//Cyber Battlefield/Networking – Layers & Translation

In this lesson, we discuss two important aspects of networking. The first concerns the concept of layering, in which the various networking protocols are separated into distinct layers, each with a specific purpose. The second is translation, in which we introduce a scheme for rewriting IP Addresses when the total number available is insufficient.

Introduction: Protocols, Services, and Utilities

There is a protocol that constrains radio communication between aircraft and control towers, Airplane. Look at the following transcripts and see if you can identify the rules governing things like identifying yourself and the entity you want to communicate with, acknowledging receipt of message, and turn-taking.

BR51: "Tower, BR51 request takeoff VFR to the West."
Tower: "BR51, Tower, you are cleared for takeoff to the West."
BR51: "Tower, BR51, copy, cleared for takeoff."

This second transcript shows a different pattern in terms of turn-taking.

BR51: "Dulles Tower, this is Bay Raider 51, 35 miles to the West, final stop Dulles."
Tower: "Standby"
Tower: "BR51, this is Dulles, cleared to Dulles"
BR51 : "Tower, BR51, copy, cleared to Dulles."
In subsequent lessons, we will explore some of these protocols, services, and utilities. For now, though, let's take a look at different types of protocols, and how they interact.

Tactical Voice Communications

The document ACP 125 gives a protocol for communications between Allied Forces on tactical voice nets, to "provide a standardized way of passing speech and data traffic." The protocol specifies such things as a phonetic alphabet ("ALFA, BRAVO, ..., ZULU"), prowords (e.g., "say again", "roger" ), how to unambiguously record a message (e.g., zero written as: Ø, letter Z written as: Ƶ), and brevity codes (e.g., the brief phrase "Birds away" means "Friendly surface-to-air missiles have been fired at the designated target").

When you pick up that VHF bridge-to-bridge radio on one of the YP's, the ACP 125 protocol tells you how you should talk!

Here's an example dialog between call signs S7 and CC:

CC: "Sierra Seven this is Charlie Charlie,
		 radio check, over."
S7: "This is Sierra Seven, roger, over."
CC: "Sierra Seven, Charlie Charlie, immediate execute,
		 turn starboard niner, I say again, turn starboard
		 niner, standby ... execute, over."

Layered Protocols: The TCP/IP Stack

The different protocols that make up the Internet are organized into what's viewed as stacked layers. Before we define this model, called the TCP/IP Stack, we will consider an analogy.

Network Address Translation

We've learned that each host on the Internet has an IP Address, and that network packets get routed based on the destination host's IP Address. In general, that's true. We've also learned that the IPv4 address space is essentially all allocated. There are plenty of IPv6 addresses, but we won't discuss the details of IPv6 in this course. However, there is another workaround for the limited IPv4 address space, called Network Address Translation, or NAT. We discuss the operation of NAT in this course because it's very widely used, and because it has some security relevance.