Format: nLength: 3Fixed length
DE 70
Network Management Information Code
What it is
Network management (0800/0810) messages are the heartbeat of an ISO 8583 link. DE 70 says why the message was sent: 001 sign-on, 002 sign-off, 101 key change (new working MAC/PIN key), 161–164 cutover messages, 301 echo test. Hosts answer with 0810 and DE 39 = 00.
Example values
001Sign-on request.301Echo test (keep-alive).Specification reference
Defined in ISO 8583:1987 (base). Card networks publish their own dialect tables (Visa BASE I / V.I.P., Mastercard CIS) that refine formats, lengths, and — for private-use elements — the entire layout. Always confirm against the interface specification you implement.