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Call Quality Degraded On TCP?


Rick Guyton
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Has anyone else noticed that call quality over TCP is noticeably degraded? In diagnosing an un-related issue I swapped a phone over to TCP and though it fixed the issue I was having, I noticed calls on those phones seemed noticeably degraded. I understand that there's more overhead with TCP. But these guys were on a 100/100 meg connection and using less than 10%...

Just curious if anyone else has seen this.
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Switching to TCP just changes signaling. If you were using UDP, it didn't work well, you switched to TCP and your "signaling" issues went away but you now have audio issues, you've actually proven that the internet or network IS the problem.

TCP covers up connectivity problems, which is why we don't like it. UDP has no error correction built-in, so errors and unreliable links become problematic. TCP corrects errors on it's own, but you can't use it for audio because it adds delay. So audio still remains UDP. Thus, if TCP "fixes" your original issue, then really TCP likely just "covered up" your original issue and now UDP is still used for audio but is still having the same issue.
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Nothing surprises me about Comcast ;-) It's definitely better in some places than others though.

I was about to say Verizon FiOS is like heaven when we have a customer with it, but their new "Quantum" routers have serious issues with SIP signaling where random phones don't ring, or phones keep ringing after calls are answered. We immediately replace the Quantum routers with something else and all of the problems go away. We've literally never gotten any other complaint from a FiOS customer (and now we get none because we know to switch the router out before setting them up).

My fear is that Comcast will start doing the same thing. So far so good with their issued modem/router units (knock on wood), but the huge problem with Comcast is that if you have a static IP, you HAVE to use their modem/router and there is no way around it. What happens when their routers start causing VoIP issues but the customer has to have a static IP? Then what?

And if you're wondering why Comcast requires you to use their modem/router when you have static IPs, it has to do with a combination of how they handle subnetting and their specific implementation of RIP. Basically comes down to how they have decided to ensure you aren't announcing the wrong IPs.

And no, bridge mode might not be the solution either because their bridge mode is still doing Layer 3 functionality.
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We actually believe Comcast was de-prioritizing UDP SIP/RTP for a customer (different voice platform) since by sending the traffic over a GRE tunnel between the customer router and our data center where they couldn't inspect it and it resolved their signaling and audio issues. Using SRTP didn't really solve anything because the headers are still available for identifying traffic type but the tunnel made a difference.

Fairly certain that is illegal (continue to just say NO to internet fast lanes!) so good luck getting them to admit to it but something to consider when using ISPs who offer the same services on their own Network.
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Something to keep in mind... "Comcast" is really American Cable Systems. Which became Comcast in 1969. Then they bought Group W Cable in 1986. Then Storer Communications in 1985. Then it bought Maclean-Hunter's US division. 

Then it started rolling out internet via the "@Home" network (anyone remember this?). This was partially via a company named "Excite", who went bankrupt, and Comcast bought their assets.

Then they bought Prime Communications. and some VeriSign stock. and MediaOne (via a trade with AT&T). Also they bought AT&T Broadband. and Patriot Media in 2007.

shall I go on?

If you think during each of these mergers, they walked in and within 90 days ripped & replaced all the customer equipment, billing systems, routers, switches, fiber cables, etc. with a nice unified system... Wellllll hehehe ummm 


In reality they're JUST getting to that point now with just their portal and ticketing systems (within the past couple years). They still operate the territories somewhat separately.

Why am I saying all this? My guess is they have different equipment and programming in each region.

Hence the weird, inconsistent network results.

There is no "Comcast" there's just "merger mess with a nice name."
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I was recently told from an insider that Comcast runs their "nodes" at 87-92% utilization and that they intermingle residential and business accounts.

I believe WOW runs closer to 65% utilization and does not intermingle business and residential.  I don't have all the details or a complete understand on how this stuff works but I figured I would share it anyways.
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sorry i'm late to the party - we went through about 30 days of a sh%t storm trying to engineer around Comcast in Nashville. Same issues plus there was noticeable delay on most calls. I'm talking 2-3 seconds like when we used to call overseas in the 80's. Yeah, you remember.
We tried everything - including buildng an IPsec tunnel into our office and then routing out. It seemed to fix the issue once Comcast couldn't inspect but was going to be a pain to backhaul all that voice and add complexity. The issue presented itself more often when there were 2 or more concurrent calls. We also got a Comcast SE to admit they throttle RTP for non-Comcast VoIp customers!

In the end we removed the VPN tunnel and have aggressively throttled the bandwidth on our router using overthrottling. The Comcast modem is bridged with a static IP so just passes traffic, in theory. We have a QoS policy applied to the voice VLAN and since the throttling never gets anywhere near 75% of the tested capacity of the line (up and down) it seems Comcast's de-prioritization never kicks in. BOO YA COMCAST
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