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I'd like you to reexamine a change. Please visit
https://gerrit.osmocom.org/c/osmo-pcu/+/32049
to look at the new patch set (#2).
Change subject: doc: Add details regarding BSC co-location
......................................................................
doc: Add details regarding BSC co-location
As of now the manual only focusses on the BTS co-located scenario. Since
we recently introduced support for Ericsson RBS 2000/6000 base stations,
we also had to add support for the BSC co-located scenario. Let's update
the manual accordingly.
Related: OS#5198
Change-Id: Ib2a3b60849fd312b21073a3511b8ca36b4536343
---
M doc/manuals/chapters/configuration.adoc
M doc/manuals/chapters/overview.adoc
2 files changed, 103 insertions(+), 15 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-pcu refs/changes/49/32049/2
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Gerrit-Branch: master
Gerrit-Change-Id: Ib2a3b60849fd312b21073a3511b8ca36b4536343
Gerrit-Change-Number: 32049
Gerrit-PatchSet: 2
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laforge has submitted this change. ( https://gerrit.osmocom.org/c/osmo-bsc/+/32032 )
(
2 is the latest approved patch-set.
No files were changed between the latest approved patch-set and the submitted one.
)Change subject: doc: bts-examples: discuss Ericsson RBS EGPRS configuration
......................................................................
doc: bts-examples: discuss Ericsson RBS EGPRS configuration
Add a configuration file example to illustrate how exactly EGPRS is
configured on ericsson RBS BTSs.
Related: OS#5198
Change-Id: I2fb5b4d9300b16b0fac48f33b5db81442ab25031
---
M doc/manuals/chapters/bts-examples.adoc
M doc/manuals/chapters/running.adoc
2 files changed, 148 insertions(+), 1 deletion(-)
Approvals:
laforge: Looks good to me, approved
Jenkins Builder: Verified
diff --git a/doc/manuals/chapters/bts-examples.adoc b/doc/manuals/chapters/bts-examples.adoc
index f840b39..27278fb 100644
--- a/doc/manuals/chapters/bts-examples.adoc
+++ b/doc/manuals/chapters/bts-examples.adoc
@@ -175,6 +175,7 @@
between the two nanoBTS units, as well as the coaxial/RF AUX cabling.
====
+[[example_e1_cfg]]
=== Example configuration for OsmoBSC with E1 BTS
The following configuration sample illustrates the usage of BTSs that are
@@ -273,6 +274,139 @@
<9> The bandwidth of one E1 timeslot matches the bandwidth of 4 GSM air interface timeslots. The E1 timeslot is split up into four sub-slots, which are then assigned to one GSM air interface timeslot each. Since the first timeslot on the first TRX is already used for signaling we begin the sub-slot counting with sub-slot 1 for alignment reasons.
+=== Example configuration for OsmoBSC with Ericsson RBS E1 BTS and EGPRS
+
+The following example illustrates the usage of Ericsson RBS2000/RBS6000 BTSs.
+This classic E1 BTS has no built in PCU and therefore requires the configuration
+of a BSC co-located OsmoPCU (see also: <<cfg_bsc_co_located_pcu>>).
+
+It should also be noted that the Ericsson RBS2000/RBS6000 series is the first
+BTS of this type to be supported by OsmoBTS and OsmoPCU. The implementation has
+been made possible through funding by the NLnet Foundation.
+
+Ericsson RBS2000/RBS6000 BTSs feature two GPRS modes. A 16kbps GPRS mode where
+only CS1 and CS2 are supported and an EGPRS mode where MCS1 to MCS9 are
+supported. OsmoPCU offers support for both modes but since the 16kbps mode only
+supports classic GPRS with CS1 and CS2 it is more of experimental interest
+and shall not be discussed further. The following example will describe how
+to configure the 64kbps mode with EGPRS.
