SIP vs PRI Pros and Cons for Business PBX

Business telephone lines have gone through several transformations. What started out as analog landlines evolved into digital T1 CAS trunks, then ISDN PRI, and finally SIP packet based network connections. Amazingly, all of these technologies are still available. We’ll take a closer look into the two most popular configurations used in multi-line PBX business phone systems.

The Primary Rate Interface
ISDN PRI is short for the mouthful of an expression that is Integrated Services Digital Network Primary Rate Interface. Often the shorthand PRI or ISDN PRI is used for obvious reasons.

ISDN PRI is a standard telecom service that is based on the earlier T1 line specification. T1 got its start as a means of consolidating 24 pairs of twisted wire phone lines into 2 pair to save the expense of long distance cabling and overloading of telephone poles. This was accomplished by digitally multiplexing the 24 separate channels so that they were all transported together on a single 1.5 Mbps digital signal. An additional advantage of going digital was the reduction of noise and crosstalk on long distance phone calls.

A major benefit of the T1 specification is that existing phone company infrastructure can be reused, including wire landlines and microwave relays. High frequency digital signals degrade over distance fairly quickly, so regenerative repeaters were added to the lines to build the signal back up. With this arrangement, T1 could be offered over long distances to serve virtually all of the customers who were using the old analog phone lines.

One issue with T1 was that if each of the 24 channels carried only the audio telephone conversations, other wiring would have to be provided for signaling. A better solution was to multiplex signal bits into the data stream by robbing a bit here and a bit there in each of the channels. This degraded the audio very slightly and allowed the T1 CAS (Channel Associated Signaling) system to be self-contained.

Additional features, such as caller ID, were introduced by the phone companies and desired for business phones and especially call centers. This is where PRI comes in. The same basic T1 line organization was kept, except that only 23 channels were assigned as individual telephone lines. One complete channel was assigned to handle all of the signaling, data and other background services.

Most PBX systems today have interface cards where you directly plug-in a ISDN PRI cable and have 23 phone lines (or as many as you have ordered) at your command. If you need more than 23 lines, you plug in additional PRIs to add more channels.

Is there a Secondary Rate Interface?
No, but there is a related standard called BRI or Basic Rate Interface. The phone companies thought this would catch on as a two phone line system or higher speed dial-up modem service. By the time it was heavily deployed, computer communications had moved on to broadband and BRI never caught on. It has been popular for radio station broadcasts and remote announcing, such as voice over artists, because it can carry high quality audio signals. Recently, this service has been replaced by broadband Internet and is very difficult to find anymore.

What is SIP and How Does It Compare to PRI?
SIP is Session Initiation Protocol. It is a technology competitor to PRI. SIP is really a standard for transmitting VoIP or Voice or Internet Protocol phone calls over networks typically shared with other computing devices.

As you probably suspect, SIP is a packet based protocol versus the channel based protocol used by ISDN and T1. In channelized systems, a complete voice channel is assigned to a phone call for as long as the call is in progress. If no one is talking, the line just sits there idle. There is no sharing of facilities. In VoIP telephony, the conversation is broken up into small packets that are routed on the network to their destination. Many conversations can be on a network at the same time along with file transfers, print jobs and everything else digital. If there is a pause in one conversation, no packets are sent to the network for that channel only.

As you can see, VoIP is more efficient at sharing the network facilities. It comes at a cost though. Sometimes everybody wants to talk or send data at the same time. Unless the network is carefully designed, it can become flooded with too many packets to handle and things back up. This network congestion causes delays in transfer that breaks up phone conversations. Any packets lost will also distort the conversation.

Network Considerations for SIP
Careful network engineering is necessary to ensure that the sensitive voice packets are transferred without delay or corruption. Usually, these data streams are given a priority using Class of Service mechanisms within the network.

A network line dedicated to SIP is called a SIP trunk. This is the equivalent of an ISDN PRI line. Any digital line capable of carrying Ethernet packets can be a dedicated SIP trunk, although T1 lines, DS3 bandwidth and Carrier Ethernet services are often used for SIP. By giving the SIP phone conversations their own line, there is no interference from other data packets. SIP trunks are most often used to connect business and call center PBX systems directly to phone service providers. Like PRI, most PBX systems have network interface cards that plug directly into a SIP trunk.

SIP vs PRI
One protocol isn’t necessarily more appropriate than the other. It depends on the application. Most PBX systems can be set up to connect to SIP trunks or PRI trunks regardless of whether the phone sets themselves are analog handsets or VoIP phones. SIP trunks are particularly useful with newer Unified Communications or Unified Communications as a Service (UCaaS) systems that integrate computers, desk sets video conferencing and mobile phones into a single interoperable system. In these systems everything is in packet format and running on a single network.

Which is Right For You?
The best choice in telephone trunks is the one that works best with the system you have or the system you desire, and at the lowest cost for the performance you need. Prices of both PRI and SIP have fallen dramatically over the last few years, so you owe it to yourself to see what telephone trunk line options are available for your business needs.

SIP Trunks vs EoC vs T1

Time was, not so long ago, that your choices for a dedicated symmetrical bandwidth business line were anything you want... as long as it is a T1. That’s all changed the last few years. Now you shop around to compare T1 with newer Ethernet over Copper and Sip Trunks.

What about DSL, Cable, satellite and 3G wireless? They don’t fall into this category because they are based on shared rather than dedicated bandwidth and asymmetrical rather than symmetrical bandwidth. Likewise, DS3, SONET and Ethernet over Fiber aren’t in the same league because they offer much higher bandwidths at proportionally higher prices.

Still, If you like Ethernet over Copper you’ll like Ethernet over Fiber as you move up in bandwidth. DS3 and SONET are higher bandwidth versions of T1 lines. SIP trunks can be any bandwidth over fiber as well as copper. Let’s take a closer look at the similarities and differences among SIP Trunks, EoC and T1 lines.

T1 lines are the granddaddy of business telecom digital lines. They run at a fixed bandwidth of 1.5 Mbps. Fractional T1 lines have been sold, but you don’t see these as much any more. In fact, 1.5 Mbps is considered entry level for most businesses. If you need or want more bandwidth, you can bond multiple T1 lines together to get bandwidths from 3 to 12 Mbps.

T1 lines also come in different flavors. T1 point to point service connects two business locations with a private line. Some companies set up their own multi-location networks by connecting each branch location to headquarters with one or more T1 lines. A router at HQ then directs communications among all the sites.

T1 dedicated Internet service is a T1 line that connects to the Internet at 1.5 Mbps. Lots of companies got their first Internet service via a single T1 line. The advantage of using T1 for this is that your upload and download bandwidths are the same and the bandwidth never varies. You may still experience congestion on the Internet itself.

T1 telephone service uses a single T1 line channelized into 24 separate phone lines. It replaces multiple analog lines for key telephone and PBX phone systems. Each line is responsible for signaling and two-way audio. A newer variation on T1 telephone is ISDN PRI. This is a T1 line that offers 23 channels plus a separate control and signaling channel that handles these jobs for the other 23. The result is faster call setup and tear down plus the inclusion of data like Caller ID.

Ethernet over Copper (EoC) is similar to T1 in that it uses ordinary copper pairs that may previously carried analog business phone service. The differences are that EoC can carry much higher bandwidths than T1 or bonded T1 from 3 Mbps on up to 45 Mbps or higher. The tradeoff is that you need to be close to the telco office to get the higher speeds. If you can, EoC will give you at least twice the bandwidth for the same money as T1 and bonded T1. You can order it as a private point to point connection or a dedicated Internet service.

SIP Trunking is a slight different animal. The primary purpose of a SIP Trunk is to transport VoIP phone calls between your location and your service provider’s. Most often, lower speed SIP Trunks are partitioned to carry both phone conversations and broadband Internet. Class of Service (CoS) is tagged to telephone and data packets so that they don’t interfere. SIP Trunking can be a cost saver over separate data and telephone services.

Which digital line service is right for your company? Compare bandwidth, features and prices on SIP Trunks, Ethernet over Copper and T1 lines available for your business location.

USA Digital Offers Comprehensive Call Center Services

Call centers and company contact centers have special requirements for the high volume telephony services they use. USA Digital serves this market with a suite of high performance cost effective telecom services.

USA Digital Communications Inc., often called USA Digital for short, is a licensed, certified carrier in all 50 states. Since founding in 1991, their business has been known for rapid growth and customer retention. Wouldn’t a lot of companies like to claim that? The secret to USA Digital’s success may be summed up as excellent customer service combined with an extensive range of services to support both voice and data needs.

