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• Internet Protocol Suite: Transition Control Protocol (TCP) vs. User Datagram Protocol (UDP)

  How do we communicate over the Internet?  How is data transferred from one machine to another? These types of act ivies can only be done by using one of two Internet protocols currently. The collection of Internet Protocol consists of the Transition Control Protocol (TCP) and the User Datagram Protocol (UDP).  Both protocols are used to send data between two network end points, however they both have very distinct ways of transporting data from one endpoint to another. If transmission speed and reliability is the primary concern when trying to transfer data between two network endpoints then TCP is the proper choice. When a device attempts to send data to another endpoint using TCP it creates a direct connection between both devices until the transmission has completed. The direct connection between both devices ensures the reliability of the transmission due to the fact that no intermediate devices are needed to transfer the data. Due to the fact that both devices have to continuously poll the connection until transmission has completed increases the resources needed to perform the transmission. An example of this type of direct communication can be seen when a teacher tells a students to do their homework. The teacher is talking directly to the students in order to communicate that the homework needs to be done.  Students can then ask questions about the assignment to ensure that they have received the proper instructions for the assignment. UDP is a less resource intensive approach to sending data between to network endpoints. When a device uses UDP to send data across a network, the data is broken up and repackaged with the destination address. The sending device then releases the data packages to the network, but cannot ensure when or if the receiving device will actually get the data.  The sending device depends on other devices on the network to forward the data packages to the destination devices in order to complete the transmission. As you can tell this type of transmission is less resource intensive because not connection polling is needed,  but should not be used for transmitting data with speed or reliability requirements. This is due to the fact that the sending device can not ensure that the transmission is received.  An example of this type of communication can be seen when a teacher tells a student that they would like to speak with their parents. The teacher is relying on the student to complete the transmission to the parents, and the teacher has no guarantee that the student will actually inform the parents about the request. Both TCP and UPD are invaluable when attempting to send data across a network, but depending on the situation one protocol may be better than the other. Before deciding on which protocol to use an evaluation for transmission speed, reliability, latency, and overhead must be completed in order to define the best protocol for the situation.  

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• SSL / HTTP / No Response to Curl

  - by Alex McHale

  I am trying to send commands to a SOAP service, and getting nothing in reply. The SOAP service is at a completely separate site from either server I am testing with. I have written a dummy script with the SOAP XML embedded. When I run it at my local site, on any of three machines -- OSX, Ubuntu, or CentOS 5.3 -- it completes successfully with a good response. I then sent the script to our public host at Slicehost, where I fail to get the response back from the SOAP service. It accepts the TCP socket and proceeds with the SSL handshake. I do not however receive any valid HTTP response. This is the case whether I use my script or curl on the command line. I have rewritten the script using SOAP4R, Net::HTTP and Curb. All of which work at my local site, none of which work at the Slicehost site. I have tried to assemble the CentOS box as closely to match my Slicehost server as possible. I rebuilt the Slice to be a stock CentOS 5.3 and stock CentOS 5.4 with the same results. When I look at a tcpdump of the bad sessions on Slicehost, I see my script or curl send the XML to the remote server, and nothing comes back. When I look at the tcpdump at my local site, I see the response just fine. I have entirely disabled iptables on the Slice. Does anyone have any ideas what could be causing these results? Please let me know what additional information I can furnish. Thank you! Below is a wire trace of a sample session. The IP that starts with 173 is my server while the IP that starts with 12 is the SOAP server's. No. Time Source Destination Protocol Info 1 0.000000 173.45.x.x 12.36.x.x TCP 36872 > https [SYN] Seq=0 Win=5840 Len=0 MSS=1460 TSV=137633469 TSER=0 WS=6 Frame 1 (74 bytes on wire, 74 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 0, Len: 0 No. Time Source Destination Protocol Info 2 0.040000 12.36.x.x 173.45.x.x TCP https > 36872 [SYN, ACK] Seq=0 Ack=1 Win=8760 Len=0 MSS=1460 Frame 2 (62 bytes on wire, 62 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 0, Ack: 1, Len: 0 No. Time Source Destination Protocol Info 3 0.040000 173.45.x.x 12.36.x.x TCP 36872 > https [ACK] Seq=1 Ack=1 Win=5840 Len=0 Frame 3 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 1, Ack: 1, Len: 0 No. Time Source Destination Protocol Info 4 0.050000 173.45.x.x 12.36.x.x SSLv2 Client Hello Frame 4 (156 bytes on wire, 156 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 1, Ack: 1, Len: 102 Secure Socket Layer No. Time Source Destination Protocol Info 5 0.130000 12.36.x.x 173.45.x.x TCP [TCP segment of a reassembled PDU] Frame 5 (1434 bytes on wire, 1434 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 1, Ack: 103, Len: 1380 Secure Socket Layer No. Time Source Destination Protocol Info 6 0.130000 173.45.x.x 12.36.x.x TCP 36872 > https [ACK] Seq=103 Ack=1381 Win=8280 Len=0 Frame 6 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 103, Ack: 1381, Len: 0 No. Time Source Destination Protocol Info 7 0.130000 12.36.x.x 173.45.x.x TLSv1 Server Hello, Certificate, Server Hello Done Frame 7 (1280 bytes on wire, 1280 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 1381, Ack: 103, Len: 1226 [Reassembled TCP Segments (2606 bytes): #5(1380), #7(1226)] Secure Socket Layer No. Time Source Destination Protocol Info 8 0.130000 173.45.x.x 12.36.x.x TCP 36872 > https [ACK] Seq=103 Ack=2607 Win=11040 Len=0 Frame 8 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 103, Ack: 2607, Len: 0 No. Time Source Destination Protocol Info 9 0.130000 173.45.x.x 12.36.x.x TLSv1 Client Key Exchange, Change Cipher Spec, Encrypted Handshake Message Frame 9 (236 bytes on wire, 236 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 103, Ack: 2607, Len: 182 Secure Socket Layer No. Time Source Destination Protocol Info 10 0.190000 12.36.x.x 173.45.x.x TLSv1 Change Cipher Spec, Encrypted Handshake Message Frame 10 (97 bytes on wire, 97 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 2607, Ack: 285, Len: 43 Secure Socket Layer No. Time Source Destination Protocol Info 11 0.190000 173.45.x.x 12.36.x.x TLSv1 Application Data Frame 11 (347 bytes on wire, 347 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 285, Ack: 2650, Len: 293 Secure Socket Layer No. Time Source Destination Protocol Info 12 0.190000 173.45.x.x 12.36.x.x TCP [TCP segment of a reassembled PDU] Frame 12 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 13 0.450000 12.36.x.x 173.45.x.x TCP https > 36872 [ACK] Seq=2650 Ack=578 Win=64958 Len=0 Frame 13 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 2650, Ack: 578, Len: 0 No. Time Source Destination Protocol Info 14 0.450000 173.45.x.x 12.36.x.x TCP [TCP segment of a reassembled PDU] Frame 14 (206 bytes on wire, 206 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 2038, Ack: 2650, Len: 152 No. Time Source Destination Protocol Info 15 0.510000 12.36.x.x 173.45.x.x TCP [TCP Dup ACK 13#1] https > 36872 [ACK] Seq=2650 Ack=578 Win=64958 Len=0 Frame 15 (54 bytes on wire, 54 bytes captured) Ethernet II, Src: Dell_fb:49:a1 (00:21:9b:fb:49:a1), Dst: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6) Internet Protocol, Src: 12.36.x.x (12.36.x.x), Dst: 173.45.x.x (173.45.x.x) Transmission Control Protocol, Src Port: https (443), Dst Port: 36872 (36872), Seq: 2650, Ack: 578, Len: 0 No. Time Source Destination Protocol Info 16 0.850000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 16 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 17 1.650000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 17 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 18 3.250000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 18 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer No. Time Source Destination Protocol Info 19 6.450000 173.45.x.x 12.36.x.x TCP [TCP Retransmission] [TCP segment of a reassembled PDU] Frame 19 (1514 bytes on wire, 1514 bytes captured) Ethernet II, Src: 40:40:17:3a:f4:e6 (40:40:17:3a:f4:e6), Dst: Dell_fb:49:a1 (00:21:9b:fb:49:a1) Internet Protocol, Src: 173.45.x.x (173.45.x.x), Dst: 12.36.x.x (12.36.x.x) Transmission Control Protocol, Src Port: 36872 (36872), Dst Port: https (443), Seq: 578, Ack: 2650, Len: 1460 Secure Socket Layer

