[Discuss-gnuradio] Using two USRP's

[Meenal]

I want to connect two USRP's in such a way that TX from one goes to RX of 
another via cables, and vice versa. When I try to run my script ( which 
works perfectly okay if the same usrp board is used for both TX and RX) 
throws up a runtime error like:

address@hidden ./usrp_grphy.py
Traceback (most recent call last):
  File "./usrp_grphy.py", line 258, in ?
    main ()
  File "./usrp_grphy.py", line 243, in main
    (tx_fg, tx_s) = run_tx(tx_sock, payload+8)
  File "./usrp_grphy.py", line 163, in run_tx
    snk = usrp.sink_c (1,usrp_interp)
  File "/usr/local/lib/python2.3/site-packages/gnuradio/usrp.py", line 89, 
in sink_c
    return ((usrp0.sink_c, usrp1.sink_c)[look_for_usrp(which)])(which, 
*args, **kwargs)
  File "/usr/local/lib/python2.3/site-packages/gnuradio/usrp.py", line 69, 
in look_for_usrp
    raise RuntimeError, "Unable to find USRP #%d" % (which,)
RuntimeError: Unable to find USRP #0

How can I make this work?
Thanks
Meenal