[racket] networking error[simple server and client]

hello~
I finally made it,sending string to localhost and receive it
but when I try to send to other computer, it doesn't work
does my code has problem?
the source is looks like this
server
#lang racket
(define server (tcp-listen 12345))
(define-values (s-in s-out) (tcp-accept server))
(read-line s-in)


client
#lang racket  ; An echo server
(define-values (in out) (tcp-connect "159.4.64.153" 12345))
(print "string" out)

the client side error is this
tcp-connect: connection to 59.4.64.153, port 12345 failed (at step 6: No
connection could be made because the target machine actively refused it.;
errno=10061)

this error is appear as well as when I try to send something while server is
not running

and I also want to know how can I send variables

could somebody please give me some useful urls or advice?

thanks in advanced
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