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No. 38/2009 (Nov. 16, 2009)
Revival after the ratification of the 802.11n standard. Adoption of the 802.11n standard in September this year encouraged manufacturers to launch products based on the approved protocol.
Atheros Communications, appreciating the importance of mobile devices, released on the market AR6003 chipset for cellular phones and smartphones. With module size of 5x5 mm, it consumes 20% less energy than previous models, being more efficient. The chipset allows to operate in 802.11a/b/g/n.
Although the rapidly increasing use of n standard in laptops, its real introduction to the mass market may be the application of the new technology for the Microsoft Xbox 360 console (release on November 10th).
Another example of development is the implementation of wireless networks for multimedia transmission based on 802.11n. Within two years, Cisco Systems and Verizon communications will deploy a campus-wide wireless network including over 6 thousand 802.11n access points located in 256 buildings of Purdue University's West Lafayette campus, Indiana. It will enable the students to use mobile collaborative technologies and applications, including video and voice over IP. So far, there have been installed over 600 access points.
The sign of rising popularity of a new technology are applications in household gadgets. An example of such a device can be eStarling photo frame, allowing to exchange images wirelessly in 802.11n standard.
Atheros Communications, appreciating the importance of mobile devices, released on the market AR6003 chipset for cellular phones and smartphones. With module size of 5x5 mm, it consumes 20% less energy than previous models, being more efficient. The chipset allows to operate in 802.11a/b/g/n.
Although the rapidly increasing use of n standard in laptops, its real introduction to the mass market may be the application of the new technology for the Microsoft Xbox 360 console (release on November 10th).
Another example of development is the implementation of wireless networks for multimedia transmission based on 802.11n. Within two years, Cisco Systems and Verizon communications will deploy a campus-wide wireless network including over 6 thousand 802.11n access points located in 256 buildings of Purdue University's West Lafayette campus, Indiana. It will enable the students to use mobile collaborative technologies and applications, including video and voice over IP. So far, there have been installed over 600 access points.
The sign of rising popularity of a new technology are applications in household gadgets. An example of such a device can be eStarling photo frame, allowing to exchange images wirelessly in 802.11n standard.
Wi-Fi photo frame equipped with wireless module supporting n standard
(Source: eStarling)
(Source: eStarling)
Views from a television tower - where is it? Till 1868, the city seen from the television tower was called Edo. It is now one of the largest cities in the world and the nation's capital.
The pictures were taken from the television tower built in 1958. It is about 13 meters higher than the Eiffel Tower, reaching 333 m, but weighting only 4000 tons (Eiffel Tower weights 7000 tons). The tower is used as radio and television transmitter and also as observation platform. So far, it has been visited by more than 150 million people.
Where is the tower? You can find out at the end of this issue.
The pictures were taken from the television tower built in 1958. It is about 13 meters higher than the Eiffel Tower, reaching 333 m, but weighting only 4000 tons (Eiffel Tower weights 7000 tons). The tower is used as radio and television transmitter and also as observation platform. So far, it has been visited by more than 150 million people.
Where is the tower? You can find out at the end of this issue.
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Till 1868, the city seen from the television tower was called Edo.
What is its name today? - The answer at the end of the Newsletter.
MAC layer - a few words on WiFi - part 12. During CFP (Contention Free Period), the PCF (Point Coordination Function) uses Polling method to choose the station having the right to broadcast information.
Stations wishing to transmit data without collisions must send the appropriate query to the PC (Point Coordinator). The queries are sent in DCF (Disturbed Coordination Function) mode. If the PC accepts a query, the station is inserted into PL (Polling List). The PC calls for stations to broadcast according to the list, by sending CF-Poll frames.
Stations wishing to transmit data without collisions must send the appropriate query to the PC (Point Coordinator). The queries are sent in DCF (Disturbed Coordination Function) mode. If the PC accepts a query, the station is inserted into PL (Polling List). The PC calls for stations to broadcast according to the list, by sending CF-Poll frames.
At the beginning of each CFP, the PC checks the occupancy of the channel. If during the PIFS (PCF Interframe Space) period the channel is free, the PC sends a management frame - Beacon.
Based on the parameters contained in the Beacon frame, the rest of the stations set NAV (Network Allocation Vector). Thanks to that, during CFP (Contention Free Period) no station will compete for the control of the medium. After the SIFS (Short Interframe Space) time, from the moment the Beacon has been sent, the PC sends one frame out of the following: Data, CF-Poll, Data+CF-Poll, CF-End - to the station that is the first one on the PL (Polling List). The station after receiving one of these frames has the right to send one MPDU (MAC Protocol Data Unit), after the SIFS period.