Call center operations are a special focus for USA Digital. It starts with digital line services from T1 through OC12. T1 is a popular service and provided by many carriers. However, not all of those T1 services are optimized for cost on high volume calling. For instance, USA Digital offers initial six second billing minimum. That’s typical in the industry. But then USA Digital billing switches to one second increments. That alone can save you 30% in the cost of the minutes you use.

Another big saver is 4 digit versus 2 digit rounding. Those decimal points might seem arcane, but in high volume calling minor fractions of a second add up to big money. That’s especially true if 4 digital rounding is combined with low dedicated interstate rates on T1 service.

USA Digital has a service team experienced in provisioning voice lines, PRI’s, CO meet-point circuits, cross connects and SS7 links. That same experience is applied as you move up the circuit class to DS3 (T3) trunks and into the fiber optic services from OC3 to OC12. These OCx connections are truly business carrier class services needed by the largest call center operations and requiring the highest levels of expertise for support. An OC3 gives you the capacity of about 3 DS3’s and OC12 is the bandwidth of 4 OC3’s or 12 DS3’s. USA Digital can deliver OC3s in the form of 3 DS3’s that may be separated into individual T1 services.

In addition to bandwidth, dedicated outbound services are a specialty of USA Digital. They offer FTC telemarketing sale rule and do not call services to make sure you are in compliance with government regulations for outbound call centers. Their do not call services are capable of blocking 100% of calls registered to both state and national do-not-call lists. In addition, USA Digital provides customized Caller ID Service so that you can communicate appropriate caller information over your service lines.

USA Digital’s services are appropriate for in-house customer service contact centers up through major independent call centers and carriers, including ILEC, CLEC and wireless. Beyond traditional switched circuit voice trunks, they also support VoIP (SIP, H3223), point to point dedicated lines, and MPLS networks for linking multiple business locations.

Can you benefit from business telecom services like these? If so, you’ll want to get customized telecom service pricing and consultation for USA Digital and other competitive service providers as soon as possible. You could be looking a major cost savings.

The Analog Telephone Adaptor Enables VoIP

The role of the ATA or Analog Telephone Adaptor is to turn regular telephones into VoIP telephones. To perform this magic, the ATA has to fool the telephone set into thinking it is plugged into a standard telephone line. It also has to fool the broadband Internet connection into thinking it is plugged into a SIP (Session Initiation Protocol) telephone compatible with the VoIP provider's service.

The electrical interface is perhaps the easiest to achieve. On the analog side, the phone plugs into a standard RJ-11 jack like you would find on a wall socket. This delivers the standard -48 V DC to power the handset along with the dial tone, AC ringing, and Caller ID signals when needed. It has to detect standard DTMF (Dual Tone Multi-Frequency) touch-tone waveforms from the keypad and convert them to digital format for IP signaling using Session Initiation Protocol, the standard for VoIP.

How does the analog voice become digital and back to analog again? That's the function of the Codec or Coder/Decoder. The standard in use since digital telephony was invented is G.711. But there are other codecs that must also supported. These may include G.723, G.729, G.728 and G.726.

On the network side, The ATA has to terminate a standard Ethernet connection, usually 10/100 Mbps through a RJ-45 connector labeled as WAN. Many newer ATAs take this a step further by including a second Ethernet port labeled LAN. This is for connection to a PC in lieu of connecting the PC directly to DSL, Cable Modem or T1 WAN. The ATA performs the function of an Ethernet switch or router. This is not just to save the cost of a separate device so that PC and telephone can share the same broadband connection. When a router is included in the ATA, it then has the ability to ensure quality of service by giving voice packets priority over computer data packets so that using the PC doesn't interrupt telephone calls.

Maintaining voice quality while minimizing bandwidth is also the function of signal processing within the ATA. Some common processes include line echo cancellation and dynamic jitter buffer that compensates for variations in Internet line speed. PLC or Packet Loss Concealment deals with missing or out of sequence packets. Either the packet is replaced with a zero packet, a copy of an already received packet, or an interpolation between the preceding and following packets. VAD or Voice Activity Detection senses when you are talking and stops generating packets while you are listening to reduce bandwidth needs. Because digital lines have no traditional analog "hiss", people sometimes equate silence with a lost connection. CNG or Comfort Noise Generation recreates that low level background noise to indicate that the connection between phones is still in place.

All of these functions have been integrated into a package you can hold in your hand, in the HandyTone 502 ATA that is provided at no cost when you order PhonePower VoIP telephone service for residential and small business use. You can use the analog phone you have now, including cordless phones with multiple handsets.

