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Abstract: This article has proposed future fixed telecom network
evolution strategy and mode based on the characteristics of China's
existing telecom network as well as the next generation network
based on IP.
Key words: telecom network, evolution
1 Preference
In the "Ten-Five" period, along with the development
of informatin technology, especially the packet voice, integrated
networks as well as the IP broadband, the cost of tranditional telecom
services have been reduced dramatically by adopting IP network.
Voice may become the feature of the broadband IP network. Under
this circumstance, how to evolute China's telecom network, especially
for thoses network operators who own the huge fixed telephone network,
and to which strategies of network evolution be adopted, is the
purpose of this article.
2 Telecom network status
Currently, China's telecom network is consisted of three network
platforms: voice network, data network and IP network. The voice
network includes PSTN and PLMN; data network includes packet communication,
data, frame relay and ATM; IP network includes internet and broadband
IP MAN.
Among them, voice network provides mainly the real time voice
services, data network provides mainly the data transmission and
exchange video services, IP network provides mainly the information
exchange, data transmission, etc.
On the whole, the current telecom network is the bundling between
services and networks. See exhibition 1. The different services
need different networks to support. The varioty service networks
can share only the resources below the transmission layer. The detailed
features are shown below:
Services and network bundling together and can not provide flexible
service
Networks share the infrastructure at the bottom layer
Network equipment has certain intelligence, such as PSTN/PLMN,
and need certain knowledge on services
PSTN/PLMN has less openess
Equipment interconnected through standard specifications
Different networks have different control protocols
3 The next Generation Network architecture
From network operator and service flexibility point of view,
take the IP technology into consideration, the current 2 trends
are: media gateway controller plus media gateway (soft switching),
and pure SIP mode.
The network architecture of the media gateway controller plus
media gateway mode was proposed by ISC, see exhibition 2. The network
is mainly consisted of media gateway controller (MGC), media gateway,
signalling gateway, application server and media server.
The pure SIP network architecture was proposed by IETF, see
exhibition 3. The network is mainly consisted of SIP terminal user
proxy, SIP proxy server, re-direction server and location server.
The differences between the 2 modes are shown as exhibition
1.
Based on the analysis of the above-mentioned two technologies,
the pure SIP mode has more vitality, while the soft switching mode
is more suitable for the telecom operators' current service mode.
From the technology point of view, these two modes will be more
practical by year 2003.
The MGCP/H.248 end mode in Soft switching and the pure SIP mode
will be more suitable for the application of IP metropolitan area
network of the LAN access; while the big media gateway of the soft
switching mode will more suitable to replace the existing local
or circuit switch (packet switch).
Therefore, whether or not to adopt the the big media gateway
of the soft switching will depend on whether it can reduce the cost
up to the circuit switch of PSTN.
MGCP/H.248 mode and SIP mode can save lot for the narrow band
users' access equipment and circuits, however, due to the high cost
at the end user, it is hard to predict whether it can be accepted
by mass users.
To add SIP user agent software in the computer can reduce the
cost, and easy to intergrate with IP sevice, and easy to be upgraded,
and with more flexibility. Moreover, WINDOWS XP itself has bundled
SIPuser agent software. Therefore, this mode has more vitality.
Based on the above-mentioned situation, it is therefore suggested
that the fixed telecom network company will focus on how to add
voice service on IP MAN, and to increase value added service, i.e.
to develop the pure SIP packet voice on the broadband MAN, and to
boundle instant messageand user presence business; to promote MGCP/H.248
mode and SIP mode on the newly established community using broadband
LAN access; the big media gateway in the soft switching will mainly
suitable for the broadband IP MAN voice service and PSTN interconnection.
It is not recommended that using soft swtiching plus media gateway
to replace the existing local and long distance telephone switching
system. For those need to newly add and replace the local switching
system will depend on the cost of the media gateway.
On the whole, the future telecom network will gradually evulate
to the following structure, i.e. to add the control layer on the
INTERNET network, to provide voice servie over IP using soft switching
/SIP agent server. See the structure in exhibition 4.
The next generation network mainly has 4 layers:
Application layer
Mainly consists of various application servers to provide services,
such as WWW server, E-MAIL server, intelligent network SCP, video
server, PINT server, etc.
Control layer
Consists a series of servers that provide authentication, billing,
management, strategy policy control, quality of service, call agent,
SIPserver, user control server, etc.
IP transmission layer
Consists of network equipment that provide IP transmission service,
such as routers, LAN switching, etc.
Access and adapation layer
Consists of a series of gateway and access equipment, includes
the signal gateway that interconnected with PSTN, relay gateway，wireless
gateway that linking 2G and 3G mobile wireless network, as well
as the narrow band dial-up server that provides access services,
broadban dial-up server, and Lan access switching system, etc.
