WCDMA Network Solution

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    Chapter 10 Huawei WCDMA Network Solution

             This chapter begins with the evolution of different versions of the WCDMA system to
             enable readers to have an overall understanding of the WCDMA system, followed by
             an introduction to Huawei’s WCDMA total network solution from the perspective of
             specific network construction.


10.1 Overview of WCDMA Evolution

10.1.1 Overview of Standard Evolution

             The WCDMA technology has gone through R99/R4/R5/R6 stages since it comes into
             being. The R99 protocol was functionally frozen in March 2000(December 1999 in
             3GPP official document) and almost became mature after two years of improvement.
             The R4 protocol was functionally frozen in March 2001. The R5 protocol was
             functionally frozen in March 2002 (with some functions frozen in June), and the R6
             protocol is estimated to finalize its functions in December 2004.


                                                                                                 3 GPP R6
                                                                                                 The protocol is
                                                                                             further improved with
                                                                                                  WLAN in it.
                                                                       3 GPP R5
                                                                   IMS domain is added to
                                                                    support the end-to-end
                                                                             VoIP.
                                               3 GPP R4
                                          The bearer and control
                                           of the CS domain are
                                            separated; support
                    3 GPP R99                   TDM/ATM/IP
                                                 networking
                    The core network
                   inherits the network
                  system of GSM/GPRS
                    and uses the TDM
                    networking mode.
                                                                                                      Function-finalized
                                                                                                         time point

                         2000/03                  2001/03                  2002/03            Under planning


                                                Development trend of 3G protocols


             Compared with GSM and GPRS networks, the most significant change of the WCDMA
             system is the change of the radio network. In the WCDMA network, the Radio Access
             Network (RAN) is used to replace the Base Station Subsystem (BSS).



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             The WCDMA core network in the R99 version can be regarded as a combination of
             GSM and GPRS core networks in terms of networking, namely, the R99 core network is
             classified into the Circuit Switched (CS) domain and the Packet Switched (PS) domain.
             The architectures of the CS domain and the GSM core network are basically the same,
             so are the architectures of the PS domain and the GPRS core network.

             In contrast to the R99 version, the biggest change of the R4 core network is that the
             network element function of MSC in the CS domain of the R99 core network is fulfilled
             by the MSC Server and MGW in the R4 version, where the MSC Server processes the
             signaling while the MGW processes the voice. There is no change in PS domain. For
             details, refer to the architecture description in Chapter 3.

             The core network using the R4 protocol has two networking modes: TDM and IP. When
             the TDM mode is adopted, the R4 network planning and construction are identical with
             that of R99 to a large degree. For example, in constructing tandem and signaling
             networks, many considerations are just the same. When the IP mode is adopted, the
             R4 network planning and construction are largely different from that of R99.

             In contrast to the R4 version, an IMS (IP Multimedia Subsystem) domain is added in the
             R5 core network, together with the corresponding equipment and interfaces, but there
             is nearly no change in the network structure of CS and PS domains. Meanwhile, some
             equipment functions are upgraded due to the enhancement of the network functions.

                                   Alternative                                                           Legacy mobile
                                                                 Applications &                            signaling
                                     Access                       Services *)                              Network
                                    Network
                                                                   SCP
                                                                                                                                                   Multimedia
                                                                                                                                 CSCF
                                                                                                              R-SGW                               IP Networks
                                                                                         Mh                            Mw
                                                 SGSN                                                     Ms
                       GGSN                                        CAP
                                                                                                                                   Mm
                                                  Gn                        HSS *)             Cx
                     Other PLMN                                                                           CSCF
                                                                              Gr                                            Mg
                                                    Gp                                              Gi            Mr                    Gi
                                                                             EIR
                                                                                                                MRF
                                                  ERAN
                                                                                   Gf
                          TE          MT                                                      Gc                  Gi             MGCF          T-SGW *)
                               R            Um         Iu-ps'
                                                                              SGSN                            GGSN                      Mc
                                                            Iu                                                           Gi
                                                                                               Gn
                                                                        1
                                                                  Iu                                                                                 PSTN/
                        TE           MT          UTRAN                                                                           MGW
                                                                               MGW                                                               Legacy/External
                               R            Uu                                                       Nb
                                                                 Iu 2                   Mc                                          Mc
                           1
                         Iu = Iucs (RTP, AAL2)
                                                                                                         Nc
                           2                                                MSC server                                GMSC server             T-SGW *)
                         Iu = Iu(RANAP)

                                                                                                                       MAP
                                                                                         MAP                     Mh
                                                   Applications
                                                   & Services *)                                   HSS *)                R-SGW *)


                                                                                                                  *) those elements are duplicated for figure
                     Signalling Interface
                                                                                                                 layout purpose only, they belong to the same
                     Signalling and Data Transfer Interface                                                      logical element in the reference model



                                                                 Networking of the R5 network


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             The IMS domain is overlaid with the original PS/CS domain. It is used to control the
             subscribers’ services. Subscribers can use all kinds of access techniques of the PS/CS
             domain to access the IMS domain. In the future, new services based on the 3GPP R5
             IMS domain will have nothing to do with the access techniques that subscribers adopt.
             At that time, no matter what technique is adopted, the service needs to be developed
             only once by the service developers.

             The IMS domain adopts SIP as the basic session protocol. As the SIP is used to unify
             the session model of voice/data services, the IMS domain provides more flexible and
             simple support to multimedia services.

             It also provides abundant service development interfaces. Operators can even provide
             open session messages to the trusted service providers. Therefore, the services will
             become even more open and flexible.


10.1.2 Network Construction Solutions

             It becomes a persisting issue for operators and equipment providers to construct a
             WCDMA network with powerful functions and stable performance and also to consider
             the factors ranging from engineering technical difficulties, capital investment and the
             network compatibility to evolution.

