Книга: Code 2.0
Code on the Net
Code on the Net
I’ve spent lots of time talking about “code.” It’s time to be a bit more specific about what “code” in the context of the Internet is, in what sense should we consider this code to be “open”, and in what contexts its openness will matter.
As I’ve mentioned, the Internet is constructed by a set of protocols together referred to as TCP/IP. The TCP/IP suite includes a large number of protocols that feed different “layers” of the network. The standard model for describing layers of a network is the open systems interconnect (OSI) reference model. It describes seven network layers, each representing a “function performed when data is transferred between cooperating applications across ” the network. But the TCP/IP suite is not as well articulated in that model. According to Craig Hunt, “most descriptions of TCP/IP define three to five functional levels in the protocol architecture. ” In my view, it is simplest to describe four functional layers in a TCP/IP architecture. From the bottom of the stack up, we can call these the data link, network, transport, and application layers.
Three layers constitute the essential plumbing of the Internet, hidden in the Net’s walls. (The faucets work at the next layer; be patient.) At the very bottom, just above the physical layer of the Internet, in the data link layer, very few protocols operate, since that handles local network interactions exclusively. More protocols exist at the next layer up, the network layer, where the IP protocol is dominant. It routes data between hosts and across network links, determining which path the data should take. At the next layer up, the transport layer, two different protocols dominate — TCP and UDP. These negotiate the flow of data between two network hosts. (The difference between the two is reliability — UDP offers no reliability guarantee.)
The protocols together function as a kind of odd UPS. Data are passed from the application to the transport layer. There the data are placed in a (virtual) box and a (virtual) label is slapped on. That label ties the contents of the box to particular processes. (This is the work of the TCP or UDP protocols.) That box is then passed to the network layer, where the IP protocol puts the package into another package, with its own label. This label includes the origination and destination addresses. That box then can be further wrapped at the data link layer, depending on the specifics of the local network (whether, for example, it is an Ethernet network).
The whole process is thus a bizarre packaging game: A new box is added at each layer, and a new label on each box describes the process at that layer. At the other end, the packaging process is reversed: Like a Russian doll, each package is opened at the proper layer, until at the end the machine recovers the initial application data.
On top of these three layers is the application layer of the Internet. Here protocols “proliferate.” These include the most familiar network application protocols, such as FTP (file transfer protocol, a protocol for transferring files), SMTP (simple mail transport protocol, a protocol for transferring mail), and HTTP (hyper text transfer protocol, a protocol to publish and read hypertext documents across the Web). These are rules for how a client (your computer) will interact with a server (where the data are), or with another computer (in peer-to-peer services), and the other way around.
These four layers of protocols are “the Internet.” Building on simple blocks, the system makes possible an extraordinary range of interaction. It is perhaps not quite as amazing as nature — think of DNA — but it is built on the same principle: keep the elements simple, and the compounds will astound.
When I speak about regulating the code, I’m not talking about changing these core TCP/IP protocols. (Though in principle, of course, they could be regulated, and others have suggested that they should be.) In my view these components of the network are fixed. If you required them to be different, you’d break the Internet. Thus rather than imagining the government changing the core, the question I want to consider is how the government might either (1) complement the core with technology that adds regulability, or (2) regulates applications that connect to the core. Both will be important, but my focus is on the code that plugs into the Internet. I will call that code the “application space” of the Internet. This includes all the code that implements TCP/IP protocols at the application layer — browsers, operating systems, encryption modules, Java, e-mail systems, P2P, whatever elements you want. The question for the balance of this chapter is: What is the character of that code that makes it susceptible to regulation?
- Appendix D. TCP options
- What NAT is used for and basic terms and expressions
- ICMP Destination Unreachable
- ICMP connections
- A Short History of Code on the Net
- Улучшенный протокол локальных соединений (XNET)
- Системные переменные ROWS_AFFECTED, GDSCODE, SQLCODE, TRANSACTIONJD, CONNECTIONJD
- 4.4.4 The Dispatcher
- About the author
- Chapter 7. The state machine
- Chapter 16. Commercial products based on Linux, iptables and netfilter
- Appendix E. Other resources and links