MSO VoIP Adjunct Interface to Legacy Key Telephone Systems

Transcription

1 WHITE PAPER MSO VoIP Adjunct Interface to Legacy Key Telephone Systems Alrington McNichol Sr. Manager, Product Marketing Walter Daniel Consulting Engineer ARRIS 3871 Lakefield Drive Suwanee, GA September 2007 All contents are Copyright 2007 ARRIS Group, Inc. All rights reserved.

2 Table of Contents 1. Overview Business Telecommunications Systems & Services U. S. Key Telephone Systems Deployments Key Telephone Systems & Services Issues Key Systems Interoperability Testing Test Cases and Set Up Interoperability Test Environment Test Results MSO VoIP Adjunct Interface to Legacy Key Telephone Systems Replace ILEC Dedicated Lines Advanced Applications Strategies Deployment Recommendations Installation Transmission Loss Plan Incoming Alerting Signals (Ringing) Loop Start vs. Ground Start Trunk Signaling Protocol Loop Diagnostics Conclusion Bibliography Page 2 of 12 September 2007

3 1. Overview There is a near constant barrage of Voice over Internet Protocol (VoIP) information for those of us in the worlds of business, telecommunications and finance. The Vonage brand, which used to be number one for Internet telephony, seems to have coined the phrase VoIP with its many television commercials. Of course, there are several flavors of VoIP being offering with different grades of service designed for both residential and business needs. We are concentrating on business services. Frost & Sullivan 2 estimated that there were about 5.8 million small, medium, and large businesses in the U.S. at the end of According to the latest information from the U.S. Census Bureau 1, there are approximately 5.7 million businesses in the U.S. with 7.2 million locations. Not counting the Small Office Home Office (SOHO) portion of the Small and Medium Business (SMB) segment, there are many locations with voice and data business communication solutions including Private Branch exchanges (PBXs) and Key Telephone Systems (KTSs), which historically utilized Time Division Multiplexing (TDM) technologies. Going forward, this small and medium (SMB) market segment holds large revenue potential for IP telephony vendors and service providers who specifically design solutions for this segment. Inter exchange and Local Exchange Carriers (IXC/LECs) traditionally served the business market with a range of access methods such as fiber optic interfaces and copper T1 connections to PBXs, along with Centrex voice features out of Class 5 end office switches. There are also central office lines that extend to customer premises in order to provide public switched telephone (PSTN) access for KTSs. Now that Cable Operators Hybrid Fiber/Coax (HFC) plant is near ubiquitous, they can easily offer additions and alternatives for these TDM systems utilizing Internet Protocol technologies. MSOs must make numerous decisions regarding what strategies, technologies and communication features to offer, as well as choosing from among the various means to market and sell business services. MSOs will decide what devices and configurations to support keeping in mind that SMBs have invested in TDM KTSs, many of which are still within their useful life cycles. MSOs KTS connectivity strategies may be providing immediate benefits of IP protocols while allowing additional time before SMBs evolve into a full IP infrastructure. Some MSOs may only opt for offering lessexpensive trunk connections to replace IXC/LEC KTS trunk connections. In any case, MSOs can effectively be in a position to ultimately up sell the replacement of the TDM KTSs. For the VoIP Adjunct up sell strategy, integration and installation recommendations will have to be contemplated in detail. This paper addresses the market and the strategies, along with the interoperability concerns that could come into play. 2. Business Telecommunications Systems & Services As the installed base of PBXs and KTSs continues to grow each year, there are challenges facing SMBs in managing existing customer premises telecom equipment involving enhanced applications and associated services. Telecom professionals in vertical industries such as Healthcare, Manufacturing, Education, Financial, Government and Retail are all willing to listen to MSOs business services sales pitches. In a recent Vertical Market Perspective: Operational Priorities and Telecom/IT Spending Opportunities by Frost & Sullivan 3, businesses were asked: What is the implementation status of each of the following voice services / systems at your organization? For each system, they were asked to indicate whether it is currently being used, may be introduced in the next 1 2 years, or not in use and unlikely to be introduced in the next 1 2 years. The check marks on the responses below indicate that, among several solutions, MSOs are already offering the benefits of T1 connections to TDM PBXs. MSOs are also already marketing hosted IP PBX or IP Centrex solutions. IP Centrex solutions provide alternatives to on premises hardware along with the normal accompaniment of maintenance and support fees. For enterprises preferring to use on premises IP PBXs, MSOs are offering IP trunking connectivity and Page 3 of 12 September 2007

