A Three-dimensional IP-based Telecom Metropolitan Area Network Model

In recent years, the telecom industry, particularly in the area of data services, has grown rapidly. With Presently, the main problem of the IP network is whether the existing network can cope with the challenge of the increase of the number of customers and diversified services, especially new services like IPTV, Softswitch based VoIP, 3G and more. ZTE puts forward a three-dimensional IP-based Metropolitan Area Network (MAN) solution.

1 Status Quo and Problems of MAN
Before the advent of MAN, IP network only refers to Local Area Network (LAN) and Wide Area Network (WAN). The WAN was confined by the transmission resources of that day, thus employing routers. The LAN was constructed based on Ethernet, in which the main equipment was switch. The Ethernet features simplicity, low price and high scalability. These advantages of the LAN have caused its invasion into the area of WAN. Within the invaded area, LAN technologies and WAN management modes are both adopted, which gives birth to the IP-based MAN.
The early MAN catered for public on-line services. Generally speaking, before and after the appearance of IP WAN, there existed a group-user network to provide VIP clients with a data exchange channel, which was the perform of present Virtue Private Network (VPN) services over MAN. The group-user network employing the DDN/FR/ATM technologies grew up independently of IP MAN. Lately with the advent and maturity of Multiple Protocol Label Switching (MPLS), this new technology was deployed to construct group-user VPN in some cases. At the initial stage of IP MAN, there existed a mass of redundant bandwidth that was used later in many places to provide VPN services for VIP clients.

    The general advantages of the IP MAN are becoming more and more evident with the development of network technology, especially after the maturity of the technology of MPLS VPN. In addition, the previous services of MAN are hoped to be carried over to IP MAN, such as public online services by the IP MAN itself, group-user VPN service, voice and video services with a higher demand on network QoS.

    The status quo of MAN can be summed up as follows:

• Some networks in the scope of MAN are constructed according to services, of which the IP MAN is dominant.
• At the present stage, IP MAN mainly provides public online access services, but it will gradually carry other services.
• Numerous Ethernet switches are employed in IP MAN to provide huge quantities of cheap bandwidth.
• MPLS VPN has been introduced in IP MAN on a small scale.
• With the rapid development of network, there are diverse access modes and points in MAN at the present stage.
  

    The operation of the present MAN encounters a host of difficulties. Firstly, numbers of networks coexit in MAN, with diverse and half-phased out technologies, while most old equipment leads to difficult maintenance and high cost. Secondly, in the scope of MAN, same services sometimes are carried by different networks. For example, the group-user services are carried on both the DDN network and IP MAN. Presently, there is no solution to this problem. Thirdly, the IP MAN has undergone rapid development and a large amount of investment has been put into it, but now it still takes the online services as its main mission, meanwhile endures low Average Revenue per User (ARPU). Fourthly, the early IP MAN is mainly used for the public to surf the Internet, which does not require the guaranteed QoS for point-to-point communications and the high security of data transmission. At the time when more services are expected to be carried over the IP MAN, and more services require guaranteed QoS and high security, the existing IP MAN, with redundant bandwidth and difficulties in developing new services, is facing
great challenges.

    For the above-mentioned reasons, operators are thirst for carrying all services over one network. Several networks coexist within the existing MAN, of which the IP MAN is the best choice. Nevertheless, the IP MAN also has some problems in handling these services, which can be explained in detail as follows:

    (1) The existing IP MAN is out of order, in which the Layer 2 switching and Layer 3 routing are mixed. So it cannot meet the requirements of providing QoS guaranteed services.

    (2) The IP MAN mainly implements L3 switching architecture. With a single access mode, poor access capability and without overall planning of service access points, this kind of access mode is hardly possible to support
"full-coverage full-service network".

    (3) Highly positioned Provider Edge Router (PE) is a networking that cannot take the advantages of MPLS VPN technology. Layer 2 network too large, which is confined by the Virtual LAN (VLAN) ID resources and makes network troubleshooting difficult.

    (4) It causes serious waste of optical fibers and transmission resources. In order to attract more group users, IP MAN mainly employs the direct optical-fiber connection mode. Users are directly connected to PE. In some cases nearly half of the fibers in MAN are used only to connect group users, really being a great burden of carriers.

    (5) The IP MAN equipment has differentiated capabilities. Most IP MAN is unable to deploy either the QoS guaranteed services or the multicast services over the entire network.

    In summary, after years of rapid development, IP MAN has been constructed with different technologies. Although it has met the demand of the number of users surfing the Internet at present, it just acts as an access network to the Internet. With mess architectures, single access mode and non-unified technical systems, the present IP MAN will hardly meet the new demands brought by the double increase of users and bandwidth demands, as well as the further deployment of carrier-grade services. Under such circumstances, ZTE proposed a three-dimensional IP MAN solution, providing new ideas to the architecture, access mode, and technical system of MAN.

2 Three-dimensional IP MAN
The three-dimensional IP MAN solution means a physical network can carry multiple services and meet the service demands for relevant network functions and performances. On the other hand, IP MAN can carry telecom services such as Softswitch Voice over IP (VoIP), 3G and IPTV.

    Figure 1 is the architecture of IP MAN.