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• sendmail: Error during delivery. Service not available, closing transmission channel

  - by user2810332

  I have a module in my system that will trigger an email and send it to user. The email will be sent to user when the product in my system is going to expired soon. I test the whole module in localhost and there is no problem with it. Then, I finally moved the module in my server but it gives this error. sendmail: Error during delivery: Service not available, closing transmission channel. It will also create a notepad in my desktop that contains information like this : command line : C:\wamp\sendmail\sendmail.exe -t -i executable : sendmail.exe exec. date/time : 2011-06-18 01:10 compiled with : Delphi 2006/07 madExcept version : 3.0l callstack crc : $fecf9b34, $5562b2fa, $5562b2fa exception number : 1 exception class : EIdSMTPReplyError exception message : Service not available, closing transmission channel. main thread ($15b0): 0045918a +003e sendmail.exe IdReplySMTP 501 +1 TIdReplySMTP.RaiseReplyError 0043ff28 +0008 sendmail.exe IdTCPConnection 576 +0 TIdTCPConnection.RaiseExceptionForLastCmdResult 004402f4 +003c sendmail.exe IdTCPConnection 751 +10 TIdTCPConnection.CheckResponse 0043feba +002a sendmail.exe IdTCPConnection 565 +2 TIdTCPConnection.GetResponse 004403fd +002d sendmail.exe IdTCPConnection 788 +4 TIdTCPConnection.GetResponse 0045ab97 +0033 sendmail.exe IdSMTP 375 +4 TIdSMTP.Connect 004b5f14 +1060 sendmail.exe sendmail 808 +326 initialization 77013675 +0010 kernel32.dll BaseThreadInitThunk thread $cf8: 77a400e6 +0e ntdll.dll NtWaitForMultipleObjects 77013675 +10 kernel32.dll BaseThreadInitThunk thread $1088: 77a41ecf +0b ntdll.dll NtWaitForWorkViaWorkerFactory 77013675 +10 kernel32.dll BaseThreadInitThunk May I know what is the problem of this error ? Is it something like firewall in the server that block my sendmail.exe or anything else ? FYI, I'm using Wamp and Sendmail to send the email. This is my first time seeing error like this. I need an explanation on this. Thank you.

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• sendmail.exe: Error during delivery. Service not available, closing transmission channel

  - by user2810332

  I have a module in my system that will trigger an email and send it to user. The email will be sent to user when the product in my system is going to expired soon. I test the whole module in localhost and there is no problem with it. Then, I finally moved the module in my server but it gives this error. sendmail: Error during delivery: Service not available, closing transmission channel. It will also create a notepad in my desktop that contains information like this : command line : C:\wamp\sendmail\sendmail.exe -t -i executable : sendmail.exe exec. date/time : 2011-06-18 01:10 compiled with : Delphi 2006/07 madExcept version : 3.0l callstack crc : $fecf9b34, $5562b2fa, $5562b2fa exception number : 1 exception class : EIdSMTPReplyError exception message : Service not available, closing transmission channel. main thread ($15b0): 0045918a +003e sendmail.exe IdReplySMTP 501 +1 TIdReplySMTP.RaiseReplyError 0043ff28 +0008 sendmail.exe IdTCPConnection 576 +0 TIdTCPConnection.RaiseExceptionForLastCmdResult 004402f4 +003c sendmail.exe IdTCPConnection 751 +10 TIdTCPConnection.CheckResponse 0043feba +002a sendmail.exe IdTCPConnection 565 +2 TIdTCPConnection.GetResponse 004403fd +002d sendmail.exe IdTCPConnection 788 +4 TIdTCPConnection.GetResponse 0045ab97 +0033 sendmail.exe IdSMTP 375 +4 TIdSMTP.Connect 004b5f14 +1060 sendmail.exe sendmail 808 +326 initialization 77013675 +0010 kernel32.dll BaseThreadInitThunk thread $cf8: 77a400e6 +0e ntdll.dll NtWaitForMultipleObjects 77013675 +10 kernel32.dll BaseThreadInitThunk thread $1088: 77a41ecf +0b ntdll.dll NtWaitForWorkViaWorkerFactory 77013675 +10 kernel32.dll BaseThreadInitThunk May I know what is the problem of this error ? Is it something like firewall in the server that block my sendmail.exe or anything else ? FYI, I'm using Wamp and Sendmail to send the email. This is my first time seeing error like this. I need an explanation on this. Thank you.

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• Does a router have a receiving range?

  - by Aadit M Shah

  So my dad bought a TP-Link router (Model No. TL-WA7510N) which apparently has a transmitting range of 1km; and he believes that it also has a receiving range of 1km. So he's arguing with me that the router (which is a trans-receiver) can communicate with any device in the range of 1km whether or not that device has a transmitting range of 1km. To put it graphically: +----+ 1km +----+ | |------------------------------------------------->| | | TR | | TR | | | <----| | +----+ 100m+----+ So here's the problem: The two devices are 1km apart. The first device has a transmitting range of 1km. The second device only has a transmitting range of 100m. According to my dad the two devices can talk to each other. He says that the first device has a transmitting and a receiving range of 1km which means that it can both send data to devices 1km away and receive data from devices 1km away. To me this makes no sense. If the second device can only send data to devices 100m away then how can the first device catch the transmission? He further argues that for bidirectional communication both the sender and the reciver should have overlapping areas of transmission: According to him if two devices have an overlapping area of transmission then they can communicate. Here neither device has enough transmission power to reach the other. However they have enough receiving power to capture the transmission. Obviously this makes absolutely no sense to me. How can a device sense a transmission which hasn't even reached it yet and go out, capture it and bring it back it. To me a trans-receiver only has a transmission power. It has zero receiving power. Hence for two devices to be able to communicate bidirectionally, the diagram should look like: Hence, from my point of view, both the devices should have a transmission range far enough to reach the other for bidirectional communication to be possible; but no matter how much I try to explain to my dad he adamantly disagrees. So, to put an end to this debate once and for all, who is correct? Is there even such a thing as a receiving range? Can a device fetch a transmission that would otherwise never reach it? I would like a canonical answer on this.

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• Linux - Multiple service statuses with one command

  - by Jimbo

  I'm trying to retrieve a list of multiple service statuses in Unix. I'm using the service command: man page. The statuses all start with the transmission-daemon string, for example. I require the ability to list multiple services' statuses, with a single command. Here is what I'm currently trying (and failing) with: Here I'm trying to grab a list of statuses using grep. service $(ls /etc/init.d | grep "transmission-daemon") status Here I'm trying to list all statuses, and then grep for them. service --status-all | grep "transmission-daemon" This produces the following, which isn't much help: How can I effectively achieve what I require with a single command, so that I can then continue piping to awk for further customisation? Desired example output: transmission-daemon started transmission-daemon2 stopped transmission-daemon3 started

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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• Linux program to convert audio file of fax transmission to image?

  - by bdk

  I have a number of uncompressed audio files recorded off of an analog (POTS) telephone line of fax transmissions. Is there a Linux utility or library I could use to convert these files into images of the fax they contain? I'm not looking to send/receive a fax via a modem, but just to "replay" the communications tones and parse out the fax message.I'm guessing this may not be possible due to duplex issues and not knowing which end of the conversation is sending what,but thought I'd ask to see if anyone knew of something.

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• xen debian: domU can't get out side