4 adding layers of advanced value added features and services. This paper will focus on the key system owners, which are in significant numbers as the response below shows. 2.1 U. S. Key Telephone Systems Deployments A KTS is defined as a telephony system that caters to the small and medium sized business segment, with a minimum capacity of two, that may extend up to about 100 stations. KTSs larger than 20 lines are considered by some manufacturers as having the potential to evolve into PBXs. The following information shows the recent and forecasted U.S. KTS deployments. ARRIS Estimates: 2006 North America KTS Market Share Avaya 27.4% Nortel 23.1% NEC 16.6% Toshiba 3.8% Cortelco LG Samsung Tadiran Not Available Not Available Not Available Not Available Stations Shipped 2,500,000 2,000,000 1,500,000 1,000, , Year 150, ,000 50,000 0 Systems Shipped Panasonic Not Available KTS Stations KTS Systems Vertical/Comdial Not Available Notes: 1 Systems larger than 20 stations may be considered PBXs 2 Lines shipped include new lines and add on lines 3 Most lines shipped are part of new systems 4 By 2011, there will be approximately Million KTS lines shipped 5 The average size per system is stations Page 4 of 12 September 2007

5 Recently, the top three traditional KTS vendors have been facing significant competition from open source telephony solutions, hosted options and newly emerging IP based small system vendors. However, it is evident, from the sustained residue of older telephony systems using TDM technology, and from the above survey, that the success of IP telephony does not mean the immediate extinction of TDM KTSs. In fact, these traditional telephony systems are expected to survive for at least another decade. In migrating to VoIP, KTS owners and business decision makers always consider cost, system management, and feature availability. A decision to upgrade from a reliable, highly appreciated yet increasingly antiquated TDM based telephony solution may be a wise choice. Among companies wishing to stay with their legacy KTSs, mainly due to cost issues, many have shown a willingness to phase in IP Telephony for incremental growth, instead of an immediate forklift. 2.2 Key Telephone Systems & Services Issues A key telephone system is a multi telephone system typically used in small office environments. These system solutions are specifically aimed at the small and medium business market and at Fortune 500 firms that have smaller remote offices staffed with personnel that may not have the necessary technical skills needed to perform maintenance functions on complex telephony systems. The Key System Unit (KSU), noted for its expandability, is the heart of the system. The KSUs are typically connected to the Public Switched Telephone Network (PSTN) by trunks. From time to time, there may be modules added to the KSUs to increase the number of stations and the selections of connected trunks. These trunks are the same as those used to offer Plain Old Telephone Service (POTS) service. PSTN Virtual Demarcation Customer Premises Key System SS7 & PSTN I/LEC Digital Switch Line Cards Trunk Lines KSU Stations Business locations with KTSs have different traffic requirements regarding volumes of station to station (intra KSU) versus station to trunk calls. The call volume considerations determine the ultimate trunk to station ratios. For example, if a customer s business with 12 stations requires low outside trunk access, a 3:12 trunk to station ratio may be sufficient. However, if more incoming or outgoing trunk calls are made, access is required at a higher ratio, i.e. may be a 6:12 trunk to station ratio. Some businesses may have mostly outgoing with very little incoming traffic, or vice versa. With any trunk ratio the trunk lines may be designed as two way, incoming or outgoing. 3. Key Systems Interoperability Testing With the considerations above, including the associated marketing strategies, the technical issues on which the selling points depend must be hashed out. Interoperability testing typically determines whether the associated network components are interoperable, which will help to minimize or eliminate unforeseen negative issues. Interoperability Page 5 of 12 September 2007