    The three-dimensional IP MAN can be illustrated as follows:
    The first dimension refers to the network level. As we know, the MAN has three layers: the core layer, convergence layer and access layer. In IP MAN, all these layers are integrated into the MPLS domain to form an MPLS network of "full coverage, full services". Therefore, with the vision of whole network, the service types, access modes, equipment functions and capabilities at different layers can be properly chosen and well planned. The core idea about the network level is to realize "full-coverage full-service network".

    The second dimension is service. At this level, multiple services distributed on different logic planes are carried in a single MAN. These services can be ranked according to their QoS requirements (from low to high). Then QoS can be achieved in the entire network. Similarly, the security strategy of the entire network can be made. The core idea about the service level is to setup logic networks. Overlapped logic networks build up a solid network, in which different services can be categorized and isolated by thelogic networks.

    The third dimension is technology. It is the footstone of a three-dimensional IP MAN. Updated technologies should be adopted to realize the convergence of networks. In the present IP MAN, some technologies cannot be employed for the entire network. However, in the three-dimensional IP MAN, technologies such as MPLS VPN technology must support the entire network.

    Figure 2 illustrates the access modes of IP MAN services.

    The following part will present a detailed description of each level of the three-dimensional IP MAN.

2.1 Network Level
The three-dimensional IP MAN is a network of "full coverage, full services", in which L2 switching and L3 routing are clearly separated. Then the existing MAN will be divided into the L2 access network and L3 MAN, thus achieving unified QoS and carrying out security strategy.

    The three-dimensional IP MAN is a flattened network, which requires less nodes and hierarchies to implement the
"full-coverage full-service network" strategy. That also means higher requirements on the density of ports
and the capacity of switches. The flattened network is just supported by large switching capacity and
high-density ports.

    The three-dimensional IP MAN claims well-defined and specific functions of the network equipment. To meet this demand, the service access should be realized at the network edge, and specialized access routers are required. Besides, the Broadband Remote Access Server (BRAS) should be deployed at the edge access layer. Equipment on different layers has similar but definite functions, quite different from the present MAN where the equipment is expected to have integrated and complete functions.

2.2 Service Level
From the viewpoint of service, the three-dimensional IP MAN is a multi-service IP network, not only providing access to the Internet but also carrying telecom-level IP services. It can meet all the requirements of a bearer network for diversified services, including QoS and security.

    For each service, the three-dimensional IP MAN is just like a private logic network, although all logic networks belong to a physical network. Service security is ensured through the isolation of services, resulting from the separation of logic networks.

    Service identification at the access point enables the handling of different services to specific logic network, which imposes higher requirements on BRAS and service access routers.

    The equipment inside the network is able to perceive services. The network management system is responsible not only for the management of the network elements but also for the monitoring of services.

    Different logic planes have different QoS. Services demanding the same QoS are carried on the same plane, and vice versa. The QoS is ensured by the guaranteed QoS of network planes.

2.3 Technology Level
The development of new technology and its mature application are prerequisite to three-dimensional IP MAN. Currently the mature technologies include:

    (1) Tera bit switching and 10 G port technologies. They are used for mass subscriber access and supporting network flattenization.

    (2) MPLS/BGP VPN (L3 VPN),VPWS/VPLS (L2 VPN) technologies. They are basic technologies for the construction of three-dimensional IP MAN. With MPLS VPN´s natural isolation technology, a physical plane can be logically divided into a number of virtual planes. So a physical MAN can function as several logic private networks.

    (3) MPLS Traffic Engineering, Fast Reroute (TE/FRR) technology. It is adopted for improving network usability and performance of MAN to carry telecom services.

    (4) Multicast technology. It is employed for carrying new services such as IPTV, and more.

    (5) QoS technology. The implementation of entire network QoS strategy, especially the dynamic Resource Reservation Protocol (RSVP), ensures the QoS of telecom services.

    (6) Security technology. It ensures the security of networks and services.

    (7) Network management technology. It is for the management of network elements and supervision of services, which is required by the telecom services.

    (8) IPv6 technology. It is used to meet the need of sustained increase of subscribers and for new services such as mobile IP.

    ZTE´s solution of the three-dimensional IP MAN gives a picture of the development trend of MAN and can solve series of problems of the development of MAN. It can be used to construct next generation MANs.

3 Constructing Three-dimensional IP MAN with ZXR10
ZTE´s ZXR10 product series meet the functional and performance demands of MAN at all network scales and layers. It provides an integrative solution to three-dimensional IP MAN, and includes T1200, T128, T64E, General Excellent Router (GER), T16C and more, as shown in Figure 3.

    As gateway equipment at the core layer of MAN, T1200 and T128 on the high end support Terabit switching and 10 G ports. T128 and T64E at the convergence layer provide high-density ports. T64E, GER and T16C at the access layer provide diversified access means.

    ZXR10 product series support IPv6, MPLS/MPLS VPN/MPLS TE/FRR, multicast/controllable multicast, QoS and unified network management, and meet the technical requirements of "full-coverage full-service network" for three-dimensional IP MAN.

4 Conclusion
The increase of the number of users, the demand of each user for high bandwidth and the launch of telecom-level services are driving the existing MAN towards three-dimensional IP MAN. ZTE is devoted to provide high-quality MAN equipment. ZXR10 series are time-tested mature products, and qualified for the construction of next generation MAN.

Manuscript received: 2005-05-17