Labels:text | screenshot | font | black and white OCR: Help File mode <iface> [vcldatagram] Control the default transmission mode on the specified AX.25 interface. In datagram mode, IP packets are encapsulated in AX.25 UI frames and transmitted without any other link level mechan- isms, such as connections or acknowledgements. In vc (virtual circuit) mode, IP packets are encapsulated in AX.25 I frames and are acknowledged at the link level according to the AX.25 protocol. Link level connections are opened if necessary . In both modes, ARP is used to map IP to AX.25 addresses. The defaults can be overridden with the type-of-service (TOS) bits in the IP header. Turning on the "reliability" bit causes I frames to be used, while turning on the "low delay" bit uses UI frames. (The effect of turning on both bits is undefined and subject to change) . In both modes, IP-level fragmentation is done if the datagram is larger than the interface MTU. In virtual circuit mode, how- ever, the resulting datagram (or fragments) is further fragmented at the AX.25 layer if it (or they) are still larger than the AX.25 paclen parameter. In AX.25 fragmentation, datagrams are broken into several I frames and reassembled at the receiving end before being passed to IP. This is preferable to IP fragmentation whenever possible because of decreased overhead (the IP header isn't repeated in each fragment) and increased robustness (a lost fragment is immediately retransmitted by the link layer).
(.png)
