path information unit (SNA) (PIU)

In the SNA architecture, data packets are referred to as Path Information Units (PIU). Such a Path Information Unit consists of three data fields: the Transmission Header( TH), the Request/Response Header( RH) and the Request/Response Unit( RU).

Structure of the Path Information Unit (PIU)

Unlike other network protocols, where the data packet is routed through the network by means of an address, in SNA the messages are sent to the Network Addressable Unit( NAU), which routes the messages through the network. The addresses are assigned to the Network Addressable Unit by the Control Point when the Physical Units( PU) or the Logical Units( LU) are enabled.

The Path Information Unit is created by adding a transmission header to the Path Control Layer (Layer 3) to the Basic Information Unit ( BIU) from the Transmission Control Unit (Layer 4).