GSUP: document inter-MSC handover additions
Message formats of the new messages look mostly the same (IMSI, Message Class, Source Name, Destination Name, AN-APDU). That is, because AN-APDU is storing results, error reasons etc. This can be seen clearly in osmo-msc.git: * src/libmsc/msc_a_remote.c:msc_a_remote_fsm_communicating() * src/libmsc/msc_i_remote.c:msc_i_remote_fsm_ready() The message squence charts in the E Procedures section are directly based on Neels' interMSC_HO_GSUP_msgs.txt [1]. It seems that using AN-APDU made some other new IEs redundant: RR Cause, BSSAP Cause, Session Management Cause had been added to GSUP for the MSC handover, and are documented now, but they are currently not used in osmo-msc.git. The new message OSMO_GSUP_MSGT_E_ABORT is not used either, so I left a stub for it in the message format section. I mentioned in the Source Name IE section, that source and destination names are sent as nul-terminated strings. This is for legacy reasons, Neels wrote a nice summary in the commit message of [2]. [1] https://osmocom.org/attachments/3720/interMSC_HO_GSUP_msgs.txt [2] Change-Id: I9ca8c9eef104519ed1ea46e2fef46dcdc0d554eb (osmo-msc) Related: OS#3774, OS#3619 Change-Id: I6b9f23d08cfe53c8b77f51c6afb900c2badc9e2c
This commit is contained in:
parent
5c1ac995db
commit
4c101e8136
|
|
@ -219,6 +219,112 @@ msc {
|
|||
}
|
||||
----
|
||||
|
||||
=== Procedures (E Interface)
|
||||
|
||||
The E interface connects two MSCs in the traditional GSM MAP world. It is used
|
||||
for the inter-MSC handover. In GSUP, we don't need that extra connection, as we
|
||||
route the messages over the GSUP server (OsmoHLR) instead.
|
||||
|
||||
Whenever MSC-A is sending to MSC-B, and vice-versa, the message needs to pass
|
||||
through the GSUP server. In order to make the following message sequence charts
|
||||
easier to read, this step has been omitted.
|
||||
|
||||
==== E Handover
|
||||
|
||||
MSC-A has an active RAN connection and hands it over to MSC-B.
|
||||
|
||||
.E Handover (Normal Case)
|
||||
["mscgen"]
|
||||
----
|
||||
msc {
|
||||
hscale="1.5";
|
||||
A [label="MSC-A"], B [label="MSC-B"];
|
||||
|
||||
A => B [label="E Prepare Handover Request\n\n(AN-APDU: Handover Request)"];
|
||||
|||;
|
||||
A <= B [label="E Prepare Handover Result\n\n(AN-APDU: Handover Request Ack)"];
|
||||
|||;
|
||||
A <= B [label="E Process Access Signalling Request\n\n(AN-APDU: Handover Detect)"];
|
||||
|||;
|
||||
A <= B [label="E Send End Signal Request\n\n(AN-APDU: Handover Complete)"];
|
||||
}
|
||||
----
|
||||
|
||||
==== E Subsequent Handover
|
||||
|
||||
MSC-B has an active RAN connection, and asks MSC-A to hand it over to MSC-B'.
|
||||
|
||||
.E Subsequent Handover (Normal Case)
|
||||
["mscgen"]
|
||||
----
|
||||
msc {
|
||||
hscale="1.5";
|
||||
A [label="MSC-A"], B [label="MSC-B"], B_ [label="MSC-B'"];
|
||||
|
||||
B => A [label="E Prepare Subsequent Handover Request\n\n(AN-APDU: Handover Required)"];
|
||||
|||;
|
||||
A => B_ [label="E Prepare Handover Request\n\n(AN-APDU: Handover Request)"];
|
||||
|||;
|
||||
B_ => A [label="E Prepare Handover Response\n\n(AN-APDU: Handover Request Ack)"];
|
||||
|||;
|
||||
A => B [label="E Prepare Subsequent Handover Response\n\n(AN-APDU: Handover Request Ack)"];
|
||||
|||;
|
||||
B_ => A [label="E Process Access Signalling Request\n\n(AN-APDU: Handover Detect)"];
|
||||
|||;
|
||||
B_ => A [label="E Process Access Signalling Request\n\n(AN-APDU: Handover Complete)"];
|
||||
|||;
|
||||
A => B [label="E Close"];
|
||||
}
|
||||
----
|
||||
|
||||
==== E Forward and Process Access Signalling
|
||||
|
||||
MSC-A is forwarding a message from its BSS (Base Station Subsystem) to MSC-B.
|
||||
MSC-B forwards the message to its BSS, and answers to MSC-A with a Process
|
||||
Access Signalling Request.