  - by iftol

  hi every body. i'm a trainee as a sysAdmin, it is my first expérience with virtualization. i have a server setup debian xen 3 with 2 physical interfaces. eth 0 for local network 10.0.0.1 and eth1 for internet (194.X.X.4). i created 3 VMs (web server, mail server and dabase server) with local ip addresses 172.10.0.x/24. the problem i had first is that domU can't ping dom0. i asked the sysAdmin of our ISP and he sais that he fogot to setup the bridginb. so he ceated a bridge with 172.10.0.1/24 after that i was able to ping the real server (194.X.X.4). but i can't go out side from my VMs, how can i fixe this issue? real or physical server ifconfig eth0 Link encap:Ethernet HWaddr 23:26:34:84:ce:xe inet adr:10.1.3.12 Bcast:10.1.3.255 Masque:255.255.255.0 adr inet6: fe80::226:b9ff:fe84:ceb4/64 Scope:Lien UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:412006 errors:0 dropped:0 overruns:0 frame:0 TX packets:411296 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:1000 RX bytes:31410957 (29.9 MiB) TX bytes:31178370 (29.7 MiB) Interruption:36 Mémoire:d6000000-d6012100 eth1 Link encap:Ethernet HWaddr 23:26:34:84:ce:xe inet adr:194.x.x.4 Bcast:194.254.167.255 Masque:255.255.255.0 adr inet6: fe80::226:b9ff:fe84:ceb6/64 Scope:Lien UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:25872332 errors:0 dropped:0 overruns:0 frame:0 TX packets:414578 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:0 RX bytes:2642278343 (2.4 GiB) TX bytes:35436775 (33.7 MiB) lo Link encap:Boucle locale inet adr:127.0.0.1 Masque:255.0.0.0 adr inet6: ::1/128 Scope:Hôte UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:1308073 errors:0 dropped:0 overruns:0 frame:0 TX packets:1308073 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:0 RX bytes:109871395 (104.7 MiB) TX bytes:109871395 (104.7 MiB) peth1 Link encap:Ethernet HWaddr 23:26:34:84:ce:xe UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:31818694 errors:0 dropped:0 overruns:0 frame:0 TX packets:414818 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:1000 RX bytes:5197318822 (4.8 GiB) TX bytes:37904897 (36.1 MiB) Interruption:48 Mémoire:d8000000-d8012100 vif281.0 Link encap:Ethernet HWaddr fe:ff:ff:ff:ff:ff adr inet6: fe80::fcff:ffff:feff:ffff/64 Scope:Lien UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:207 errors:0 dropped:0 overruns:0 frame:0 TX packets:298 errors:0 dropped:2 overruns:0 carrier:0 collisions:0 lg file transmission:32 RX bytes:24629 (24.0 KiB) TX bytes:28404 (27.7 KiB) vif281.1 Link encap:Ethernet HWaddr fe:ff:ff:ff:ff:ff adr inet6: fe80::fcff:ffff:feff:ffff/64 Scope:Lien UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:45 errors:0 dropped:47063 overruns:0 carrier:0 collisions:0 lg file transmission:32 RX bytes:0 (0.0 B) TX bytes:4449 (4.3 KiB) vif282.0 Link encap:Ethernet HWaddr fe:ff:ff:ff:ff:ff adr inet6: fe80::fcff:ffff:feff:ffff/64 Scope:Lien UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:78 errors:0 dropped:0 overruns:0 frame:0 TX packets:13 errors:0 dropped:1 overruns:0 carrier:0 collisions:0 lg file transmission:32 RX bytes:5041 (4.9 KiB) TX bytes:714 (714.0 B) xenbr0 Link encap:Ethernet HWaddr fe:ff:ff:ff:ff:ff inet adr:172.10.0.1 Bcast:172.10.0.255 Masque:255.255.255.0 adr inet6: fe80::5c72:c6ff:fe49:7fe/64 Scope:Lien UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:7180 errors:0 dropped:0 overruns:0 frame:0 TX packets:8615 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 lg file transmission:0 RX bytes:756804 (739.0 KiB) TX bytes:791206 (772.6 KiB) brtcl show bridge name bridge id STP enabled interfaces eth1 8000.0026b984ceb6 no peth1 vif281.1 xenbr0 8000.feffffffffff no vif281.0 vif282.0 network-multi-bridge /etc/xen/scripts/network-virtual start vifnum="0" bridgeip="172.10.0.1/24" brnet="172.10.0.0/24" VM webserver eth0 Link encap:Ethernet HWaddr 00:16:3E:42:33:70 inet addr:172.10.0.2 Bcast:172.10.0.255 Mask:255.255.255.0 inet6 addr: fe80::216:3eff:fe42:3370/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:3 errors:0 dropped:0 overruns:0 frame:0 TX packets:27 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:126 (126.0 b) TX bytes:2036 (1.9 KiB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:0 (0.0 b) TX bytes:0 (0.0 b) Thank you for your help.

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• How come ftp protocol produces transmission errors sometimes if the data is using TCP, which is checksummed?

  - by Cray

  Every once in a while, downloading (especially large) files through ftp will produce errors. I am guessing that's also partly the reason why all major sites are publishing external checksums along with their downloads. How is this possible if ftp goes through TCP, which has checksum inbuilt and resends data if it is transmitted corruptly? One could argue that this is due to the short length of the CRC in the TCP protocol (which is 16bit I think, or something like that), and the collisions are simply happening too often. but 1) for this to be true, not only must there be a CRC collision, but also the random network error must modify both the CRC in the packet, and the packet itself so that the CRC will be valid for the new packet... Even with 16 bitCRC, is that so likely? 2) There are seemingly not many errors in, say, browsing the web which also goes through TCPIP.

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• What are the frequencies of current in computers' external peripheral cables and internal buses?

  - by Tim

  From Wikipedia, three different cases of current frequency are discussed along with the types of cables that are suitable for them: An Extra Ordinary electrical cables suffice to carry low frequency AC, such as mains power, which reverses direction 100 to 120 times per second (cycling 50 to 60 times per second). However, they cannot be used to carry currents in the radio frequency range or higher, which reverse direction millions to billions of times per second, because the energy tends to radiate off the cable as radio waves, causing power losses. Radio frequency currents also tend to reflect from discontinuities in the cable such as connectors, and travel back down the cable toward the source. These reflections act as bottlenecks, preventing the power from reaching the destination. Transmission lines use specialized construction such as precise conductor dimensions and spacing, and impedance matching, to carry electromagnetic signals with minimal reflections and power losses. Types of transmission line include ladder line, coaxial cable, dielectric slabs, stripline, optical fiber, and waveguides. The higher the frequency, the shorter are the waves in a transmission medium. Transmission lines must be used when the frequency is high enough that the wavelength of the waves begins to approach the length of the cable used. To conduct energy at frequencies above the radio range, such as millimeter waves, infrared, and light, the waves become much smaller than the dimensions of the structures used to guide them, so transmission line techniques become inadequate and the methods of optics are used. I wonder what the frequencies are for the currents in computers' external peripheral cables, such as Ethernet cable, USB cable, and in computers' internal buses? Are the cables also made specially for the frequencies? Thanks!

