Change in osmo-gsm-manuals[master]: bsc: document handover
Hello Harald Welte, Jenkins Builder, I'd like you to reexamine a change. Please visit https://gerrit.osmocom.org/11532 to look at the new patch set (#3). Change subject: bsc: document handover .. bsc: document handover Add chapter "Handover", explaining: - intra- and - inter-BSC handover, - HO algorithm 1 and - algorithm 2 - new neighbor configuration Adjust copyright, add revision and add me as author. Change-Id: I7afb3f66c98abda07fc8acc76e00c46091fe55e2 --- M OsmoBSC/Makefile A OsmoBSC/chapters/handover.adoc A OsmoBSC/chapters/handover_inter_bsc.dot A OsmoBSC/chapters/handover_intra_bsc.dot M OsmoBSC/osmobsc-usermanual-docinfo.xml M OsmoBSC/osmobsc-usermanual.adoc 6 files changed, 642 insertions(+), 2 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/32/11532/3 -- To view, visit https://gerrit.osmocom.org/11532 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-gsm-manuals Gerrit-Branch: master Gerrit-MessageType: newpatchset Gerrit-Change-Id: I7afb3f66c98abda07fc8acc76e00c46091fe55e2 Gerrit-Change-Number: 11532 Gerrit-PatchSet: 3 Gerrit-Owner: Neels Hofmeyr Gerrit-Reviewer: Harald Welte Gerrit-Reviewer: Jenkins Builder (102)
Change in osmo-gsm-manuals[master]: bsc: document handover
Neels Hofmeyr has submitted this change and it was merged. (
https://gerrit.osmocom.org/11532 )
Change subject: bsc: document handover
..
bsc: document handover
Add chapter "Handover", explaining:
- intra- and
- inter-BSC handover,
- HO algorithm 1 and
- algorithm 2
- new neighbor configuration
Adjust copyright, add revision and add me as author.
Change-Id: I7afb3f66c98abda07fc8acc76e00c46091fe55e2
---
M OsmoBSC/Makefile
A OsmoBSC/chapters/handover.adoc
A OsmoBSC/chapters/handover_inter_bsc.dot
A OsmoBSC/chapters/handover_intra_bsc.dot
M OsmoBSC/osmobsc-usermanual-docinfo.xml
M OsmoBSC/osmobsc-usermanual.adoc
6 files changed, 642 insertions(+), 2 deletions(-)
diff --git a/OsmoBSC/Makefile b/OsmoBSC/Makefile
index 1533482..b9f50d0 100644
--- a/OsmoBSC/Makefile
+++ b/OsmoBSC/Makefile
@@ -2,7 +2,7 @@
ASCIIDOC = osmobsc-usermanual.adoc osmux-reference.adoc aoip-mgw-options.adoc
include $(TOPDIR)/build/Makefile.asciidoc.inc
-osmobsc-usermanual.pdf: chapters/*.adoc
+osmobsc-usermanual.pdf: chapters/*.adoc chapters/*.dot
aoip-mgw-options.pdf: aoip-mgw-options.adoc mgw/*.msc
VTY_REFERENCE = osmobsc-vty-reference.xml
diff --git a/OsmoBSC/chapters/handover.adoc b/OsmoBSC/chapters/handover.adoc
new file mode 100644
index 000..1120690
--- /dev/null
+++ b/OsmoBSC/chapters/handover.adoc
@@ -0,0 +1,552 @@
+== Handover
+
+Handover is the process of moving a continuously used channel (lchan) from one
+cell to another. Usually, that is an ongoing call, so that phones are able to
+move across cell coverage areas without interrupting the voice transmission.
+
+A handover can
+
+- stay within one given cell (intra-cell, i.e. simply a new RR Assignment
Command);
+- occur between two cells that belong to the same BSS (intra-BSC, via RR
Handover Command);
+- cross BSS boundaries (inter-BSC, via BSSMAP handover procedures);
+- move to another MSC (inter-MSC, inter-PLMN);
+- move to another RAN type, e.g. from 2G to 3G (inter-RAT,
inter-Radio-Access-Technology).
+
+The physical distance is by definition always very near, but handover
+negotiation may range from being invisible to the MSC all the way to
+orchestrating completely separate RAN stacks.
+
+OsmoBSC currently supports handover within one BSS and between separate BSS.
+Whether inter-MSC is supported depends on the MSC implementation (to the BSC,
+inter-MSC handover looks identical to inter-BSC handover). Inter-RAT handover
+is currently not implemented.
+
+At the time of writing, OsmoMSC's inter-BSC handover support is not complete
+yet, so OsmoBSC can perform handover between separate BSS only in conjunction
+with a 3rd party MSC implementation.
+
+.Handover support in Osmocom at the time of writing
+[cols="^,^,^,^,^"]
+|
+| | intra-BSC HO (local BSS) | inter-BSC HO (remote BSS) | inter-MSC HO |
inter-RAT HO
+| OsmoBSC | rxlev, load-based | rxlev | (planned) | -
+| OsmoMSC | (not involved, except for codec changes) | (planned) | (planned)
| -
+|
+
+
+=== How Handover Works
+
+This chapter generally explains handover operations between 2G cells.
