36 Chapter 1: Introduction to the EIU297-8991-910 Standard 03.01 August 1999System-wide limitationsThe EIU is collocated in an LPP shelf with other ASUs such as the linkinterface unit (LIU7) and frame relay interface unit (FRIU). The exactconfiguration of ASU-type units depends on the applications. The LPP isconnected to the DMS-bus through eight DS30 links in a load-sharingarrangement.Each DS30 has a transfer capacity of approximately 256 Kbyte/s. A single EIUcan route long messages (1518 bytes) from the LAN to the DMS-bus at a ratethat can overload the DS30 and cause the link to fail (SysB state). This linkfailure causes traffic to switch to an alternate DS30 link. If the systemmaintains the level of traffic that caused the initial failure, each DS30 linktopples one by one until the LPP is isolated from the DMS-bus. Further, aseach DS30 link overloads, all pending messages on that link are lost, includingSS7 messages.Note: When deployed, fiber SR128 links through the MS will provideenhanced capacity to alleviate link capacity overload.The IP throttling feature throttles IP messages to and from the EIU to providea measure of protection against DS30 link overload. Application groups canengineer throttling to permit them to override the defaults. Completeprotection is still not guaranteed due to other message sources, such as SIPC,MTS, logs, and OMs. Further, multiple EIUs on the same LPP can stillsimultaneously send a large message on the same link which, when combinedwith other messages in the LMS RX FIFO queue, can still cause an overload.IP throttling has also been implemented to protect the links between the MSand EIUs that are on FLIS or SNSE LIS.A problem common to all ASU types is that the F-bus receive buffers can beoverloaded. If this happens too many times within a certain time interval, therate adaptor detects the error and fails the link. Engineering rules are requiredto ensure any ASU type is not overloaded. Refer to Provisioning Rules for LPP,SSLPP, and SNSE LIS, System Engineering Bulletin SEB 92-02-001.Limitations associated with maintenanceThe operating company can datafill a maximum of eight EIUs in the LIUINVtable. That is, the maximum number of EIUs on a switch is eight. As a furtherlimitation, each LPP can have a maximum of four EIUs. The FLIS can have upto eight EIUs.These limitations are not only a datafill issue. Other factors must be studiedbefore these values can be increased, such as traffic load through an LPP orFLIS, EMI emissions, and routing issues. Currently, with 8 EIUs and 28 LIU7sin a 36 processor LPP configuration, the emissions are just within allowablelimits.
