diff --git a/src/encoding.cpp b/src/encoding.cpp
index 4855b22..b45657a 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -381,9 +381,9 @@
 	block->u.Packet_Uplink_Ack_Nack.UnionType    = 0x0;      // PU_AckNack_GPRS = on
 	block->u.Packet_Uplink_Ack_Nack.u.PU_AckNack_GPRS_Struct.CHANNEL_CODING_COMMAND                        = bts->initial_cs_ul - 1;             // CS1
 	block->u.Packet_Uplink_Ack_Nack.u.PU_AckNack_GPRS_Struct.Ack_Nack_Description.FINAL_ACK_INDICATION     = final;           // FINAL ACK INDICATION
-	block->u.Packet_Uplink_Ack_Nack.u.PU_AckNack_GPRS_Struct.Ack_Nack_Description.STARTING_SEQUENCE_NUMBER = tbf->dir.ul.v_r; // STARTING_SEQUENCE_NUMBER
+	block->u.Packet_Uplink_Ack_Nack.u.PU_AckNack_GPRS_Struct.Ack_Nack_Description.STARTING_SEQUENCE_NUMBER = tbf->dir.ul.window.v_r(); // STARTING_SEQUENCE_NUMBER
 	// RECEIVE_BLOCK_BITMAP
-	for (i = 0, bbn = (tbf->dir.ul.v_r - 64) & mod_sns_half; i < 64;
+	for (i = 0, bbn = (tbf->dir.ul.window.v_r() - 64) & mod_sns_half; i < 64;
 	     i++, bbn = (bbn + 1) & mod_sns_half) {
 	     	bit = tbf->dir.ul.v_n[bbn];
 		if (bit == 0)