For devices designated type DL_ETHER, GLD provides support for both Ethernet V2 and ISO 8802-3 (IEEE 802.3) packet processing. Ethernet V2 enables a data link service user to access and use any of a variety of conforming data link service providers without special knowledge of the provider's protocol. A service access point (SAP) is the point through which the user communicates with the service provider.
Streams bound to SAP values in the range [0-255] are treated as equivalent and denote that the user wants to use 8802-3 mode. If the value of the SAP field of the DL_BIND_REQ is within this range, GLD computes the length (not including the 14-byte media access control (MAC) header) of each subsequent DL_UNITDATA_REQ message on that Stream and transmits 8802-3 frames having those lengths in the MAC frame header type fields. Such lengths never exceed 1500.
All frames received from the media that have a type field in the range [0-1500] are assumed to be 8802-3 frames and are routed up all open Streams that are in 8802-3 mode (those Streams bound to a SAP value in the [0-255] range). If more than one Stream is in 8802-3 mode, the incoming frame is duplicated and routed up each such Stream.
Streams bound to SAP values greater than 1500 (Ethernet V2 mode) receive incoming packets whose Ethernet MAC header type value exactly matches the value of the SAP to which the Stream is bound.