Nortel Networks 553-3001-211 manual Typical trunk interface unit block diagram, TS0

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trunk line through an impedance matching and balance network. The trunk interface also includes the logic necessary to place outgoing call signaling onto the trunk, or the logic to connect to special services such as recorded announcement and paging equipment.

Figure 14 shows a typical example of the logic that performs these functions. Each part of the trunk interface unit is discussed in the following section.

Figure 14

Typical trunk interface unit block diagram

DS-30X		Variable gain
		filters	Isolation
Network loop				Tip
		2-wire	transformer
		to
	CODEC	4-wire		Interface
		conversion
				(protection)
		and
				Ring
		balance
		network
				Signaling
	Signaling			leads
				(E&M,
TS0	logic
				DX, etc.)
				553-6159

Coder/Decoder circuit

The coder/decoder (codec) performs Analog to Digital (A/D) and Digital to Analog (D/A) conversion of the line analog voiceband signal to and from a digital PCM signal. This signal can be coded and decoded using either the A-Law or the µ-Law companding algorithm. On some trunk cards the decoding algorithm depends of the type of codec installed when the board is built. On others, it is an option selected using a software overlay.

553-3001-211 Standard 2.00 September 2004