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• Is it possible to download corrupted torrent files, even with a download client builtin checksum verification?

  - by Somebody still uses you MS-DOS

  I downloaded some mkv/mp4 files with my new router (I can download directly from it, using transmission), and all of them seem to be corrupted: lags, strange artifacts when using vlc, crashes with mp4, etc. When a downloaded part is corrupted, transmission warns you and downloads that part again. My question is: even after the transmission verification, is it possible that the downloaded file is still corrupt?

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• Unable to download torrents when using a VPN

  - by chad

  I am running Ubuntu 13.04 and using OpenVPN and vpnbook. When I am using a VPN I am unable to download torrents. I have tried it on 3 different torrent clients (qBittorrent, Deluge, and Transmission). Deluge just says "Checking" and never begins downloading. qBittorrent says "stalled" next to the torrent and Transmission does not say anything and just doesn't download. Is there some network setting I am missing or some OpenVPN config I need to do?

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• How to use TCP/IP Nagle algorithm at Apple Push Notification

  - by Mahbubur R Aaman

  From Apple's Developer Library The binary interface employs a plain TCP socket for binary content that is streaming in nature. For optimum performance, you should batch multiple notifications in a single transmission over the interface, either explicitly or using a TCP/IP Nagle algorithm. How to use TCP/IP Nagle algorithm in case Apple's Push Notification? How to batch multiple notification in a single transmission over the interface? Additional # In Apple's Push Notification Urban Airship is a familiar name to send large amount of push notification within several minutes. Does they use TCP/IP Nagle algorithm?

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• How can I remove gradients from Elementary theme?

  - by John

  I really don't like the gradients in the Elementary theme and I was wondering if there is a way to remove them from applications like Nautilus-Elementary, Postler, Dexter, etc. I've tried commenting out the Apps/[Application].rc in /usr/share/themes/elementary/gtk-2.0/gtkrc but it doesn't work. It still leaves the gradients in their place. I'm a big fan of the other controls in the theme: the scroll bar, the way it borders gedit and the buttons, and I'd like to keep these features, but I don't like the way it styles its windows. EDIT: The gradients I'm talking about are the ones at the top of the window. Some examples: Nautilus-Elementary: Postler: Rhythmbbox: Transmission: I'd like to create a sort of matte look, similar to this, which was done using Orta: Nautilus-Elementary: Postler: Rhythmbox: Transmission: I'd like a flat color, preferably without the line separating the top part of the application with the bottom.

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• How Stuff Works: Fiber Optic Cables [Science]

  - by Jason Fitzpatrick

  Most people are familiar with the general concept of fiber optic cables–light as a method of data transmission–but how do they really work? Find out in this informative video. Bill Hammack, of Engineer Guy Videos, shows us how fiber optic cables work using–of all things–a bucket and a laser. Check out the above video for a glimpse inside how fiber optic cables work and how your analog voice can go to from your phone’s handset to a digital stream and then back to analog sound for the benefit of your friend on the end of the fiber optic transmission cable. Fiber Optic Cables: How They Work and How Engineers Use Them to Send Messages [YouTube] What is a Histogram, and How Can I Use it to Improve My Photos?How To Easily Access Your Home Network From Anywhere With DDNSHow To Recover After Your Email Password Is Compromised

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• Default file manager changed, can't change back

  - by user16171

  (Using ubuntu 11.04) I tried to open a torrent file in chrome, and it asked for my default application, so I clicked Transmission, and then I got an error: "Failed to execute default file manager, Failed to execute child process "transmission" (No such file or directory)." Now if I click on any shortcut on the unity bar, such as the trash folder or the icon for my portable hard drive, I get this error, as well as with any download or folder from chrome or firefox. I can't seem to figure out how to fix this, as there seems to be no easy way to do it.

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• How to workaround or diagnose a kernel panic when "safely removing" external hdd?

  - by Shawn

  I'm experiencing an issue when using the "Safely Remove" option to remove my 1TB external HDD from the Unity Launcher. Not every time, but occasionally my screen will go black and display LARGE amounts of text information (which I obviously cannot screen cap). The jist of the info displayed is that unmounting or 'safely removing' the drive causes a kernel panic. Is there a Command Line command to remove mounted drives, or at least one that would show me some sort of error output when the drive is removed? I'm trying to narrow down the cause. I could be imagining this, but it seems to happen most often when I have other programs running when I remove the drive (i.e. Firefox, Transmission). Please note that my external drive is not in use when I attempt to remove it and it is not being used either by Firefox or Transmission at these times. Any help would be appreciated.

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• Torrent clients suddenly stop downloading

  - by Vasilis Baltikas

  A few days ago I noticed, that Transmission in my Ubuntu 10.04 machine suddenly couldn't download anything anymore. To overcome this I have uninstalled and reinstalled Transmission and tried downloading with other clients (Deluge, Vuze) well seeded torrents (ubuntu iso images for example) without success. On the same computer I have also installed Ubuntu 10.10 and Windows 7, which I rarely use. What makes the problem I encounter weirder, is the fact that downloading via torrents works fine in my Ubuntu 10.10 and Windows partitions but not in Lucid Lynx. Browsing the web for similar problems didn't give me answers. Any help would greatly appreciated.

