IP Broadband Access
Network Construction -- DSLAM and MSAN
Abstract: This article describes the new characteristics
shown by the broadband market recently, and details the developing
trend of the broadband access network construction in the new scenario.
I Characteristics of Broadband Market
The current broadband market is very different from that of the
previous years in the following respects:
1. Large quantity of high bandwidth value-added services
are developed, especially that of the Triple Play service based
on IP TV, VOIP and DATA.
The ARPU of the narrowband voice services, which is the main revenue-generating
services of the traditional fixed network operators, is decreasing
year by year. This decrease is attributed to the impact of VOIP
or from the mobile operators. Because of this, the broadband service
revenue is only generated from the Internet services. Also, the
current broadband subscribers have more demands on such multimedia
services as audio service and voice service rather than the essential
Internet access services.
The broadband operators spare no efforts to develop the Triple
Play services based on IP TV, VOIP and DATA to improve the ARPU
value and enhance the subscribers experience in broadband. The competitive
operators are deploying the Triple Play services to attract more
All these value-added services have specific requirements on bandwidth
2. Exit of aging narrowband telephone networks of some
The operators' narrowband telephone network equipments in some developed
countries are aging and demand large-scale network reconstruction.
The broadband-based voice service is inevitable. The narrowband
telephone subscribers will migrate into the NGN based on Softswitch
3. To reduce OPEX, operators hope to integrate multi-networks
into one, especially to realize the IP based ATM, FR, TDM and X.25.
Most fixed network operators operate many networks such as ATM,
FR, DDN, X.25, broadband network and narrowband telephone network
simultaneously. The maintenance of these networks costs an operator
a large amount of manpower and materials and keeps the OPEX value
high. This maintenance is especially obvious for an operator in
a developed country, where the labor costs high. So, to integrate
multi-networks into one is the inevitable choice to a fixed network
II Development Trend of the Broadband Access Network
The construction of the broadband access network presents the
following trends corresponding to various demands in the broadband
1. Complete IP Based Access Network
A complete IP based access network, which consists of three parts,
is a preferred solution to integrate multi-networks into one. The
three parts of an IP based access network are as follows:
1) IP based structure
The devices (including the DSLAM/MSAN, Ethernet switch and optical
transmission) related to the access network are all interconnected
through the Ethernet Interface.
2) IP based services
Services as audio services, voice services and data services (including
ATM, X.25, TDM, FR and VPN) are all over IP messages and are transmitted
in a unified manner.
3) IP based protocols
All devices of the access network are inter-worked based on the
Ethernet and IP protocols.
2. Construction of New Technologies of ADSL2+, VDSL2,
Wimax and EPON/GPON
ADSL2+ offers wider bandwidth and higher performance for copper
access, and ADSL2/2+ has been greatly improved in bandwidth and
transmission distance compared with ADSL. ADSL2+ is mainly used
in the following situations:
- Solving the problem of number allocation for a long distance
- Providing the symmetrical bandwidth private line(512k bit/s)
for small and medium commercial customers
- Application of short distance and high downlink bandwidth (ADSL2+
terminal: within 2 km, 15M bit/s).
Compared with ADSL2+, VDSL2 can provide bi-directional and symmetrical
bandwidth over 50M bit/s for short distance to satisfy the demands
of commercial customers on higher bandwidth.
For the traditional fixed network operators, the Wimax is the
supplement to the copper access and can provide broadband access
for enterprises and families in the remote area. For the competitive
operators, the WiMAX can help them to realize rapid deployment and
develop enterprise and family subscribers. Besides, those operators
operating the WiFi hotspot services can use WiMAX as the back-transfer
of WiFi to expand the coverage of WiFi.
The FTTH is based on the EPON/GPON technology and will lead the
development of the broadband access network. Because the FTTH is
not mature enough, it is better to be applied to commercial pilots
in small scale (for example, the deployment of the FTTH in some
new green fields).
3. Selecting the Access Devices that can support the Triple
Triple Play service imposes high requirements on bandwidth and QoS,
when the broadband access network is deployed, therefore; the access
devices to be chosen should support the Triple Play service in the
1) Ensure the public Internet service, VOIP services, audio
services and VPN services performs well in aspects such as backplane
capacity, slot bandwidth, switch capability, service engine, forwarding
performance and network interface.
2) Support multi-PVC or multi-VLAN at a user port to bear different
3) Support classification of priorities for different service
types and forwarding at the uplink interface based on priority.
4) Support the function of IGMP snooping or proxy, and rightly
control the Multicast service.
4. Meeting the Requirements for Migrating from Narrowband
Telephone and Integrating Multi-Networks into One Through the MSAN
The MSAN is the best choice for migrating from narrowband telephones
and for integrating multi-networks into one. The integrated access
device of the new generation is based on the pure IP core and offers
advantages such as bandwidth extension, support for new service
and function upgrading. It provides some built-in functions such
as the physical layer adapter, ONU, DSLAM and AG. It also can offer
different physical interfaces, bandwidth, QoS capability and various
broadband access modes such as POTS, ADSL, ADSL2/2+, SHDSL, VDSL/VDSL2,
LAN, E1, IMA E1, G/EPON and WiMAX. The uplink is connected to service
networks such as the traditional telecom network, Internet and NGN
through standard interfaces. The maturity of the integrated broadband
access platform facilitates the implementation of multi-service
access and integrated service mode and makes the complete service
possible. The integrated access platform will become the important
part of the broadband access network.
5. Application of MPLS and PWE3Technologies
Introduction of the MPLS technology to access network can solve
the problem of the insufficient VLAN resources (the MPLS label is
used to identify subscribers and services). The application of the
MPLS OAM technology enables the end-to-end fault protection to meet
the high reliability requirements of carrier-class services.
PWE3 is one of the key technologies used to integrate multi-networks
into one. The PWE3 technology can emulate the virtual line on the
MPLS edge equipment, put the TDM/ATM services into the MPLS tunnel
and transmit them over the MPLS network.
6. Simplification of Network Structure
The reduction in the network layers of an access network can decrease
the difficulty in bandwidth control and QoS deployment, and reduce
the OPEX value of an operator.
7. Access Device Nearer to Subscribers
In a situation that requires high speed access, ASDL2/2+ and VDSL/VDSL2
technologies can reach higher bandwidth in short distance, therefore;
the distance between access devices and subscribers should be further
shortened to realize the high bandwidth access.
The broadband access network construction must satisfy the developing
requirements of the broadband market. The broadband access network
construction should not comply with the old thoughts or views and
should develop towards the direction of access IP trend, access
mode diversification and access device simplification.