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Networking - Connecting Devices and Network Adapter Cards, NDIS and ODI, Network Resource Management

Connecting Devices and Network Adapter Cards
Connecting Devices
There are five kinds of connecting devices; Repeaters, Hubs, Bridges and two and three-layer Switches.
Repeaters and Hubs operate in the first layer of the internet model.
Bridges and two-layer Switches worked on the first two layer; Routers and three- layer Switches worked on the first three layers.
A Repeater is a device that operates only in the physical layer. Signals within a network can travel a fixed distance before Attenuation endangers the integrity of the data.
A Repeater receives a signal and, before it becomes too weak or corrupted, regenerates the original bit pattern.
A Repeater can extend the physical length of a LAN as shown in figure.
It does not actually connect two LANs; it only connects two segments of the same LAN.
The segments connected are still part of one single LAN. A Repeater is not a device that can connect two LANs of different protocols.
As we know that in different LAN Architectures length of the cable is limited. To extend this length we divide the cable into segments and install Repeaters between segments.
The whole network is still considered one LAN, but the portions of the network separated by Repeaters are called segments.
It is tempting to compare a Repeater to an amplifier, but the comparison is inaccurate.
An amplifier cannot discriminate between the intended signal and noise; it amplifies equal every thing fed into it.
A Repeater does not amplify the signal; it regenerates the signal. When it receives a weakened or corrupted signal, it creates a copy, bit for bit, at the original strength.
The location of a Repeater on a link is very important. A Repeater must be placed so that a signal reaches it before any noise changes the meaning of any of its bits.
A little noise can alter the precision of a bit's voltage without destroying its identity.
If the corrupted bit travels much farther, however, accumulated noise can change its meaning completely. At that point the original voltage is not recoverable and the error needs to be corrected.
A Repeater placed on the signal becomes list can still read the signal well enough to determine the intended voltages and replicate them in their original forms.
Although, in a general sense, the word Hub can refer to any connecting device, it does have a specific meaning, a Hub is actually a multiport Repeater.
It is normally used to create connections between stations in a physical star topology.
However, Hubs can also be used to create multiple levels of hierarchy, as shown in figure.
The hierarchical use of Hubs removes the length limitation of 9 Base-T (90 m).
A Bridge works on both the physical and the data link layers.
As a physical layer device, it regenerates the signal it receives. As a data link layer device, the Bridge can check the physical (MAC) addressed (source and destination) contained to the frame.
One may ask, what is the difference in functionality between a Bridge and a Repeater? A Bridge has filtering capability.
It can check the destination address of a frame and decide if the frame should be forwarded or dropped.
If the frame is to be forwarded, the decision must specify the port. A Bridge has a table that maps addresses to ports.
In the given figure destined for station 513B1365452 arrives at port 1. The Bridge queries its table to find the departing port.
According to the table frames for 513B1365452 leave through port 1; therefore, there is no need for forwarding; the frame is dropped.
On the other hand, if a frame for 513B1365452 arrives at port 2, the departing port is port 1 and the frame is forwarded.
In the first case, LAN2 remain free of traffic; in the second case, both LANs have traffic. In our example, we show a two port Bridge; in reality a Bridge usually has more ports.
When we use the term switch, we should be careful because a switch can mean two different things. We must clarify the term by adding the level at which the device operates.
We can have a two layer switch or a three- layer switch. Let us briefly discuss each.
Two-Layer Switch
A two layer switch is a bridge with many interfaces and a design that allows better (Faster) performance.
A bridge with a few interfaces can connect a few segments of a LAN together.
A bridge with many interfaces may be able to allocate a unique interface to each station, with each station on its own independent segment. This means no competing traffic.
Three-Layer Switch
A three-layer switch is a router with an improved design to allow better performance.
A three-layer switch can receive, process, and dispatch a packet much faster than a traditional router even though the functionality is the same.
