Time And A Packet’s Journey

Time and a packet's journeyIt’s a big deal to know what makes your network slow, yea! you know about it, LATENCY– it’s that value you see at the end of a ping test result line. But what are on a packets route that causes latency on a network?

Network Latency is the time period between a request for a network to perform an action and when the action is carried out. Latency has also been defined as “a time delay imparted by each element involved in the transmission of data”. In a nutshell, network latency can be defined as a measure of delay – in time, of data transmission.

The “four key causes of latency are: propagation delay, serialization, data protocols, routing and switching, and queuing and buffing”. 1

“Propagation delay = distance/speed”: this delay is caused by physical distance constraint on signal propagation through a given medium.

“Serialization delay = packet size in bits’/transmission rate in bits per second”: this accounts for the time taken for data to be ordered at the transmit end and re-read at the receiver end.

“Data communications protocols at various layers in the protocol”: the various network protocols have time consuming activities like handshake to establish a communication path.

“High performance IP routers and switches add approximately 200 microseconds of latency to the link due to packet processing.”: the protocol stacks in every device’s Network Interface Card (NIC) accounts for some delay in a packet’s journey. 1

Now to put things in perspective, if you wondering how you get a 10ms latency on your fiber link from Abuja to Lagos let us have the following review:

The speed of light in a vacuum is 299,792,458 meters per second, or 186,282 miles per second. In any other medium, though, it’s generally a lot slower. In normal optical fibers (silica glass), light travels a full 31% slower. 2. So for a distance of Lagos to Abuja in Nigeria, if you do the maths, a latency of 3ms is already imparted by the physical distance between both locations (propagation delay) leading to latencies of about 10ms in this distance. So in this scenario, less than 40% of network latency results from the fiber-medium of transmission, though it is the most common cause of latency, the rest are hardly considered and are difficult to define – exactly how much do they contribute at any given time? but there is no doubt of their existence.

Having slower devices on the path to a destination on your network, packet size to transmission rate ratio, network protocols and operating systems performance greatly impart on how low or high a network latency is.

From the foregoing, it is important to note that the desire to reduce latency in a network should be all encompassing of all the contributors to latency and not assumed to be strictly defined by distance alone in any network design. Now that we know, how would you improve latency on your PC, small gateway router, edge router etc.? Let me know…

Author: Chris Acheme

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