an binary format question

my customer need to use irule to record client real ip though TCP application(telnet).my irule: when SERVER_CONNECTED { scan [IP::client_addr] {%d.%d.%d.%d} a b c d TCP::option set 29 [binary format cccc $a $b $c $d] all set a [binary format cccc $a $b $c $d] log "insert ip to tcp option $a" } log output:err tmm1[20158]: 01220001:3: TCL error: /Common/test - Illegal argument (line 1) invoked from within "TCP::option set 29 [binary format cccc $a $b $c $d] all" I felt error may because the binary format,so i comment out TCP::option sentence i found log output: info tmm[20158]: 01220002:6: Rule /Common/test : insert ip to tcp option W: F5 should output an binary code,buth why "W" ? my binary format scan is error?? help me,please!many thanks!