Chapter 3. ITSP and Voice Codecs Optimization

This chapter reveals the most important things to consider when connecting voice traffic to FreeSWITCH — what you want to check out in an Internet Telephony Service Provider (ITSP) to get the best resulting quality and more bang for your bucks.

In a fiercely competitive market, many operators are floating different products and offers, targeted to the general public, to companies of a specific size, or to vertical markets.

Here you'll find an explanation of what can actually make a difference for you and your users and customers, apart from price points.

In this chapter, we will cover:

• ITSPs – what they do

• Routes (to numbers)

• DIDs (aka DDIs) — for example, numbers

• Quality

• Support

• Additional features (T38, Caller ID, Overlay)

• Integration APIs

• Codec gotchas

• High definition audio, stereo

ITSPs – what they do

An Internet Telephony Service Provider brings to its customers SIP trunking connections that allow for outbound and inbound calls to/from the Public Switched Telephone Network (PSTN), to/from the Public Land Mobile Network (PLMN), and to/from other SIP users.

ITSPs don't need to own a physical Internet backbone, nor the "last mile" of cables going from the backbone to their customers' premises. ITSPs connect to the public Internet and operate their own SIP servers and (optionally) their own gateways from SIP to PSTN (from now on we'll write only PSTN, for brevity's sake, meaning both PSTN and PLMN).

ITSP business is to sell minutes of PSTN communication to their SIP end users: Both communication coming from PSTN (a caller from PSTN wants to reach a number connected to the SIP device of an ITSP's customer) and communication going to PSTN (ITSP's customer from his/her SIP device wants to call a number connected to the PSTN).

In the real world, much SIP to SIP communication...

Routes (to numbers)

The path from an ITSP to a destination phone number is called a (SIP) route. Often the ITSP (and major carriers and Telcos alike) has many routes it can choose from to connect the outbound call originated by its customer's SIP device. This exchange of routes minutes is a very big and complex business, and, if we include the big Telcos, is one of the major businesses on Earth.

As you can imagine, the ramifications of such a business depend on local regulations, international agreements, geopolitical situations, business alliances, economic development levels, and a thousand other factors.

In some countries and regions, origination (gathering and routing of outbound calls) and/or termination (providing PSTN gateways to inbound calls) is a legal monopoly of one or few companies; in other regions and countries, regulation requirements can set the bar of entering the business in a way that floods the market with pop and mom's shops or that makes it the exclusive preserve of...

DIDs (aka DDIs) – numbers

DID stands for Direct Inward Dialing, while DDI means Direct Dial In, and both acronyms refer to the same thing: A phone number that will lead incoming calls to a device. In our case, a call to that number will be ringing a SIP device.

Normally a customer will port his/her pre-existing PSTN number(s) to his/her ITSP (that is, the customer's number will not make the landline ring anymore, but will ring the end customer's SIP device passing through the ITSP SIP network). ITSPs often have a specific branch of their customer service assisting in the number porting procedures.

DIDs are sought by customers for many reasons: As a primary way to get incoming phone calls (for example, the main phone number of a person or a company, if they have no previous number, or don't want to port it), or as a means to be present in local, regional, or international markets, so as to allow the public to reach a company for the cost of a local call, or to be compliant with regulations...

Quality of routes

Routes manage the path of a customer's outbound calls, while DIDs bring inbound traffic to the customer. They both take care of the transit of a SIP audio call from caller to callee, and have many of the same challenges to their quality in common.

White, black, and grey

The technical barrier for providing termination services (routes to PSTN) and origination services (DIDs that get calls from PSTN) is so low that in countries and regions where VoIP is under monopoly, or where a cartel of big companies control the market imposing hefty prices, the business opportunity is so compelling that a plethora of independent operators, of widely differing reliability and regulation compliance (or which are outright illegal) discreetly populate the scene.

Talking about routes and DIDs to and from these destinations, it is often referred to by the term "grey" market. That's because one side (you, the end customer) is white in the open, regulation abiding, while the other end is black in...

Various important features

Fax transmission has been designed and optimized to fully exploit the physical characteristics of traditional PSTN analogical copper lines, and has been the bête noire of VoIP for a long time. Even the best, uncompressed codecs (G711) are not able to guarantee a high success rate of T30 (for example, fax) transmissions. That's because of the hyperstrict timing requirements that were guaranteed by a real-time analogical transmission, but are practically impossible for an asynchronous digital transmission. We'll see this in a later section of this book, but the SIP solution to this problem is a protocol enhancement called T38. T38 works around the timing problems, but its implementation must be compatible end to end, and the eventual gateway to PSTN connected fax machines must be of high quality.

So, if you need faxes (inbound and/or outbound), choose an ITSP with well–known, good T38 support for routing this kind of traffic, and perform many tests before committing...

Support, redundancy, high availability, and number portability

In this last section we accumulate all the "oh so obvious" issues that can make your life as an ITSP customer very unpleasant.

What is the support policy of your candidate ITSP? How long does it take to be connected with a knowledgeable person? How knowledgeable is that person? What about nights, weekends, holidays?

And also, what kind of monitoring and operation system do they have? Are they able to immediately come up with the SIP trace of the call you have a problem with? Or do they want you to provide the trace?

How are non-critical tickets serviced, like feature request or reconfiguration of features?

How does your potential ITSP handle their own infrastructure failure? What kind of High Availability architecture have they implemented? What if its datacenter got cut out from you or destroyed? Do they have a parallel datacenter? Do they depend on a single upstream provider for their connectivity? In case of an outage, you'll...

Summary

In this chapter we saw what to look for when making commercial choices about our upstream and downstream providers.

What is the mission of an ITSP? What kind of services do they sell? What technologies are involved in their operation? What should we be aware of? What questions should we ask? What are the hints that tell the good from the bad ones, and the features that define the one that is right for us?

We understood the differences between white and black routes to international destinations, their different pricing, reliability, quality. Then we saw the same with DID (DDI), the phone numbers we want people to call in order to reach us.

We closed the chapter with a reasoned laundry list of other features that can greatly affect our experience as Service Provider Customers.