Introduction to Microsoft Networking

I f you were to study the internal combustion engine, you would
have to know how that relates to the entire automobile and just
where all the pieces fit together. This sense of proportion helps
to make the learning easier by putting all the pieces together. Just like
the automobile engine, before you can really understand the TCP/IP
protocol stack, you have to understand the way that Microsoft
networking fits together.
This chapter looks at all the parts of Microsoft networking. This is not
specific to the Windows NT product, but generally describes the way
that any Microsoft network operating system works.
The OSI Reference Model
Chapter 1, “Introduction to TCP/IP,” mentioned the Open Systems Interconnection
(OSI) reference model. Every networking model is built on layers. The OSI reference
model was designed as a guide for vendors to use as they built their own networking
architectures. (It is not an actual architecture.) Windows NT networking fits the OSI
model. This discussion uses it as a comparison to the TCP/IP model, which is different,
yet manages to achieve the same purpose (and which NT also fits). The layers in
the OSI model have the following functions:
u Application. Generates the requests and processes the requests that it
receives.
u Presentation. Creates the SMB (Server Message Block) (in NT’s case) that
tells the other system what is requested, or contains the response to the request.
This layer also deals with type conversions when the communicating hosts are
different.
u Session. Provides a method for creating and maintaining a logical connection
between two hosts. It also tracks the resources currently in use.
u Transport. Puts the information into a “language” that the other system
understands.
u Network. Deals with directing which system or systems receive the information
on the other end. In other words, it tracks which MAC (Media Access
Control—the unique number that each network card has) address to send to.
u Data Link Control. Deals with the framing of the information sent on the
wire.
u Physical. Puts the information on to the physical network and receives packets
(or frames) from the network.
A discussion of Microsoft networking architecture should help you understand that
when data is being moved between two systems, the information from each of the
layers becomes the data of the layer that resides below it. In this manner, an SMB
(Server Message Block), which is created by the Application and Presentation layers,
becomes the data for the Session layer (or in NT, the TDI boundary).
What Is Microsoft Networking?
Microsoft provides a great deal of flexibility in networking by providing the layered
approach to the networking components. Primarily, Microsoft uses NetBIOS (Network
Basic Input/Output System) as its internal networking protocol. NetBIOS
provides the following several services essential to networking:
u Name management. In NetBIOS networking, computer names are used to
identify the different systems on a network. This function allows for NetBIOS
names to be registered at a computer and enables the computer to know to
which requests to respond. NetBIOS names are 16 bytes in length with the 16th
byte being used to identify the service that registered the name (for example,
workstation, server, and so on).
u Connection-oriented data transfer. This function enables the transfer of
data from one system to another by using a session, and also enables a series of
checks and balances to ensure that the data being transferred is correct.
u Connectionless data transfer. This part of NetBIOS enables computers to
make announcements and send queries to all computers on the network
without having to create sessions. It is used to locate other computers on the
network, or to let other computers know about this one. This provides a
transport for such purposes as logon validation, server announcements, name
queries, and so on.
u Session management. This service tracks and maintains sessions with other
computers on the network, enabling the system to keep track of other computers
with which you work so that those computers can communicate with each
other more quickly. Rather than having to identify yourself every time you
communicate with another system, you can just use the session.
NetBIOS uses a structure called an SMB (Server Message Block) to communicate
between the system requesting the service and the system that will provide the service.
On the system that generates the request, an SMB is created by the redirector (the
component that gets access to the other computer) that, in Microsoft Windows NT
networking, is the workstation service. The SMB describes what the other system is to
do (put this data on the drive, send some data to the SMB, start a session, and so
forth) and includes that actual data where required.
The redirector and the server services are the Application layer discussed earlier in
relation to the OSI model. These actually create the requests and respond to them.
These services also handle the Presentation layer; they create the SMBs (how requests
are formatted for the other computer).
As figure 2.1 shows, the SMB is a method of communications between a redirector
and a server. No other parts of the network architecture use the SMB. Instead, all the
lower layers carry the data.