An integrated broadband access scheme based on SDH

1 Introduction
With the continuous decline of technology, the increasingly open telecommunications market and the explosion of data services represented by IP, the bandwidth and capacity of the network have again become hot topic and scarce resources. The backbone of developed countries, represented by the United States, is developing in the direction of ultra-high speed and large capacity, and 160gbit/s (16x10gbit/s) Wavelength division multiplexing system has been put into use. The user side of the PC speed also in leaps and bounds, but the middle of the access network still stay in the narrow band level. In order to adapt to this new situation, the broadband access technology in Access network has also presented a trend of development. The access network is extremely important to the telecom operator because it is directly connected to the end user. Faced with the trend of communication broadband, the original access network technology has begun to show a variety of unsatisfactory places, and the construction of new broadband access network has become a new topic of concern. In this case, the traditional telephone network is bound to the data business as the center, broadband and IP to feature the next generation of telecommunications network transition. The telecom business has gradually shifted from narrow-band service such as telephone to multimedia broadband service, which integrates voice, high-speed data and variable video. Faced with many access technology, how to choose the ideal solution, efficient, economic construction to meet the needs of various users of the access network is a focus of attention. The construction of broadband access network should be implemented in a phased way according to the development of society, the needs of users, the maturity of equipment and economic power. Access equipment must be flexible network, narrowband, broadband services can be connected to support future development.
2 features of integrated broadband access
This integrated access system is based on SDH. The advantages of SDH technology are brought into Access network, which makes SDH function and interface as close to users as possible is the trend of SDH development. Considering the high sensitivity of the access network to the cost and the bad performance of the operation Environment, the SDH equipment applied to access network must be a new system with high compact, low power consumption and low cost. Integrated broadband access through the V5 interface or DLC to complete narrowband access, through the insertion of different interface cards directly to the user to provide 10/100mbit/s Ethernet interface or 270MBIT/S DVB Digital Image interface, without the ATM adaptation layer can directly map the broadband services to the SDH frame, and can be half dynamic/ It is an ideal integrated broadband access solution to dynamically allocate bandwidth (NxE1 or NxT1) to meet the needs of different service interfaces, so as to effectively improve bandwidth utilization and truly realize wide-width access compatibility.
(1) based on SDH
The transmission part of this access scheme accords with the SDH system standard, and its rate, frame structure and function are consistent with STM-41. Can interconnect with any manufacturer's STM-4 or STM-6, and can also smooth upgrade to STM-4. A standard SDH branch interface. In addition to the T1 and T3 interfaces for Sonet, the E1 (2mbit/s) branch interface is also available. With 155MBIT/S optical/Electrical branch branches, the use of 155MBIT/S Optical branch disc can form light shunt. The use of 155MBIT/S Electric Branch disk multiplexing to the upper-level transmission equipment, improve system networking flexibility. In addition to being used as an access device, it can be used directly as a transmission device, which has a wide range of applications.
(2) Integrated access
Access network is a rapid development of the network, some can be used to access the technology is still emerging, who can not predict what will be the new access business, especially broadband services. Therefore, the measurement of a comprehensive access to the product quality, can not only look at its support access to the type of business, but also to see its resolution of wide/narrow compatibility technology. If the bandwidth can be allocated dynamically, no matter how the future broadband business develops, it is necessary to develop the corresponding interface disk to meet the new business requirements without making major changes to the equipment, reducing the development cycle and reducing the cost. The integrated access system uses virtual container (VC) to map the signals of different branches into STM-1. cascaded VC can map a larger data flow than a single VC, so it can use bandwidth more effectively and realize the demand for bandwidth, dynamically allocating channels. For most of the non-telecom standard broadband services, can improve bandwidth utilization. It uses the two-level multiplexing scheme, from STM-1 to E1, and from E1 to 64kbit/s at one level. When the business bit rate is greater than the E1, it is assigned multiple cascaded VC-1, and instead, one or part of the E1 is allocated. These bits are smaller than E1 and are handled in multiple 64kbit/s levels, regardless of the dynamic bandwidth allocation in cascaded VC.
(3) Network management system conforming to TMN requirements
The construction of the access network management should be based on the TMN, in the open environment, the standard management Protocol is adopted to transfer the standard management information to ensure the high adaptability and sustainable construction requirements of the network management. The TMN standardizes the management information transmitted between the network management system and the managed equipment, so long as each access network equipment provides the standard interface, regardless of its concrete implementation method, and regardless of its network mode, different access network resources can be centrally managed and unified dispatch. In the construction of Access network network management, the network management system has good adaptability and sustainability due to the technical characteristics of the network, while the TMN technology ensures the smooth transition and sustainable development of the access network management construction.
3 support for various types of access
3.1 Support Narrowband Service
In order to make full use of the advantages of SDH, SDH needs to be extended to low bandwidth users, especially wireless users, to provide flexible and comprehensive new and old business 64kbit/s level transfer platform. The implementation methods can be implemented in many ways, such as using STM-0 rate connection (sub STM-0), which is an economical and efficient scheme for small bandwidth users while maintaining all SDH management ability and function. Currently the LTU-T 15th Research group has developed a new recommendation g.708. The sstm-2n and sstm-1k interfaces are defined, in which SDH is further advanced to the user and occupies a larger share in the Access network field. The integrated broadband Access device supports narrowband access (V5 interface) and is compatible with the v5.1/5.2 research platform, and the change protocol can be upgraded. Two protocol processing schemes (end of end and end of the terminal), the user can choose according to the situation.
3.2 Support Broadband service
SDH uses virtual capacity (VC) to map different branch signals to Stm-n. In the SDH standard, the VC-1 (mapping t1/e1), VC-2 (mapping T2), VC-3 (mapping t3/e3) are adopted. cascaded VC can map a larger data stream than a single VC so that bandwidth can be used more efficiently. Another advantage of this is the ability to implement "bandwidth on Demand", which is the dynamic allocation of channels. For non-standard data rates such as Ethernet and compressed digital images, dynamic bandwidth allocation can greatly improve bandwidth utilization.
3.3 Support IP Service
The latest development trend of SDH for access network is to support IP access. At present at least need to support the Ethernet interface mapping, in addition to carrying voice traffic, you can use some of the SDH net load to transfer IP services, so that SDH can also support IP access. The Ibas device provides a two-way Ethernet interface for the user by inserting a network card as a branch disk, which works in duplex or Half-duplex mode. The bandwidth required for Ethernet interfaces can be flexibly allocated by the system (NX2MBIT/S).
Combined, the integrated broadband access system has the following advantages:
(1) The narrowband access and broadband access are considered synthetically. In addition, it solves the IP access more perfectly, realizes the integrated access of voice, digital TV and multimedia service.
(2) based on SDH, because SDH technology is very mature, can provide reliable service.
(3) Can increase the bandwidth, improve network management ability, reduce maintenance work, reduce costs.
(4) for GSM system, it can provide 2mbit/s transparent channel flexibly.
(5) can easily upgrade and expand capacity, for smooth transition to FTTH ready.