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• migrating Solaris to RH: network latency issue, tcp window size & other tcp parameters

  - by Bastien

  Hello I have a client/server app (Java) that I'm migrating from Solaris to RH Linux. since I started running it in RH, I noticed some issues related to latency. I managed to isolate the problem that looks like this: client sends 5 messages (32 bytes each) in a row (same application timestamp) to the server. server echos messages. client receives replies and prints round trip time for each msg. in Solaris, all is well: I get ALL 5 replies at the same time, roughly 80ms after having sent original messages (client & server are several thousands miles away from each other: my ping RTT is 80ms, all normal). in RH, first 3 messages are echoed normally (they arrive 80ms after they've been sent), however the following 2 arrive 80ms later (so total 160ms RTT). the pattern is always the same. clearly looked like a TCP problem. on my solaris box, I had previously configured the tcp stack with 2 specific options: disable nagle algorithm globally set tcp_deferred_acks_max to 0 on RH, it's not possible to disable nagle globally, but I disabled it on all of my apps' sockets (TCP_NODELAY). so I started playing with tcpdump (on the server machine), and compared both outputs: SOLARIS: 22 2.085645 client server TCP 56150 > 6006 [PSH, ACK] Seq=111 Ack=106 Win=66672 Len=22 "MSG_1 RCV" 23 2.085680 server client TCP 6006 > 56150 [ACK] Seq=106 Ack=133 Win=50400 Len=0 24 2.085908 client server TCP 56150 > 6006 [PSH, ACK] Seq=133 Ack=106 Win=66672 Len=22 "MSG_2 RCV" 25 2.085925 server client TCP 6006 > 56150 [ACK] Seq=106 Ack=155 Win=50400 Len=0 26 2.086175 client server TCP 56150 > 6006 [PSH, ACK] Seq=155 Ack=106 Win=66672 Len=22 "MSG_3 RCV" 27 2.086192 server client TCP 6006 > 56150 [ACK] Seq=106 Ack=177 Win=50400 Len=0 28 2.086243 server client TCP 6006 > 56150 [PSH, ACK] Seq=106 Ack=177 Win=50400 Len=21 "MSG_1 ECHO" 29 2.086440 client server TCP 56150 > 6006 [PSH, ACK] Seq=177 Ack=106 Win=66672 Len=22 "MSG_4 RCV" 30 2.086454 server client TCP 6006 > 56150 [ACK] Seq=127 Ack=199 Win=50400 Len=0 31 2.086659 server client TCP 6006 > 56150 [PSH, ACK] Seq=127 Ack=199 Win=50400 Len=21 "MSG_2 ECHO" 32 2.086708 client server TCP 56150 > 6006 [PSH, ACK] Seq=199 Ack=106 Win=66672 Len=22 "MSG_5 RCV" 33 2.086721 server client TCP 6006 > 56150 [ACK] Seq=148 Ack=221 Win=50400 Len=0 34 2.086947 server client TCP 6006 > 56150 [PSH, ACK] Seq=148 Ack=221 Win=50400 Len=21 "MSG_3 ECHO" 35 2.087196 server client TCP 6006 > 56150 [PSH, ACK] Seq=169 Ack=221 Win=50400 Len=21 "MSG_4 ECHO" 36 2.087500 server client TCP 6006 > 56150 [PSH, ACK] Seq=190 Ack=221 Win=50400 Len=21 "MSG_5 ECHO" 37 2.165390 client server TCP 56150 > 6006 [ACK] Seq=221 Ack=148 Win=66632 Len=0 38 2.166314 client server TCP 56150 > 6006 [ACK] Seq=221 Ack=190 Win=66588 Len=0 39 2.364135 client server TCP 56150 > 6006 [ACK] Seq=221 Ack=211 Win=66568 Len=0 REDHAT: 17 2.081163 client server TCP 55879 > 6006 [PSH, ACK] Seq=111 Ack=106 Win=66672 Len=22 "MSG_1 RCV" 18 2.081178 server client TCP 6006 > 55879 [ACK] Seq=106 Ack=133 Win=5888 Len=0 19 2.081297 server client TCP 6006 > 55879 [PSH, ACK] Seq=106 Ack=133 Win=5888 Len=21 "MSG_1 ECHO" 20 2.081711 client server TCP 55879 > 6006 [PSH, ACK] Seq=133 Ack=106 Win=66672 Len=22 "MSG_2 RCV" 21 2.081761 client server TCP 55879 > 6006 [PSH, ACK] Seq=155 Ack=106 Win=66672 Len=22 "MSG_3 RCV" 22 2.081846 server client TCP 6006 > 55879 [PSH, ACK] Seq=127 Ack=177 Win=5888 Len=21 "MSG_2 ECHO" 23 2.081995 server client TCP 6006 > 55879 [PSH, ACK] Seq=148 Ack=177 Win=5888 Len=21 "MSG_3 ECHO" 24 2.082011 client server TCP 55879 > 6006 [PSH, ACK] Seq=177 Ack=106 Win=66672 Len=22 "MSG_4 RCV" 25 2.082362 client server TCP 55879 > 6006 [PSH, ACK] Seq=199 Ack=106 Win=66672 Len=22 "MSG_5 RCV" 26 2.082377 server client TCP 6006 > 55879 [ACK] Seq=169 Ack=221 Win=5888 Len=0 27 2.171003 client server TCP 55879 > 6006 [ACK] Seq=221 Ack=148 Win=66632 Len=0 28 2.171019 server client TCP 6006 > 55879 [PSH, ACK] Seq=169 Ack=221 Win=5888 Len=42 "MSG_4 ECHO + MSG_5 ECHO" 29 2.257498 client server TCP 55879 > 6006 [ACK] Seq=221 Ack=211 Win=66568 Len=0 so, I got confirmation things are not working correctly for RH: packet 28 is sent TOO LATE, it looks like the server is waiting for packet 27's ACK before doing anything. seems to me it's the most likely reason... then I realized that the "Win" parameters are different on Solaris & RH dumps: 50400 on Solaris, only 5888 on RH. that's another hint... I read the doc about the slide window & buffer window, and played around with the rcvBuffer & sendBuffer in java on my sockets, but never managed to change this 5888 value to anything else (I checked each time directly with tcpdump). does anybody know how to do this ? I'm having a hard time getting definitive information, as in some cases there's "auto-negotiation" that I might need to bypass, etc... I eventually managed to get only partially rid of my initial problem by setting the "tcp_slow_start_after_idle" parameter to 0 on RH, but it did not change the "win" parameter at all. the same problem was there for the first 4 groups of 5 messages, with TCP retransmission & TCP Dup ACK in tcpdump, then the problem disappeared altogether for all following groups of 5 messages. It doesn't seem like a very clean and/or generic solution to me. I'd really like to reproduce the exact same conditions under both OSes. I'll keep researching, but any help from TCP gurus would be greatly appreciated ! thanks !

