as with the destination address dstn the source link address may range from 80 h to 9f h the sixth field which may be many words long depending on the message is the data being sent referring to fig6 a the data field is comprised of a destination lsap address 202 and a source lsap 204 address lsap 39 s are addresses used by the application programs running 14 the host computer 16 to distinguish messages among several applications sharing a station and are not distinguished or affected by the media access controller 14 the lsap addresses 202 and 204 are followed by a size field 206 which carries the size of the following data string which may be up to 267 bytes long this is followed by the actual data being transmitted 210 the seventh and eighth fields are the control characters dle and etx described above which together indicated the end of the message the ninth and tenth fields are error correction codes specifically a cyclic redundancy code that is well known in the art and used to detect errors in the transmitted message and hence improve link reliability referring to fig5 the microprocessor sram 36 shown in fig2 contains a number of variables the link timer limit 160 and slot timer limit 162 are values loaded into internal timers not shown in microprocessor 42 to time the period during.