+
+ Internal / Intra-BSC Handover
+
+The BSS is configured to know which cell is physically adjacent to which other
+cells, its "neighbors". On the MS/BTS/BSS level, individual cells are
+identified by ARFCN+BSIC (frequency + 6-bit identification code).
+
+Each BTS is told by the BSC which cells identified by ARFCN+BSIC are its
+adjacent cells. Via System Information, each MS receives a list of these
+ARFCN+BSIC, and the MS then return measurements of reception levels.
+
+The BSC is the point of decision whether to do handover or not. This can be a
+hugely complex combination of heuristics, knowledge of cell load and codec
+capabilites. The most important indicator for handover though is: does an MS
+report a neighbor with a better signal than the current cell? See
+<>.
+
+[[intra_bsc_ho_dot]]
+.Intra-BSC Handover stays within the BSS (shows steps only up to activation of
the new lchan -- this would be followed by an RR Handover Command, RACH causing
Handover Detection, Handover Complete, ...)
+[graphviz]
+
+include::handover_intra_bsc.dot[]
+
+
+If the BSC sees the need for handover, it will:
+
+- activate a new lchan (with a handover reference ID),
+- send an RR Handover Command to the current lchan, and
+- wait for the MS to send a Handover RACH to the new lchan ("Handover Detect").
+- The RTP stream then is switched over to the new lchan,
+- an RSL Establish Indication is expected on the new lchan,
+- and the old lchan is released.
+
+Should handover fail at any point, e.g. the new lchan never receives a RACH, or
+the MS reports a Handover Failure, then the new lchan is simply released again,
+and the old lchan remains in use. If the RTP stream has already been switched
+over to the new lchan, it may actually be switched back to the old lchan.
+
+This is simple enough if the new cell is managed by the same BSC:
Change in osmo-gsm-manuals[master]: bsc: document handover
Harald Welte has posted comments on this change. ( https://gerrit.osmocom.org/11532 ) Change subject: bsc: document handover .. Patch Set 2: Code-Review+2 (1 comment) https://gerrit.osmocom.org/#/c/11532/2/OsmoBSC/chapters/handover.adoc File OsmoBSC/chapters/handover.adoc: https://gerrit.osmocom.org/#/c/11532/2/OsmoBSC/chapters/handover.adoc@12 PS2, Line 12: - move to another MSC (inter-MSC); strictly speaking, there's also inter-PLMN hand-over, but AFAIK it's only a normal inter-MSC HO with a fancy name -- To view, visit https://gerrit.osmocom.org/11532 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-gsm-manuals Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: I7afb3f66c98abda07fc8acc76e00c46091fe55e2 Gerrit-Change-Number: 11532 Gerrit-PatchSet: 2 Gerrit-Owner: Neels Hofmeyr Gerrit-Reviewer: Harald Welte Gerrit-Reviewer: Jenkins Builder (102) Gerrit-Comment-Date: Wed, 31 Oct 2018 08:12:29 + Gerrit-HasComments: Yes Gerrit-HasLabels: Yes
Change in osmo-gsm-manuals[master]: bsc: document handover
Hello Jenkins Builder, I'd like you to reexamine a change. Please visit https://gerrit.osmocom.org/11532 to look at the new patch set (#2). Change subject: bsc: document handover .. bsc: document handover Add chapter "Handover", explaining: - intra- and - inter-BSC handover, - HO algorithm 1 and - algorithm 2 - new neighbor configuration Adjust copyright, add revision and add me as author. Change-Id: I7afb3f66c98abda07fc8acc76e00c46091fe55e2 --- M OsmoBSC/Makefile A OsmoBSC/chapters/handover.adoc A OsmoBSC/chapters/handover_inter_bsc.dot A OsmoBSC/chapters/handover_intra_bsc.dot M OsmoBSC/osmobsc-usermanual-docinfo.xml M OsmoBSC/osmobsc-usermanual.adoc 6 files changed, 642 insertions(+), 2 deletions(-) git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals refs/changes/32/11532/2 -- To view, visit https://gerrit.osmocom.org/11532 To unsubscribe, or for help writing mail filters, visit https://gerrit.osmocom.org/settings Gerrit-Project: osmo-gsm-manuals Gerrit-Branch: master Gerrit-MessageType: newpatchset Gerrit-Change-Id: I7afb3f66c98abda07fc8acc76e00c46091fe55e2 Gerrit-Change-Number: 11532 Gerrit-PatchSet: 2 Gerrit-Owner: Neels Hofmeyr Gerrit-Reviewer: Jenkins Builder (102)
Change in osmo-gsm-manuals[master]: bsc: document handover
Neels Hofmeyr has uploaded this change for review. (
https://gerrit.osmocom.org/11532
Change subject: bsc: document handover
..
bsc: document handover
Add chapter "Handover", explaining:
- intra- and
- inter-BSC handover,
- HO algorithm 1 and
- algorithm 2
- new neighbor configuration
Adjust copyright, add revision and add me as author.