             1. WCDMA network construction

             For operators, there are two solutions to building a WCSDMA network: Upgrading the
             old one and establishing a new one.

             As to new mobile operators, they will usually choose to establish a new WCDMA
             network. For GSM and GPRS operators, they need to consider issues such as the
             network compatibility and roaming. However, gradually they will also choose to
             establish a new one. The following is a comparison between these two solutions.

             Solution 1: Upgrading from GSM to the WCDMA R99 network:

             This solution will turn the 2G GSM network into a network with 2G/3G coexistence by
             upgrading MSC, HLR and GMSC of the GSM network into 3G MSC, 3G HLR, 3G
             GMSC.

             Requirements:
                 The upgraded MSC should support access of WCDMA and GSM radio network
                  equipment at the same time.
                 The MSC should support the lu interface based on ATM and the A interface based
                  on TDM.
                 Support AMR voice, H.324M multimedia calls and TC equipment upgrading.

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                 Support double authentication via GSM/WCDMA, 3G MAP, internal handover and
                  compatibility.
                 Support CAMEL3 VAS and the open capability of MSC OSA.
                 Support the integration of 2G/3G charging systems.
             Advantages of the upgrade solution:
                 Minimize inter-MSC handover at the initial stage.
             Disadvantages of the upgrade solution:
                 Have a big impact on the stability of the existing GSM network.
                 Require a heavy workload and increase difficulties in the compatibility test.
                 Cause the decrease of the existing network capacity, since 3G services are even
                  more complex and demand better processing capability.
                 Affect the service provisioning and cause difficulties in smooth evolution,
                  especially the provisioning of NGN technology, IN service and the third-party
                  applications.
                 Require high costs of upgrading and large investment. The 3G MSC adopts the
                  highly-advanced technical platform with large volume and high integration. Its
                  construction cost is lower than that of the 2G MSC; therefore, it would be not
                  worthwhile to upgrade the small-capacity 2G MSC.
                 The upgrading of the original charging system will have a big impact on the
                  network operation. The interworking and compatibility of multiple manufacturers
                  and nationwide roaming need to be verified.
             This solution will give a full-scale evaluation to the problems such as the impact on the
             stability of the existing network, the continuity of service capabilities, service
             processing capacity, capacity, level of integration and whether the seamless transition
             of GSM-R99-R4-R5-R6 is available after the upgrading. It is hard to know whether the
             traditional architecture of 2G switches meets the above requirements, therefore, it is
             also impossible to know the investment utilization rate of the original GSM equipment.

             Solution 2: Establishing a new WCDMA network

             This solution is to establish a new 3G MSC and a new 3G RAN based on the original
             GSM network. The GSM and WCDMA networks will coexist in a certain period of time
             with service interoperability and the WCDMA network will gradually replace the GSM
             network.

             Requirements for the core network equipment:
                 Establish a new WCDMA RAN and a new MSC to support CAMEL2, 3 IN service
                  and the access of 2G/3G networks simultaneously.
                 The existing SGSN and GGSN have relatively small traffic and can be upgrade
                  into 3G equipment. They should be compatible with GPRS access and
                  applications and support CAMEL3 IN services.

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                 For the WCDMA HLR, both solutions (upgrading the old one and building a new
                  one) are available. As there are few HLRs, the upgrading is quite easy.
                 The backbone and core networks of TMSC and GMSC should be shared. GMSC
                  upgrading can be disregarded at the initial stage but later they may support 3G
                  MAP and CAP protocols and the trigger of 3G IN services.
                 The signaling network equipment LSTP/HSTP of 2G SS7 should be shared.
                 The 2G MSC should stop capacity expansion and BSS should be connected to the
                  new 3G MSC.
             Advantages of the solution for building a new WCDMA network:
                 As a new network, it is easier for the entire network to plan the resources and
                  configurations uniformly in order to have a clear network architecture.
                 With large capacity and less offices, it can simplify the network architecture to
                  facilitate centralized maintenance and management.
                 The test becomes more convenient and comprehensive.
                 Have a small impact on the existing network during the implementation.
             Disadvantages of the solution for building a new WCDMA network:
                 There may be coordination problems with the handover between 2G and 3G
                  systems. If the manufacturers of the existing network do not set obstacles
                  deliberately, it is easy to solve this problem.

             2. Evolution from R99 to R4

             Evolving from the R99 network to the R4 network, you need replace the MSC NE of
             R99 with the MSC Server and MGW of R4 from the perspective of the protocol layer.
             However, in terms of the specific implementation, the construction solution of the R99
             network at the initial stage is closely related with the amount of investment needed for
             evolution and the difficulty of upgrading.
             1)   Solution 1: Upgrading the R99 network to the R4 network
             If the MSC NE of the R99 network has already taken into account the idea of
             processing the signaling and voice separately (that is, the MSC based on the design
             philosophy of separating bearer from control is adopted to build the R99 network), the
             evolution will be very easy no matter upgrading from R99 to the R4 of TDM networking,
             or even to the R4 of IP networking and only the equipment needs to be upgraded.

             Requirements:
                 The original R99 should be capable of separating bearer from control to facilitate
                  the transition to the R4 architecture.
                 The upgraded equipment should support all the signaling interfaces of the R4
                  network.
             Following is a comparison between the advantages and disadvantages of this solution:

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                 Advantages: It is easy to upgrade the network. You need only upgrade the original
                  equipment instead of purchasing any MSC Server or MGW. It is also easy to
                  upgrade the ATM/IP-based network. The most important thing is that it brings very
                  big flexibility to the construction and planning of the network.
                 Disadvantages: The R99 network at the initial stage should meet higher
                  requirements. The R99 network upgraded directly from the GSM network probably
                  will not meet these requirements. In this regard, you have to establish a new MSC
                  Server and MGW.
             2)   Solution 2: Establishing a new R4 network
             If the MSC of the R99 network fails to take into account the idea of processing the
             signaling and voice separately at the later stage (or if this R99 network is upgraded
             directly from the GSM network), probably the bearer and control modules cannot be
             well separated. In that case, the evolution from R99 to R4 cannot be completed through
             upgrading the MSC, or we can say it is not worthwhile. In this regard, we have to
             purchase additional MSC Server and MGW.

