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D. Au, B. Choi, R. Haridas, C. Hattingh, R. Koulagi, M. Tasker, L. Xia. Cisco IP Communications
Express: Call Manager Express with Cisco Unity Express, Cisco Press, Indianapolis, 2005.
Oliver Hersent, David Gurle, and Jean-Pierre Petit, IP Telephony: Packet-Based Multimedia
Communications Systems, Addison-Wesley, Reading, MA, 1999.
Switching to VOIP – O’Reilly
VOIP Hacking - O-Reilly
Asterisk - O-Reilly
SIP Providers
Something that takes some time to get one’s head around is that SIP providers usually do not
provide the IP network connection. The main service they perform is giving you a gateway
to the PSTN. That is, they give you telephone numbers. The gateway need not be local to
you. Indeed, you may be in California and find that your provider’s gateway is in New York.
Providers also give you access to a “SIP server” that helps with obscure things like traversing
‘NATs’ and taking care of “relocation services”. Because the SIP provider and network vendor
are independent, it’s sometimes hard to know who to blame for troubles – or praise for good
service. It’s a good idea to discuss network vendors with the SIP provider, since they have built
up a lot of experience with clients around the country and often have insight into who best can
deliver reliable Internet connectivity in your area.
Visit the Telos Website for the latest information. The short list below was created in December
2010 and the marketplace is changing rapidly. These are companies we or our clients have had
direct experience with and report positively on their experiences. Most of these providers will
allow you a free period to test their service in your environment (your ISP, with your switch,
etc). Consider that some services work better in some areas than others. Usually it’s wise to
choose a provider close to you physically.
Having said that, some Telcos and other companies offer bundled IP network and SIP service.
Generally, these are more expensive than the unbundled services, with the pitch that having
a single vendor delivers higher reliability and one-stop troubleshooting. We have seen this
approach more often outside the USA. It remains to be seen if the promise is fulfilled. We’ll
keep our eye on it.
BYOD (Bring Your Own device) Providers are recommended for broadcast application. Com-
panies such as Vonage that supply an ATA (Analog Terminal Adapter) for each “line” do not
provide “SIP credentials” for standards-based equipment such as the VX and are not oriented
to serve customers with sophisticated requirements such as broadcast stations. They tend to
be more expensive, as well. Broadcast users are better served by wholesale providers who
deal with Telephony and IT professionals.
VoicePulse is a smaller company that excels at providing tech support. They have proven
themselves excellent at solving obscure problems that many providers will just ignore.
They know Asterisk and can be counted on to give good advice. They don’t have phone
numbers everywhere, but they probably won’t disappoint you. East and West Coast gateways
are available. Local Number portability (LNP) is available.
Bandwidth.com is used by at least one station running a VX, with solid performance being
reported.
Vitelity offers reliable and very cost effective DID numbers any many local exchange areas,
and toll free and foreign numbers as well. Local number portability and SMS messaging are
also offered.
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