The Unpredictable Certainty White Papers (1997) / Chapter Skim
Currently Skimming:
Interoperation, Open Interfaces, and Protocol Architecture
Interoperation, Open Interfaces, and Protocol Architecture
Pages 133-144
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 133... ...
Thus, in the protocols that are part of the Internet protocol suite, an application such as mail (which has its own specifications and standards) depends on the transport control protocol (TCP)
|
From page 134... ...
The bearer service provides a set of capabilities sufficient to support the range of applications illustrated above it. It implements these capabilities by building on the more basic capabilities of the various network technologies below.
|
From page 135... ...
If instead Mere were competing alternatives in the definition of the bearer service, the application programmers would have to cope with this variation, which In the limit is no more useful Man having applications deal directly with the individual network technologies. In computer science terms, if there are N applications end Mtechnologies, the bearer service reduces the complexity of the resulting situation from N x M to N+M.
|
From page 136... ...
Whether it is a definition tied to one application, or to one network technology, this narrow point in the picture corresponds to a spanning layer and is what forms the foundation of the approach to interoperation. COMPARING APPROACHES TO INTEROPERATION The various examples given above suggest a fundamental way to evaluate different approaches to ~nteroperation, which is to assess what range of technology they can span "below" and what range of applications they can support "above." The essential claim of the RTIF bearer service is that the NII needs an hourglass rather than either of the two possible funnel pictures as its key spanning layer.
|
From page 137... ...
This Evader range of technology and protocol options translates into a wider range of real world deployment; IP-level Internet access reaches about 86 countries Way, while Internet mail reaches about 168.2 The price for this is that the only application support is mail. There is no access to remote login, file transfer, the World Wide Web, and so on.
|
From page 138... ...
Protocols are sometimes designed in such a way that not all the participants in the protocol can play all the roles. For example, some of Me early remote file access protocols were designed so that the functions that implemented the file server and the file user were separately specified.
|
From page 139... ...
This interface connects different network technologies and thus implies a spanning layer. However, it could be implemented In several ways as discussed above.
|
From page 140... ...
That freedom is the equivalent of what the bearer service gives us. The lower layer, whether Me operating system or the network technology, can evolve.
|
From page 141... ...
These differences are important, but He Internet protocols treat this as happening below the spanning layer. One might take a different tack and provide a (resource)
|
From page 142... ...
Again, the definition is in terms of an application, which, from the user's perspective, is the relevant objective of an interoperation test. RTIF also uses the Intemet architecture as an example of a concrete set of protocols that embody an RTIF-style bearer service approach to ~nteroperation: Stereo defines a largely symmetric bearer service, the Intemet protocol itself, which has been shown in the marketplace to span a wide range of network technologies and support a wide range of applications.
|
From page 143... ...
For example, in the case of the SNA/TCP spanning layer, the capabilities of the service are constrained by the particular protocols out of which the service was built, TCP or SNA, which offer a reliable delivery protocol with no ability to bound delivery delays. So the SNA/TCP spanning service, although it has a broad span over network technology, cannot make use of other QOS in the lower layers and thus cannot support applications such as real-time audio and video.
|
From page 144... ...
2. These numbers are from the international connectivity data collected by Larry Landweber and provided by the Internet Society as a part of its Web information collection.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.