Enterprise Survivabilityin the Age of

All-IP TelephonyThe new age of All-IP networking has arrived. Yet many

business subscribers will not switch to IP-based telephonyunless your service offering provides full confidence 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

Proposed Survivability Solution...................................3

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

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

SIP Trunks.................................................................4

Redundancy ..............................................................4

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

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

Alternatives ..................................................................5

Dual Registration .........................................................5

How it works .............................................................5

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

Survivable operation .................................................6

Installation and maintenance ....................................6

Back To Back User Agent (B2BUA) ............................6

Overview....................................................................7

Normal operation ...................................................7

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

Installation and maintenance ...................................8

SIP Proxy .....................................................................8

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

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

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

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

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

The Ideal ......................................................................9

Conclusion ...................................................................9

About Patton..............................................................10

About the authors ......................................................11

IntroductionThe new age of All-IP networking has arrived. Yetmany business subscribers will not switch to IP-based Telephony unless your service offering pro-vides full confidence their phones will work—nomatter what!

Now that session initiation protocol (SIP)-basedtelephony is well established, enabling broad adop-tion of unified communications (UC), the traditionalPublic Switched Telephone Network (PSTN) seems abit clunky and old-fashioned. Yet that old PSTNwas—and still is—highly reliable. As carrier-providers—and their subscribers—plunge head-firstin to the sea of IP Telephony, the good old PSTNremains good solid ground—a trustworthy Plan B—for those inevitable times when your subscriber’sInternet connection fails… for whatever reason.

Another way (in addition to PSTN backup) to solvethe uptime problem with Internet-based phone sys-tems is for the subscriber maintain dual access linkswith separate Internet service providers (ISPs)—ideal-ly over different physical cabling plants with variednetworking providers (fiber-optic Ethernet, coaxialcable-modem, copper DSL). This multi-providerapproach is highly resilient. In addition to providing abackup plan for the broken WAN access link, it cov-

ers potential hardware or software failures in the serv-ice-provider cloud. As another layer of redundancyfor added resilience, a second Internet TelephonyService Provider (ITSP) may be added to the mix.

Proposed Survivability SolutionThis paper proposes a flexible solution for enter-prise-telephony survivability and business continu-ity that employs an intelligent enterprise sessionborder controller (eSBC)—equipped with the nec-essary features and functions—installed on thesubscriber premise.

The Crux of the ProblemWhether your subscriber is operating a business,hotel, school, church or hospital, the problem isthe same. How are you going to keep your cus-tomer’s phone system working—no matter what?

Cloud PBXIn this age where the PBX is often in the cloud, theunfortunate reality is that a loss of connection to thecloud service, for any reason, breaks station-to-station calls within the enterprise, kills 911 emer-gency services and wipes out inbound and out-bound call capability.

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Figure 1: Proposed Survivability Solution

SIP TrunksIn SIP trunking implementations, where the IP-PBXresides on-premise, a broken Internet access link killsinbound and outbound calling. However the PBX canstill support station-to-station calls between SIP ter-minals within the local area network).

RedundancyRedundancy—rather the absence of it—is theheart of the reliability problem: the lack of redun-dant connections for Internet and wide area net-work (WAN) services. Whichever backup plan wechoose, PTSN or dual ITSP service, the questionremains: how will the service provider manage andcontrol redundant network-access connections toensure continuity of operations for the businesssubscriber? What are you going to do if the WANlink works, but something else disrupts access totrunk or cloud services?

The AnswerMany organizations that chose to move forward withadopting an All-IP communications system willdemand a comprehensive and innovative solution forthe survivability problem. Such technology shouldcombine intelligent self-learning capability with auto-mated monitoring, switching and notification mecha-nisms—all embedded in a customer-premise enter-prise session border controller (eSBC).

How to Do it1) Redundant WAN connections—The eSBC

should provide multiple on-board interfaces thatsupport WAN connections to the ISP, ITSP, andPSTN. Connectivity options may include:

• Dual Ethernet ports

• Wired cable/fiber/DSL

• Wireless LTE/WiFi

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Figure 2: Option A: Survivable PSTN Access

Figure 3: Option B: Redundant IP Access

2) Intelligent Self-learning—The eSBC shouldinclude 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-Alive. By automatically registeringSIP endpoints that reside on the enterprise LAN,the local eSBC can keep the intra-office (internal)phone system alive for station-to-station calls byhandling internal intra-office calls even whenthere is no live out-route to BroadCloud,BroadWorks or the PSTN.

3) Real-Time Monitoring—The eSBC should pro-vide IP-Link supervision. The SIP Options pingmessage (specified in the SIP protocol) is lever-aged to monitor the up/down state of SIP servers.If no response is received from a server, a WANfailure is indicated and link switchover is initiated.

4) Automatic Path Switching (re-Routing)—Whenthe eSBC must be able to detect a WAN failure,and redirect all SIP traffic over the alternate WANlink—which may be a PSTN connection, second-ary WAN, or wireless Internet-access link. Fail-over notifications should be sent to the enterpriseas well as the IP telephony service provider, whileinbound and outbound phone calls are re-routedend-to-end over the alternate (backup) path.