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• Torrent clients suddenly stopped downloading

  - by Vasilis Baltikas

  A few days ago I noticed, that Transmission in my Ubuntu 10.04 machine suddenly couldn't download anything anymore. To overcome this I have uninstalled and reinstalled Transmission and tried downloading with other clients (Deluge, Vuze) well seeded torrents (ubuntu iso images for example) without success. On the same computer I have also installed Ubuntu 10.10 and Windows 7, which I rarely use. What makes the problem I encounter weirder, is the fact that downloading via torrents works fine in my Ubuntu 10.10 and Windows partitions but not in Lucid Lynx. Browsing the web for similar problems didn't give me answers. Any help would greatly appreciated.

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• Xubuntu 12.4 upgraded fine but there are everywhere pale grey windows/menus with white fonts!

  - by Costa

  I upgraded to Xubuntu 12.4 through the update manager. Everything works fine except that many windows and menus (Ubuntu Software Center,Transmission properties etc) apear in pale grey with white fonts. For examle, it's impossible to read n change properties on Transmission. Titles apear excellently, the rest is really hard to read: white text on allmost white background ... I have tried already:rebooting, changing theme/apearance photo1 http://en.zimagez.com/zimage/-26042012-102025.php When login as guest everything works fine. I created a new account, all is fine photo2 http://en.zimagez.com/zimage/-26042012-103258.php But I still want my initiall user-account which i had so well tuned...

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• How many bits for sequence number using Go-Back-N protocol.

  - by Mike

  Hi Everyone, I'm a regular over at Stack Overflow (Software developer) that is trying to get through a networking course. I got a homework problem I'd like to have a sanity check on. Here is what I got. Q: A 3000-km-long T1 trunk is used to transmit 64-byte frames using Go-Back-N protocol. If the propagation speed is 6 microseconds/km, how many bits should the sequence numbers be? My Answer: For this questions what we need to do is lay the base knowledge. What we are trying to find is the size of the largest sequence number we should us using Go-Back-N. To figure this out we need to figure out how many packets can fit into our link at a time and then subtract one from that number. This will ensure that we never have two packets with the same sequence number at the same time in the link. Length of link: 3,000km Speed: 6 microseconds / km Frame size: 64 bytes T1 transmission speed: 1544kb/s (http://ckp.made-it.com/t1234.html) Propagation time = 6 microseconds / km * 3000 km = 18,000 microseconds (18ms). Convert 1544kb to bytes = 1544 * 1024 = 1581056 bytes Transmission time = 64 bytes / 1581056bytes / second = 0.000040479 seconds (0.4ms) So then if we take the 18ms propagation time and divide it by the 0.4ms transmission time we will see that we are going to be able to stuff ( 18 / 0.4) 45 packets into the link at a time. That means that our sequence number should be 2 ^ 45 bits long! Am I going in the right direction with this? Thanks, Mike

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• Redirect network logs from syslog to another file

