diff --git a/doc/manuals/Makefile b/doc/manuals/Makefile
index f742e07..ef80327 100644
--- a/doc/manuals/Makefile
+++ b/doc/manuals/Makefile
@@ -14,11 +14,12 @@
 # htmlcss =
 
 TOPDIR := ..
-ASCIIDOCS := osmopcu-usermanual
+ASCIIDOCS := osmopcu-usermanual osmopcu-gb
 
 include $(TOPDIR)/build/Makefile.asciidoc.inc
 include $(TOPDIR)/build/Makefile.inc
 
+osmopcu-gb.pdf: gb/*.adoc gb/*.msc
 osmopcu-usermanual.pdf: chapters/*.adoc
 
 clean:
diff --git a/doc/manuals/gb/bssgp.adoc b/doc/manuals/gb/bssgp.adoc
new file mode 100644
index 0000000..c354fc1
--- /dev/null
+++ b/doc/manuals/gb/bssgp.adoc
@@ -0,0 +1,67 @@
+== BSS GPRS Protocol (BSSGP)
+
+=== List of Messages
+
+The following tables list the BSSGP messages used by OsmoPCU, grouped by their
+level of compliance with 3GPP TS 08.18.
+
+==== Messages Compliant With TS 08.18
+
+.Messages compliant with TS 08.18
+[options="header",cols="10%,10%,20%,35%,5%,20%"]
+|===
+| TS 08.18 § | type code (hex) | This document § | Message | <-/-> | Received/Sent by OsmoPCU
+|===
+
+==== Messages Specific to OsmoPCU
+
+There are no OsmoPCU specific BSSGP messages.
+
+==== Messages Not Implemented by OsmoPCU
+
+.3GPP TS 08.18 messages not implemented by OsmoPCU
+[options="header",cols="10%,10%,80%"]
+|===
+| TS 08.18 § | type code (hex) | Message
+|===
+
+
+=== Details on Compliant BSSGP Messages
+
+FIXME
+
+=== Information Elements Overview
+
+All of the IEs handled by OsmoPCU are listed below, with limitations and
+additions to TS 08.18 specified in more detail.
+
+==== IEs Conforming to TS 08.18
+
+The following Information Elements are accepted by OsmoPCU. Not all IEs are
+actually evaluated.
+
+.IEs conforming to TS 08.18
+[options="header",cols="5%,10%,40%,5%,40%"]
+|===
+| tag (hex) | TS 08.18 § | IE name | <-/-> | Received/Sent by OsmoPCU
+|===
+
+==== IEs Not Conforming to TS 08.18
+
+.IEs not conforming to TS 08.18
+[options="header",cols="5%,10%,30%,55%"]
+|===
+| tag (hex) | TS 08.18 § | IE name | Description
+|===
+
+==== Additional Attributes and Parameters
+
+There are no OsmoPCU specific additional Attributes and Parameters.
+
+=== Details on IEs
+
+FIXME
+
+=== Gb BSSGP Initialization / PCU bring-up
+
+FIXME
diff --git a/doc/manuals/gb/gb-startup.msc b/doc/manuals/gb/gb-startup.msc
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/doc/manuals/gb/gb-startup.msc
diff --git a/doc/manuals/gb/ns.adoc b/doc/manuals/gb/ns.adoc
new file mode 100644
index 0000000..0cc073b
--- /dev/null
+++ b/doc/manuals/gb/ns.adoc
@@ -0,0 +1,67 @@
+== Network Service (NS)
+
+=== List of Messages
+
+The following tables list the NS messages used by OsmoPCU, grouped by their
+level of compliance with 3GPP TS 08.16.
+
+==== Messages Compliant With TS 08.16
+
+.Messages compliant with TS 08.16
+[options="header",cols="10%,10%,20%,35%,5%,20%"]
+|===
+| TS 08.16 § | type code (hex) | This document § | Message | <-/-> | Received/Sent by OsmoPCU
+|===
+
+==== Messages Specific to OsmoPCU
+
+There are no OsmoPCU specific NS messages.
+
+==== Messages Not Implemented by OsmoPCU
+
+.3GPP TS 08.16 messages not implemented by OsmoPCU
+[options="header",cols="10%,10%,80%"]
+|===
+| TS 08.16 § | type code (hex) | Message
+|===
+
+
+=== Details on Compliant NS Messages
+
+FIXME
+
+=== Information Elements Overview
+
+All of the IEs handled by OsmoPCU are listed below, with limitations and
+additions to TS 08.16 specified in more detail.
+
+==== IEs Conforming to TS 08.16
+
+The following Information Elements are accepted by OsmoPCU. Not all IEs are
+actually evaluated.
+
+.IEs conforming to TS 08.16
+[options="header",cols="5%,10%,40%,5%,40%"]
+|===
+| tag (hex) | TS 08.16 § | IE name | <-/-> | Received/Sent by OsmoPCU
+|===
+
+==== IEs Not Conforming to TS 08.16
+
+.IEs not conforming to TS 08.16
+[options="header",cols="5%,10%,30%,55%"]
+|===
+| tag (hex) | TS 08.16 § | IE name | Description
+|===
+
+==== Additional Attributes and Parameters
+
+There are no OsmoPCU specific additional Attributes and Parameters.
+
+=== Details on IEs
+
+FIXME
+
+=== Gb NS Initialization / PCU bring-up
+
+FIXME
diff --git a/doc/manuals/osmopcu-gb-docinfo.xml b/doc/manuals/osmopcu-gb-docinfo.xml
new file mode 100644
index 0000000..280c6f7
--- /dev/null
+++ b/doc/manuals/osmopcu-gb-docinfo.xml
@@ -0,0 +1,58 @@
+<revhistory>
+  <revision>
+    <revnumber>0</revnumber>
+    <date>February 2016</date>
+    <authorinitials>HW, MS</authorinitials>
+    <revremark>
+      Initial version, reflecting OsmoPCU master branch as on FIXME
