Question

What happens when the packets sent from a computer (at the application layer) reach various network nodes – local computers, remote computers, local attached routers/switches, remote routers/switches, hubs, etc.?

Please discuss what network nodes of different types know about the application file being transmitted (based on what information is provided in the header at the OSI layer at which that node operates) at each level of reassembly (i.e., viewing the frame packet only, reassembling frame packets to recreate the IP packet, reassembling the IP packets to recreate the TCP or UDP packets, and reassembly of the TCP/UDP packets to regenerate the full transmitted file) and how that information (provided by the data in the header) might be used by the node to provide network services.

Answer 1

step1:

Packet is the box hat contains data which can be communicated between source and destination over a network.

Basically every packet contains 3 sections which are

1.Header

2.Payload

3.Trailer

Header: contains some instruction which can include:

1.Destination Address (where does it go)

2.Source Address (from where it is coming)

3.Protocol : for ex:e-mail or streaming video

Payload: It is actual data that resides in packet

Trailer: contains some of bits which will inform about the device to which the packet was reached.

packet can reach to router or hub or switch.

step 2:

A router is a networking device that sends data packets to other networks, instead of just the local computers.

First of all router observes the destination address which is present in packet header and compare it with routing table to determine the packet's direction.

If the router has no explicit route to the destination, it sends the packet to the closest match it can find, which is often its own Internet gateway.

Routing table which may contain:

1.The IP address of the packet's final destination

2.Next hop: The IP address to which the packet is forwarded

eventually this router sends the packet to another router and so on until packet reaches its final destination.

ce does.

Network Hub:

A network hub is designed to connect computers.

When a hub receives a packet of data from a connected device, it sends that data packet to all other connected devices rather than to which device it should the send.

Network bandwidth is split between all of the connected computers.

So, the more computer that are connected, the less bandwidth that is available for each computer, which means slower connection speeds.

Switch:

A network switch also connects computers to each other, like a hub except the handling of packet data.

after receiving data packet, switch finds out what computer or device the packet is intended for and sends it to that computer only.

unlike hub, switch sends the packet to particular device rather than sending it to tha all devices connected to that network.

Bandwidths are not shared hence switch is faster than hub.

Network nodes of different types in ONS (Open Systems Interconnection) model:

it consists of 7 layers:

1.Physical layer:

The lowest layer of the OSI reference model is the physical layer.

It is responsible for the actual physical connection between the devices to enable the successful transmission of data.

Responsibilities of Physical layer:

1.It translates the data from one form to another so that it can be physically transmitted over a communication channel.

2.Bit synchronization for synchronous serial communications.

3. Physical layer specifies the way in which the different, devices/nodes are arranged in a network i.e. bus, star or mesh.

Ethernet works on this layer.

finally it sends data to the Data Link layer, which will put the frame back together.

2.Data Link Layer:

The data link layer gets the data from physical layer,sends the data from node to node..

Responsibilities of Data link layer:

1.it ensures data is free of error from physical layer

2.It converts the data into frames and adds physical addresses of sender and receiver in the header of each frame.

Data Link Layer is divided into two sub layers :

1.Logical Link Control: It controls how a computer on the network gets the access to data and transmit it.

2.Media Access Control: it controls the floe control and error checking.

Switch works in this layer.

3. Network Layer:

Network layer works for the transmission of data from one host to the other located in different networks.

Segment in Network layer is referred as Packet.

Responsibilities of Network layer:

1.it also finds the shortest route to transmit the packet from all available routes.

2.it routes the data from one network to another network.

3.error handling and packet sequencing(breaking the large packet into small packets) will be done here.

Router and different network protocols like TCP/IP works at this layer.

4.Transport Layer :

Transport layer provides services to application layer and takes services from network layer.

Transport layer receives the formatted data from the previous layers and performs Segmentation.

Data in the transport layer is referred to as Segments.

Responsibilities of Transport layer:

1.It responsible for transfer of complete message.

2.If any error is occurs, it provides acknowledgment regarding error.

3.If the message is transmitted successfully, it provides acknowledgment regarding successful transfer of data.

Transport Layer is called as Heart of OSI model.

5.Session Layer:

This layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security.

Responsibilities of session layer:

1.The layer allows the two processes to establish, use and terminate a connection.

2. The session layer allows two systems to start communication with each other in half-duplex or full-duplex.

6.Presentation Layer:

Presentation layer is also called the Translation layer.

1.data is that got from above layer is extracted and converted(ASCII to EBCDIC,JPEG) into specific format in order to transmit.

2.It compresses data.

3. it will translate the data like (encrypt and decrypt).

7.Application Layer: It is top layer of the ONS model.

It supports application and apps and end user processes.

These applications produce the data, which has to be transferred over the network

it is responsible for file transfer like email.

ex:Application – Browsers, Skype Messenger etc.

HTTP works at this layer.