WHY COX BUSINESS? SIP TRUNKING: BUSINESS CONTINUITY AND REDUNDANCY A White Paper 1 P a g e
2013 by Cox Communications. All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means, electronic, mecha nical, photocopying, recording, or otherwise, without prior written permission of Cox Communications.
Table of Contents INTRODUCTION... 1 WHAT IS FAILURE?... 2 THE APPROACHES... 3 SINGLE SITE OPTIONS... 3 SEPARATE TRUNK GROUPS WITHIN A SINGLE SITE BUSINESS... 4 INTEGRATED TRUNK GROUPS WITHIN A SINGLE SITE BUSINESS... 5 SIP TRUNK TO TDM PRI FAILOVER... 5 FAILING OVER TO PRIS... 6 PARTIAL PRI BACK-UP... 6 SUMMARY... 7 i
Introduction Private Branch Exchange (PBX) systems are one of the more common tools that businesses use to communicate within and outside of their physical structures. As more businesses retire their TDM voice switches and replace them with IP PBXs, IT managers are discovering the additional flexibility that SIP trunk service providers are able to incorporate into their SIP trunk solutions. Various SIP trunk business continuity or redundancy options provide IT managers with opportunities that can avert a single point of failure in their voice architecture. Attaining a low cost backup solution is now targeted towards defining how a business wants to manage a service disruption to their primary voice service. Some solutions are more involved than others, but like most business decisions, the final analysis weighs cost against risk. This white paper presents redundancy options that your service provider should be equipped to support. In turn, these options are designed to minimize interruptions to your voice service. When a company has a business continuity process in place, there is a higher likelihood that the company will be able to maintain normal operations in the event of a service disruption. In order to create an appropriate redundancy plan, management should define what constitutes a failure and the minimum acceptable level of operations required to maintain viable business activities. Cox Business: SIP Trunking - Business Continuity and Redundancy Page 1
What is a Failure? Failure can mean many things, ranging from reduced service capacity to a complete loss of service. The loss may affect a particular location or inbound and/or outbound calls across the enterprise. It may also be related to internal network elements rather than external facilities acquired from a service provider. Preparation in the design and implementation of a redundancy plan can mitigate various operational impacts that can occur as a result of partial or total disruptions to a company s voice service. The level of operations that a business can maintain during a disruption in their voice service is usually related to the cost/benefit of avoiding or minimizing the effect of the disruption. Many businesses assume they need a solid-gold redundancy version, until they understand the pricing associated with such a plan. Then, the decision leans more toward gold plating, or will silver suffice? Full operational redundancy means the business does not miss a beat. For example, some redundancy options can enable continuous operations within acceptable limitations, however, the ability to maintain normal call capacity may be compromised. The challenge is that there are multiple components involved in delivering a voice call to an end-user and any of these components can have a significant impact on the daily operations in the event of a failure. These challenges exist in both a customer s network and within the service provider s network. Some of these components include: The service provider s network PSTN switching platforms IP network feature servers Network session border controllers The physical IP network itself up to and include building access at customer s location Customer premises e-sbc On the customer s end Customer s LAN IP PBX Switches Routers IP Phones Cox Business: SIP Trunking - Business Continuity and Redundancy Page 2
The diagram below represents the complexities inherent in a modern day voice delivery network. It further illustrates a typical SIP trunk deployment that uses TDM PRIs as a redundant solution. This concept is discussed later in this presentation. Figure 1. Typical SIP Trunk Deployment with TDM PRIs In the end, there is a balance between the cost of losing functionality versus the cost of providing high availability, which is driven by the risk to the business. Helping business customers define the appropriate balance is key to designing a suitable redundant solution. The Approaches Just as there are multiple components involved in providing voice service, there are several options to achieve a manageable redundancy plan. Cox Business has created three general categories for its SIP trunk deployment program that involves options which range from basic to complex. These general groupings are: Single-site SIP trunk solutions Multiple-site SIP trunk solutions Multiple-network solutions that use TDM PRI in conjunction with SIP trunks The following sections provide you with additional information about these