mirror of
https://github.com/RangeNetworks/openbts.git
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116 lines
4.8 KiB
C++
116 lines
4.8 KiB
C++
/*
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* Copyright 2011, 2014 Range Networks, Inc.
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*
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* This software is distributed under multiple licenses;
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* see the COPYING file in the main directory for licensing
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* information for this specific distribution.
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*
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* This use of this software may be subject to additional restrictions.
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* See the LEGAL file in the main directory for details.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*/
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#ifndef BSSG_H
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#define BSSG_H
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#include "Interthread.h"
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#include "Defines.h"
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#include "ByteVector.h"
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#include "ScalarTypes.h"
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#include "BSSGMessages.h"
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// BSSG.cpp handles link layer communication to the SGSN.
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namespace BSSG {
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// GSM 08.16 describes the NS layer.
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// GSM 08.18 sec 10 describes the PDU messages that the SGSN can send to the BSS.
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// GSM 48.018 is the updated spec with PS-HANDOVER related commands.
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// Definitions:
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// NSE - Network Service Entity. There is one or more NSE inside the BSS for signaling.
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// NSEI == Network Service Entity Indicator
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// BVC = BSSGP Virtual Connection, transport peer-to-peer through the BTS.
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// LSP = Link Selector Parameter, points to one MS, eg, the MS's TLLI.
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// NSVCI = Network Service Virtual Connection Identifier.
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// NSEI = Network Service Entity Identifier
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// BVCI - BSSGP Virtual Connection ID. BVCI 0 = signaling, BVCI 1 = PTM (point-to-multipoint),
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// all other values are point-to-point.
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// GSM08.18sec5.4.1: "This parameter is not part of the BSSGP PDU across
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// the Gb interface, but is used by the network service entity across the Gb."
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// It corresponds to a cell, and can be used instead of routing area id
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// at operators discretion.
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// LSP - Link Selector Parameter, something used only inside the BSS or SGSN,
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// and not transmitted, to uniquely identify NS-VC. We wont use it.
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// Just so you dont have to read all the manuals, here is how it works:
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// The NS and BSSG layers are for BTS to SGSN communication.
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// The NS protocol is the inner-most layer. This stuff was designed for frame relay,
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// so there is an NSVCI which, despite the name, identifies a specific physical connection,
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// and the NSEI, which identifies a group of NSVCIs that connect the BTS to the SGSN.
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// The idea is you can take down individual NSVCs without taking down the complete communication link.
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// You can also block/unblock individual NS connections.
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// The next layer up is the BSSG layer. Endpoints are identfied by BVCI.
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// The first two BVCIs are reserved: BVCI 0 for signaling messages handled directly by the BSSG controller,
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// BVCI 1 for point-to-multipoint messages, and all other BVCIs are for BTSs that share this BSSG+NS link.
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// So in a normal system, multiple BTS could communicate over a single NSEI consisting of
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// a group of NSVCI. Each BTS would have a BVCI assigned,
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// and the network connections have NSVCIs and NSEIs assigned.
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// All this is entirely irrelevant to us, because our BTS talks to the SGSN using UDP/IP,
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// and the SGSN actually identifies the connection by remembering the endpoint UDP/IP address
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// of the BTS when it first calls in, which puts a hard limit of something like 2**48 BTS per SGSN,
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// which should be enough. (That was a joke.)
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// However, we still use the NS and BSSG messages that reset and block/unblock the lines,
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// so we have to assign dummy numbers for the NSVCI, NSEI, and BVCI.
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// The messages supported at the BSSG level include signaling messages (to BVCI 0)
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// that support, eg, blocking/unblocking of an individual BTS, UL_UNITDATA and DL_UNITDATA
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// to transfer PDUs (Packet Data Units), which consist of L3 Messages or user data
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// wrapped in LLC layer wrappers that flow through the BTS as RLCData blocks to L3 in the MS,
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// and a few special messages that go to the BTS, like paging and MS capabilities.
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// See BSSGMessages.h
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const unsigned SGSNTimeout = 1000; // In msecs
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// The main interface to the SGSN.
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class BSSGMain {
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public:
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// Only BSSG downlink messages are put on the receive queue; other types are handled immediately.
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// The transmit queue may have any type of BSSG/NS message.
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InterthreadQueue<BSSGDownlinkMsg> mbsRxQ;
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InterthreadQueue<NSMsg> mbsTxQ;
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InterthreadQueue<NSMsg> *mbsTestQ; // Only used for testing
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Thread mbsRecvThread;
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Thread mbsSendThread;
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int mbsSGSockfd;
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Bool_z mbsIsOpen;
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Bool_z mbsResetReceived;
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Bool_z mbsResetAckReceived;
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Bool_z mbsAliveReceived;
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Bool_z mbsAliveAckReceived;
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Bool_z mbsBlocked; // We dont implement blocking, but we track the state.
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// These are identifiers for the BSC and NS link, which we dont use.
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UInt_z mbsBVCI; // Our BTS identifire. Must not be 0 or 1.
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UInt_z mbsNSVCI;
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UInt_z mbsNSEI;
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BSSGMain() { mbsSGSockfd = -1; }
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bool BSSGOpen();
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bool BSSGReset();
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BSSGDownlinkMsg *BSSGReadLowSide();
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};
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void BSSGWriteLowSide(NSMsg *ulmsg);
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extern BSSGMain gBSSG;
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};
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#endif
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