+
+In the following example we also expect that the user is already familliar
+with the E1 configuration example above (see also: <<example_e1_cfg>>)
+
+.OsmoBSC configured for single-TRX E1 Ericsson DUG20 with EGPRS
+====
+----
+e1_input
+ e1_line 0 driver dahdi
+ e1_line 0 port 3
+network
+ network country code 1
+ mobile network code 1
+ encryption a5 0
+ neci 1
+ handover 0
+ pcu-socket /tmp/pcu_bts <1>
+ bts 0
+ type rbs2000
+ band GSM900
+ om2000 version-limit oml gen 12 rev 10
+ cell_identity 0
+ location_area_code 0x0001
+ training_sequence_code 7
+ base_station_id_code 63
+ ms max power 15
+ cell reselection hysteresis 4
+ rxlev access min 0
+ channel allocator mode set-all ascending
+ rach tx integer 9
+ rach max transmission 7
+ oml e1 line 0 timeslot 1 sub-slot full
+ oml e1 tei 62
+ gprs mode egprs <2>
+ gprs routing area 0
+ gprs network-control-order nc0
+ gprs cell bvci 2
+ gprs nsei 101
+ gprs nsvc 0 nsvci 101
+ gprs nsvc 0 local udp port 23100
+ gprs nsvc 0 remote udp port 23000
+ gprs nsvc 0 remote ip 127.0.0.1
+ gprs nsvc 1 nsvci 0
+ gprs nsvc 1 local udp port 0
+ gprs nsvc 1 remote udp port 0
+ gprs nsvc 1 remote ip 0.0.0.0
+ is-connection-list add 4 712 36 <3>
+ trx 0
+ rf_locked 0
+ arfcn 123
+ nominal power 42
+ max_power_red 12
+ rsl e1 line 0 timeslot 1 sub-slot full
+ rsl e1 tei 0
+ timeslot 0
+ phys_chan_config CCCH+SDCCH4
+ hopping enabled 0
+ e1 line 0 timeslot 1 sub-slot full
+ timeslot 1
+ phys_chan_config TCH/F
+ hopping enabled 0
+ e1 line 0 timeslot 3 sub-slot full <4>
+ timeslot 2
+ phys_chan_config TCH/F
+ hopping enabled 0
+ e1 line 0 timeslot 4 sub-slot full
+ timeslot 3
+ phys_chan_config TCH/F
+ hopping enabled 0
+ e1 line 0 timeslot 5 sub-slot full
+ timeslot 4
+ phys_chan_config TCH/F_TCH/H_SDCCH8_PDCH <5>
+ hopping enabled 0
+ e1 line 0 timeslot 6 sub-slot full
+ timeslot 5
+ phys_chan_config TCH/F
+ hopping enabled 0
+ e1 line 0 timeslot 7 sub-slot full
+ timeslot 6
+ phys_chan_config TCH/F
+ hopping enabled 0
+ e1 line 0 timeslot 8 sub-slot full
+ timeslot 7
+ phys_chan_config TCH/F
+ hopping enabled 0
+ e1 line 0 timeslot 9 sub-slot full
+----
+====
+
+<1> This configures the PCU socket path (see also: <<cfg_bsc_co_located_pcu>>)
+
+<2> This configures the general GPRS parameters. The configuration is no
+different from BTS with built-in PCU.
+
+<3> The Ericsson RBS2000/RBS6000 series has an built in “Interface Switch” (IS)
+that offers flexible way to reconfigure the interconnection between the internal
+components of the BTS and the external E1 line. Since 16kbps subslots cannot
+supply the bandwidth required for EGPRS the IS must be configured to connect
+the 64kbps interface of the TRU to the external E1 line. For a more detailed
+description of the IS see <<cfg_ericsson_rbs_is>>.
+
+<4> Since we are using the 64kbps TRU interface we must configure a full E1
+timeslot per air interface time slot. For Speech this will have no effect on
+the TRAU frame format. The only difference is that always the first 16kbps
+subslot of the assigned E1 timeslot is used. OsmoMGW will be instructed
+accordingly by OsmoBSC, so no re-configuration of OsmoMGW is required.
+
+<5> In this example we will use air interface TS 4 as PDCH. As mentioned
+earlier Ericsson RBS2000/RBS6000 supports the 'DYNAMIC/OSMOCOM' timeslot model.
+PDCH timeslots must be configured as dynamic timeslots. It is not possible to
+configure static PDCHs. Therefore the phys_chan_config must be set to
+TCH/F_TCH/H_SDCCH8_PDCH in order to use the air interface timeslot as PDCH.
+
+NOTE: As of March 2023 the BSC co-located PCU support for Ericsson RBS was
+tested only with a single BTS. Even though OsmoBSC and OsmoPCU should be able
+to handle multiple BTS, unexpected bahviour should be taken into account.
