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NETWORK ARCHITECTURE & NETWORK TOPOLOGY

NETWORK ARCHITECTURE  & NETWORK TOPOLOGY

1. The way in which computers participate in a network with each other is called network architecture. 

2. The type of architecture chosen by an organisation depends on geographical location, number of users, the requirements of specific application packages, level of technical support available, existing systems, and of course cost etc 
Type of Network Architecture:- 
1. Peer to Peer Network 
2. Clint Server Network 
3. Hybrid Network

1. Peer to Peer Network 
Peer to peer is an approach to computer networking where all computers share equivalent responsibility for processing data differs from client-server networking, where certain devices have responsibility for providing or "serving" data and other devices consume or otherwise act as "clients" of those servers. Some main features of the Peer to Peer network 
a) Resources shared in a de
b) Shared resources include files and printers
c) Should be used where nodes 
d) Files are not stored centrally

e) Allows easy node
f) Support is usually part of OS
g) Sharing of files is responsibility of each participant
h) Participants form a ‘Workgroup’
i) Workgroup is assigned a name 
j) Peer to peer is best where Employees have little or no network experience
k) Peer to peer should be used with less than 15 nodes
l) Peer to peer does not require a server
m) It has very Little concern about security
n) Easy to configure
o) No requirement for server hardware/software
p) Users can manage their own resources
q) No need for a network administrator
r) Reduces total cost  

Disadvantages 
a) Provide a limited number of connections
b) May slow performance of nodes
c) Do not allow central management 
d) Do not have a central store of files 
e) Users responsible for managing own resources 
f) Offers very poor security 
g) Uses share-level security 
h) Allows password protection of resources 
i) Options are: 
j) Give access to all 
k) Assign a single password and give to all users who require access to the resource 
l) With share-level security a password cannot be assigned to a single individual – it 
assigned to the resource (soon everyone knows what the password is). 
 
2. Clint Server Architecture 
Clint Server network Architecture is a network in which there may be one or more servers for different purpose and clients to access the resources of server or the service provided by the different servers. The servers create the policy and client follows them. This type of architecture is most preferred architecture as it gives a centralized management of all the resources like clients, files, folders, printers, mail etc. The all administrative work like management of clients, assigning them various rights, assigning permission on folders, updating of computers, managements of computers all can be done from a central place thereby gives full control on the network. Some of the features of the client server architecture are as follows 

 Features:- 
1. Most common architecture 
2. Sometimes ‘next step’ after an organisation has outgrown peer-to-peer 
3. Centralised model for data storage, security, running applications and network administration 
4. Provide services such as printing, email etc 
5. Allow a high level of security to be implemented 
6. Can be centrally managed 

 Advantages:- 
1. Inexpensive but powerful way of managing the network 
2. Open systems means it can be expended as per requirements
3. Grows easily 
4. Individual client operating systems are required

 Disadvantages:- 
1. Maintenance nightmares 
2. Support tools lacking 
3. Retraining required 

Multi server Networks:- 
    A network in which more than one servers (physically) are used is called a multi server Networks. Whether a network will have single server or multi server depends on various factor like total no of clients, volume of traffic, type of role, server has to perform etc however a multi server network always gives more stability to the network. Some of the features of the multi server network are as follows - 

1. Each server provides a different service (or duplicates to provide redundancy) 
2. Typically 50 – 500 users 
3. Improves performance 
4. Servers optimized for their service 
5. Much more complex than single-server 
6. Supports thousands of users across company’s geographical locations 
7. May involve hundreds of servers 
8. Each location looks like a simple client-server system, but is linked to the corporate network 
9. A WAN extends the client-server model across many LANs (involving several servers to satisfy a request) 

Hybrid Networks:- 
    A LAN with a mixture of topologies and access methods is known as hybrid Networks. For example, a network that includes both a token ring and a CSMA/CD bus or A computer network made up of more than one platform or operating system or A network composed of both public and private facilities are known as Hybrid Network. Some of the features are as follows 1. Incorporates the best features of workgroups in Peer-to-Peer with the performance, reliability and security of server-based systems. 
2. Allows access to central resources, but also allows users to function at the Peer-to-Peer level 
3. Users do not have to log in to a central server 
4. Client-server apps are still centrally managed 
5. Users can assign local access to their resources 
6. Workgroups can manage resources without need for assistance from network administrator 
7. Network access can become burdensome 
8. Users required to remember multiple passwords 
9. Files can be duplicated. 
10. Files stored on the workstation are not backed up.

NETWORK TOPOLOGY
The actual layout of a network and its media is called its physical topology and the way in which the data access the medium and transmits packets is the logical topology. 
    A glance at a network is not always revealing the type of network topology it actually has. Cables emerging from a Hub do not make it necessarily a Star Topology – it may actually be a bus or a ring. Choice of Logical Topology affects the Physical Topology – and vice versa. Design carefully – it may be difficult to change part way through the installation. Choice determines cable installation, network devices, network connections, protocols (and where to drill holes in the building!) 
Type of Physical Topologies 
1. Bus 
2. Ring 
3. Star 
4. Extended Star 
5. Mesh 
6. Hybrid 
Factors Affecting choice of a Topology 
1. Cost 
2. Scalability 
3. Bandwidth Capacity 
4. Ease of Installation 
5. Ease of fault finding and maintenance

