Network O/S setup

• 2 Major Types of Multitasking
1. Preemptive - O/S can take control of the processor without the task's cooperation
• Advantage of preemptive multitasking: CPU activity can be switched from local tasks to a network task
2. Non-preemptive (Cooperative)
• the task itself decides when to give up the processor
• no other program can run until the non-preemptive program gives up the control of the processor
• A Network O/S
• ties together all the PCs and peripherals in the network
• coordinates the functions of all PCs and peripherals in a network
• provide security for and access to database and peripherals in a network
• Client Software
• redirector
• process of forwarding requests is done by a redirector
• intercepts requests in the PC
• determines if they should be left alone to continue in the local PC's bus or redirected out to the network to another server
• designator
• a piece of software that manages the assignment of drive letters to both local and remote network resources or shared drives
• e.g. share drive in other PC, alphabet as a designator, such as G:
• when an association is made between a network resource and a local drive letter (mapping a drive), the designator takes care of remembering the path to the network resource.
• when users or applications access the drive, the designator substitutes the resource's network address for the drive letter before the request is sent to the redirector.
• peripherals
• redirectors can send requests to either computers or peripherals (e.g. LPT1: or Com1 can refer to local OR network printers. Just give these ports a path to the network device.
• Server Software
• makes it possible to SHARE resources (data, printers, modems, etc.) with workstations
• provides network security as well
• makes sure two users don't use the same resources at the same time.
• managing users - create, privileges, remove users
• network management tools to track network behaviour
• The server also
• Provides logon authentication for users
• Manages users and groups
• Stores management, control, and auditing tools for network administration
• Provides fault tolerance for protection of network integrity
• Windows NT Server
• When installing you must
• name the domain or workgroup
• name the server
• the 1st server installed in a domain must be installed as the primary domain controller (PDC), every domain is required to have one and only one PDC
• a backup domain controller
• keeps a copy of the domain's directory database
• authenticates logons
• can be an application server
• Configuring the network adapter card - default protocol for NT server is TCP/IP
• TCP/IP installation
• IP address
• logical 32-bit address to identity a TCP/IP host
• has two parts: network ID and host ID
• subnet mask - is used to mask a portion of the IP address so that TCP/IP can distinguish the network ID from the host ID - 255.255.0.0
• default gateway - (gateway = ROUTER) -  For communication with a host on another network, an IP host must be configured with a route to the destination network otherwise only communication on the local segment
• manual install - assign IP address, subnet mask and the default gateway
• automatic install - DHCP (Dynamic Host Configuration Protocol) service,
• when a DHCP server is configured on the network, clients that support DHCP (NT W/S & NT Server) can request TCP/IP configuration info (IP address, subnet mask, default gateway and so forth) from the DHCP server

• Here's the remote printing process:
1. the PC's redirector put the print job onto the network cable
2. print server's network software takes the print job from the cable and send it into a queue with other items waiting from access to the shared printer
• UNC syntax: \\print_server_name\printer_share_name
• network uses a spool (simultaneous peripheral operation on line)
• a spooler is a memory buffer in the print server's ram that holds print jobs If there are too many print jobs to fit into RAM, the overflow wait to print on the print server's hard drive.
• To share a printer you must:
• load printer drivers so the printer will print correctly
• Create a share name for the printer
• identify a port so the redirector will know where to send the print job
• set the information and output parameters so the network operating system will know how to handle and format the print job.
• PDL - (Printer Description Language)
• the printer uses the PDL to construct text and graphics to create the page image
• PDLs are like blueprints
• You can manage the printer remotely

X.400 Components

• X.400 defines a whole range of protocols for transferring mail between e-mail servers.
• The Three main components are:
• UA=> user agents
• MTA => Message Transfer Agent
• MTS => Message Transfer System
• E-mail Client (UA, User Agent) responsible for all user interaction such as
• reading and composing messages. It runs on the
• MTA (Message Transfer Agent) responsible for transferring messages from
• one user's mailbox to another or to other MTAs for delivery.
• MTS
• Responsible for  transferring messages of all types for the UA that creates the message to the destination UA
• Directory services Personal Address Book, Global Address List.

