Huawei takes the lead in ASON standardization

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By Zhang Fatai

With its robust network protection & recovery capability, timely & comprehensive connection provisioning, and intelligent network management, ASON/GMPLS is being gradually recognized as a premier option for optical network development.

Unique value of ASON

Compared to traditional optical transport networks, an automatically switched optical network (ASON) features an innovative intelligent control plane that lies between the original management plane and the transport plane. The control plane establishes call and connection, provides real-time allocation on demand of network resources, and conducts dynamic path calculation, E2E service scheduling, and automatic network recovery, thus enabling intelligent optical network operation.

The ASON control plane features intelligent topology discovery and automatic connection provisioning, both of which reduce the manual configuration workload and subsequent maintenance costs & complexity. ASON can also provide flexible service level differentiation, while its mesh structure enables multi-failure resistance of the caliber required for carrier-grade service.

Leading the industry with WSON

Wavelength division multiplexing (WDM) is making optical fiber the mainstream transport network technology. A traditional WDM network is a point-to-point static network; with the advent of intelligent optical switching technologies such as ROADM, the dynamic management of connections becomes possible. Operators can schedule and configure wavelengths without any network redesign, thus offering, adding, and modifying connections dynamically. However, due to WDM’s wavelength-continuity constraints and cross-connection restrictions for optical equipment, the wavelength cannot cross from one channel to another, as it would in a TDM network (such as SDH). This brings about a complex wavelength allocation issue in routing and wavelength assignment (RWA). Furthermore, the WDM network’s wavelength connection signals are also subject to mutual influences between linear and nonlinear effects. These issues greatly increase the complexity of network control and management.

To control and manage WDM networking more flexibly, conveniently, and effectively, Huawei has proposed the concept of a wavelength switched optical network (WSON), which is based on WDM transmission technology and a generalized multiprotocol label switching (GMPLS) control plane. WSON is designed to tackle challenges in automatic optical fiber/wavelength discovery, wavelength routing, and impairment model-based routing. WSON enables dynamic E2E scheduling, configuration, and intelligent wavelength protection, thus improving usability and stability, increasing network resource utilization, and simplifying the O&M for WDM networking.

With its intelligent connection provisioning and multi-failure tolerance, WSON can significantly reduce operator CAPEX and OPEX by addressing the following issues.

Automatic optical wavelength discovery – WSON tracks down wavelength availability and the potential connectivity between the input and output ports.

Automatic wavelength connection provisioning – WSON automatically routs wavelengths and determines wavelength scheduling nodes and specific wavelengths that are available, thus avoiding wavelength conflicts.

Wavelength protection and restoration – WSON provides wavelength protection models such as 1+1/1:N and permanent 1+1; enables 50ms switching; reroutes wavelength dynamically or in a preset fashion; and features multi-failure restoration functionality.

Impairment control at the optical level – In a WDM network, wavelength connection signal quality can be affected by linear and nonlinear optical impairments. While calculating a path, WSON can intelligently consider and manage wavelength switch restrictions, tunable lasers, physical impairments, and other optical layer restrictions. It also conducts on-line impairment control through the control plane.

To enable multi-vendor WSON interconnection, Huawei has been actively promoting WSON standardization. In June 2007, Huawei first proposed the WSON concept at the IETF, attracting widespread attention from the industry. In December 2007, Huawei led the effort to establish the WSON Standard Design Group comprising dozens of mainstream operators and equipment manufacturers. In 2008, four individual WSON drafts, submitted by Huawei, were accepted by the IEFT as working group (WG) documents. In 2011, WSON framework (RFC6163) and wavelength label (RFC6205) standards, submitted by Huawei, were also released as RFCs. Huawei was also the first to propose impairment control framework standardization for WSON, leading to the release of RFC6566 in March 2012.

An encore with OTN ASON

With the rapid development of network technologies, new transport needs are emerging. To carry IP services, OTN should support fine granularity switching and flexible transmission bandwidth. To carry the 40G/100G Ethernet services defined by the IEEE, OTN should provide containers with a higher rate. To meet these needs, a plethora of new features have been added, based on the original OTN specifications (primarily on the electrical layer), including ODU0 (Optical Data Unit) for low-speed signal transmission (1.25Gbps), ODU4 for high-speed signal transmission (100Gbps), ODU2e for Ethernet services, ODUflex for variable bandwidth, and new timeslot categories with a bandwidth granularity of 1.25Gbps.

OTN technology includes complete system structure for the electrical and optical layers; both have their respective needs in terms of network survivability. In an OTN ASON network, WSON can be applied for intelligent scheduling at the optical layer. As for the ODU electrical layer’s ASON control plane, the following issues should be prioritized.

ODU automatic discovery at the electrical layer – Path monitor (PM) byte, GCC-1, and GCC-2 can be used to support automatic information discovery for connectivity between various network elements, ODU adaptability & multiplexing ability, and timeslot availability.

ODU connection provisioning – Point-and-click establishment of ODU connection.

Multi-layer scheduling and control for ODU – Automatic connection scheduling at different levels – ODU0, ODUflex, ODU1, ODU2, ODU3, and ODU4, enabling automatic multiplexing.

Network survivability – Protection & restoration mechanisms for the optical layer, ODU electrical layer, and joint recovery at both the optical and electrical layers could be applied to improve OTN survivability.

To promote OTN ASON development and resolved interconnection problems, Huawei has been actively involved in OTN ASON standardization. After leading the G.709 standardization effort to define new OTN features such as ODU0, ODU4, and ODUflex, Huawei has again taken the lead by proposing the OTN control structure at the IETF in 2009, winning widespread support from mainstream vendors. Huawei has also teamed up with other vendors to submit certain drafts for the OTN ASON’s control plane to the IETF, including the OTN control framework, control information model, routing solution, and signaling solution. These documents have been accepted by the IETF as WG documents, indicating that OTN ASON standards have gradually matured and stabilized.

As of the end of 2011, Huawei built more than 70 WSON/OTN ASON networks (including the world’s first) in over 50 countries around the world, accumulating a rich body of delivery and O&M experience along the way. Leading operators such as Vodafone, China Mobile, Telefónica, Telecom Italia, Bharti (India), and MTN (South Africa) have placed their trust with Huawei for their WSON/OTN ASON needs.

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