             Following is a comparison between the advantages and disadvantages of this solution:
                 Advantages: The new network has powerful functions and is capable of smooth
                  transition to the later all-IP networking as well as R5.
                 Disadvantages: It is required to establish a new network, which makes the cost
                  higher than the upgrade solution.
             To summarize, it is a continuous evolution process from GSM to R99 and then from
             R99 to R4 in terms of the whole version evolution. During the WCDMA network
             construction at the earlier stage, if the solution to upgrading the GSM network to the
             R99 network is adopted, you need rebuild the MSC Server and MGW NE in upgrading
             from R99 to R4. However, if you establish new R99 network with the MSC that is able to
             separate bearer from control, the cost at the initial stage may be higher than that of the
             upgrade solution, but it is conducive to the later smooth transition to R4 and R5.
             Therefore, the comprehensive investment efficiency of the solution for establishing a
             new R4 network will be much higher.

             3. Evolution from R4 to R5

             In R5, an IMS domain is added. The logic block diagram of the IMS domain is shown in
             Figure 10-3, where the Go interface is interconnected with the GGSN while the Mb
             interface is used for the external network to access the IMS domain.




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                               IP Multimedia Networks                                      Legacy mobile
                                                                                           signalling Networks
                                     PSTN
                         Mb    Mb        PSTN
                                                     BGCF                CSCF
                                          PSTN                                       Mm
                                                            Mk      Mk

                                                                               Mw                    C, D,
                                                    Mj      BGCF                                     Gc, Gr
                                                                        Mi
                                                                                      Cx
                                    IM-          MGCF                                          HSS
                                    MGW                     Mg           CSCF
                                           Mc

                                                              Mr                      Dx       SLF
                                    Mb                                    Mw


                                                                    P-CSCF
                           MRFP                  MRFC        PCF                          UE
                                         Mp                                     Gm

                         Mb    Mb         Mb                       Go                      IM Subsystem




                                                  Logic blocks of the IMS domain


             The functional and logic entities of the IMS include BGCF, CSCF, MGCF, IM-MGW,
             MRFC, MRFP, HSS and SLF. Some logic entities can be evolved from the R4 function
             entities while others must be added.

             Therefore, it is better to establish new equipment of the IMS domain for evolution from
             R4 to R5 and upgrade the functions of the equipment in the original CS and PS
             domains.


10.2 Total Network Solution

             Lots of factors should be considered in the WCDMA network construction. For example,
             the operators should carefully consider the following issues: The investment of
             construction capitals, the utilization of the existing network resources, the planning of
             the networking form, the smoothness of network upgrading, the implementation
             difficulty etc.., as described below.


10.2.1 CS Domain Construction Solution

             The construction of the CS domain in the core network is always the focus no matter
             you upgrade the GSM network to the WCDMA network or upgrade the versions of



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             different protocols in the WCDMA network. Presented below is about the solution of
             establishing a new WCDMA CS domain network.

             The network resources of the current operators are abundant: TDM networks, IP
             networks and ATM networks. The bearer used for networking is decided by the
             condition of the specific bearer resources.

             1. Solution 1: Building the CS network in the R99 protocol mode

             When this solution is adopted, the original TDM transmission network can still be used
             for transmission of the R99 CS domain. As for the gateway and toll tandem equipment,
             you can upgrade the original GW or establish WCDMA equipment through stacking.
             The advantages and disadvantages of the two modes are already given in the previous
             chapter.

             With the R99 construction solution, we can make the best of the resources such as
             transmission resources, gateway office and tandem office, the good compatibility with
             the original network equipment can be well guaranteed, and voice services can be
             provided with good QoS. Therefore, this solution is an economical and quick method to
             introduce the 3G systems.

             2. Solution 2: Building the CS network in the R4 protocol mode

             In building the CS domain through the R4 network which separates MGW from the
             MSC Server, you can use ATM/IP in the internal core network for transmission and use
             the GMSC for the conversion of voice codec as well as the conversion of ATM/IP to
             TDM.

             The advantages of building the network through R4 are given as follows:
                It makes networking very flexible. You can configure the network capacity flexibly
                 through MGW according to the local traffic and conduct centralized management
                 and configuration through the MSC Server.
                It helps evolve to the future packet-based network. It is also helpful to save the
                 bandwidth for transmission.
                With Trfo technology, the voice quality is improved and the voice codec equipment
                 can be saved.
             The disadvantages of building the network through R4 are as follows:
                It is not easy to reuse the original PSTN equipment, because the ATM/IP
                 technology is also used in the transmission of the signaling and it is difficult to use
                 the original signaling network. We need the signaling gateway to interwork with
                 PSTN.




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                 With the separate architecture, we need to take the interworking between the MSC
                  Server and MGW into consideration. However, the test of the compatibility may
                  lead to the delay of the network construction.

             3. Solution 3: Building the R99 network through R4 (with bearer and control separated)

             In building the CS domain through the MGW and MSC Server of R4, the MGW and
             MSC SERVER are located in the same place when it comes to the construction; and
             the MSC Server accesses the MGW via the LAN.Other characteristics are the same as
             that of the R99 network. Therefore, solution 3 has the same advantages and
             disadvantages as solution 1.

             Compared with solution 1, the major advantage of solution 3 is that it facilitates the
             transition to the R4 architecture as these facilities have been equipped with ATM/IP
             interfaces and the signaling processing capability for the R4 networking. A gradual
             transition is available through replacing boards or adding the corresponding MGW to
             enable the transition from the R99 to the R4.