+
=== E1 Line number and MGCP trunk number
The switching of the voice channels is done via OsmoMGW, which acts as a media
converter between E1 and VoIP (RTP). OsmoBSC will use the E1 line number to
diff --git a/doc/manuals/chapters/running.adoc b/doc/manuals/chapters/running.adoc
index 6d690ce..54c36c9 100644
--- a/doc/manuals/chapters/running.adoc
+++ b/doc/manuals/chapters/running.adoc
@@ -219,7 +219,7 @@
More detailed configuration is described in <<smlc-config>>.
-
+[[cfg_bsc_co_located_pcu]]
==== Configure BSC co-located PCU
While small IP based BTSs usually come with a built in PCU (BTS co-located
--
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Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-Change-Id: I2fb5b4d9300b16b0fac48f33b5db81442ab25031
Gerrit-Change-Number: 32032
Gerrit-PatchSet: 3
Gerrit-Owner: dexter <pmaier(a)sysmocom.de>
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Gerrit-Reviewer: laforge <laforge(a)osmocom.org>
Gerrit-MessageType: merged
laforge has submitted this change. ( https://gerrit.osmocom.org/c/osmo-bsc/+/32029 )
Change subject: bts: bts: Explain Ericsson's interface switch (IS)
......................................................................
bts: bts: Explain Ericsson's interface switch (IS)
The built in interface switch in ericsson RBS base stations no where
explained. From the example configuration files alone it is not possible
to understand how the IS configuration works. Let's add a chapter that
explains how the IS configuration works.
Related: OS#5198
Change-Id: Ib6ebd7fdfe9063c0d8cacf53ffd27f6099d9038a
---
M doc/manuals/chapters/bts-examples.adoc
M doc/manuals/chapters/bts.adoc
2 files changed, 153 insertions(+), 1 deletion(-)
Approvals:
Jenkins Builder: Verified
pespin: Looks good to me, but someone else must approve
laforge: Looks good to me, approved
diff --git a/doc/manuals/chapters/bts-examples.adoc b/doc/manuals/chapters/bts-examples.adoc
index 1f3652b..f840b39 100644
--- a/doc/manuals/chapters/bts-examples.adoc
+++ b/doc/manuals/chapters/bts-examples.adoc
@@ -263,7 +263,7 @@
<4> OML always requires a TEI (Terminal Equipment Identifier) to set up. This number can be found in the manual of the BTS.
-<5> This BTS has an built in “Interface Switch” (IS) that offers flexible way to reconfigure the interconnection between the internal components of the BTS and the external E1 line. This depends on the exact BTS type and configuration.
+<5> This BTS has an built in “Interface Switch” (IS) that offers flexible way to reconfigure the interconnection between the internal components of the BTS and the external E1 line. This depends on the exact BTS type and configuration. See also <<cfg_ericsson_rbs_is>>
<6> Similar to OML we assign TS1 to RSL as well.
diff --git a/doc/manuals/chapters/bts.adoc b/doc/manuals/chapters/bts.adoc
index d119acc..e6179aa 100644
--- a/doc/manuals/chapters/bts.adoc
+++ b/doc/manuals/chapters/bts.adoc
@@ -645,3 +645,140 @@
<2> This number affects how long the MS waits before (re-)transmitting RACH
requests.
<3> How often to retransmit the RACH request.
+
+[[cfg_ericsson_rbs_is]]
+=== Configuring Ericsson RBS Interface Switch (IS)
+
+Ericsson RBS2000/RBS6000 base stations feature a so called "Interface Switch" (IS),
+which is a built-in switchboard that interconnects between internal components
+of the BTS. It also connects to the external E1 connections. This allows to
+adapt the BTS to specific E1 networking requirements that may differ from the
+usual timeslot configuration.
+
+The internals of an Ericsson RBS are quite complex. In the following we will
+only explain how to connect transceiver units (TRU) to an E1 interface pointing
+to the outside world.
+
+==== Understanding the is-connection-list VTY option
+
+The IS operates on 16kbps subslots (ICPs), which means that there are no fixed
+borders between E1 timeslots. Any number of consecutive subslots may be
+connected through. However, depending on the components that are connected it
+may still be a requirement to align on E1 timeslot borders.