|
||||
|
||||
.E Process and Forward Access Signalling (Normal Case)
|
||||
["mscgen"]
|
||||
----
|
||||
msc {
|
||||
hscale="1.5";
|
||||
A [label="MSC-A"], B [label="MSC-B"];
|
||||
|
||||
A => B [label="E Forward Access Signalling Request\n\n(AN-APDU: DTAP, e.g. CC, SMS, ...)"];
|
||||
|||;
|
||||
B => A [label="E Process Access Signalling Request\n\n(AN-APDU: DTAP, e.g. CC, SMS, ...)"];
|
||||
}
|
||||
----
|
||||
|
||||
==== E Routing Error
|
||||
|
||||
The GSUP server can not route any of the requests above, and responds with an
|
||||
E Routing Error. Possible reasons for not being able to route the message are
|
||||
missing routing IEs, a mismatching source name IE (<<gsup-ie-source-name>>),
|
||||
the destination not being connected to the GSUP server or a failed attempt to
|
||||
send the message from the GSUP sever to the destination. To figure out, what
|
||||
went wrong in detail, refer to the GSUP server's logs.
|
||||
|
||||
In the traditional GSM MAP world, the participants of an E procedure are
|
||||
directly connected, hence this routing error message does not exist in MAP.
|
||||
|
||||
.E Routing Error example
|
||||
["mscgen"]
|
||||
----
|
||||
msc {
|
||||
hscale="1.5";
|
||||
A [label="MSC-A"], HLR [label="GSUP Server (OsmoHLR)"], B [label="MSC-B"];
|
||||
|
||||
A => HLR [label="E Prepare Handover Request"];
|
||||
HLR => A [label="E Routing Error"];
|
||||
}
|
||||
----
|
||||
|
||||
////
|
||||
End of "Procedures (E Interface)" chapter. Remember to place unrelated
|
||||
procedures at the end of the "Procedures" chapter, not here!
|
||||
////
|
||||
|
||||
=== Message Format
|
||||
|
||||
==== General
|
||||
|
|
@ -722,6 +828,207 @@ Direction: EIR (via HLR) => VLR
|
|||
|51|IMEI Check Result|<<gsup-ie-imei-result>>|M|TLV|3
|
||||
|===
|
||||
|
||||
==== E Prepare Handover Request
|
||||
|
||||
Direction: MSC-A=MSC-I => MSC-B=MSC-T (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Prepare Handover Error
|
||||
|
||||
Direction: MSC-B=MSC-T => MSC-A=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Prepare Handover Result
|
||||
|
||||
Direction: MSC-B=MSC-T => MSC-A=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Prepare Subsequent Handover Request
|
||||
|
||||
Direction: MSC-B=MSC-I => MSC-A (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Prepare Subsequent Handover Error
|
||||
|
||||
Direction: MSC-A => MSC-B=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Prepare Subsequent Handover Result
|
||||
|
||||
Direction: MSC-A => MSC-B=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Send End Signal Request
|
||||
|
||||
Direction: MSC-B=MSC-T => MSC-A=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Send End Signal Error
|
||||
|
||||
Direction: MSC-A=MSC-I => MSC-B=MSC-T (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Send End Signal Result
|
||||
|
||||
Direction: MSC-A => MSC-B=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Process Access Signalling Request
|
||||
|
||||
Direction: MSC-B=MSC-T => MSC-A=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Forward Access Signalling Request
|
||||
|
||||
Direction: MSC-A => MSC-B=MSC-I (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|62|AN-APDU|<<gsup-ie-an-apdu>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Close
|
||||
|
||||
Direction: MSC-A => MSC-B (via HLR)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|===
|
||||
|
||||
==== E Abort
|
||||
|
||||
This message was added to GSUP for the inter-MSC handover. But so far it is not
|
||||
used yet.
|
||||
|
||||
==== E Routing Error
|
||||
|
||||
Direction: GSUP Server (HLR) => GSUP Client (MSC)
|
||||
|
||||
[options="header",cols="5%,45%,20%,10%,10%,10%"]
|
||||
|===
|
||||
|IEI|IE|Type|Presence|Format|Length
|
||||
| |Message Type|<<gsup-ie-msgtype>>|M|V|1
|
||||
|01|IMSI|<<gsup-ie-imsi>>|M|TLV|2-10
|
||||
|0a|Message Class|<<gsup-ie-message-class>>|M|TLV|3
|
||||
|60|Source Name|<<gsup-ie-source-name>>|M|TLV|2-...
|
||||
|61|Destination Name|<<gsup-ie-destination-name>>|M|TLV|2-...
|
||||
|30|Session ID|<<gsup-ie-session-id>>|M|TLV|6
|
||||
|31|Session State|<<gsup-ie-session-state>>|M|TLV|3
|
||||
|===
|
||||
|
||||
|
||||
=== Information Elements
|
||||
|
||||
[[gsup-ie-msgtype]]
|
||||
|
|
@ -986,6 +1293,7 @@ IEI that shall be used for the encoding.
|
|||
|0x07|Freeze P-TMSI|<<gsup-ie-empty>>
|
||||
|0x08|MSISDN|ISDN-AddressString/octet, <<gsup-ie-msisdn>>
|
||||
|0x09|HLR Number|<<gsup-ie-hlr>>
|
||||
|0x0a|Message Class| <<gsup-ie-message-class>>
|
||||
|0x10|PDP Context ID|<<gsup-ie-pdpctxid>>
|
||||
|0x11|PDP Type|<<gsup-ie-pdptype>>
|
||||
|0x12|Access Point Name|<<gsup-ie-apn>>
|
||||
|
|
@ -1012,6 +1320,12 @@ IEI that shall be used for the encoding.
