Client/Server Protocols

For communicating with the network servers each workstation requires network client software.
Microsoft calls this the 'redirector' while Novell calls it the 'requester.'
styThe software intercepts instructions that are designed for the network.
It then passes them onto the card driver and to the network cable itself.
This is done through transport protocol.
Lets take a look at some examples:
A person wants to send a print job somewhere on a network.
What the client software will do is it will intercept the printing order and identifies that the print job is not for the local printer.
It will then pass on the print job to the network printer and not the local printer.
It will pass on the message to the protocol and the card driver.
This will change it into a format that the network will understand.
Redirectors/Requesters also keep a track of drive designators.
Anything that involves C: is generally recognized as Local.
Whereas anything that involves G: is passed onto the network resource.
Using an NT network as an example the redirector will know that G: is really \\servername\sharename and will pass the instruction to the destination machine.

Server message Block (SMBs)
Microsoft Windows and the OS/2 are the two operating systems that use this protocol.
This protocol is used to request files from the servers and divert them to clients.
Lets take an example of a file request using the standard NT protocol:
The workstation application requests the use of a network file resource with an SMB message.
The request is then passed over to the redirector which then passes it down through the other layers of the OSI model onto the network.
When the request reaches the server the process is reversed.
SMBs allow a machine to share its files and printers to make them available for other machines to use.

NetWare Core Protocols (NCPs)
NCPs provide a similar function to SMBs in the NetWare environment.
They function at 4 layers of the OSI model application down to Transport.
NCPs provide a group of functions that manage the interchange between client and
server.
They are responsible for performing all file and print services between clients and servers.

Service Advertising Protocol (SAP)
The NetWare environment also uses the SAP protocol.
The most important function of this protocol is service advertisement
This is performed at the Application layer of the OSI model.
Service providers like file servers and print servers broadcast a SAP packet every 60 seconds to advertise their presence on the network.
When this packet is sent it informs the client that the service is still available.
Clients may also send a service query packet to request information.

Network Client software
All network operating systems may use different protocols to manage communications between the client and the server.
In order for this to work successfully the client software also has to be different.
Taking Windows 95 as example:
The operating system has both client software for Microsoft and Novell networks as well.
In order to communicate both the client for NetWare and client for Microsoft networks have to be installed.