The Network Layer document describes the requirements and services for Network Interconnection ECUs (NIECU) thatenable electronic control units (ECUs) on a network segment to intercommunicate with other ECUs on different networksegments of the vehicle network. This document defines various types of NIECUs. The information in this documentapplies only to ECUs that are intended to provide networking services. It is not necessary for an ECU to provide any ofthese services in order to be compliant with the SAE J1939 protocol.