The Zarak Abacus 1 Switch Simulator / Bulk Call Generator – we have a love / hate relationship with this one.  Compared with the Ameritec CRS-A Crescendo:

Abacus1 Benefits

Analog, T1, E1 easily combined into a single system.
High density of port interfaces possible.
Analog port impedance software adjustable
Complex switch simulation available
Emulates subscriber side or CO side

Ameritec Benefits

Much easier to use, few bugs, firmware upgrades much easier
Generally lower cost per port
System feels significantly more rugged.
Can be used from the CLI or a GUI console (Featurecall)

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Spirent Communications, Inc. makes no representations, warranties or guarantees to you with respect to this equipment or its imbedded software. Spirent Communications, Inc. is under no obligation to maintain, update, repair or service this equipment or its imbedded software.