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• Oracle PL/SQL: Performance of CLOB data type in PL/SQL

  - by drupalspring

  If I use many CLOB variables in the PL/SQL stored procedure to store many long length string , are there any performance issues? Is the length of the CLOB is also variable? Are there any known limitations/disadvantages for CLOB instead using varchar2 and long?

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• Oracle 11g OCA,OCP study material required.

  - by Mohan

  Hi, kindly let me know where to find this material.. need it urgently for preperation. regards Mohan

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• How to get Mobile Country and Network code on an iPhone

  - by Johan

  Is there any way of getting the mnc and mcc numbers on an iPhone?

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• WCF - Network Cost

  - by Mubashar Ahmad

  Dear Devs I have a wcf service deployed on IIS with basicHttpBinding and aspNetCompatibilityEnabled=true I have a test client as well which invokes multiple service functions simultaneously. To check the performance of service call on client and server I calculated the Avg time it takes to complete a service request on client(in proxy code) and on server as well. after a test of 8 hrs (server and client were on the same machine) i came to know that average response time on client is around 34ms where as the Avg execution time on server is around 3ms so the difference is 31ms. I would like to know why every call is taking 31ms is it justified? and how can i reduce this?

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• Where are the real risks in network security?

  - by Barry Brown

  Anytime a username/password authentication is used, the common wisdom is to protect the transport of that data using encryption (SSL, HTTPS, etc). But that leaves the end points potentially vulnerable. Realistically, which is at greater risk of intrusion? Transport layer: Compromised via wireless packet sniffing, malicious wiretapping, etc. Transport devices: Risks include ISPs and Internet backbone operators sniffing data. End-user device: Vulnerable to spyware, key loggers, shoulder surfing, and so forth. Remote server: Many uncontrollable vulnerabilities including malicious operators, break-ins resulting in stolen data, physically heisting servers, backups kept in insecure places, and much more. My gut reaction is that although the transport layer is relatively easy to protect via SSL, the risks in the other areas are much, much greater, especially at the end points. For example, at home my computer connects directly to my router; from there it goes straight to my ISPs routers and onto the Internet. I would estimate the risks at the transport level (both software and hardware) at low to non-existant. But what security does the server I'm connected to have? Have they been hacked into? Is the operator collecting usernames and passwords, knowing that most people use the same information at other websites? Likewise, has my computer been compromised by malware? Those seem like much greater risks. What do you think?

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• Create Oracle Cursor

  - by Mohammad

  Hi, I create a cursor like this: SQL> CREATE OR REPLACE PROCEDURE Update_STUD_FinAid ( AIDY_CODE IN VARCHAR2 ) IS 2 CURSOR PublicationC IS 3 SELECT SGBSTDN_USER_ID from SGBSTDN 4 WHERE SGBSTDN_TERM_CODE_EFF ='201030'; 5 BEGIN 6 close PublicationC; 7 8 OPEN PublicationC; 9 10 FOR PublicationR IN PublicationC 11 LOOP 12 DBMS_OUTPUT.PUT_LINE( PublicationR.SGBSTDN_USER_ID ); 13 END LOOP; 14 15 close PublicationC; 16 17 END; 18 / Procedure created. And then when I run the Procedure then I get this error: ERROR at line 1: ORA-06512: at line 2 Please advise. Thanks

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• How to access web server of any machine of my network from the outside

  - by Luc

  Hello, I have an ip like username.dyndns.org, this is the external IP of my router. On my lan, I have several machine (m1, m2, ...) , each running a dedicated web server. Is it possible to reach each machine from the outside with something like: http://m1.username.dyndns.org http://m2.username.dyndns.org ? Do you know what needs to be configured in my router for NAT ? Also, is there a special directive in Apache to do so ? Thanks a lot, Regards, Luc

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• moving audio over a local network using GStreamer

  - by James Turner

  I need to move realtime audio between two Linux machines, which are both running custom software (of mine) which builds on top of Gstreamer. (The software already has other communication between the machines, over a separate TCP-based protocol - I mention this in case having reliable out-of-band data makes a difference to the solution). The audio input will be a microphone / line-in on the sending machine, and normal audio output as the sink on the destination; alsasrc and alsasink are the most likely, though for testing I have been using the audiotestsrc instead of a real microphone. GStreamer offers a multitude of ways to move data round over networks - RTP, RTSP, GDP payloading, UDP and TCP servers, clients and sockets, and so on. There's also many examples on the web of streaming both audio and video - but none of them seem to work for me, in practice; either the destination pipeline fails to negotiate caps, or I hear a single packet and then the pipeline stalls, or the destination pipeline bails out immediately with no data available. In all cases, I'm testing on the command-line just gst-launch. No compression of the audio data is required - raw audio, or trivial WAV, uLaw or aLaw encoding is fine; what's more important is low-ish latency.

