Internet Telephony Service Providers

As VoIP technology matured and stabilized, telephone service providers began extending VoIP connectivity to their customers, allowing for simple, flexible connection alternatives to traditional TDM links. Internet Telephony Service Providers (ITSP) connections are typically much less expensive, available in smaller bandwidth increments than Tl or PRI links, and can route nonvoice data traffic concurrently. QoS configuration is supported (and in fact is required for proper VoIP operation). Most ITSP links use SIP, but H.323 is an option. The gateway configuration is relatively simple, with the creation of a VoIP dial peer pointing at the provider with the parameters they supply. PSTN calls are routed to the provider, who then routes calls to their PSTN connection, usually with a toll-minimizing route that dramatically reduces long-distance costs to the customer.


Understanding Call Setup and Digit Manipulation

Successfully completing a phone call requires that the correct digits are sent to the terminating device, whether on the VoIP network or the PSTN. PSTN calls are typically more complex because of the varying local and international requirements for the number of digits required to route the call. Over and above this basic requirement are the additional complexities imposed by requirements of the business: we may want to change our ANI number, add or strip access codes, compensate for undesirable default behavior, or build specialized functionality for our particular purposes. This section deals with digit manipulation and troubleshooting.

Translation rules use regular expression syntax, which can be quite complex. The following table defines the characters used, and examples follow.