K28.5

In synchronous serial data transmission, recognizing the start of a frame and the payload data is crucial for recovering the data stream. Clock and Data Recovery( CDR) was a first step in this direction, followed by 4B5Bencoding and 8B10B encoding to reliably distinguish high density data.

The second step was the marking of the beginning of the frame. This bit structure, which marks the beginning of a transmission or the start of the user data, is designated differently in the different networks: InFDDI with 4B5B coding, the character is called JK; in Fibre Channel, it is called K28.5.

K28.5 is therefore a special 10-bit character that indicates the start of a Fibre Channel transmission and is used for synchronization of the sender and receiver. No special value is assigned to the K28.5 character, which is created during 8B10B encoding. The K28.5 character is used in all technologies that work with 8B10B coding, so in addition to Fibre Channel also in Gigabit Ethernet, Sonet and EPON. In Synchronous Optical Network( SONET) the K28.5 character is called A1A2 and in SMTPE Time Reference Signal( TRS).