+
+The configuration of the IS is done using the is-connection-list command. The
+first two numbers are the ICP numbers that specify the first subslot on both
+sides that shall be interconnected. The third number (contiguity index) specifies
+how many of the following subslots shall be connected.
+
+In the following example we connect 4 blocks with 12 subslot each. The numbers
+on the left are the ICP numbers of the E1 connection pointing to the outside.
+The numbers in the middle are the ICP numbers of the subslots occupied by the
+transceivers (one TRX per block). The third number is the contiguity index that
+spans over 12 subslots or 3 E1 timeslots.
+
+.Example: 4 TRX BTS (4 x 12 subslots)
+----
+network
+ bts 0
+ is-connection-list add 4 512 12
+ is-connection-list add 16 524 12
+ is-connection-list add 28 536 12
+ is-connection-list add 40 548 12
+----
+
+==== E1 port and TRU ICP numbers
+
+On the outside connection, the ICP counting begins at E1 timeslot 0 (port A)
+but since E1 TS 0 is reserved for framing and synchronization of the E1 line
+itself the first usable subslot is subslot 4 (beginning of E1 TS 1). Depending
+on the configuration the BTS may have multiple E1 ports. The counting scheme
+will repeat itself. This means the next usable ICP can be found at an offset
+of 128.
+
+.External connections of a BTS with two E1 ports
+[options="header",cols="50%,25%,25%"]
+|===
+|Function |Subslot offset (ICP) |ICP count
+|E1 port A |4 |124
+|E1 port B |132 |124
+|===
+
+Depending on the transceiver configuration, a RBS2000/RBS6000 base station
+usually features two sets of ICPs for each TRX. The reason for this is that with
+the introduction of EGPRS more bandwidth than a single 16kbps subslot could
+deliver was required. The solution to this was to add an entirely new set of IS
+ICPs where full 64kbps E1 timeslots instead of 16kbps subslots could be
+used to serve a single air interface timeslot. The two sets of ICPs must not be
+mixed. Only one set may be used at a time.
+
+.ICPs to use TRU with 16kbps subslots per TRAU
+[options="header",cols="50%,25%,25%"]
+|===
+|Function |Subslot offset (ICP) |ICP count
+|TRU-0, RSL/OML |512 |4
+|TRU-0, TRAU TS0..TS7 |516 |8
+|TRU-1, RSL/OML |524 |4
+|TRU-1, TRAU TS0..TS7 |528 |8
+|TRU-2, RSL/OML |536 |4
+|TRU-2, TRAU TS0..TS7 |540 |8
+|TRU-3, RSL/OML |548 |4
+|TRU-3, TRAU TS0..TS7 |552 |8
+|TRU-4, RSL/OML |560 |4
+|TRU-4, TRAU TS0..TS7 |564 |8
+|TRU-5, RSL/OML |572 |4
+|TRU-5, TRAU TS0..TS7 |576 |8
+|TRU-6, RSL/OML |640 |4
+|TRU-6, TRAU TS0..TS7 |644 |8
+|TRU-7, RSL/OML |652 |4
+|TRU-7, TRAU TS0..TS7 |656 |8
+|TRU-8, RSL/OML |664 |4
+|TRU-8, TRAU TS0..TS7 |668 |8
+|TRU-9, RSL/OML |676 |4
+|TRU-9, TRAU TS0..TS7 |680 |8
+|TRU-10, RSL/OML |688 |4
+|TRU-10, TRAU TS0..TS7 |692 |8
+|TRU-11, RSL/OML |700 |4
+|TRU-11, TRAU TS0..TS7 |704 |8
+|===
+
+NOTE: Each air interface timeslot is served by its individual TRAU, so it is
+possible to route each subslot (ICP) dedicated to TRAU individually. The
+connections on the other end may contain gaps and do not have to be
+consecutive.
