s/dos NETWORK notes:

S/DOS network consists of several parts and modules.

1. NETBIOS drivers

2. Redirector and server program

3. NET.EXE utility to control network

4. NETSETUP utility to setup server resources

5. Auxilary utilites: LANCACHE, NET_ADDR.


1. NETBIOS drivers are network protocol drivers. They implement network 
SESSION level of OSI (Open Systems Interconnection) standard. 
Application using NETBIOS drivers can establish reliable network connection
called session between network nodes, send and receive data through this
session.
S/DOS netbios drivers can lay over abstact packet driver. 

It means that NETBIOS protocol requeres minimal service to send and receive
packets throughout (abstract ) network. For standard NE1000 NE2000 Ethernet
network adapters and for serial connection S/DOS netbios driver works directly 
with hardware  - sends and receive packets itself.

For other hardware NETBIOS driver can use standard IPX driver for sending and
receiving packets.

2. Network redirector and server programs.

REDIR.COM 

This main module of client software redirects all requests to network disks
or files and sends these requests to network server. After that server performs request
and sends the result back to client. 

Almost all requests are redirected by DOS using Network Redirector INT 2F 
and INT 2a interface. 

Besides printer can be redirected. Standard BIOS INT 17 is intercepted by 
network redirector.

So, client REDIR.COM sends requests (like OPEN FILE XXX, READ FILE HANDLE YY,
FIND FILE ????.???) using NETBIOS network protocol.

SERVER.COM
Since server program works in background it must perform all requests of network
clients despite of DOS state.

DOS can be in tree states: 
   1. Application performs some operation without using DOS function. 
Than DOS is "free" and any TSR software can call DOS function to read or write
file.
   2. Application calls DOS for file or disk operation. Than DOS switches to its
own stack, sets some DOS variables and perform disk or file operation.
At this moment no TSR program can interrupt DOS and call it again to perform
another DOS operation. In order to do it safety TSR must swap DOS data area
called SDA(swappable data area), restore TSR context SDA, call DOS. After
completing DOS operation TSR must restore foreground application SDA.

But actually SDA is not swappable at every moment. There are DOS "Critical
sections" when even SDA is not swappable. These critical sections
are the third DOS state.
  3. Critical section occurs when DOS calls one of device drivers like disk
driver. To control DOS state application should check InDOS flag and
intercept INT 2a Microsoft network interface.

Ok, when SERVER.COM can pop-up it reads the queue of client request.
After that it checks request for access rights and performs it if all is OK.
The result of request is sent back to client.

SERVER.COM also uses NETBIOS protocol to send and receive any data.

In S/DOS server program redirection function are also implemeted. 
It means that SERVER.COM program also includes network redirector code
and functions.

3. NET.EXE program is to control network. 
It attatchs client to server with LOGIN command, maps local disk or printer
to network resource with USE command.

See S/DOS network user guide for more detailed information

4.NETSETUP program is to setup network server resources, define access rights
of users, defines password of user.

See S/DOS network user guide for more detailed information
