSTN For Tagged Calls . . No
|
| DS1 Parameters:
|Alarm Debounce Timer - Service Limit (300-3200). . . . . . 500
|B8ZS Zero Code Suppression - (Yes/No). . . . . . . . . . . Yes
|
| Universal T1 and Enhanced Dual T1 Card only:
|Operation Mode (CSU/DSX-1) . . . . . . . . . . . . . . . . DSX-1
|CSU Tx Line Build-Out(0,7.5,15,22.5 db). . . . . . . . . .
|DSX-1 line Length(0-133,134-266,267-399,400-533,534-655 ft) 0-133
|Extended Super Frame (Yes/No). . . . . . . . . . . . . . . Yes
|Inverted D channel ( DPNSS only ) (Yes/No) . . . . . . . . No
|
| Universal E1 and Enhanced Dual E1 only:
|CRC-4 enabled(Yes,No). . . . . . . . . . . . . . . . . . . No
|E1 line Length(0-133,134-266,267-399,400-533,534-655 ft) . 0-133
|E1 Impedance (75,120 ohms) . . . . . . . . . . . . . . . . 120
|
| Italian Parameters:
|Digital Link Fault Delay Timer (0-360 sec) . . . . . . . . 240
|
| Universal T1/E1 Coding Conversion Parameters:
|Voice conversion (Nil/ADI/Invert/Inverted ADI). . . . . . . Invert
|Data conversion (Nil/ADI/Invert/Inverted ADI). . . . . . . Invert

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| MSDN-DPNSS-DASSII TRUNK CIRCUIT DESCRIPTOR ASSIGNMENT
|
| Trunk Circuit Descriptor Number: 15
|
| Descriptor | Value
|------------------------------------------------------------------------------
|Signalling Protocol (MSDN-DPNSS/DASS II) . . . . . . . . . MSDN-DPNSS
|Card Type (Cept/DS1/UNIVERSAL E1|T1/R2/BRI). . . . . . . . UNIVERSAL T1
|Dual Seizure Priority (Incoming/Outgoing). . . . . . . . . Incoming
|ISDN BRI Mode (blank/NT/LT). . . . . . . . . . . . . . . .
|
| Transmission Parameters
|
|Far End Connection (Main PBX/Satellite PBX/Toll/Local) . . Local Office

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