             Huawei provides products based on the CS domain of all kinds of protocol versions,
             including the MSC products based on R99 architecture and the R99 MSC products
             based on the architecture of separate bearer and control as well as the MSC Server
             and MGW products of R4. The versions used to build WCDMA networks vary with the
             construction solution of the operators.


10.2.2 PS Domain Construction Solution

             The construction of the PS domain comprises two aspects: 1) the construction of NEs
             such as SGSN, GGSN, CG, and DNS; 2) the construction of the GPRS backbone
             network, namely the construction of the WCDMA PS domain backbone network.

             1. Construction of the WCDMA backbone network

             There are several construction methods for the WCDMA backbone network:
                 By using the existing IP network.
                 By using the existing ATM network.
                 By using the private line network.
                 By using the above methods for hybrid networking according to the local
                  conditions.
             Please note that if we use the existing IP network to build the backbone network, we
             need VPN and firewall for security, while if we use ATM, the firewall is unnecessary.

             Normally in the PS domain of the WCDMA system, we can use the PVC of ATM or IP
             for bearing on the Gn interface.

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                 As for the provincial Gn interface, if we use the ATM network, it is enough to
                  achieve high security without adding a firewall at the Gn interface, while if we use
                  the IP network, the cost is relatively low but extra methods are needed to ensure
                  the security, such as a firewall and IPSec encryption.
                 As for the interconnection with external networks, the IP mode is always needed.
                  However, for the interconnection with the GPRS backbone network, a firewall
                  must be set.

             2. Construction of NEs in the PS domain

             The NE form of the PS domain and the basic functions are just the same no matter it is
             the GPRS network, or the R99/R4/R5 network of WCDMA.

             As to new operators of WCDMA, they should establish a new WCDMA PS domain
             network.

             As to the operators of the existing GPRS network, there are two solutions for building
             the PS domain NEs.

             Solution 1: Upgrading the existing GPRS network to the WCDMA network:

             As the difference between the GPRS network and the WCDMA PS domain network lies
             in their access networks, the SGSN-related interface modules need to change their Gb
             interface into the lu-PS interface.

             Requirements:
                 SGSN should support the access of the original BSS and the new RAN at the
                  same time.
                 SGSN, GGSN and CG should support the relevant procedures and services of
                  GPRS and WCDMA.
                 It is required to support the integrated billing of GPRS and WCDMA.
             Advantages:
                 It is not difficult for upgrading. You can save part of your investment.
                 The original equipment has been tested on the network, so it enjoys higher
                  stability as compared with the new equipment.
                 The existing packet network architecture can be maintained to keep the overall
                  stability of the existing network.
                 It has little impact on the facilities in the original equipment room. We need not
                  reconsider building any new equipment room or placing the facilities.
             Disadvantages:
                 Upgrading the old one may impact the existing network.
                 Service availability after the upgrading varies with the original GPRS platform.



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             In fact, the difficulty of implementing this solution and the upgrading smoothness
             depend on the building ability of the GPRS network equipment. If the original GPRS NE
             is developed on the basis of the GPRS protocol without considering the subsequent
             transition to WCDMA, it will be very difficult to upgrade the GPRS NEs, especially to
             upgrade it smoothly. You can do nothing but establish a new suite of WCDMA PS
             domain equipment. On the contrary, if the original GPRS NEs have powerful functions
             with good foresight and universal architecture, it can be upgraded smoothly and save a
             lot of investment.

             Solution 2: Establishing a new WCDMA packet network

             If the original GPRS network cannot be upgraded smoothly, or it is not worthwhile to
             upgrade it, the operators can choose to establish a new WCDMA packet network.

             The new WCDMA network can coexist with the original GPRS network at the initial
             stage, but it shall gradually switch the GPRS subscribers to the WCDMA packet
             network.

             The disadvantage of this solution is that investment is needed in building the new
             equipment. It does not allow us to utilize the original equipment, and we still have to
             consider building new equipment rooms and placing these equipment.


10.2.3 NMS Solution

             1. Huawei WCDMA NMS solution

             Huawei WCDMA NMS is able to operate, maintain and manage equipment flexibly
             through combining the centralized management and maintenance system iManager
             M2000 and the LMT. Huawei iManager M2000 products are NMS products in the EML,
             which forms a double maintenance and management system with the LMT of each
             product, namely, single-point maintenance and centralized maintenance.

             iManager M2000 can provide standard CORBA interfaces or directly open the core
             database to the upper layer. It helps form a multi-level OMS-oriented NMS solution
             after it is connected to the NML layer NMS of the third party. This solution is used to
             meet the NMS requirements in the NEF, EML and NML layers, while the management
             of the SMT and BMT layers required by the 3G NMS is implemented under the help of
             the OSS, as shown in the following figure.




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                                          Network hierarchy of iManager M2000


             2. Characteristics of Huawei WCDMA NMS

             With iManager M2000 as the core, Huawei can provide a whole suite of solutions
             based on the O&M network hierarchy to the applications. Its characteristics are shown
             in the following figure.




                                            Huawei O&M network construction
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             1)   Dimensional and layered O&M network architecture
             M2000 is capable of centralized management and maintenance of WCDMA NEs,
             including MSC, RNC, SGSN, GGSN, CG, HLR and Node B, so as to manage them at a
             single terminal. Users can define the subnets according to their own needs and classify
             the NEs based on the different subnets. For example, they can classify the RAN side
             and CN to conduct layered management in the same NMS.

             M2000 also provides northbound CORBA interfaces to the upper NMS in order to
             communicate with them and carry out layered management of the network, so that
             different layers of the NMS meet different demands.

             All WCDMA NEs also provide LMT software for themselves. When W2000 is not
             available, the software can still operate and maintain these NEs.
             2)   Comprehensive maintenance and management functions to meet different O&M
                  requirements
             M2000 integrate the LMT system of each NE. It allows us to maintain all the NEs
             through directly calling the LMT system of each NE on the topo.

