Technology overview of ASON automatic switching Optical Network

I. Overview

The development of modern optical communication networks starts from PDH and goes through SDH/SONET/OTN to the current ASON automatic switching optical network, which fully reflects the high speed and ultra-high speed from low speed, from point-to-point topology to rings and MESH, from low-speed power reuse to high-speed power reuse and optical reuse, from management of links and network elements to management of end-to-end services. Today, supporting ASON has become a necessary condition for optical equipment manufacturers to promote their optical devices. Especially in China, AlCAtel is located in Beijing with AT&T adopting Ciena's smart optical equipment, lucent has deployed smart optical network products in Jiangsu, and domestic operators have expressed a warm welcome to ASON. The reason why ASON is so important has won unanimous praise from operators and manufacturers, mainly due:

(1) the technology at the network transmission layer has become increasingly mature, including virtual cascade, general frame rules for Generic Framing Procedure, and LCAS (Link Capacity Adjustment Scheme Link Capacity Adjustment solution) new technologies and RPR (Resilient Packet Ring elastic grouping Ring), MSPP/MSTP (Multi Service Provisioning Platform/Transport Platform Multi-Service configuration/Transfer Platform) and other new platforms provide a variety of options for Voice/Data Network convergence;

(2) regardless of the product or platform used, operators can reduce the complexity of network operation and maintenance and reduce the network failure rate, it is always the most eager to improve the effective utilization of resources and launch new and flexible bandwidth services faster than competitors;

(3) ASON provides a unified control and management platform for various network devices, provides powerful tools for manufacturers to promote intelligent optical networks, and fully considers how to meet the needs of operators.

Ii. ASON technical features and protocol standards

1. ASON composition and service

ASON consists of the following three independent planes: transmission plane, control plane, and management plane. (There is also an uncommon DCN plane used to carry control signals ). Like ATM, ASON supports three types of connections: Permanent Connection, Swithched Connection, and Soft Permanent Connection ). Permanent connections are also called custom connections, which are completed by the network management system or manually. The exchange connection is a signaling-driven connection. End users can establish connections between any two connection endpoints as needed. Both SPC and PC connections are initiated by the management plane. The difference lies in the use of signaling or network management interfaces in the optical network. When the optical network uses signaling to establish a connection, it involves the signaling part in the control plane. The control entities of each network element need to dynamically interact with each other, in addition, the routing part in the control plane must also exchange routing information between entities. The establishment of signaling chains requires the support of network Naming and Addressing policies.

2. ASON Interface Definition and network protocol family

Because AS0N is an Overlay Model in the Network architecture, the ASON Network logic is divided into UNI (User Network Interface ), i-NNI (Inter-Network Interface internal Network-Network Interface) and E-NNI (Exterior-Network Interface external Network-Network Interface) three parts.

UNI is mainly used between optical network clients and optical network devices. It is a bidirectional signaling interface between business requestor and service provider to control plane entities, the main function is to establish a connection, remove the connection, modify the connection, and query the status. Route information is not exchanged between the two. The optional functions include Neighbor Discovery and service discovery. UNI1.O is designed for SDH interfaces, and Ethernet support will be added to UNI2.O in the next edition. UNI2.0 is also more concerned about the information integrity and security of signaling than 1.0. At present, UNI has three types of Hou protocols: PNNI (VPC-network interface Private NNI), CR-LDP (Label Distribution Protocol Constrained Routing-Label Distribution Protocol) and RSVP-TE (Resource Reservation Protocol with Traffic Extension Resource Reservation Protocol -- Traffic Extension ).

I-NNI is a bidirectional control interface between control plane entities in a domain. Because the operation in the domain is generally performed by the same device manufacturer, it is not recommended that the standardization be implemented. Each device manufacturer can use the proprietary interface protocol or the well-known interface protocol. I-NNI interfaces use protocols including routing and messaging protocols, which can be OSPF-TE (Open Shortest Path First-Traffic Engineering with Traffic Engineering extensions), IS-IS-TE (Intermediate System-Intermediate System routing protocol-with Traffic Engineering extended Intermediate System-Traffic Engineering) or BGP (Border Gateway Protocol Border Gateway Protoco1) protocol, signaling Protocols are mainly CR-LDP and RSVP-TE.

