As you can see by the following I've got 1 PPP device, but 2 copies of BSD compression apparently being used.
rjc@snoopy:~$ifconfig
lo Link encap:Local Loopback
inet addr:127.0.0.1 Bcast:127.255.255.255 Mask:255.0.0.0
UP BROADCAST LOOPBACK RUNNING MTU:3584 Metric:1
RX packets:4882 errors:74 dropped:0 overruns:0
TX packets:0 errors:4882 dropped:74 overruns:0
eth0 Link encap:10Mbps Ethernet HWaddr 00:00:C0:A1:72:D6
inet addr:203.29.19.1 Bcast:203.29.19.63 Mask:255.255.255.192
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:156 dropped:0 overruns:0
TX packets:0 errors:16545 dropped:165 overruns:2
Interrupt:9 Base address:0x6000
eth0:0 Link encap:10Mbps Ethernet HWaddr 00:00:C0:A1:72:D6
inet addr:10.10.10.10 Bcast:10.255.255.255 Mask:255.0.0.0
UP RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0
TX packets:0 errors:0 dropped:0 overruns:0
eth0:1 Link encap:10Mbps Ethernet HWaddr 00:00:C0:A1:72:D6
inet addr:10.10.10.8 Bcast:10.255.255.255 Mask:255.0.0.0
UP RUNNING MULTICAST MTU:1500 Metric:1
RX packets:1 errors:0 dropped:0 overruns:0
TX packets:0 errors:0 dropped:0 overruns:0
ppp0 Link encap:Point-Point Protocol
inet addr:203.29.19.1 P-t-P:10.10.10.9 Mask:255.255.255.255
UP POINTOPOINT RUNNING MTU:1500 Metric:1
RX packets:0 errors:14 dropped:1 overruns:1
TX packets:0 errors:0 dropped:23 overruns:0
rjc@snoopy:~$cat /proc/modules
bsd_comp 3668 2
isofs 17572 1
ide-cd 15560 1
cdrom 5184 0 [ide-cd]
rjc@snoopy:~$