+
+.ICPs to use TRU with 64kbps subslots per TRAU
+[options="header",cols="50%,25%,25%"]
+|===
+|Function |Subslot offset (ICP) |ICP count
+|TRU-0, RSL/OML |712 |4
+|TRU-0, TRAU TS0..TS7 |716 |32
+|TRU-1, RSL/OML |748 |4
+|TRU-1, TRAU TS0..TS7 |752 |32
+|TRU-2, RSL/OML |784 |4
+|TRU-2, TRAU TS0..TS7 |788 |32
+|TRU-3, RSL/OML |820 |4
+|TRU-3, TRAU TS0..TS7 |824 |32
+|TRU-4, RSL/OML |856 |4
+|TRU-4, TRAU TS0..TS7 |860 |32
+|TRU-5, RSL/OML |928 |4
+|TRU-5, TRAU TS0..TS7 |932 |32
+|TRU-6, RSL/OML |964 |4
+|TRU-6, TRAU TS0..TS7 |968 |32
+|TRU-7, RSL/OML |1000 |4
+|TRU-7, TRAU TS0..TS7 |1004 |32
+|TRU-8, RSL/OML |1036 |4
+|TRU-8, TRAU TS0..TS7 |1040 |32
+|TRU-9, RSL/OML |1072 |4
+|TRU-9, TRAU TS0..TS7 |1076 |32
+|TRU-10, RSL/OML |1108 |4
+|TRU-10, TRAU TS0..TS7 |1112 |32
+|TRU-11, RSL/OML |1144 |4
+|TRU-11, TRAU TS0..TS7 |1148 |32
+|===
+
+NOTE: In case voice TRAU frames are transferred, only the first of the four
+16kbps subslots is used. When the timeslot is switched to GPRS/EGPRS, the
+full 64kbps bandwidth will be used. This also means that the set of four
+ICPs per TRAU must be connected consecutively. Also the connection
+to the outside must be aligned to E1 timeslot borders.
\ No newline at end of file
--
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Gerrit-Change-Id: Ib6ebd7fdfe9063c0d8cacf53ffd27f6099d9038a
Gerrit-Change-Number: 32029
Gerrit-PatchSet: 3
Gerrit-Owner: dexter <pmaier(a)sysmocom.de>
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Gerrit-Reviewer: keith <keith(a)rhizomatica.org>
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Gerrit-Reviewer: pespin <pespin(a)sysmocom.de>
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Gerrit-MessageType: merged
laforge has submitted this change. ( https://gerrit.osmocom.org/c/osmo-bsc/+/32030 )
Change subject: doc: running: Describe how to configure a co-located PCU
......................................................................
doc: running: Describe how to configure a co-located PCU
The manual does not yet mention the possibility to configure a BSC
co-located PCU. Lets add a short description to the chapter
Running OsmoBSC, Configure primary Links that enables users to get an
idea where exactly the BSC co-located PCU has its place in the RAN
infrastructure and which links it is connected with. Also give a short
example how to setup the unix domain socket path.
A more detailed description, especially about the timeslot configuration
will be added with a follow up patch for bts.adoc
Related: OS#5198
Change-Id: I3af3cd8ef7099bb94f4cb25513e9dfdc5fcc1b5a
---
M doc/manuals/chapters/bts.adoc
M doc/manuals/chapters/running.adoc
2 files changed, 65 insertions(+), 0 deletions(-)
Approvals:
keith: Looks good to me, but someone else must approve
Jenkins Builder: Verified
laforge: Looks good to me, approved
diff --git a/doc/manuals/chapters/bts.adoc b/doc/manuals/chapters/bts.adoc
index e6179aa..9107aa1 100644
--- a/doc/manuals/chapters/bts.adoc
+++ b/doc/manuals/chapters/bts.adoc
@@ -181,6 +181,7 @@
means of `si5 neighbor-list (add|del) arfcn <0-1023>` for SACCH (SI5).
+[[config_gprs_pcu_pars]]
=== Configuring GPRS PCU parameters of a BTS
In the case of BTS models using Abis/IP (IPA), the GPRS PCU is located
diff --git a/doc/manuals/chapters/running.adoc b/doc/manuals/chapters/running.adoc
index 70f9d28..6d690ce 100644
--- a/doc/manuals/chapters/running.adoc
+++ b/doc/manuals/chapters/running.adoc
@@ -218,3 +218,47 @@
----
More detailed configuration is described in <<smlc-config>>.
+
+
+==== Configure BSC co-located PCU
+
+While small IP based BTSs usually come with a built in PCU (BTS co-located
+PCU), this does not have to be the case with any BTS. Especially larger E1 BTS
+usually make use of a BSC co-located PCU.