E-NNI is a two-way control interface between different entities belonging to the Inter-Domain control plane, supporting call control, resource discovery, Connection Control, connection selection, connection routing selection. Unlike I-NNI, it exchanges route accessibility information between different domains, shielding the topology information inside the network. E-NNI information interaction between multi-layer topology structures, especially the difficulty and focus of standardization.

ASON is mainly promoted by three international standards organizations, IETFOIF and ITU-T.

(1) IETF

MPLS from IETF to GMPLS is the basis for the generation of ASON. The CR-LDP of the signaling protocol used by ASON is the result of the recent standardization of IETF, while the routing protocols of ASON include RSVP-TE, BGP, both based on the original protocol, the requirements for the development of optical networks have been expanded accordingly. The latest LMP Link Management Protocol is also being revised.

(2) OIF

The most noteworthy job of OIF for ASON is UNI1.0. With UNI1.0, data equipment manufacturers and telecom equipment manufacturers have a reliable basis for automatic device interconnection. Now we have the second version of UNI1.0, and we are still in the process of standardization. We have introduced the Ethernet service and supported UNI2.0, which supports dynamic bandwidth change. Another key area of 0IF research is E-NNI, which aims to provide interconnection possibilities between equipment domains.

(3) ITU-T

The advantage of ITU-T is that in terms of Protocol framework construction, network management and service provision, according to the suggestion of ITU-T, ASON only supports cascade model and defines G.8080/Y. the ASON structure distinguishes calls and connections. abstract models are used to abstract the Signaling protocol, and the routing protocol requirements are proposed. DCN can be subdivided into SCN (Signaling Connection Network) and MCN (Network Management Connection Network) carefully consider the ASON Network Management problem.

3. ASON technical advantages

Compared with the existing SDH networking technology, ASON has the following advantages:

(1) The unified distributed control/management layer is irrelevant to the underlying physical implementation technology. Theoretically, it supports switching and management of various bandwidth granularities, whether it is an IP router, both ATM switches and optical cross-connection devices can be used;

(2) quick customization and support for different SLA (Service Level Agreement) Level circuits not only shortens Service provision time, increases network resource utilization, but also provides new bandwidth services, such as BODS (On-Demand bandwidth service) and OVPN (optical Virtual Private Network;

(3) Support for end-to-end connection establishment, monitoring, protection and recovery, support for various network topologies, including the mesh network, and enhance the network traffic engineering capability.

Iii. Future Prediction of ASON Market

Prior to the emergence of ASON, DWDM technology doubled every six months to meet the Gilder's law, greatly improving the capacity shortage problem on the backbone network's long-distance link, no need to build new optical fiber, but only need to increase the number of wavelength channels, operators can fully meet the needs of a huge amount of bandwidth, the great wealth of bandwidth does not mean that operators can quickly meet the needs of users to respond to bandwidth, in the context of increasingly data-driven network traffic and sudden increase, the demand for multi-granularity, dynamic bandwidth changes, and fast circuit deployment makes ASON increasingly important and common. Currently, many vendors such as Ciena, Huawei, ZTE, Lucent, and Alcatel claim to support ASON devices. In the foreseeable future, ASON will have huge market demands in the following four aspects.

1. Generation and upgrade of Metro Transmission Networks ASON + MSTP

Today, when the business model is more data, the traditional SDH cannot meet the needs of data services at all, and the MSTP (Multi-Service Transfer Platform) developed based on SDH is) it is becoming the first technology in the construction of a new generation of man. Due to business development needs, ASON and MSTP are combined to provide lower-layer physical transmission channels. Intelligent Network Control and Management by ASON is an inevitable choice in the future.

