implementation of a local area network (abstract only)  thriftnet was created by dr. tobin maginnis and dr. donald miller in 1979 as a locally developed basic network for file transfer and establishment of a virtual terminal between two computers connected by a pair of serial line units or slus. this network has been described as an unobtrusive network in the sense that it requires no operating system modifications and uses existing terminal lines for intercomputer communication. (turbeville 85).  thriftnet-version 2 was ported or implemented on the microvax from the pdp-11 because:  groups of programs from the pdp-11's unix system needed to be modified and uploaded to the microvax's ultrix system and  the microvax needed to communicate with the other computers within the network enabling the user of the microvax to use other systems' utilities.  thriftnet is a basic network that controls communication and file transfer between two computers connected by two slus in half or full duplex mode. the two computers in this case are the pdp-11 and the microvax with unix and ultrix operating systems respectively.  in version 2. there are only three files involved called thrift. rcv. and thrift.h. thrift and rcv are the two c programs that create thriftnet. thrift.h is an include file of constants and variables common to both. thrift establishes communication and starts file transfers between the two computers while rcv is sued to verify communications and receive the file from the host machine. [turbeville 85] [maginnis 82]  thriftnet is established in a series of steps. the thrift program when invoked sets the terminal in a raw sight bit mode which invokes rev in the connecting computer. rcv then sends back ack and the computer wordsize. this sets a flag that signals that communications have been established. now the user can login. to transfer a file thrift starts by asking for the file spec from the master system as well as what to call the file when transferred. the name and specs of the file are sent to the receiving computer with an ack returning. the master then sends 131 bytes at a time. the group of data is then checked for errors and if correct. rcv sends out an ack and writes the block to the computer's disk, but if incorrect, rcv sends out a nak and disregards the block causing retransmission of the block. this goes on till eof is reached. at that point everything is reset to a virtual mode.  the characters are sent in groups of 131 bytes. in each group. there is a start byte. 128 characters, stop byte, and a logitudinal redundancy check character or lrcc. the lrcc is calculated by doing an exclusive or the previous characters of the data block. if the receiving computer doesn't get the correct number of characters or a correctly calculated lrcc. the receiving computer will send a nak which causes a retransmission five transmissions are allowed before the file transfer is aborted. [henry 85] [turbeville 85]  the first step in porting thriftnet was to type in thrift.h and rcv.c into the microvax. one problem was when a nak(0) was inadvertently left cut of the code when typed in causing the program to wait forever on a nak that would never appear. another obstacle was that all unix system calls had to be changed to ultrix. the code also generated warning statements because of slight differences in the c compilers. to correct this, some sections of code had to be rewritten while others required the use of masks also the numeric constants for the bauds were changed to be compatible with ultrix. the constants for raw, echo, and eightb were also checked.  sherry lesiker