             M2000 provides centralized management for the entire network, including integrated
             fault, integrated performance, and integrated configuration to pulse-diagnose the
             running status of equipment in the entire network.

             M2000    provides    a   comprehensive       security   management        mechanism.     The
             maintenance of NEs can be verified by two-level authority, i.e., the user logs in to the
             M2000 client as a M2000 user to operate and maintain the NEs after passing the
             authentication of the BAM.

             The M2000 system also provides mature anti-virus protection policies.
             3)   Characteristic NMS functions
             The M2000 system can also integrate some tools for the purpose of such as network
             optimization, network planning and reporting to perform some special functions.

             It provides the remote maintenance method based on a combination of dialing and
             Internet to maintain all the NEs remotely.

             With the M2000 system as a core, we can provide a mature O&M solution to the entire
             WCDMA network, so as to meet the requirements of different users.

             3. Application of NMS construction in 3G networks

             In general, the NMS construction comes after the network construction. It mainly
             connects all the products through computer networks for operation, maintenance and
             management.


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                                 Networking of the WCDMA O&M network


             The above figure shows the construction of the O&M system in the WCDMA system
             networks, including the access and management of the CS domain and PS domain
             equipment on the CN side, and the centralized maintenance and management of the
             RAN equipment.

             From the above figure, we know that iManager M2000 follows the TCP/IP to access
             and manage all the NEs. It accesses the OM unit of each NE directly, such as BAM.
             The O&M network and each service network are isolated and use different IP
             addresses and network segments.

             The iManager M2000 connects with the upper-level NMS through the network, using
             the agreed protocol such as CORBA and open database interfaces for communication.


10.2.4 Signaling Network Solution

             1. R99 signaling network solution

             1)   Principles for signaling network construction
                 High reliability of the equipment to ensure high security of the signaling network.
                 Supporting dual backup of the network without single point failure to ensure high
                  security of the signaling network.
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                 Powerful processing capability to adapt to the expansion of network scale and the
                  growth of services.
                 Low delay to ensure the service connection speed.
                 Even load distribution to evenly plan the flow of load on the signaling network.
             The load of the trunk signaling is light, and if each site has a direct signaling link, there
             will be too many signaling links; therefore, in most regions the signaling link is available
             only for the interconnection between the TMSC and the STP equipment, while the
             interaction between the TMSC and other sites is completed via the STP.

             Generally, the dual-net dual-plane networking mode is adopted for the signaling
             network to ensure high security of the signaling network. STP equipment should have
             powerful processing capability to adapt to the network scale expansion and the service
             growth. It also should have low delay to ensure the service connection speed. In
             addition, the signaling links in the 3G mobile networks need to be organized carefully to
             avoid too many signaling transfer points. At present, the networking modes of the fixed
             and mobile signaling networks are the same. A direct signaling link should be set
             between two SPs with a large information volume, especially between the MSC/VLR
             and the local HLR when the transmission condition permits. There are two SCCP
             addressing modes: GT and DPC addressing modes. The GT addressing mode is
             adopted for inter-province networks while the DPC + SSN addressing mode for
             intra-province networks. In this way, the work amount of GT translation of the STP
             equipment can be greatly reduced.
             2)   Difference between the mobile signaling network and the fixed signaling network
             The hierarchical signaling network is suitable for the fixed signaling network. At present,
             for the fixed signaling network a pairs of independent HSTPs are generally set in the
             provincial capital to form a dual-plane mesh network. For each of the local networks, a
             pair of LSTPs are available to transfer the PSTN signaling and the intelligent network
             information. An important application of the LSTP is to complete the inter-office
             conversion from mesh signaling network to hierarchical signaling network, which
             greatly reduces the amount of direct signaling links and improves the reliability.
             However, the mobile network features high capacity of local SPs, few SP sites and
             large signaling flow between local SPs, so it is better to adopt direct links between SPs,
             and in that case the signaling link convergence functionality of STP is not applicable to
             the mobile network, rather, the signaling networking of mesh topology is recommended
             for the local mobile network.

             If the STP network of PSTN directly serves as the mobile signaling network, it
             functionally makes no difference except the following issues:
                 The mobile communication system use the GT addressing mode largely and the
                  processing of GT code is in the SCCP layer, so the STP network of PSTN need to
                  be upgraded if not support SCCP function.

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                 The signaling of the local mobile network usually adopts direct links and the
                  signaling to other local networks should pass the STP. However, the LSTP of the
                  current PSTN is only used to transfer the signaling of the local network, thus all the
                  signaling information to the LSTP should be transferred from the HSTP, which
                  increases the load of the HSTP (that is, it has to transfer both the domestic
                  roaming signaling and the intra-area signaling).
                 There exist multiple intra-area signaling transfers, which causes time delay of the
                  connection and affects the QoS to some extent.
             3)   Signaling network construction solution
             Two networking solutions are available for the mobile signaling network:

             Solution 1: The mobile equipment of each local network is only connected with the
             LSTP, which is used to transfer the intra-province signaling and hand over the
             inter-province signaling to the HSTP.

             Advantages of solution 1 are simple structure and easy capacity expansion. Its
             disadvantage is also obvious: The inter-province signaling passes LSTP and this
             increases the load of the LSTP and the time-delay of inter-province roaming and call
             signaling processing.

             Solution 2: The mobile equipment of each local network is connected with both the
             LSTP and the HSTP. The mobile equipment of the local networks recognize the
             intra-province signaling and the inter-province signaling to forward the signaling to
             different STPs for processing.

             The advantage of solution 2 is that it reduces the load of LSTP and the signaling
             processing delay. Its disadvantage is that the capacity expansion is not convenient.
             With the increase of the network nodes, the utilization of the signaling links to the HSTP
             will be inefficient to some extent.

