2.1 The Architecture of the Networks


Network Architecture is the complete framework of network organization.

1.1 Elements of a Network

(1) Devices:

  a. Sender and receiver devices
E.g. desktop, laptop, and IP phone.
An end device (sometimes is called host) refers to a device that is either the sender or the receiver
of a message on a network. An end user is a person or group using an end device.
Servers are hosts that are set up to store and share information with other hosts called clients

2.1 The Architecture of the Networks


  b. Intermediary devices connect each computer to the network or connect multiple individual
      networks to form an internetwork.

      Examples of intermediary devices:
Network access devices: connect devices to the network.
e.g. hubs, switches, and wireless access points.
Internetwork devices connect one network to one or more other networks.
e.g. router, and bridge.
Modems: connect device to servers and networks through telephone or cable.
Security devices to secure the network. e.g. firewall

  c. Network representation connects the devices to transmission medium.
Examples include.
Network interface card (NIC) provides the physical connection to the network at the
end device. NIC generates electrical signals to represent the bits and places the bits on
the transmission medium to travel over the network
Connectors (physical port) connect the transmission medium to network devices.

2.1 The Architecture of the Networks


(2) Messages: is the data to be communicated. Messages are converted into bits, binary-coded
digital signals. All messages are divided into smaller segment that can be easily transported
together overthe transmission medium.
The date is divided into segments and then send across the network.


Figure Segmentation

2.1 The Architecture of the Networks


(3) Transmission medium(network media) of network provides the channel over which the data
(signal) transmits fromthe sender to the receiver. There are three main types of transmission
medium of network, each type has different physical properties and uses different methods to
encode data. These types are:

       1. Copper uses electrical pluses encoding.
       2. Fiber-optic cable uses light pulses encoding.
       3. Wireless uses electromagnetic waves encoding.

Choosing network transmission medium depends mainly on
(1) the transmission medium distance;
(2) the cost of setup;
(3) the environment in which the transmission medium carry the signals;
(4) the bandwidth requirements for users

2.1 The Architecture of the Networks


(4) Protocol is a sequence of rules that govern data communications.
Rules govern every step of the process, from the way cables are designed to the way the
digital signals are sent.

1.2 Network Topology
1. The physical topology of a network refers to the way in which the network is laid out physically.
2. It is the geometric representation of the relationship of all links and linking devices to one another.
3. The logical topology defines how the devices in a network communicate across the physical topology.
4. The four basic topologies are : bus, star, ring, and mesh.
Bus Topology: A bus topology consists of a main run cable (called bus or backbone) acts
as a backbone to link all the devices in a network,
Star Topology: In star topology, each device has a dedicated point-to-point link only to
a central controller, such as hub or switch.
Ring Topology: In ring topology, each device has a dedicated point-to-point connection with only
the two devices on either side of it

2.1 The Architecture of the Networks


Mesh Topology: In mesh topology, every device has a dedicated point-to-point link to every
other device,
Hybrid Topology: A combination of the other topologies. Examples include
Star-Bus
Star-Ring


2.1 The Architecture of the Networks


(5) Both Star-Bus and Star-Ring are centered in a hub that contains the actual bus or ring

Topology Advantages Disadvantages
Bus
  1. Easy to connect a new device to the backbone cable.
  2. Needs less cable length than a star topology, i.e., less expensive.
  3. System is simple and reliable.
  1. If there is a break in the backbone cable, then entire network will shut down and so it may difficult to identify where is the problem.
  2. Has bad performance when the number of devices increases since the network traffic will be heavy. Therefore, it not used as a standalone solution in a large building.

2.1 The Architecture of the Networks


Star
  1. Easy to install.
  2. Adding or removing devices will not disrupt the network.
  3. Easy to detect faults.
  4. Centralized control.
  1. If the central device fails, then devices attached are disabled.
  2. Compared to the bus topology, a star network generally requires more cable.
  3. More expensive than bus topology because of the cost of the central device.

2.1 The Architecture of the Networks


Ring
  1. Equal access for all devices.
  2. Perform well under heavy traffic.
  1. The entire network will shut down if one device (or cable) fails.
  2. Difficult to troubleshoot.
  3. Adding or removing devices disrupt the network.
Mesh
  1. Provides increased redundancy and reliability.
  2. Ease of troubleshooting.
  1. Expensive to install because it uses a lot of links.

2.1 The Architecture of the Networks


The choice of topology depends on:

  1. Number and type of devices and transmission medium used.
  2. Cost of hardware (i.e., devices and transmission medium) and software supporting communication.
  3. Way the network is managed.

1.3 Network Criteria

The most important network criteria are
1. Performance:(also called Quality of service (QoS)) is the rate of transferring error free data.
It can be measured in many ways, including transit time and response time. Transit time is
the amount of time required for a message to travel from one device to another. Response
time is the elapsed time between an inquiry and a response. The performance of a
network depends on a number of factors:

2.1 The Architecture of the Networks


  1. Number of users: More users on a network lead to slower the network will run.
  2. Type of transmission medium: type of physical connection used to connect devices together.
  3. Capabilities of the connected hardware: faster device and transmission medium lead to faster the network will run.
  4. Efficiency of the software: how well is the network operating system and applications written?
  5. Distances between devices on the network.

2. Reliability:is the measure of how often a network is useable. It can be represented as a probability
that the first failure occurs at a certain time.
3. Fault tolerancemeans that the network will continue to function normally even when some
of the components (hardware or software) of the network fail.
4. Scalabilitydescribes the network's ability to grow and react to future changes. A scalable network
can accept new users and equipment without having to start over on the design.
5. Securityis the process of protecting data in computer network from unauthorized access, use,
disclosure, destruction, modification, or disruption