Enterprise Survivabilityfor Subscribers of

BroadSoft-Based ServicesMany business subscribers will not switch to IP-based

telephony unless your service offering provides fullconfidence their phones will work—no matter what!

Authored by

W. Glendon FlowersProduct Marketing Manager

Patton Electronics Co.

Marc AeberhardProduct Line Manager, Patton Electronics Co.

Copyright © 2018,Patton Electronics Company.

All rights reserved.

Printed in the USA.

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Contents

Introduction..................................................................3

The Crux of the Problem .............................................3

Cloud PBX.................................................................3

Multi Box ...................................................................3

Redundancy ..............................................................3

Proposed Survivability Solution ................................4

The Answer ..................................................................4

How to Do it.................................................................4

Local Keep-Alive .......................................................5

Alternatives ..................................................................6

Dual Registration .........................................................6

How it works .............................................................6

Normal Operation......................................................6

Survivable operation .................................................7

Installation and maintenance ....................................7

Back To Back User Agent (B2BUA) ............................7

Overview....................................................................8

Normal operation ...................................................8

Survivable operation ..............................................8

Installation and maintenance ...................................9

SIP Proxy .....................................................................9

Overview....................................................................9

Normal operation ...................................................9

Survivable operation ..............................................9

Installation and maintenance ...................................9

Mobile Re-Direct..........................................................9

The Ideal: Patton’s Unique eSBC Solution ...............10

Conclusion .................................................................10

About Patton..............................................................11

About the authors ......................................................12

IntroductionThe new age of All-IP networking has arrived.BroadSoft and BroadCloud platforms are majorenablers for service providers delivering such servic-es to business and enterprise subscribers.

However, a survivability solution on the subscriberpremise is critical to winning business-subscriberconfidence. Without such a proven solution, carrier-providers cannot guarantee E911 service and station-to-station calling service. In the event of access-linkfailure or any failure within the network core, accessto basic services and/or BroadWorks or BroadCloudmust be ensured.

Now that session initiation protocol (SIP)-basedtelephony is well established—enabling broadadoption of unified communications (UC)—the tradi-tional Public Switched Telephone Network (PSTN)seems a bit clunky and old-fashioned. Yet that oldPSTN was—and still is—highly reliable. As we allplunge head-first in to the sea of IP Telephony, thegood old PSTN remains solid ground—a trustworthysurvivability option—for those inevitable times whenyour Internet connection or cloud service fails forwhatever reason.

In addition to PSTN backup, another way to solve theuptime problem with Internet-based phone systemsis to maintain dual access links with separate Internetservice providers (ISPs)—ideally over different physi-cal cabling plants with varied networking providers(fiber-optic Ethernet, coaxial cable-modem, copperDSL). This multi-access approach is highly resilient.A dual-access-link solution provides a backup planfor the broken wide-area-network (WAN) access link.

The Crux of the ProblemMany business subscribers will NOT switch to IP-

based Telephony unless your service offering

provides full confidence their phones will work—nomatter what!

Cloud PBXIn this age where the PBX often resides in the cloud,

the unfortunate reality is that a loss of connection to

the cloud service, for any reason, breaks station-to-

station calls within the enterprise, kills 911 emer-

gency services and wipes out inbound and outbound

call capability.

SIP TrunksIn SIP-trunking implementations, where the IP-PBX

resides on-premise, a broken Internet-access link

kills inbound and outbound calling. However the PBX

can still support station-to-station calls between SIP

terminals within the local area network.

RedundancyRedundancy—rather the absence of it—is the

heart of the reliability problem: the lack of redun-

dant connections for Internet (WAN) access and

telephony services. Whichever backup plan we

choose, PTSN or dual/multi-WAN services, the

question remains: how will the service provider

manage and control redundant network-access

connections to ensure continuity of operations for

the business subscriber? What are you going to do

if the WAN link works, but something else disrupts

access to trunk or cloud services?

