2.1.1 CAMEL
Phase 3 Intelligent Service
To introduce the intelligent network into the mobile communication
system, the European Telecommunications Standards Institute (ETSI) defined
CAMEL in Gsm Phase 2+ in 1997 to provide subscribers with service consistency
unrelated to the specific service network. The CAMEL feature is not a
supplementary service but a network feature. Even the subscriber is not in the
HPLMN (Home public land mobile network), the CAMEL feature can be a means of
helping network operators provide the subscriber with the specific service.
The network structure of CAMEL Phase3 is shown in Figure 2-3. Several function
entities are added into the GSM network: GsmSSF (Service Switching Function),
GsmSRF (Specialized Resource Function) and GsmSCF (Service Control Function).
CAP Phase3 protocol interface is employed between GsmSCF and GsmSSF, and
between GsmSCF and GsmSRF. While an internal protocol interface is used between
MSC and GsmSRF, the others use MAP Phase3 interfaces.
The equipment designed specially for GsmSCF implementation
is called the SCP, for GsmSSF implementation the SSP, and for GsmSRF
implementation the IP.
CAMEL mainly embodies
the separation of switching and services. The fundamental idea is as follows:
The switch only implements the basic call connection function, but the control
of all intelligent services is implemented by another network layer, i.e., the
intelligent network. Of them, the Service Switching Function (SSF) implements
the switching function, reports various events during the call to the Service
Control Function (SCF) and possibly suspends the call, waiting for further
instruction of SCF. The triggering points of these events are called the
Detection Points (DPs). SCF implements the service logic control function. The
essential of the CAMEL mechanism is a control mechanism between SCF and SSF.
2.1.2 LCS
Figure 2-4 shows the network
structure of LCS implementation. Here, when MSC/SGSN supports LCS, new
interfaces to various network entities are added: The Lg interface between
MSC/SGSN and GMLC, the Lh interface between GMLC and HLR, and the Lc interface
between GMLC and gsmSCF.
The functions of the LCS system are described as follows:
l
LCS Client
LCS Client is the source of sending location requests, and uses
the location result to implement related services based on location. There are
four kinds of clients according to the LCS Client functions.
1)
Value-added LCS Clients - Using
LCS to support various value-added services, they may include UEs or no
specific UEs.
2)
PLMN operator LCS Clients - Using
LCS to enhance or support some tasks related to O&M, such as supplementary
service, IN related service, bearer service and telecommunication service.
3)
Emergency services LCS Clients
- Using LCS enhance the support of emergency calls from the subscribers.
4)
Lawful Interception LCS Clients
- Using LCS to implement various legal requests and acceptance services.
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GMLC (Gateway
Mobile Location
Center
GMLC is a gateway device in the network connecting to the external
LCS Client. After getting related location request messages through the Le
interface, it is responsible for HLR addressing, and delivering the location
requests to the SGSN through the Lg interface. GMLC is also responsible for
delivering related location results to related LCS Clients, or convents the
results into local coordinate information upon request.
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MSC/SGSN/VLR
MSC/SGSN/VLR mainly implements the coding/decoding of related
location information, version negotiation and processing of related signaling
protocol information. In addition, it provides interface functions of related
signaling tracing, maintenance and management. MSC/SGSN/VLR needs to implement
the main processing and control of location procedure, and user privacy
protection, and provides charging information according to the processing.
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HLR
HLR stores the subscription data related to LCS, and provides the
MSC number of the located subscriber.
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Target UE
The Target UE (also referred as MS) is a target mobile phone
located. The network needs to locate the current or last location of the mobile
subscriber according to the location request. Generally, the target MS is the
object to be located. But for MO-LR (Mobile Originated-Location Request), the
target MS is the MS that initiates the location request.
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RNC
In 3G networks, RNC implements the specific locating testing and
calculation in LCS implementation.
The external client requests the location information of a target
UE/MS from GMLC (or non real-time location information request).
1)
GMLC checks the ID of the
client and the requested service, and then gets UE/MS identification from the
request information.
2)
GMLC delivers a message to
HLR/HSS to query the address of SGSN or MSC/MSC Server. Upon receipt of the
needed address, GMLC will deliver a location request to SGSN.
3) If GMLC belongs to another PLMN, SGSN needs to check whether the LCS
request is allowed. Then SGSN will check whether the request can be initiated
according to the subscription information of the target UE/MS. If any item
fails, SGSN will directly return a failure response. If the check is passed,
the SGSN then delivers a location request to RAN.
4)
If RAN stores location
information that meets the requirements of SGSN, it returns a location report
to SGSN. Otherwise, RAN needs to initiate a special location processing message
with the used location method. RAN returns a location information report that
SGSN has estimated.
5)
SGSN returns the estimated
location information and acquisition time to GMLC.
6)
GMLC returns the location
information to the LCS Client. GMLC records the LCS Client CDR and the CDR of
SGSN inter-network cooperation.
2.1.3 MMS
Service
MMS can run in different types of networks. The terminals can be
used in 2G and 3G networks. The MMS Environment (MMSE)
includes all necessary service units, such as transfer, storage and
notification functions. These service units can be in one network, or in
different networks. Figure 2-6 illustrates the
structure of the MMS system.
NMS User Agent: As the MMS functional part of
the user terminal equipment, it must be able to support the MMS capability.
MMS Server: As the core part, it receives, notifies, dispatches,
sends and forwards the multimedia messages. Equivalent to a control center, it
dispatches different services. In one MMSE there may be multiple MMS Servers,
e.g. MMS Server, E-Mail Server, SMS Server and FAX Server.
MMS Relay: Acting as a bridge between the MMS User Agent and the
MMS Server, it eliminates the difference between different servers and between
different networks.
MMS User DB: Composed of the MMS Subscription Database, the MMS
Profile Database and the HLR, it enables users to flexibly customize services
as they wish.
In terms of physical entities, the MMS Server, the MMS Relay and
the MMS User DB can be integrated to form a Multimedia Messaging Service Center
(MMSC). In this way, the MMSC exists as an independent entity and can be
directly superimposed on the existing GPRS network.
In practice, different manufacturers may adopt different
networking modes based on their own comprehension of the protocols. Next we
will introduce a WAP-based networking mode in the GPRS network. In this mode,
the WAP gateway is added between the MMSC and the wireless network to implement
the interconnection between these two. Figure 2-7 lists the
implementation flow of the multimedia messaging service.
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