Three concepts will help the understanding of what is required to connect and use a wireless network. We need to have a way to address our transmission such that it can be sent from source point A to final destination point Z. We learned early on computer information is aggregated by the use of bits and bytes. How these bits and bytes are interpreted is dependent upon the protocol being used by a hardware or software vendor. These bits and bytes are then assembled into larger entities called fields, packets, frames, datagram’s, segments, and messages. We’re interested in packets, frames and datagrams for the limited scope of this discussion. Data is not sent as a continuous string of bits, rather is broken up into small blocks called packets. There is no generally accepted definition of the format of a packet. Therefore, the notion of frame comes into play to define a specific type of packet related to a specific type of network i.e. Ethernet, RS232, WLAN, etc. A packet sent across a TCP/IP (Transmission Computer Protocol/Internet Protocol) connection is called a datagram and consists of a header followed by data. The header contains IP addresses for the source and destination computers.
Every device has a unique address that was incorporated at time of manufacture. This address is called many things but I’ll use one of the most common -- "MAC" (Media Access Control). This address is analogous to the house number in your street address. This address is used to identify the next place to send a packet called a hop. In our case, the hops would be from the laptop to the PC card, from PC card to the Access Point ("AP"), from the AP to the host computer, etc. The laptop, PC card, AP, host computer each has a unique MAC address enabling the data to be sent on to the proper place. The MAC destination address is changed at each hop. A protocol within the IP protocol referred to as Address Resolution Protocol (ARP) is used to determine the MAC address of the next hop.
Second, the packet needs an address that follows it all the way from source to the intended destination. This is called an IP (Internet Protocol) address. Over 2 billion IP addresses exist under the IP V4 standard. But remarkably that has turned out to be too few in today’s environment. So, various methods have been developed to create more addresses until a new standard (V6) providing for more addresses can be implemented (though that may be some years away). The ISP provides the customer with one IP address to connect to their server. If one wants more than one number the ISP will expect them to be purchased at a considerable added cost. A device (hardware or software) to get around this limitation is called Network Address Translation (NAT). The computers connected to the LAN are assigned IP numbers by the NAT. The NAT in turn upon receiving a datagram from a computer with an internal assigned IP number translates that number to the ISP’s IP address and inserts it into the datagram in place of the internal number. In Windows, a NAT capability is provided and is called Internet Connection Sharing (ICS). One of the methods to generate the internal assignment of IP numbers is called Dynamic Host Configuration Protocol (DHCP). In the newer systems the assignment of an IP can be done automatically. One simply checks the box in TCP/IP Network properties that says “ Obtain IP address automatically”. The host computer running DHCP sees this instruction and executes the assignment of an IP to a computer (laptop/desktop) when it makes request to join the local area network (LAN). The IP address assigned is temporary i.e. it is lost when exiting network; the next time one accesses the network the host computer will automatically assign another IP address. The assigned IP address does not change from source to final destination unlike the MAC addresses, which change at each hop.
If one enters a domain name (i.e. www.rversonline.com) in your web browser another capability is required called DNS (Domain Name Server). The DNS must convert the domain name to an IP address that is incorporated into header and sent on for execution.
For incoming data the Access Point broadcasts the data across the park to all computers. The computers check the datagrams header and reject the data if not destined for them. The single computer with proper MAC address accepts the transmission and processes data. However, any PC can intercept all the datagrams if desired. Network administrators in the normal course of their work do this. The computer is set to "promiscuous mode", i.e. accept all incoming messages. Thus, the requirement to reemphasize the need to enable encryption for one’s messages or data transfers. Banks, for example, will routinely require that your computer have 128 bit encryption capability to use their on line banking services.