| 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"]; |
| |
| } |