equipment problem message logging. The pub/sub pattern scales well for small networks with a small number of publisher and subscriber nodes and low message volume. However, as the number of nodes and messages grows, the likelihood of instabilities increases, limiting the maximum scalability of a pub/sub network. Example throughput instabilities at large scales include: Load surges—periods when subscriber requests saturate network throughput followed by periods of low message volume (underutilized network bandwidth) Slowdowns—as more and more applications use the system (even if they are communicating on separate pub/sub channels) the message volume flow to an individual subscriber will slow For pub/sub systems that use brokers (servers), the argument for a broker to send messages to a subscriber is in-band, and can be subject to security problems. Brokers might be fooled into sending notifications to the wrong client, amplifying denial of service requests against the client. Brokers themselves could be overloaded as they allocate resources to track created subscriptions. Even with systems that do not rely on brokers, a subscriber might be able to receive data that it is not authorized to receive. An unauthorized publisher may be able to introduce incorrect or damaging messages into the pub/sub system. This is especially true with systems that broadcast or multicast their messages. Encryption (e.g. Transport Layer Security (SSL/TLS)) can prevent unauthorized access, but cannot prevent damaging messages from being introduced by authorized publishers. Architectures other than pub/sub, such as client/server systems, are also vulnerable to authorized message senders that behave maliciously. See also Atom, another highly scalable web-syndication protocol Data Distribution Service (DDS) Event-driven programming High-level architecture Internet Group Management Protocol (IGMP) Message brokers Message queue Observer pattern Producer–consumer problem Push technology RSS, a highly scalable web-syndication protocol Usenet WebSub, an implementation of pub/sub References Architectural pattern (computer science) Distributed computing architecture Message-oriented middleware Software design patterns