Cabletron Systems CyberSWITCH CSX150 User Manual

Also see for CyberSWITCH CSX150: User guide Quick start guide

Contents

USER’S GUIDE318 CyberSWITCHHowever, the PPP link exists on an end-to-end basis with the remote peer, a domain which exceedsthat controlled by the signalling-type entities just cited. Thus, not every end-to-end failure will bedetected. Some examples of such failures include:• an ISDN peer’s D-channel “process” is functional, but it’s B-channel “process” has failed• the underlying physical circuit has an end-to-end fault in one or both directions which does notaffect the D-channel or control path• the underlying physical circuit has been mistakenly looped backIn such cases, the Link Failure Detection feature can discern the fault(s). A properly functioningremote device is obligated to return an Echo-Reply to each Echo-Request, which verifies the fullend-to-end path of the point-to-point link. Furthermore, the Echo-Request frames carry a PPPelement known as the “Magic Number” which can be used to ascertain if an inbound Echo-Requesttruly came from the peer or was looped back.PPP Link Failure Detection can be enabled or disabled within the PPP Options configuration menu.When enabled, two other configurable parameters then control the mechanism. Upon entrance ofa PPP link into Network Phase (the point at which device data transfer is allowed), Echo-Requestswill be sent at a configured frequency. As long as Echo-Replies are received, the link is deemed tobe functional.A second parameter specifies the maximum number of Echo-Request attempts which will betransmitted without a reply. If this limit is reached, a message is logged and the link is reported asfaulty. Thus, the configured frequency multiplied by the configured maximum attempts yields theapproximate time it will take to detect a failed link.Note: Within the CyberSWITCH, there are certain accesses which also present the ability toenable/disable the periodic transmission of link maintenance type packets. For example,the packet-based Frame Relay access supports the configurable enable/disable of“Keepalives” in order to avoid the extra per-packet costs which the periodic Echo-Requestframes might incur. The PPP Link Detection Failure feature will honor such access-basedconfiguration, in addition to the explicit enable/disable configuration status of the PPPfeature itself.PPP R EFERENCE D OCUMENTSPoint-to-Point Protocol (PPP) is also described in more detail in the set of RFCs listed below:• RFC 1661 The Point-to-Point Protocol• RFC 1638 PPP Bridging Control Protocol (BCP)• RFC 1549 PPP in HDLC Framing• RFC 1547 Requirements for an Internet Standard Point-to-Point Protocol• RFC 1334 PPP Authentication Protocols• RFC 1332 The PPP Internet Protocol Control Protocol (IPCP)