ahi@duvan.UUCP (Anders Hillbo) (02/08/86)
We want to connect a VAX 750, running UNIX BSD 4.2, with an Interlan controller and a custom made display station (Intel iSBC 186/51 & 82586 based) to transfer image data. We decided to use Ethernet and an UDP/IP implementation on the displaystation to be able to run in user mode on the Vax. The problem is SPEED (on the 750). A typical image consists of something between 64 kbyte and 1 Mbyte of data and the time to transfer the picture is how long you wait for the picture to show on the screen. The microprocessor based display station is just now capable of sending data in up to 300 kbyte/s , while the VAX computer only send data in 33 kbyte/s (UDP/IP, 1024 byte buffers, one user on the system). If raw IP is used (super user alone on the system), the speed increases to 182 kbyte/s. Also when sending TO the Vax the interface or something seems to drop packets if 4 of them arrive immediatly after each other. (I thought Interlan could handle back-to-back packets). We know that the packets leave the sender correctly by spying on the ether from a another displaystation which of course receives all packets with out any problem. The goal is a transfer rate at about 100 kbyte/s. The questions: . Why cant the UDP-interface send packets in a faster speed? Maybe if you could use bigger packets? . Is the limitation in the Vax750 or the interface? . Is this a well known problem? Anyone else with similar problems? . What are the real rules for trailer encapsulation. 4.2 only seems to do it when the package is 512 or 1024 bytes. Anders Hillbo CS Dept, Royal Inst of Tech. Stockholm, Sweden
cak@purdue.UUCP (Christopher A. Kent) (02/11/86)
In article <776@duvan.UUCP>, ahi@duvan.UUCP (Anders Hillbo) writes: > We want to connect a VAX 750, running UNIX BSD 4.2, with an Interlan > controller and a custom made display station (Intel iSBC 186/51 & 82586 > based) to transfer image data. We decided to use Ethernet and an UDP/IP > implementation on the displaystation to be able to run in user mode on the > Vax. > > The problem is SPEED (on the 750). > > The display station is just now capable of sending data in up to 300 kbyte/s. > the VAX computer only send data in 33 kbyte/s > > Also when sending TO the Vax the interface or something seems to drop packets > if 4 of them arrive immediatly after each other. (I thought Interlan > could handle back-to-back packets). > > The goal is a transfer rate at about 100 kbyte/s. I expect that the main problem is the VAX's i/o system; it can't handle the interrupt load quickly enough. The Interlan card can handle back-to-back packets, but on a limited basis; it has some internal buffer space, but it's not infinite. I'd go for bigger packets. There's no reason not to use full ethernet packets (1500 bytes), but you'll probably have to hack the VAX's kernel. I'm afraid I've only done this for the TCP layer, so I can't give you exact directions. We never used trailers here, because we have some binary-only equipt that doesn't understand them. I believe that the VAX only does trailers on those sizes because that's when it uses "tear-away" pages for buffers; tuning your packet sizes to use trailers and pages will also help a lot (the mbuf mechanism has a lot of overhead. Good luck, chris