Point-to-point link security can be obtained by devices called link encryptors. As these devices are not generally expected to interoperate, not many formal standards have been adopted in this area. ANSI X3.105 addresses this subject and an adaptation was made by ISO and published as ISO/IEC 9160.
Note: within LANs, additional security protocols can be applied (Secure Data Exchange protocol or SDE, defined in the IEEE Standard for Interoperable LAN/MAN Security or SILS). It can provide additional integrity checking and encryption.