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"];

}
