Product Related Information/September 2007 How to ensure Quality of Service on Trunks

3-Jun-15 Product Related InformationPage 2 Moving to VoIP requires a proper networking architecture The user experience of the telephone system is that it is “always available” The Internet was largely built around HTTP and –„Quality“ means availability –Response times did not matter as long as it was less than a few seconds –But Internet technology can be used for voice The goal of this presentation is to show the “do” and “don’t” in VoIP –Some approaches are tempting, but not suitable for business VoIP –Choose an architecture that is safe and accept no risks This presentation deals only with trunks –Connect remote offices no in scope –QoS inside the LAN is also another topic

3-Jun-15 Product Related InformationPage 3 Play safe: Just use a PSTN gateway Connect to PSTN through PSTN gateway –Telephone rates have become reasonable over the past few years –Economically very feasible option Run the traffic in the LAN –Most of the time, the regular LAN is sufficient –Or run the traffic in a VLAN with higher priority This might sound boring, … –… but you probably want other kind of excitement than dropping calls and angry customers –… you can go from there and extend your installation with other gear PSTN Gateway pbxnsip PBX LAN

3-Jun-15 Product Related InformationPage 4 Advantages of digital PSTN compared to analog PSTN Analog PSTN is a very old technology Advantages of digital PSTN –Digital audio quality (superior impression to customers) –No problems with static cross talk –No problems with gain –No gain problems makes echo compensation much easier –Fast dialing, very useful for parallel forking to cell phones –Clean connect/disconnect detection (necessary requirement for parallel forking) –Better Caller-ID indication, Called-Party indication Examples for digital PSTN –ISDN –T1/E1/J1 –SIP Trunking—if QoS is ensured

3-Jun-15 Product Related InformationPage 5 If you have to use FXO, avoid some common pitfalls Gain is very important –The perceived audio quality depends to a large extend simply on the gain –Asymmetric gain (talking/listening) will lead to a loud echo on one side –Once the echo is there it is difficult to get rid of it –Keep the gain relatively low, that is an impact of using old technology You cannot fork calls to cell phones when using FXO –The FXO does not give a clear connected information (tone detection is instable, especially when vanity ring back is in use) –The dialing process is quite slow Invest your money into a good PSTN gateway, it will pay back

3-Jun-15 Product Related InformationPage 6 ITSP can provide great service if you make sure you don‘t get stuck in traffic jam You must make sure that VoIP calls have enough bandwidth For example: –Choose two physically separate ways to access Internet –T1 for VoIP traffic (symmetrical bandwidth) –Cable for all other traffic –DHCP server provides cable router as default IP gateway –Devices can be on the same LAN –PBX uses T1 router as default IP gateway Can be combined with a PSTN gateway Router 1Router 2 T1 Cable PBX PC

3-Jun-15 Product Related InformationPage 7 Combining both VoIP and other traffic will lead to quality problems Okay, economically it is tempting to use a cheap cable contract and run the company’s telephone traffic over it –But it is not realistic –Sooner or later voice packets will get dropped –Registrations will drop –Several service companies that put high hopes on this model went bankrupt Don’t use your clients as test dummies Router 1 Cable PBX PC

3-Jun-15 Product Related InformationPage 8 Hosted PBX with no control over QoS is not a good idea Economically even more tempting… But still not realistic –Same problems as with SIP trunking over shared line –Maybe even worse because now client completely depends on that access line Ensure that QoS is in place or forget about this model –You must provide the router that does ensure the bandwidth on CPE –You must a router on the service provider side that ensures QoS (possibly a SBC) Many providers already failed with this model, don’t be the next in line Router 1 Cable Phone PC

3-Jun-15 Product Related InformationPage 9 The Bottom Line Take no risks, or they will find you –PSTN is a boring, but safe way of getting VoIP working in the office –If you do SIP trunking, consider having separate Internet access points for VoIP and all other traffic –Don’t share VoIP and data on an unmanaged Internet access point and/or without your service providers cooperation If you play safe, you will have a great telecommunication system that will make your clients happy

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