Tactical Wireless Communications and Networks: Design Concepts and Challenges

1.3 Pitfall of the OSI Model

The literature is full of criticism of the OSI model and any of its deviations including the IP model. The fact of the matter is that IP technology is now the dominating technology and it is with us to stay. Techniques such as cross layer signaling, merging of protocol stack layers (especially layers 2 and 3), tradeoffs between network coding, and transport layer reliability are the path to more optimal performance of both commercial and tactical wireless communications based on the IP model. The attempts to develop a new technology or a super-layer concept are facing many challenges and could take a very long time to materialize, given the dominance of IP. One of the known problems with the OSI model is the amount of overhead bits transmitted over the physical media in comparison to the information bits. Since each layer works independently with its own headers, the ratio of overhead to information contents can be very high. Figure 1.4 demonstrates this problem where the information content in the packet (at the transport layer) is expressed by the white rectangle. The transport layer adds its own header(s) shown in light gray (think of UDP and RTP–real-time protocol–headers or the TCP header). The network layer adds its own header, shown in the medium gray (consider the IP header). The DLL treats the entire packet (information and headers) as a bit stream and adds its own overhead that may contain redundancy bits for error correction, as well as trailers, ...