Project

General

Profile

interMSC_HO_GSUP_msgs.txt

osmith, 05/20/2019 08:18 AM

 
1
GSUP messages on the E-interface (MSC<->MSC)
2
============================================
3

    
4
Draft blueprint of requried IEs.
5

    
6
Interesting specs
7
-----------------
8

    
9
- 3GPP TS 29.010
10
- 3GPP TS 29.002
11

    
12

    
13
Message sequences
14
-----------------
15

    
16
  MSC-A=MSC-I        MSC-B=MSC-T                         (MSC-T: transitional MSC, with a potential RAN connection)
17
    ------------------>  request prepareHandover         (an_apdu == Handover Request)
18
    <------------------  response prepareHandover        (an_apdu == Handover Request Ack)
19
    <------------------  request processAccessSignalling (an_apdu == Handover Detect)
20
    <------------------  request sendEndSignal           (an_apdu == Handover Complete)
21
                     MSC-B=MSC-I                         (MSC-I: internal MSC, the one with the active RAN connection)
22

    
23

    
24
  MSC-A              MSC-B=MSC-I             MSC-B'=MSC-T
25
    <------------------                          request prepareSubsequentHandover  (an_apdu == Handover Required)
26
    ------------------------------------------>  request prepareHandover            (an_apdu == Handover Request)
27
    <------------------------------------------  response prepareHandover           (an_apdu == Handover Request Ack)
28
    ------------------>                          response prepareSubsequentHandover (an_apdu == Handover Request Ack)
29
    <------------------------------------------  request processAccessSignalling    (an_apdu == Handover Detect)
30
    <------------------------------------------  request processAccessSignalling    (an_apdu == Handover Complete)
31
    ------------------>                          request close
32
                     MSC-B clears            MSC-B'=MSC-I
33

    
34

    
35
  MSC-A              MSC-B=MSC-I
36
    ------------------>  request forwardAccessSignalling (an_apdu == DTAP, e.g. CC, SMS, ...)
37
    <------------------  request processAccessSignalling (an_apdu == DTAP, e.g. CC, SMS, ...)
38

    
39

    
40
    ------------------> source_name=MSC-A;  destination_name=MSC-B
41
    <------------------ source_name=MSC-B;  destination_name=MSC-A
42

    
43

    
44
GSUP Message Contents
45
---------------------
46

    
47
Prefix these messages to mark them as part of the E-interface; e.g.
48
OSMO_GSUP_MSGT_E_PREPARE_HANDOVER.
49

    
50
message_type:
51
 	[prepareHandover|prepareSubsequentHandover|sendEndSignal]x{Request,Error,Result}
52
	[processAccessSignalling|forwardAccessSignalling|close|abort] (x{Request})
53
imsi: BCD (handle to associate with subscriber connection)
54
source_name: blob (string: osmo-msc: sender's gsmnet->msc_ipa_name, to route messages)
55
destination_name: blob (string: osmo-msc: IPA_NAME as in https://gerrit.osmocom.org/c/osmo-msc/+/12446, or received from previous source_name IE)
56
session_state: osmo_gsup_session_state
57
session_id: uint32_t
58
handover_number:                    (MSC-A <-- MSC-B, Handover Request Ack)
59
        extension: [Extension=0|NoExtension=1] (1 bit; should currently always be == 1)
60
        nature_of_nr: [GSM340_TYPE_NATIONAL|GSM340_TYPE_INTERNATIONAL|...] (3 bit)
61
        number_plan: GSM340_PLAN_ISDN (4 bit)
62
        msisdn: BCD
63
an_apdu:
64
        access_network_proto: [ts3G-48006=1|ts3G-25413=2] (i.e. BSSAP or RANAP; 1 byte value; 3GPP 29.002 AccessNetworkProtocolId)
65
        data: blob up to 2560 bytes (complete BSSAP or RANAP message; 3GPP 29.002 LongSignalInfo)
66
cause_rr: enum gsm48_rr_cause (3GPP TS 44.018 10.5.2.31) (for 'abort' message type or 'Error' responses)
67
cause_bssap: enum gsm0808_cause (3GPP TS 48.008 3.2.2.5) (for 'abort' message type or 'Error' responses)
68
cause_sm: enum gsm48_gsm_cause (3GPP TS 24.008 10.5.6.6 / Table 10.5.157) (for 'abort' message type or 'Error' responses)
69

    
70

    
71
Of which are newly added message IEs:
72
- source_name
73
- target_name
74
- handover_number
75
- an_apdu
76
- cause_*
77

    
78

    
79
GSUP Message Contents, maybe added at a later stage
80
---------------------------------------------------
81

    
82
So far this information is only in-band in the BSSAP/RANAP messages.
83
There is currently no need to copy them to the GSUP message structures.
84

    
85
target_cell_id: osmo_cell_global_id (MSC-A --> MSC-B, Handover Request)
86
encryption_info: gsm0808_encrypt_info
87
integrity_protection_info: gsm0808_encrypt_info
88
aoip_supported_codecs: gsm0808_speech_codec_list
89
...
Add picture from clipboard (Maximum size: 48.8 MB)