cosmetic: Document foce_two_phase feature based on specs

Change-Id: I4f8e3d0dcb721d51838b50aba5b40d0551c8d0c5
---
M src/bts.cpp
1 file changed, 15 insertions(+), 0 deletions(-)

diff --git a/src/bts.cpp b/src/bts.cpp
index 177544a..fe48018 100644
--- a/src/bts.cpp
+++ b/src/bts.cpp
@@ -970,6 +970,12 @@
 		LOGP(DRLCMAC, LOGL_DEBUG, "MS requests single TS uplink transmission "
 		     "(one phase packet access)\n");
 		if (bts->pcu->vty.force_two_phase) {
+			/* 3GPP TS 44.018 3.5.2.1.3.1: "If the establishment cause in the
+			 * CHANNEL REQUEST message indicates a request for one phase packet access,
+			 * the network may grant either a one phase packet access or a single block
+			 * packet access for the mobile station. If a single block packet access is
+			 * granted, it forces the mobile station to perform a two phase packet access."
+			 */
 			LOGP(DRLCMAC, LOGL_DEBUG, "Forcing two phase access\n");
 			chan_req.single_block = true;
 		}