X.500

• is a set of directory services developed to help users in distributed networks locate users on other networks to whom they want to send messages

• Post Office (Information store, Message store) location of all user messages.

Transport/Delivery protocols

• POP3 (Post Office Protocol) and IMAP4 (Internet Mail Access Protocol)
• describes how e-mail client interact with email server.
• SMTP (Simple Mail Transport Protocol)
• describes how e-mail servers transfer email message to their intended recipients.
• SMTP works with other e-mail programs to provide both a client and a server the function to send and receive e-mail messages.
• used on the Internet, UNIX and in the TCP/IP stack
• MIME (Multipurpose Internet Mail Extension)
• defines the method in which files are attached to SMTP messages.
• MHS (Message Handling Service) within NetWare
• similar to X.400 => one computer on the network is the MHS sever and it translates messages between computers that may be using different e-mail systems

Directory Services

• LDAP (Lightweight Directory Access Protocol)
• X.500 (see above)

Messaging APIs

• MAPI (Message Application Programming Interface)
• MS standard and incorporated throughout all of its office products.
• VIM (Vendor-Independent Messaging) from Lotus
• Scheduling

Groupware

• eg. BBS, Internet news, Interactive conferences, MS Exchange, Lotus Notes.
• Group discussions
• Workflow automation.
• Help Desk
• Collective document creation.
• Internal publishing

• server's O/S, the client's O/S & the redirector have to be compatible
• Different clients have to be able to understand each other to communicate. How can you get this done?
• the client solution
• implement the appropriate redirector on the client, the redirector forwards your request to the appropriate destination
• use multiple redirectors to communicate with different clients

• the server solution
• install a service on the service
• E.g. to let MAC clients share network resources, add Service for Macintosh; Add FPNW for NetWare clients

• Centralized Computing
• Here the application operates on the server and all clients interact with the central application through client side interface terminals - dumb terminals
• when a client requests data from a database, the system moves all the data across the network to the client
• this causes the network to slow down for other clients
• Client/Server Computing
• the client computer makes a request and a computer acting as the server fulfills the request
• the client software uses the structured query language (SQL) to translate what the user sees into a request that the database can understand. Therefore portions of the application reside on the client and some on the server.
• Here's an example using SQL:
• The client requests the data
• The request is translated into SQL
• The SQL request is sent over the network to the server
• The database server carries out a search on the computer where the data exists
• The requested records are returned to the client
• The data is presented to the user
• The application (MS Access for example) is the client, or FRONT END
• The database server (SQL Server) is the server or BACK END
• The Client
• The front end client runs an application that
• presents an interface to the user (this doesn't reside on the server at all)
• formats requests for data
• displays data it receives from the server
• The user uses an on-screen form, called a search key to specify search requests
• the data can be presented to the user in various ways  - different users access the same database to present information in a way that suits them
• Front End Tools
• query tools
• user applications
• e.g. Excel provides front end access to back end databases
• program development tools
• Visual Basic is used to develop front end tools to access backend data.
• The Server
• usually dedicated to STORING and MANAGING data
• most of the database activity happens on the server
• sorting
• data updates, additions, deletions, and protection
• Stored procedures
• short, pre-written data-processing routines used by client applications
• stored on the server and can be used by any client
• one stored process can be called by any number of client applications instead of having to incorporate the same routine into the code of each program
• this means
• processing is done on the server instead of the client
• network traffic is reduced because one request begins a series of stored procedures on the server instead of many different requests
• security controls can prevent unauthorized use of some procedures
• Client / Server Architecture
• single server
• multiple servers with special tasks
• distributed server arrangements
• servers across a WAN link synchronized to endure they all have the same data in common
• Data Warehouse. One server stores large amounts of data and forwards the most sought after data to intermediate servers that format the data. This off loads some of the processing from the intermediate servers that care contacted by clients (pic. p.409).

Advantages of the Client / Server Environment

1. Less network traffic => only results of query are sent over the network
2. The server is more powerful that the client and does most of the processing
3. More RAM and storage space on server means you don't have to spend as much MONEY on each client
4. Back end data is more easily secured and BACKED UP