A Hardware device designed to take incoming Packets, analyzing the packets and then directing them to the appropriate locations, moving the packets to another network, converting the packets to be moved across a different type of network interface, dropping the packets, or performing any other number of other types of actions.
A router has a lot more capabilities than other network devices such as a hub or a switch which are only able to perform basic network functions.
For example, a hub is often used to transfer data between computers or network devices, but does not analyze or do anything with the data it is transferring.
A network router, however, may take the data being sent over a network, change how it is packaged, and send it to another network or over a different type of network.
For example, routers are commonly used in home networks to share a single internet connection with multiple computers.
Short for Bridge Router, a "Brouter" is a networking device that serves as both a Bridge and a router.
Core router
A core router is a router in a computer network that routes data within a network but not between networks.
Edge router
An edge Router is a router in a computer network that routes data between one or more networks.
Virtual router
A Virtual Router is a backup router used in a VRRP setup.
Route Forwarding
Routing tables hold the data for making forwarding decisions. Although this is a simple example, routing tables become very complex. Static routing uses fixed tables, but dynamic routing uses routing protocols that let routers exchange data with each other.
Ethernet Cable Media Connector Types
Most of network adapter cards have more than one interface connections.
If a card has more than one interface, the selection of which connector to use, will be controlled either by setting of jumpers or DIP (Dual Line Package) switches on the card itself, or by using a software-selectable option.
The BNC connector is used to connect the end of the cable to a device, such as a TV set or thinnet network.
A thicknet network connection uses a-15 pin attachment unit interface (AUI) cable to connect the 15 pin (DB 15) connector on the back side of the network adapter card to an external transceiver.
The AUI was developed to create a kind of medium independent interface between the PLS (physical layer) and MAU (Medium Attachment Unit).
A twisted pair Ethernet network (9 base T) connection uses an RJ-45 connector (RJ stands for Registered Jack). The RJ45 is a keyed connector can be inserted in only one way.
Configuration options
To configure a network adapter cards we generally have three configurable options that must be set properly for the network adapter card to function in our computer:
the interrupt request line (IRQ), the base I/O port address, and the base memory address.
Interrupt (IRQ)
When your network card sends a request to your computer, it uses an interrupt- an electronic signal sent to the computer's Central Processing Unit.
Each device in your computer must use a different interrupt request line (IRQ).
In most cases, you can use IRQ3 or IRQ5 for your network card. IRQ5 is the recommended setting. This is the default for most systems.
Base I/O Port
The base I/O port specifies a channel through which information is transferred between your computer's hardware and its CPU.
The port appears to the user as an address. Each hardware device must have a different base I/O port number.
The port numbers (in Hexadecimal format) 300 to31f are usually available for you to assign to your network card such as-
0000 to 000f - Direct Memory Access Controller
0060 to 0060 - Standard Keyboard
200 to 20f - Game port
230 to 23f - Bus mouse
03f6 to 03f6 - Hard Disk Controller
Base Memory Address
The base memory addresses shows or addressed a memory location in your computer's memory (RAM).
This location is used by the network card as a buffer area to store the incoming and outgoing data frames.
This setting is some times called the RAM start address often; the memory address for a network card is D800.
You must select a base memory address that is not already being used by another device.
There are five kinds of connecting devices; repeaters, Hubs Bridges and two and three-layer switches.
A Repeater is a device that regenerates the original bit pattern.
A Hub is actually a multiport-Repeater.
A bridge regenerates the signal it receives with filtering power that can check the destination address of a frame.
Network adapter cards move data from the local computer to the network and Vice-Versa.
Common connector types found on the back of network adapter cards include a co-axial BNC, a -15- pin attachment unit interface (AUI) connector for Thicknet and an RJ-45 connector for twisted - pair Ethernet.
Network adapter cards have configurable options that may need to be set .
these options include the interrupt (IRQ); the base I/O port specifies a channel through which information is transferred between your computer's hardware.
The base memory address defines the address of a location in your computer's memory.
NDIS stands for Network Device Interface Specification.
