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By Xiong Qianjin

Mr. Balint is a senior network planner for a well-known European multinational telecom corporation who recently launched its IPTV service. This resulted in a sharp subscriber increase, which in turn greatly increased Mr. Balint's workload over the past months in the context of answering the following questions. Which bearer technology best serves the high bandwidth, high quality and low delay required by IPTV services? How many fiber resources are available network-wide after mass direct fiber connections are used? What is their efficiency? Which technology is capable of sustainable development in terms of accommodating future service expansion?

Since he found the answer to all the above questions, GE MADM, he and his family are currently holidaying in the Mediterranean.


Mass Macro-Granule Ethernet Services Need to be Transported

With the real-time and broadband data traffic becoming mainstream, subscribers are experiencing changes in broadband Internet surfing, which in turn is influencing the network strategies of operators. Bearer network structures are becoming flatter and more simplified, and the mainstream service interfaces of broadband MAN (Metropolitan Area Network) are being switched from TDM 2M/155M/622M to GE/10GE. Therefore, much attention is being focused on broadband MAN transport network and suitable methods for transporting mass macro-granule Ethernet services.

To date, Metro WDM has generally been selected to construct broadband MAN transport network, but the traffic environment is changing and the traditional Metro WDM system merely replaces fibers, which no longer meets operators' requirements. As mass GE services are currently in vogue, the Metro WDM system requires innovation. Broadband MAN transport network construction therefore leans toward the integration of leading technologies and concepts such as ROADM, GE MADM, as well as the convergence of layer-2 switching feature and WDM.


GE MADM Powers the Metro WDM

• Achieving a network-wide GE routing reconfiguration
  
  The GE ADM is able to add or drop, as well as pass-through GE services in a single wavelength at the same rate. At the same time, it is neither able to dispatch nor to consolidate GE services among the different wavelengths at the same rate or the different wavelengths at different rate. The GE MADM, however, is able to achieve multi-directional and multi-rate GE cross-connect capability. This further enhances the flexibility of GE services and the Metro WDM network, elevates wavelength utilization, and lowers CAPEX and OPEX.
  
  Fig.1 shows that, the small service capacity of convergence and access layers' will increase the pressure of high cost of a Metro WDM. Capacity, cost and network requirements demand the use of 2.5G, 5G and 10G GE MADMs, which can be smoothly selected and interconnected to provide end-to-end GE services. 2.5G or 5G MADM can be deployed at the access or convergence layers to bear few GE services, while implementation of the 10G MADM at the core layer is able to facilitate the mass GE service transport.
  
  Consequently, the GE services can be conveniently accessed from the 2.5G GE ADM/MADM access layer and converged at the 5G GE ADM/MADM convergence layer, before arriving at the 10G GE ADM/MADM core layer. On the drop side of the access or convergence layer located at the other end, intermediate wavelength services can be automatically dispatched and connected without manual jumper. This helps configure and provide end-to-end GE services. Moreover, this type of cross-wavelength & cross-rate dispatch and consolidation renders physical network topology and wavelength connection limits irrelevant, and realizes GE channel traffic equilibrium across the entire network.

Fig.1 Network architecture after IP network transformation

• Converging the Ethernet channel to elevate the bandwidth utilization
  
  The transport capability of Ethernet services is critical in a Metro WDM system. When all Ethernet channels are fully loaded at the wavelength level, they can be directly dispatched, multiplexed and transparently transported in the Metro WDM. If they are not fully loaded, the Metro WDM's Ethernet channel utilization requires further elevation.
  
  Huawei's Metro WDM systems are based on layer-2 data switching technologies such as VLAN. They provide Ethernet channel convergence, including the convergence of multiple GEs into one GE or multiple GEs. Each GE port allows controllable bandwidth, and port bandwidths can be set on the NMS (Network Management System), for example, 1-4 GE bandwidths' allocation for 8-16 GE ports. Consequently, Metro WDMs can operate EPL or EVPL services, and the system boasts a synergy between the data layer-2 switching and the GE MADM functions. This enhances both wavelength and GE channel utilization, which further improves transport link bandwidth efficiency while lowering network construction costs.
  
