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Saturday, March 19, 2011

Main Distribution Frame (MDF)




This article gives you a some picture of Main Distribution Frame (MDF). 
Main Distribution Frame
Jumper wire punching Tool
 


 Arrestor  is used for protect MDF  telephone connection from lightening.


punching jumper wire to MDF
 Arrestor
 
Main Distribution Frame (MDF)

Sunday, March 13, 2011

In Band and Out of band signaling


In Band signaling - In-band signaling is the sending of voice data and control information in the same voice band (300Hz to 3.4 kHz) on the same channel, as used for data.
           Ex- When we dial a number this number is encoded and transmitted across the telephone line as Dual-Tone Multi-Frequency (DTMF) tones. This tone is handed by the telephone exchange switch. Then the switch is routed the call according to the Dual-Tone Multi-Frequency (DTMF) tones. When the trunk circuits were in idle (not in use), it would have a 2600 Hz signal (single tone).A failure in the trunk circuit facility would cause the absence of 2600 Hz tone. This control toned is gone through same channel which voice data is going.

Out of band signaling - Out-of-band signaling is the exchange of call control information in a separate band from dedicated channel (as in Common Channel Signaling). Out-of-band signaling establishes a separate digital channel for the exchange of signaling information. This channel is called a signaling link. Then the signaling links are used to carry all the necessary signaling messages between nodes.
Ex- When we take a call by dialing numbers, there is a trunk selected, and other pertinent information are sent between switches using their signaling links, rather than the trunks which will ultimately carry the conversation.

Digital Transmission


The fundamental transmission concept is to transmit the minimum possible frequency or the bandwidth with maximum possible number of channels or the bit rate.
When we consider the analog transmission we can’t transmit much distance than digital transmission. Therefore we need to use small bandwidth. Using that small bandwidth can transmit much distance. Therefore we use modulation techniques to reduce the bandwidth. FDM multiplexing system is combining number of channels to convey over common transmission medium. Major advantage of analogue transmission is occupied band width is low When we use frequency modulation in low pass filter there are two, out come upper side bandwidth and lower side bandwidth. By choosing the lower side bandwidth we can reduce bandwidth of the signal.
In digital transmission we can have more than solutions compare to analog.
Theoretically we know Nyquist Theorem, it tells us relationship between bandwidth and channel capacity.

                             C = 2Blog2M
C- Channel capacity   ,    B – Bandwidth       ,    M – signal levels 

If we want increase channel capacity for a value of bandwidth need to increase signal levels.
In digital transmission we can use time division multiplexing (TDM).using this technique we can reduce bandwidth. In this TDM large numbers of channels are put into one line and transmit. . In the digital transmission can use the available bandwidth of the channel much more efficiently as compared to analogue system.

Tuesday, March 1, 2011

xDSL Family


ADSL - Asymmetric Digital Subscriber Line
RADSL - Rate adaptive Digital Subscriber Line
VDSL - Very high Bit rate Digital Subscriber Line
HDSL - High Bit rate Digital Subscriber Line
SDSL – Symmetric Digital Subscriber Line

There are some characteristics included in all of the DSL technologies. When we consider the bandwidths of these DSL technologies are depends on the length of the loop (distance to the central office from the user end). 

ADSL
In ADSL there are many versions. They are ADSL, ADSL2, ADSL2+, The Downlink and Uplink will depend on this versions. The data transfer rates downstream are much faster than the upstream data rates in ADSL.
The data rate of ADSL is highly dependent upon the distance from the Central Office (CO) to the Consumer Premises (CPE). At a distance of 9000 ft we can achieve 8 Mbps downstream and while at 18000 ft we can only get 1.544 Mbps downstream. ADSL operates at frequencies above 4 kHz, typically from 30 kHz to 1.1 MHz (Upstream is in the range from 30 kHz to 138 kHz, downstream ranges from 138 kHz, to ~1.1 MHz).

Applications
ADSL is used by home consumers and many small business owners who mainly want to download files. It is used for carrying voice, data and video at reasonable rate. We can download large data files, streaming video, audio, and multimedia from the Internet fast. But, generally, cannot upload much more than e-mail messages.

 RADSL

RADSL stands for Rate Adaptive Digital Subscriber Line. Rate Adaptive simply means that the speed of the connection is adjusted to meet the line conditions that each transmit and receive unit sees. And the upstream is 128kbps – 1Mbps and downstream 600kbps – 7Mbps.RADSL same as ADSL but the distance will increase due to adjustment of streams.

Applications
RADSL is used by home consumers and many small business owners who mainly want to download files and small uploads. It is used for carrying voice, data and video at reasonable rate.

VDSL


This is the fastest DSL technology. VDSL stand for Very high bit-rate Digital Subscriber Line. Not like other DSL technologies the capacity of the link depends on the service offering and spectrum regulations. It has 55.2 Mbps of download speed and 16 Mbps Upstream over single twisted pair. And it has 34 Mbps of download speed and upstream if the link is symmetric. It uses much wider bandwidth than ADSL IT also depends on loop condition.

Applications
VDSL is capable of supporting high bandwidth applications such as HDTV as well as telephone services (VOIP) and high quality video conferencing.


HDSL
HDSL stands for High-bit-rate Digital Subscriber Line. The main characteristic of HDSL is that it is symmetrical. That means an equal amount of bandwidth is available in both directions. HDSL can carry as much on a single wire of twisted-pair cable as can be carried on a T1 line (up to 1.544 Mbps) in North America or an E1 line (up to 2.048 Mbps) in Europe over a somewhat longer range and is considered an alternative to a T1 or E1 connection.
The primary disadvantage of HDSL is that it requires two twisted pairs of wires to operate, which increases the deployment cost for service providers. Also, HDSL does not support Plain Old Telephone Service (POTS) on the same lines as the data.

Applications
It uses for business applications, server access in large organizations and traditional T1 roles.

SDSL
SDSL Broadband provides a high-speed internet access service, with matching upstream and downstream data rates ranging from several speeds from 128kbit/s to 2Mbit/s. Unlike ADSL, it cannot co-exist with a conventional voice service on the same pair as it takes over the entire bandwidth. So using your phone line and the SDSL simultaneously is impossible. It typically falls in price between ADSL and T-1, and it is mainly targeted at small and medium businesses who may host a server on site.
Applications
Medium businesses who need to host a server on site, high quality video conferencing and multiple voice lines.