Verilink Red Zone Encryption (REMS) (880-502423-001) Product Manual - Manual (Page 32)

Theory of operation
3-6 Red Zone Encryption Management System (REMS) User Manual
After the BRCs are frame synchronized, a 1.544 Mbps path is provided
though the aligned BRCs from the near- to the far-end encryptor.
Encryptor
synchronization Encryptor synchronization is initiated by the FBR encryptor re-sync lead
and occurs in spite of the BRC frame bit insertion discussed above. After
the encryptors synchronize, a 1.544 Mbps path is provided through the
framed BRCs and synchronized encryptors from the near- to the far-end
FBR.
FBR alignment
and framing The following steps provide an abbreviated description of the FBR
alignment process. It is this alignment process that eliminates the errors
mentioned above in the BRC sync process.
Assume that the position of the D4/ESF frame bit entering the near-end
FBR from its DTE is not initially aligned with the arbitrarily overwritten
ESF frame bit generated by the near-end BRC.
The decrypted plain text signal delivered to the far end FBR then would
contain the original, unerrored FBR code, which replaces the D4/ESF
frame pattern in its original position and random errors every 386 bits in
some other (as yet undetermined) bit position.
Receipt of unerrored FBR code signals the far end FBR that the near-end
FBR is not properly aligned. This initiates the FBR alignment process.
The end result of this alignment process is that the near-end DTE D4/ESF
bit position will be shifted in time to correspond to the arbitrarily
generated ESF bit position in the Black Zone.
Any errors caused by the overwriting process in the Black Zone are then
limited to the FBR code (instead of the payload) and are then simple to
correct because the FBR code is redundant. The net result is
■
no errors on any payload bits
■
no errors in the network ESF framing and CRC-6 bits, and
■
corrected errors in the FBR code