By Huang Hairong
IP+OTN synergy can potentially facilitate the rapid growth of IP backbone networks, which is increasingly pressuring operation and maintenance (O&M) efforts for any & all operators who employ them.
Statistics indicate that the IP traffic growth is exceeding Moore's Law, tripling every eighteen months. Bandwidth-hungry services such as video are driving some operators to expand their network constantly; China Telecom has to set new targets every year. Traditionally, this is done by adding nodes and layers, leading to increased CAPEX/OPEX and stagnant margins.
IP backbone network architecture is being flattened and interconnected to lower bandwidth costs, while the IP and optical layers are also converging; this can be divided into four stages – IP-over-DWDM, IP-over-OTN, IP-over-OTN/ASON, and IP+OTN synergy. Through the unified network interface (UNI), IP+OTN synergy facilitates interconnection between the IP and transport layers, which enables network optimization and lowers costs for bandwidth/network expansion.
Challenges to overcome
IP+OTN synergy encompasses traffic, protection, and O&M. Traffic synergy requires optimization of both the IP and transport networks, where λ-level and ODUk traffic are both offloaded to transport layers, at reduced cost, through physical ports or cOTN/VLAN sub-interfaces. Protection synergy enhances network reliability by combining the protection mechanisms on both the IP and transport networks.
O&M synergy is achieved through the network management system (NMS); through which operators can enhance O&M efficiency through E2E backbone network planning, monitoring, optimization, service provisioning, and troubleshooting. In addition, O&M synergy effectively supports both traffic and protection synergy. It enables IP-optical layer interaction through the GMPLS-UNI and the path-computation element (PCE).
However, there are still three major challenges remaining that must be overcome for IP+OTN synergy to come into being.
Difficult planning for traffic & protection
Statistics show that over half of network traffic flows through core routers. Operators need to expand network capacity constantly to meet traffic growth. DWDM/OTN costs less than routers, though it can bear traffic of the same speed; it should therefore be utilized for heavy-traffic services whenever possible, with light-traffic services still carried by routers for statistical multiplexing. Traffic offload can help alleviate the pressure on routers and reduce the number of hops, while generating other benefits such as lowered costs and enhanced QoS. However, this is easier said than done. Services must be mapped between multiple layers, including IP/MPLS, ODUk, and WDM; such mapping must consider the performance and reliability of each layer, so that bandwidth demands are minimized over the entire network.
Another hindrance is the fact that one fault at the optical layer may cause multiple faults on the IP layer. Cross-layer planning must ensure the separation of shared risk link groups (SRLGs) at the IP layer. When the service protection mechanism is enabled for both the IP and optical layers, protection redundancies should be avoided. Cross-layer planners should also consider offloading traffic from the IP layer to the less costly optical layer, to reduce the costs of the backbone network.
Inefficient service provisioning
Typically, when bandwidth is insufficient for new service provisioning or service expansion, the router initiates a request to the transmission equipment through GMPLS-UNI. If the transport layer has sufficient resources, a connection is automatically established.
This may seem to be a solid process, but a flaw lurks within. Network management and service provisioning involve numerous O&M departments, including transmission, data communications, and network monitoring; a unified management system would ensure efficient cooperation between departments, while reducing manual-input errors and ensuring accurate information sharing. IP+OTN synergy will also complicate IP networking, which means that operators must enhance their configuration and management efficiency.
According to statistics from a European operator, a fault alarm at the transport layer increases ten-fold at the router layer. This added noise makes identification and resolution of the root problem onerous. Automatic alarm correlation and a unified alarm database are both needed so that low-priority cases are filtered out and troubleshooting efficiency is enhanced.
Huawei IP+OTN O&M refinements
To address the O&M problems brought about by IP+OTN synergy, Huawei has leveraged its experience to develop an integrated O&M solution.
Automatic cross-layer planning
Multilayer network optimization should focus on traffic offload, while following a step-by-step process of manual, semi-automatic, and intelligent optimization.
Physical ports can be optimized manually while WDM equipment can make adjustments at the wavelength level, but both processes are still complex. Great skill is needed when adjusting key traffic nodes, as precise traffic adjustment is less efficient and less accurate, making coarse adjustment more suitable at this level.
Semi-automatic optimization simplifies planning and improves accuracy through traffic monitoring and offline optimization. It involves multiple layers and methods. The GMPLS-UNI, a key interface between the IP & optical layers, is implemented at this stage. Semi-automatic optimization requires tools that monitor traffic and optimize multiple layers, in addition to the GMPLS-UNI supported by routers and WDM devices.
Ideally, intelligent optimization for multilayer networks would be automatic and done in real time, yet this will require support from multi-layer PCE and offload servers; it will also require mature standards.
Huawei offers a multilayer network planning tool (ML-NPT) that facilitates IP+OTN synergy. With its advanced algorithms, this tool helps plan the IP and OTN layers automatically, and then exports data which includes optimal routing, TCO, costs of each network layer/node, and wavelength deployment. With Huawei ML-NPT, operators can use less costly devices to enhance bandwidth and performance. By working with the SRLG, this tool can enable protection synergy for both the IP and optical layers.
Unified O&M synergy
Unified management can be realized through a unified NMS that integrates the management systems used by various O&M departments, enabling timely service provisioning, monitoring, and troubleshooting. If an IP service error occurs, the unified NMS can help explore various routes, view lower-layer WDM service and fiber routing information, and then locate the faulty layer and route segment.
When standards such as Y.1731, 802.1ag, 802.3ah, 802.3ba, and 802.3ae are implemented, unified operation, administration, and maintenance (OAM) can be realized for both the IP and optical layers. The unified NMS can then locate faults directly through OAM testing at the IP layer.
The unified NMS defines the alarm correlation rules, based on optical-IP layer alarm relationships, which means that it can automatically identify the root alarms and therefore minimize the time wasted during maintenance.
Huawei U2000 enables unified management of the access layer, transport layer, and IP routers, while supporting timely and visualized service provisioning, template configuration, and deployment at the IP and optical layers. The U2000 also provides cross-layer topology display and correlates alarms at the IP and optical layers.
Partnering with Vodafone
In 2009, Huawei partnered with Vodafone to initiate a joint IP+optical innovation project in the U.K., which has since been upgraded to a Vodafone strategic project dubbed Multilayer Optimization (MLO). This project has subsequently explored cost-efficient protection of the IP backbone against simultaneous fiber blockages. As of December 2011, proof-of-concept (POC) testing has been completed in five phases, verifying the feasibility of key technologies such as ODUFlex, GMPLS-UNI, PCE, multilayer planning tools, unified OAM, and traffic offload through various VLAN sub-interfaces.
After testing the ML-NPT, visualized service management, cross-layer service correlation, and root alarm analysis functions of the U2000, Vodafone is very enthusiastic about it, especially its cross-layer O&M capability. Vodafone is expected to run a unified team to locate network faults, improve O&M efficiency, and reduce costs.
IP+OTN O&M is becoming more intelligent, with new technologies emerging that optimize multilayer networks and automatically locate cross-layer faults. With IP RAN and broadband bearer service/network development, IP+OTN synergy will gradually extend from the IP backbone to the metro network. Huawei will continuously explore IP+OTN O&M technologies and promote/develop relevant standards for the foreseeable future.