9.6. Residential QoS
Providing reliable voice quality using VoIP in the home or small office is a challenge for several reasons. First, residential broadband connections aren't always operated by the same people operating the VoIP service; this limits the ability of VoIP implementers to troubleshoot and support network- related problems. Second, most broadband Internet connections aren't supported by a backbone that has QoS measures. While it is common for many ISPs to prioritize in the style of 802.1p, almost none of them guarantee a service level. Finally, residential broadband routers haven't historically supported any QoS measures internally, though this is changing.
There aren't solutions to the shortcomings of the ISP's networks, but installing a QoS measure in the home is a good step to take. As with enterprise networks, the QoS enforcement points are routers. Some residential broadband routers now offer 802.1p packet prioritization, and a few even offer DiffServ support. Expect this feature to become more common.
In the meantime, experimenting with QoS measures doesn't require a pricey Cisco router. You could use a Linux computer configured as a gateway router to implement DiffServ as in Project 9.1.
9.6.1. Dial-Tone Providers That Offer VoIP Service
Some Internet service providers now offer telephone service via VoIP using broadband connections that they own. While this telephone service tends to be more expensive than that which comes from a third-party provider that doesn't own the "last-mile" data link, there's a greater likelihood that this type of service will have end-to-end QoS. Check with your ISP to see.
IP-Centrex is a way the telephone company can deliver dial-tone services to a PBX system or a group of IP phones with a VoIP gateway router. The dial-tone services are trunked from the phone company to the subscriber using IP-based packet streams. IP-Centrex offerings tend to be equipped with QoS. Check with your phone company.
9.6.2. Residential and Small-Office VoIP Routers
A new breed of residential gateway routers has begun to appear on the scene: routers with a built-in SIP or SCCP client and one or more analog RJ11 telephone connections. These devices enable routing and firewalling of Internet traffic, as well as ATA-type functionality so the connect analog phone(s) can make and receive VoIP calls over the Internet.
Inside the router's firmware, a SIP proxy and IP precedence measures may even exist, so groups of IP phones can be used to dial voice calls over the Internet. Some of these routers even offer to route calls over a local analog PSTN phone line if the Internet service fails. Check the specs to see what your VoIP router is capable of.