HP 635n Practical IPsec Deployment for Printing and Imaging Devices - Page 18

Before we get into this particular technique, we need to discuss Ethernet and how it relates to TCP/IP. Refer to Figure 15 - Models. Academic Model Application Data TCP/UDP IP Ethernet Sandwich Model Alternate Representations of TCP/IP Messaging Ethernet Header Ethernet Data IP Header Ethernet Data IP Data TCP/UDP Header TCP/UDP Data Actual Data "Russian Dolls" Model TCP/UDP Data Actual Data Ethernet Data IP Data TCP/UDP Header Ethernet Data IP Header Ethernet Trailer Ethernet Header Figure 16 - Models Figure 16 shows three different ways of visualizing how networking protocols relate to one another. The first model is called the Academic Model. Essentially, each protocol maps to a layer or block. Ethernet is a physical layer / Media Access Control layer. It is on the bottom. What Ethernet considers data is actually all the blocks above it. The next layer is for the IP protocol and it is at the Internet layer. The next layer is for the transport layer and it is for TCP or the Transport Control Protocol or UDP the User Datagram Protocol. The last layer is for applications like Telnet or FTP. The second model is the Sandwich Model which shows more of how an Ethernet packet is on the wire as well as the third model or Russian Dolls model. All of these pictures are to help in the visualization of what is actually happening on the networking cable. 18