User manual

PPPoE (RFC2516)

PPP over Ethernet. Transmission protocol used for ADSL connections. In Italy, this is usually an

alternative to PPPoA. In fact, data packets, whether in PPPoA or PPPoE, are transmitted on the

ATM network. The correct term for this protocol is in fact Ethernet over ATM.

PVC

Permanent Virtual Circuit. Virtual connection between two fixed endpoints of the network.

Routing, frame and ATM network terminal.

RFC

Abbreviation of request for comments. Refers to each of the documents that define the stan-

dard communication protocols on the network.

Spanning tree

Bridges must ensure that there are no vicious circles in the network, i.e. that a single frame

does not continue to travel round and round eternally looking for a path to its destination,

unnecessarily occupying the network. This happens when there are several possible paths

available between two networks or segments. Frames continue to propagate themselves on

all possible segments and sometimes turn back, thus creating vicious circles. The frame leaves

“through the door” and returns “through the window” continuously. To intercept these “wan-

dering frames”, one of the possible paths is chosen and all of the frames addressed to a partic-

ular destination are routed on that path. The path chosen must be the shortest of those avail-

able. The decision is made using an algorithm called spanning tree. If the path originally cho-

sen goes missing due to a network fault, the bridge switches to a second one, thus maintain-

ing connection continuity. The end result is that the network appears to be structured like a

large hierarchical tree without duplicate paths between any of its stations. The efficiency of

this method is limited to local networks and does not work well on wide area connections as it

involves the continuous exchange of information between bridges.

Telnet

Protocol similar to TCP/IP that allows the user to establish an interactive connection to a

remote PC. It is a client/server application used to query databases or use specific services on

a server.

VCI

Virtual Channel Identifier. The VCI, along with the VPI, unequivocally identifies the physical

logical circuit assigned to a single ADSL subscriber in the ATM network.

WAN