6 testing must be based on standards and acceptable guidelines, and testing should be carried out by reputable organizations with experience to match the tasks. In this case, MSOs must be certain that the KTSs and the VoIP interfaces successfully pass all mandatory test categories for their technical and marketing strategies to be assured. The emta is a DOCSIS 2.0 based, PacketCable 1.5 compliant multiline interface designed to support small business and residential multiple dwelling unit (MDU) applications utilizing subscriber line interfaces and a 10/100BaseT Ethernet port. PacketCable provides a flexible toolkit with which operators can simultaneously deliver a wide variety of residential and business services. In the business services arena, PacketCable 2.0 support is great for applications such as Session Initiation Protocol (SIP) trunking for IP PBXs and IP Centrex services. For the longer term, it is also designed for high end wireless services, such as fixed mobile convergence and other leading edge capabilities, such as presence enabled communications. VoIP technology interoperability tests were performed between three of the most popular Legacy Key Systems and a multiline emta. Testing with the emta fell into two major categories. The first category is the objective testing, for example: When I pick up a phone and dial 9, do I get a PSTN dial tone? Others within this category include call origination, termination and ring trip (in silent and ring cycles). The second category of testing is subjective: voice quality testing. Generally, these interface/interoperability test cases were designed to verify or measure the following parameters and characteristics: Ringing voltage Loop current feed Ring trip time Return loss Maximum loop resistance for call connectivity 3.1 Test Cases and Set Up The tests were completed with the use of an HP Transmission Impairment Measurement Set (TIMS). Calls are placed through the TIMS. Tests include digital loop system loss, frequency response, idle channel noise, intermodulation distortion, and envelope delay. These tests were performed with normal and boost ringing mode settings of the emta. Key System Under Test RF DOCSIS Multiline EMTA Trunk Trunk 0 1,500 ft Analog Telephone KSU CMTS Analog Station Transmission Impairment Measuring Test Set Page 6 of 12 September 2007

7 3.2 Interoperability Test Environment MSO VoIP Adjunct Interface to Legacy Key Telephone Systems The multiline emta connects to a Cable Modem Termination System (CMTS) via an RF cable and is then provisioned using a configuration file. At this stage, the emta lines are assigned to a call management server in order to provide loop start connection services. Each key system is outfitted with trunks as configuration permits via its interface card. A Hewlett Packard Transmission Impairment Measurement Set (TIMs) provided voice quality parametric testing and measurements through analog lines that the key systems either natively provide, or that is provided through an analog termination adaptor (ATA). 3.3 Test Results Each test was conducted and a Pass/Fail was awarded for each scenario. For objective testing a pass is awarded for completion of the task. For subjective testing, Pass is awarded for meeting the voice quality standards provided by Functional Criteria for the PSTN Digital Loop Carrier (DLC) Systems Analog Transmission Criteria. The systems tested will remain undisclosed while permission to publish is being sought. Test (mode) KTS Vendor 1 KTS Vendor 2 KTS Vendor 3 Dial Tone (boost) Pass Pass Pass Dial Tone (normal) Pass Pass Pass Origination (boost) Pass Pass Pass Origination (normal) Pass Pass Pass Termination (boost) Pass Pass Pass Termination (normal) Pass Pass Pass Ring Trip Ring Cycle (boost) Pass Pass Pass Ring Trip Ring Cycle (normal) Pass Pass Pass Ring Trip Silent Cycle (boost) Pass Pass Pass Ring Trip Silent Cycle (normal) Pass Pass Pass DLC System Loss (boost) Pass Pass Pass DLC System Loss (normal) Pass Pass Pass Frequency Response (boost) Pass Pass Pass Frequency Response (normal) Pass Pass Pass Idle Channel Noise (boost) Pass Pass Pass Idle Channel Noise (normal) Pass Pass Pass Intermodulation Distortion (boost) Pass Pass Pass Intermodulation Distortion (normal) Pass Pass Pass Envelope Delay (boost) Pass Pass Pass Envelope Delay (normal) Pass Pass Pass 4. MSO VoIP Adjunct Interface to Legacy Key Telephone Systems As mentioned earlier, 16 percent of survey respondents said they currently have and another 18 percent said they would deploy TDM key systems within the next twelve months. As the bombardment of IP solutions continues, MSOs can expect SMBs to be wrestling with mission critical growth and productivity issues. A hybrid VoIP/TDM approach may be the answer for many businesses when additions become overly expensive or when support for legacy key systems starts to disappear. VoIP Interfaces to TDM systems can provide stopgap measures while projecting a complete strategy for unified VoIP and data architectures. 4.1 Replace ILEC Dedicated Lines Using embedded multimedia terminal adapters (emtas) for trunking to legacy TDM Key Systems can provide a competitive first step advantage designed to engage the business customer. MSOs may advise KTS owners to forego Page 7 of 12 September 2007

