Application of GMPLS in control plane of Automatically Switched Optical Network

This article first introduces the overall structure of the ASON Control Plane, then compares GMPLS with MPLS, and finally focuses on the specific application of gmpls in the ason Control Plane.

I. ASON Control Plane Overview

1. Reasons for introducing a control plane

As mentioned above, the reason why the ASON network becomes an intelligent optical network is that it can dynamically allocate optical channels according to customer needs. The implementation of this capability depends on the switched connection introduced in the ASONN network ). In ASON, connections are not all static and fixed connections implemented by management control, but are divided into three types: Exchange connection, permanent connection provisioned connection) and soft permanent connection soft-permanet connection. The difference between the three connections lies in the different components that play a major role in connection establishment. The initiation and maintenance of permanent connections are completed by the management plane, and the routing messages and command messages for specific services in the transmission plane are also sent by the management plane, the control plane does not work in a permanent connection. Exchange connections are the opposite of permanent connections. the initiation and maintenance of such connections are completed by the control plane. The control plane uses the user network interface UNI to receive user requests, after processing, the request is provided with a specific optical channel that can meet the user's needs in the transfer plane, and the results are reported to the management plane; the management plane does not play a direct role in the connection establishment process. It only receives the connection establishment message from the control plane. The soft permanent connection is between the above two connections, and its establishment and removal requests are also sent by the management plane, however, the configuration and operations on specific resources in the transfer plane are completed by issuing commands on the control plane.

From the above analysis, we can see that the introduction of exchange-type connections makes the ASON network a real exchange-Type Intelligent Network. It is precisely because of the exchange connection that the ASON network can generate proper optical channels according to user requirements. This capability is closely related to the control plane in the ASON network. This is why the control plane is introduced.

2. control plane structure

The ASON network control plane is essentially an IP network that can control the lower-layer transmission network. Therefore, it conforms to the standard IP network hierarchy. A hierarchical model can be divided into multiple management domains. A management domain can be divided into multiple subdomains. Of course, a management domain can only have a single subdomain). Each subdomain can contain multiple subnetworks. Communication between different management domains, and between different sub-domains of the same management domain is through the external network-network interface E-NNI) to exchange information, and different sub-networks in the same sub-domain through the internal network-network interface I-NNI) to exchange information. The customer and the control network communicate information through UNI.

Ii. Comparison between GMPLS and MPLS

GMPLS and MPLS are two confusing technical terms. It is easy to confuse the application of GMPLS in the control plane with that of MPLS in the data plane. Although GMPLS evolved from MPLS, its application in the control plane is quite different from MPLS.

In essence, MPLS is designed only for group switching networks. The advantage of MPLS technology is that it can provide traffic engineering capabilities and stronger transmission capabilities that traditional networks cannot provide.

A major difference between GMPLS and MPLS lies in their different functional points. MPLS focuses on data stream transmission, while GMPLS focuses on connection management. This type of connection management allows specific management of the data plane, and the data plane can also include an interface with group switching enabling packet switcble) and an interface without group switching enabling. Furthermore, such interfaces without group switching capabilities can be divided into time division multiplexing enabling time division multiplex capable), wavelength switching enabling LSC: Lambda Switch Capable) FSC: Fiber-Switched Capable.

Another difference between MPLS and GMPLS is that MPLS needs to establish a label switching path LSP between a pair of routers), while GMPLS only needs to exchange the router LSR in any two similar labels) you can create an LSP between them. That is to say, in GMPLS, the range of the LSP endpoint device is extended from the vro to multiple marked exchange vrouters. For example, we can create a time-division multiplexing LSP between two SDH/SONET plug-ins ADM), or create an LSP Between Two Wavelength switches, a fsc lsp can be formed between two optical fiber exchange systems.

GMPLS also allows an LSP to be nested in another LSP to form a layer of LSP. This capability enables the GMPLS network to have better scalability.

Iii. Application of GMPLS in ASON Control Plane

1. Plane Control Function

GMPLS is mainly used in ASON Control Plane. An ASON Control Plane must have multiple functions, of which three are the most basic. They are:

· Resource discovery: provides the ability to automatically discover resources available in the network;

· Routing control: Provides routing capabilities, topology discovery capabilities, and traffic engineering capabilities;

· Connection management function: Use the features mentioned above to provide end-to-end connection services for different businesses.

Specifically, connection management can be divided into several different operations, such as connection establishment, deletion, modification, and query. The connection establishment operation allows you to establish an end-to-end connection (LSP) through UNI. The connection deletion operation allows you to delete an LSP that is no longer needed. The connection modification operation allows you to change the attributes of an existing LSP, you can change the attribute values that are not suitable for the LSP without affecting the normal operation of the existing LSP. The connection query operation allows you to obtain the attribute values of the LSP.

In addition to the above basic functions, as the existing optical network has higher and higher requirements on network survivability, it also requires the control plane to have good connection protection and recovery functions.

2. control plane service

The introduction of control plane allows optical networks to provide services that traditional networks cannot provide in multi-vendor environments. These services include the provision of end-to-end connections, the implementation of automatic traffic engineering, the implementation of mesh network protection and recovery, and the provision of optical Virtual Private Network (OVPN.

End-to-end connection is a basic service provided by the control plane. After the control plane is introduced, the connection establishment time can be greatly shortened from several hours or even days to only a few seconds), and no need to manually search which port or time slot is available, you do not need to manually configure the cross-connection devices in the node. All these devices are automatically completed by the control plane. Now, the operator only needs to determine the parameters required for the connection, and upload these parameters to the input node through graphical user interface GUI or command line. After the input node receives the connection parameter passed by the user, It can automatically determine the path of the entire path and use the signaling to automatically establish an end-to-end path.

