SAE J1979-2 describes the communication between the vehicle's OBD systems and test equipment required by OBD regulations. On-Board Diagnostic (OBD) regulations require passenger cars and light-, medium-, and heavy-duty trucks to support a minimum set of diagnostic information to external (off-board) “generic” test equipment.
To achieve this, SAE J1979-2 is based on the Open Systems Interconnection (OSI) Basic Reference Model in accordance with ISO/IEC 7498-1 and ISO/IEC 10731, which structures communication systems into seven layers. When mapped on this model, the services specified are broken into:
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Diagnostic services (layer 7), specified in:
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ISO 14229-1
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SAE J1979-2 OBDonUDS
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Presentation layer (layer 6), specified in:
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SAE J1930, SAE J1930DA
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SAE J1979DA
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SAE J2012, SAE J2012DA
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SAE J1939DA, SAE J1939-73
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Session layer services (layer 5), specified in:
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ISO 14229-2
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Transport layer services (layer 4), specified in:
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DoCAN: ISO 15765-2 Transport protocol and network layer services
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ISO 15765-4
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DoIP: ISO 13400-2 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 2:Transport protocol and network layer services
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Network layer services (layer 3), specified in:
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DoCAN: ISO 15765-2 Transport protocol and network layer services
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ISO 15765-4 Requirements for emissions related systems
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DoIP: ISO 13400-2 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 2:Transport protocol and network layer services
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Data link layer (layer 2), specified in:
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DoCAN: ISO 15765-4, ISO 11898-1, -2
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DoIP: ISO 13400-3 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 3: Wired vehicle interface based on IEEE 802.3
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Physical layer (layer 1), specified in:
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DoCAN: ISO 15765-4, ISO 11898-1, -2, in accordance with Table 1
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DoIP: ISO 13400-3 Road vehicles - Diagnostic communication over Internet Protocol (DoIP) - Part 3: Wired vehicle interface based on IEEE 802.3