VOIP over virgin fibre

Adam M

Active Member
Hi all,

Am in the process of trying to move my office phones from ISDN over to VOIP. The company who provides our current ISDN lines does a VOIP package but she has told me the following and I'd like to understand this better.

"Unfortunately the VOX system is not compatible with Virgin broadband, Virgin have something SIP ALG enabled on their routers which they are not happy to remove. Having this setting enabled causes call quality issues on VOX and other VOIP systems."

Does this sound reasonable to anyone?


Well-known Member
Yes it does... passing voice across a bog standard internet connection isnt ideal and will give you issues. Any half decent Voip company will not support a voice service over the internet

Ideally you should invest in a voice only network connection - but saying that it depends how bothered you are about voice quality and how many critical calls your doing.

Adam M

Active Member
Really helpful answer - thank you!

we need telephony but the reality is that we make and receive very few calls.


Any half decent Voip company will not support a voice service over the internet
I think I know what you are saying, but VOIP means voice over IP so a VOIP provider offers exactly that - voice over an internet connection.

The traffic can be allocated to be different classes for different data types - so For example over here TC1 is voice only (only offered on a deviated voice port in an FTTH NTD) whereas TC4 is best effort for all data amd would be the standard for residential connections. TC 2 here is all data but with a service level agreement so proper business grade.

SIP ALG is part of the router firewall - the SIL part is VOIP but the Application Layer Gateway is for almost all situations pointless and actually as it rewrites packer destinations it invariably breaks things. It can be useful in multiple NAT but for residential connections rule number one is a kid double or more NAT (if you don’t know what you are doing and just want to plug and play).

so if the ISP controls all router settings on the connection, it is possible they insist SIP ALV in set to on. A third party VSP is then stuffed since they will have at the top of their customer service setup to find SIP ALG on the router and turn it off.

so long story short - yes sounds right if Virgin do indeed lock settings to have SIP ALG set to on.

Adam M

Active Member
I was a bit confused but “any half decent voip company will not support a voice service over the internet”.

I did think that’s what voip meant but assumed there were dedicated layers within the internet that are maybe reserved for voice calls.


Well-known Member
Sorry i may have confused with that comment... working in the telecoms industry our service will not support voice issues across a bog standard broadband link, regardless of how big the pipe is..

if you are registering to something like sipgate for the handful of calls then its fine..

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