Causes of Latency

[alihassan1618]

Hi, Guys, Another dive to the technical topic!

Which two causes of latency are true?(choose two)

1. High bandwidth on a link
2. Split horizon
3. Propagation delay
4. Serialization delay
5. Under-utilization of a link

i think "Propagation Delay" causes latency issues on a WAN Link, but i'm totally blind about 2nd Answer.

[GRANT3779]

There is a thread here that should give you what you need. Great info from Daniel and Joseph.

Should hopefully answer your query.

https://community.cisco.com/t5/switching/how-to-understand-serialization-delay-and-bdp/td-p/2409563

[Giuseppe Larosa · Accepted solution]

Hello Alihassan1618,

the correct answers are:

propagation delay : related to the speed of electromagnetic waves over the medium it is usually a fraction of c speed of light in vacuum divided by refraction index ( on fiber cables for example) and the distance. It is important when distance are in the order of hundreds of kilometers or more.

and

serializiation delay : it is the time to put on wire all the bits that form a frame (L2 PDU) that carries an IP packet ( L3 PDU).

In addition to this there is the time the packet waits in a software or hardware queue on the device if QoS is implemented on each router hop on the path.

Hope to help

Giuseppe

[Joseph W. Doherty]

In addition to what Giuseppe correctly notes are the answers, serialization delay depends on the "bandwidth". More bandwidth reduces this delay. "Modern" high speed Ethernet often much reduces this latency compared to older WAN media bandwidths. However, propagation delay is the same regardless of bandwidth. This is important to understand as many assume more bandwidth makes the network faster, but especially in WANs, distance based latency often makes a network appear "slow". (Especially when dealing with intercontinental WAN links, many find it difficult to understand obtaining more bandwidth doesn't "fix" a "slow" network.)

To decrease the impact of serialization delay on LANs, some switches support "cut-through" switching (which means beginning transmission of a frame while a portion of it is still being received) rather than the usual "store-and-forward" switching. (BTW, old fashion hubs offer less latency than a switch.)