Navigating Network Complexity: Next-generation routing with SDN, service virtualization, and service chaining by Russ White & Jeff (Evgeny) Tantsura

Author:Russ White & Jeff (Evgeny) Tantsura [White, Russ]
Language: eng
Format: epub
Publisher: Pearson Education
Published: 2015-11-12T23:00:00+00:00

The Four-Layer Model

One of the reasons why engineers have so much difficulty fitting the IP transport stack into the seven-layer model is that it was developed with a different model of network communications in mind. Instead of a seven-layer model, the IP transport stack was designed around a four-layer model, roughly described in RFC 1122 and illustrated in Figure 7.4.

Figure 7.4 Four-Layer Model

In this model:

• The link layer is roughly responsible for the same functions as the physical and data link layers in the OSI model—controlling the use of physical links, link-local addressing, and carrying frames as individual bits across an individual physical link.

• The Internet layer is roughly responsible for the same things as the Network layer in the OSI model—providing addressing and reachability across multiple physical links and providing a single packet format and interface regardless of the actual physical link type.

• The transport layer is responsible for building and maintaining sessions between communicating devices and providing a common transparent data transmission mechanism for streams or blocks of data. Flow control and reliable transport may also be implemented in this layer, as in the case of TCP.

• The application layer is the interface between the user and the network resources, or specific applications that use and provide data to other devices attached to the network.

In this model, Ethernet fits wholly within the link layer; IP and all routing protocols fit in the Internet layer; and TCP and UDP fit within the transport layer. Because of this neatness, this is a cleaner model for understanding IP as its deployed today, although it doesn’t provide the detailed structure of splitting up the various levels of signaling that might be useful in a more research-oriented environment.

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