Networkto Network Signaling

Network-to-network communication is normally carried across the following transmission media:

• T1/E1 carrier over twisted pair

T1 is a 1.544-Mbps digital transmission link normally used in North America and Japan. E1 is a 2.048-Mbps digital transmission link normally used in Europe.

• T3/E3, T4 carrier over coaxial cable

T3 carries 28 T1s or 672 64-kbps connections and is 44.736 Mbps. E3 carries 16 E1s or 512 64-kbps connections and is 34.368 Mbps. T4 handles 168 T1 circuits or 4032 4-kbps connections and is 274.176 Mbps.

• T3, T4 carrier over a microwave link

• Synchronous Optical Network (SONET) across fiber media

SONET is normally deployed in OC-3, OC-12, and OC-48 rates, which are 155.52 Mbps, 622.08 Mbps, and 2.488 Gbps, respectively.

Network-to-network signaling types include in-band signaling methods such as Multi-Frequency (MF) and Robbed Bit Signaling (RBS). These signaling types can also be used to network signaling methods.

Digital carrier systems (T1, T3) use A and B bits to indicate on/off hook supervision. The A/B bits are set to emulate Single Frequency (SF) tones (SF typically uses the presence or absence of a signal to signal A/B bit transitions). These bits might be robbed from the information channel or multiplexed in a common channel (the latter occurs mainly in Europe). More information on these signaling types is found in Chapter 3, "Basic Telephony Signaling."

MF is similar to DTMF, but it utilizes a different set of frequencies. As with DTMF, MF tones are sent in-band. But, instead of signaling from a home to an end office switch, MF signals from switch to switch.

Network-to-network signaling also uses an out-of-band signaling method known as Signaling System 7 (SS7) (or C7 in European countries). This section covers some of the benefits of SS7, however SS7 is covered in depth in Chapter 4, "Signaling System 7."

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