Traditionally, there should be a Central Office (CO) located nearby for telephone service provisioning. The service area is covered by many COs. However, the physical limitation of voice signal over twisted pair is 18,000 feet. In high density population region a Central Office is cost-effective, whereas in rural area, the subscribers are geographically dispersed.
Some service users are located a long way from the central office and require a very long local loop. One problem with very long loops is that the electrical signals dissipate energy as they traverse the loop, making the signals weak. In a very simplistic way, it is like a radio signal. As you go farther away from the transmitter, the weaker the signal gets, resulting in lower signal-to-noise levels. Telephone companies found two primary ways to deal with long loops: Using loading coils to modify the electrical characteristics of the local loop. The loading coil could be viewed as a low pass filter which only allows signal within voice frequency spectrum to go through. But the loading coils are not compatible with the higher frequency attributes of DSL transmissions and they must be removed before DSL service can be provisioned. Setting up some remote terminals to terminate the signals at the immediate point, then aggregates and backhauls to the Central Office. This immediate point is called Digital Loop Carrier (DLC) remote terminal for which they convert analog voice signal to digital signals on T1/E1, or fiber. The DSL transmission only be supported over contiguous wire loop. Therefore, the DSL service must terminate at the RT.
Traditional Voice phone is modulated to frequencies below 3,400 Hz. A modem with V.90 supported also was modulated within this frequency spectrum and thus the highest achievable speed was 56Kbps. Getting more bandwidth (transmitting the data more quickly) can be achieved by eliminate the 3,400 Hertz boundary. In order to do this, another modulation technique should be considered. Digital Subscriber Line (DSL) comes with idea which utilizes usage of a higher frequency spectrum of the copper twisted pairs.
The human range of audible frequencies is roughly 0~20kHz. Nonetheless, everyday speech can be adequately transmitted using only the 300 Hz-3.3 kHz range. Designing the PSTN to support only 0~4kHz greatly reduces the cost and complexity of PSTN. Since only 4k of frequency is used in the copper line, some geniuses at ITU-T asked, why not make usage of the rest higher frequency? ADSL was produced by this idea. ADSL (Asymmetric Digital Subscriber Line) is a copper-loop transmission technology that solves the bottleneck problem often associated with the last mile between NSP and user. The need for download speed is considered to be more important when ADSL standard was developed. The connection from Central office to the service user has to be a dedicated line.
As we move from the low-speed analog world to the higher-speed digital world, you can notice an important change has taken place in the topology in the CO. Whereas analog modem traffic can be carried via the telephone switch, high speed data will typically altogether bypass the switch and be processed by DLC (Digital Loop Carrier) system.
Let’s take a look at the DSL-based Service Infrastructure, we can see, at the customer premises side, a splitter and a DSL router is added, at Central office side, a DSLAM and another splitter are added. In premise side, data comes from a computer is modulated to higher frequency, voice signal from the phone remains in lower frequency, the splitter combines those signals together and sending them over a single pair of DSL line to the CO. In the CO side, there is also a splitter which divide the signals to two parts, the lower frequency from 0 to 4 kHz passes to the telephone switch system and finally get to PSTN; higher frequency goes into a DSLAM (DSL Access Multiplexer ) and finally all subscriber’s data traffic been multiplexed and transmitted to the central data network. A DSLAM can be based on IP or ATM, which are called IP-DSLAM and ATM-DSLAM respectively. This is decided by which bone network DSLAM connects to, if it’s a IP network, the DSLAM should be a IP based DSLAM; if it’s ATM network, we should use ATM based DSLAM. ZyXEL used to produce ATM-DSLAM too, however, ATM based DSLAM is not quite been deployed nowadays. And the splitter at CO side has always been built in DSLAMs.
All content & right are reserved by Netis Systems Co., Ltd
Netis is a Shenzhen Based R&D company
It has 2 Manufacturing units and 3 R&D centers in China, Taipei
Rich experience in SoHo and SMB product line.
2000 member company of which 50% members are in R&D
Netis is very focused for India Telecom and Channel retail
• We have 3 types of ADSL modem routers
– DL4201, Single port ADSL2+ Modem Router which has 1 ADSL Port
and 1 Ethernet 10/100
– DL4311, 150Mbps ADSL2+ Modem Router with 4 Ports Ethernet, out of
4 Ports Ethernet port no.4 can be use as a Ethernet WAN also.
– DL4322, 300Mbps ADSL2+ Modem router with 4 Port Ethernet with
• We have following product line in DSL Ethernet
– WF2412, 150Mbps DSL router with 1WAN 10/100 and 4Port LAN with 5dbi built in
– WF2411, 150Mbps DSL router with 1WAN10/100 and 4Ports LAN with 5dbi Fixed
– WF2419, 300Mbps DSL router with 1WAN/100 and 4Port LAN with 2*5dbi Fixed
– WF2409, 300Mbps MIMO DSL router with 1WAN10/100 and 4Ports LAN with
3*5dbi Fixed External Antenna
– WF2501, 150Mbps high gain DSL router with 1WAN10/100 and 4Ports
LAN with 1*5dbi detachable Antenna.
– WF2420, 300Mbps DSL router with 1WAN10/100 and 4Ports LAN with
5dbi built in antenna
– WF2471, 600Mbps Dual band DSL router with 1WAN10/100 and 4Ports
LAN with 4*5dbi Fixed External Antenna
– WF2405, 150Mbps Travel router with 1WAN 1USB port
– WF2710, 750Mbps dual band DSL router with 1WAN 10/100 and 4 Ports
LAN with 3*5dbi Fixed Antenna.
Wireless USB Adapters
• WF2120, 150Mbps NANO wireless USB adaptor
• WF2111, 150Mbps wireless USB adaptor with Soft AP
• WF2123, 300Mbps Wireless USB adaptor
• WF2150, dual band wireless USB adaptor
• WF2119, 150Mbs wireless USB adaptor with 5dbi external
antenna with soft AP
• WF2301, 150Mbps wireless outdoor Access Point, good
solution for hotspots / Hotel/ Education and Point to Point
wireless up to 5KM.