bradyvolpe.com

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In this series of blogs I address a myrid of subject matters that involve troubleshooting DOCSIS and services that are provided over DOCSIS such as high speed data (HSD), Voice-over-Internet Protocol (VoIP), and Internet Protocol TV (IPTV).  Many of the blogs include primers that cover fundamentals of the services, such as a VoIP primer so that one has the essential building block for sound troubleshooting.

Troubleshooting DOCSIS – VoIP Impairments

In this blog I am going to digress for a moment from my standard DOCSIS 101 tutorial and spend a little time on DOCSIS troubleshooting basics, especially with respect to Voice-over-Internet Protocol (VoIP). I am doing this as due to many offline questions specific to this topic. Don’t worry, though I may start to inter-mix some troubleshooting blogs now and again, just check the DOCSIS 101 page to stay on top of the latest DOCSIS tutorial blogs.

Troubleshooting DOCSIS – VoIP Impairments > Packet Loss

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.

Troubleshooting DOCSIS – VoIP Impairments > Delay & Jitter

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 most disruptive impairment in VoIP networks.  The effects of delay to the caller generally appear as echo and talker overlap.

Hacking DOCSIS Cable Modems

Recently a reader contacted me and said that theft of service, especially uncapping cable modems via hacking, was still impacting his network.  Not surprisingly, one vendor’s CMTS was able to ward off the hacker’s while another vendor’s CMTS was unable to prevent the uncapping and subsequent theft of service.  I will protect the vendor’s identities because I believe that the CMTS is the first line of defense.  Vendors have put into place very effective, CMTS specific techniques, such as Cisco’s TFTP-Enforce which prohibits a cable modem from registering and coming on line if there is no matching TFTP traffic through the CMTS preceding the registration attempt.  But often individual techniques are “hacked” (such as in the TFTP-Enforce bypass method found on hacker sites).  What this indicates is that any reliance on a single point or method of hack-proofing your network WILL NOT WORK.  You must implement a layered approach consisting of a number of CMTS, DHCP, TFTP and potentially SNMP and Kerberos related methods.  The later would apply for MTAs and set top boxes.  For now we will just focus on cable modems and the realm of CMTSs and DHCP/TFTP servers.  Here are is the bare minimum of what you should be doing: