DSLAM now is very important and widely used by large ISPs, one of the examples is PT Telekomunikasi Indonesia or PT. Telkom Indonesia, this device is used to connect all customers to communicate with the internet through its ISP backbone network, and it is very closely related to the ADSL modem that you have.
DSLAM (Digital Subscriber Line Access Multiplexer) is a piece of equipment that enables a DSL network. DSLAM collects connections from subscribers and forwards through the high-speed lines to the Internet Service Provider (ISP). Access from end-users via DSLAM will be centralized via BRAS.
DSLAM can accommodate many customers connected to one high-speed backbone network, both ATM switches and IP base. DSLAM provides high-speed data transmission services by utilizing existing copper cables.
In DSLAM devices, a splitter is usually installed which functions to separate voice signals and data signals, where the voice signal will go to the telephone exchange device and the data signal will be directed to BRAS via transmission media which can be in the form of E-1, STM-1 (Synchronous Transport Module-1 ) (Fiber Optic). E1 is a digital line that can accommodate 30 PSTN telephone lines. Furthermore, BRAS will be directed to each cooperating ISP.
There are two types of modulation used in DSLAM devices in speedy service configurations, namely CAP (Carrierless Amplitude / Phase Modulation) and DMT (Discrete Multitone).
CAP is a modulation technique that works by dividing the frequency spectrum contained in the speedy line into three parts, namely voice channels (ranging from 0 - 4 kHz), upstream channels (25 Khz - 188 KHz), and downstream channels (240 kHz and above). This separation is intended to minimize the possibility of interference between these channels.
While the DMT modulation technique works by dividing the frequency into 256 channels, each of which is 4,3125 kHz wide. In this modulation technique, the data rate sent to each channel can be set separately. In this way, DMT modulation can eliminate channels that experience interference or interference on the channel.
DSLAM is a device that provides simultaneous high-speed digital data services and analog telephones on the central side. In general, the components in DSLAM consist of a Backbone Interface and a Line Interface Module (LIM).
The backbone interface is the interface between DSLAM and the Switch network. Since most countries in Asia, including Indonesia, refer to the European standardization system, this interface should use the ESTI standard for 155 Mbps wherever possible.
LIM is a combined module between an ADSL modem (ATU-C) and a POTS Splitter. ATU-C in DSLAM has the same function as ATU-R, namely converting digital signals into analog signals and vice versa. POTS Splitter separates digital signal and analog telephone signal. Also, DSLAM functions to regulate data transmission, data from several subscribers will be concentrated and then transmitted to the ATM Switch, and large amounts of data from ATM will be distributed by DSLAM to each subscriber channel. ATM (Asynchronous Transfer Mode) is a switching and multiplexing technology that has a wide bandwidth and a small delay. In DSL technology, each subscriber is connected directly to the DSLAM device so that there is no decrease in customer performance if there is an additional subscriber.
The principle of DSLAM works in principle with ADSL. DSLAM separates voice signal frequencies from high-speed data traffic, and controls and routes digital subscriber line (xDSL) traffic between end-user devices, such as routers, modems, and network interface cards, and service provider networks.
DSLAM transmits digital data into the voice network (POTS). DSLAM switches voice channels (usually using a splitter) so that the signal can be sent via the PSTN, and the existing data channels are then transmitted via DSLAM which is actually a collection of DSL modems. After eliminating analog voice signals, DSLAM collects the signals coming from the end-user and combines them into a single signal and wide bandwidth, through a multiplexing process. The unified signal is transmitted at Mbps speed into the channel by the backbone switching equipment through the access network (AN), which is commonly known as the network service provider (NSP). The signal sent via the internet or another network appears again at the destination telephone exchange, where another DSLAM is waiting. DSLAM is flexible and can support various types of DSL contained in a telephone exchange, which also provides dynamic routing and IP numbering for the customer (end-user). If there is no place in the MDF or it turns out that the distance between the central government and the customer is too far, the solution is to use a mini DSLAM. This mini DSLAM can be placed on the RK between the STO and the customer.
The parameters used to determine DSLAM performance are:
- Throughput, the effective data transfer rate, measured in bps. Throughput also refers to the amount of data that can be sent at one time. It really depends on the availability of bandwidth on the network.
- Upstream and downstream speed, namely the speed when uploading and downloading.
- SNR (Signal to noise ratio), which is the ratio of the peak signal to the measured noise. The SNR value is influenced by the signal strength and the amount of noise. Roughly speaking, regardless of the signal power and noise values, the greater the SNR value, the better the quality will be obtained (it could be a large signal or a small noise).
- Attenuation (dB), namely the magnitude of the cable attenuation factor. The cable has a velocity factor that causes the length of the cable, the greater the loss. Each cable has a different value depending on the material and cable cross-sectional area. That way, the smaller the Line Attenuation value, the better.
- Output power, namely the amount of power generated from a device.
DSLAM constituent components
DSLAM consists of:
- Splitter - Low Pass Filter to pass sound bands and high pass filter to pass ADSL bands
- Customer modules can be ADSL, SDSL, VDSL, and others. For speedy services, the ADSL module is used. The ADSL module on the DSLAM side is called ATU-C, while the ADSL on the subscriber side is called LATER. ADSL Transceiver Unit - Central Office (ATU-C), performs basic multiplexing, demultiplexing, receiving, system control functions and provides interfaces for loops, transport networks as well as operating and switching systems. ADSL Transceiver Unit - Remote (ATU-R), provides an interface for local distribution used for broadband services via the service module.
Principles of Data Network Using DSLAM Device
The telephone network consists of a telephone exchange, RK (Rumah Kabel), DP (Distribution Point), and customers. At this time, PT. TELKOM not only offers voice data services (telephone) but also offers services in the form of digital data. These digital data include VoIP, IPTV, internet, etc. For this reason, a DSLAM device is needed that has the following functions:
- As a voice and data filter.
- As a DSL modulator/demodulator.
- As a multiplexer.
From this, a local network diagram can be drawn as follows:
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| Gambar Jaringan DSLAM antar gedung |
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| Gambar Jaringan DSLAM ke Pelanggan |
DSLAM Architecture
Judging from ATM DSLAM, DSLAMs and IP-DSLAM ethernet architectures typically consist of multiple xDSL or Ethernet / Gigabit Ethernet uplink cards for a basis. The line card and uplink card are connected by a high capacity backplane which can form an ATM or ethernet bridge or switch. The advantage of the latest DSLAM is that it supports many services and supports multiple DSL technologies (including ADSL, ADSL2, ADSL2 +, SDSL, and VDSL) so that this equipment supports multiplex DSL line cards.
From the traffic processing aspect, the DSLAM architecture is based on two models, namely centralized and diffuse. In a centralized model, all complex traffic processes are carried out by one central uplink card. Centralized architecture is the best architecture for large capacity centralized DSLAM. The example for DSLAM is centered on the intel IXP2400 NP. In the spread model, some or all of the complex traffic processes are processed on a smart line card based on a programmed network by a processor (Line card Traffic Processor or LTP).
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