Change-Id: I7afb3f66c98abda07fc8acc76e00c46091fe55e2
---
M OsmoBSC/Makefile
A OsmoBSC/chapters/handover.adoc
A OsmoBSC/chapters/handover_inter_bsc.dot
A OsmoBSC/chapters/handover_intra_bsc.dot
M OsmoBSC/osmobsc-usermanual-docinfo.xml
M OsmoBSC/osmobsc-usermanual.adoc
6 files changed, 642 insertions(+), 2 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/osmo-gsm-manuals
refs/changes/32/11532/1
diff --git a/OsmoBSC/Makefile b/OsmoBSC/Makefile
index 1533482..b9f50d0 100644
--- a/OsmoBSC/Makefile
+++ b/OsmoBSC/Makefile
@@ -2,7 +2,7 @@
ASCIIDOC = osmobsc-usermanual.adoc osmux-reference.adoc aoip-mgw-options.adoc
include $(TOPDIR)/build/Makefile.asciidoc.inc
-osmobsc-usermanual.pdf: chapters/*.adoc
+osmobsc-usermanual.pdf: chapters/*.adoc chapters/*.dot
aoip-mgw-options.pdf: aoip-mgw-options.adoc mgw/*.msc
VTY_REFERENCE = osmobsc-vty-reference.xml
diff --git a/OsmoBSC/chapters/handover.adoc b/OsmoBSC/chapters/handover.adoc
new file mode 100644
index 000..3c9204e
--- /dev/null
+++ b/OsmoBSC/chapters/handover.adoc
@@ -0,0 +1,552 @@
+== Handover
+
+Handover is the process of moving a continuously used channel (lchan) from one
+cell to another. Usually, that is an ongoing call, so that phones are able to
+move across cell coverage areas without interrupting the voice transmission.
+
+A handover can
+
+- stay within one given cell (intra-cell, i.e. simply a new RR Assignment
Command);
+- occur between two cells that belong to the same BSS (intra-BSC, via RR
Handover Command);
+- cross BSS boundaries (inter-BSC, via BSSMAP handover procedures);
+- move to another MSC (inter-MSC);
+- move to another RAN type, e.g. from 2G to 3G (inter-RAT,
inter-Radio-Access-Technology).
+
+The physical distance is by definition always very near, but handover
+negotiation may range from being invisible to the MSC all the way to
+orchestrating completely separate RAN stacks.
+
+OsmoBSC currently supports handover within one BSS and between separate BSS.
+Whether inter-MSC is supported depends on the MSC implementation (to the BSC,
+inter-MSC handover looks identical to inter-BSC handover). Inter-RAT handover
+is currently not implemented.
+
+At the time of writing, OsmoMSC's inter-BSC handover support is not complete
+yet, so OsmoBSC can perform handover between separate BSS only in conjunction
+with a 3rd party MSC implementation.
+
+.Handover support in Osmocom at the time of writing
+[cols="^,^,^,^,^"]
+|
+| | intra-BSC HO (local BSS) | inter-BSC HO (remote BSS) | inter-MSC HO |
inter-RAT HO
+| OsmoBSC | rxlev, load-based | rxlev | (planned) | -
+| OsmoMSC | (not involved, except for codec changes) | (planned) | (planned)
| -
+|
+
+
+=== How Handover Works
+
+This chapter generally explains handover operations between 2G cells.
+
+ Internal / Intra-BSC Handover
+
+The BSS is configured to know which cell is physically adjacent to which other
+cells, its "neighbors". On the MS/BTS/BSS level, individual cells are
+identified by ARFCN+BSIC (frequency + 6-bit identification code).
+
+Each BTS is told by the BSC which cells identified by ARFCN+BSIC are its
+adjacent cells. Via System Information, each MS receives a list of these
+ARFCN+BSIC, and the MS then return measurements of reception levels.
+
+The BSC is the point of decision whether to do handover or not. This can be a
+hugely complex combination of heuristics, knowledge of cell load and codec
+capabilites. The most important indicator for handover though is: does an MS
+report a neighbor with a better signal than the current cell? See
+<>.
+
+[[intra_bsc_ho_dot]]
+.Intra-BSC Handover stays within the BSS (shows steps only up to activation of
the new lchan -- this would be followed by an RR Handover Command, RACH causing
Handover Detection, Handover Complete, ...)
+[graphviz]
+
+include::handover_intra_bsc.dot[]
+
+
+If the BSC sees the need for handover, it will:
+
+- activate a new lchan (with a handover reference ID),
+- send an RR Handover Command to the current lchan, and
+- wait for the MS to send a Handover RACH to the new lchan ("Handover Detect").
+- The RTP stream then is switched over to the new lchan,
+- an RSL Establish Indication is expected on the new lchan,
+- and the old lchan is released.
+
+Should handover fail at any point, e.g. the new lchan never receives a RACH, or
+the MS reports a Handover Failure, then the new lchan is simply released again,
+and the old lchan remains in use. If the RTP stream has already been switched
+over to the new lchan, it may actually be switched back to the old lchan.
+
