for example a protocol such as q 921 pri layer 2 or x 25 or frame relay as received may require processing according to processing programs dedicated for respective protocols the protocol processed information is then transmitted to the cpu for constructing or removing links used for call transactions between the ports or slots connected into the switch as described above according to the principles of the invention as shown in the preferred embodiment these processors may be located directly on peripheral cards in the switching unit in this way the protocol processing units are accessible for installation removal or modification as required the protocol processors provided on peripheral cards permit dedicated processing of each received protocol independently of any other protocols and without intervention of the central processing unit a schematic of the pcu and associated data paths between the cpu and a peripheral card shelf containing the pcu card is as shown in fig3 as shown the pcu in the preferred embodiment has 32 ports 0 to 31 and is located on a peripheral card communicating with the tsu in the preferred embodiment through 32 channels accordingly the 64 kbps pcm data may be operated at a 2 048 mbps rate representing the 32 channels at 64 kbps each each of the switching unit slot or port connections to the pcu o through 31 represent designated slot or port within the telephone switch within the pcu each of the pcu slots or connections are dedicated to a switching unit port or slot connection by the cpu the pcu is directly connected through back plane of the switching unit of the telephone switch to the switching unit and.