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Methods of Providing 1:N redundancy or more for X-Zone Systems Disclosure Number: IPCOM000004589D
Original Publication Date: 2001-Feb-23
Included in the Prior Art Database: 2001-Feb-23
Document File: 3 page(s) / 165K

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Randy Ekl: AUTHOR [+2]


Methods of Providing 1:N redundancy or more for X-Zone Systems

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Methods of Providing 1:N redundancy or more for X-Zone Systems

by Randy Ekl, David Helm, and Vidya Narayanan


X-Zone is a packet-switched system designed to carry voice and data from two-way radios, primarily for public safety systems. As most of the calls involve point-to-multipoint communication, multicast becomes the natural choice in the IP-based X-Zone architecture. As with all IP networks, providing QoS, reliability, and redundancy in an efficient manner becomes extremely important in X-Zone systems.

The X-Zone architecture has a number of routers situated on a LAN at the core of a zone, with the site routers connected to different core routers via Frame Relay PVCs. Each site router is connected to two core routers via two different PVCs for sake of redundancy. Inter-zone communication is also achieved through FR PVCs between what are called exit routers of different zones.

Systems based on the X-Zone architecture need to provide a minimum of 1:N redundancy with minimal complexity in configuration, also ensuring that the load on any one router does not exceed the capacity of that router at any time, even in the event of a single router failure. Existing approaches to this issue require N:N redundancy. This calls for a more efficient approach which can avoid having N:N redundancy without any added complexity.


Prior approaches propose providing N:N router redundancy, in which case, no router would ever have more load than it can handle, even in the case of router failures (upto N router failures can be tolerated). In this case, all primary links from the sites belonging to one core would go to that core router and all secondary links from those sites would go to a single different core router as shown in the above picture by the solid and dotted lines respectively. With this solution, however, if only X:N redundancy is provided, where X N, there is a risk of exceeding a particular core router capacity upon failure of a single core router. Consequently, this solution demands that there be N:N redundancy even to cover a single router failure case and this could be overkill and very costly when there are a large number of core routers.


One idea is to provide M: N redundancy, where M N, with the secondary links from sites belonging to one core router distributed across multiple (X) core routers. This causes the load to be balanced across more than one router on a core router failure. The specific number of core routers and the specific configuration depends on the number of sites in the system, as well as the level of redundancy wanted (M, above).

Consider the following simplified picture of an MSO in X-Zone. Assume R is the minimum number of Core routers required to handle the load, and assume M are the number of failures router failures to guard against. Then determine N R M. Configure N core routers CR-1 through C...