+
+In the case of OsmoBSC this means that an instance of OsmoPCU is running next
+to OsmoBSC. Both processes share a unix domain socket to exchange signaling
+traffic and configuration parameters.
+
+.OsmoBSC with co-located OsmoPCU'
+[graphviz]
+----
+digraph G {
+ rankdir=LR;
+ BTS [label="BTS"];
+
+ subgraph cluster_ran {
+ label="RAN";
+ PCU [label="OsmoPCU"];
+ BSC [label="OsmoBSC"];
+ MGW [label="OsmoMGW"];
+ { rank=same BSC MGW PCU }
+ }
+
+ BTS->PCU [label="GPRS/TRAU", style=dotted];
+ BTS->BSC [label="Abis"];
+ BTS->MGW [label="SPEECH/TRAU", style=dotted];
+ BSC->MGW [label="MGCP"];
+ BSC->PCU [label="PCU_SOCK"];
+}
+----
+
+Apart from the configuration of the PCU socket path the configuration is not
+much different from those where the PCU is integrated inside the BTS. See also
+see also <<config_gprs_pcu_pars>> for a detailed description.
+
+.Configure socket path to co-located PCU
+----
+network
+ pcu-socket /tmp/pcu_bts
+----
--
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dexter has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-pcu/+/32049 )
Change subject: doc: Add details regarding BSC co-location
......................................................................
doc: Add details regarding BSC co-location
As of now the manual only focusses on the BTS co-located scenario. Since
we recently introduced support for Ericsson RBS 2000/6000 base stations,
we also had to add support for the BSC co-located scenario. Let's update
the manual accordingly.
Related: OS#5198
Change-Id: Ib2a3b60849fd312b21073a3511b8ca36b4536343
---
M doc/manuals/chapters/configuration.adoc
M doc/manuals/chapters/overview.adoc
2 files changed, 103 insertions(+), 15 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-pcu refs/changes/49/32049/1
diff --git a/doc/manuals/chapters/configuration.adoc b/doc/manuals/chapters/configuration.adoc
index ca3963d..cae9eb0 100644
--- a/doc/manuals/chapters/configuration.adoc
+++ b/doc/manuals/chapters/configuration.adoc
@@ -328,6 +328,25 @@
<1> Time out if the SGSN doesn't answer our RIM RAN-INFO request request after 500 ms
<2> Keep resolved remote neighbor System Information cached for 60 seconds
+[[cfg_e1_line]]
+=== Configuring E1 line for CCU access
+
+Depending on the configuration the PCU may require direct access to a BTS CCU
+(channel coding unit) via an E1 line. This is in particular the case when
+OsmoPCU runs in co-location with OsmoBSC.
+
+The exact timeslot configuration is passed to the PCU via the pcu_sock
+interface. Only basic E1 line settings are required. However, it is important
+that the E1 line number is the same as the E1 line number that is used in the
+timeslot configuration of OsmoBSC.
+
+.Example: Configure an E1 line
+----
+e1_input
+ e1_line 0 driver dahdi
+ e1_line 0 port 2
+ no e1_line 0 keepalive
+
=== GPRS vs EGPRS considerations
diff --git a/doc/manuals/chapters/overview.adoc b/doc/manuals/chapters/overview.adoc
index 5b831d3..d228dee 100644
--- a/doc/manuals/chapters/overview.adoc
+++ b/doc/manuals/chapters/overview.adoc
@@ -2,14 +2,17 @@
=== About OsmoPCU
-OsmoPCU is the Osmocom implementation of the GPRS PCU (Packet Control
-Unit) element inside the GPRS network.
+OsmoPCU is the Osmocom implementation of the GPRS PCU (Packet Control Unit)
+element inside the GPRS network. Depending on the BTS type the PCU will be
+co-located within the BTS or run in co-location with the BSC.
-The OsmoPCU is co-located within the BTS and connects to OsmoBTS via its
-PCU socket interface.
+[[pcu_co_located_with_bts]]
+==== OsmoPCU in co-location with OsmoBTS
-On the other side, OsmoPCU is connected via the Gb interface to the
-SGSN.
+In small base stations, the PCU is usually co-located inside the BTS. In this
+scenario OsmoPCU and OsmoBTS run on the same host system. Both are
+interconnected using a unix domain socket based interface.