|
|||
|0x46|SM Alert Reason|<<gsup-ie-sm-alert-rsn>>
|
||||
|0x50|IMEI|<<gsup-ie-imei>>
|
||||
|0x51|IMEI Check Result|<<gsup-ie-imei-result>>
|
||||
|0x60|Source Name|<<gsup-ie-source-name>>
|
||||
|0x61|Destination Name|<<gsup-ie-destination-name>>
|
||||
|0x62|AN-APDU|<<gsup-ie-an-apdu>>
|
||||
|0x63|RR Cause|<<gsup-ie-cause-rr>>
|
||||
|0x64|BSSAP Cause|<<gsup-ie-cause-bssap>>
|
||||
|0x65|Session Management Cause|<<gsup-ie-cause-sm>>
|
||||
|===
|
||||
|
||||
[[gsup-ie-empty]]
|
||||
|
|
@ -1192,6 +1506,102 @@ not permitted on the network (e.g. because it is on a blacklist).
|
|||
|0x02|NACK
|
||||
|===
|
||||
|
||||
[[gsup-ie-message-class]]
|
||||
==== Message Class
|
||||
|
||||
Indicate, which kind of message is being sent. This allows to trivially dispatch
|
||||
incoming GSUP messages to the right code paths, and should make writing a GSUP
|
||||
to MAP converter easier.
|
||||
|
||||
This IE was introduced together with inter-MSC handover code. Inter-MSC messages
|
||||
must include this IE and set it to the appropriate type. The intention of
|
||||
creating this IE was to use it with all GSUP messages eventually.
|
||||
|
||||
[options="header",cols="10%,20%,70%"]
|
||||
|===
|
||||
|Type|Always present|Description
|
||||
|1|no |Subscriber Management
|
||||
|2|no |SMS
|
||||
|3|no |USSD
|
||||
|4|yes|Inter-MSC
|
||||
|===
|
||||
|
||||
[[gsup-ie-source-name]]
|
||||
==== Source Name
|
||||
|
||||
When the GSUP server is asked to forward a message between two GSUP clients, the
|
||||
source name is the IPA name of the client where the message is coming from. The
|
||||
source name IE is present, when the GSUP server forwards the message to the
|
||||
destination. Although redundant, the source name IE is also sent from the source
|
||||
to the GSUP server (so it is easier to follow the network traces).
|
||||
|
||||
Source and destination names are sent as nul-terminated strings.
|
||||
|
||||
.Message forwarding example
|
||||
["mscgen"]
|
||||
----
|
||||
msc {
|
||||
hscale="1.5";
|
||||
A [label="GSUP Client A"],
|
||||
HLR [label="GSUP Server (OsmoHLR)"],
|
||||
B [label="GSUP Client B"];
|
||||
|
||||
A => HLR [label="Source: A, Destination: B"];
|
||||
HLR => B [label="Source: A, Destination: B"];
|
||||
}
|
||||
----
|
||||
|
||||
|
||||
[[gsup-ie-destination-name]]
|
||||
==== Destination Name
|
||||
|
||||
The receiving counterpart to source name (<<gsup-ie-source-name>>).
|
||||
|
||||
[[gsup-ie-an-apdu]]
|
||||
==== AN-APDU
|
||||
|
||||
This IE encodes the AN-APDU parameter described in 3GPP TS 29.002 7.6.9.1.
|
||||
|
||||
.Access Network Protocol
|
||||
[options="header",cols="10%,90%"]
|
||||
|===
|
||||
|Type|Description
|
||||
|0x01|BSSAP
|
||||
|0x02|RANAP
|
||||
|===
|
||||
|
||||
[packetdiag]
|
||||
----
|
||||
{
|
||||
colwidth = 8
|
||||
node_height = 24
|
||||
|
||||
0-6: AN-APDU IEI
|
||||
7: Res
|
||||
8-15: Length of IE content
|
||||
16-23: Access Network Protocol
|
||||
24-31: Data
|
||||
}
|
||||
----
|
||||
|
||||
[[gsup-ie-cause-rr]]
|
||||
==== RR Cause
|
||||
|
||||
This IE contains the reason for release or completion of an assignment or
|
||||
handover. See 3GPP TS 44.018 10.5.2.31 for reference.
|
||||
|
||||
[[gsup-ie-cause-bssap]]
|
||||
==== BSSAP Cause
|
||||
|
||||
This IE indicates why an event is happening on the BSSAP interface. See 3GPP TS
|
||||
48.008 3.2.2.5 for reference.
|
||||
|
||||
[[gsup-ie-cause-sm]]
|
||||
==== Session Management Cause
|
||||
|
||||
This IE contains the reason for rejecting a session management request. See 3GPP
|
||||
TS 24.008 10.5.6.6 / Table 10.5.157 for reference.
|
||||
|
||||
=== Session (transaction) management
|
||||
|
||||
Unlike TCAP/MAP, GSUP is just a transport layer without the
|
||||
|
|
|
|||
Loading…
Reference in New Issue