jay@rosevax.UUCP (Jay Warrior) (07/24/86)
> > > Mark, > > Re : 802.2 Type 2 operation > > 802.2 offers you Type 1 or Type 2 operation. Type 1 is pure datagram stuff with > the ARPANET's "take your chance" approach while Type 2 goes the other extreme > and do both flow control and error recovery. > > The general idea is that if you are going for a heavy weight Tranpsort Layer > already such as TCP or TP-4, you should leave every thing to that layer and > chose Type 1. If you are going to use light weight Tranpsort layer such as TP-0, > then Type 2 is for you. (Interestingly, IBM is using Type 2 since under SNA, > the link layer is the only level that will do error recovery). > > Hence unless we can get IEEE802.2 to create a Type 1.5, we don't think it is > worth our while to spend the cycles required for Type 2. (Actually, having a > Type 1.5 that will do low level acknowlegement but without flow control and > error recovery procedure may be quite useful - particularly for network level > gateway machines). > > Leong Your type "1.5" service is a proposed addendum to 802.2, called acknowledged connectionless service. This service, actually called Type 3 service is a "send one frame, receive one acknowledgement" service. If you are interested in the details, the service is specified in ISA-S72.01-1985, the PROWAY Industrial Data Highway standard from the Instrument Society of America. The goal was to provide for reliable data transfer without the overhead of a connection oriented service for real time, process control networks. This service works best over a 802.4 token bus by the way,the "real time extentions" in that standard are meant to support this service. --jay ihnp4!rosevax!jay