Other VoIP service providers have also gone the route of providing their customers with complimentary ATAs to make the transition from traditional analog to digital VoIP as easy as possible.

IP Phones Are In Demand

Enterprise VoIP is growing like crazy, but consumer adoption of IP phones is lagging far behind. That's the assessment of a recent study of the IP phone market. Is it that residential users aren't embracing new communication technology the way businesses are, or is there another explanation?

IP networks have been chipping away at the switched telephone network franchise for years. The reasons for this are both technical and financial.

For the consumer, the primary impetus has been to leverage their relatively expensive broadband (compared to dial-up) Internet service to also provide telephone services. There are many residential VoIP phone companies that offer bundled local and long distance service along with a dozen or two calling features all for one bundled price. For many consumers that price is lower that what you get ordering from the incumbent local telephone company.

There have also been a wealth of bundled CLECs or competitive local exchange carriers that competed with the incumbents, but changes in the telecom rules make leasing the telephone wires to your house too expensive for CLECs to offer an overall cost savings.

How do VoIP providers compete? They avoid the cost of leasing phone wires by using broadband services you already pay for. That can be either DSL or Cable, but the point is that most people buy broadband for their computers. VoIP uses the same connection as an alternative "phone wire" without additional cost. They also let consumers save money by reusing the phone they already have. You unplug your telephone set from the wall and plug it into an ATA or Analog Telephone Adapter box that is provided by the VoIP company, usually at no extra cost.

This is one reason that there is little to no demand for consumer IP phones. The residential marketplace isn't sophisticated enough yet to take advantage of services, like computer/telephone integration, or additional phone services, like videophone, that are practical with VoIP but not over traditional analog phone wires. Most consumers are still using corded handsets or cordless multi-telephone sets like the ones offered by Uniden.

The enterprise VoIP marketplace is quite different. Companies have various reasons for migrating to VoIP, but almost all are related to saving money directly or improving productivity to save money. While it is possible to get a better deal on local dial tone and long distance minutes using SIP Trunking instead of analog lines or T1 PRI digital phone lines, the real driver is the in-house phone system itself.

Traditional PBX telephone systems are large, proprietary and expensive to buy and maintain. They are rapidly giving way to IP PBX systems that are more like computer appliances than dedicated phone systems. IP telephony in-house offers the opportunity to converge the telephone and data networks into a single Ethernet connection to the desktop. Administrative and technical support can be considerably less for one network versus two, once the engineering has been accomplished to ensure quality of service for both voice and data users.

Like consumer VoIP, a business can acquire analog telephone adaptors and continue to use their existing handsets on the company LAN. But many additional features become available by switching to desk sets designed for IP services. The phone itself contains the network interface plus text display, video, and other features that make it as much a computer peripheral as a telephone. These phones are called IP phones or SIP phones. SIP is the switching technology used by VoIP telephone systems. There are many vendors of business IP phones, with Cisco being a major player.

Another point the report makes is that corded phones are the standard now, but will be replaced more and more by cordless and wireless handsets. That includes cell phones that are integrated into the corporate IP PBX systems, and perhaps wireless VoIP phones that will operate over the new LTE cellular broadband and WiMAX wireless networks that are just now starting to be deployed.

Tricks That T1 Lines Do

When someone says T1 line, what do you think of? I'll bet that most of the time it's a dedicated broadband Internet connection. But there are lots of other uses for T1 connections that might benefit your business.

The dedicated T1 Internet connection is an obvious answer because so many businesses now depend on their Internet connection as either their means of doing business or as a productivity booster. T1 lines have advantages over consumer oriented services such as DSL and Cable broadband. T1 is a regulated telecommunications service that gets top attention in the event there is line trouble. These lines are so dependable, and need to be, that they are usually offered with a service level agreement. T1 lines are symmetrical. You get the same 1.5 Mbps bandwidth both for both upload and download. Since T1 is a dedicated service, meaning available for your exclusive use, there is no bandwidth sharing with other customers to restrict your line speed.

Here's a trick T1 lines do that you may not be aware of. Where 1.5 Mbps was once considered a lot of bandwidth, many companies are finding they really need higher speeds these days. T1 lines can be bonded together to create larger bandwidths. You order a second T1 line to double your bandwidth to 3 Mbps, three lines give you 4.5 Mbps and four lines give you 6 Mbps. You don't have to worry about making these connections. Your service provider takes care of it without any changes to your company LAN.

