Evaluating Out-of-Band Signaling

All the protocols mentioned previously are classified as in-band signaling, because the overhead used to manage the call is located within the same timeslot as the voice portion of the call. Refer to Figure 8-2 to see how each channel has a section of usable bandwidth and a section devoted to the over-head and maintenance of the call.

Out-of-band signaling takes the overhead of each call, and, instead of using space on the same channel as the voice portion of the call, it aggregates the overhead on a single channel that might not be attached to your circuit. Out-of-band protocols allow your phone system to receive additional information on each call, or they may simply shorten the amount of time it takes to connect a call. The information you require from your telecom service, the limitations of your existing hardware, and the amount of money you can spend for the features all define the best protocol for your company.

You have three basic options for out-of-band signaling in the TDM world, each with its own strengths and weaknesses. Review them before you chat with your hardware vendor to find out what it takes to integrate them in your phone system.

Integrated Services Digital Network: ISDN

The Integrated Services Digital Network protocol, commonly referred to as ISDN, is the most common out-of-band signaling option used at the T-1 level. The protocol is standard on many new multiplexers and MUXing cards (such as those made by Dialogic) that can be installed in a PC environment to perform the functions of a channel bank. The ISDN protocol provides a wealth of information available on inbound calls, as well as detailed information for your carrier on outbound calls. DNIS, ANI delivery, and ANI Infodigits are standard features on most ISDN circuits. The reason that ISDN can provide all this additional information on each call is because it uses an entire channel for overhead. Figure 8-3 shows you what the overhead looks like on a T-1 with 24 channels, one of which is reserved for overhead and identified by shading in the figure.

Figure 8-3: Standard configuration for ISDN, with 23 bearer channels and 1 data channel, which handles the overhead.

 Remember  All ISDN circuits should be provisioned as B8ZS/ESF at the line coding and framing level, to allow you 64 kbps useable bandwidth for each channel. Most carriers require you to order the circuit as B8ZS/ESF. It might be technically possible to use the ISDN protocol with AMI/SF circuits, but it just isn’t done.

Understanding B and D channels

ISDN circuits consist of channels that transmit the voice portion of the call, called bearer (or B) channels, and channels that just handle the overhead, called data (or D) channels. In Figure 8-3, the 23 channels that are white are the B channels; they transmit only the voice portion of calls. The shaded channel is the D channel; it transmits the overhead for those 23 B channels. This is a standard configuration for ISDN, with one D channel on the 24th timeslot of every T-1 in the system. Sometimes people like to mix things up and place the D channel on the first timeslot rather than the last one, but it’s generally on one end of the circuit.

 Remember  There is a lot of space on the D channel — actually more than enough space to handle the 23 calls on a single T-1. To use the D channel’s space more efficiently, you can use a single D channel to service multiple T-1s. Some companies hate losing an entire channel just for the sake of having a more advanced protocol. If you can use that one channel for more than one circuit, the loss seems somehow more palatable. You need to remember a few things if you use one D channel for multiple T-1s:

• All the T-1s must be from the same carrier. You can’t bring in a pair of T-1s from Sprint and another pair from Qwest and expect one D channel to handle them both.

• You need to confirm that your hardware and your carrier’s hardware can handle the configuration. Talk to your vendor before you make big plans.

• You can experience problems during peak calling times. Just because the hardware says you can use one D channel for up to seven T-1s doesn’t mean that doing so gives your system optimum performance. When you push the limits of your hardware and try to handle too many circuits with one D channel, your channels can lock up or disconnect, or you can experience other quality and completion issues.

Choosing your favorite ISDN flavor

All carriers offer a handful of options when it comes to ISDN. Some call them protocols, and some call them switch types. The bottom line is that you have to set your hardware to speak the same ISDN language as your carrier. Some of your domestic ISDN choices are:

• NI1: National ISDN 1 (Bellcore standard)

• NI2: National ISDN 2 (Bellcore standard)

• 5ESS: AT&T standard

• DMS100: Northern Telecom standard

Your carrier might not provide every ISDN protocol listed here. If there is a nuance that makes NI2 perfect for your business, be sure to confirm that your carrier can provide it. Some carriers only offer NI1, and they won’t pay to upgrade all of their switches when they are really waiting for NI3 to arrive. You really need to conform to the preferred protocol of your carrier with ISDN if possible, or choose a different carrier. The problems you encounter
if your carrier is using a less-preferable protocol may be much more troubling than if you simply used your second- or third-choice hardware. The ten-millisecond reduction in call setup or tear down time isn’t worth the increased percentage of timing related call failures.