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• Enable mobile network

  - by Sebi

  In my application it is necessary to have internet connection. Therefore i check while starting if a Internet connection is availaible. If not I ask the user if he would establish an Internet Connection, and what type (wifi oder mobile). The wifi connection i can establish with the following code WifiManager wifiManager = (WifiManager) getSystemService(Context.WIFI_SERVICE); wifiManager.setWifiEnabled(true); But how do i establish a mobile connection? Coulnd't find a single code snippet at Google.

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• Network Connection NSNotification for OSX?

  - by Andrew

  I simply need to have a notification post when a valid IP address is assigned. I have tried polling via SCReachability, but that seems to be inefficient. Any suggestions? This seems like it should be simple, but I've been struggling for several hours to get anything working.

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• Converting a Table in Oracle Database into an XML file

  - by Geethapriya.VC

  Hi, I need to create XML file, given a table/view in the Database. The actual requirement would be: The code has to get the table/view name as input parameter, read the schema of the same, create a corresponding XML file with the same structure as that of the table/view, and load the XML with the data of the table/view. Language preferred here is JSP. Kindly let me know how to go about this idea. Thanks in advance, Geetha

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• Advance Queue sample in Oracle

  - by user171523

  I am looking for an end to end example in Advanced Queueing in Oralce 10G. I am in the process of understanding Adv Queuing i would like to try it out.

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• Simple non-network concurrency with Twisted

  - by Rince

  Dear pythoners, I have a problem with using Twisted for simple concurrency in python. The problem is - I don't know how to do it and all online resources are about Twisted networking abilities. So I am turning to SO-gurus for some guidance. Python 2.5 is used. Simplified version of my problem runs as follows: A bunch of scientific data A function that munches on the data and creates output ??? < here enters concurrency, it takes chunks of data from 1 and feeds it to 2 Output from 3 is joined and stored My guess is that Twisted reactor can do the number three job. But how? Thanks a lot for any help and suggestions.

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• What is the best way to transmit Java objects over a network

  - by tomdee

  I am trying to transmit objects of a particular class from one server to another. The options I'm looking at are: Serialize the data as JSON and send it over the wire using HTTP, and de-serialize at the other end. Serialize the data into some binary form and transmit using TCP sockets. What are the best practices in this area? What are the gotchas? Ideally I would like the interface to be versioned, so the sender and receiver can be upgraded independently. I'm considering the JSON approach as I already have code that will serialize/deserialize the objects into JSON.

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• Creating IIS Instance over network using MSBuild

  - by Dan

  Is there a way to have MSBuild create an instance of IIS on another remote machine? I do the builds (which occur locally using TeamCity AFAIK), but would like the code to be pushed up to our testing server once the build is completed. I am using IIS 6.x (Windows XP dev and Windows 2k3 Server for testing).

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• How to display image that is located on another server on the network (ASP.NET)

  - by eviljack

  I've got a ASP.NET site that's located on a local server (MY_SERVER). And one of the things it does is pull up tiff files which are located on another server (ANOTHER_SERVER). The location of each of these files is stored in SQL. I pull up each of these images and am supposed to display them. The problem is: the files are not named with a tiff extension (does it matter?) they aren't displaying at all. I am using an Image control to display these images, and I'm not sure if it matters that the extension is not set (does the image control know the difference between an jpg and a tiff without the extension?) I am guessing the images aren't displaying because they are not on the same server MY_SERVER that the images are located (ANOTHER_SERVER). Any ideas on how to fix this?

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• Add network service

  - by user302655

  I have a kernel service driver , i want to install it with an installer . I use Wix that already copy files in driver store but i still need to add the service to the nerwork manualy (in local area connection properties) How can i do this in wix or in javascript ?