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 tool fraud anddenial of service attacks, including call admis-sion control, accesses control lists, andTLS/SRTP encryption

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

• Link Quality monitoring and reporting

• Cloud support for touchless provisioning, con-figuration, and management

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 worksA survivability node is installed within the enterpriseLAN, which does not participate in the normal SIPsignaling or call flow. Each SIP endpoint is configuredwith the address of the survivability node as a sec-ondary (backup) SIP registrar. If the WAN connectiongoes down, or if the SIP server within the primary

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ITSP becomes unreachable for any reason, local SIPendpoints (hard or soft SIP phones) target the localsurvivability node for SIP registration and call control.

Normal OperationThe survivability node does not participate in theSIP call-control stream during normal operation. SIPendpoints (phones) register over the WAN-accesslink to the primary ITSP, which provides all call-con-trol processing. During normal operation statusinformation for the SIP phones is NOT available tothe survivability node.

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 be

pre-configured with the address of the fallback SIP

registrar (survivability node). Phones that don’t sup-

port such fallback configuration won’t work during an

outage of the Internet-access link.

Delayed activation. Failover does not happen

instantaneously. It can take several minutes for all

the phones to detect WAN-access failure and re-

direct registration and call flows through the local

survivability node.

Inconsistent operation. Since each phone must

separately detect the failed WAN link, internal exten-

sions may not all be reachable immediately because

each phone must independently switch to the surviv-

ability node.

Back To Back User Agent (B2BUA)PROs: Powerful—Going well beyond the basics of

survivable station-to-station and E911 calling the

back-to-back user agent (B2BUA) continues to pro-

vide SIP-service demarcation, QoS, SIP-header

manipulation, and SIP security when the ITSP service

is down or un-reachable.

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Figure 4: Dual Registration Normal Operation

CONs: Labor-intensive—For moves, adds, and

changes (MACs) the B2BUA must be configured (or

RE-configured) with registration credentials for every

SIP endpoint. Another consideration: for certain

enterprises, especially when the VoIP service is host-

ed, the added functions this approach provides might

be overkill (i.e. unnecessary).

OverviewThe B2BUA is set up as the primary registrar for all

local SIP endpoints (phones). Credentials for all end-

points are managed and processed by the B2BUA

device. Typically a central location provisions and

manages the endpoint configurations over a remote

connection to the B2BUA. Each new SIP endpoint

must be configured in the B2BUA in order to provide

survivability functions.

Normal operationThe B2BUA provides secure network separation

between the enterprise LAN and the service-provider

WAN. The B2BUA receives (terminates) and re-sends

(re-initiates) SIP messages from local SIP phones and

remote entities (SIP servers, SIP endpoints) accessed

via the WAN.

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Figure 5: Dual Registration Survivable Operation

Figure 6: B2BUA Normal Operation

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 althernet 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.

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-configuredto re-direct call flows to a proxy server when theprimary SIP server fails. While it can reroute SIPcalls over any alternate access link that is availableand operating, the SIP proxy does not provide anyWAN-link failover mechanism. Further the SIPproxy does not provide the added security features,header manipulation or other feature/benefits theB2BUA offers.

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Figure 7: B2BUA Survivable Operation

Figure 8: SIP Proxy

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 canprovide 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: The SIP proxy, if not doing authentication, isquite straight-forward to set up and configure. Still, allthe phones must be pre-configured with the proxyaddress configured for the application to work.

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 phonenumbers (instead of business numbers) are present-ed to the called party.

The IdealWhether a TDM failover or dual-WAN approach isselected, a fully-automated survivability solution mustNOT require human intervention for link switching orre-configuration of network elements. It must employintelligent technology to be self-learning. The flexibleeSBC might be installed as a stand-alone survivabilityappliance, yet ideally it should also provide the securi-ty, routing, gateway and other eSBC functions enu-merated above, as well as the standard survivabilitymechanisms discussed in this white paper, including:

• Dual registration

• B2BUA

• Mobile re-direct

ConclusionA flexible eSBC can function as a stand-alone surviv-ability appliance for enterprise IP-telephony to pro-vide all functions cited above. It must employ intelli-gent technology for self-learning of local SIP endpointcredentials. Further, WAN-link failover must be han-dled automatically by customer premise equipment.Ideally the eSBC should provide all the other func-tions enumerated above: gateway, routing, security,and so on.

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The solution described above is available from PattonElectronics in the SmartNode eSBC product line.

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

In addition to the common industry-standard surviv-ability techniques, Patton’s-survivability solutionincludes the following differentiating features andfunctions:

• 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 meansno 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

Additional benefits that come with the PattonSmartNode brand include:

• Interoperability—SmartNode eSBC devicesinteroperate seamlessly with standard SIP-basedtelephony service offerings and are certified withall the well-known SIP-based service providers,softswitch vendors, and telephony devices.

• Automated Provisioning—SmartNode deviceswork with the Patton Cloud to support automat-ed provision from remote locations

• 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.

• Patton Cloud—The Patton Cloud service sup-ports SmartNode eSBCs by providing edgeorchestration functions that include featurelicense management, provisioning, configuration,and other element management services all theway to the customer premise—along with failovernotifications.

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

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 andtechnical 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.

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tel: +1.301.975.1007fax: +1.301.869.9293

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

Document: 07M-ENTSURVALLIP-WP