+      (commit FIXME).
+    </revremark>
+  </revision>
+</revhistory>
+
+<authorgroup>
+  <author>
+    <firstname>Max</firstname>
+    <surname>Suraev</surname>
+    <email>msuraev@sysmocom.de</email>
+    <authorinitials>MS</authorinitials>
+    <affiliation>
+      <shortaffil>sysmocom</shortaffil>
+      <orgname>sysmocom - s.f.m.c. GmbH</orgname>
+      <jobtitle>Software Developer</jobtitle>
+    </affiliation>
+  </author>
+  <author>
+    <firstname>Harald</firstname>
+    <surname>Welte</surname>
+    <email>hwelte@sysmocom.de</email>
+    <authorinitials>HW</authorinitials>
+    <affiliation>
+      <shortaffil>sysmocom</shortaffil>
+      <orgname>sysmocom - s.f.m.c. GmbH</orgname>
+      <jobtitle>Managing Director</jobtitle>
+    </affiliation>
+  </author>
+</authorgroup>
+
+<copyright>
+  <year>2015-2016</year>
+  <holder>sysmocom - s.f.m.c. GmbH</holder>
+</copyright>
+
+<legalnotice>
+  <para>
+	Permission is granted to copy, distribute and/or modify this
+	document under the terms of the GNU Free Documentation License,
+	Version 1.3 or any later version published by the Free Software
+	Foundation; with no Invariant Sections, no Front-Cover Texts,
+	and no Back-Cover Texts.  A copy of the license is included in
+	the section entitled "GNU Free Documentation License".
+  </para>
+  <para>
+	The Asciidoc source code of this manual can be found at
+	<ulink url="http://git.osmocom.org/osmo-gsm-manuals/">
+		http://git.osmocom.org/osmo-gsm-manuals/
+	</ulink>
+  </para>
+</legalnotice>
diff --git a/doc/manuals/osmopcu-gb.adoc b/doc/manuals/osmopcu-gb.adoc
new file mode 100644
index 0000000..261f7db
--- /dev/null
+++ b/doc/manuals/osmopcu-gb.adoc
@@ -0,0 +1,89 @@
+OsmoPCU Gb Protocol Specification
+=================================
+Harald Welte <nhofmeyr@sysmocom.de>
+
+== Introduction
+
+This document describes the Gb interface of *OsmoPCU*. Based on 3GPP TS
+FIXME and FIXME, this document indicates which of the 3GPP specified Gb
+messages and IEs are implemented according to 3GPP specifications, which of
+these are not or not fully implemented, as well as OsmoPCU-specific extensions
+to the Gb interface not specified by 3GPP.
+
+Extensions to the Gb interface specific to OsmoPCU are detailed in this
+document. For details on the messages and IEs that comply with abovementioned
+3GPP specifications, please refer to those documents.
+
+.3GPP document versions referred to by this document
+[cols="20%,80%"]
+|===
+|3GPP TS 08.56 | version 8.0.1 Release 1999
+|3GPP TS 08.58 | version 8.6.0 Release 1999
+|3GPP TS 08.60 | version 8.2.1 Release 1999
+|3GPP TS 12.21 | version 8.0.0 Release 1999
+|===
+
+.IETF documents referred to by his document
+[cols="20%,80%"]
+|===
+|IETF RFC 768 | User Datagram Protocol
+|IETF RFC 791 | Internet Protocol
+|===
+
+== Overview
+
+The OsmoPCU Gb interface consists of the NS (Network Services) and
+BSSGP (Base Station Subsystem Gateway Protocol), encapsulated in UDP
+(User Datagram Protocol) and IP (Internet Protocol) version 4.
+
+.UDP port numbers used by OsmoPCU Gb/IP
+[options="header",width="50%",cols="35%,65%"]
+|===
+|TCP Port Number|Usage
+|23000|NS over UDP
+|===
+
+The NS-over-UDP link is established in the PCU -> SGSN direction, i.e.
+the PCU is running as client while the SGSN is running as server.
+
+Establishment of the NS-over-UDP link is only possible after OsmoPCU
+has been configured viat the *PCU socket* interface from OsmoBTS.
+
+OsmoBTS in turn receives relevant configuration parameters from
+OsmoBSC or the BSC component inside OsmoNITB.
+
+.Overview of Gb link establishment
+["mscgen"]
+----
+include::gb/gb-startup.msc[]
+----
+
+=== Identities
+
+The Gb interface identities of the PCU are configured via BSC ->
+OsmoBTS -> PCU Socket. They consist of
+
+NSEI:: NS Equipment Identifier
+NSVCI:: NS Virtual Connection Identifier
+BVCI:: BSSGP Virtual Connection Identifier
+
+For an explanation of those identifiers and their use in the NS and
+BSSGP protocols, please see the reelvant 3GPP specifications for NS
+and BSSGP.
+
+In most cases, all above identities belong to different namespaces and
+must be unique within their respective namespace and within the SGSN
+they connect to.
+
+This means that typically each OsmoPCU has one unique set of NSEI,
+NSVCI and BVCI in your network.
+
+include::gb/ns.adoc[]
+
+include::gb/bssgp.adoc[]
+
+include::../common/chapters/port_numbers.adoc[]
+
+include::../common/chapters/glossary.adoc[]
+
+include::../common/chapters/gfdl.adoc[]