The following sequence works. Figuring out why is left as an exercise to
the reader ;-)

Commands:

lrcpc4:~/w/atm/switch/tcp# ./sw_tcp -b -d
lrcpc4:~# atmtcp virtual 1 switch localhost 1 bg
lrcpc4:~# atmtcp virtual 2 switch localhost 2 bg
lrcpc4:~# atmaddr -a 2 +1
lrcpc4:~/w/atm/switch/tcp# atmsigd -b -c 2.conf
lrcpc15:~# atmtcp virtual 1 switch lrcpc4 3 bg
lrcpc15:~# atmaddr -a 1 +2
lrcpc15:~/w/atm/switch/tcp# atmsigd -b -c 1.conf
lrcpc15:~$ ttcp_atm -r -a
lrcpc4:~$ ttcp_atm -t -a +2

--- switch.conf ---------------------------------------------------------------

command "atmsigd -c s1.conf -b -m switch 1.0.100 /tmp/1" socket /tmp/1 {
    itf 2 1.0.100
    route +1
}
command "atmsigd -c s2.conf -b -m switch 1.0.101 /tmp/2" socket /tmp/2 {
    itf 3 1.0.101
    default
}

--- s1.conf -------------------------------------------------------------------

debug log stderr
debug level warn
sig level debug
sig vpci 0 itf 2

--- s2.conf -------------------------------------------------------------------

debug log stderr
debug level warn
sig level debug
sig vpci 0 itf 3

--- 1.conf --------------------------------------------------------------------

debug log stderr
debug level warn
sig level debug
io vc 1.0.5
sig vpci 0 itf 1

--- 2.conf --------------------------------------------------------------------

debug log stderr
debug level warn
sig level debug
io vc 2.0.5
sig vpci 0 itf 2

--- -

The following picture shows a simplified view of the configuration. Note
that the command-line options have been choosen for clarity (and minor
details like the vpci settings in the configuration file have been
omitted) and are not identical with the ones given above.


+-----------------------------------------------------------------------+
| ./sw_tcp                                                              |
|                                                                       |
| +---------+          +----------------------------------+ 1.0.100     |
| |         |--/tmp/1--| atmsigd -m switch 1.0.100 /tmp/1 |---+         |
| |         |          +----------------------------------+   |         |
| | <relay> |                                                 +-----+   |
| |         |          +----------------------------------+   |     |   |
| |         |--/tmp/2--| atmsigd -m switch 1.0.101 /tmp/2 |---+     |   |
| +---------+          +----------------------------------+ 1.0.101 |   |
|      |							    |   |
|      |                      +--------------+                      |   |
|      |                      |              |                      |   |
|      |  control             |              |                      |   |
|      +----------------------|              |                    itf 1 |
|                             |   <fabric>   |                      |   |
|                             |              |                      |   |
|        2.0.5 <--> 1.0.100   |              |                      |   |
|        3.0.5 <--> 1.0.101   | 2     3    1 |                      |   |
|                             +--------------+                      |   |
|                               |     |    |                        |   |
+-------------------------------|-----|----|------------------------|---+
   			        |     |    |                        |
                   +------------+     |    |                        |
                   |                  |    |                        |
+-----------------------------------+ | +-----------------------------------+
|atmtcp virtual 2 switch localhost 2| | |atmtcp virtual 1 switch localhost 1|
+-----------------------------------+ | +-----------------------------------+
                   |                  |
	       itf 2 (+1)	      +---- - - - - - ----+
		   |					  |
           +---------------+        |  on lrcpc15:	  |
           | atmsigd 2.0.5 |				  |
           +---------------+	    |		          |
							  |
				    |   +--------------------------------+
                                    |   |atmtcp virtual 1 switch lrcpc4 3|
                                    |   +--------------------------------+
                     					   |
				    |		       itf 1 (+2)
                     					   |
				    |		   +---------------+
                                		   | atmsigd 1.0.5 |
				    |		   +---------------+

In order to control the switch with swc, add the line
  control <path>
to switch.conf, e.g.
  control /var/run/tcpswc

Then invoke swc as follows:
  swc <path> show

To add VCs, use  add <itf>.<vpi>.<vci> , to add VPs, use  add <itf>.<vpi>.?