DST-REF / SRC-REF (2 bytes)

PDU Part: Fixed Part

Field: destination / source reference

Length: 2 bytes

Contents: connection identifier.

Each transport entity chooses a reference to be used by the peer entity which is 16 bits long and which is arbitrary under the following restrictions:

1. it shall not already be in use nor frozen

2. it shall not be zero.

The mechanism is symmetrical and provides identification of the transport connection independent of the network connection. The range of references used for transport connections, in a given transport entity, is a local matter.