Abstract: In order to transmit the needs of multiple media on highway wide-area network, the working principle and technical characteristics of DPT technology are analyzed by contrast method. DPT technology is applied in the engineering practice of expressway networking, and DPT technology can be very It is a good solution to the needs of the highway wide area network to transmit a variety of media.
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The development of highways in China is moving from the construction of highways to the modern management of highways. The turning point is the gradual formation of highway network and the new requirements for information transmission and exchange, such as the "one card" of toll collection system. engineering. Obviously, the traditional three systems (communication systems, charging systems, monitoring systems) are not able to achieve this requirement.
Therefore, it has become an inevitable trend to establish a wide-area computer network of expressways and construct a business information system for highway traffic.
1 How DPT technology works
DPT (Dynamic Packet Transport) technology uses a completely new mechanism to transmit IP packets directly over the fiber, while its MAC layer address uses spatially multiplexed MAC addresses. The Spatial Reuse Protocol (SRP) is a media-independent MAC layer protocol that can be used on various physical layer technologies. A typical use consists of two reverse fiber optic SRP rings, each of which can be used to transmit data and transmit control signals in the opposite direction. Its working principle is shown in Figure 1.
In order to distinguish between the two rings, one may be called the inner ring and the other is the outer ring. When the SRP is running, the data is sent in one direction (downstream) and the control signal (upstream) is transmitted on the other fiber in the opposite direction. The two fibers are controlled by each other, so there are two upstream streams and two downstream streams. In this way, SRP can maximize the transmission bandwidth of the fiber. At the same time, because the control signal is not interfered by the data stream (such as queuing, sudden congestion, etc.), it can be transmitted quickly, which provides a guarantee for further optimization of the bandwidth and high-speed self-healing of the network.
Figure 1 How DPT works
Due to the media-independent nature of SRP, DPT technology can run transparently on a variety of existing critical fiber infrastructures: bare fiber, wavelength division multiplexing (WDM) or SDH point-to-point or ring. The media-independent nature also enables DPT to operate in a mixed environment of the above media, providing a solution for a smooth transition to pure IP-optimized fiber networks.
2 Features of DPT technology
Dynamic IP fiber transmission technology DPT has the following characteristics:
Spatial multiplexing: A fiber optic ring can transmit data in segments, thus providing at least twice the bandwidth boost factor.
Double-ring structure: Two fibers transmit data at the same time, which doubles the bandwidth.
Fair mechanism: All nodes have equal control over bandwidth, which provides the best guarantee for statistical multiplexing of bandwidth.
Statistical multiplexing: Network bandwidth is used in segments, and the excess bandwidth between any nodes can be used by other nodes to double the available bandwidth.
as shown in picture 2.
Figure 2 Statistical multiplexing diagram of DPT
Scalability: The number of nodes on a ring can be up to 128, the single port rate can be up to 10 Gb/s, and the geographic range can be extended to a sufficient extent like SDH.
Reliability: Provides better network self-healing capabilities than SDH's Automatic Protection Switching (APS). Not only can the fiber be switched within 50 ms, but because it is IPAw are, IP traffic can be recovered in 50 ms without re-convergence of the routing table.
IP service mapping: It can directly map and support the priority of IP packets, directly support the broadcast of IP packets and other IP service control functions.
Plug and Play: Simple ring structure and automatic discovery mechanism make the configuration of network devices very simple. For example, in a mesh network, adding 2 nodes requires 2N ports, and in a ring network, adding a node requires only one pair of ports.
Unified network management: Network management from the physical layer to the link layer to the network layer requires no different network management systems.
High-performance price ratio: Each device on an SRP ring always needs only one pair of SRP ports (in a point-to-point mesh network, each node needs N2 ports), so that the network no longer needs to add ports when the network is expanded, which greatly reduces the number of ports. Network cost. At the same time, its high reliability also greatly reduces operating and maintenance costs and increases production efficiency.
For a new generation of carrier-grade networks, DPT is an extremely important technology for a new era network infrastructure. DPT's various technical features are designed to further reduce investment and operations while ensuring high-quality services. Cost, thereby increasing production efficiency.
Taken together, DPT technology will bring the following benefits to SDH Wnet:
(1) Effective investment. The establishment of the IP fiber ring has fundamentally changed the investment structure of the highway wide area network, greatly improving the investment efficiency. For example, wide-area networks no longer need to invest in expensive time-division multiplexing (TDM) devices (such as SDH devices) to achieve the same bandwidth; at the same time, they can use spatial multiplexing and statistical multiplexing techniques for the most efficient use. These bandwidths result in higher benefits. For another example, the integrated network management method from the physical layer to the IP layer not only greatly reduces operating costs, but also greatly improves production efficiency.
