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Successful Migration --IP Broadband Network Construction of China Telecom


Successful Migration
-- IP Broadband Network Construction of China Telecom

Abstract: This document is a narrative the migration from ATM broadband networks to IP broadband networks in China. It aims to provide reference to the operators who are constructing and are ready to construct IP broadband networks.


In June, millions of gnus and zebras migrate from Serengeti Plain to Maasai Mara Plain for their thirst for fresh food. They cross Mara River in defiance of the threat of death. This is the most magnificent animal migration in the world.

In the process of broadband network construction of China Telecom, the network development experiences a migration from ATM broadband networks to IP broadband networks. Although this migration cannot rival the animal migration in Maasai Mara, it fully exhibits the admirable foresight and courage of China Telecom.


1. Start

In year 2000, broadband networks in China started to be constructed.
With the increasing broadband subscribers, China telecommunications industry should solve the following problems urgently:

1) Short ATM network resources
At the initial stage, DSLAM only provided ATM uplink interface, and BRASs were placed in nodes of the core network. ATM MAN (Metro Area Network) was required to converge ATM interfaces and traffic. However, the ATM MAN designed to provide leased line services was just constructed and the scale was small.

Hence, the rapid development of broadband access services consumes the ATM network resources soon.

2) High costs of ATM network expansion
An investigation from Planning Dept. of China Telecom shows that expanding the ATM network is not an optimal approach to address the needs of broadband service development. At that time, an ATM switch was highly priced. The cost of adding a port even exceeded the price of a DSLAM device.

3) Quick consumption of fiber resources
In the case of short network resources and high expansion cost, China Telecom had to schedule resources across areas to satisfy the increment of broadband subscribers. At that time, generally, DSLAM was connected to ATM switches across areas. In this case, large amount of fibers were required. Resources were wasted and operation & maintenance were difficult.

In spite of the above-mentioned problems, broadband networks continue to be constructed, because broadband services decide the future development of fixed network operators. To solve the above-mentioned problems, the Planning Dept. of China Telecom performed ATM subtending function of DSLAM as a temporary solution and searched for a long-term solution.
In year 2000, the Ethernet MAN emerged. Although its cost was advantageous, its application was immature. Investigations showed that the Ethernet MAN may satisfy the long-term development of broadband networks. Hence, China Telecom decided to replace the ATM MAN with the Ethernet MAN. As DSLAM did not provide Ethernet interfaces at that time, China Telecom together with Huawei defined technical specification of DSLAM with Ethernet uplink interface, and Huawei was responsible for developing the prototype.

The trial running of the prototype proved the feasibility of the Ethernet MAN, and cost advantage. Thus, China Telecom expanded the scale of the IP/Ethernet MAN and started to use IP DSLAM on a large scale.


2. Migration

The migration from ATM networks to IP networks was not smooth. Problems emerged with the expansion of networks.

  • BRASs placed in core network resulted in too large layer-2 network within the MAN. Due to the inherent deficiencies of layer-2 Ethernet network, broadcast storm floods in the MAN.
  • Due to the limited number of VLANS, subscribers cannot be located. Accounts are embezzled and management of large quantity of MAC addresses is complicated.

At that time, Metro Ethernet Forum (MEF) was just founded and DSL Forum did not give consideration to the evolution from ATM DSLAM to IP DSLAM. In addition, the network construction mode was immature. Despite the above situations, China Telecom took the initiative in building a solution together with equipment suppliers.

Together with equipment suppliers, China Telecom set standards of the Ethernet MAN and IP DSLAM to direct the network constructions. Details are as follows:

  • In year 2001, set the standard of Ethernet access, defined the access model in Ethernet, and clarified requirements
  • Between the year 2002–2004, modified the DSLAM standard and optimized technology requirements of Ethernet uplink
  • Between the year 2002–2004, modified the standards of MSTP and LAN Switch and optimized technology requirements of Ethernet MAN construction

By standard formulation and network optimization, the above-mentioned problems were solved. Accordingly, China Telecom strengthens confidence in constructing IP broadband networks.

  • From year 2002, the purchase of IP DSLAM increased.
  • At the end of year 2003, the deployment of IP DSLAM exceeded that of ATM DSLAM.
  • In year 2005, IP DSLAM will replace ATM DSLAM.


3. Find a New World

After the evolution to Ethernet, a lot of advantages were brought to China Telecom, not only CAPEX of broadband network construction decreases, but also the sustainable development.
To provide the same bandwidth, the price of an ATM port is made10 to 20 times as much as that of an Ethernet port. After the evolution to Ethernet MAN, the uplink bandwidth of DSLAM increases by 10 times. (The GE port replaces the ATM STM-1 port.)

Less subtending of DSLAM simplifies the network structure. Network congestion reduces and the bandwidth for Internet access increases by several tens of times. Customer satisfaction increases, which promotes the increment of broadband subscribers.

The deployment of IP DSLAM and the Ethernet MAN brings a wider range of services, especially, IPTV service. IP DSLAM and the Ethernet MAN have the advantage over the ATM network of supporting multicast service and providing large bandwidth. With IP DSLAM and Ethernet MAN, multicast service can be deployed on a large scale. To address the needs of large-scale deployment of multicast service, from year 2004, China Telecom deployed IP DSLAM in ATM DSLAM nodes and changed ATM DSLAM to IP DSLAM.

The development of IP broadband networks promotes the development of IP VPN. With the end-to-end IP networks, the deployment of L2/L3 IP VPN is simplified and efficiency of the deployment increases. The decrease of network layers helps to simplify network deployment. At present, IP VPN has become the highlight of service development of China Telecom. In the years to come, China Telecom will benefit more from IP VPN.

The development of the IP broadband network helps to reduce OPEX. At the initial stage, the backbone network was based on IP and Ethernet and the convergence network and access network were based on ATM. Due to different management approaches, configuration was converted frequently, thus decreasing efficiency of operation & maintenance of the network.
With the evolution of IP/Ethernet DSLAM and IP/Ethernet MANs, end-to-end management over broadband networks can be implemented, service provisioning is simplified, and ATM PVC configuration is avoided.

Facts show that the migration from ATM broadband networks to IP broadband networks is correct. The migration brings about a reduction of CAPEX and OPEX and a wider range of services.


4. Conclusion

In the 21st century, the Asia-Pacific region ranks the largest telecommunications market in the world and plays a key role in leading the recovery of the global telecommunications industry. Half of global broadband subscribers reside in the Asia-Pacific region. Besides the subscriber population, the open telecommunications environment and fierce competition makes the Asia-Pacific region the leader in using the new technology, especially the broadband access field. New technologies, such as IP DSLAM, IPTV and FTTH are applied in the Asia-Pacific region on a large scale. The global telecommunications industry focuses on the Asia-Pacific region and hopes to gain reference and experience from the broadband network development in the Asia-Pacific region.

Despite the lack of ready standards and reference of operation modes, China Telecom resolutely makes a decision to carry out migration from ATM networks to IP networks and paves the way for the development of broadband networks.

With the maturity of the standards and technologies, with the references from more and more operators, are you still hesitant about migration?

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