From a technical development, first of all the existing cable access network must transform to digital subscriber line series of technology as the representative of the copper access technology is an important means of transformation ; HFC system and asymmetric Cable Modem is the transformation of the existing CATV network pilot scheme ; but from the point of development, optical fiber access, especially broadband optical access means supplemented by wireless access will dominate.

SDH has been widely used in the core network. At present, the bandwidth demand and technology have been shown to be necessary to SDH technology on the great advantage in access network domain, the function of SDH and the interface as near as possible to the user. Application of SDH in access network the main advantages are as follows.

(1 ) to the requirements of high reliability, high quality and large business enterprise users, SDH can provide an ideal network performance and operational reliability. This can be the direct use of SDH system in a point-to-point or ring topology form and the user is connected.

(2 ) can increase transmission bandwidth, improve management capacity, ease of maintenance and reduce operation and maintenance costs.

(3 ) the SDH inherent flexibility allows the network operator can more quickly and effectively required users to provide long-term and short-term business and networking needs. For the development of extremely rapid cellular communication system, using a SDH system is especially suitable for the rapid and flexible, can provide the required 2Mb / S transparent channel.

Of course, taking into account the access network to the cost of the high sensitivity and operating environment is bad, apply to access SDH devices must be highly compact, low power consumption and low cost of the new system. In order to make full use of the advantage of SDH SDH, need to be further extended to low bandwidth users, especially wireless users, provide 64KB / S level flexibility and can be integrated with existing and new business transmission platform.

The specific implementation method can have multiple, using STM - 0 speed connection (SUb STM 0), for the small bandwidth users is a kind of economic and effective solutions, while maintaining all the SDH management capacity and function. The ITU - T fifteenth study group has developed a new G.708. Provides two interface transmits the TUG - 2 - Zn and transmission interface sSTM TU - 12 sSTM - Ik interface.

When using sSTM Zn interface, each frame of each TUG - 2 to 108 bytes plus a 9 byte multiplex section overhead. The interface can be used for optical fiber and metal wire and wireless transmission technology. When n, l, 7 488Mb / s signal Hu ; when the N - 2 when the signal rate is 14 4Mb / S; while N - 4 when the signal rate of 28.224Mb / S.

When using the sSTM-1k interface, K value is limited to 1, 2, 4, 8 and 16, and is mainly applied to the wireless transmission technology, its rate were 2.88Mb / S, 5.184Mb / S, 9.792Mb / S, 19.008Mb / 8 and 37.44Mb / S. Because SDH access network has strong compatibility alkyl good self-healing protection ability, can form a transmission and access hybrid network, network oriented development to upgrade capacity, is conducive to the development of broadband access and other advantages, the SDH will be developed further in the access network domain to hold larger share.

The access network with the latest SDH development trend is to support IP access, at least need to support Ethernet interface mapping, in addition to carry voice business, can use some SDH net load to the delivery of IP services, so that the SDH can support IP access.

ATM based passive optical network ( APON) can be achieved by the use of ATM concentration and statistical multiplexing, combined with passive branching device for optical fiber and optical line terminal sharing function, the cost is expected to be compared with the traditional circuit exchange based PDH / SDH access system low 20% ~ 40%. Therefore, from a long-term point of view, in the face of increasingly rich and colorful multimedia services and the explosive growth of IP business pressure, APON may be a combination of ATM multiple service multiple bit rate support ability and the passive optical network transparent broadband transmission ability compared with the ideal long-term solutions, represents the twenty-first Century broadband access technology the latest development direction.

ATM - PON digital signal in the nominal bit rate 8kHZ should be integer times of its nominal speed line has two kinds: suitable for FTTCab / C / B / H 155 52Mb / s symmetry and applicable to FTTCab / C / B asymmetric rate ( 622.08Mb / s downlink, uplink 155.52Mb / s). The bidirectional transmission method to basically have two kinds, the first kind of adopts single-fiber WDM ; second using unidirectional double fiber space division multiplexing way, working in the 1310urn area, in order to make full use of the low cost of the light source. With narrowband PON difference is not using bidirectional time compression multiplexing ( TCM), mainly on account of IC rate and cost constraints factors.

APON can be used is an important factor in the price. Because APON is a passive system, so that the installation, provisioning and maintenance cost is reduced greatly. APON target price is a narrowband PON 1.5 times, but the business scope and business quality will be far superior to the band PON. Are expected to soon available, initially mainly green business, later gradually expanded to other business, be be worthy of the name of the full service access network system.

Access network with PON technology was the telecommunications industry is popular, but because the price is exorbitant, make it difficult for the operators to accept. Along with the multimedia era and the development of network convergence, which is based on ATM and APON emerge as the times require, it is further improved the traditional PON performance, and better cost-effective. Is expected in the near future, the APON will be in AN get promotion.

The use of ATM technology to transmit the MPEG - 2 signal. Realization of video on demand ( VOD) is is years ATM forum, ITU - T organizations such as a central study content, AN is also the development of another trend. The current ATM network provides two kinds of connection oriented service, constant bit rate ( CBR) and variable bit rate ( VBR), MPEG - 2 signal can be respectively to the two service access. But in the access, they have their respective advantages, at the same time are not the most ideal method. As a CBR service access to the buffer memory for smoothing, MPEG - 2 adapted to CBR business.

In theory, only when the memory capacity is large enough, the VBR MPEG - 2 could become a really smooth CBR service access. It is obviously unrealistic, but with the memory capacity enlargement, delay will increase, affecting the business in real time. While MPEG - 2 VBR service access, due to ITU on B - ISDN AALZ standard has not yet been developed and perfect, cannot use AALZ on MPEG - 2 adapter, ATM forum was prepared by AALS adapter VOD scheme, but the technology is complex, the cost is high.

Based on fiber loop ( FITL) and ATM technologies for interactive digital video access system ( SDV), is currently abroad experiment, which in addition to the traditional support voice of narrowband services, can also provide VOD, digital broadcast video services and analog broadcast video services; and, in the SDV network between different units can also be used for information flow (such as images, ATM digital package) exchange. SDV has more than HFC advantages, therefore have the potential to become the best choice to realize the interactive multimedia services, caused the telecommunications industry attention.

SDV is based on PON, FTTC and one-way HFC combination, it adopts hierarchical surface, a dimension FITL system used for the transmission of telephone and data ; another level based on the SDH ATM cell support digital video interactive broadband business, analog video access to WDM mode superposition or cable separating.