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Proposed Survivability SolutionThis paper proposes a flexible solution for systemsurvivability and business continuity that employs anintelligent enterprise session border controller(eSBC)—equipped with the necessary features andfunctions—installed on the subscriber premise.

The AnswerMany Organizations that chose to move forwardwith adopting an All-IP communications system willdemand a comprehensive and innovative solutionfor the survivability problem. Such technologyshould combine intelligent self-learning capabilitywith automated monitoring, switching and notifica-tion mechanisms—all embedded in a customer-

premise enterprise session border controller(eSBC). This solution is embodied in theSmartNode eSBC from Patton Electronics.

How to Do it1) Redundant WAN connections—Fully interoper-

able and certified with BroadSoft platforms, thePatton SmartNode eSBC provides multiple on-board interfaces that support WAN connectionsto the ISP, ITSP, and PSTN. Connectivity optionsmay include:

• Dual Ethernet ports

• Wired cable/fiber/DSL

• Wireless LTE/WiFi

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Figure 1: Proposed Survivability Solution

Figure 2: Option A: Survivable PSTN Access

2) Intelligent Self-learning—The SmartNode eSBCincludes a SIP registrar function. The intelligentCPE engages in discovery operations to learn andrecord the fully qualified domain name (FQDN) ofSIP servers residing in the provider networks.Further, the eSBC discovers and records theFQDN of each local IP endpoint (hardware SIPphones, IP softphones) located within the sub-scriber LAN environment:

Local Keep-AliveBy automatically registering SIP endpoints that resideon the enterprise LAN, the local eSBC can keep theintra-office (internal) phone system alive for station-to-station calls by handling internal intra-office callseven when there is no live out-route to BroadCloud,BroadWorks or the PSTN.

3) Real-Time Monitoring—The eSBC provides IP-Link supervision. The SIP Options ping message(specified in the SIP protocol) is leveraged tomonitor the up/down state of SIP servers. If noresponse is received from a server, a network fail-ure is indicated and link switchover is initiated.

4) Automatic Path Switching (re-Routing)—Whenthe eSBC detects a WAN failure, it redirects allSIP traffic over the alternate WAN link, which maybe a PSTN connection or a secondary Internetaccess link, such as a second Ethernet port or anoptional wireless uplink. Fail-over notifications aresent to the enterprise and can be configured tonotify the provider delivering BroadSoft-based

services. Inbound and outbound phone calls arere-routed end-to-end over the alternate (backup)path. This automatic path switching enables out-bound calling. If BroadWorks or BroadCloudbusiness continuity services have been config-ured to use alternative numbers to reach thecalled party, inbound calling is also preserved.

5) Configurable notifications—Notification can beaccomplished via syslog, SNMP, SMS, or email.Any or all of the above notification methods maybe turned on or off as required by the systemadministrator.

6) Other Pluses—Of course, any high-quality CPEshould provide all the other value-added benefitsavailable with modern eSBC technology…

• SIP normalization for interoperability assurance

• Codec transcoding for bandwidth manage-ment and WAN optimization

• Security mechanisms against toll fraud anddenial-of-service attacks, including calladmission control, accesses control lists, andTLS/SRTP encryption

• Quality of Service (QoS) for the upstream anddownstream paths

• Link quality monitoring and reporting

• Cloud support for edge orchestration,touchless provisioning, configuration, andmanagement

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Figure 3: Option B: Redundant IP Access

AlternativesVarious vendors offer an array of redundancy andfailover solutions. Most if not all such solutions requirehuman intervention to configure IP end-points, edgedevices and/or cloud services. Here we will present asummary of the four most popular survivabilityapproaches (other than the Patton solution) currentlyavailable in the market, with pros and cons for each:

• Dual Registration (survivability node)

• Back-to-Back User Agent (B2BUA)

• SIP Proxy Server

• Mobile Re-Direct

Dual RegistrationPROs: Dual registration is likely the simplest way toimplement a basic survivability solution.

CONs: Activation may be delayed and inconsis-tent. Maintenance is complex and requires humanintervention.

