Port Switching and VLANs
From almost any perspective, It's becoming easy to attain consensus on what would be the most popular items on network managers' wish lists. They include relieving bandwidth constraints, reducing the increasing costs of reconfigurations, increasing security, and reducing the overall cost of network ownership. It's just as easy to gain consensus on the most popular approaches network managers are using, or planning to use, in the attempt to address these important issues: Ethernet switching and virtual LANs are the answers.
The Growth of Ethernet Switching
Ethernet switching is being used by many network managers concerned with lengthening the life of their current networks. Client/server, multimedia, imaging, and other applications make the bandwidth of traditional shared LANs insufficient. The immediate need of most network managers is to push even more data through an already congested pipe. Legacy LANs are not designed to handle this traffic and network managers are caught between a rock and a hard place - the promise of the future, and the reality of today.
Shared LANs have limited performance due to the contention algorithms that determine how to allocate a precious resource equally among users. Segmenting (or creating separate 'channels' that allow concurrent network conversations) is the solution to the network crunch. When analyzing how finely to segment a network, one must take consideration of both performance and cost issues. While putting each user on a dedicated Ethernet switch port might provide the maximum theoretical performance boost, its not cost-effective. The successful network manager must decide how to balance both performance improvement and the cost of that improvement.
Virtual LAN Planning
A VLAN is a logical grouping of users in a network regardless of physical location. Traffic within a VLAN is isolated, thereby saving other users on the network from having to process the VLAN's broadcast packets. Prior to VLANs, user groupings (or subnets) were based on physical LAN segmentation. VLANs no longer tie users to physical segments. This makes for a flexible placement of users, enhances security, and reduces the costs of moves, adds, and changes. It allows network managers to place users on different floors or in different buildings on the same "LAN" - a feat that was previously impossible without re-wiring or a major network design overhaul due to cable-length limitations and network complexity. The properly configured VLAN provides the ultimate in network flexibility and affords the benefits of supporting any logical configuration and reducing costs. It allows network managers to fulfill the specific requirements of the business units in their organizations in a simpler way, without
rewiring or physically re-designing the network.
The Port Switch
The heart of every Ethernet hub is a device called a repeater. Packets from any port are forwarded to all other ports, and if collisions occur, the repeater enforces a collision to all ports, thus creating an Ethernet segment (or 'collision domain'). Repeater ports are functionally identical, but usually one port is designated as a backbone port to provide connectivity with other repeaters, bridges and routers.
On the other hand, the port switch contains n Ethernet segments and the ability to create up to n networks, with any port assigned to any network.
The port switch is a superset of the single-segment hub since it is possible to assign all of the ports to a single segment. Therefore, the port switch can replace the single-segment hub in all applications and provide the added flexibility at no additional cost.
Port switches can be used to balance loads, by adding networks and moving nodes around, and to provide a physical level of security by isolating sensitive traffic to its own segment. Because most port switches are fully SNMP compliant, it can also be used to allow moves, adds, and changes without any need to modify the physical wiring infrastructure. With the proper external software functionality, this can be done automatically by recognizing the node address. Port switching has the features needed in VLANs and it can be used as a front-end to Ethernet switches that can create VLANs.
The port switch does not replace the switching hub in all applications, but can make Ethernet switches more effective and reduce the overall costs of an Ethernet switched LAN. Port switching is inherently less expensive than bridges or routed switching since its based on simple repeater technology, requires little memory and processing power, and can be integrated easily into ASICs.
New 16 Port Hub from Lantronix
Lantronix's LMR16TA is a low cost 16-port hub for twisted pair Ethernet. The LMR16TA offers 16 UTP ports, and has an auto-selectable AUI/BNC port for connecting to different Ethernet media. A wide variety of LEDs aid network diagnosis and management. The LMR16TA offers either a 120VAC or 220VAC external power supply