8 expensive growth by capping the KTS and instead add phone and computer communication terminals with VoIP and data capabilities for select groups of employees, then gradually phase out the existing TDM KTS over time. Before deciding on the appropriate sales tactics, MSOs should perform technical and business assessments to determine the potential cost savings of different alternatives. MSO sales personnel must understand all the components of the solution and be prepared to explain to the business what the underlying costs and savings are. MSOs can start by replacing the dedicated outside trunk to the business premises. (See the diagram below.) In this case, the voice and signaling packets from the MSO s Hybrid Fiber Coax (HFC) cable goes to an emta. The RF signals are converted to analog voice and loop start signaling protocols according to PacketCable standards. The Loop Start trunk from the emta is extended to the KTS via RJ11 connectors or may be converted by a 25 pair connector via a punch down block. Key System Multiline EMTA SS7 & PSTN MSO Headend Trunk Coax from HFC Lines KSU Stations I/LEC Digital Switch Line Cards 4.2 Advanced Applications Strategies MSOs should pick the hybrid VoIP/KTS solution that fits the business best rather than try to force the business to change in order to take advantage of the technology. In many cases, the latest and greatest technical solution isn't the best thing for the business and a slower migratory approach is prudent. Target risk tolerant customers first and use them as references with more risk averse customers later on. Risk averse customers may include hospitals, public safety, call centers, etc. Beyond the strategy of first providing an analog trunk signaling support for key systems, there are several other promising adjunct features to consider. Now that there is a foot in the door, MSOs may concentrate on less missioncritical services first to demonstrate VoIP feasibility, then broaden the reach after customers understand the practicalities of VoIP performance capabilities. Probe the customer to determine which features, services, locations, etc. they are willing to consider next. Minimize perceived risks and provide justifications for adding or switching to more advanced features. Other tactics may include offering differentiators that offset perceived risks; offering a productivity improving application such as using IP video surveillance to monitor the business from home or visa versa; or using unified communications to distribute IP enabled call centers. MSOs may consider line hunting features on VoIP lines. Hunting features allow sharing of a group of lines with several individual stations to accept incoming calls reliably. In a hunt group, these stations would be organized in such a way that each incoming call would try the first line of the group. If that line is busy, the call tries the second line, then hunts to the third, and so on. A multiline emta can provide Multi line Hunt Groups (MLHG) to connect outside callers to a call center located on the premises. With MSO implementation, this feature would be provisioned and activated at the call Page 8 of 12 September 2007

9 management server and would extend to the lines of the multiline emta. The figure below shows a completed adjunct where the stations, although separated from the lines, are offering differentiated services. Key System Multiline EMTA SS7 & PSTN MSO Headend Coax from HFC Trunk Lines KSU Stations Lines w/voip Services Simply put, businesses care less about IP, SIP, telephony, or other technical terms they care more about the cost of the required voice and data applications. Once the costs are fully understood, the MSO must be able to discuss the benefits in business terms, not technology terms. The MSO may decide to up sell additional lines of IP related advanced features such as voic via , user self management, and increased mobility. By virtue of the above diagram, find me/follow me, toll free service, auto attendant, unified messaging integration, conferencing, and account/authorization codes features are also potential add ons to be considered. 4.3 Deployment Recommendations With their IP based network infrastructure, MSOs have a competitive advantage in that they can be a low cost provider of these services relative to the incumbent providers. The business customers themselves acknowledge the cost effectiveness of IP technology and are able to replace many TDM based PBXs and Key Telephone Systems with hosted IP solutions. However, there are many other technical considerations in making sure that compatibility is assured Installation emtas for business application may be wall mounted, but also may be rack mounted in the case of a multiline version. While some emtas are available with internal Lithium Ion battery backup, multiline emtas (for greater than four lines) may be powered by 120Vac, which may be supplied by local power supplies (LPSU). Business applications with multiple buildings in close proximity may require trunk lines running from the main multiline emta to a remote Key System. Any call originated from a Key System via an emta to another emta anywhere, would route via the service provider s network and not be considered a local intercom (tandem) station to station call. Installers must use caution in running inter building lines from emtas and should verify the power cross and surge protection compliance for inter building applications. Page 9 of 12 September 2007