  
• Providing the GE sub-wavelength protection
  
  Generally, a transport network offers two types of protection: one is the optical layer wavelength level protection, and the other is VC level protection, or dada equipment protection at the packet level in an SDH ring network. When GE MADM is deployed, GE channel or shared protection at the sub-wavelength level can be directly provided.
  
  Such a protection scheme is dedicated to GE transport. When an optical wavelength between any two nodes is interrupted, the services of a given GE channel in the working path are also interrupted. The traditional protection schemes are far less comprehensive. Even if a single GE channel is interrupted, all services borne by the optical wavelength in question have to be switched even if the other GE channels in the same wavelength are normal. Different GE channels might be used by different subscribers, and so when one GE channel is interrupted or if a fiber is cut, wavelength protection switching affects all services for all subscribers. This is particularly not acceptable for leased lines services or group valued customer services. When a fiber cut occurs between two nodes in a network that uses GE MADM, only the interrupted GE channel is switched to the standby path or standby wavelength. The other normally functioning GE channels continue to transport services in the working path free of interruption.
  
  If the entire network is configured with 2.5G, 5G or 10G GE MADM wavelengths, the GE MADM features allow them to be shared during the protection process. As a result, channel efficiency and network expandability are greatly enhanced. Such a rapid and reliable protection scheme lays a solid foundation for GE transport at the carrier-class.
  
  
• Providing and configuring the end-to-end GE services
  
  The GE MADM is also able to provide and configure end-to-end GE services. If the OADM and GE MADM features are configured at a Metro WDM node requiring GE service pass-through, NMS can directly click a node where the GE services are to be added or dropped, and thus query whether GE channels between nodes are configurable and available. These nodes can also be clicked to create or delete GE services between nodes, instead of having to configure GE services node by node at the intermediate nodes. This lowers OPEX and achieves genuine flexibility in terms of service provisioning.

GE MADM is Becoming a Mainstream Technology

At present, the main IP network service interfaces are FE/GE/10GE and few POS (2.5G/10G/40G). In terms of MAN development, service capacity, transport distance and cost performance, the GE has become a mainstream interface for data service interworking. The sharp increase of GE interworking means that the effective transport of associated services and low construction costs of a carrier-class MAN with high OAM and QoS capabilities has assumed critical importance. Therefore, operators'focus has shifted from backbone networks to MANs that support multi-services.

In terms of new generation broadband MAN construction, Huawei's Metro WDM systems integrate technologies such as GE ADM/MADM, ROADM and Ethernet service convergence. With GE ADM/MADM's flexible cross-connect capability, Huawei's Metro WDMs are able to provide rapid end-to-end GE services. The Metro WDM solution helps realize network-wide reconfiguration of GE routings under a complex network topology. They also remove the network limits and improve the overall efficiency. Ethernet service convergence enables Huawei's Metro WDMs to provide EPL or EVPL services, which lowers IP DSLAM network service transport costs and reduces the number of physical ports required in service equipment. The GE protection switching at the sub-wavelength level enables operators to provide high quality leased lines to valued group customers.

Huawei's Metro WDM systems have been successfully commercialized for operators such as China Telecom, China Mobile, BT, KPN, Novis and GTS. In order to achieve its IP over WDM strategy, KPN of Netherlands has adopted Metro6100/6040 to construct a broadband service bearer network. Huawei's Metro WDMs bear mass GE/10GE services in KPN's broadband network, and the unified C/DWDM platform provides a complete network solution from the access layer to the core layer.

BT offered the following comments praising Huawei's GE ADM/MADM and asserting its commercial value: "Huawei's unique GE ADM/MADM solution evolves the MAN WDM networks from the traditional point-to-point WDM toward a future-oriented and flexible data transmission bearer network. The 5G bit-rate solves the PMD issue of mass aged fibers in the access layer of the existing network. Moreover, the shared cross-connection technology of the GE ADM/MADM family achieves the convergences of 2.5G, 5G to 10G services, which forms an integrated and seamless data transport solution."