Chapter 1: Introduction to the EIU 25

second-level message switches are referred to as local message switches (LMS).

The frame transport bus (F-bus) is a 32-Mbit/s messaging bus that resembles the MS in its protocol. The use of a narrower data path allows access to two buses through a single backplane. This feature lets a single processor card connect to both planes of the LMS and to survive faults on one plane. Links interconnecting planes of the LMSs are provided to allow transparent message rerouting in the case of single faults.

Note: Because the interconnecting F-bus is a wire bus, it is limited to a single cabinet.

Inter-message switch links required with LPP

Inter-message switch links (IML) between the MS planes are also required to improve robustness. For example, two peripherals (such as an applications processor and an EIU) can lose communication with each other if they message through different planes of the MS. In this scenario, assume that one peripheral is messaging through plane 0 only because of a failure. If the second peripheral loses its link to plane 0, the two peripherals cannot communicate even though they can communicate to the DMS-core for maintenance purposes.

For this reason, there is a pair of IMLs in integrated service node (ISN) switches. These IMLs are DS512 links that operate at 1024 Kbit/s. Other improvements to the MS hardware are also required to conform with the ISN maintenance strategies.

Data communications interface architecture

The overall architecture of the data communications subsystem is based partially on the premise that the processing and the access method for these entities must be separate.

For this reason, application processors (AP) have the intelligence to drive the link protocols. This arrangement allows freedom to change access methods and allows flexibility in satisfying the processing requirements for each protocol. The emphasis is on providing locally attached, nonswitched connections primarily for OAM interfaces. An example of the overall data flow for the data communications environment is shown in figure 2.

DMS-100 Family EIU User Guide TELECOM12

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Cabletron Systems DMS-100 manual Inter-message switch links required with LPP, Data communications interface architecture