Local Area NetworksOverview of simple LANs

Networking basics: LANTCP/IP is the protocol used in the Internet and

dominates the internet and transport layersThe subnet layer -- the Local Area Network (LAN),

however, uses the OSI standards, predominantly based on Ethernet technologies.

Each device in a subnet has a special number (MAC address) and this number is hardwired in the device: Network Interface Card (NIC), hub, etc.

Network traffic and devicesMost of the traffic in networks happens at the

LAN, subnet layer, with users sharing data, using applications available in the LAN, etc.

The main devices at the subnet layer are cabling, Network Interface Card (NIC) , hubs and switches.

The NICs are placed in a PC or other device (e.g. a network printer) and is linked to a subnet using (generally) Ethernet cat 5 (category 5) cable.

Of course, the cable needs to be connected to a subnet device which links the PCs, printers, etc. These devices are either a hub or a switch.

LAN with single Hub

LAN with multiple Hubs

Hubs and SwitchesThe difference between a hub and a switch is simple:

when the hub receives a message for a device, it sends the message to all devices (broadcasts), and it is up to the device to check and see if the message is for it or not, if it is it should get it.

A switch receives a message to a device and delivers the message directly to that device; it does not broadcast.

Hubs were cheaper than switches, and were used in most subnets, but increasingly switches are getting cheaper and switches are becoming the device of choice in the subnet.

How switches work

Networking basics: internetA subnet communicates with another subnet through

an internet (lower case i, not the big Internet) -- a local connection among LANs

Any station (PC, etc) communicates with another station simply by giving the internet address of the other station.

This internet address (IP number) is assigned permanently or dynamically to each device in the internet (it is not hardwired like the MAC address).

Internet Routers