A physical network is a group of computers connected so they can directly communicate with each other using the same protocol data connection without being connected by routers. Thus, any computer on an Ethernet network office every other computer on the network directly, it is not necessary to transmit information between two different shared media networks (eg between a LAN Ethernet network and Token Ring).

Computers can be connected to hubs, switches or bridges, but remain a single network, because data can be transmitted between two computers on the same data link protocol. In some cases, switches make minor changes in the data link protocol (eg Ethernet and Fast Ethernet bridge), because these technologies using the data link protocols, but work at different speeds.

The transport protocol and network protocol terms are somewhat synonymous.

Note: Transport Protocol is the collective name for two and includes protocols such as NetBEUI, which can not be used to send data between networks. Protocol-specific network protocols such as TCP / IP or IPXJSPX that can transfer data between networks. In particular, network protocols with the sending of packets between the networks (the IP part of TCP / IP) transport protocols provide flow control, error correction and connection services (TCP part of TCP / IP), software services over the actual performance, both with the same software. Microsoft uses the term for any transport protocol suite that provides all these services.

A cross is a collection of networks connected by routers that are configured (or route forward) data between networks based on a set of transfer rules. The different networks need to avoid the kind of data binding, because the router (sometimes called gateway in UNIX environments) can connect to any type of data binding. The router examines the destination address of each packet and determines which of its ports closer to the target computer. One of the following events occurs:

• The router can not match the packet directly to an entry in the routing table and send the packet directly to the host or router.

• If the router doesn’t't have enough information to determine whether a packet should go, it just sends the packet to another router (default gateway) that he hopes will know how the package process.

• If a router does not know how to give the package and have no default gateway, the destination is unreachable because the two networks are not properly connected.

Any computer with a routing software can function as a router, but the networks do not use dedicated routers more experienced delays (latency) and bottlenecks in the networking hardware that use dedicated routers do.

Dedicated routers are just computers that are optimized for the routing function and perform any function other public purposes. They do not need video screens or keyboards, usually have no hard drive, and use RISC microprocessor May esoteric different dedicated routers are similar to those for general use in the computer hardware, and most run a small version of the UNIX operating system. They are quite expensive generally twice the price of a multihomed server running the routing function. You may find you can live with lower total throughput of a multihomed server as a router on your network.

The Internet is an international network of major internal based on TCP / IP protocol suite. Almost all large companies and universities worldwide, and many small businesses and individuals connected to the Internet. Intranets are private networks that may or may not be connected to the Internet, intranets are based on Internet protocols. TCP / IP suite of protocols that the government and universities have developed over the past two decades, making very large networks to be connected. The remainder of this chapter discusses the various protocols used by the TCP / IP that are important for the creation and connection of networks.

TCP / IP suite embodies many other protocols, but they are not so important whether or not implemented in many versions of the suite. The entire suite is referred to collectively as TCP / IP (Transmission Control Protocol and Internet Protocol reason are the two most common and important protocols), or the Internet protocols.