Background of IP-over-WDM
The number and scope of IP-based applications is rapidly increasing, driven by the popularity of both the Internet and the fast development of broadband technologies. As the main driver of global information networks, Internet Protocol (IP) will gradually displace conventional voice traffic to become the dominant service type.
In traditional data service networks, connnections are direct router-to-router via fibre. This is a problemtic area where the major problems will arise: as IP-based traffic increases the fibre insufficiency will become increasingly apparent, but topological studies suggest that the maintenace problems will arise when the said fibres are installed. For long-haul applications especially, a large amount of data equipment is required, thus, significantly affecting the CAPEX.
To successfully address these issues, a new cost-effective service bearer network must be built which can support large-capacity, long-haul transport as well as accommodate the characteristics of IP services. The WDM system has emerged as the foremost solution to high-speed transmission and is evolving towards IP-over-WDM networks.
Technical analysis of IP-over-WDM
IP-over-WDM arichitectures deliver the following advantages as a result of the technology-specific characteristics:
- WDM achieves a significant increase in the tranmission capacity of trunk lines compared with traditional SDH and ATM transport. ZTE's WDM system can carry 40, 80, 160 wavelengths per fibre and deploy 2.5 Gbps,10Gbps, and 40Gbps wavelength. The low-rate data services can be aggregated into full bandwidth transmission in order to improve the fibre utlisation efficiency.
- WDM simplifies the legacy star typology to linear and ring typologies which offer more economical management and protection options.
- WDM enables powerful and cost-effective ultra long-haul transmission. ZTE's WDM equipment can be applied in non-REG long-haul data transmission over 1000km and is used commercially both in China and abroad.
- WDM with transmission transparency can easily accommodate different data rates and modulation formats. The ZTE WDM equipment enables the transport of comprehensive data services, such as GE, 2.5G POS, 10G POS, 10G VLAN.
- WDM provides complete optical layer protection schemes that ensure high network survivability. ZTE's WDM transmission equipment allows 1+1 multiplex section protection, path protection schemes of 1+1and 1:N, 2-fibre bi-directional multiplex section/path ring-shared protection. Among them, the unique 2-fibre bidirectional path ring-shared protection combines perfectly the wavelength utilization ratio and protection efficiency. In terms of fault restoration speed, the protection and restoration mechanism of an optical network is better than an IP network.
WDM has been created to support multiple protocols (eg, IP, TDM, ATM) on a single wavelength, as well as applications with long-haul and large-capacity requirements. Optical and IP convergence pose significant challenges for the development of IP-over-WDM, ranging from a fast network re-route and dynamic bandwidth allocation to IP service performance failure detection.
Development trends of IP-over-WDM
T-MPLS: IP-over-WDM solution
The development of WDM has the following features as impacted by the increasing IP service usage of the WDM network:
- Data packaging: The circuit-switched networks will be replaced with packet-switching technology and the timeslot structure inherent to TDM circuits will migrate to a frame structure.
- Network model: The simple overlay model will be replaced by the peer model that enables simplified network structure and management;
- QoS: Provide different levels of QoS and real-time performance monitoring to support the growing demands for multiple services types;
- Intelligent Network: IP traffic is sporadic in nature and theerfore requires dynamic bandwidth allocation.
Transport-multiprotocol label switching (T-MPLS) meets the afore-mentioned requirements and, has recently been recommended as a preferred network solution to transport IP traffic over WDM.
The T-MPLS is designed for the multi-service transport node and lays the foundation for the next phase of convergence. It is therefore capable of carrying a variety of client traffic types (such as Ethernet, IP/MPLS, FR, ATM, TDM, etc.).
T-MPLS is defined in the G8110.1 Reommendation, which was confirmed during an ITU-T Plenary Meeting in Feburary this year in Geneva.
T-MPLS is a connection-oriented packet-switched transport layer technology which is based on MPLS. As the intermediate adaptation layer, T-MPLS offers Layer-2/3 service-agnostic capability. A T-MPLS layer network can operate independently of the service layer and its associated control networks.
T-MPLS technology has following advantages:
- A carrier-class transport technology that can support both voice and data, meeting the trend of network transformation;
- Converge L2 and L3 protocols to define a uniform data transport plane;
- High service scalability;
- Uses traditional protection schemes, transport-centric OAM tools for end-to-end maintenance, protection and monitoring;
- Utilises the existing transport layer (wavelength and/or TDM). T-MPLS behaves consistently with existing transport technologies and can migrate to the GMPLS-based common control plane;
- Omits IP-oriented routing complexity, reducing CAPEX and OPEX.
T-MPLS is an enabling technology for the next generation core transport network which uses a simplified architecture including only a pure optical layer and an electrical layer. T-MPLS technology has considerable potential to attract multiple vendors as it represents the integration of packet transport requirements into the existing transport architecture. ZTE places a high value on its R&D, and this new technology is currently the most promising solution for IP-over-WDM networks.
GMPLS/ASON: Future-oriented technology
The T-MPLS network only consists of packet switching nodes with preconfigured transmission resources. The transmission circuit must be configured manually as resources can't be dynamically allocated to meet the changing demands at the packet-switching node. Consequently, the traditional MPLS requires an extension and update to enable on-demand provisioning to adapt to the future intelligent optical network.
The protocols of GMPLS are an extension of the existing ones in MPLS to allow different switching capabilities. GMPLS is used to establish connections between packet switching nodes through circuits, wavelength, and even fibres, bridging the gap between management of the traditional transport infrastructure and the IP layers, thus paving the way for seamless IP optical integration.
With development of technologies related to realizing IP-over-WDM, there is an increasing demand for bringing intelligence to converged optical-data networks. ASON is intended to provide an evolutionary path to the next generation network optical networks with built-in intelligence.
ASON introduces intelligence to the optical transport network by means of a control plane. ASON integrates transmission and data services by applying dynamic switching to optical networks. The ASON control plane can support automatic traffic engineering, automatic topology discovery and automatic service discovery as well as multiple protection and restoration schemes.
The most accepted proposal for the ASON control plane is based on GMPLS. With GMPLS technology, service providers can achieve multi-layer, multi-vendor interoperability and provide more services on the optical network such as optical bandwidth-on-demand (BoD) and optical virtual private network (OVPN).
Using ASON/GMPLS networks to automate some of the network operations can significantly reduce the costs for service providers. The emergence of the GMPLS/ASON technology marks a breakthrough in optical network development, and ZTE has it listed as a primary direction of strategic development.
The inevitable and absolute dominance of IP traffic dictates that the network infrastructure should integrate both IP and WDM. It is commonly accepted that the T-MPLS technology is the solution to integrate IP and WDM. ASON/GMPLS is a enabler for future intelligent optical network, and prepares the transmission network for the transition to all-IP. ZTE closely follows the development trends of IP-over-WDM, thereby establishing a leading-brand presence in these advanced fields.