TCP/IP Design Goals

TCP/IP Design Goals
When the U.S. Department of Defense began to define the TCP/IP network protocols, their design goals included the following:

•       TCP/IP had to be independent of all hardware and software manufacturers. Even today, this is fundamentally why TCP/IP makes such good sense in the corporate world: It is not tied to IBM, Novell, Microsoft, DEC, or any other specific company.
•     It had to have good built-in failure recovery. Because TCP/IP was originally a military proposal, the protocol had to be able to continue operating even if large parts of the network suddenly disappeared from view, say, after an enemy attack.
•        It had to handle high error rates and still provide completely reliable end-to-end service.  It had to be efficient and have a low data overhead. The majority of IP packets have a simple, 20-byte header, which means better performance in comparison with other networks. A simple protocol translates directly into faster transmissions, giving more efficient service.  It had to allow the addition of new networks without any service disruptions.

        As a result, TCP/IP was developed with each component performing unique and vital functions that allowed all the problems involved in moving data between machines over networks

to be solved in an elegant and efficient way. Before looking at both TCP and IP individually, you should understand where TCP/IP fits into the broader world of network protocols and, particularly,

how it compares to the theoretical reference model published by the International Organization for Standardization (ISO) as the OSI model.

     The popularity that the TCP/IP family of protocols enjoys today did not arise just because the protocols were there, or even because the U.S. government mandated their use. They are popular because they are robust, solid protocols that solve many of the most difficult networking problems and do so in an elegant and efficient way.

The Internet, an internet, an intranet, and an extranet
The title of this sidebar may be a bit confusing and look a bit informal with the odd capitalization, but it’s for a very good reason. While internet is a truncated version of internetwork, a lot of play has come from the root of these words. Let’s examine the word internetwork first, just to make sure we understand where all the variants come from. As you know, a network is a conglomeration
of devices tied together with a common technology. Well, once you establish two or more of these networks, work can be started on bringing them together. The interconnection and intercommunication between these autonomous networks is known as an internetwork or just internet. We know we have an internet when we use routers or other layer 3 devices to interconnect the networks. What kind of fun can we have with these words?

First of all, just by capitalizing the word internet to form Internet, we get the proper name of the global commercial internetwork that is tied together by TCP/IP (actually, all of these entities are)
and that has a scope of the planet we call home. If those Mars rovers have IP addresses, the scope suddenly gets a bit grander. That’s the flexibility of TCP/IP for you. What if we analyze the
meaning of inter? An internet is connectivity and communication across network boundaries. Does that mean, then, that an intranet is connectivity and communication within a network?
Gotcha. An intranet is more an opposite of the Internet, in terms of scope. If the Internet spans many administrative boundaries, encompassing many disparate networks, then an intranet,
while often an internet (how’s that for a catch?), encompasses only networks under a single administrative domain, a large corporation’s internal internetwork. Did you catch that? An intranet can be an internet, but not the Internet. Fun, huh?
Well, then, that just leaves extranet. Think of an extranet as an intranet becoming a very controlled Internet. That is, if an intranet is made up of all networks under a single administrative control, then an extranet is the expansion of that to include one, two, or just a few additional outside networks. Said differently, an extranet is an intranet interconnected and intercommunicating with networks that are under separate administrative control. This isn’t nearly as
unruly as the Internet, because this interconnectivity arose from some sort of partnership or affiliation between the parties. Let’s say, for instance, that a manufacturing company wants to have a vendor monitor its inventory so that whenever materials that the vendor supplies reach a minimum threshold, an order can be generated automatically, without personnel from the manufacturing company getting involved. That would require some sort of limited vendor access to internal manufacturing company resources. While the manufacturing company wants the vendor to have access to all that they need to help automate the supply process, they don’t want the vendor accessing sensitive financial, personnel, or possibly engineering information. By tweaking the firewalls just so, the vendor’s trusted network assets can be allowed access to the manufacturing company’s inventory control system but nothing else. That’s an extranet. While there’s a big difference between them all, they are all very similar. They are all generally TCP/IP internetworks.

Benefits of Using TCP/IP over Other Networking Protocols
   There are several benefits to using the TCP/IP networking protocol:

•     TCP/IP is a widely published open standard and is completely independent of any hardware or software manufacturer.
•     TCP/IP can send data between different computer systems running completely different operating systems, from small PCs all the way to mainframes and everything in between.
•     TCP/IP is separated from the underlying hardware and will run over Ethernet, Token Ring, and X.25 networks, to name a few, and even over dial-up telephone lines.
•     TCP/IP is a routable protocol, which means it can send datagrams over a specific route, thus reducing traffic on other parts of the network.
•     TCP/IP has reliable and efficient data-delivery mechanisms.
•     TCP/IP uses a common addressing scheme. Therefore, any system can address any other system, even in a network as large as the Internet. (We will look at this addressing scheme in the section “Understanding IP Addressing” later in this chapter.)