76
Switchboard Theory and Concepts
Switchboard is useful because it’s not always simple to connect two devices, which are essentially “peers”, over
the Internet. There are two major reasons for this. First, to initiate a stream to a device over the Internet requires
knowing its IP address. This is the number that gets applied to the destination field of the IP packet, so Internet
routers can determine how best to send it along its way. Every device that connects directly to the public Internet
must have one.
However, when web browsing, or sending email, this information is usually hidden from the user. In the traditional
client/server scenario, such as web browsing, a Uniform Resource Locator (URL) is used to represent the IP address
of the web page (which is decoded by a DNS server). Once a computer requests a web page from a web server, the
web server can automatically derive the reply address from the request and respond to it. So the traditional four
segment decimal address (e.g. 70.22.155.130) is completely obscured to the user.
Even if you know your IP address, it’s quite possible that address will change over time. This is because the vast
majority of Internet users establish their addresses via DHCP, a protocol whereby a server (maintained by the ISP)
will deliver one of their available addresses to the client on initial connection. That address is “leased” from the
server for a particular time period. After the “lease” expires, the server is free to change it.
The commonly used Network Address Translation (NAT) router adds to the confusion, making codecs even harder
to find. Most LAN-based Internet connections (as opposed to computers connected directly to ISPs) actually
negotiate with a local router containing its own DHCP server. This router assigns the LAN computer or device a
“private” IP address (
Figure
62
).
FIgure 62
locAl AreA network
Summary of Contents for ACCESS MultiRack
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