COMSPHERE 3600 Series Data Service Units4-46 July 1999 3610-A2-GB41-70DBM-V/DBM-S/DBM-D Dial on DTR CapabilityWhen the central site loses access to its remote DSUs,the DBM-Vs, DBM-Ss, and DBM-Ds can initiate backupbased upon the state of the DBM’s DTR lead. To activatethis capability, set the Primary Core configuration optionto Yes and set the DTRCallCon configuration option toOrig. Then, the DBM-V/DBM-S/DBM-D originates abackup call when DTR is raised and drops the call whenDTR goes low.For additional information, refer to ConfigurationOptions, Chapter 6, in the COMSPHERE 3600 SeriesData Service Units, Models 3610 and 3611, Operator’sGuide.Digital Bridge/DBM-V/DBM-S/DBM-D InterfaceSince both the digital bridge port and the DBM providea DCE interface, a digital bridge interface or crossovercable is used to complete the communication path (referback to Figure 4-28).The digital bridge broadcasts data from the controllingDTE to all ports in the digital-sharing group, even if theDBMs connected to the ports are not in Dial Backupmode with an active call: the data is simply ignored by theDBMs.When a call has been established between a central-siteDBM and a remote DBM, the DBM-V, DBM-S, orDBM-D enters Dial Backup mode, accepts data from thedigital bridge port, then transmits data over the backupline and through the remote DBM to its associated DTE.Digital Bridge/DBM-V/DBM-S/DBM-D –Switched LSD OperationSome DTEs require the LSD interface to be ON whendata is present and Off when no data is present. In thiscase, the connected DBMs and associated tributary DBMsmust be configured to enable the V.13 feature.However, most DTEs that would be connected toPort 1 do not utilize the LSD interface lead. In this case,the connecting DBMs are not required to have the V.13feature enabled.Tributary DSU ConsiderationsIn multipoint backup, the firmware version of thetributary DSU-DBM in a multipoint circuit determines thefeatures available. It is recommended that all tributarieshave Release 2.4 or greater firmware, which provides thefollowing features:• Multiple Call (MultiCall) configuration option. Ifthe DBM is triggered by the DSU to attemptbackup, the DBM calls the first number in itsBackup Directory. If that number is busy after threeattempts, the DBM places a call to the secondnumber in the directory. The DBM steps through all10 entries in the Backup Directory in an attempt toplace the call, skipping all blank entries. Thisconfiguration option gives the tributaries moreflexibility and a better success rate when calling thebridge.• V.13 Signaling (V.13 Signl) configuration optionfor switched LSD emulation.• Automatic restoration.• All the DBM features available under the earlierrelease.With the earlier release, multiple call and automaticrestoration capabilities were not available. Release 4.25 isrequired for 14.4 kbps and 56 kbps backup speeds via4-wire access, and release 6.18 is required for 56 kbpsbackup speeds via 2-wire access.Setup – DSU Rate Equals DBM RateFor a network where the DSU rate equals the DBMrate, partial or full backup can be accomplishedautomatically by the tributary DSU-DBM when theydetect network failures.Each tributary DSU should be configured for automaticbackup, and the Backup Directory of its associated DBMshould contain the telephone number of a central-siteDBM associated with the digital bridge. The DBMs andDBM-Vs, DBM-Ss, or DBM-Ds need to be paired offand, in each DBM, a pointer set to the telephone numberof the associated DBM-V, DBM-S, or DBM-D. Thus,each DBM will call a different central-site DBM. (Referto the Configuration Branch section in Chapter 5 forfurther details regarding configuration options.)
