FXS stands for Foreign Exchange Station. You connect a regular analog phone or a ‘station’ to a FXS port. This port provides battery feed to the phone. XOP Networks Ringdown Firebar Conference Server provides FXS ports. In a typical deployment analog Red phones can be connected to it over copper wire pairs.

T1 refers to a Time Division Multiplex based carrier routinely used in North America. This interface carries 24 voice channels. Each voice channel uses 64 Kbits/sec. A T1 line also has an 8 Kbits/sec signaling/framing channel. Therefore the bit rate for a T1 carrier is 24 x 64K + 8000 = 1.544 Mb/s.

There are two types of framing formats used with T1 carriers. These are called D4 and ESF.

The T1 carrier needs to maintain a certain 1’s density so that the network equipment at each end can recover timing clock even if no traffic is being carried. There are two mechanisms in use for that purpose. These are referred to as AMI (Alternate Mark Inversion) or B8ZS (bipolar 8-zero substitution).

The older T1 trunks (> than 10 years in service) are generally set up for D4/AMI and those in last 5-10 years are generally set up for ESF/B8ZS.

The XOP Networks equipment supports both flavors of T1s.

A communication line that was developed by European standards that multiplexes thirty voice channels and two control channels onto a single communication line. The E1 line uses 256 bit frames and transmitted at 2.048 Mbps.

E1 refers to a TDM (Time Division Multiplex) based carrier used in Europe and South America. Japan uses a variant called J1.

SIP Trunk is a telephony term for a Data path that serves the function of a traditional T1 or E1 trunk but uses the SIP (Session Initiated Protocol). This facilitates the integration of voice and data on the same physical carrier.

Before SiP became ubiquitous, some early Voice over Data networks were set up using the H.323 protocol.

H.323 is an umbrella recommendation from the International Telecommunications Union (ITU) that sets standards for multimedia communications over Local Area Networks (LANs) that may not provide a guaranteed Quality of Service (QoS). H.323 specifies techniques for compressing and transmitting real-time voice, video, and data between a pair of videoconferencing workstations. It also describes signaling protocols for managing audio and video streams, as well as procedures for breaking data into packets and synchronizing transmissions across communications channels.

E1’s can be deployed in a 75 ohm architecture where the signal traveled on Coax cable and used BNC connectors. They can be deployed in a 120 ohm architecture where the signal travels over twisted pair and uses the more familiar RJ-45 connector. A Balun is a device that allows a 75 Ohm E1 to be converted to a 120 ohm E1 (or vise versa) to facilitate connection to equipment that does not support the native connector.

CAS (Channel Associated Signaling) is a protocol used over T1 and E1 trunks where each DS0 or channel has bits that carry the call control signaling states, ie idle, seize, wink, release. This is inefficient from a network standpoint because the entire DS0 is used to convey just a few bits of signaling before the voice path is established.

An ISDN PRI (Primary Rate Interface) is referred to a trunk that carries signaling for associated voice channels in one common time slot. This is also referred to as Common Channel Signaling. In North America the dominant carrier is a T1 line with 24 time slots. So when a T1 line is configured with 23 bearer channels and one signaling channel it is called ISDN PRI in 23B+D configuration. The protocol also supports higher signaling densities in a architecture called NFAS (Non Facility Associated Signaling) which is not very common.

ANI (Automatic Number Identification) is the field in a CAS call that carries the Caller ID information. In PRI this field is called the Calling Number, In a SiP invite, this is the FROM address. This information is critical for displaying Caller ID at the end device.