• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 744
  • Last Modified:

Delayed ACKs

Can anyone tell me what delayed acks are supposed to look like on a sniffer?

Initially, I thought it was supposed to look like this:

Host A--------(1514byte frame)------> Host B

Host A--------(1514byte frame)------> Host B

Host A--------(1514byte frame)------> Host B

Host A <------------ACK----------------  Host B

But isnt the above TCP's sliding window protocol?


thanks!
0
dissolved
Asked:
dissolved
  • 5
  • 3
1 Solution
 
jlevieCommented:
That could easily be part of an FTP transaction using a sliding window protocol. What port numbers were involved?
0
 
dissolvedAuthor Commented:
Hi, it was actually HTTP traffic.

 Could someone post what the following would look like on a sniffer:

1. Delayed ACKs

2. Sliding window protocol

3. Nagle algorithm

I'm assuming, the nagle algorithm looks like this:

Host A---------(60byte frame)---->   Host B
Host A  <----------ACK-------------    Host B
Host A---------(60byte frame)---->   Host B
Host A  <----------ACK-------------    Host B

I've read TCP/IP illustrated but am still having trouble recognizing what they would look like.
Thanks
0
 
jlevieCommented:
>  Hi, it was actually HTTP traffic.

Oh, that was probably just packet fragmentation. To determine what you have it is necessary to take the IP headers apart and look at the transfer sizes and sequence numbers.
0
What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

 
dissolvedAuthor Commented:
packets were not fragged.   DF flag was set each time.  

From my understanding, delayed ack is applied to the receiver. Where as nagle algorithm is applied to the sender.  I heard they can compliment each other in terms of piggybacking data.

What I want to know is where does the sliding protocol comes into play here.  I think if the packet is full size (1460 bytes of data), then it doesnt use the nagle algorithm. Rather, it uses sliding protocol.  I also believe nagle is used mostly in interactive sessions.

Can anyone correct me?

Thanks
0
 
jlevieCommented:
> From my understanding, delayed ack is applied to the receiver.

True.

> Where as nagle algorithm is applied to the sender.

Also true.

> What I want to know is where does the sliding protocol comes into play here.

That is an optimization at the TCP/IP stack level and is a means of flow control. Basically the receiver side sets the window size to be the buffer space (usually at the kernel level) remaining. The sender is free to push data out at window sized transfers or less  as long as the receiver isn't advertising a zero window size. Window size advertisements can be occuring while data packets are being received and that will happen if the application is reading data from the buffer at a rate similar to the data arrival rate. In that case a steady-state condition can occur where data packets are in transit while window advertisements are also in transit, which is a very efficient form of data transfer.
0
 
dissolvedAuthor Commented:
You said the sender can send as much data to the receiver as long as it doesnt go past the receivers window.  The sender can even send less.

If the sender sends less than the receivers window size, how will the receiver know when to ACK?  Won't the delayed ACK timer go off?
0
 
jlevieCommented:
Let me think about that...
0
 
jlevieCommented:
ACK or delayed ACK would be a function of the packet size and frequency, as I understand it. Essentially that means that the sliding window and ACK behavior are independent functions.
0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

  • 5
  • 3
Tackle projects and never again get stuck behind a technical roadblock.
Join Now