Skip to main content

Network Congestion Symptoms


By using a network protocol analyzer such as Wireshark, a Network Administrator can determine if congestion is present on their network.  The key is looking for duplicate ACKs.

Consistent duplicate ACKs are an indication that network congestion may be present. The problem is worth investigating.

To manage the reliability of data between two endpoints, TCP uses ordered sequence numbers (SYN) and acknowledgements (ACKs). 
For example, data is broken up into packets, and each packet is given a sequence number.

(Data to be sent) = Packet A – SYN 1, Packet B – SYN2, Packet C – SYN3

Each packet is sent in sequential order, and as each packet arrives to its destination, the destination endpoint sends a unique acknowledgement (ACK) back to the transmitter as a way to verify the data has been received in its proper order.

ACK 1 [Packet A – SYN1], ACK 2 ACK 1 [Packet B – SYN2], ACK 3 [Packet A – SYN3],

If the data arrives out of order, a duplicate ACK is sent to the transmitting endpoint, because it did not receive the next expected ACK in the proper sequence. Three duplicate ACKS sent in a row will trigger the request for a re-transmission of the packet.


Network congestion will equate to performance issues on the network, and packets arriving out of order are a sign that it is present.  There are a couple of areas a Network Administrator can look, one being Layer – One (physical cabling, EMI interference), network adapter or a problem with the actual transmitting endpoint.  For instance, the processor or other component at the endpoint.  
Labels:

Comments

Post a Comment

Popular posts from this blog

"This content requires HDCP for playback" Apple TV fix

Perhaps you are having issues viewing Netflix, iTunes or any other streaming content via your Apple TV device? First, the short answer regarding the fix (in most cases)... 1). Leave your Apple TV device ON. 2). Turn OFF your TV for 10 seconds. 3). Turn ON your TV. 4). Now attempt to view the content on your Apple TV (hopefully without error). Behind the answer... Depending on the content being streamed, there is an authentication process that takes place when you request content. The user is usually oblivious of the this, that is until something goes wrong. HDCP stands for (H)igh bandwidth (D)igital (C)ontent (P)rotection. Even if you are only mildly interested in the 'what' of HDCP, I highly recommend checking out this simple yet concise and exhaustive explanation on Wikipedia, which can be found here... High-bandwidth Digital Content Protection - An Overview More specific information regarding the HDCP issue and Apple TV can be f...
11 comments
Read more

Get List of Exchange Public Folder User Permissions

In the past, end users who should not have had the ability to delete certain Exchange Public Folders from within their Outlook client accidentally  were able to do so.  When these users were initially set up for access to the folders, they were given the permission of 'Owner.'  Reason being, staff at the time were not set on how to grant the proper least priority permissions which would enable the users to make changes within in the folders without escalated permission that also allowed them to delete the folders. To correct the problem, I first needed to know who had what permissions to each folder.  What follows are several commands which can be used within the Microsoft Exchange Management Shell that allows you to obtain such information.  You can either output the information on screen, or to a file where you can use such a tool such as Excel to examine and sort the data. In the following examples, replace FOLDERNAME with the name of your ...
Post a Comment
Read more