             To fully capitalize on the existing HSTP resources and create new LSTPs to transfer
             the inter-province signaling, solution 1 with minimum changes may be adopted for
             networking.
             4)   Introducing high speed signaling links to the mobile network
             At present, the SS7 network of the TDM-based mobile network aims to providing
             transmission bandwidth and reliability for the signaling network and further improving
             the signaling network management functions. From the perspective of network
             development, the capability of 3G signaling networks is much greater than that of GSM.
             That is, with the expansion of the signaling network capacity and scale, and the
             improvement of the signaling network reliability, the signaling protocol needs to be
             upgraded further, so as to enrich the services provided to the subscribers.

             At present, the SS7 mobile signaling network generally adopts 64Kbit/s signaling links.
             Restricted by the SS7 protocol, the maximum signaling bandwidth between the nodes
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             of the mobile signaling network is only 1024K (64K16), which cannot satisfy the
             requirements for the signaling bandwidth between the MSC and the HLR. The mobile
             signaling network needs to adopt 2Mbit/s high speed signaling links as soon as
             possible to increase the bandwidth between the nodes.

             To further improve the network reliability, the transmission paths of the signaling
             network should be dispersed as much as possible and the signaling network
             management functions should be enhanced.

             2. R4 signaling network construction

             In the 3G R4 stage, the bearer of call-independent signaling can only be the
             TDM-based SS7. It may be upgraded to the optional IP-based SIGTRAN or still adopt
             the TDM-based SS7. According to the 3GPP specifications, the SCCP/TCAP-based
             MAP/CAP signaling must adopt the M3UA/SCTP SIGTRAN bearer mode, and M3UA
             provides the upper SCCP with the primitive interface completely equal to the MTP3
             protocol, so no matter the 3G R4 signaling bearer is TDM/SS7 or IP/SIGTAN, it is
             required to construct a hierarchical private roaming signaling network with network
             layer signaling transfer capability, that is, the STP network as shown in the following
             figure:


                                                    Other PLMN SS7
                                                  signaling network or
                                                 toll signaling network



                         IP-based STP signaling
                        network. All pieces of STP
                        equipment have SCCP and
                       M3UA transfer capability; STP
                          may be served as SG
                                                                                                Other PLMN




                                                 IP bearer network




                                                Figure 10-1 R4 signaling network construction


             If the hierarchical structure matches and the TMSC server processing delay is enough,
             the IP STP equipment may be integrated with the TMSC server equipment physically,
             so as to effectively reduce the networking investment of the operators.

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10.3 Internetworking Solution

             For the interworking with other networks, the first thing to consider is the service
             interworking. Presently, the services provided by the operators include fixed telephone
             service, IP access service, IP toll service and mobile phone service. In addition, the
             multimedia video phone service may be a key service of the 3G networks, for which the
             interworking should be considered.

             For the interworking with other networks, the second thing to consider is the allocation
             of key resources to services, which affects the QoS. For the voice communication, it is
             required to consider the proper configuration of EC resources while preventing other
             services from wasting the EC resources.

             For the interworking with other networks, it is required to consider the security and
             reliability of the whole network. It is better for the gateway exchange construction to
             follow the principles of large capacity and paired construction.

             For the interworking with other networks, it is better to access the nearby network to
             affectively avoid the alternative routes of the mobile subscribers. The remote network
             may also be accessed for this purpose, which is useful for the charging settlement and
             the full utilization of EC functions.


10.3.1 Numbering Plan

             Now, the numbering plans adopted by the mobile communication include the network
             numbering plan and the PSTN numbering plan.

             The net numbering plan is the numbering plan adopted in current China mobile
             communication system. Both China Mobile and China Unicom adopt this kind of
             numbering plan. No further description is given for the network numbering plan in this
             document.

             The PSTN numbering plan is to number the mobile subscribers and equipment with the
             original PSTN coding scheme. The plan is consistent with the PSTN as to the dialing
             scheme with a short number and easy availability of the number.

             Advantages of the PSTN numbering plan:
                 The types of the numbers are the same, so such original equipment of PSTN as
                  the tandem exchange and the toll exchange may be still adopted by only adding
                  relevant data configurations.
                 Compared with the network numbering plan, its number length is shorter for the
                  convenience of dialing by fixed subscribers.
             However, the following problems may occur in this kind of numbering plan:
                 Alternative routes may occur when the called is roaming.
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                 After the separation of North Telecom and South Telecom, this plan may obtain
                  different number resources from different regions, or be different from the dialing
                  habits of subscribers. It is not certain whether subscribers can accept such a plan.
             The situation of severe competitions among the operators in the China domestic
             communication market comes into being. The operators build their independent
             networks, which interconnect via gateway exchanges. The adoption of the PSTN
             numbering plan will greatly increase the data configuration pressure of some gateway
             exchanges, such as the international incoming calls or the international roaming.

             With MAP routing analysis and call routing analysis, the adoption of the net numbering
             plan is helpful for the network selection with simple data configurations. It is better to
             adopt this numbering plan for the call among some international gateway exchanges or
             some operators, while the PSTN numbering plan is useful to select the geographical
             position of the call or MAP signaling routes.


