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IP Broadband Access Network Construction --DSLAM and MSAN
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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 broadband subscribers.

All these value-added services have specific requirements on bandwidth and QoS.

2. Exit of aging narrowband telephone networks of some operators.
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 and IMS.

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 operator.


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 market:

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 line
  • 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 Play Service.
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 following respects:

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 services.
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 Equipment
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.


III. Conclusion

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.

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