10 4.3.2 Transmission Loss Plan MSO VoIP Adjunct Interface to Legacy Key Telephone Systems The voice transmission loss between the PSTN and the Trunk interface of the Key System will vary according to the length of copper cable to the KSU. Telco cable that can extend as far as three miles may have bridged taps that could result in unusually high transmission loss. When factored into the service qualification process, some Key Systems may require transmit and receive levels between the on premises station and the trunk be altered. On short loop applications, some loss may be provisioned (padding) in order to meet transmission loss plan objectives. On long copper loops, which have significant loss, transmit and receive loss in the Key System may be required to be provisioned to zero. emtas are designed for short loop applications, but may still allow inter building applications with cable resistance up to 130 ohms, which is equivalent to 1,500 ft of a 26 AWG twisted pair cable. A major benefit of using the emta within which the line card resides, is that the copper loop between the emta interface and the KSU interface is very short and will not contribute any significant transmission loss. Most emtas default to a specific transmit and receive loss plan template when powered up. The MSO s transmission engineer should determine this loss plan in advance. Usually the emta vendor can provide several firmware transmission templates, which can be downloaded if the default plan is not correct. An incorrect loss plan can cause problems such as low level voice, high level voice, echo, distortion or an unsymmetrical (different one way relative to the opposite direction) loss Incoming Alerting Signals (Ringing) The ringing mode from the PSTN is unbalanced. This means that the ringing signaling is applied to the Ring lead while the Tip lead is at or near ground potential. This traditional mode has been used in North America since inception. The ringing waveform is sinusoidal; the frequency is 20 Hz with a magnitude between 84 Vrms (root mean squared) and 104 Vrms. All Key Systems will detect this ringing signal as an indication of an incoming call. emtas, as mentioned previously, are designed for short loops and have no reason to generate high magnitudes of ringing. They will typically generate in excess of the minimum required through the maximum specified loop. Specifications require that an emta must generate sufficient ring voltage that will develop 40 Vrms across a 5 REN (Ringing Equivalency Number) load at the end of the specified loop length. Typical emta open circuit ring voltage levels are 55 to 60 Vrms with loop length specified up to about 1,500 feet. Most emtas have electronic Subscriber Line Interface Circuit (SLIC) with maximum supply voltage limitations. This voltage limitation may limit the level of ring voltage and DC offset that can be generated. In order to maximize the ringing voltage, three changes may be considered relative to the traditional method of ringing. One is that the waveform is changed to trapezoidal, which allows for greater RMS voltage for the same magnitude of a sinusoidal waveform. The second change may be that the ringing mode is changed to balanced rather than unbalanced. This implies that the Tip and Ring lead each drive the trapezoidal waveform to the maximum allowed level. The Ringing signal on one lead is inverted to form a differential or push pull drive. The third change is to reduce the DC offset voltage to around 10 to 20 Vdc, in comparison to the traditional ringing signal where the ringing signal is superimposed on a 48Vdc offset. To apply these recommendations, the MSO provider should verify that the Key System is compatible with balanced ringing and minimum DC voltage offset Loop Start vs. Ground Start Trunk Signaling Protocol Key System Ground Start or Loop Start trunk lines are available from the PSTN. The closer the incoming traffic equals the outgoing traffic on a loop start trunk, the more likely the chance of a glare condition. A glare condition exists most predominantly on a two way loop start trunk line. When an incoming call terminates on the Key System loop start trunk there is a delay in the trunk becoming busy prior to the detection of ringing. A failure due to glare is caused when an inside line seizes the trunk line at a moment in time when an incoming trunk line is receiving a call. Page 10 of 12 September 2007

