Question

UDP socket programming difficulties

Asked by: t7wang

Hi,

    I am trying to implement a layer of protocol on top of UDP to provide reliable transport.  When I run my program under windows environment, I am getting weird problems with packet losses.  My test environment includes 2 pentium 4 machines connected through a cross-over cable.  And I set my sender to send data at a relatively low rate.  But my receiver doesn't seem to be able to get all the packet after I run my program for 30s or so.  I am suspected the packets are being dropped by OS.  Maybe windows has a rather small queue for UDP connection?

Thanks for your help!

This Question has been solved and asker verified All Experts Exchange premium technology solutions are available to subscription members.

Subscribe now for full access to Experts Exchange and get

Instant Access to this Solution

  • Plus...
  • 30 Day FREE access, no risk, no obligation
  • Collaborate with the world's top tech experts
  • Unlimited access to our exclusive solution database
  • Never be left without tech help again

Subscribe Now

Asked On
2003-10-20 at 11:10:33ID20772276
Tags

udp

Topic

Windows Programming

Participating Experts
4
Points
125
Comments
8

Trusted by hundreds of thousands everyday for fast, accurate and reliable tech support.

  • "The time we save is the biggest benefit of Experts Exchange to Warner Bros. What could take multiple guys 2 hours or more each to find is accessed in around 15 minutes on Experts Exchange." Mike Kapnisakis, Warner Bros.
  • "Our team likes having a resource that is more secure than just using Google and most experts using this service really know their stuff. It's nice to look here first versus using Google." Dayna Sellner, Lockheed Martin
  • "Anytime that I've been stumped with a problem, 9 out of 10 times Experts Exchange has either the accepted solution or an open discussion of the potential solution to the problem." Kenny Red, eBay Inc.

See what Experts Exchange can do for you.

Got a question?

We've got the answer.

Experts Exchange has been collecting answers to technology questions since 1996…3 million and counting! If you have a question, chances are we already have your answer.

Screenshot of Experts Exchange Knowledgebase

Need individual assistance?

Our experts are ready to help.

If you can't find the exact answer you're looking for, ask our exclusive community of 50,000 experts. You’ll get a personalized answer from a trusted professional.

Screenshot of Experts Exchange Knowledgebase

Want to learn from the best?

Read articles from industry experts.

Thousands of free tech tips, tricks, how-to’s and tutorials are available in our peer reviewed articles section. See for yourself how smart our experts are, no login required.

Screenshot of an Article

Working on a long term project?

Store your work and research.

Save solutions to your questions, answers you’ve discovered through searching plus helpful articles in your personal knowledgebase for easy future access.

Screenshot of Experts Exchange Knowledgebase

Access the answers to your technology questions today.

Subscribe Now

30-day free trial. Register in 60 seconds.

What Makes Experts Exchange Unique?

Members of the expert community talk about why the experience at Experts Exchange is different than what you will find anywhere else.

Trusted by the world's most respected brands.

image of each brand's logo

Faithfully serving IT professionals since 1996.

Experts Exchange Logo

Try it out and discover for yourself.

Subscribe Now

30-day free trial. Register in 60 seconds.

Related Solutions

  1. udp
    i am trying to make a UDP client\server program. so far i am able to send text to the server but i would like to open the cd rom on the server how can i do this in delphi 3 using UDP where do i put the code on server or client?
  2. UDP or TCP Streams
    I am currently studying Sockets in Delphi and I'm having some trouble. Can anyone post source code that implements either TCP Streams or Reliable UDP Streams. The code must use raw Winsock functions. I would really appreciate it. Thanks!
  3. Application Protocol Using UDP.
    Hi I want to construct an application protocol that will provide reliable delivery of component messages over IP networks. The protocol will use UDP but I need to to provide a reliable service to the application i.e. no duplication of data, it should also deal with timeouts ...
  4. udp monitoring
    Hi All Posted here as I assumed a lot of VoIP applications would be udp based. Got a SMB client who uses a realtime app - they're in the transport industry. This app goes haywire periodically and costs them a lot of $. It has two parts a gateway PC that talks to their tru...
  5. UDP connection
    I have an application that needs to recieve UDP Calls. On the visual control in delphi I set the remote and local host properties to "LocalHost" and the local port to 44966 and the remote port to 44967. Then using a sample application from http://www.torry.net/vcl...