We can not only see the process of establishing end-to-end connections, but also the user's ability to establish real-time connections to the optical network through the UNI interface. This is the bandwidth request on demand (bandwidth on demand) service. This capability of on-demand bandwidth requests is especially suitable for IP networks with sudden business characteristics.

In addition to the above services, OVPN is also a service that gives users great flexibility. It enables users to manage their own networks. However, OVPN is essentially a logical network. Its Introduction enables users to manage their own networks and shields users from the actual network conditions. This greatly reduces the complexity of operator operation management while taking into account the security needs. OVPN will undoubtedly be a promising service in the future.

3. control plane protocol

To achieve the above functions of the ASON Control Plane, we must use a series of public protocols to use public protocols because they ensure the interoperability of different vendors ). Among these public protocols, GMPLS occupies a very important position. GMPLS extends MPLS from the functional plane to support communication systems based on non-group switching interfaces. GMPLS first defines several general tags that can be used to establish an LSP between non-group exchange lsrs. These non-group exchange LSR can be SDH/sonet adm, digital Crossover Connector, dense wavelength division multiplexing system, or Optical Crossover Connector. These generic markup objects include generic markup requests, generic markup, explicit markup control, and protection markup. General tags can be used to represent time slots, wavelengths, wavelength bands, and space division multiplexing locations.

In addition to defining the general tags above, GMPLS also defines new features for LSP for implementing non-group switching, including upstream recommendation tag, tag group, and bidirectional LSP creation. These functions are not available in MPLS. The establishment of two-way LSP helps to shorten the connection establishment time and accelerate protection and recovery when a fault occurs. Bidirectional LSP is especially important for circuit switching networks.

4. signaling protocol

The signaling protocol is also an important issue in the ASON Control Plane. There are currently two widely used signaling protocols, one is the Label Distribution Protocol CR-LDP based on restricted Routing: Constraint-based Routing-Label Distribution Protocol ); another is the Resource Reservation Protocol RSVP-TE Based on Traffic Engineering expansion: Resource Reservation Protocol-Traffic Engineering Extension ). Both protocols can carry all objects defined in the GMPLS protocol, but there are many differences between the two protocols, so there are many differences in the specific implementation. Now, IETF has two different teams to work on these two aspects.

The signaling protocol is used to complete the connection operation task. Specifically, LSP must be created, deleted, modified, and queried. In addition to the two main signaling protocols, lightweight signal protocol is also being developed for the protection and recovery of optical networks ).

5. Traffic Engineering expansion of the Routing Protocol

According to the previous analysis, GMPLS and Related Signaling Protocols can be used to complete the connection management function. The control plane not only contains signaling functions, but also functions such as routing and Automatic Topology discovery. Therefore, in addition to signaling protocols, other protocols are required to complete other functions in the ASON Control Plane.

Currently, routing protocols are run in many circuit switching networks. For example, in the section data communication channel of SONET, the Inter-Domain system IS running-IS) protocol. These traditional circuit switching networks run routing protocols for network topology discovery and transmission of operational communication data packets. Adding or removing a node in the network changes the network topology, and the information about this topology change can be transmitted to each related node in the network through the routing protocol. Therefore, the routing protocol is used to transmit signaling messages and Topology resource messages. However, a major disadvantage of the traditional routing protocol is that it does not support traffic engineering.

It should be noted that the concept of Traffic Engineering has different meanings for the group switching network and circuit switching network. Generally, the overall goal of a traffic project is to maximize network resources and usage. For a group switching network, the goal is to minimize the packet loss rate and latency and maximize the output; for a circuit switching network, the traffic engineering goal is to achieve the highest resource utilization and channel reliability.

This article mainly considers the traffic engineering of the circuit switching network, so that its goal is to select the optimal channel in real time based on user requests. Here, the parameters of the traffic engineering include the link reuse capability, maximum and minimum bandwidth capacity, shared risk link group support capability, protection support capability, and traffic engineering matrix.

The main difference between a routing protocol with traffic engineering capabilities and a traditional routing protocol is that the former periodically sends an optional packet in the network, this Optional package contains available resource messages and traffic engineering parameter information. When the Network Element in the network receives this Optional package, it should be able to use the information carried in this package for optimal route computing.

Therefore, we can conclude that the routing protocol with traffic engineering capabilities should support resource discovery, topology discovery, and traffic engineering capabilities. Similar to the signaling protocol, there are also two widely used extended routing protocols. This IS the IS-IS protocol supporting traffic engineering and Open Shortest Path Priority Protocol OSPF ). Similarly, there are two different groups in IETF to standardize the work.

6. Link Management Protocol

In order to correctly communicate the GMPLS mark indicating cross-connection between network elements, the correct connection port must be identified between network elements. This function is implemented through The Link Management Protocol LMP. In addition to confirming the correct connection between networks, LMP also provides functions such as link binding, resource information discovery and reporting. These features help achieve network scalability and scale. LMP is applicable to any network type, especially optical networks.

Iv. Conclusion

The introduction of control plane has greatly changed the optical network. GMPLS is the core protocol for implementing the ASON network control plane. It provides a new method for building optical networks. It not only provides multi-level, multi-vendor control plane interoperability, but also makes the emergence of new types of services possible. Moreover, due to the emergence of GMPLS and ASON Control planes, operators no longer have to spend a lot of manpower and material resources on Link Management. The ASON Control Plane also supports automatic network traffic engineering, automatic network topology discovery, and automatic business discovery. In addition, the ASON Control Plane supports multiple protection and recovery solutions with the support of GMPLS. In short, the emergence of GMPLS and ASON Control planes is a revolutionary advance in optical networks.