+(see also: <<pcu_sock_iface>>)
[[fig-gprs-pcubts]]
.GPRS network architecture with PCU in BTS
@@ -31,12 +34,62 @@
}
----
+NOTE: Depending on the hardware architecture, OsmoPCU may also have direct
+access on the PHY interface to exchange PDCH traffic efficiently. The socket
+interface is then only used for signalling.
+
+==== OsmoPCU in co-location with OsmoBSC
+
+Classic E1 based BTSs usually do not include a PCU. Instead those base stations
+typically rely on an external PCU that is co-located with the BSC. The
+signalling traffic (paging, channel assignments ect.) is then exchanged with the
+BTS via RSL, while the PDCH traffic is handled by the PCU through a dedicated
+TRAU frame based E1 connection.
+
+OsmoPCU supports this scenario as well. Due to the dedicated E1 connection, the
+implementation is complex and strongly hardware specific. As of now (March 2023)
+OsmoPCU supports Ericsson RBS2000/RBS6000 only. This implementation has been
+made possible through funding by the NLnet Foundation.
+
+[[fig-gprs-pcubts]]
+.GPRS network architecture with PCU in BTS
+[graphviz]
+----
+digraph G {
+ rankdir=LR;
+ MS0 [label="MS"]
+ MS1 [label="MS"]
+ MS0->BTS [label="Um"]
+ MS1->BTS [label="Um"]
+ BTS->BSC [label="Abis"]
+ BSC->MSC [label="A"]
+ BTS->PCU [label="pcu_sock"]
+ PCU->SGSN [label="Gb"]
+ SGSN->GGSN [label="GTP"]
+ PCU [color=red]
+ { rank=same BTS PCU }
+}
+----
+
+When OsmoPCU runs in co-location to OsmoBSC, both are connected through the
+same unix domain socket interface as mentioned above.
+(see also: <<pcu_co_located_with_bts>>) The socket is used to pass signalling
+traffic between PCU and BSC while the PCU controls the PDCH by directly talking
+to the BTS CCU (channel coding unit) through a dedicated E1 connection. The
+E1 line interface uses TRAU frames and is vastly comparable to the interface that
+is used when speech is transferred.
+
+Since the PCU is mainly set up by OsmoBSC (or OsmoBTS) via the PCU socket, the
+configuration in the BSC co-located scenario is no different from the BTS
+co-located scenario. However, since the PCU requires a direct E1 connection to
+the BTS an E1 line must be set up. (See also: <<cfg_e1_line>>)
+
=== Software Components
OsmoPCU consists of a variety of components, including
* Gb interface (NS/BSSGP protocol)
-* `pcu_sock` interface towards OsmoBTS
+* `pcu_sock` interface towards OsmoBTS (or OsmoBSC)
* TBF management for uplink and downlink TBF
* RLC/MAC protocol implementation
* per-MS context for each MS currently served
@@ -53,17 +106,18 @@
Gb implementation to be used from OsmoPCU, OsmoGbProxy as well as
OsmoSGSN.
-==== `pcu_sock` Interface to OsmoBTS
+[[pcu_sock_iface]]
+==== `pcu_sock` Interface to OsmoBTS/OsmoBSC
-The interface towards OsmoBTS is called 'pcu_sock' and implemented as a
-set of non-standardized primitives over a unix domain socket. The
+The interface towards OsmoBTS/OsmoBSC is called 'pcu_sock' and implemented
+as a set of non-standardized primitives over a unix domain socket. The
default file system path for this socket is `/tmp/pcu_bts`.
-The PCU socket can be changed on both OsmoBTS and OsmoPCU to a different
-file/path name, primarily to permit running multiple independent BTS+PCU
-pairs on a single Linux machine without having to use filesystem
-namespaces or other complex configurations.
+The PCU socket path can be freely configured to a different file/path name,
+primarily to permit running multiple independent BTS+PCU (or BSC+PCU) pairs
+on a single Linux machine without having to use filesystem namespaces or other
+complex configurations.
-NOTE: If you change the PCU socket path on OsmoBTS by means of the
+NOTE: If you change the PCU socket path on OsmoBTS/OsmoBSC by means of the
`pcu-socket` VTY configuration command, you must ensure to make the
identical change on the OsmoPCU side.
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