Free Tech Articles

  1. WARNING: 5 Reasons why you should NEVER fix a computer for free.
    It is in our nature to love the puzzle. We are obsessed. The lot of us. We love puzzles. We love the challenge. We thrive on finding the answer. We hate disarray. It bothers us deep in our soul. W...
  2. SCCM OSD Basic troubleshooting
    SCCM 2007 OSD is a fantastic way to deploy operating systems, however, like most things SCCM issues can sometimes be difficult to resolve due to the sheer volume of logs to sift through and the dispe...
  3. Migrate Small Business Server 2003 to Exchange 2010 and Windows 2008 R2
    This guide is intended to provide step by step instructions on how to migrate from Small Business Server 2003 to Windows 2008 R2 with Exchange 2010. For this migration to work you will need the fo...
  4. Create a Win7 Gadget
    This article shows you how to create a simple "Gadget" -- a sort of mini-application supported by Windows 7 and Vista. Gadgets can be dropped anywhere on the desktop to provide instant information, ...
  5. Outlook continually prompting for username and password
    There have been a lot of questions recently regarding Outlook prompting for a username and password whilst using Exchange 2007. There are a few reasons why this would happen and I will try to cover t...
  6. Backup Exchange 2010 Information Store using Windows Backup
    There seems to be quite a lot of confusion around the ability to backup Exchange 2010 using the built in Windows Backup feature. This stems from the omission of this feature prior to Exchange 2007 s...

Cloud Class Webinars

  1. Avoiding Bugs in Microsoft Access
    Alison Balter takes and in-depth look at avoiding bugs in Access. In this webinar you will learn about using the immediate window to debug your applications, invoking the debugger, using breakpoints to troubleshoot, stepping through code, setting the next statement to execute, ...
  2. Top 10 Best New Features in Visio 2010
    Scott Helmers gives live demonstrations of the top 10 new features in Visio 2010. This webinar will teach you how to create compelling diagrams by adding shapes to the page with a single click, linking the shapes in a diagram to data in Excel (or SQL Server, or SharePoint), ...
  3. IT Consultant Business Secrets Revealed
    Michael Munger, Experts Exchange tech pro and IT consultant, pulls back the curtain on his very successful businesses and answers question on every IT consultant and business owner should know about. He shares secrets on what he did to solve the 5 most common problems in IT, ...
  4. Disaster Recovery and Business Continuity
    Quest CTO, Mike Billon, gives an overview of the steps involved in building a dunamic disaster recovery plan. Through case studies and an examination of software/hardware tooles for monitoring and testing, you'll gain a better understandin of where you are, where you want ...
  5. Organize Your Visio Diagrams with Containers and Lists
    Scott Helmers uses cross functional flowcharts, wireframe diagrams, data graphic legends and seating charts to teach you: how to ustilize all three new structured diagram components in Visio 2010, the best practices for organizeing shapes in previous version of Visio, how to organize ...
  6. How to Us Objects, Properties, Events and Methods in Microsoft Access
    Alison Dalter gives an in-depbth look at objects, properties, events and methods in Microsoft Access. In this webinar you will learn about using the object browser, referring to objects, working with properties and methods, working with object variables, understanding the ...

Join the Community

Give a Little. Get a Lot.

Join the community of experts here and help other tech pros by answering question in your area of expertise. You can earn FREE access to all Experts Exchange's premium features and resources.

Join the Community

Answers

 

by: _nn_Posted on 2003-10-20 at 14:00:45ID: 9586346

Well, you could try to increase the buffer sizes by calling setsockopt()
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winsock/winsock/setsockopt_2.asp

Tune the values for SO_RCVBUF and SO_SNDBUF. This way you'll make sure that it's indeed the culprit... or maybe not. There are possibly many other reasons why the connection could be unreliable. If tuning the sizes of the buffers doesn't help, and if other network programs (file sharing for instance) works ok between the boxes, you'll have to question your program design.

 

by: mxjijoPosted on 2003-10-21 at 09:46:54ID: 9591986


How sure are you, when you say the OS drops packets ??
Did you use a sniffer to verify it ??
You can easyly trace down if there is a packet drop by using "netstat" with -s option.