If the CF-Poll frame requires to confirm proper packet reception - ACK ( Acknowledgment ) - the station must send the Data+CF-ACK frame.
Once the transmission is successfully completed by the station, the PC successively repeats this procedure for the other stations on the PL. If the station received the CF-Poll frame but has no frame to transmit, it should send null frame in response (unless it is necessary to send confirmation to the CF-Poll frame - then the station should respond with CF-ACK frame).
Lack of response from a station to the broadcast query for the duration of SIFS period causes that the medium is again under the control of the PC which asks the next station from the PL. Completion of the PL list is signaled by the PC through transmission of either CF-End or CF-End+ACK frame, the latter in the case of additional confirmation of correct reception of the frame.
After that, all stations belonging to the BSS (Basic Service Set - a group of logically connected wireless devices) can clear their NAVs and - after DIFS (DCF Interframe Space) time - they may begin to compete for access to the channel.
Based on the parameters contained in the Beacon frame, the rest of the stations set NAV (Network Allocation Vector). Thanks to that, during CFP (Contention Free Period) no station will compete for the control of the medium. After the SIFS (Short Interframe Space) time, from the moment the Beacon has been sent, the PC sends one frame out of the following: Data, CF-Poll, Data+CF-Poll, CF-End - to the station that is the first one on the PL (Polling List). The station after receiving one of these frames has the right to send one MPDU (MAC Protocol Data Unit), after the SIFS period.
If the CF-Poll frame requires to confirm proper packet reception - ACK ( Acknowledgment ) - the station must send the Data+CF-ACK frame.
Once the transmission is successfully completed by the station, the PC successively repeats this procedure for the other stations on the PL. If the station received the CF-Poll frame but has no frame to transmit, it should send null frame in response (unless it is necessary to send confirmation to the CF-Poll frame - then the station should respond with CF-ACK frame).
Lack of response from a station to the broadcast query for the duration of SIFS period causes that the medium is again under the control of the PC which asks the next station from the PL. Completion of the PL list is signaled by the PC through transmission of either CF-End or CF-End+ACK frame, the latter in the case of additional confirmation of correct reception of the frame.
After that, all stations belonging to the BSS (Basic Service Set - a group of logically connected wireless devices) can clear their NAVs and - after DIFS (DCF Interframe Space) time - they may begin to compete for access to the channel.
Example of frame exchange between PC and two stations (STA A, STA B) during PCF period
It turned out that PCF (Point Coordination Function) is not good for real time transmission. During TBTT (Target Beacon Transmission Time) the PC has to wait for a free medium (listening) at least for PIFS time, before starting the Beacon frame. If the medium is busy near TBTT, the Beacon frame is postponed, causing delay in the transmission till the next CFP.
The length of transmission required by the stations on the PL is unknown to the PC. MSDU frame of any station may be too long and will be divided into fragments of a specified length. In addition, the time of MSDU transmission is not controlled by the PC, due to different modulation and coding schemes used in 802.11. To ensure QoS (Quality of Service), the privileged transmissions would require prioritization. Such diversification of services is not provided in the PCF.
In the next issue we will tell a little about QoS.
The length of transmission required by the stations on the PL is unknown to the PC. MSDU frame of any station may be too long and will be divided into fragments of a specified length. In addition, the time of MSDU transmission is not controlled by the PC, due to different modulation and coding schemes used in 802.11. To ensure QoS (Quality of Service), the privileged transmissions would require prioritization. Such diversification of services is not provided in the PCF.
In the next issue we will tell a little about QoS.
Which amplifiers for DVB-T? To amplify signals in large antenna systems one requires channel amplifiers - this also applies to the DVB-T installations.
The spectrum of DVB-T signal differs from the spectrum of a single analog channel, which is presented in the following figures. The challenge for the amplifier to increase the level of the DVB-T signal is well visible there. Due to steep slopes and use of subcarriers in the whole width of the channel (usually carrying a whole multiplex), the key parameters of the amplifier become flat gain across the channel and selectivity.
The spectrum of DVB-T signal differs from the spectrum of a single analog channel, which is presented in the following figures. The challenge for the amplifier to increase the level of the DVB-T signal is well visible there. Due to steep slopes and use of subcarriers in the whole width of the channel (usually carrying a whole multiplex), the key parameters of the amplifier become flat gain across the channel and selectivity.
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The spectrum of analog PAL signal (www.allinon.com) | The spectrum of DVB-T signal (www.wikipedia.org) |
DIPOL recommends to use renown Alcad channel amplifiers. The ZG-421 R905039 amplifiers are tuned to ordered channel and feature perfect selectivity, high gain (53 dB) and a very large output level (120 dB) which allows to feed up to 200 subscriber outlets. The R905039 amplifier ensures proper amplification of all subcarriers of the digital signal.