11 When this condition exists, the inside station, hoping to receive dial tone, is connected to the incoming trunk caller. There are two unguarded intervals where an inside line could mistakenly seize the trunk in this fashion. If the loop start trunk terminates during ringing there is an unguarded ring detection interval. If the line terminates during a silent ring period there could be an unguarded silent ringing interval lasting up to 4 seconds. This is why two way loop start trunks are not optimal during heavy traffic conditions. There are two ways to overcome this problem. One way is to have two loop start trunks (or trunk groups) one incoming group and one outgoing group. However, this may be a more expensive solution. The second way is to use a ground start trunk. The use of ground start trunks will significantly reduce the glare condition during high trunk traffic conditions. On incoming (terminating) calls the Key System trunk will immediately receive a tip ground from the PSTN which will make that trunk busy for outgoing calls. When the trunk key is pressed for an outgoing call on a station, a ground is placed on the ring lead of the Key System Trunk, which is detected by the PSTN. This will instantly make the trunk busy for any incoming calls. Ground Start trunks have a handshaking protocol, and loop start trunks do not. emtas have loop start line interfaces, which should serve most small business with good performance. The MSO should understand and analyze the traffic conditions on the outside trunk access in advance of the installation. This will prevent any possible glare condition problems if a particular customer has applications with high traffic conditions on trunks Loop Diagnostics PSTN service providers may have limited loop diagnostics regarding foreign voltages, leakage resistance, permanent off hook, and ringer load testing on trunks. A loop diagnostic feature can speed up the process of diagnosing insidewiring issues and thus return the equipment back to service quicker. Some emtas have loop diagnostic capability in compliance with Telcordia GR 909 CORE specifications. This feature may be remotely initiated and provide test results back to a central location. 5. Conclusion Incumbent voice service providers like Verizon and AT&T have unlimited business calling plans and by bundling lowcost Digital Subscriber Line (DSL) with higher cost basic services, they provide strong price competition to attract SMB customers. By way of a competitive response, MSOs are employing services such as IP trunking for IP PBXs and are also offering alternatives such as IP Centrex or hosted IP PBX services. By 2011, there will be an additional Million KTS lines shipped to small and medium businesses. These KTSs are usually lower than 20 stations, which is the sweet spot for MSO business services. The average size per KTS is around stations. To add muster to their SMB revenue potential, MSO can use emtas to augment these KTSs for IP capabilities. KTS Interoperability tests have demonstrated compatibility between the emta and three of the most prevalent key systems deployed in North America. The multiline emta interoperability testing performed against the three most prevalent key systems in North America passed all the tests in the test plan. An MSO VoIP Adjunct strategy will benefit SMB customers by providing reduced calling costs, dynamic data bandwidth allocation, self administrative portal, etc. without initially replacing the existing key telephone system. With such a strategy, where the emta can provide up to 12 lines for trunk connections and/or multiple lines for business expansion, MSOs can add voice and data capacity or add special applications only available with VoIP technology. MSOs are now able to help dispel migration fears while driving IP adoption via replacing the trunk lines to the KTS. IP enablement of existing KTSs will put the MSO in a better position to help the SMB customer gradually migrate to a full IP converged network. Page 11 of 12 September 2007

12 6. Bibliography 1 US Census Bureau Release/www/releases/archives/business_ownership/index.html 2 Frost & Sullivan North American Enterprise Telephony System Markets N11A Frost & Sullivan Vertical Market Perspective: Operational Priorities and Telecom/IT Spending Opportunities, by Imran Khan Industry Analyst, Enterprise Communications, San Antonio, TX, July 24, 2007 The capabilities, system requirements and/or compatibility with third party products described herein are subject to change without notice. ARRIS and the ARRIS logo are l trademarks of ARRIS Group, Inc. Other trademarks and trade names may be used in this document to refer to either the entities claiming the marks and the names of their products. ARRIS disclaims proprietary interest in the marks and names of others. Page 12 of 12 September 2007