We now turn to a deeper analysis of the ubiquitous Ethernet LAN protocol. Current user-level Ethernet today is usually 100 Mbps, with Gigabit and 10 Gigabit Ethernet standard in server rooms and backbones, but because the potential for collisions makes Ethernet speeds scale in odd ways, we will start with the 10 Mbps formulation. While the 10 Mbps speed is obsolete, and while even the Ethernet collision mechanism is largely obsolete, collision management itself continues to play a significant role in wireless networks.
- 2.7: Virtual LAN (VLAN)
- One approach is to continue to keep LANs local, and use IP routing between different subnets. However, it is often convenient (printers are one reason) to configure workgroups onto a single “virtual” LAN, or VLAN. A VLAN looks like a single LAN, usually a single Ethernet LAN, in that all VLAN members will see broadcast packets sent by other members and the VLAN will ultimately be considered to be a single IP subnet (7.6 IPv4 Subnets).
Ethernet dominates the LAN layer, but is not one single LAN protocol: it comes in a variety of speeds and flavors. Higher-speed Ethernet seems to be moving towards fragmenting into a range of physical-layer options for different types of cable, but all based on switches and point-to-point linking; different Ethernet types can be interconnected only with switches. Once Ethernet finally abandons physical links that are bi-directional (half-duplex links), it will be collision-free and thus will no longer need a minimum packet size.
Other wired networks have largely disappeared (or have been renamed “Ethernet”). Wireless networks, however, are here to stay, and for the time being at least have inherited the original Ethernet’s collision-management concerns.