10.3.2 Gateway Exchange Solution

             1. Requirements for gateway exchange construction

             1)   Have such features as large-capacity trunks, powerful signaling processing
                  capacity and abundant voice resources, thus satisfying the development trend and
                  construction requirements of the gateway exchange for “large capacity & few
                  offices”.
             2)   Have a variety of interfaces (at least E1 interfaces available) to support diverse
                  services and access modes; and provide ISP with the PRI interface to adapt to the
                  fast development of the Internet.
             3)   Have echo cancellation function to reduce the echo resulting from the
                  two-wire/four-wire transformation between mobile calls and fixed calls with the
                  relevant echo canceller configured in the gateway exchange.
             4)   Have the built-in SDH to provide the 155M interfaces for implementing the
                  centralized traffic, few office directions and large trunk groups in the gateway
                  exchange, so as to reduce the networking cost, the utilization area of equipment
                  room and the system power consumption.
             5)   Have the ability to analyze the calling number of the incoming trunk.
             6)   Support flexible networking: For the local network without LSTP or enough LSTP
                  capacity, the gateway exchange may be served also as LSTP; for the mobile
                  network providing abundant services, it is required to support 2M signaling or
                  multi-signaling point technology to satisfy the high capacity requirement of the
                  signaling links; For the exchange with over 4096 circuits in a single office direction,
                  the switching equipment must support multi-signaling point technologies.
             7)   Have the SSP/IP function, the CAMEL and upgrading capabilities for the
                  convenience of CAP capability expansion according to the service requirements.
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             2. Gateway exchange construction solution

             The networking of the GMSC is very simple. The GMSC is usually the external
             interface exchange of an operator. For the outgoing calls, it is to transfer the voice
             channels out directly; for the incoming calls, it needs to inquire the MSRN of the called,
             and then connect the call according to the MSRN. At the early stage of construction,
             generally the GMSC is also served as the VMSC. With the increase of VMSCs,
             independent GMSC construction gradually begins (if there are more than three VMSCs)
             to reduce alternative voice channels between these VMSCs.

             For the former mobile operators, construction of the mobile gateway exchange is to
             build new ones and upgrade old gateway exchanges. It is required to consider the
             networking setting problems of the gateway exchange, that is, the planning of the
             gateway exchange.

             For the operators that own fixed networks, the following solutions are available for the
             construction of their mobile gateway exchange:
             1)     Solution 1: The fixed gateway exchange is integrated with the mobile GMSC by
                    upgrading the fixed network gateway exchange



                                 Operator A                                    Operator B
                                             Gateway                               Gateway
                                            exchange                              exchange




                                                             Gateway
                                                            exchange
                                     Operator C                        Operator C
                                       PSTN                            3G network


                 Figure 10-2 Position of the upgraded fixed network gateway exchange (fixed/3G integrated gateway
                                                           exchange)


             The following functional upgrading should be carried out for the fixed gateway
             exchange:
                   Increase MAP functional modules for route enquiry.
                   Increase EC functional modules.
                   Increase the functions of CAMEL3 SSPs.
                   Increase relevant billing functions.
                   Enhance the number analysis function.
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             If only partial upgrading can be achieved for the current fixed gateway exchange, some
             local networks should be set separately and some may be integrated. For the office that
             can be upgraded, it is also necessary to check the current traffic load of the gateway
             exchange. If the traffic load is heavy, the switch should be checked to find whether
             capacity expansion can solve the load problem. For this reason, the following
             requirements should be satisfied before carrying out the upgrading:
                 The current traffic load is light.
                 The current traffic load is heavy but it may be solved through capacity expansion.
                 The equipment vendors ensure the exchange can be upgraded smoothly.
             Advantages of the solution:
                 The GW and GMSC integration is in accordance with the network construction
                  trend of large capacity and few offices. Especially at the early stage of networking,
                  the existing resources of the fixed gateway exchange are utilized to carry out
                  efficient networking, thus shortening the construction cycle and reducing the
                  construction cost.
             Disadvantages of the solution:
                 It requires to upgrade the fixed gateway exchange, which may affect the existing
                  network.
                 Part of the gateway exchange cannot be upgraded, which makes the networking
                  structure unclear.
             2)   Solution 2: Build a new 3G mobile gateway exchange for the fixed network
             This solution is to build a new 3G mobile gateway exchange separated from the fixed
             gateway exchange, as shown in the figure below:



                             Operator A                                   Operator B
                                       Gateway                               Gateway
                                       exchange                             exchange


                                          Gateway
                                         exchange                          Gateway
                                                                          exchange
                                 Operator C                               Operator C
                                   PSTN                                   3G network




                                Figure 10-3 Position of the new 3G mobile gateway exchange


             Advantages of the solution:


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                 There is no change to the old gateway exchange, no risks from the upgrading, and
                  no impact on the existing fixed network from the traffic load.
                 The networking structure is clear, which is helpful for future network optimization
                  and upgrading.
                 It is helpful for the integrated operators to carry out independent operation
                  management and independent accounting of the mobile and fixed networks.
                 The EC allocation and utilization is clear, which is helpful to reduce the EC costs.
             Disadvantages of the solution:
                 At the early stage of construction, it causes the trunk waste; and compared with
                  the integrated gateway exchange solution, it increases the constructions costs
                  and operation costs of the office and its auxiliary equipment.
                 Although the integrated operators have fixed telephone networks, they treat their
                  mobile phone networks the same as those of other mobile operators with two GWs
                  passed, which increases the links of the call and affects the network quality.
             Generally, independent accounting is required for each internal network of the
             integrated operators. At present, the interconnection and accounting of the internal
             networks are carried out by building their respective gateway exchanges. Thus, each
             private network needs its own independent gateway exchange, which results in
             repeated investment and does no good to the unified internal accounting.


10.3.3 Echo Canceller (EC) Configuration Solution

             The EC configuration is critical for the interconnection between the 3G mobile network
             and the PSTN. The EC has the automatic detection function to detect the modern
             signals and can disable the EC function automatically, so it will not affect the data
             service functions. However, the equipment cost is fairly high. To configure EC
             resources where unnecessary will increase the costs of network construction.

             EC should be configured as near as possible to the fixed telephone. Generally, the EC
             can cancel 64 ms echo of the toll calls within about 6500 km. Echo problems occur if
             the distance is more than this figure.

             1. Access mode of the EC

             MSC provides two types of echo cancellers: Embedded echo canceller and
             independent echo canceller.

             The embedded echo canceller is based on the concept of exclusive use of resources,
             that is, one trunk circuit exclusively occupies one echo canceller. When the E1 signals
             access the MSC, the signal echo cancellation function is implemented.