2. Flexible wavelength services for long-distance transmission networks

On the long-distance Backbone Transmission Network, flexible configuration of wavelength upstream and downstream (such as through Reconfigurable Optical upstream and downstream multiplexing (R-OADM), wavelength resizing or long-distance trunk Link Protection/recovery, it can be provided by the Distributed Intelligent Control of ASON, And the ULH technology that provides ultra-long distance transmission, real-time long-distance and large-capacity circuit configuration, scheduling, and protection can be completed within several minutes, this greatly reduces the complexity, error-prone, and flexibility of manual configuration circuits.

3. Flexible Support for Metro access, such as 3G base stations, enterprise network edge routers, gateways, and IAD

In addition to the original SDH interface, the new generation of MSTP has added support for Ethernet, MPLS, and even RPR (elastic grouping ring) access. Considering the broadband needs of future wireless 3G applications, for example, interconnection between 3G base stations and Speed upgrade of enterprise network equipment, using ASON to provide users with secure, high-speed, two-layer VPN or one-layer VPN to meet interconnection needs is a promising new business.

4. Support for NGN

NGN is the next generation of future communication networks. It is a group-based, control-and call-separation-based, Softswitch, business-driven, and open network architecture system that separates call and load. In essence, ASON uses the exchange technology in the business transmission environment instead of grouping, but circuit-based. However, it is independent from the physical transmission/exchange technology of devices, it also satisfies the two separation features and is open to future businesses. ASON must comply with the NGN framework agreement and be an important demonstration network that meets this agreement.

Iv. ASON limitations

So far, no technology is perfect, and the same is true for the developing ASON. ASON defects mainly exist in:

1. Standards to be improved

ASON standards have made great progress so far, but there is still much work to be done in terms of interconnection, robustness of network management and management plane. As multiple standardization organizations are involved, standard communication is also troublesome.

2. Immature Test Equipment

The maturity of devices must first rely on the maturity of the testing equipment. Currently, companies that call the GMPLS/ASON protocol testing have not yet launched mature products, which are constantly affected by standard updates, it is also difficult to come up with the actual product at the moment.

3. Effectiveness of traffic engineering, protection/restoration, and other special functions

When operating networks, operators are always pursuing real-time monitoring capabilities, network optimization, and network survivability improvement. ASON claims to be able to solve these problems, however, its real effectiveness has not yet been tested on a real large-scale network site, and it is impossible to determine whether to completely solve the problem or simply mitigate the problem.

4. Support for new businesses

ASON supports many business types, such as SDH, OTN, Ethernet, and storage network. It also has scalability for new businesses. In fact, ASON is mainly used to promote the bandwidth that can be quickly deployed, this applies to wavelength leasing, wavelength dialing, and OVPN. ASON claims to support service connections that can ensure QoS or SLA, including point-to-point unidirectional/bidirectional connections and point-to-point unidirectional connections. However, for the latter, the Multicast mechanism (Multicast) like in the IP network has not been clearly defined and verified. Therefore, for some applications, for example, video broadcast in the region where the audience is located does not have a particularly efficient way to save bandwidth.

5. Integrated Network Management

ASON provides a new network control and management platform that meets the requirements of the TMN framework. However, it does not exclude or completely replace the existing transmission network management system or the ATM network management system, when it comes to the underlying management, it also needs to cooperate with the existing management system and integrate it. In actual operation, it will produce complicated problems.

V. Conclusion

At present, various standardization organizations are accelerating the ASON standardization process, and operators have also organized ASON tests. Experts also have different understandings about the evolution trend of ASON networks. However, in any case, the emergence of ASON represents the development trend of optical network technology, it can solve problems such as fast bandwidth deployment, end-to-end configuration, and protection/recovery, and provide QoS/SLA and distributed network control capabilities. Although it has limitations in some aspects, its inherent excellent performance will surely become the first choice for operators to manage optical networks in the future.

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