How it works

A survivability node is installed within the enterprise

LAN, which does not participate in the normal SIP

signaling or call flow. Each SIP endpoint is configured

with the address of the survivability node as a sec-

ondary (backup) SIP registrar. If the WAN connection

goes down, or if the SIP server within the primary

ITSP becomes unreachable for any reason, local SIP

endpoints (hard or soft SIP phones) target the local

survivability node for SIP registration and call control.

Normal Operation

The survivability node does not participate in the

SIP call-control stream during normal operation. SIP

endpoints (phones) register over the WAN-access

link to the primary ITSP, which provides all call-con-

trol processing. During normal operation status

information for the SIP phones is NOT available to

the survivability node.

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Figure 4: Dual Registration Normal Operation

Survivable operationWhen the SIP phones cannot reach their primary SIPserver, they fail-over to the pre-configured backupserver (survivability node). Redirecting SIP registra-tion and call control to the to the local server pre-serves station-to-station calling within the enterprise,as well as E911 emergency calls to the PSTN over anE1/T1, FXO or BRI connection.

Installation and maintenanceSIP phone configuration. For the dual-registrationsolution to work, each and every SIP phone must bepre-configured with the address of the fallback SIPregistrar (survivability node). Phones that don’t sup-port such fallback configuration won’t work during anoutage of the Internet-access link.

Delayed activation. Failover does not happeninstantaneously. It can take several minutes for all thephones to detect WAN-access failure and re-directregistration and call flows through the local surviv-ability node.

Inconsistent operation. Since each phone mustseparately detect the failed WAN link, internal exten-sions may not all be reachable immediately becauseeach phone must independently switch to the surviv-ability node.

Back To Back User Agent (B2BUA)PROs: Powerful—Going well beyond the basics ofsurvivable station-to-station and E911 calling theback-to-back user agent (B2BUA) continues to pro-vide SIP-service demarcation, QoS, SIP-headermanipulation, and SIP security when the ITSP serviceis down or un-reachable.

CONs: Labor-intensive—For moves, adds, andchanges (MACs) the B2BUA must be configured (orRE-configured) with registration credentials for everySIP endpoint. Another consideration: for certainenterprises, especially when the VoIP service is host-ed, the added functions this approach provides mightbe overkill (i.e. unnecessary).

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Figure 5: Dual Registration Survivable Operation

OverviewThe B2BUA is set up as the primary registrar for alllocal SIP endpoints (phones). Credentials for all end-points are managed and processed by the B2BUAdevice. Typically a central location provisions andmanages the endpoint configurations over a remoteconnection to the B2BUA. Each new SIP endpointmust be configured in the B2BUA in order to providesurvivability functions.

Normal operationThe B2BUA provides secure network separationbetween the enterprise LAN and the service-providerWAN. The B2BUA receives (terminates) and re-sends(re-initiates) SIP messages from local SIP phones andremote entities (SIP servers, SIP endpoints) accessedvia the WAN.

Survivable operationThe B2BUA monitors the WAN link at all times,regardless of whether the ITSP service is available. Ifa ping response is not received from the ITSP after aconfigurable timeout threshold, the B2BUA reroutescalls to an alternative connection (E1/T1, FXO, wire-less, or alternate Ethernet line).

In survivability/fallback mode, the B2BUA is able topreserve station-to-station calling because it knowsthe previously registered addresses of all the SIPphones. The B2BUA solution can also supportinbound calls—but only if failover call routing is bepre-configured within the ITSP.

8Figure 6: B2BUA Normal Operation

Figure 7: B2BUA Survivable Operation

Installation and maintenanceAll SIP endpoints must be configured for a single reg-istrar: the local B2BUA. This solution is easier to setup for new installations. When an existing hostedimplementation needs to be changed, every SIP end-points has to be touched and reconfigured to registerwith the B2BUA.

From a maintenance perspective, this setup requiresmore effort than a SIP proxy solution (covered below)because the B2BUA must manage and maintain allthe local SIP user identities and credentials.

