Subnetting is taking a single network IP address and subdividing it, thus creating more subnets and allowing your network to grow. The default gateway is where all packets are sent through when a workstation can’t find the destination on the local subnet. The default gateway (often a router) will take in the packets and search the adjacent subnets for the destination. If it finds the destination on a neighbouring subnet, a router will recreate the packets and send the data on its way. If it doesn’t find the destination on a neighbouring subnet, it will send the packets to its own default gateway, or in accordance with its own routing tables and protocol.
The difference between a public and private network: A public network sits in front of a firewall, and does not enjoy its protection. A private network sits behind the firewall, and does. So, you need to be sure to install your firewall on the outer edge of the network to make as much of it private as possible.
A firewall is what keeps intruders (hackers, clumsy surfers, corporate spies, etc) out of your network. Just as a real firewall will protect one side of a building from fire on the other sides, a network firewall acts as a barrier to network traffic on one side to protect the network on the other. To understand this concept, it is most helpful to realize that your network is part of the larger Internetwork. Out in “public,” in front of the firewall, most anything can happen. Your “private” network sits behind the firewall, which helps keep your little part of the Internet “private.”
A firewall can be configured with rules to control which packets will be accepted into the private network, and which can pass out of it. It reads the headers of every packet, in- or out-bound, and compares that information with its settings. Packets that do not comply are dropped.
Click here
for an article about how firewalls work.
Click here
for a how-to article on firewalls and proxy servers.
Click here
for a firewall FAQ.
The difference between packet switching and circuit switching, in general, is in the use of resources. In circuit switching, there is a dedicated connection between the sender and receiver that is maintained throughout the exchange. In circuit-switched networks, network resources are static (“set in copper” if you will) from the sender to receiver before the start and until the end of the transfer, thus creating a logical “circuit”.
In packet-switched networks, the message is broken into packets, each of which can take a different route through the network to the destination where the packets are reassembled into the original message. So, in packet-switched networks, resources are not reserved and a session's messages may have to wait for network resources.
Here’s a graphic that visually compares the two:
Of course, it’s not really that simple. Not all networks can be neatly classified as pure circuit-switched networks or pure packet-switched networks. An example of this would be Asynchronous Transfer Mode (ATM, see below). ATM creates a fixed channel between two points before data transfer begins, but transmits the data in packet-like cells.
A resource comparison between the two switching types would look
like this:
| Resource | Circuit Switching | Packet Switching |
| Dedicated path? | Yes | No |
| Available Bandwidth? | Fixed | Dynamic |
| Could bandwidth be wasted? | Yes | No |
| Store-and-forward transmission? | No | Yes |
| Each packet follows the same route? | Yes | No |
| Call setup? | Required | Not required |
| When can congestion occur? | At setup time | On every packet |
| Charge? | Per minute | Per packet |
Circuit switching and packet switching each have their advantages and
disadvantages.
Circuit-switched networks:
By contrast, packet switched networks:
Cramsession
InfoCenter article on Circuit Switching vs Packet Switching
X.25 Packet Switching
tutorial
Packet
switching simulation
Packet
Switching Demo (requires Flash)
TelecomWriting.com
on circuit and packet switching
Bell Labs
Technology: Understand Digital Circuit Switching