Channel amplifier Alcad ZG-421
Comparison of frequency characteristics of ZG-401 and ZG-421 amplifiers
The ZG-421 R905039 amplifiers allow to equalize levels of signals in different channels, and due to perfect selectivity, can be used in systems that operate adjacent channels.
Modern outdoor color camera with IR illuminator - n-cam 210 + IR. n-cam 210 + IR camera is equipped with highest quality 1/3'' CCD Super HAD II sensor from SONY, being an improved version of SONY CCD Super HAD. SONY Super HAD II provides much better results than the predecessor - mainly in low-light conditions, where the new sensor ensures better colors and higher sensitivity.
Comparison of images from two cameras: on the left - CCTV camera equipped with CCD SONY Super HAD;
on the right - CCTV camera with CCD SONY Super HAD II.
Source: http://www.sony.net
on the right - CCTV camera with CCD SONY Super HAD II.
Source: http://www.sony.net
High quality SONY sensor, very good sensitivity (0.01 lx) and resolution (420TVL) make the n-cam 210 + IR camera the market leader within its price range. The built-in lens of 6 mm focal length ensures viewing angle of 45o. The images obtained from the camera reflect the actual colors and allow to see small details, the edges of objects are sharp. The camera is very well prepared for operation in difficult lighting conditions. Due to high sensitivity of the camera, color images are free of "snow" even in relatively low lighting.
The built-in IR illuminator allows operation even in complete darkness. It switches on automatically when light intensity falls below 3 lx, and the camera continues operation in B/W mode. The range of IR lighting (according to the manufacturer) is 25-30 meters and may be shorter in specific conditions (e.g. in fog).
The set includes bracket for mounting the camera on a ceiling or wall. The cables can be hidden inside the bracket. The camera can operate outdoors (IP66). It is equipped with cables terminated with standard connectors: video - BNC, power - 2.1/5.5 socket.
The built-in IR illuminator allows operation even in complete darkness. It switches on automatically when light intensity falls below 3 lx, and the camera continues operation in B/W mode. The range of IR lighting (according to the manufacturer) is 25-30 meters and may be shorter in specific conditions (e.g. in fog).
The set includes bracket for mounting the camera on a ceiling or wall. The cables can be hidden inside the bracket. The camera can operate outdoors (IP66). It is equipped with cables terminated with standard connectors: video - BNC, power - 2.1/5.5 socket.
n-cam 210 + IR camera is equipped with highest quality 1/3'' CCD Super HAD II sensor from SONY,
being an improved version of SONY CCD Super HAD
being an improved version of SONY CCD Super HAD
Internet transmissions - video learning and videoconferencing. Using cheap cameras with excellent image parameters and very sensitive microphones: PiXORD P405 K1133, PiXORD P405W K1134, PiXORD P405M K1135, PiXORD P405MW K1138, PiXORD P410 K1231 - one can easily perform video and audio streaming in the Internet. The cameras can be used for remote monitoring, videoconferencing, and live transmitting of training courses, lectures, etc. (e-learning).
Such an installation is independent of any communication software (like Skype) and offers better video quality than web cameras (e.g. PiXORD P405M and PiXORD P405MW cameras ensure resolution of 1280 x 1024 pixels), being easy to configure.
Such an installation is independent of any communication software (like Skype) and offers better video quality than web cameras (e.g. PiXORD P405M and PiXORD P405MW cameras ensure resolution of 1280 x 1024 pixels), being easy to configure.
Example of using CCTV cameras for remote monitoring, video-conferencing or e-learnig
12 questions for those who plan to build CCTV installation - part 5. In this part of the 12 questions, we raise very important issues concerning the construction of CCTV systems. These are: defining the rights of access to the system, so that every user could fully execute them - but only at the assigned level, and the optimum setting of image parameters in order to maximize the effectiveness of the system.
8. What is the anticipated method of system control?
It is indispensable to determine the place of control post and the hierarchical structure of control rights for the staff, such as access to the images from the cameras, to the archive, to setup functions etc. It is strongly advised to block all functions that are not used in normal operation of the system.
9. What should be the resolution/s (detail) and frame rate/s (smoothness) of the images?
Insufficient parameters of cameras do not allow to achieve the goals of video monitoring, while excessive performance of the equipment will cause unnecessary costs and possible overloading of the system. Generally, except very dynamic environments, it is more important that images are more detailed than captured at higher frame rates, because even a single high-resolution frame can usually provide more information than a long series of blurred images.