BUS Topology:- 
A network topology in which nodes are connected to a single cable with terminators at each end or A network architecture in which all the nodes are connected to a shared cable or A LAN architecture in which all the devices are connected to a bus, or one communication line. Bus topology does not have a central point. 
 Some main features are as follows :- 
1. Network maintained by a single cable 
2. Cable segment must end with a terminator 
3. Uses thin coaxial cable (backbones will be thick coaxial cable) 
4. Extra stations can be added in a daisy chain manner
5. Standard is IEEE 802.3 
6. Thin Ethernet (10Base2) has a maximum segment length of 200m 
7. Max no. of connections is 30 devices 
8. Four repeaters may be used to a total cable length of 1000m 
9. Max no. of nodes is 150 
10. Thick Ethernet (10Base5) used for backbones 
11. Limited to 500m 
12. Max of 100 nodes per segment 
13. Total of four repeaters , 2500m, with a total of 488 nodes is permissible 

Advantages 
1. Inexpensive to install 
2. Easy to add stations 
3. Use less cable than other topologies 
4. Works well for small networks

Disadvantages 
1. No longer recommended 
2. Backbone breaks, whole network down 
3. Limited no of devices can be attached 
4. Difficult to isolate problems 
5. Sharing same cable slows response rates

Ring Topology 
    A system of local area networking in which each node or station is connected to two others, ultimately forming a loop is called a ring topology. Data are passed in one direction only, being received by each node and then transferred to the next node or A LAN topology that connects each node in a ring to create a circle. Each node acts as a repeater to regenerate the signal. Some of the features of Ring Topology are:- 
1. No beginning or end (a ring in fact!!) 
2. All devices have equality for access of media 
3. Single ring – data travels in one direction only. 
4. Each device has to wait its turn to transmit 
5. Most common type is Token Ring (IEEE 802.5)
6. A token contains the data, reaches the destination, data extracted, acknowledgement of receipt sent back to transmitting device, removed, empty token passed on for another device to use. 
This is the main principle how a token Ring works. 

Advantages 
Data packets travel at great speed 
1. No collisions 
2. Easier to fault find 
3. No terminators required 

Disadvantages 
1. Requires more cable than a bus 
2. A break in the ring will bring it down 
3. Not as common as the bus – less devices available 

Star Topology 
    A network topology in which nodes are connected to a common device such as hub or concentrator is called a star topology or A physical network topology in which all nodes are connected to a central connectivity device (e.g. a hub or switch).The main features of a star topology is as follows 
1. It is Like the spokes of a wheel (without the symmetry) 
2. Centre point is a Hub or switch 
3. Segments meet at the Hub 
4. Each device needs its own cable to the Hub 
5. Predominant type of topology 
6. Easy to maintain and expand 
7. Easy to add devices as the network expands 
8. One cable failure does not bring down the entire network (resilience) 
9. Hub provides centralised management 
10. Easy to find device and cable problems 
11. Can be upgraded to faster speeds 
12. Lots of support as it is the most used 

Disadvantages 
1. A star network requires more cable than a ring or bus network 
2. Failure of the central hub can bring down the entire network 
3. Costs are higher (installation and equipment) than for most bus networks

Extended Star Topology
A Star Network which has been expanded to include when more than one Hub/Switch is connected to form a topology same is known as topology. 

Mesh Topology (Web) 
    This is a topology in which devices are connected with many redundant (alternative) 
interconnections between network nodes. In a true mesh topology every node has a connection to 
every other node directly as well as indirectly to meet any unexpected failover approach. Some 
features of the mesh topology is as follows
1. Not common on LANs
2. Most often used in WANs to interconnect LANS
3. Each node is connected to every other node
4. Allows communication to continue in the event of a break in any one connection
5. It is “Fault Tolerant”
6. Expensive 
7. Difficult to install 
8. Difficult to manage
9. Difficult to troubleshoot
10.Improves Fault Tolerance

Hybrid Topology 
A network topology that uses two or more network topologies is known as Hybrid Topologies.
Features:- 
1. Old networks are updated and replaced, leaving older segments
2. Hybrid Topology 
3. Commonly Star-Bus or Star
4. Star-Ring uses a MAU (Multi station Access Unit)

Logical Topologies 
    Also called signal topology. The logical topology is the way in which the signals act on the network media or the way in which the data passes through the network from one device to the next without regard to the physical interconnection of the devices. 
    Logical topologies are bound to the network protocols that direct how the data moves across a 
network. The Ethernet protocol is a common logical bus topology protocol. IBM's Token Ring is a 
common logical ring topology protocol. 
A network's logical topology is not necessarily the same as its physical topology. For example, twisted pair Ethernet is a logical bus topology in a physical star topology layout. While IBM's Token Ring is a logical ring topology, it is physically set up in a star topology. A Physical Star topology could be either a Bus or Ring in logical terms i.e in terms of data passing method. To further understand the same we can say that data packet inside a network will either be passed to all nodes in simultaneously like a BUS topology or one by one ,if it is transmitted simultaneously it is called logical BUS and if it is transmitted one by one to all nodes it is called logical ring.(for more better understanding students can refer working of Ethernet and token ring in subsequent chapters) 
There are two types of logical topology 
1. Logical BUS 
2. Logical Ring
 
Logical Bus
Features 
1. Modern Ethernet networks are Star Topologies (physically) 
2. The Hub is at the centre, and defines a Star Topology 
3. The Hub itself uses a Logical Bus Topology internally, to transmit data to all segments 

Advantages 
1. A single node failure does not bring the network down 
2. Most widely implemented topology 
3. Network can be added to or changed without affecting other stations
Disadvantages 
1. Collisions can occur easily 
2. Only one device can access the network media at a time 

Logical Ring 
Features 
1. Data in a Star Topology can transmit data in a Ring
2. The MAU (Multi station Access Unit) looks like an ordinary Hub, but data is passed internally using a logical ring 
3. It is superior to a Logical Bus Hub

Advantages:- 
1. The amount of data that can be carried in a single message is greater than on a 
logical bus 
2. There are no collisions 

Disadvantages:- 
1. A broken ring will stop all transmissions 
2. A device must wait for an empty token to be able to transmit


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