various redundancy options in order of increasing network complexity and cost. While implementation costs for these solutions increase with each level of complexity, the probability of a failure in your voice network that impacts your business operations declines proportionately. Single Site Options A low-cost option for a small-medium business (SMB) customer, defined as a company with less than 100 employees located in one building, already has valuable redundant functionality built into its SIP trunk service, depending on their service provider. The Call Forward Always (CFA) and Call Forward Not Reachable (CFNR) features, which are included in every Cox Business SIP trunk deployment, enable the entire trunk group to be diverted to a single telephone number at another location. For example, this solution is activated if there is a loss of service to the building or if there is a problem with the building itself; e.g., power outage, flood, fire, etc. These features re-route all calls directed to the primary SIP trunk group to another location. This transition can be initiated through manual intervention by the customer s administrator or automatically. The telephone number to which calls will be forwarded can be anywhere and can be associated with any other Cox Business: SIP Trunking - Business Continuity and Redundancy Page 3
service, such as another trunk group or a mobile phone. The limitation of this application is that all of the details associated with original calling number, such as Caller ID, are lost when the call is received at the interim location. Of course, the secondary site must be equipped and staffed to handle the calls that are forwarded to that location. Individual IP PBX station users can also be provided with a Personal Mobility Option as a low-cost redundancy solution. When provisioned with this service, individual DID users have the ability to send their calls to another telephone number. However, in this scenario, the number to which calls are forwarded can be different for each DID, as required. Therefore, in the event of loss of service or during busy conditions within the SIP trunk group, business operations remain unaffected. The location of the alternate telephone number can be anywhere or associated with another device, such as a mobile phone. Keep in mind that the Personal Mobility Option must be provisioned on a DID basis and is configured by the individual DID owner. Separate Trunk Groups within a Single Site Business The next level of network redundancy options (apart from CFA or CFNR) for a single site SMB customer, pertains to the installation of additional trunk groups so that capacity for specific DID ranges are maintained. Separate trunk groups for key operational functions within the business, such as Sales and Customer Service, assure capacity if there is a surge in traffic to or from a particular DID or group of DIDs. A surge within one trunk group will not impact the other trunk group. For example, if there is an event that drives an unexpected high volume of traffic to Customer Service, then the entire trunk group may become full. If Sales and Customer Service share the same trunk group, Sales may be unable to receive or make calls. This level of redundant options provides Sales and Customer Service with their own trunk groups. If the Customer Service trunk group reaches capacity, Sales can continue to operate normally. Figure 2. Typical SIP Trunk Deployment with TDM PRIs The advantage of this application is that even if the service for Trunk Group 2 (Customer Service) is disrupted, Sales calls can continue on Trunk Group 1. It is important to note, however, that this configuration does not allow calls to failover from one trunk group to another. In other words, if either trunk group becomes busy, calls are not routed to the other trunk group even if that trunk group has idle capacity. The next level of SIP trunk redundancy options discussed below addresses this condition. Cox Business: SIP Trunking - Business Continuity and Redundancy Page 4
Integrated Trunk Groups within a Single Site Business This solution provides a business with options that leverage call routing schemes at a relatively low cost. A customer who elects this option wants survivability if a trunk group fails without stranding any DIDs on the failed trunk group. This choice uses two or more trunk groups that have DIDs assigned to both trunk groups. Under normal operating conditions, a percentage of all traffic is assigned to one trunk group and the remaining percentage is assigned to another trunk group. However, if one trunk group fails, all of the traffic is diverted to the second trunk group until the failed trunk group is restored. This concept is known as Load Balancing. Load Balancing can be provided for a single site or a multi-site business through the deployment of four routing options. These options are: Ordered Allocates traffic between two or more trunk groups evenly Overflow Allocates traffic primarily to a single trunk group, but will direct traffic to a secondary trunk group whenever the