With the rapid development of mobile communication technology, 3G/LTE has moved from paper standards to reality. The development of mobile communication technology has painted a beautiful prospect for a more convenient communication life in the future. At the same time, the development of mobile communication technology has also posed some new challenges to mobile backhaul networks.

The trend of comprehensive IP based telecommunications services today is also reflected in the field of mobile communication. REL561 1MRK002496-AC mobile communication services are transforming from voice services with Time Division Multiplexing (TDM) as the core to diverse types of services such as voice and data with IP based services as the core. With the continuous advancement of 3G network IPization and the deepening of mobile data services, users have increasingly high requirements for the service perception, quality of service (QoS), and statistical reuse efficiency of 3G mobile backhaul networks. On the other hand, as the business interface of 3G networks changes from E1 interface to FE interface, the bandwidth of the business interface also shows rapid growth. In the future, Long Term Evolution (LTE) base stations may even have 1000 Mbit/s GE interface.

Figure 1 shows a schematic diagram of the evolution of mobile communication technology. Figure 1 clearly illustrates the significant increase in uplink and downlink bandwidth rates during the evolution from 2G to 3G/LTE. The increase in interface speed will synchronously lead to a surge in transmission network bandwidth. The pressure of bandwidth surge requires mobile backhaul networks to improve transmission efficiency and reduce network costs.

 

The dominant technology for mobile backhaul networks in the 2G era is the Synchronous Digital Hierarchy/Multi Service Transport Platform (SDH/MSTP), which is mainly designed for the aggregation and efficient transmission of Time Division Multiplexing (TDM) circuit services. MSTP was originally designed to address the issue of IP services being carried over transport networks. Unfortunately, this improvement is not thorough. Its IPization is mainly reflected in the user interface, but the core is still TDM circuit switching, using rigid pipes to carry packet services. This makes MSTP suffer from drawbacks such as low transmission efficiency, high cost, and poor scalability when carrying grouping services such as IP and Ethernet with variable packet length and burst traffic.

SDH/MSTP, as a meritorious technology in the 2G era, has gradually become unsuitable after the development of mobile communication to the 3G/LTE stage and will constrain the future development of mobile services. In this context, the Packet Transport Network (PTN), which integrates packet technology and SDH technology, has emerged.

1. PTN Technology Features

Based on the IPization and broadband requirements of mobile communication in the 3G/LTE stage mentioned above, the mobile backhaul network needs to have traditional grouping technologies such as efficient statistical multiplexing, flexible perception of business characteristics, and differentiated quality of service (QoS); As the carrier of telecom level services, end-to-end service management, hierarchical operation and maintenance management (OAM), and telecom level protection are the “excellent revolutionary traditions” that mobile backhaul networks hope to inherit. So, is there a technology that can combine both advantages? The answer is PTN

PTN is a connection oriented packet technology with REL561 1MRK002496-AC as its core. It has end-to-end service management, hierarchical OAM, and carrier level protection transmission characteristics. It mainly carries carrier level Ethernet services and is compatible with TDM, ATM and other comprehensive transmission technologies.

The PTN packet kernel provides a powerful elastic pipeline with statistical multiplexing capability, high bandwidth utilization, and better adaptability to the strong burst characteristics of packet services. PTN inherits the transmission network characteristics similar to SDH, powerful OAM and telecom level protection capabilities, and graphical interface network management capabilities, which can bring users a consistent experience with the mobile backhaul network

At present, PTN has two major technological options: Multi Protocol Label Switching Transport Application (MPLS-TP) [2] and Carrier Backbone Bridging Traffic Engineering (PBB-TE). The former is a downward extension of core network technology, using IP based Multi Protocol Label Switching (MPLS) technology to simplify complex control protocols and transport planes; On the basis of MPLS, in addition to connectionless features such as second to last hop (PHP), label merging, and equivalent multipath (ECMP), OAM and protection switching functions have been enhanced, providing reliable QoS and bandwidth statistical multiplexing functions. The latter is an upward extension of local area network technology, based on IEEE 802.1ah’s MAC in MAC [3] technology, which turns off the self-learning function of operator media access control (MAC) addresses, increases the configuration of network management and network control, and forms a connection oriented packet transmission technology. Currently, MPLS-TP has become the de facto mainstream choice.

At present, the MPLS-TP standard is mainly led by the two major international standard organizations, ITU-T and IETF. Since the establishment of the Joint Working Group (JWT) by the two major standards organizations in February 2008, the MPLS-TP standard has made significant progress. As of the end of February 2009, there have been 5 RFCs, 2 suggested standard documents, and 13 working group draft documents. It is expected that the release of various key standards will be completed in 2011.

Key Technologies for Applying PTN to Mobile Backhaul Networks

PTN, as a comprehensive transmission network technology with dual attributes of packet and transmission, has become the mainstream solution for IP based mobile backhaul networks in the 3G/LTE era. This is largely supported by the following key technologies.

2.1 End to end pseudo wire simulation technology

Despite the rapid development of 3G, traditional TDM services will still be a source of lucrative profits for telecommunications operators for a long time, so PTN must have multi service carrying capacity. The end-to-end pseudo wire simulation (PWE3) technology emerged to meet this requirement. MPLS-TP adopts PWE3 circuit simulation technology to adapt to all types of customer services, including Ethernet, TDM, ATM, etc., and provides end-to-end, dedicated line level transmission pipelines.

As a business simulation mechanism, PWE3’s technical essence is to encapsulate business data with a special circuit simulation message header, carrying basic business attributes such as frame format information, alarm information, signaling information, and synchronization timing information of the business data in the special message header, in order to achieve the purpose of business simulation [4]

The end-to-end services in the PTN network are shown in Figure 2. PWE3 requires the establishment and maintenance of pseudo wires (PW) in the tunnels of packet switched networks (PSN), the use of PW encapsulation to transmit business data at the operator’s edge devices (PE), and the preservation of the attributes and characteristics of the business itself as realistically as possible. For customer equipment, PW represents a link or circuit exclusively occupied by a specific business, known as a virtual circuit. The customer’s device (CE) does not perceive the presence of the core network and believes that the services being processed are all local services.