Ideas for introducing PTN in 2G Backhaul

As a connection-oriented transmission technology, PTN draws on the characteristics of SDH technology, such as perfect protection switching, rich OAM, good synchronization performance, layer network architecture, and powerful network management. At the same time, PTN also draws on the ideas of QoS management, packet switching, and pseudo-wire technology from MPLS/Ethernet, making PTN a comprehensive transmission technology with packet switching as the core, packets as the transmission unit, and mainly carrying carrier-grade Ethernet services, and compatible with TDM, ATM and other services. The characteristics of PTN cater to the needs of 2G/3G multi-service bearing, making PTN technology favored by operators from the very beginning.

At present, when deploying PTN, operators mainly consider the application of 3G Backhaul. Usually, PTN is built independently without any interaction with the traditional SDH network. The main factors are: on the one hand, PTN is a new technology, which requires long-term verification and accumulation of various experiences in the existing network; on the other hand, PTN construction and deployment should not affect the existing network or the mature 2G network. This PTN network construction idea can achieve the rapid construction of PTN bearer network for 3G wireless services, but the new problem introduced is that two networks with different technologies, SDH and PTN, are gradually formed at the Backhual level, resulting in an increasingly large network scale and increasingly complex operation and maintenance. Another problem faced by operators is that while continuously building 3G wireless networks, there is still a large amount of expansion and supplementary construction of 2G wireless networks. Since 2G wireless is basically carried by SDH networks, the expansion and supplementary construction of 2G base stations lead to the continuous expansion of SDH networks, and operators will face the situation of building PTN and SDH networks at the same time.

In order to protect the investment of operators, this article analyzes in detail the idea of ​​introducing PTN in the 2G Backhaul scale to help operators build a unified Backhaul bearer network.

PTN and SDH interleaving network

The interleaving network of PTN and SDH is shown in the figure. PTN equipment is added to the location of 2G base station expansion and integrated into the SDH network. From the user's perspective, PTN and SDH equipment are no different and can be deployed quickly. However, for PTN equipment, if interleaving networking with SDH equipment is to be achieved, PTN equipment needs to have the following functions:

The line-side interface of PTN is changed from the commonly used Ethernet interface to the STM-N interface;

In order to ensure that services and alarms from other sites pass through the PTN node, PTN equipment needs to support AU4/TU12-level function pass-through. Since PTN equipment is based on packet switching, the equipment needs to implement AU4/TU12-level PWE3 processing (or similar function processing, there is no relevant standard), and PWE3 processing is required for E1 services above and below this site. The processing of these functions will make the SDH service line card processing of PTN extremely complicated;

On the other hand, when PTN and SDH are interleaved in the network, the line interface can only use STM-N, which is different from the Ethernet interface commonly used in PTN. As more and more PTNs are deployed, SDH is gradually withdrawn from the network. When the network evolves to a full PTN network, it is not appropriate to use STM-N as the PTN line interface. At this time, replacing the PTN line interface with an Ethernet interface will increase a lot of additional investment.

Considering various factors such as equipment complexity and network evolution, it is not recommended to use PTN and SDH interleaving networking to carry 2G base stations.

PTN and SDH group different layer networks

The schematic diagram of the network with different layers of PTN and SDH groups is shown below. In this network, PTN is located at the access layer and SDH is located at the aggregation layer.

PTN needs to have the following functions:

Most PTN nodes use Ethernet interfaces for networking and use the basic functions of PTN;

PTN and SDH adjacent nodes use STM-N interfaces for networking. The STM-N interfaces of PTN need to have the following functions:

PWE3 function of E1;

E1 to STM-N mapping and demapping function;

TU12 alarm and PW alarm conversion function;

Using PTN and SDH groups with different layer networks, the service protection method is to enable PW 1+1 protection on PTN equipment and TU12 SNCP protection on SDH equipment. Since the STM-N interface board of PTN has the PW and TU12 alarm conversion function, the end-to-end protection of E1 services can be guaranteed.

The PTN and SDH groups can be in different layer networks, with PTN at the aggregation layer and SDH at the access layer, and end-to-end protection of the service can also be achieved.

Currently, most PTN equipment is equipped with a Ch STM-N interface board. The above networking function can be realized by simply implementing the conversion function between PW alarm and TU12 alarm on the board. The equipment is not complicated to implement and is technically feasible.

On the other hand, from the perspective of network deployment, the access layer PTN + aggregation layer SDH networking mode is adopted to transform the access layer transmission network from SDH to PTN, which has little impact on the entire network business and has the possibility of engineering implementation; the access layer SDH + aggregation layer PTN networking mode is adopted, and it is recommended to build a new aggregation layer PTN. Since the number of aggregation layer equipment nodes is relatively small, it is also possible to implement the project.

Considering various factors such as equipment complexity and network evolution, it is recommended that PTN and SDH groups use different layers of networks to implement PTN carrying of 2G base stations.

summary

In line with the development trend of IP-based networks, ZTE has launched the iPTN series of new-generation metropolitan converged packet transmission equipment. This series of products adopts the architecture of the full packet switching core, integrates multi-service adaptation interfaces, MPLS forwarding technology with transmission characteristics, synchronous clock, carrier-grade OAM and protection functions, and provides users with end-to-end bearer network solutions in the context of the evolution of telecommunications services to IP. At the same time, in order to solve the coexistence and interoperability problems between PTN and traditional SDH networks, the iPTN series provides a variety of STM-N interfaces to meet various networking applications and realize the smooth evolution requirements of user networks.