(2) Enhance IP services. DPT technology directly supports and enhances various IP services, such as V oIP, video, VPN, etc., and is more stable and reliable, thus bringing more profitable value-added service profits to operators.
(3) The robustness of the network. With advanced performance monitoring, error monitoring, error location, and intelligent protection switching mechanism (IPS), the network has advanced self-healing capabilities to make IP services stable and reliable. Reliability is an important feature of high-speed fiber-optic networks; this is just like the construction of highways, while reducing crossovers, reducing traffic lights, leveling roads to increase speed and expand capacity, traffic rules are more stringent: farther safe distance, strictly prohibited Pedestrian crossing, etc., and adding emergency lanes to improve reliability. Without sufficient reliability guarantees, the network cannot “speed up†like a highway; otherwise, it will have catastrophic consequences.
(4) Fully expandable. As a key IP optimization optical technology for the new era of communication, DPT provides a continuous development path for the network with a new and more stable and reliable network architecture.
3 Using DPT technology to construct highway wide area network
In the engineering design, the DPT primary ring node and the secondary ring node can be set according to the geographical distribution and the data traffic of each point. The link between the primary ring and the secondary ring can be performed by using a ring tangent.
As the backbone network design of the highway, DPT switches are placed at the management level. The central office implements the management of each sub-center, and each sub-center implements the management of the management office within the area under its jurisdiction. The design principle should be:
The backbone network should cover the area under its jurisdiction from the geographical area. The number of nodes on the ring network should not be too much. It is mainly connected to the sub-center level and the management office under the jurisdiction of the center. The transmission rate should be chosen to be higher than the transmission rate of the secondary network.
The construction of the secondary ring network should be based on the sub-center jurisdiction and traffic configuration, and multiple secondary ring networks can be linked outside the backbone network. Finally, the entire highway is completely covered by the secondary ring network.
The transmission rate selection of the secondary ring network should be one order of magnitude lower than that of the backbone ring network. For example, if the backbone ring network is STM4, the secondary ring network should be STM1.
The application of the DPT ring network is mainly to solve the problem of chain connection of the highway network, that is, adopting a method similar to the SDH ring, which is very effective for long-distance links. However, for the network connection in the metropolitan area, the combination of IPOS and DT P can be used to construct the metropolitan area network, as the case may be. This is shown in Figure 3.
It is worth noting that the DPT double fiber ring has a similar form of link to the SDH double fiber ring, but the connotation is quite different.
(1) The function of the SDH secondary ring is to make a backup for the primary ring, that is, when the primary ring fails, it automatically switches to work on the secondary ring. Usually does not carry data, it is a "cold backup" way. The DPT ring is not. In the normal period, both the primary ring and the secondary ring participate in data transmission, which doubles the bandwidth.
When a fault occurs, the secondary loop automatically takes over the primary loop in 50 ms, which is a "hot backup" method. In this way, the transmission bandwidth of the fiber can be maximized. At the same time, because the control signal is not interfered by the data stream (such as queuing, sudden congestion, etc.), it can be transmitted quickly, which provides a guarantee for further optimization of the bandwidth and high-speed self-healing of the network.
Figure 3 Example of constructing a provincial highway network using a DPT ring network
(2) DPT technology can run transparently on existing important fiber infrastructures such as bare fiber, wavelength division multiplexing (WDM), SDH point-to-point or ring. The media-independent nature also enables DPT to run in a mixed environment of the above media, making it easy to implement different network topologies and network applications.
(3) Since the DPT ring can easily realize the access of the secondary secondary ring, the bandwidth of the network can be segmented, and the surplus bandwidth between any nodes can be used by other nodes, thereby multiplying the application. bandwidth.
(4) The DPT ring can provide better network self-healing than SDH's Automatic Protection Switching (APS). Not only can the fiber be switched within 50 ms, but because it is IPAw are, IP traffic can be recovered in 50 ms without re-convergence of the routing table.
(5) The frame format of the underlying DPT is still the frame format of SDH, but its upper interface is completely IP interface, which can directly map and support the priority of IP packets, directly support the broadcast of IP packets and the control functions of other IP services. There is a great benefit to the end IP application.
(6) Since the DPT ring supports all three layers from the physical layer to the link layer to the network layer. Different from SDH, the network management of DPT no longer needs the network management system at different levels, which realizes the end of the network!
4 Conclusion
The wide area network of the expressway must cover the charging system, monitoring system and communication system from the business. It must contain on the transmission media: data, images and audio. This requires the establishment of a highway wide-area fiber network with a broadband interface to accommodate the common transmission of the above three media. DPT technology can solve this problem well, and DPT technology will be more and more applied to highway networking because of its advantages.
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