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
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:
l 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.
l It helps evolve to the future packet-based network. It is also
helpful to save the bandwidth for transmission.
l 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:
l 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.
l 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.
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:
l By using the existing IP network.
l By using the existing ATM network.
l By using the private line network.
l 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.
l 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.
l 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:
l SGSN should support the access of the original BSS and the new RAN
at the same time.
l SGSN, GGSN and CG should support the relevant procedures and
services of GPRS and WCDMA.
l It is required to support the integrated billing of GPRS and WCDMA.
Advantages:
l It is not difficult for upgrading. You can save part of your
investment.
l The original equipment has been tested on the network, so it enjoys
higher stability as compared with the new equipment.
l The existing packet network architecture can be maintained to keep
the overall stability of the existing network.
l 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:
l Upgrading the old one may impact the existing network.
l Service availability after the upgrading varies with the original
GPRS platform.
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
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 Signaling Network Solution
1. R99
signaling network solution
1) Principles for signaling network construction
l High reliability of the equipment to ensure high security of the
signaling network.
l Supporting dual backup of the
network without single point failure to ensure high security of the signaling
network.
l Powerful processing capability to
adapt to the expansion of network scale and the growth of services.
l Low delay to ensure the service
connection speed.
l 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:
l 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.
l 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).
l 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 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.
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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