Using ISDN for telemarketing

You will want to change to ISDN protocol if your primary business is telemarketing. Recent federal regulations require telemarketing businesses to present a valid Caller ID number when placing telemarketing calls. The ISDN protocol enables you to select a phone number to use as your company’s Caller ID. You can change the Caller ID number based on the calling campaign, and can even display a toll-free number.

A note if you already have ISDN service

 Technical Stuff  ISDN was initially released, not in the full T-1 variety called PRI (Primary Rate Interface), which is discussed previously, but as a smaller service called Basic Rate Interface (BRI). The service was developed and released to handle the massive demand for desktop videoconferencing features. The BRI service was much smaller than the full T-1 version and consisted of one D channel and two B channels. The service was initially problematic, because the available hardware was not very compatible and installation was troublesome. The key selling point of the BRI was a feature called bonding, which allowed users to combine both B channels into a single 128KB path, instead of existing as two individual channels with 64KB of bandwidth. Users could even bond together several BRI circuits to create a 256kbps connection as well. Unfortunately, not many people wanted to videoconference, and as DSL and other technologies were released, BRI lines became less popular. If you have a BRI line, you need to know that most long-distance carriers don’t support bonding; AT&T, MCI, and possibly Sprint still offer this support, but who knows for how long? If you have two BRIs and use your 256 kbps connection to transmit CD-quality music from a microphone in Hawaii to a recording studio in New York, that is great, but don’t change your long-distance carrier unless you know it also supports bonding.

Currently, you can input only numbers, not letters, into the Caller ID field. Federal law states that you must also list the company name, if your carrier supports the service. The only problem is that no long-distance carrier can support alpha characters (letters) in the Caller ID field. Anything the long-distance carrier receives that isn’t a number is stripped when the call is sent to the destination.

 Warning!  ISDN users are frequently charged monthly fees based on the number of D channels used. Every carrier offers different pricing, but watch for hidden costs when using ISDN. Many carriers charge an installation fee and a monthly rate for D channel cards. Ostensibly, the monthly charge is used to recover your carrier’s cost to purchase D channel cards for its network, but it seems more like a profit center. To give you an idea of what kinds of charges you might see, your company can conceivably be charged $250 for installation and $200 per month per D channel. If you have 28 T-1s, each with their own D channels, you are looking at an installation fee of $7,000 and a monthly recurring charge of $5,600. Um, did someone say ouch? Before you order your ISDN circuits, check with your carrier about additional fees.

Signaling System Seven: SS7

The Signaling System Seven, or SS7, protocol is the epitome of out-of-band signaling. The SS7 configuration is even more removed than ISDN, because the SS7 link that handles the overhead is on a completely separate and noncontiguous circuit. Figure 8-4 shows how the SS7 link is positioned in comparison to the circuit whose calls it manages.

Figure 8-4: SS7 Link T1 with 24 voice channels and an autonomous SS7 link.

The main reason businesses use the SS7 protocol is because they need a very quick connect time for all of their calls. In fact, telecom carriers and large telecom customers often use SS7. If your business experiences an unacceptable level of latency on domestic calls, and you spend more than $50,000 on your long-distance every month, it’s time to look into SS7.

Understanding how SS7 functions

The SS7 protocol is like having a scout when you are on safari. The protocol reads the phone number you have dialed and runs out ahead of the body of the call, checking the possible routes to get you to your destination. If it discovers an outage in Dallas, Texas, the SS7 link finds an open path through Chicago, Illinois. After it finds an open path, the SS7 signal secures the path by reserving timeslots for the voice path to travel. After SS7 establishes the path, your call takes the road that was built, and the call is completed quickly.

All the work that SS7 does prevents your call from having to worm its way to the destination through primary and secondary route paths, so your connect time is much faster. The SS7 protocol also shortens the time required to tear down the call after you hang up, so it’s more efficient on the front and back end of the call. Did I mention that it’s fast?