A new potential of IP CCTV cameras from ACTi - Event Handler. Traditional CCTV cameras are passive devices - they can "see" but cannot act. ACTi Event Handler transforms set of ACTi IP cameras into active partner of the security system. Event Handler is a software package that is built into the firmware of ACM camera series. Some functions of the package are very innovative - not available in any other similar devices! What's important, the users of existing ACTi cameras of the series can download and install the new software for free.
What is in fact the Event Handler?
The Event Handler is an interface between events and responses, observing the rules easily programmed by the user.
When something happens at the camera point: someone passes by, a door opens, a fire breaks out, or there is a change in lighting - these are the events (or triggers). For each event, the user may assign any rule that can change operating parameters of the video surveillance system, providing the desired response. As an example, motion in the area of detection may increase the camera resolution and frame rate. Or the switching into night mode can trigger uploading of pictures to an ftp server and increase of contrast level.
An interesting solution is the ability to control parameters of another camera. For example, an event activating alarm input of camera 1 may cause that camera 2 (PTZ) will change the monitored area, going to the previously programmed position.
The new firmware for ACTi cameras is available HERE
Below there are shown available operation combinations of the Event Handler.
What is in fact the Event Handler?
The Event Handler is an interface between events and responses, observing the rules easily programmed by the user.
When something happens at the camera point: someone passes by, a door opens, a fire breaks out, or there is a change in lighting - these are the events (or triggers). For each event, the user may assign any rule that can change operating parameters of the video surveillance system, providing the desired response. As an example, motion in the area of detection may increase the camera resolution and frame rate. Or the switching into night mode can trigger uploading of pictures to an ftp server and increase of contrast level.
An interesting solution is the ability to control parameters of another camera. For example, an event activating alarm input of camera 1 may cause that camera 2 (PTZ) will change the monitored area, going to the previously programmed position.
The new firmware for ACTi cameras is available HERE
Below there are shown available operation combinations of the Event Handler.
The Event Handler flow chart
- 3G repeater Signal 3G-500 A67100 solves problems with low signals in 3G networks (1920-2170 MHz). With low signals, connectivity would be impossible or limited to lower rates (GPRS, EDGE).
Application: hotels, boardinghouses, industrial buildings, underground parking lots etc. - DCS repeater Signal DCS-500 A67120 solves problems with low signals in DCS networks (1710-1880 MHz). Application: hotels, boardinghouses, industrial buildings, underground parking lots etc.
DIPOL also offers the following GSM repeaters:
Tokyo. The construction of the Tokyo Tower is modeled on the Eiffel Tower. The tower performs a similar, iconic function as its Parisian precursor. Currently, the Tokyo Tower is the highest building in the city, but in 2011 it will be outstripped by the 610 meters high Tokyo Sky Tree.
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The construction of the Tokyo Tower is modeled on the Eiffel Tower
We have written about:
ULTIAIR employed by a city's ISP. The investor, Internet service provider in Krakow, required high performance and reliability of radio links, with high throughput in the whole backbone network. The main goal was broadband (30 Mbps) wireless connectivity to the central node and between the root node and branch nodes scattered in Nowa Huta district. The contractor, Zax.pl, has chosen ULTIAIR devices...
- archive DWR of Feb. 2, 2009
ULTIAIR employed by a city's ISP. The investor, Internet service provider in Krakow, required high performance and reliability of radio links, with high throughput in the whole backbone network. The main goal was broadband (30 Mbps) wireless connectivity to the central node and between the root node and branch nodes scattered in Nowa Huta district. The contractor, Zax.pl, has chosen ULTIAIR devices...
- archive DWR of Feb. 2, 2009
How to share a standard USB printer for all WLAN users? The wireless print server TP-LINK TL-WPS510U N3310 is ideal for use in offices and homes, eliminating the need of connecting cables from mobile computers to the printer. It also allows to print documents from many computers on one printer...
- archive DWR of Feb. 9, 2009
Prevention and diagnostics of problems with LAN cabling - Multifunctional Cable Tester N7058. NetWork Cable Tester N7058 with LCD display enables the user to verify proper installation of Ethernet cabling (CAT 5e, 6e) and telephone lines. The tester allows to check...
- archive DWR of March 2, 2009
Index of published issues
- archive DWR of Feb. 9, 2009
Prevention and diagnostics of problems with LAN cabling - Multifunctional Cable Tester N7058. NetWork Cable Tester N7058 with LCD display enables the user to verify proper installation of Ethernet cabling (CAT 5e, 6e) and telephone lines. The tester allows to check...
- archive DWR of March 2, 2009
Index of published issues
