// How did we get here you ask? Peering received a handover request on BTS2 (us), allocated a channel and set the handoverPending flag,
// created a transaction with the specified IMSI, returned an L3 handover command which BTS1 sent to the MS, which then
// sent a handover access to BTS2, and here we are!
void ProcessHandoverAccess(L3LogicalChannel *chan)
{
using namespace SIP;
// In this function, we are "BS2" in the ladder diagram.
// This is called from the DCCH dispatcher when it gets a HANDOVER_ACCESS primtive.
// The information it needs was saved in the transaction table by SaveHandoverAccess.
LOG(DEBUG) << *chan;
RefCntPointer<TranEntry> tran = chan->chanGetVoiceTran();
if (tran == NULL) {
LOG(WARNING) << "handover access with no inbound transaction on " << chan;
chan->chanRelease(L3_HARDRELEASE_REQUEST,TermCause::Local(L3Cause::Handover_Error));
return;
}
LOG(DEBUG) << *tran;
if (!tran->getHandoverEntry(false)) {
LOG(WARNING) << "handover access with no inbound handover on " << *chan;
chan->chanRelease(L3_HARDRELEASE_REQUEST,TermCause::Local(L3Cause::Handover_Error));
return;
}
// clear handover in transceiver and get the RSSI and TE.
// This instructs L2 to stop looking for and stop sending HANDOVER_ACCESS.
// However, we cant just flush them out of the queue here because that is running in another
// thread and it may keep pushing HANDOVER_ACCESS at, so we keep flushing them (below)
// However, we should NEVER see HANDOVER_ACCESS after the ESTABLISH, yet I did.
GSM::HandoverRecord hr = chan->getL2Channel()->handoverPending(false,0);
// TODO: Move this into L1?
if (hr.mhrTimingError > gConfig.getNum("GSM.MS.TA.Max")) {
// Handover failure.
LOG(NOTICE) << "handover failure on due to TA=" << hr.mhrTimingError << " for " << *tran;
// RR cause 8: Handover impossible, timing advance out of range
abortInboundHandover(tran,L3RRCause::Handover_Impossible,dynamic_cast<L2LogicalChannel*>(tran->channel()));
chan->chanRelease(L3_HARDRELEASE_REQUEST,TermCause::Local(L3Cause::Distance)); // TODO: Is this right? Will the channel be immediately re-available?
return;
}
chan->getL2Channel()->l1InitPhy(hr.mhrRSSI,hr.mhrTimingError,hr.mhrTimestamp);
// Respond to handset with physical information until we get Handover Complete.
int TA = (int)(hr.mhrTimingError + 0.5F);
if (TA<0) TA=0;
if (TA>62) TA=62;
// We want to do this loop carefully so we exit as soon as we get a frame that is not HANDOVER_ACCESS.
Z100Timer T3105(gConfig.GSM.Timer.T3105); // It defaults to only 50ms.
// 4.08 11.1.3 "Ny1: The maximum number of repetitions for the PHYSICAL INFORMATION message during a handover."
for (unsigned sendCount = gConfig.getNum("GSM.Handover.Ny1"); sendCount > 0; sendCount--) {
T3105.set();
// (pat) It is UNIT_DATA because the channel is not established yet.
// (pat) WARNING: This l3sendm call is not blocking because it is sent on FACCH which has a queue.
// Rather than modifying the whole LogicalChannel stack to have a blocking mode,
// we are just going to wait afterwards. The message should take about 20ms to transmit,
// and GSM uses roughly 4 out of every 5 frames, so 20-25ms would transmit the message continuously.
chan->l3sendm(L3PhysicalInformation(L3TimingAdvance(TA)),GSM::L3_UNIT_DATA);
// (pat) Throw away all the HANDOVER_ACCESS that arrive while we were waiting.
// They are not messages that take 4 bursts; they can arrive on every burst, so there
// can be a bunch of them queued up (I would expect 5) for each message we send.
while (L3Frame *frame = chan->l2recv(T3105.remaining())) {
switch (frame->primitive()) {
case HANDOVER_ACCESS:
// See comments above. L2 is no longer generating these, but we need
// to flush any extras from before we started, and there also might be have been
// some in progress when we turned them off, so just keep flushing.
LOG(INFO) << "flushing HANDOVER_ACCESS while waiting for Handover Complete";
delete frame;
continue;
case L3_ESTABLISH_INDICATION:
delete frame;
// Channel is established, so the MS is there. Finish up with a state machine.
startInboundHandoverMachine(tran.self());
return;
default:
// Something else?
LOG(NOTICE) << "unexpected primitive waiting for Handover Complete on "
<< *chan << ": " << *frame << " for " << *tran;
delete frame;
abortInboundHandover(tran,L3RRCause::Message_Type_Not_Compapatible_With_Protocol_State,chan);
chan->chanRelease(L3_HARDRELEASE_REQUEST,TermCause::Local(L3Cause::Handover_Error)); // TODO: Is this right? Will the channel be immediately re-available?
return;
}
}
}
// Failure.
LOG(NOTICE) << "timed out waiting for Handover Complete on " << *chan << " for " << *tran;
// RR cause 4: Abnormal release, no activity on the radio path
abortInboundHandover(tran,L3RRCause::No_Activity_On_The_Radio,chan);
chan->chanRelease(L3_HARDRELEASE_REQUEST,TermCause::Local(L3Cause::Radio_Interface_Failure)); // TODO: Is this right? Will the channel be immediately re-available?
return;
}
static void abortInboundHandover(RefCntPointer<TranEntry> transaction, RRCause cause, L3LogicalChannel *LCH=NULL)
{
LOG(DEBUG) << "aborting inbound handover " << *transaction;
unsigned holdoff = gConfig.getNum("GSM.Handover.FailureHoldoff");
gPeerInterface.sendHandoverFailure(transaction->getHandoverEntry(true),cause,holdoff);
}