But the tricky part with UDP is you cannot send large packets (If i recall it correctly,  1470 on Win2k server)
So, your data might get fragmented. Again the packets may not arrive in teh same sequence as you sent.
I guess for secure UDP (I dont see many people work on secure UDP though) this might be a problem.
I'd say you should investigate a little more on where exactly the packets are lost. Errors could happen even at athe cleint side. BTW, are you getting any errors on *any* of your sendto()s and recvfrom()s ???

~ J

 

by: adgPosted on 2003-10-23 at 04:45:12ID: 9605799

Which blocking technique are you using? WSAAsyncSelect? WSAEventSelect? Blocking sockets and UNIX style select()? The reason I ask is you may be sending when the outgoing buffer is full. in this case, your packets would be "dropped" right there in the send() call. Are you checking all return values for errors?

When you say "sending at a low rate" does that mean a tight loop of small packets, or are you performing a delay between packets?

 

by: t7wangPosted on 2003-10-23 at 06:53:19ID: 9606704

Hi All,

    Thanks for all the help and followups.  I am checking for all my socket API calls and there are no errors.  I tried setsockopt(), setting send/recv buffers to 64 kb, and it helped with the small file i was originally testing with but doesn't do the job.  So I guess it's definitely a problem with OS buffer overflow.  My current protocol is one layer above UDP and it calls recvfrom() and sendto() in busy loops to communicate.  What do you guys think it's reasonable send rate for applications like this?  Thanks!

 

by: NickRepinPosted on 2003-10-27 at 16:59:31ID: 9630847

UDP is an unreliable protocol by definition. UDP packets can be lost or duplicated. There's nothing you can do about it.

Your program must be able to recover if a packet was lost or duplicated, or use TCP.

 

by: adgPosted on 2003-10-29 at 21:51:34ID: 9647922

The problem is most likely that UDP provides no flow control. The UDP protocol is allowed to drop packets whenever it sees fit. If your outgoing queue is full, it is acceptable (according to the definition of UDP) for the OS to drop a random packet from the queue to make room for the new one. It is also acceptable for busy routers to drop a random packet when buffers are full.

UDP is also allowed to reorder packets, meaning that if one packet takes a shorter/faster route than the one sent previously, it is possible for acknowledgements and/or data packets to be received out-of-order.

You need to use acknowledgements to implement flow control - limit how much you send before receiving an aknowledgement. For a guideline for flow control, TCP sends an acknowledgement every two packets, or every two seconds, whichever comes first.

The 'window' is the number of packets outstanding to allow before receiving an acknowledgement. TCP uses an initial window of one segment, which is doubled on every acknowledgement, up to a limit. Dropped packets reset the window. Duplicate acknowledgements usually indicate a dropped packet.

Sophisticated flow control and retransmission methods layered on top of UDP begin to become so much like TCP that you might as well have used TCP in the first place.

UDP is best for question/answer style transactions where the question and the answer preferably fit in one packet. If you try to implement a long stream of UDP data, you really should use TCP. Perhaps UDP packets could help decide which end should listen, and exchange IP and port data for the TCP transfer.

Another time UDP is really good is if your application can tolerate dropped packets and don't want to hold up the data stream waiting for a dropped packet to be retransmitted.

20120131-EE-VQP-002

3 Ways to Join

30-Day Free Trial

The Experts

98% positive feedback on 31,087 answers since March 2000. angeliii is a Microsoft Most Valuable Professional for his work with MS SQL Server & Develoment.

He has also proven his knowledge of Visual Basic Programming, PHP Scripting and Oracle Databases.

The Experts

97% positive feedback on 10,752 answers since July 2000. lrmoore has more than 18 years experience in the networking industry.

The six-time Mircosoft MVPs specialties include firewalls, virtual private networking, and network management.

Testimonials

"...and excellent source for support... Kind of like having your very own IT dept." Electriciansnet

Testimonials

"I was apprehensive at signing up at first. However... it has already made my life as an IT administrator much easier." JaCrews

Testimonials

"WOW! You guys have great, active, and knowledgeable people on here." moore50

Business Clients

Business Clients

In the Press

"If you’ve got a question... Experts Exchange can supply an answer.”

In the Press

"...an invaluable aid for both IT professionals and those who require tech support."

In the Press

"where IT professionals provide quick answers on just about any topic"

Business Account Plans

Loading Advertisement...