1. August 25, 2008 Alcatel Lucent ABSTRACT: 1x System Reliability is important in the face of major events, such as an earthquake. There are several ways in which reliability can be improved. This contribution considers several. RECOMMENDATION: For Discussion and Information. Notice Contributors grant a free, irrevocable license to 3GPP2 and its Organization Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner’s name any Organizational Partner’s standards publication even though it may include portions of the contribution; and at the Organization Partner’s sole discretion to permit others to reproduce in whole or in part such contributions or the resulting Organizational Partner’s standards publication. Contributors are also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution. This document has been prepared by the contributors to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on the contributors. Contributors specifically reserve the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of the contributors other than provided in the copyright statement above. 1x System Reliability 3GPP2 TSG-A WG4 3GPP2 A40-20080825-xxx

2. 2 The Problem Operators face the issue of maintaining service in their 1x networks even in the case of major events, such as an earthquake. Multiple solutions are available to enhance the reliability of a 1x network:  N+1 sparing  1+1 sparing  M x N sparing  M x N backup  MSC Pool This contribution examines these different approaches.

3. 3 Basic Reliability Issues The greater the number of components in a system, the greater the number of points of failure. Adding more components into a system increases the possibility of failure.

4. 4 N+1 Sparing N+1 sparing uses a single spare MSC as a backup for up to N other MSCs. If one of the N MSCs fails, the base stations attached to it are connected to the backup (spare) MSC. Movement of the connections can be either manual or automated. No additional components are added in the active system, so no additional ponts of failure are introduced. When one component fails, it is replaced by reconnecting to another spare component.

5. 5 N+1 Sparing Before MSC Failure Each MSC is attached to a set of Base Stations. A single standby MSC is ready to take over from any of the other MSCs. BSC MSC

6. 6 N+1 Sparing After MSC Failure Each MSC is attached to a set of Base Stations. A single standby MSC is ready to take over from any of the other MSCs. The number of points of failure is not increased. The cost of extra connectivity (extra E1 lines, etc.) is minimized. BSC MSC

7. 7 1+1 Sparing 1+1 Sparing is a special case of N+1 sparing, where N=1. Each MSC has a second MSC as a backup. This solution works well when multiple MSCs may experience failure at the same time, such as in the event of a major earthquake. It may be more costly to the operator to have these extra MSCs standing by. No additional components are added in the active system, so no additional ponts of failure are introduced. When one component fails, it is replaced by reconnecting to another spare component.

8. 8 M x N Sparing M x N backup is an arrangement where a pool of N spare MSCs can be connected to M different active MSCs in the case of failure. Any of the N MSCs can operate as a spare for any of the M active MSCs. This solution provides greater reliability in the case of a major event, but does not require the expense of a spare MSC for each active MSC. Connection schemes for connecting each of the active MSCs to any of the spare MSCs will be more complex, but certainly implementable with existing cross connect technology. BSC MSC

9. 9 M x N backup M x N backup involves having M+N active MSCs, where each of these M+N active MSCs is backed up by up to N other MSCs. If an MSC fails, the base stations attached to it are reconnected to one of up to N other MSCs. BSC MSC BSCMSC Backup Arrangements

10. 10 M x N backup M x N backup is less costly because there are no MSCs in only a “spare” state. However, backup procedures can be more complex. No additional components are added in the active system, so no additional ponts of failure are introduced. When one component fails, it is replaced by reconnecting to another spare component.

11. 11 MSC Pool In an MSC Pool arrangement, additional components are added to the system, adding additional points of failure. BSC MSC BSC Pool Router

12. 12 MSC Pool Basically, MSC Pool accomplishes what M x N backup accomplishes, but there are drawbacks:  Each Pool Router must examine every downlink message to see if it is a Handoff Request message. If it is, that Pool Router must remember the association of that mobile with the MSC that sent the message, and the BSC that receives it.  The possibility of failure of a Pool Router requires that either:  Each BSC is connected to multiple Pool Routers to allow all traffic to be routed to another Pool Router, or  Some sort of sparing or backup approach to the use of Pool Routers. M x N backup, M x N sparing, N + 1 sparing, and 1 + 1 sparing do not face these issues.

13. 13 Summary In order to increase the reliability of a 1x network, some means must be found to substitute another MSC when one fails. Sparing and backup configurations provide access to another MSC with varying degrees of complexity, and varying costs to the operator. The number of system points of failure in sparing and backup configurations are not increased. MSC Pool may actually decrease the reliability of the 1x network by adding points of failure to the system. Each of the Pool Routers must itself have a backup or spare.