You can also go the other way. Perhaps you don't need even 1.5 Mbps of bandwidth but you really do need the performance and availability of a T1 line. Fractional T1 service might be right for you. This service is just what you think. You get a fraction of the full bandwidth for a lower monthly leasing cost.

T1 lines don't have to connect to the Internet. A private line or point to point connection can be ordered to connect two business locations. Since the line is direct and private, you don't have security issues that come from using a public network like the Internet. Security can also be managed by running encryption software that creates a VPN or Virtual Private network using public Internet connections.

T1 can be used for voice as well as data. In fact, the first application for T1 lines was by the telephone companies. They used them, and still do, to transport multiple telephone calls between their switching offices. You can order a channelized T1 line, also called a T1 telephone line or telephone trunk. This arrangement aggregates up to 24 separate telephone lines onto one T1 line. T1 phone lines are popular for PBX phone systems and call centers. A special form of channelized T1 line, called ISDN PRI or T1 PRI gives you up to 23 outside phone lines plus a data channel that provides Caller ID information and very fast switching times.

T1 lines can also do double duty when they connect you to a specialized service provider. An Integrated T1 service offers up to a dozen telephone lines plus broadband Internet access over a single T1 line. Usually whatever bandwidth isn't being used for telephone calls is automatically assigned to Internet access.

SIP Trunking uses T1 lines to carry both telephone and Internet service for companies that have switched to VoIP telephone systems and have IP PBX systems instead of the traditional PBX telephone system. This service extends your converged voice and data network to a service provider who terminates the calls to the public telephone system and provides your broadband Internet access.

Which type of T1 line service is right for you? It's likely that one or more of these services is a good match for your business needs. Using our GeoQuote (tm) search engine, you can check T1 options and prices in seconds. Go ahead. You may be surprised by how little you'll pay for the service you really need.

Buy Convergence By The Byte

XO Communications is changing the game on legacy telecommunication carriers by offering IP Network services priced by amount of bandwidth used rather than number of lines or channels in service. What's putting the nail in the coffin of TDM based telephony services is both a switch to an IP based network and the use of Session Initiation Protocol (SIP) for telephone trunking. By starting with a packet switched network and then transmitting everything in packet protocol, voice and data traffic is easily combined on a single circuit.

Convergence, the idea of using a single network for voice, video and data, is an idea that has been gaining popularity with IT departments looking to simplify network management. It's also popular with executives eying potential cost reductions as networks are merged. The fly in the ointment has been the abrupt disconnect between the local area network and wide area network services. With IP inside the plant and TDM outside, there's an exercise in protocol conversion and call termination needed to make everything work.

XO is changing that paradigm with its IPfolio. Two things make IPfolio different from industry practice. First is that a suite of IP services all run on a single underlying network so seamlessly that you can mix and match at will to create a custom solution for your operation. It's something like a telecom buffet. You can choose from an IP VPN to connect multiple business sites, SIP based telephone trunking for your IP PBX phone system, and dedicated Internet access with dynamic bandwidth allocation. Voice is treated as a data application, the real secret to network convergence.

The second unique feature of IPfolio, and perhaps the more disruptive to the industry, is that your services are priced by how many Mbps you use, not feature by feature or even by service bundles. You can scale the bandwidth you need between 1.5 and 45 Mbps. Within that range, you'll get unlimited local calling and site to site calls between company locations. It is SIP based VoIP telephony, so you are not limited by channel allocations or phone "lines". Pack as many calls as will fit into the bandwidth you are paying for. This service is compatible with leading PBX systems, including those from Cisco, Avaya and other suppliers. Optional services include long distance plans sized from 2K to 40K minutes per month.

The XO MPLS IP-VPN portion of the IPfolio is an MPLS network solution with VPN capabilities to connect multiple business locations securely. It's set up for multiple classes of services to ensure that applications run smoothly and that large data downloads don't disrupt real-time voice communications.

The XO IPfolio tries to encompass all of the communications services that businesses need and offer them with a pricing structure more geared to IP based telecommunications. IPfolio was introduced in 2007 in selected cities and is now available nationwide.

If you think that your company might benefit from converged IP services or more cost effective traditional line services, let our team of expert consultants get you competitive quotes tailored to your needs. You might be surprised by how much you can save over your current solutions.