Osmocom Mobile Switching Centre
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osmo-msc/doc/sequence_charts/inter_msc_ho.msc

82 lines
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msc {
hscale=2;
bsca [label="BSC-A"], ai[label="MSC-I (at MSC-A)"], a[label="MSC-A"], bt[label="MSC-T (at MSC-B)"], bi[label="MSC-I (at MSC-B)"], bscb[label="BSC-B"],
ct[label="MSC-T (at MSC-C)"], bscc[label="BSC-C"];
ai note bt [label="'MSC-A,I,T' are explained in 3GPP TS 49.008 '4.3 Roles of MSC-A, MSC-I and MSC-T'"];
ai note ai [label="I = Internal; the MSC that does BSSMAP to the BSC (may change to a remote MSC-B after HO)"];
a note a [label="A = first; the MSC that has MM control (never changes)"];
bt note bi [label="B = second; the MSC that acts as BSS relay for MSC-A"];
bt note bt [label="T = transitory; the MSC that a handover is going towards (may be MSC-A for inter-BSC HO, may be a remote MSC-B)"];
bsca => ai [label="BSSMAP Handover Required"];
ai -> a [label="BSSMAP Handover Required"];
a rbox a [label="MSC-A routes all MSC-T messages to remote MSC-B."];
a => bt [label="MAP Prepare Handover"];
a note bt [label="in Osmocom, MAP messages are actually sent as GSUP, to the HLR"];
bt rbox bt [label="MSC-B routes all MSC-A type messages back to MSC-A."];
bt rbox bt [label="MSC-B generates a Handover MSISDN"];
bt => bscb [label="BSSMAP Handover Request"];
bt <= bscb [label="BSSMAP Handover Request ACK"];
a <= bt [label="MAP Prepare Handover Response"];
a => bt [label="establish SIP call to Handover MSISDN via external MNCC"];
ai <- a [label="BSSMAP Handover Command"];
bsca <= ai [label="BSSMAP Handover Command"];
--- [label="MS sends RACH to new cell"];
bt <= bscb [label="BSSMAP Handover Detected"];
a <= bt [label="MAP Access Signaling Request"];
bt <= bscb [label="BSSMAP Handover Complete"];
a <= bt [label="MAP Send End Signal"];
bt rbox bt [label="MSC-B drops the generated Handover MSISDN"];
a abox a [label="MSC-A accepts the new MSC-B and BSC"];
ai note bt [label="previous MSC-I (A) gets dropped, MSC-T (B) becomes the new MSC-I"];
ai rbox a [label="MSC-A performs all MSC-I tasks via MAP at remote MSC-B's MSC-I."];
bt abox bi [label="MSC-I"];
ai abox ai [label="discard"];
bsca <= ai [label="BSSMAP Clear Command"];
...;
...;
--- [label="Another inter-MSC handover"];
a note bi [label="MSC-A remains in charge"];
bscb => bi [label="BSSMAP Handover Required"];
bi => a [label="BSSMAP Handover Required"];
a rbox a [label="MSC-A routes all MSC-T messages to remote MSC-C."];
a => ct [label="MAP Prepare Handover"];
ct rbox ct [label="MSC-C routes all MSC-A type messages back to MSC-A."];
ct => bscc [label="BSSMAP Handover Request"];
ct <= bscc [label="BSSMAP Handover Request ACK"];
a <= ct [label="MAP Prepare Handover Response"];
a => bi [label="MAP Prepare Handover Response"];
bscb <= bi [label="BSSMAP Handover Command"];
--- [label="MS sends RACH to new cell"];
ct <= bscc [label="BSSMAP Handover Detected"];
a <= ct [label="MAP Access Signaling Request"];
ct <= bscc [label="BSSMAP Handover Complete"];
a <= ct [label="MAP Send End Signal"];
a abox a [label="MSC-A accepts the new MSC-C and BSC"];
bi note ct [label="previous MSC-I (B) gets dropped, MSC-T (B) becomes the new MSC-I"];
ai rbox a [label="MSC-A performs all MSC-I tasks via MAP at remote MSC-C's MSC-I."];
ct abox ct [label="MSC-I"];
bi abox bi [label="discard"];
bscb <= bi [label="BSSMAP Clear Command"];
}