NDIS was developed as a standard for defining an interface for communication between the MAC layer and the protocol driver that reside on the network and transport layers of the Open System Interconnection (OSI) model.
Network Devices & Interface Specification
NDIS provides a very flexible environment for data exchange.
It defines the software Interface, called the NDIS interface, used by protocols drivers to communicate with the network adapter.
Advantages of a standardize Interface
1) Standards provide a general format so the protocol drivers only need to know how to issue and accept NDIS commands to communicate with the underlying MAC drivers and do not need to know the implementation details of any specific MAC driver.
Therefore any NDIS - compliant protocol driver can communicate with any NDIS - compliant MAC driver.
A process called binding is used to establish the initial communication channel between the protocol driver and the MAC driver.
The binding process allows a protocol driver and MAC driver to exchange information concerning their respective NDIS driver.
2) NDIS clearly defines which functions are performed by the protocol driver and which functions are performed by the MAC driver.
The network adapter manufacturer writes a small MAC driver that knows how to issue and accept NDIS commands at its top end and how to communicate with the network adapter at the bottom.
Interchangeable NDIS Drivers
Because NDIS has become a widely accepted device driver specification adapter drivers that conform to the NDIS standard have been able to work with a wide range of networking software that supports NDIS.
3) NDIS provides a way to bind multiple protocol and MAC drivers together so that you can use multiple network adapters at the same time.
NDIS uses a software driver called the protocol manager to bind the MAC and protocol drivers.
Multiple MAC and protocol drivers
The advantage of supporting multiple protocol drivers on a single network card is that the workstations can have simultaneous access to different types of network servers, each using a different protocol driver.
The Open Datalink Interface (ODI) specification was defined to simplify driver development and to provide support for multiple protocol drivers on a single network adapter.
ODI allows Novell Netware drivers to be written without concern for the protocol driver that will be used to communication with them.
Parts of ODI
1) Protocol Driver
The ODI version of the IPX/SPX, Protocol IPXODI.COM is used to communicate between the LSL and the applications.
2) Link Support Layer (LSL.COM)
The Link Support Layer provides a foundation for the MAC driver to communicate with multiple protocol drivers.
LSL.COM performs functions similar to the protocol manager in NDIS.
3) Multiple Link Interface Driver (MLID)
The (MLID) is the component that communicates between the adapter and the LSL.
This is the hardware dependent code created by the adapter card manufacturer. This code usually carries the name of the supported adapter.
The NDIS specification allows for a flexible environment of data exchange. This interface is used by protocol drivers to communicate with the network adapter.
Any NDIS - compliant MAC driver. NDIS clearly defines which functions are performed by the MAC driver together so that you can use multiple protocol drivers with multiple network adapters at the same time.
The Open Datalink Interface (ODI) specifies driver development and provides support for multiple protocols on a single new adapter.
The ODI interface is made up of three main pieces; the Link Support Layer (LSL), the Multiple Link Interface Driver (MLID) and the ODI version of the IPX/SPX protocol, IPXODI.COM.
Network Resource Management
In any network configuration, at least one of the computers on the network is configured to share resources.
The process of making a resource available to other computer is called sharing the resource.
On most networks, servers can enforce security so that users can only access network resources if they have the correct privileges.
This chapter discusses options for managing network resources and describes models of network security.
Server Based Networks
Dedicated server, Client server and peer to peer computing describes three types of network configurations that share resources.
A dedicated server is a type of network configuration in which specific computers take on the role of a server, the other computers on the network accessing the resources, means all the decisions are handled by a single machine.
In a peer to peer network configuration, each station can operate both as a client and as a server.
Dedicated server
To understand a server- based network, it is important to know the meaning of the term node in a network.
A node is a processing location that can be a PC or some other device such as a networked printer.
Usually, server based networks include many nodes and one or more servers, which control user access to the network's resources.
As described earlier, this central computer is known as the file server, network server, application server, or just the server.
