IBM SC30-3681-08 manual Link Establishment Packets

Using PPP

establishment type packets that LCP de®nes. They may implement some of the additional LCP packet types, and they also may de®ne additional packet types beyond what LCP uses. Unlike LCP packets, the structure of an NCP frame may be modi®ed according to options negotiated by LCP during the link establishment phase.

Link Establishment Packets

Link Establishment Packets establish and con®gure a point-to-point link including the following packet types:

Con®gure-Request

LCP packet code ®eld is set to 1. LCP transmits this packet type when it wants to open a point-to-point link. Upon receiving a Con®gure-Request, a peer station's LCP entity sends an appropriate reply, depending on whether it is ready to process packets.

Con®gure-Ack

LCP packet code ®eld is set to 2. The peer transmits this packet type when every con®guration option in a Con®gure-Request packet is acceptable. Upon receiving the Con®gure-Ack (ack = acknowledgment), the originating station checks the Identi®er ®eld. This ®eld must match the one from the last-transmitted Con®gure-Request or the packet is invalid.

Both ends send Con®gure-Request and both ends must receive a Con®gure-Ack before the link opens. Options negotiated for one direction may differ from that negotiated for the other direction. There is no ªmaster-slaveº relationship. Rather, each end works symmetrically.

Con®gure-Nak

LCP packet code ®eld is set to 3. The peer transmits this packet type when some part of the con®guration option in a Con®gure-Request packet is unacceptable. The Identi®er ®eld is copied from the received Con®gure-Request and the Data (option) ®eld is ®lled with the received unacceptable con®guration options. The Identi®er ®eld must match the one from the last-transmitted Con®gure-Request or the packet is invalid and is discarded.

When the originator receives a Con®gure-Nak packet, a new Con®gure-Request packet is sent that includes modi®ed, acceptable con®guration options.

Con®gure-Reject

LCP packet code ®eld is set to 4. The peer transmits this packet type when some part of the con®guration options in a Con®gure-Request packet is unacceptable. The Identi®er ®eld is copied from the received Con®gure-Request and the Data (option) ®eld is ®lled with the received unacceptable con®guration options. The Identi®er ®eld must match the one from the last-transmitted Con®gure-Request or the packet is invalid and is discarded.

When the originator receives a Con®gure-Reject packet, a new Con®gure-Request packet is sent that does not include any of the con®guration options received in the Con®gure-Reject packet.

Code-Reject

LCP packet code ®eld is set to 7. The transmission of this packet type indicates that the LCP ªcodeº ®eld on a received packet is not recognized as a valid value. While this can indicate an error, it also can indicate that the peer does not implement some feature that you are trying to use.

454MRS V3.2 Software User's Guide