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• use Blat to send mail in local network problem

  - by issac

  i trying to use Blat to send mail in local mail server but the error message keep return saying that the smtp server does not like the sender name. i have keep trying different sender name but still cannot, anybody know how to fix it? Pls help..

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• Get Cell RSSI(Network Signal Strength) on Android 1.5

  - by Brandon

  Is there any way to retrieve the current cellular Signal Strength (RSSI) on Android 1.5? I know there's a way to listen for signal strength updates through the TelephonyManager, but this seems to only give a "state," not a numeric value. Is using the RSSI field on a neighboring cell fairly accurate? I'm guessing not, but I'm running out of ideas.

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• Network access when the Android phone is asleep

  - by Immortal

  I'm using a combination of alarm (set with AlarmManager) and background service to periodically synchronize data in my application. The only problem I have is that when sleep policy terminates Wi-Fi connection the synchronization no longer works. Is there a way to "wake up" the Wi-Fi connection that has been put to sleep? GMail somehow manages to do that because it notifies me about new e-mail even if the phone entered sleep mode.

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• Java Socket fails to transmit data over the network

  - by Mark Griffin

  I'm experiencing a bizarre problem with sockets between a Java Knopflerfish client bundle and a PHP (CLI, not web) server. The client/server pair work fine when both are located on the localhost, and all data is transmitted successfully. However, when the Java client exists on a different machine, connections to the server are successful, but no data is received by the PHP script. Packet analysis confirms that the data sent by the Java client is received on by the server - PHP just seems to have problems getting its hands on it. As a further note, I've done some tests with telnet as the client. The PHP server script receives all data fine from any host. This leads me to believe that the problem has something to do with the way java is setting up the socket or that there is some networking issue that I'm not familiar with. Any thoughts would be appreciated. Can post code samples if desired.

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• Varchar2 and Oracle quick question

  - by DAVID

  Hi guys im using varchar2 for a product name field, but when i query the databa from the run SQL command line it shows too many empty spaces, how can i fixe this withouth changing the datatype here is the link to the ss http://img203.imageshack.us/img203/20/varchar.jpg

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• About Network Address Translation (NAT)?

  - by Rudi

  Just curious about a particular scenario of NAT. Let's suppose we have 4 computers sharing a global IP address under the NAT. I understand that the NAT box keeps an internal record to know which computer to forward requests to. But let's say on computer #2 I'm trying to download a file. And let's say on computer #1, #3, and #4, I'm just browsing the web normally. When the browser initiates a TCP connection to get that file, how does it know which computer to give it to? I mean like, each of the four computers is using port 80 to browse the web right? How does the NAT's record distinguish which "port 80" belongs to which computer?

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• updating a table conditionally with values from a group by sub query in oracle

  - by user333147

  the problem is Update the salary of all the employees by 50% who had worked on 5 or more than 5 projects, by 30% (= 3 projects), by 20 % (= 1 projects) the number of project is got by performing a group by query on the EMPLOYEE_PROJECT_HISTORY; i have tried these queries 1) update emp set emp.sal= case when jemp.pcount >=5 then emp.sal+ (emp.sal*50)/100 when jemp.pcount >=3 then emp.sal+ (emp.sal*30)/100 when jemp.pcount >=1 then emp.sal+ (emp.sal*20)/100 else emp.sal+ (emp.sal*20)/100 end from employee emp join (select empno as jempno,count(projectno) as pcount from EMPLOYEE_PROJECT_HISTORY by empno) jemp on emp.empno=jemp.jempno ; 2)update employee a set a.sal= case (select count(b.projectno) as pcount from EMPLOYEE_PROJECT_HISTORY b group by b.empno ) when b.pcount >5 then a.sal = a.sal+ (a.sal*50)/100 when pcount >3 then a.sal = a.sal+ (a.sal*30)/100 when pcount >1 then a.sal = a.sal+ (a.sal*20)/100 end;

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