SIP ProxyPROs: The SIP Proxy approach is less complex thanthe B2BUA method, with fewer parameters to config-ure and maintain. Multiple alternate paths (if accessi-ble) can be configured and supported.

CONs: All the SIP phones must be pre-configured tore-direct call flows to a proxy server when the primarySIP server fails. While it can reroute SIP calls over anyalternate access link that is available and operating,the SIP proxy does not provide any WAN-link failovermechanism. Further the SIP proxy does not providethe added security features, header manipulation orother feature/benefits the B2BUA offers.

OverviewThe SIP proxy server (RFC 3261) is essentially arouter, examining headers only, and does examine orprocess the payload of deeper protocol units such asRTP. While is similar to the B2BUA solution, it is a bitsimpler to implement and maintain. A SIP proxy can

provide local authentication and maintain a userdatabase, yet the SIP phones must also authenti-cate with a SIP server within the ITSP network.

Normal operationLocal SIP phones are configured to send registrationrequests and call data to the SIP proxy. The proxyserver forwards (does NOT retransmit) the call-signal-ing information to the SIP server within the ITSP. TheSIP proxy adds a route header that tells the SIP serv-er how to reach the local SIP endpoints—using theproxy as a hop.

Survivable operationWhen the primary SIP server becomes unreachable,the SIP proxy re-reroutes SIP calls to the SIP serverin an alternate ITSP (this must be pre-configured inthe proxy server). In this case, the SIP Proxy onlyaddresses ITSP-related problems—not a WAN linkoutage. However, if the local network architectureoffers alternate outbound WAN connections, the SIPserver will re-route call traffic to an available uplinkwhen the primary WAN link fails.

Installation and maintenanceThe SIP proxy, if not doing authentication, is quitestraight-forward to set up and configure. Still, all thephones must be pre-configured with the proxyaddress configured for the application to work.

Mobile Re-Direct PROs: Preserves inbound (downstream) calling byforwarding calls to one or several mobile phones.

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Figure 8: SIP Proxy

CONs: Partial solution for survivable phone service.Inadequate for most businesses.

Some ITSPs offer a mobile re-direct service, whichprovides a partial survivability solution for enterprises.When the WAN-access link fails, the ITSP can re-route incoming calls to a mobile phone. This solutiononly applies to inbound (downstream) calls. In somecases all the numbers handled by a SIP trunk arerouted to a single mobile phone. While this mecha-nism ensures very basic reachability, it severelyrestricts the level of service for an organization. Ofcourse workers can always use their mobile phonesto make outbound calls. However, such business-class features as conferencing and forwarding aremissing. And, obviously, personal mobile phone num-bers (instead of business numbers) are presented tothe called party.

The Ideal: Patton’s Unique eSBCSolutionSmartNode eSBCs can be configured to support allthe most-effective common industry-standard surviv-ability mechanisms discussed in this white paper,including:

• Dual registration

• B2BUA

• Mobile re-direct

In addition to the common industry-standard surviv-ability techniques, Patton’s-survivability solutionincludes the following value-added differentiatingfeatures and functions:

• Automatic path switching (WAN-link failoverand call re-routing)

• Redundant WAN connections—All WAN con-nection types are supported (Ethernet, PSTN,Wireless)

• Intelligent self-learning of FQDNs for remoteSIP servers and local SIP-endpoints. This means

no configuration or reconfiguration is required forany network elements.

• Real-Time Monitoring of Internet access linksand SIP service entities (softswitches, servers,registrars)

• Configurable Notifications for state/statuschanges

Because it is automated, the Patton survivabilitysolution is unique in the telephony market today.

Manufactured in the USA, SmartNode eSBCs provid-ed all the features and functions cited above, com-bined in a single customer-premise device.

ConclusionA flexible eSBC can function as a stand-alone surviv-ability appliance for enterprise IP-telephony to pro-vide all functions cited above. Whether a TDM failoveror dual-WAN approach is selected, a fully-automatedsurvivability solution must not require human inter-vention for link switching or re-configuration of net-work elements. It must employ intelligent technologyfor self-learning of local SIP endpoint credentials.Further, WAN-link failover must be handled automat-ically by customer premise equipment. Ideally theeSBC should provide all the other functions enumer-ated above: gateway, routing, security, and so on.

