bradyvolpe.com

DOCSIS 1.0 enabled data over coax with a “best effort” service using a data request-grant methodology. DOCSIS 1.1 and subsequent specifications added guaranteed Quality of Service (QoS) by providing Unsolicited Grant Synchronization (UGS) which means that a cable modem does not have to send a data request in order to receive a bandwidth grant from the CMTS. The new UGS service is an enabling technology which has allowed cable operators to successfully deploy the highly revenue generating Voice-over-IP (VoIP) services. In the following sections I will illustrate the differences between best-effort (request-grant) and QoS (UGS) services.

In this blog I will address delay and jitter as they pertain to VoIP in a DOCSIS network.  Delay, jitter and packet loss are the three primary impairment in a VoIP network, but packet loss was addressed in my Troubleshooting DOCSIS – VoIP Impairments > Packet Loss blog. After packet loss, delay is the second [...]

In this blog I am going to focus on VoIP packet loss, which is just one of the three (3) primary types of VoIP impairments that are present in a DOCSIS network. I will cover many RF and IP terms in this blog that I have not discussed in my previous tutorials, not to worry! This terminology is all fodder for future blogs.

To review, the three fundamental impairments which impact call quality of VoIP communications are as follows:

* Packet Loss – The complete or partial loss of a packet containing actual voice payload.

* Delay – The time a packet takes to traverse the space between the source and destination of a voice call. The space is comprised of both the physical distance the data must travel in addition to the active network routing and switching elements, which contribute additional delay.

* Jitter – The variance of inter-packet arrival time from one transmitted packet to the next sequential packet.