User`s guide

FX-16NW

The VLAN feature of the Switching Hub lightens traffic on a network and

strengthens network security, all by dividing the original broadcast domain

into smaller groups; ports on the Switch are divided and grouped into

several VLAN groups. Each VLAN group acts as a separate small domain,

and packets being sent in one VLAN group (including broadcast packets)

are not transmitted to other VLAN groups. This feature gives the following

advantages to the Switch over other switching hub products:

Improved Networking Efficiency

By separating nodes in a high-traffic work group into multiple smaller

groups, the existing broadcast domain is divided into smaller domains and

prevents packets from being sent to other (small) workgroups. Since

unnecessary data transmission to other workgroups is cut, networking

efficiency over the entire network improves considerably.

Enhances Security

Network communication among VLAN groups is logically disabled.

Therefore, confidential documents or data can be contained in one specific

VLAN group of users who are authorized to handle the information.

Cost Reduction

With the VLAN support, the Switch can create multiple domains all by

VLAN

The Switching Hub also supports Flow Control technology for preventing

packets from overflowing the packet buffer. The flow control technology

used in half-duplex mode is called “Back Pressure”, while the flow control

scheme used in full-duplex operation is called “IEEE 802.3x”. In Back

Pressure, a collision signal is sent out whenever the packet buffer becomes

full. On the other hand, a switching hub with IEEE 802.3x support transmits

a “pause” command to the source node to stop the data flow itself. To

utilize IEEE802.3x flow control, the attached network card must also

support IEEE802.3x flow control. (Currently, most of the network cards on

the market do not support this feature. PCI’s FNW-9800-T Fast Ethernet

adapter card complies with IEEE802.3x flow control ahead of other

vendors.)

If either the switch or network interface card does not support flow control,

the source device (PC) will continue to send packets to the switch even

when its packet buffer is full. As a result, packets received by the switch

will overflow and those overflowed packets are lost. Upper layer protocols

handle the lost packets, and TCP/IP (as one of the protocols) requests the

PC to resend the packets. Since packet overflow itself at the switch persists,

PCs will be forced to consume extra system resources by sending packets

again and again even though most of the packets are lost continuously.

About Flow Control