Glossary
PPPoA
PPPoE
Protocol Timeout. The amount of time (in seconds) during which a connection in the specified range remains open when there is no data transfer. After a connection has been established on a given port, the sender and receiver usually determine when the session is finished and the connection is closed. However, if the connection is left open and data transfer stops, the system must eventually close the connection and reclaim the resources in order to protect your network. In some cases, the system might close the application during normal operation (for example, if there is a long pause between data transfer). If this is the case, lengthening the timeout may help.
PVC (permanent virtual circuit). A virtual circuit that is permanently available. Used to establish connections between hosts that communicate frequently.
R
Router. The central switching device in a
S
Subnet Mask. The IP addressing system allows subnetworks or “interchanges” to be created, and devices numbers or “extensions” to be established within these subnetworks. These numbers are created using a mathematical device called a subnet mask. A subnet mask, like the IP address, is a set of four numbers in dotted decimal notation. Subnet masks typically take three forms:
•255.0.0.0
•255.255.0.0
•255.255.255.0
The number 255 “masks” out the corresponding number of the IP address, resulting in IP address numbers that are valid for the network. For example, an IP address of 123.45.67.89 and a subnet mask of 255.255.255.0 results in a sub network number of 123.45.67.0 and a device number of 89.
The subnet mask used for the network typically corresponds to the class of IP address assigned, as shown in the following table.
IP Address Class | Corresponding Subnet Mask | |
Class A | 1.xxx.xxx.xxx to 126.xxx.xxx.xxx | 255.0.0.0 |
Class B | 128.0.xxx.xxx to 191.255.xxx.xxx | 255.255.0.0 |
Class C | 192.0.0.xxx to 223.255.255.xxx | 255.255.255.0 |