Files and programs used by more than one user are often stored on the server.
A file server network is a fairly simple example of this kind of nodes and server network.
This arrangement gives each node access to the files on the server, but not necessarily to files on other nodes.
When a node needs information from the server, it requests the file containing the information. The server simply stores files and forwards them to nodes that request them.
One way to identify a Dedicated server network is the point at which network resources such as files are made available to users.
In this environment, users gain access to files, printers, and other network based objects by obtaining rights and permissions given through a centrally controlled server or groups of servers.
Users must log on to the network to gain access to its resources.
Client/Server Networks
One popular type of server-based network is the client/server network, where individual computers share the processing and storage workload with a central server.
This arrangement requires special software for the nodes and the server. It does not, however, require any specific type of network.
Server-based networks rely on special-purpose computers called servers that provide centralized repositories for network resources, and incorporate centralized security and access controls.
In comparison, peer-to-peer networks have no centralized security or maintenance functions.
There are a number of reasons to implement a server-based network, including centralized control over network resources through the use of network security and control through the server's configuration and setup.
From a hardware standpoint, server computers typically have faster CPUs, more memory, larger disk drives, and extra peripherals-such as tape drives in comparison with client machines.
Servers are also built to handle multiple requests for shared resources quickly and efficiently. Servers are usually dedicated to servicing network client requests.
In addition, physical security-access to the machine itself-is a key component of network security. Therefore, it's important for servers to be located in special, controlled-access rooms that are separate from general access office areas.
Server-based networks also provide centralized verification of user accounts and passwords. Windows NT, for example, uses the domain model concept for management of users, groups, and machines, and for control of network resource access.
Before users can access network resources, they must provide their name and password to a domain controller, a server that checks account names and passwords against a database of such information.
The domain controller will only allow valid account and password combinations to access certain resources.
Also, only network administrators can modify the security information in the domain controller's database.
This approach provides centralized security, and it permits you to manage resources with varying degrees of control, depending on their importance, sensitivity, or location. There are other negative aspects of server-based networks.
Centralization of resources and control does simplify access, control, and aggregation of resources, but it also introduces a single point of failure on networks.
If the server is not operational, a server-based network is not a network at all.
On networks with more than one server, loss of any single server means loss of all resources associated with that server.
Also, if the server that goes down is the only source of access control information for a certain set of users, those users can't access the network, either.
Here are some benefits of server-based networks:
. They provide centralized user accounts, security, and access controls, which simplifies network administration.
. More powerful equipment means more efficient access to network resources as well.
. Users only have to remember a single password for network login, which allows them to access all resources that they have permission to access.
Peer to Peer Networks
In a peer to peer network, all nodes on the network have equal relationships to all others, and all have similar types of software that support the sharing of resources.
In a typical peer to peer network, each node has access to at least some of the resources on all other nodes.
If they are set up correctly, many multi-user operating systems give users access to files on hard disks and to printers attached to other computers in the network.
Many client operating systems, such as Windows2000 professional, Windows Me, and the Macintosh OS, feature built in support for peer to peer networking.
This enables users to set up a simple peer to peer network using no other software than their PC's own operating systems.
Here are some benefits of peer-to-peer networks:
. They are easy to install and configure.
. Individual machines do not depend on a dedicated server.
. Users are able to control their own shared resources.
. This type of network is inexpensive to purchase and operate.
. You don't need any equipment or software other than an operating system.
. It is not necessary to have an employee act as a dedicated administrator to run the network.
. This type of network is well suited for networks with 9 or fewer users.
In any network configuration, at least one of the computers on the network is configured to share resources.
Dedicated server, Client server and peer to peer computing describes three types of network configurations that share resources.
A dedicated server is a type of network configuration in which specific computers take on the role of a server in the client/server network,
Individual computers share the processing and storage workload with a central server In a peer to peer network,
All nodes on the network have equal relationships to all others, and all have similar types of software that support the sharing of resources.



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