Zultys products support the full complement of telephony interfaces. The MX250 supports analog circuits (FXS and FXO) and digital circuits (T1, E1, PRI and BRI) simultaneously. The MX250 provides three slots to accommodate telephony interfaces. Interface modules are used to connect to analog trunks (FXO), ISDN BRI, T1 and E1 digital circuits (CAS, ISDN, and MFC R2).

Additionally, analog phones and devices such as single line telephones or fax machines may be connected to the MX system via the FXS module. Two analog FXS circuits are provided as standard connections to the system. In many installations, this saves the client the initial investment in an FXS module when no more than two analog devices are needed. The built-in FXS ports of the MX250 may be configured to provide failover protection in the case of loss of commercial power by automatically switching the first two analog PSTN phone lines to these analog FXS ports.

The MX250 supports T1 and E1 ISDN PRI service and T1 Channel Associated Signaling (CAS). The CAS protocols supported are loop start and ground start with caller ID, and E&M emulation with wink-start DID service. The ISDN protocols supported over T1 are Lucent Custom, Nortel custom, US National (NI-1), and Japanese ISDN. The ISDN protocol supported over E1 is ETSI (European Telecommunications Standards Institute) with sub-addressing. For E1 Zultys also supports the Chile, Venezuela and Mexico variants of MFC R2. The ISDN protocols supported over BRI are Japanese ISDN and ETSI, with or without SPIDs (Service Profile Identification).

The MX250 also comes standard with two analog FXS station ports. In the event of a power failure, the first 2 analog PSTN trunks of an equipped FXO card may be automatically switched to these FXS ports to provide power failure transfer. This ensures that the enterprise retains minimal access to outside calling services during a power outage.

The MX30 provides one slot for the insertion of a trunk interface module of the client’s choice. Module choices include the 4-port FXO4 Module, 2-port BRI Module, and the 10-channel PCM module. The MX250 expands this capacity to a total of three card slots. These slots may be configured with 8-port FXO module, the 4-port BRI module, and the full 24-channel PCM module.


Analog trunking is frequently referred to as “plain old telephone service” (POTS). These types of services are generally delivered to the customer’s premise via copper wires, for which each trunk is represented as a 2-wire pair. Analog trunks generally support inbound and outbound calling, although they may be ordered from the PSTN carrier as inbound only or outbound only. In either case, analog trunks are connected to the MX system via the FXO module.

Digital trunking is a service provided by PSTN carriers as ISDN circuits (Integrated Services Digital Network). The advantage of digital trunking is that many trunks are delivered over a 4-wire connection from the servicing entity. Each digital trunk circuit is capable of carrying up to 24 (T1) or 30 (E1) simultaneous conversations. Clients may find that ISDN service provides a lower month recurring cost for more trunks than a far fewer number of analog trunks. This is due to the economy of scale that is provided by the delivery of digital service over far fewer wires. Additionally, the ability to carry voice, data and video over the same connection further drives the total cost of digital trunks down. Digital trunks are connected to the MX system via DTE (MX25 & MX250) or STE (MX30) modules.

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