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A case study: DX 200 Exchange
nSSU: Subscriber Signaling Unit: controls access network
nCCSU:Common Channel Signaling Unit (SS7).
nCCMU: Common Channel Signaling Management Unit: (as MTP, SCCP) nPAU: Primary Rate Access Unit: controls basic (64 kbit/s) system interfaces n LSU: Line Signaling Unit: takes care of signaling between transit exchanges and access networks nMFSU: MULti-frequency Service Unit: Takes care of signaling when multiple frequency signals are used
MTP: Message transfer part of SS7
SCCP: Signaling connection control part
=SS7 bearer part: network service
                              part (NSP)