  - by w0rldart

  I keep logging way to much info (not needed, for now) in my syslog, and not daily or hourly... but instant. If I want to watch for something in my syslog I just can't because the network log keeps interfering. So, how can I redirect network logs to another file and/or stop logging it? Dec 10 17:01:33 user kernel: [ 8716.000587] MediaState is connected Dec 10 17:01:33 user kernel: [ 8716.000599] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:01:33 user kernel: [ 8716.000601] ==>rt_ioctl_giwfreq 11 Dec 10 17:01:33 user kernel: [ 8716.000612] rt28xx_get_wireless_stats ---> Dec 10 17:01:33 user kernel: [ 8716.000615] <--- rt28xx_get_wireless_stats Dec 10 17:01:39 user kernel: [ 8722.000714] MediaState is connected Dec 10 17:01:39 user kernel: [ 8722.000729] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:01:39 user kernel: [ 8722.000732] ==>rt_ioctl_giwfreq 11 Dec 10 17:01:39 user kernel: [ 8722.000747] rt28xx_get_wireless_stats ---> Dec 10 17:01:39 user kernel: [ 8722.000751] <--- rt28xx_get_wireless_stats Dec 10 17:01:44 user kernel: [ 8726.904025] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:01:45 user kernel: [ 8728.003138] MediaState is connected Dec 10 17:01:45 user kernel: [ 8728.003153] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:01:45 user kernel: [ 8728.003157] ==>rt_ioctl_giwfreq 11 Dec 10 17:01:45 user kernel: [ 8728.003171] rt28xx_get_wireless_stats ---> Dec 10 17:01:45 user kernel: [ 8728.003175] <--- rt28xx_get_wireless_stats Dec 10 17:01:51 user kernel: [ 8734.004066] MediaState is connected Dec 10 17:01:51 user kernel: [ 8734.004079] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:01:51 user kernel: [ 8734.004082] ==>rt_ioctl_giwfreq 11 Dec 10 17:01:51 user kernel: [ 8734.004096] rt28xx_get_wireless_stats ---> Dec 10 17:01:51 user kernel: [ 8734.004099] <--- rt28xx_get_wireless_stats Dec 10 17:01:57 user kernel: [ 8740.004108] MediaState is connected Dec 10 17:01:57 user kernel: [ 8740.004119] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:01:57 user kernel: [ 8740.004121] ==>rt_ioctl_giwfreq 11 Dec 10 17:01:57 user kernel: [ 8740.004132] rt28xx_get_wireless_stats ---> Dec 10 17:01:57 user kernel: [ 8740.004135] <--- rt28xx_get_wireless_stats Dec 10 17:01:57 user kernel: [ 8740.436021] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:02:03 user kernel: [ 8746.005280] MediaState is connected Dec 10 17:02:03 user kernel: [ 8746.005294] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:02:03 user kernel: [ 8746.005298] ==>rt_ioctl_giwfreq 11 Dec 10 17:02:03 user kernel: [ 8746.005312] rt28xx_get_wireless_stats ---> Dec 10 17:02:03 user kernel: [ 8746.005315] <--- rt28xx_get_wireless_stats Dec 10 17:02:09 user kernel: [ 8752.004790] MediaState is connected Dec 10 17:02:09 user kernel: [ 8752.004804] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:02:09 user kernel: [ 8752.004808] ==>rt_ioctl_giwfreq 11 Dec 10 17:02:09 user kernel: [ 8752.004821] rt28xx_get_wireless_stats ---> Dec 10 17:02:09 user kernel: [ 8752.004825] <--- rt28xx_get_wireless_stats Dec 10 17:02:15 user kernel: [ 8757.984031] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:02:15 user kernel: [ 8758.004078] MediaState is connected Dec 10 17:02:15 user kernel: [ 8758.004094] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:02:15 user kernel: [ 8758.004097] ==>rt_ioctl_giwfreq 11 Dec 10 17:02:15 user kernel: [ 8758.004112] rt28xx_get_wireless_stats ---> Dec 10 17:02:15 user kernel: [ 8758.004116] <--- rt28xx_get_wireless_stats Dec 10 17:02:16 user kernel: [ 8759.492017] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:02:19 user kernel: [ 8762.002179] SCANNING, suspend MSDU transmission ... Dec 10 17:02:19 user kernel: [ 8762.004291] MlmeScanReqAction -- Send PSM Data frame for off channel RM, SCAN_IN_PROGRESS=1! Dec 10 17:02:19 user kernel: [ 8762.025055] SYNC - BBP R4 to 20MHz.l Dec 10 17:02:19 user kernel: [ 8762.027249] RT35xx: SwitchChannel#1(RF=8, Pwr0=30, Pwr1=25, 2T), N=0xF1, K=0x02, R=0x02 Dec 10 17:02:19 user kernel: [ 8762.170206] RT35xx: SwitchChannel#2(RF=8, Pwr0=30, Pwr1=25, 2T), N=0xF1, K=0x07, R=0x02 Dec 10 17:02:19 user kernel: [ 8762.318211] RT35xx: SwitchChannel#3(RF=8, Pwr0=30, Pwr1=25, 2T), N=0xF2, K=0x02, R=0x02 Dec 10 17:02:19 user kernel: [ 8762.462269] RT35xx: SwitchChannel#4(RF=8, Pwr0=30, Pwr1=25, 2T), N=0xF2, K=0x07, R=0x02 Dec 10 17:02:19 user kernel: [ 8762.606229] RT35xx: SwitchChannel#5(RF=8, Pwr0=30, Pwr1=25, 2T), N=0xF3, K=0x02, R=0x02 Dec 10 17:02:19 user kernel: [ 8762.750202] RT35xx: SwitchChannel#6(RF=8, Pwr0=30, Pwr1=25, 2T), N=0xF3, K=0x07, R=0x02 Dec 10 17:02:20 user kernel: [ 8762.894217] RT35xx: SwitchChannel#7(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF4, K=0x02, R=0x02 Dec 10 17:02:20 user kernel: [ 8763.038202] RT35xx: SwitchChannel#11(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF6, K=0x02, R=0x02 Dec 10 17:02:20 user kernel: [ 8763.040194] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:20 user kernel: [ 8763.040199] BAR(1) : Tid (0) - 03a3:037e Dec 10 17:02:20 user kernel: [ 8763.040387] SYNC - End of SCAN, restore to channel 11, Total BSS[03] Dec 10 17:02:20 user kernel: [ 8763.040400] ScanNextChannel -- Send PSM Data frame Dec 10 17:02:20 user kernel: [ 8763.040402] bFastRoamingScan ~~~~~~~~~~~~~ Get back to send data ~~~~~~~~~~~~~ Dec 10 17:02:20 user kernel: [ 8763.040405] SCAN done, resume MSDU transmission ... Dec 10 17:02:20 user kernel: [ 8763.047022] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:20 user kernel: [ 8763.047026] BAR(1) : Tid (0) - 03a3:03a5 Dec 10 17:02:21 user kernel: [ 8763.898130] bImprovedScan ............. Resume for bImprovedScan, SCAN_PENDING .............. Dec 10 17:02:21 user kernel: [ 8763.898143] SCANNING, suspend MSDU transmission ... Dec 10 17:02:21 user kernel: [ 8763.900245] MlmeScanReqAction -- Send PSM Data frame for off channel RM, SCAN_IN_PROGRESS=1! Dec 10 17:02:21 user kernel: [ 8763.921144] SYNC - BBP R4 to 20MHz.l Dec 10 17:02:21 user kernel: [ 8763.923339] RT35xx: SwitchChannel#8(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF4, K=0x07, R=0x02 Dec 10 17:02:21 user kernel: [ 8763.996019] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:02:21 user kernel: [ 8764.066221] RT35xx: SwitchChannel#9(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF5, K=0x02, R=0x02 Dec 10 17:02:21 user kernel: [ 8764.210212] RT35xx: SwitchChannel#10(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF5, K=0x07, R=0x02 Dec 10 17:02:21 user kernel: [ 8764.215536] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:21 user kernel: [ 8764.215542] BAR(1) : Tid (0) - 0457:0452 Dec 10 17:02:21 user kernel: [ 8764.244000] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:21 user kernel: [ 8764.244004] BAR(1) : Tid (0) - 0459:0456 Dec 10 17:02:21 user kernel: [ 8764.253019] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:21 user kernel: [ 8764.253023] BAR(1) : Tid (0) - 045c:0458 Dec 10 17:02:21 user kernel: [ 8764.256677] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:21 user kernel: [ 8764.256681] BAR(1) : Tid (0) - 045c:045b Dec 10 17:02:21 user kernel: [ 8764.259785] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:21 user kernel: [ 8764.259788] BAR(1) : Tid (0) - 045d:045b Dec 10 17:02:21 user kernel: [ 8764.280467] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:21 user kernel: [ 8764.280471] BAR(1) : Tid (0) - 045f:045c Dec 10 17:02:21 user kernel: [ 8764.282189] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:21 user kernel: [ 8764.282192] BAR(1) : Tid (0) - 045f:045e Dec 10 17:02:21 user kernel: [ 8764.354204] RT35xx: SwitchChannel#11(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF6, K=0x02, R=0x02 Dec 10 17:02:21 user kernel: [ 8764.356408] ScanNextChannel():Send PWA NullData frame to notify the associated AP! Dec 10 17:02:21 user kernel: [ 8764.498202] RT35xx: SwitchChannel#12(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF6, K=0x07, R=0x02 Dec 10 17:02:21 user kernel: [ 8764.642210] RT35xx: SwitchChannel#13(RF=8, Pwr0=30, Pwr1=28, 2T), N=0xF7, K=0x02, R=0x02 Dec 10 17:02:22 user kernel: [ 8764.790229] RT35xx: SwitchChannel#14(RF=8, Pwr0=30, Pwr1=28, 2T), N=0xF8, K=0x04, R=0x02 Dec 10 17:02:22 user kernel: [ 8764.934238] RT35xx: SwitchChannel#11(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF6, K=0x02, R=0x02 Dec 10 17:02:22 user kernel: [ 8764.935243] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:22 user kernel: [ 8764.935249] BAR(1) : Tid (0) - 048e:0485 Dec 10 17:02:22 user kernel: [ 8764.936423] SYNC - End of SCAN, restore to channel 11, Total BSS[05] Dec 10 17:02:22 user kernel: [ 8764.936436] ScanNextChannel -- Send PSM Data frame Dec 10 17:02:22 user kernel: [ 8764.936440] SCAN done, resume MSDU transmission ... Dec 10 17:02:22 user kernel: [ 8764.940529] RT35xx: SwitchChannel#11(RF=8, Pwr0=29, Pwr1=26, 2T), N=0xF6, K=0x02, R=0x02 Dec 10 17:02:22 user kernel: [ 8764.942178] CntlEnqueueForRecv(): BAR-Wcid(1), Tid (0) Dec 10 17:02:22 user kernel: [ 8764.942182] BAR(1) : Tid (0) - 0493:048e Dec 10 17:02:22 user kernel: [ 8764.942715] CNTL - All roaming failed, restore to channel 11, Total BSS[05] Dec 10 17:02:22 user kernel: [ 8764.948016] MMCHK - No BEACON. restore R66 to the low bound(56) Dec 10 17:02:22 user kernel: [ 8764.948307] ===>rt_ioctl_giwscan. 5(5) BSS returned, data->length = 1111 Dec 10 17:02:23 user kernel: [ 8766.048073] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:02:23 user kernel: [ 8766.552034] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:02:27 user kernel: [ 8770.001180] MediaState is connected Dec 10 17:02:27 user kernel: [ 8770.001197] ==>rt_ioctl_giwmode(mode=2) Dec 10 17:02:27 user kernel: [ 8770.001201] ==>rt_ioctl_giwfreq 11 Dec 10 17:02:27 user kernel: [ 8770.001219] rt28xx_get_wireless_stats ---> Dec 10 17:02:27 user kernel: [ 8770.001223] <--- rt28xx_get_wireless_stats Dec 10 17:02:28 user kernel: [ 8771.564020] QuickDRS: TxTotalCnt <= 15, train back to original rate Dec 10 17:02:29 user kernel: [ 8772.064031] QuickDRS: TxTotalCnt <= 15, train back to original rate

