single data center, providing Internet-wide distributed messaging through web syndication protocols such as RSS and Atom. These syndication protocols accept higher latency and lack of delivery guarantees in exchange for the ability for even a low-end web server to syndicate messages to (potentially) millions of separate subscriber nodes. Disadvantages The most serious problems with pub/sub systems are a side-effect of their main advantage: the decoupling of publisher from subscriber. Message delivery issues A pub/sub system must be designed carefully to be able to provide stronger system properties that a particular application might require, such as assured delivery. The broker in a pub/sub system may be designed to deliver messages for a specified time, but then stop attempting delivery, whether or not it has received confirmation of successful receipt of the message by all subscribers. A pub/sub system designed in this way cannot guarantee delivery of messages to any applications that might require such assured delivery. Tighter coupling of the designs of such a publisher and subscriber pair must be enforced outside of the pub/sub architecture to accomplish such assured delivery (e.g. by requiring the subscriber to publish receipt messages). A publisher in a pub/sub system may assume that a subscriber is listening, when in fact it is not. A factory may utilize a pub/sub system where equipment can publish problems or failures to a subscriber that displays and logs those problems. If the logger fails (crashes), equipment problem publishers won't necessarily receive notice of the logger failure, and error messages will not be displayed or recorded by any equipment on the pub/sub system. This is also a design challenge for alternative messaging architectures, such as a client/server system. In a client/server system, when an error logger fails, the system will receive an indication of the error logger (server) failure. However, the client/server system will have to deal with that failure by having redundant logging servers online, or by dynamically spawning fallback logging servers. This adds complexity to the client and server designs, as well as to the client/server architecture as a whole. However, in a pub/sub system, redundant logging subscribers that are exact duplicates of the existing logger can be added to the system to increase logging reliability without any impact to any other equipment on the system. In a pub/sub system, the feature of assured error message logging can be added incrementally, subsequent to implementing the basic functionality of