Enterprise session border controller aids small remote office contact center deployments

By Brad (Biju) Oommen

Originally published in 
https://www.ucnetworkmanagement.com/topics/ucnetworkmanagement/articles/439113-enterprise-session-border-controller-aids-small-remote-office.htm 

August 13, 2018

Enterprise Session Border Controller Aids Small Remote Office Deployments

By Biju Oommen -

Distributed contact centers are migrating to Session Initiation Protocol (SIP) and IP-based communications infrastructure.  These technologies reduce costs while increasing business agility and productivity.  For converged voice networks, the Enterprise Session Border Controller (eSBC) can play a pivotal role in ironing out interoperability concerns while securely enabling SIP communications.

Because eSBCs manage and control SIP signalling and associated RTP (real-time protocol) audio streams, they are able to address challenges pertaining to SIP VoIP service quality, security, and SIP interoperability, including handling codec mismatches and subtle differences in SIP flavors.

At small remote office contact centers, for instance, if we can deploy eSBCs that also incorporate support for E1/T1 ISDN PRI connectivity and/or analog FXO connectivity, it would offer resiliency and high availability for the voice services.  In the event of a catastrophic failure of the MPLS WAN link – if the interconnecting WAN link goes down – local voice calls from the branches can be re-routed over the available E1/T1 PRI or analog lines.

The solution is also useful for organizations migrating to SIP trunks from PRIs or analog lines, as it would facilitate a phased migration from a TDM system to an IP telephony system while leveraging the existing incumbent facilities to deliver quality voice services and high availability.

Figure 1: Block schematic remote small contact center offices without eSBC

For a before and after comparison of the SIP communications architecture and topology, we have come up with  block schematics depicting remote small contact center offices without (Figure 1) and with (Figure 2) an eSBC.

Figure 2: Remote Small Contact Center Offices with eSBC installed

For our application illustration, ensuing discussions and subsequent eSBC testing, we will requisition and use the Patton SmartNode 5570 eSBC + Router equipped with 1 ISDN PRIT1/E1 interface.

Let us take a closer look at the preceding schematics and deployment strategy.  You will find we have retained the MPLS networks with expedited real-time class Class of Service allocation for voice on the data pipes for SIP trunks and remote office connectivity.  However, you will note that we have added an eSBC equipped with ISDN T1/E1 PRI ports at the small remote contact center offices.

The benefits that accrue from the eSBC deployment are manifold:

• You have toll-fraud control at the demarcation point;
• QoS and codec selections are under your control;
• You can implement media transcoding (allowing  deployment of SIP endpoints that support G.722 codec);
• Interoperability with your ITSP that supports and perhaps offers only a G.711 codec;
• You have a demarcation point for SIP hand-off, making monitoring and troubleshooting easy;
• Your contact center endpoints, such as SIP-based IP phone attributes and your branch IP network topology is not visible to the ITSP SIP endpoints; and
• You have call admission control while thwarting SIP DOS attacks and achieving SIP interoperability by normalizing SIP.

To top it all off, even when the SIP trunks are down, contact center agents with IP phones at the remote branches can place outbound calls through the ISDN T1/E1 PRI ports.  When the SIP service becomes unreachable, the survivability agent can take over and connect the SIP sessions locally, allowing station-to-station, emergency, and external breakout calls.

The Patton SmartNode 5570 is one appliance that comes equipped with one or two T1/E1 PRI ports.  It also offers security features such as SIP TLS, SRTP, stateful firewall, split configuration domain (for service demarcation purposes between you and your ITSP SIP provider), call transcoding for up to 16 calls, and more.

Functionality Testing

For this brief functional testing exercise, the primary focus was on the eSBC SIP functionality.  We used the SmartNode 5570 eSBC and router equipped with one T1/E1 port and running software release version 3.13.0-18025.  During the course of our testing, we connected the SmartNode 5570 to a test SIP trunk provided by an ITSP.  The SmartNode 5570 was our demarcation point.

We successfully placed inbound and outbound calls from the PSTN to the test SIP endpoint in the lab.  The test SIP phone successfully registered with the 5570.  As a matter of fact, we successfully placed inbound and outbound calls through a variety of SIP endpoints.  For the preliminary T1 testing we used a T1 physical loopback connector and then enabled the ISDN E1/T1 interface port on the 5570 with the following settings:

• Port type:  T1
• Line-code:  B8ZS
• Clock mode:  Slave mode
• Framing:  ESF
• Line-Build-Out: 133ft
• Application Mode:  Shorthaul
• LOS Threshold

Conclusion

In the realm of small remote branch voice communications, if your business objectives are TDM to SIP migration and/or branch voice service survivability as a part of your Business Continuity and Disaster Recovery (BCDR) plans, they both can be achieved in equal measure by deploying an eSBC equipped with T1/E1 interfaces, including the Patton SmartNode 5570 Enterprise Session Border router.

About the author:  

Brad (Biju) Oommen is a network architect and principal consultant. His work revolves around multi-vendor product and technology integration. It spans the domains of IP Telephony, Multi-media Contact Center, VoIP-H.323/SIP, SDH, EoS, WiFi/VoWiFi, SSL VPN, application acceleration, email and network security, SEM, SAN, IP networks, Fiber, IoT and Microwave communications. He can be contacted at bijuoommenzurich@yahoo.com or bijuoommentoronto@yahoo.ca