Interfaces and services (contd.)
IDU sent from n+1 to n through SAP. IDU = ICI + SDU. ICI is not part of the data but helps n+1 do its job by containing things like # of bytes.
Layer n may break SDU into several parts each part being prepended with a header. Each part + header is called a PDU. Peer entities (conceptually) communicate using PDU’s
Network software/Interfaces and services.