Personal Home Network for VoIP

A typical personal home network is the level that most experimenters start at when first trying out VoIP. Usually, they start off with services like Skype, Free World Dialup or GoogleVoice and find that they don't have the flexibility or options that they need. The next step is experimenting with a small server based open source PBX platform like Asterisk or FreeSwitch, or a small OEM PBX like the discontinued Linksys SPA-9000 shown below are configured. The open source PBXs will work fine on an old PIII 800 Mhz PC with 512MB Ram and 10GB hard-drive.

Discontinued but still available Linksys SPA-9000 PBX

Old pile of PCIII, $20 each including monitors - great for testing out Asterisk at home

A home network usually consists of a modem of some type: dial-up, cable, satellite or ADSL connected up to the Internet. Dial-up modems connect directly to only one PC and all the other broadband modems (ADSL, Cable and Satellite) should be connected to a router that may provide a WiFi service, firewall capabilities and have an integral 4 or 8 port Ethernet switch. The computers and printers are cabled to the switch and mobile devices like laptops and iPods connected via WiFi.

Typical Home Network

Dial_up Modem

A dial-up modem does not really have sufficient bandwidth for VoIP as one VoIP call requires a minimum of 100 kbps bandwidth with the uLaw codec. Dial-up modems only have about 56 kbps of bandwidth available. Codecs are available that can compress the voice call better but you are in a position where the choice is to send only voice or data but not both. Incoming data traffic that you have no control over will seriously affect the quality of the voice call.

Broadband Modems

Cable modems, ADSL modems and Satellite modems fall into the broadband category. They have enough bandwidth to transport both data and voice traffic to the Internet (Wide Area Network - WAN). The modems are connected to the router by an Ethernet link. The connection between the modem and router is typically 100 Mbps but the WAN connection has a lot less bandwidth. The bandwidth is based on the plan that you purchase from your Internet Service Provider (ISP). The toughest part is to find out exactly how much bandwidth that you have. There are several free online websites that can test the speed of your Internet connection such as Speedtest.net.

VoIP Traffic Tests

A fast Internet connection only gives you a portion of the picture. There are several other factors that affect the quality of the Internet connection in relationship to VoIP: delay and jitter. Delay is the amount of time that it takes for the traffic to get from the source to the destination. The magic number that you want to be under is 150 mSec one way or 300 mSec round trip. Too much delay and conversations become awkward and out of sync between the two parties. Jitter is how much difference there is in the round trip delay between packets. For voice traffic, the maximum amount of jitter between packets should be 2 mSec or less. There are free online services such as myspeed.visualware.com that will measure your Internet speed, delay and jitter.

WiFi Broadband Router

The broadband router is usually a combination of devices: wireless access point, router, firewall and Ethernet switch - all rolled into one package! There is one Ethernet port labeled WAN that is dedicated for connection to the broadband modem. It is on the public side of the Internet. There are typically 4 Ethernet ports dedicated for the LAN side and they use private IP addresses. Lately, there have been broadband routers that have 8 Ethernet ports - I use a D-Link DIR-632 one quite happily. Network Address Translation (NAT) allows you to hide many computers on a LAN using private IP addresses that appear to the rest of the world as one busy public IP address on the WAN side. The WiFi connections are considered connected on the LAN side also.

Firewall

The firewall portion of the broadband router is extremely important as it provides security for your LAN. On your PC, you should have a software firewall running to protect your software. The broadband router's firewall is a hardware firewall and its job is to protect your network. Make sure that you have configured your router with a unique password and are NOT using the default password!

Traffic Patterns

With a home network like this default setup, there is no traffic shaping going on. All traffic is treated the same: voice and data have the same prioritiy. There is only one network and one network address (ex. 192.168.1.0/24). A voice call can be interrupted and/or delayed when data traffic occurs. There is no control over the traffic coming into the network from the WAN. Fortunately, there isn't too much data traffic occuring when making a VoIP call so the effects are minimal. Also the expectation of the quality of the VoIP call by the home user is quite low. Typically, they are happy that they can make a free long distance call. What can be done to improve the quality of the VoIP call? That takes us to the next stage: the Small Office Home Office (SOHO) network.

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Copyright July 2013 Eugene Blanchard