228 CHAPTER 8 (Web hosting top) PERSISTENT COMMUNICATIONS PATTERN The
Monday, October 22nd, 2007228 CHAPTER 8 PERSISTENT COMMUNICATIONS PATTERN The last scenario is explicitly called a server push; however, in theory all three implemen tation types could be considered a server push because all three involve the server sending data to the client. There are two attributes that separate the various implementation types: what the representation of the resource is, and whether a user has to be identified when accessing a resource. Associated Patterns The Persistent Communications pattern has some overlap with the Decoupled Navigation pattern. Specifically, for the Decoupled Navigation pattern it is possible to trigger an event that would call the same server-side resource as the Persistent Communications pattern. The Persistent Communications pattern differs in that its purpose is focused on the server sending data to the client. The purpose of the Decoupled Navigation pattern is not to push data from the server to the client, but to provide a mechanism for separating navigational functionality. The Persistent Communications pattern does not implement the Content Chunking pattern, or at least is not required to implement the Content Chunking pattern. More likely, the Persistent Communications pattern will send data that implements the Infinite Data pattern. The Persistent Communications pattern is a very specific pattern for a very specific situation, as outlined in the preceding Applicability section. Using it in any other situation complicates the solution. In those cases, it would make more sense to make the Decoupled Navigation pattern behave like the Persistent Communications pattern. Architecture Explaining the architecture of the Persistent Communications pattern is relatively simple. The problem, though, is that the explanation might have you scratching your head on why such a solution was created in the first place. The solution might seem inefficient and overly complex, and you might think it could have been solved in another way. It is not possible to solve the server-to-client communications in any other way because of how the Internet architecture is implemented. Even if there were no implementation problems from the perspective of the Internet, defining and implementing the Persistent Communications pattern would still be necessary because the HTTP protocol was not intended for such functionality. The design of the HTTP protocol allows for only stateless interaction that starts with the client, is processed by the server, and ends with the client. The challenge here is that HTTP is being asked to do what it was never designed to do, and this pattern is presenting some solutions. Before you learn about the architecture of the Persistent Communications pattern, first you need to understand the problem of the broken Internet. Why the Internet Is Broken It is a bold statement to say that the Internet is broken. I don t mean that it is unfixable or bad, but that the Internet has transformed into an architecture that is not optimal. The not optimal part relates to Internet Protocol (IP) addresses. To understand the transformation, let s go back in time and look at how the Internet worked in the late eighties, as illustrated in Figure 8-2.
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