The eSBC-based survivability solution describedabove is available from Patton Electronics in theSmartNode product line. In addition, for BroadSoft-based IP telephony deployments, SmartNode eSBCsoffer the following added value propositions:

• Interoperability—SmartNode devices are certi-fied with BroadSoft and BroadCloud platformsand interoperate seamlessly with all standardSIP-based telephony devices and services.

• Automated Provisioning—SmartNode deviceswork with Broadsoft Device ManagementSystem (DMS) to support automated provisionfrom remote locations. For a detailed discussion

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of Patton’s auto-provisioning solution, see thePatton white paper Auto-Provisioning Solutionfor SIP Trunks Serving Customer-Chosen IP PBX

• Split Management Domain—Also known assplit configuration domain, this feature clarifiesand enforces the secure demarc by separatingthe customer-facing configuration from the carri-er-facing configuration. This feature allows theservice provider to manage the WAN-facing con-figuration while only the customer (and/or theintegration partner that provides installation serv-ices) can manage the LAN/iPBX-facing configu-ration. The carrier-provider defines whichSmartNode parameters may be configured bythe customer/installer and which parameters areaccessible only to the service-provider.

• Embedded PacketSmart Probe—Available as alicensed feature in SmartNode eSBCs, theembedded PacketSmart Probe works seamlesslywith BroadSoft IP-telephony services to providecontinuous, real-time, health and quality-of-ser-vice monitoring of customer networks and activecalls 24 x 7 x 365. Proactive alerting and automat-ed reporting enable service providers to identifylocal-area-network (LAN) and wide-area-network(WAN) issues that may impair VoIP service quality.

• Patton Cloud—The Patton Cloud service sup-ports SmartNode eSBCs by providing edgeorchestration functions that include feature

license management, provisioning, configuration,and other element management services all theway to the customer premise—along with failovernotifications—all in seamless interoperation withBroadSoft-based services.

About PattonPatton is all about connections. It is our joy and mis-sion to connect real-world customer challenges withhigh-quality, right-priced solutions—complementedby unrivaled customer service and technical support.Incorporated 1984, Patton has built everything frommicro-sized widgets that connect "this-with-that," tocarrier-grade Telecom gear that connects sub-scribers to service-providers. Patton's specialty isinterconnecting legacy TDM and serial systems withnew-generation IP-based voice, data, and multi-media technologies.

Headquartered in Gaithersburg, MD, USA, Pattonequipment—including VoIP, Ethernet extension, andwireless router technologies—is up-and-running incarrier, enterprise and industrial networks worldwide.Patton works in connection with a growing network oftechnology, business, and sales-channel partners. Toconnect with local-market requirements, Patton oper-ates training and support centers in Switzerland,Hungary, Lebanon, Australia and the USA.

Patton… Let's Connect!

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About the authorsW. Glendon FlowersProduct Marketing Manager,Patton Electronics Co.

Glendon is responsible for creat-ing corporate marketing and tech-nical content including pressreleases, web copy, white papers,

case studies, educational and tutorial pieces as wellas other publications. He serves as editor in chief forPatton's email newsletter and other outbound com-munications. He holds a Bachelor of Science inComputer Science from UMUC and a Bachelor ofMusic in percussion performance from UMCP.

Marc AeberhardProduct Line Manager, Patton Electronics Co.

Marc Aeberhard is SmartNodeProduct Line Manager at Patton,based in Switzerland. He is a spe-cialist in Business administration

and technical management and holds a Swiss federaldiploma. He is involved in Telecommunication tech-nology for close to 20 years and is with the companyfor more than 10 years where he previously was lead-ing the technical support team in Western Europe.

7622 Rickenbacker DriveGaithersburg, MD 20879 USA

tel: +1.301.975.1007fax: +1.301.869.9293

web: www.patton.comemail: marketing@patton.com

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