Ethernet only support for EMAS 3 -------------------------------- There are two variations of this scheme. 1. That all, or most, of the Ring TCPs are switched to Ethernet PADs. 2. That all, or most, of the Ring TCPs are switched to X25 PADs. An overall assumption is also made that the EMAS 2 engine or engines are supported on the ethernet. If it/they are not, then increased X25 gateway traffic must be allowed for. Scheme 1 -------- Assuming about 100 users maximum (Oct '85 - Jan '86), a traffic load of about 50 pkts/sec (all pkts) for interactive and a similar amount for RJE/FTP should be allowed for. This figure is possibly low if there is a larger amount of inter-EMAS traffic than at present because of the split in the user community. Approximately 20 pkts/sec will come from ethernet pads and about 5 pkts/sec will go to other ethernet hosts. This leaves about 75 pkts/sec that will go through the X25 gateway. In addition to the above figures, it is reasonable to assume that about 25 to 30 connections will be made from the ethernet pads to non-ethernet services, thus adding about 15 pkts/sec to the load on the gateway. This leads to a total of 90 pkts/sec through the gateway. Ethernet Comtec PADs should be available in the 2nd quarter of 1985. Scheme 2 -------- The figures above remain true, but instead of the PAD to X25 traffic we will now get almost the entire 100 pkts/sec to EMAS 3 going through the X25 gateway. Consequences ------------ Two or three chanlans will probably be necessary for EMAS 3 as well as one EMLAN for each EMAS 2 system (possibly in addition to the OSLAN EMLAN). The 90 pkts/sec through the X25 gateway will need a total line capacity of approximately 100K.baud. Based on all existing measurements - it is possible that the new gateway will use the line capacity much more effectivly but this remains to be proved. At the current stage a maximum of 19.2Kb is planned for the OSLAN X25 gateway, so at least three to four would be required which would cause some problems with load sharing etc. The new CPSE ethernet gateway, operating at 2Mb, would be able to handle this load but it probably will not be available until summer '85 and even then will not be sufficiently robust to withstand serious user pressure. The above figures do not allow for extra traffic being generated by the other ethernet hosts, eg. the GEC Series 63 and the IBM 4341. In addition it must be remembered that all the current problems with ethernet protocol differences are sorted out far enough in advance so that all the, very new, boxes fully interwork with each other. Conclusion ---------- It is perhaps foolhardy to base a service on EMAS 3 soley on an ethernet connection at this early stage in ethernet development. X25 and Ethernet Solution ------------------------- This route gives us both a safer path to a reasonable user service but still helps to carry us forwards. The problem with this solution is both the extra person power required to do it over the ethernet only course and the six month delivery time being quoted by GEC for the IBM interface. B.A.C.Gilmore 21st June 1984.