Brief Introduction to DCME 
　　Digital Circuit Multiplication Equipment， abbr. DCME， integrates DSI, VBR, LRE technologies and any other effective transmission technologies to highly multiply the traffic capacity of digital circuits.  There are two ways for quick transmission: I. to broaden the road, such as building cables,  adopting more advanced Modem, etc. ； II. remove the redundant part of the signal resources, so as to condense the signals and enlarge the load capacity. DCME applies the second way. 
　　The second way can still be divided into PCME and DCME. The former adopts block encoding combined with RE technology, such as IP-Phone. It can complete the block exchange via node router/ exchange, which demands totally one coding/ decoding only, applicable for voice coding technologies with low speed, such as the 6.3/5.6Kbit/s in ITU-T G.723. However, PCME's disadvantages are its large time delay----it takes time to pack, discharge, fill and exchange voice and decode LRE, and echo offset must be set in the gateway. In addition, for OO block voice, dozens and even hundreds greater treatment capacity is required to exchange the router or block exchange than the time slot-based circuit exchange. So the IC technology with higher speed and larger capacity are necessary to reduce the cost.
　　DCME  can complete the real-time transmission via the permanent or dynamic virtual circuit, whose main tem delay come from the LRE coding/ decoding with more advantages than PCME. In addition, there's no need to change the  existing circuit exchange or transmission equipments. So it is widely used.  

DCME's application
　　In China, DCME has been in use in the national circuits of the Beijing and Shanghai import & export offices since late 1980s. In the following ten years, the five times of expansion of the satellite circuit promoted the increase of the number of DCME. In 1997, with the development of DCME-6, DCME began to enter the digital microwave, mobile telecommunication and  circuit leasing markets. Now the 8～16 multiple DCME is mainly used in satellite circuits with the time delay over 10ms，while  4～6 multiple DCME with the time delay below 10ms is applied in the mobile telecommunication, such as the DCME-6 developed by NUPT.

DCME technology' s developing trend
　　DCME's standardization is a subject of SG-15（tranmission network, system and equipment）. In 1988,the G.763 frame suggestion was created. In 1994, the complete  G.763 suggestion cam into being， i. e. "ADPCM（ G.726） and DSI-based DCME". In 1998,  G.767 suggestion was put forward, which extended the voice compression in G.763 from ADPCM（G.726）to LD-CELP（G.728）. In April 2000，the DCME solutions with CS-ACELP method （G.729） was discussed. And the new suggestion G.768 in the future. "8Kbit/s CS-ACELP, DSI and fax modulation/re-modulation technology-based DCME"
　　In the DCME suggestions of ITU-T，G.763 is a basic one. The DSI technology can increase the circuit benefit by 2.5 times, and the low-speed coding technology can get 32K/16K/8Kbit/s voice coding speed, whose coding is defined by ITU-T G.726（ADPCM），G.728（LD-CELP），G.729（CS-ACELP）.  In G.729 appendix D, the 6.4 Kbit/s method is provided. All of the above counting methods are advisable. In addition, to avoid the block-up in rush hours, the  VBR technology is recommended. 32/24/16Kbit/s in ADPCM. We can see the complicated data treatment technology is applied in DCME. 
　　The combination of DSI and LRE technology will gain a 5～20 multiple benefit increase in voice transmission. 
　　To overcome the shortcoming of LRE counting method, ITU-T recommended G.766--- demodulate the fax signal in DCME, transfer its Modem signal at the rate of below 14.4 Kbit/s， and then readjust it to 64 Kbit/s FAX signal at the far end. 
　　DCME's Modem signal transfer depends on the 40 Kbit/s channel with ADPCM G.726 or LD-CELP appendix J method, which is applicable for Modem speed≤14.4 Kbit/s。
　　For the V.34 high-speed Modem， which is not applicable for compression coding, the G.711/G.712 A/μ rate PCM method is applied by way of direct transparent transfer with the original 64 Kbit/s.

Challenge and trend of DCME 
　　DCME's application in ground network faces the challenge of the  DWDM technology, which multiplies the fiber optical transfer capacity by tens with lower cost than DCME. DCME's application climax in circuit leasing is due to the separation of the China Telecom and China Mobile, which leads to great benefit and higher cost of the circuit leasing.  
　　When the circuit leasing cost falls to a certain degree,  DCME's ground application will be limited. However, in terms of satellite and wireless broad-band network, due to the the limited channel opening （compared with fiber optical, wireless channel is an open but not closed channel） and band width, DCME technology has still some market share. And the PCME with IP grouping and opposite instruction to the computer network and multimedia communication development will be developed to promote the router technology to higher speed and larger capacity and lead to the combination of the computer and communication technology, until its performance-cost ratio falls to the real-time voice circuit exchange technology level.