Provides the communication path between the SPE and the packet bus in the PPN
Provides the link access procedure on the D-channel (LAPD) for up to 8,192 links
Provides termination for ISDN-BRI and ISDN-PRI signaling links, expansion archangel links connecting the processor to the expansion archangels on EI circuit packs in each PN, and center stage control network links connecting the processor the processor with SNI circuit packs in the CSS
Supports firmware downloading
Provides X.25 termination to the DCS links and adjuncts such as CDR and Audix