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• Empty /var/log after running cron bash script

  - by Ortix92

  I wrote a little bash script and all of a sudden my /var/log folder is completely empty except for the log I created for the bash script. This is the script I'm running every hour with cron: #!/bin/bash STL_DIR=/path/to/some/folder/i/hid LOGFILE=/var/log/stl_upload.log now=`date` echo "----------Start of Transmission----------" 2>&1 | tee -a $LOGFILE echo "Starting transfer at $now" 2>&1 | tee -a $LOGFILE rsync -av -e ssh $STL_DIR [email protected]:/users/path/folder 2>&1 | tee -a $LOGFILE echo "----------End of transmission----------" 2>&1 | tee -a $LOGFILE printf "\n" 2>&1 | tee -a $LOGFILE I want to be clear that I'm not 100% certain this is related to the empty logs folder. So if anyone could give me a pointer as to what could be going on about the reason why my log folder is empty, that'd be great.

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• MPEG2-TS streaming: UDP or RTP?

  - by Juan Jose Polanco Arias

  Hello I'm working on an IPTV streaming server in Linux (Ubuntu Server 12.04 LTS) that has a DVB-S/S2 card to obtain satellite channels. Then with MuMuDVB I map all channels in the transponder to a multicast group, for multicast transmission. Now for the MuMuDVB software I can either use UDP for transmission or I can add the RTP header. I was wondering what would be the most convenient for MPEG2-TS because I've heard that RTP is used primarily for MPEG4, but It's also said that RTP can be used for MPEG2-TS. Thanks for your help.

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