Feature Summaries
The following summaries describe VH-4802 features in areas such as standards compliance, functionality, performance, and options.
IEEE 802.1D Bridge
The VH-4802 switch is fully compliant with IEEE 802.1D transparent bridging specifications. An address table is provided for learning, filtering, and forwarding. The switch can support up to a maximum of 12K addresses. Addresses are automatically learned by the switch, and can be individually assigned specific forwarding treatment by the network administrator if desired. Forwarding table configuration can be made out- of-band via the console interface or in-band via SNMP or Telnet. Static and dynamic addresses are both stored in this table. One static address is assigned per port by default. The Static Unicast Address Table Configuration screen in the console menus allows you to assign additional static addresses if required.
Spanning Tree Protocol
The VH-4802 switch supports the IEEE 802.1D Spanning Tree Protocol. This protocol allows redundant connections to be created between different LAN segments for purposes of fault tolerance. Two or more physical paths between different segments can be created through the switch, with the Spanning Tree Protocol choosing a single path at any given time and disabling all others. If the chosen path fails for any reason, a disabled alternative is activated, thereby maintaining the connection. This prevents network traffic from circulating in an endless loop formed by multiple connections to the same LAN segment.
Spanning Tree parameters are configurable using the Spanning Tree Configuration Menu of the console menus, the on-board Web agent, or via SNMP (see Appendix B, “Spanning Tree Concepts,” in the Management Guide for more information).
Frame Buffering and Frame Latency
The VH-4802 switch is a store-and-forward switching device. Each frame is copied into switch memory before being forwarded to another port. This method ensures that all forwarded frames conform to a standard Ethernet frame size and have a correct cyclic redundancy check (CRC) for data integrity. This switching method prevents bad frames from traversing the network and using up valuable network bandwidth, as with cut-through switching technology.
To minimize the possibility of dropping frames on congested ports, the VH-4802 switch provides 512 KB of frame buffering per port. This buffer space is used to queue packets for transmission on congested networks. This is an additional advantage over cut-through switching technology, which drops packets immediately when experiencing collisions.
