Network - DOS Requester
In Novell's NetWare 3.12 and 4.x, the DOS Requester is client software that runs on a workstation and mediates between applications, DOS, and NetWare. The DOS Requester replaces the NETX.COM network shell program used in earlier versions of NetWare. The software actually consists of a terminate-and-stay resident (TSR) manager (VLM.EXE) and several Virtual Loadable Modules (VLMs), which can be loaded at startup or as needed. The software also includes modules for dealing with security, DOS redirection, transport-layer protocols, and NDS (NetWare Directory Services) or bindery commands. The figure "Structure of NetWare's DOS Requester" illustrates the components. VLM.EXE is the VLM manager, and is responsible for loading the appropriate module at the appropriate time. VLM also controls memory usage and communication between relevant modules. CONN.VLM is the Connection Table Manager, which allows clients to connect to a network (assuming, at least for now, that the user is authorized to do so). The DOS Requester's components fit into a three-layer structure: n The DOS Redirector, the REDIR.VLM module, resides at the DOS Redirection Layer. This module provides DOS file services and callouts. This is the topmost of the three layers. n The Service Protocol Layer has modules for providing NetWare-specific services, and also file, print, and security services. The components that make up this layer are described below. n The Transport Protocol Layer is the lowest of the three layers, and is responsible for making sure packets are transmitted and that the connection is maintained. The TRAN.NLM module is the Transport protocol multiplexor, and is responsible for enabling communications between the available protocols (IPX or TCP) and the resources at the service protocol layer. The IPX and TCP protocols are handled by IPXNCP.NLM or TCPNCP.NLM, respectively. If necessary, the AUTO.VLM module can be used to reconnect a workstation to a server automatically-for example, to reestablish a broken connection. AUTO.VLM will automatically recon- figure the system to its original state. The following services are provided at the Service Protocol Layer: n NetWare services are provided to handle the different flavors of NetWare: NetWare 2.x and 3.x (which use binderies), NetWare 4.x (which uses Net- Ware Directory Services, or NDS), and Personal NetWare. These flavors are handled, respectively, by BIND.VLM (for 2.x and 3.x), NDS.VLM (for 4.x), and PNW.VLM (for Personal Net- Ware). The module for the appropriate protocols is determined and called by NWP.VLM-the NetWare Protocol multiplexor. n File services are handled by the FIO.VLM (file input/output) module. This module uses a basic file transfer protocol by default. If desirable or necessary, however, FIO can use special methods when reading or writing. These measures include using a cache (CACHE) or a packet-burst protocol (PBODI), or transmitting large internet packets (LIP). 290 DOS Requester n Print services are provided by the PRINT.VLM module. Since PRINT.VLM uses the FIO capabilities, it can use any of the special measures listed for FIO.VLM. The print module's behavior depends on the settings it finds in the NET.CFG configuration file. n Security services (both encryption and authentication) are provided through RSA.NLM, a module that implements the Rivest, Shamir, and Adleman public-key encryption algorithm. Unlike the NetWare shell, the DOS Requester may be called by DOS to do a task that is network-based and that DOS is, therefore, unable to perform. For example, DOS may use the DOS Requester to access file services on a remote machine. The DOS Requester still processes NetWare requests to get them into the appropriate format and then sends the requests on to the server. BROADER CATEGORY Network Shell COMPARE NETX STRUCTURE OF NETWARE'S DOS REQUESTER AUTO VLM. EXE C O N N RSA NDS BIND PNW NWP REDIR PRINT FIO TRAN IPXNCP TCPNCP SECURITY NMR