             The independent echo canceller is based on the concept of resources sharing. All the
             echo cancellers are placed in the ECPOOL (Echo Cancellation Resources Pool). The
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             echo canceller is occupied upon request and then released after use for reoccupation
             by other connections. The number of independent echo cancellers may be configured
             flexibly according to the traffic and the number of trunk equipment generating the echo
             to maximize the resources sharing.

             From the perspective of system resources occupation, the ECPOOL should occupy the
             interface frame slot. For the call connection that requires echo cancellation, if an
             independent echo canceller is adopted, then four switching timeslots will be occupied in
             the central switching network: One is connected to the incoming E1 timeslot, one to the
             outgoing E1 timeslot, and the other two to the echo canceller as shown in the following
             figure. And if an embedded echo canceller is adopted, then the connection is the same
             as the common call connection with only two switching timeslots occupied: One is
             connected to the incoming E1 timeslot, and the other to the outgoing E1 timeslot shown
             in the following figure. That is, the independent echo canceller realizes the global
             sharing of echo cancellation resources by occupying more system resources than the
             embedded echo canceller. In particular, the EC is usually configured on the GMSC
             equipment with great capacity. The shared EC will greatly reduce the number of E1s
             that can access the GMSC.




                                                                   TDM     NET                    TDM
                                      RNS                  TC                              EC                PSTN



                              Occupation of the network resources when the independent echo canceller is adopted

                                                                             ECP


                                                                     TDM                           TDM
                                       RNS                  TC                                                  PSTN
                                                                             NET



                              Occupation of the network resources when the embedded echo canceller is adopted



                                 Figure 10-4 Occupation of the EC resources in two cases


             Although the embedded EC can save the switching resources, sometimes the ECs are
             wasted. For example, the data services (including dial-up access and multimedia calls)
             are converted with IWF equipment and need no EC to cancel echo any more. In such a
             case, EC will not affect these services, but it is a waste of the EC processing resources.
             The embedded EC is suitable for the GSM network, in which there are few such
             services and little waste of EC resources.


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             In the other case, PSTN calls the mobile subscriber and then forwards the call to
             another PSTN subscriber, thus forming an end-to-end PSTN-to-PSTN call and causing
             a waste of the embedded EC resources.

             The adoption of ECPOOL may cause a waste of EC resources, because the TUP
             protocol and ISUP protocol on the network do not support the EC processing. In this
             way, the GMSC with ECPOOL resources does not know whether the exchanges in the
             call route have applied for EC. Incorrect judgment will cause excessive or insufficient
             EC resources to be requested, thus lowering the communication quality.

             2. Configuration of data service channels

             The data service, multimedia service and fax service need no EC equipment. PSTN
             calls the mobile network, and the call is forwarded to the PSTN again without passing
             the EC equipment. When interconnecting with the PSTN, the data service and the
             voice service may have their respective trunk groups or office directions, with one for
             speech call and one for data service or multimedia service. This requires that the
             GMSC should have the ability to select different routes for the data service and the
             voice service.

                                                     Office             Office     PSTN
                                                  direction 1        direction 2


                                             Voice direction           Data direction


                                                         Integrated GMSC




                                                                 Office             PSTN
                                                                direction



                                              Voice trunk group         Data trunk group

                                                           Integrated GMSC




                                            Data and voice service channels


             If the data or multimedia traffic is not large, then data services and voice services may
             not be separated. In the current GSM network, they are usually not separated.
             However, the 3G multimedia service is considered as a key service with wide
             application, so it may be separated to some extent.



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10.3.4 Routing Mode

             The routing mode is considered generally from the perspective of the caller.

             1. Access to the nearby network is recommended for internal calls of the operator

             Considering the fact of internal calls and all revenues to the same operator, technically
             the mode of accessing the nearby network is recommended.

             The advantage of this mode is that it may effectively reduce the alternative routes of the
             mobile services. Its disadvantage is that it does no good to the fully play of the EC
             function when the mobile network calls the toll fixed network.

             2. Access to the remote network is recommended for the calls among operators (a
             subscriber of the local network calls a subscriber of other networks)

             In this mode, the toll service adopts its own toll network, thus achieving the maximum
             benefits during internetwork settlement.


10.3.5 R4 Interworking

             The 3G R4 network is characterized by the separation of the MSC server from the
             MGW and the use of ATM/IP as the transmission bearer. Just like R99, the R4 network
             needs the interworking of the bearer connections and the conversion of the user plane
             media stream formats, as well as the echo control and the interworking of control layer
             protocols. As to the service interworking mode, R99 and R4 are almost the same.

             On the whole, the interaction between the 3G R4 core network and the PSTN is
             completed via the ISUP signaling and trunk signaling. Just like the traditional core
             network, 3G R4 should be configured with a dedicated gateway exchange to fulfill the
             interworking requirements as described above, so as to simplify the internetwork
             interactive connections and reduce the number of interactive points for the
             convenience of internetwork settlement and interworking resources management.
             Based on the architecture of separating the 3G R4 core network bearer from control, it
             is clear that the GMSC server undertakes the signaling interworking in the application
             layer of the control plane. The signaling bearer interworking is completed by the
             independent signaling gateway SG equipment or GMSC server, while the interworking
             function between the bearer connection and the multimedia layer depends on the
             MGW equipment.

             In the traditional mobile network and the PSTN interworking model, the interworking
             between the signaling control plane and the bearer plane is implemented by the
             centralized GMSC with large capacity. In the 3G R4 model where bearer is separate
             from control, the same MSC server with large capacity may control several MGWs, so
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             the interworking may be more flexible according to the MGW capability and the
             peripheral networking conditions, for instance, the independent gateway MSC server or
             the integrated MSC server (that combines the local exchange and gateway exchange
             functions) controls the interworking between the multiple local MGWs that provide TDM
             interfaces and the local PSTN network.




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