diff --git a/libs/freetdm/src/ozmod/ozmod_wanpipe/ozmod_wanpipe.c b/libs/freetdm/src/ozmod/ozmod_wanpipe/ozmod_wanpipe.c
index 7b359ff804..4fa255465b 100644
--- a/libs/freetdm/src/ozmod/ozmod_wanpipe/ozmod_wanpipe.c
+++ b/libs/freetdm/src/ozmod/ozmod_wanpipe/ozmod_wanpipe.c
@@ -267,7 +267,8 @@ static unsigned wp_open_range(zap_span_t *span, unsigned spanno, unsigned start,
             }
 #endif
 
-			if (type == ZAP_CHAN_TYPE_CAS) {
+			if (type == ZAP_CHAN_TYPE_CAS || 
+				((span->trunk_type == ZAP_TRUNK_T1 || span->trunk_type == ZAP_TRUNK_E1) && type != ZAP_CHAN_TYPE_B)) {
 #ifdef LIBSANGOMA_VERSION
 				sangoma_tdm_write_rbs(chan->sockfd,&tdm_api,chan->physical_chan_id,wanpipe_swap_bits(cas_bits));
 #else