4 Fixed telecom network evolution during the "Ten-Five"
period
According to the archtechtures of the next generation, and take
the fixed telecom network situation into consideration, it is suggested
that the fixed telecom network will take the following strategies
in the next 3-5 years evolution:
Not to have the large -scale change on PSTN network;
To build the convergence IP telecom network on broadband IP
network, and to provide voice service for the broadband IP accessers.
See exhibition 5.
Based on this strategy, the local telecom network may take the
network module in exhibition 6 in the following 3-5 years. The lcoal
telecom network mainly consists of 2 parts: broadband network of
packet switch and narorw ban voice network of the circuit switch.
Among them, the broadband network packet switch will be devivided
into broadband network platform and service center, and broadband
network platform consists of the 4 following components:
" Broadband IP MAN backbone
Consisted with gigabit router and gigabit 3 layer switch, etc
high speed IP router and and switch equipment, it is applicable
for the high speed IP router technology, 3 layer router switching
technology and MPLS technology based on optic fiber or optical network,
to provide broadband, high speed IP router and VPN services.
" Broad band data backbone network
Composed of ATM broadband switching system, providing the bursty
PVC and SVCservice, mainly for the private lines supporting narrow
and broadband platform.
" Integrated access network of multiple service
Provides various narrow and broadband access. It consists of
broadband LAN access equipment, ADSL equipment, narrow band access
equipment, broadband ATM multipal service access wuipment, media
gateway equipment, fibre, type five and wisted cable, etc.
" Media gateway
Provide tranditional network and IP inter-network medai exchange
service. The gateway mainly has 2 categories: access gateway and
network gateway. access gateway mainly provides the exchange from
the traditional telecom access (such as analog, TDM) to IP packet;
network gateway mainly serves as interconnection between broadband
IP MAN and PSTN/PLMN、IN/CAMEL.
Service center includes the service center based on IP and ATM.
The service center based on broadband IP MAN includes the followings:
" Media service center
Mainly provides INTERNET service and interactive multi-media
service. It includes the information browsing, e-mail, IP TV, VOD,
real time network broadcast, e-eduation and e-medication, etc.
" Data center
Mainly provides hosting, IP private line access, ASP platform,
e-business platform, etc.
" Telecom service center
Mainly provides real time voice service over IP. It includes
IP telephony, IP voice intelligence, mobile SMS, IP fax and mobile
communication service.
5 The evolution of Access Layer Network
The access layer architechture during the "Ten-Five"
period is shown in exhibition 7.
The access layer network will mainly adopt FTTB or FTTC mode.
Its equipment will be divided into 2 main categories: LAN access
equipment and media gateway/TDM/ATM integrated access equipment.
Among them, the broadband access will adopt the XDSL and LAN
cabling. For where cabling is not easy, wireless LAN will be used
to provide broadband access.
Media gateway/TDM/ATM integrated access equipment is the main
way of narrow band and data private line access. Users may access
fixed telephone network and dial-up access braodband MAN through
twisted cable; users may access broadband data network through ADSL
or DDN, or FR, etc; mobile comminication users may access 2G or
3G mobile communication network through base station equipment and
wireless gateway.
Along with the technology mature in the soft switching and media
gateway, the narrow band access equipment will be integrated the
function of media gateway. Users may access directly to the broadband
IP MAN through twisted cabling or wireless base station. Dial-up
server will also be replaced by the media gateway, narrow band dial-up
users will be diverted to broadband IP MAN at the access network.
Integrated media gateway equipment will mainly provide IP telecom
network access,which includes the 3G mobile communication services
of the whole IP architechture. See exhibition 8.
6 Conclusion
Based on the above-mentioned points of view, this article has
proposed the following evolution strategies for China's telecom
network operators in the following years to come:
Focus on how to develop the voice services on IP MAN, and increase
added value sevices, i.e. to develop the pure SIP packet voice on
broadband MAN, and to boundling real time message and presence,
i.e. to develop the pure SIP pachet voice mode on the broadband
MAN, boundling the real time message and PRESENCE services;
The big media gateway in the soft switching will mainly serve
in the inter-exchange of broadband IP MAN voice service and PSTN;
Not recommend to use soft switching plus media gateway to replace
the existing local and long distance switching systems. For the
newly added and need to be changed local telephone switching systems,
it will up to the cost of media gateway. Not to change dramatically
to the PSTN;
Access layer network will focus on the development of broadband
access. When large demand for the divertion of the narrow band IP
dial-up services, it is suggested to adopt the gateway mode.
Biography:
Zhang Yan Chuan, graduated from Beijing University of Post and
Telecommunications in 1992, and served in the Planning Research
Institute under MII upon graduation. Zhang now is the deputy engineer-in-chief,
and senior engineer in the Chinese Academy of Telecommunication
Technology under MII.
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