diff --git a/pcu/GPRS_Components.ttcn b/pcu/GPRS_Components.ttcn
index 2a8726f..f48eae1 100644
--- a/pcu/GPRS_Components.ttcn
+++ b/pcu/GPRS_Components.ttcn
@@ -651,7 +651,9 @@
 }
 
 /* One phase packet access (see 3GPP TS 44.018, table 9.1.8.1) */
-const BIT8 chan_req_def := '01111000'B;
+const BIT8 chan_req_def := '01111000'B; /* 01111 { 0xx | x0x | xx0 } */
+/* Single block (two phase or RR signalling) packet access */
+const BIT8 chan_req_sb  := '01110000'B; /* 01110xxx */
 
 /* Establish an Uplink TBF by sending RACH.ind towards the PCU */
 function f_pcuif_tx_rach_rx_imm_ass(uint16_t ra := bit2int(chan_req_def),