Ordering up SS7 service

If you are interested in ordering SS7, you should first call your hardware vendor to determine what it takes to integrate your system into an SS7 environment. You then need to find an SS7 provider. Your carrier can give you an SS7 connection to its network, and order the SS7 link to make it all happen, but you still have to be able to accept the SS7 configuration on your phone system. Unless you want to order more than $20,000 in hardware and keep an SS7 tech on staff at all times, you’ll need to hire an outside company to care for your SS7 connection. It’s best to begin the search for an SS7 provider by getting suggestions from your carrier.

After you find an SS7 provider, the SS7 provider needs to give you some information so that you can pass it on to your carrier and complete the order:

• The name of your SS7 provider: In order to coordinate your order for the SS7 link, your carrier needs to know who you are doing business with. This should be the easiest piece of information you have to provide.

• The CLLI code of your SS7 provider: The CLLI (pronounced silly) code identifies the physical address (in telecom terms) of the building that holds the SS7 provider’s hardware. For example, a CLLI code of LSANCA01 indicates that your SS7 provider’s hardware is located in the 1 Wilshire Building in Los Angeles, California. The SS7 provider should have no problem providing the information.

• The point code of your SS7 provider: Your SS7 carrier’s point code spec-ifies the piece of hardware that will be receiving the SS7 signaling information. Again, this is information that is readily available to the SS7.

• The TCIC range to use: The TCICs (pronounced tea-kicks; stands for Trunk Circuit Identification Codes) range identifies the individual channels of your T-1 or DS-3 that will be using the SS7 link.

After you have this information, you can submit your order, wait for your SS7 provider to install and test the SS7 link with your carrier, and then cut the service onto your circuit. There are mountains of information printed about SS7 and the specifics of the signaling protocol, but as long as you know the previous information, you can order the circuit. After it’s installed, just keep the SS7 provider’s number handy in case there is a problem and you need to troubleshoot.

 Tip  SS7 is a mature protocol used within the world of telecom and has evolved as a very stable and dependable way to transmit calls. If you would like more information about SS7 signaling, please check out en.wikipedia.org/wiki/SS7 for an in-depth review of the protocol and additional links to even more information.

Feature Group D

Feature Group D (FGD) is an older protocol that is generally used only when a hardware limitation prevents a business from receiving ANI Infodigits on inbound toll-free calls. (Please scan the section in Chapter 5 regarding pay phone surcharges if you are scratching your head about the true identity of ANI Infodigits.) Your phone system might not be able to handle ISDN, or your carrier might have a limitation in its overhead that prevents it from sending ANI Infodigits. This is the only benefit of FGD, because it’s an older protocol than ISDN, and it doesn’t use the standard touch-tone DTMF (Dual-Tone Multi-Frequency) tones to send information. Instead, it uses an older multi-frequency (MF) signaling that takes longer to send and decode. A simple domestic outbound call is sent through the FGD protocol as:

KP + II + ANI + ST + KP + 7/10 Dig + ST 

In this equation, the abbreviations represent:

• KP: Kick pulse that initiates an FGD transmission.

• II: Infodigits (identifies the origination type of the call, such as pay phone, hospital, prison, and so on).

• ANI: The origination’s phone number.

• ST: Stop tone that acts as an end notification in FGD.

• 7/10 Dig: The phone number you dialed.

The sequence and length of the individual sections of the transmission can vary, along with the sequencing of some portions of the information stream. The MF signaling requires more time, so a simple domestic call might take two or three times longer to send and connect using FGD than when using loopstart.

 Remember  The overall age of the protocol and the many variations possible make FGD a challenge. The sequencing for inbound calls on toll-free numbers can also vary, so your hardware vendor must be familiar with your equipment before you begin using FGD. Problems can persist on your circuit for days and weeks if your hardware vendor is trying to solve the problem and master the protocol at the same time.

Feature Group D is a useful protocol because it allows you to receive ANI Infodigits, but it’s more difficult to work on and it’s slower, so I wouldn’t recommend picking it as an option, and if you already have it, I would recommend moving on to something a little less cumbersome. I suggest you use ISDN if you need to capture the ANI Infodigits on your inbound toll-free calls. The hardware is easier to come by, as are technicians well versed in the protocol.