primary trunk group is full Weighted Overflow Allocates traffic on a defined percentage basis to two or more trunk groups, but will direct traffic to an alternative trunk group should any singular trunk group become full Most Idle Allocates traffic to the most idle trunk group Each option requires two or more independent trunk groups that can be provisioned at a single location or at more than one location. Typically, customers who opt for one of these solutions do so to decrease the chance of degradation on any singular trunk group. If a business has two data centers that are geographically dispersed and has a LAN deployed to connect the locations, calls can be routed to the failed location via the customer LAN (in the event that service fails at either location). This option works if the LAN has been included in the redundancy design. These applications can require in-depth network design sessions to develop an optimal solution. When it comes to redundancy planning, one size does not fit all. SIP Trunk to TDM PRI Failover So far, we have covered the redundancy options available solely within the Cox SIP trunking solutions. A follow-up question might be, What if there is a general failure in the SIP trunk network or what if the business switching technology becomes impaired? These situations can occur if the Cox geo-redundant BroadWorks network servers fail or if the link between the Cox CS2K and BroadWorks fails. Alternatively, problems may arise within a customer s infrastructure that can impact their ability to process calls. In the unlikely event that any of these scenarios occur, all SIP traffic will be disrupted. A final, yet very complex solution involves TDM PRIs that can enable a business to continue operations with a full or reduced range of services. This solution has limited availability within a particular market and requires extensive interaction with the customer s IP voice infrastructure. At a high level, a standard redundant solution that includes a TDM PRI option in a service provider s network looks similar to the diagram below. Cox Business: SIP Trunking - Business Continuity and Redundancy Page 5
Figure 3. Typical SIP Trunk Deployment with TDM PRIs Fail Over to PRIs The PRI failover option depicted above provides a business with redundant talk paths that are used in the event of a complete loss of SIP trunk service. During normal operations, voice traffic is routed through the Cox BroadWorks enterprise servers and is delivered over the private Cox IP network. In the event that the SIP trunk service fails, and if TDM PRIs have been installed in a standby mode prior to the event, voice traffic is re-routed to the PRIs by the Cox DMS100. When this service is activated, calls arrive at the proper DID station location, but are delivered over a PRI instead of the SIP trunk. Cox and the business customer must have careful coordination to ensure that inbound traffic is re-routed to the PRI trunk groups. Unlike Call Forward Unreachable or Call Forward Always, the originating DID information is not lost in this process. Outbound traffic can automatically be routed to the PRI trunk groups by the customer s PBX. This solution provides the highest level of network redundancy currently available from Cox. Other providers may offer a third option of failing over traffic to the public Internet, but this solution presents other issues, such as quality of service, security, etc., that Cox Business chooses to avoid. Partial PRI Back-Up Customers are not required to subscribe to PRI failover capacity that is equal to their SIP trunk capacity. They may elect to reduce costs by installing a reduced number of PRIs and selective assignment of specific DIDs to failover service. The decision as to which DIDs to assign to a PRI backup solution is not limited by their range. For example, a customer with 100 SIP trunks and 850 DIDs may choose to have two (2) failover ISDN PRIs (47 trunks) and enable only the 200 most important DIDs that serve key departments to have access to the failover PRIs. However, the ability to originate E-911 calls is limited if a customer elects partial PRI back-up scenarios described in this document. It is possible that an E-911 call can be blocked if a limited PRI back-up solution is implemented. Cox Business: SIP Trunking - Business Continuity and Redundancy Page 6
Summary The decision regarding which redundant solution will best satisfy a business owner s or IT manager s goals requires time, effort, and a full understanding of a business s operation. The best way to achieve this objective is to fully engage the business during the design phase of the project. Because a redundant service can only demonstrate its value to the enterprise when a failure occurs, it is critical to understand how the service works and how it is tested to assure that it functions as desired. Having this knowledge and hands-on experience enables Cox Business to offer its customers a flexible redundant solution tailored to meet their requirements. Cox Business: SIP Trunking - Business Continuity and Redundancy Page 7