General Networking, Internet - Tuesday, June 17, 2008 19:46 - 0 Comments

Troubleshooting lost packets

Detecting lost packets between your host and a node on the internet  (with ping and traceroute)

What is a lost packet?
If you click on a link, you naturally expect that link to load into your browser.  But have you ever noticed that sometimes the same link will display very quickly, and sometimes it seems to take a very long time, or it doesn’t load at all? 

To explain this, I will give a brief explanation of how the internet works.  All communication on the ‘net is relayed through “nodes” or servers.  From your computer (which is typically a dead-end node), it passes through server after server to reach the location (URL) you are trying to reach.  That location then sends information back to you, using the same process.  The original theory behind the Internet was that a group of nodes in the middle might become unavailable, but the data must still get through, so when information hits a relay that isn’t in operation, it finds another relay point and continues around the unavailable link.

Occasionally, a piece of data is trapped at a node that suddenly becomes unavailable.  While it is already being followed by other pieces of the total information being exchanged, that particular bit, which is called a packet, becomes lost to the stream.  When the following segments arrive at your computer, a checksum is performed, and the lost packet must be requested to be re-sent.  This creates a delay.  On rare occasions, the node you are sending or receiving data from becomes isolated, which results in messages such as “server not found”, or “node unavailable”.

 What is Ping?
A ping is similar to a stopwatch that measures the time it takes for information to get your machine to the node you are communicating with.  The more nodes that must be relayed through, the longer the ping result.  Blockages along the way (unavailable nodes), delay the ping because it must find an alternate route which is usually less direct.  Ideally, a ping response should be in the zero to one second range.  Ping results higher than that generally indicate a problem with nodes somewhere along the way.

 What is Traceroute?
As the name implies, Traceroute is similar to a roadmap for data transmission.  Each node that a ping or other data packet (yes, a ping is a packet of information) goes through can be mapped out, forming a continuous set of nodes between your machine and the machine you are contacting.  By storing this “map”, your host is able to immediately see when a particular is unavailable, as well as indicate the length of the route.  This route is the number of nodes involved in the trip taken by the data.

To see an amusing and informative video which explains data transmission, please visit:
http://video.google.com/videoplay?docid=3081772283028683472
Please visit the Warroirs of the Net Website: http://www.warriorsofthe.net/

To download software which analyzes Ping and Traceroute information, please visit:
http://www.sharewareconnection.com/titles/traceroute.htm

Article written by MyComputerAid.com