CH1 Introduction to Computer Networking (Part 1)

         Question 1:-Explain the following terms:

Processing Delay

The time required to examine the packet’s header and determine where to direct the packet is part of the processing delay. The processing delay can also include other factors, such as the time needed to check for bit-level errors in the packet that occurred in transmitting the packet’s bits from the upstream node to router A. Processing delays in high-speed routers are typically on the order of microseconds or less. After this nodal processing, the router directs the packet to the queue that precedes the link to router B.

Queuing Delay

At the queue, the packet experiences a queuing delayas it waits to be transmitted onto the link. The length of the queuing delay of a specific packet will depend on the number of earlier-arriving packets that are queued and waiting for transmission onto the link. If the queue is empty and no other packet is currently being transmitted, then our packet’s queuing delay will be zero. On the other hand, if the traffic is heavy and many other packets are also waiting to be transmitted, the queuing delay will be long. We will see shortly that the number of packets that an arriving packet might expect to find is a function of the intensity and nature of the traffic arriving at the queue. Queuing delays can be on the order of microseconds to milliseconds in practice.

Transmission Delay

 Assuming that packets are transmitted in a first-come-first-served manner, as is common in packet-switched networks, our packet can be transmitted only after all the packets that have arrived before it have been transmitted. Denote the length of the packet by L bits, and denote the transmission rate of the link from router Ato router B by R bits/sec. For example, for a 10 Mbps Ethernet link, the rate is R = 10 Mbps; for a 100 Mbps Ethernet link, the rate is R = 100 Mbps. The transmission delay is L/R. This is the amount of time required to push (that is, transmit) all of the packet’s bits into the link. Transmission delays are typically on the order of microseconds to milliseconds in practice.

Propagation Delay

 Once a bit is pushed into the link, it needs to propagate to router B. The time required to propagate from the beginning of the link to router B is the propagation delay. The bit propagates at the propagation speed of the link. The propagation speed depends on the physical medium of the link (that is, fiber optics, twisted-pair copper wire, and so on) and is in the range of

2108 meters/sec to 3108 meters/sec

which is equal to, or a little less than, the speed of light. The propagation delay is the distance between two routers divided by the propagation speed. That is, the propagation delay is d/s, where d is the distance between router Aand router B and s is the propagation speed of the link. Once the last bit of the packet propagates to node B, it and all the preceding bits of the packet are stored in router B. The whole process then continues with router B now performing the forwarding. In wide-area networks, propagation delays are on the order of milliseconds.D T {\displa

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Question 2:-Draw The Layered architecture of  osi-refrance model and write at least two service provided by each layered of the model.

ISO/OSI Model in Communication Networks

There are n numbers of users who use computer network and are located over the world. So to ensure, national and worldwide data communication, systems must be developed which are compatible to communicate with each other. ISO has developed this. ISO stands for International organization of Standardization. This is called a model for Open System Interconnection (OSI) and is commonly known as OSI model.

The ISO-OSI model is a seven layer architecture. It defines seven layers or levels in a complete communication system.

Functions of Different Layers :

Layer 1: The Physical Layer :

1.     It is the lowest layer of the OSI Model.

2.     It activates, maintains and deactivates the physical connection.

3.     It is responsible for transmission and reception of the unstructured raw data over network.

4.     Voltages and data rates needed for transmission is defined in the physical layer.

5.     It converts the digital/analog bits into electrical signal or optical signals.

6.     Data encoding is also done in this layer.

 

Layer 2: Data Link Layer :

1.     Data link layer synchronizes the information which is to be transmitted over the physical layer.

2.     The main function of this layer is to make sure data transfer is error free from one node to another, over the physical layer.

3.     Transmitting and receiving data frames sequentially is managed by this layer.

4.     This layer sends and expects acknowledgements for frames received and sent respectively. Re-sending of non-acknowledgement received frames is also handled by this layer.

5.     This layer establishes a logical layer between two nodes and also manages the Frame traffic control over the network. It signals the transmitting node to stop, when the frame buffers are full.

Layer 3: The Network Layer :

1.     It routes the signal through different channels from one node to other.

2.     It acts as a network controller. It manages the Sub-net traffic.

3.     It decides by which route data should take.

4.     It divides the outgoing messages into packets and assembles the incoming packets into messages for higher levels.

Layer 4: Transport Layer :

1.     It decides if data transmission should be on parallel path or single path.

2.     Functions such as Multiplexing, Segmenting or Splitting on the data are done by this layer

3.     It receives messages from the Session layer above it, convert the message into smaller units and passes it on to the Network layer.

4.     Transport layer can be very complex, depending upon the network requirements.

Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer.

Layer 5: The Session Layer :

1.     Session layer manages and synchronize the conversation between two different applications.

2.     Transfer of data from source to destination session layer streams of data are marked and are re-synchronized properly, so that the ends of the messages are not cut prematurely and data loss is avoided.

Layer 6: The Presentation Layer :

1.     Presentation layer takes care that the data is sent in such a way that the receiver will understand the information (data) and will be able to use the data.

2.     While receiving the data, presentation layer transforms the data to be ready for the application layer.

3.     Languages(syntax) can be different of the two communicating systems. Under this condition presentation layer plays a role of translator.

4.     It performs Data compression, Data encryption, Data conversion etc.

Layer 7: Application Layer :

1.     It is the topmost layer.

2.     Transferring of files disturbing the results to the user is also done in this layer. Mail services, directory services, network resource etc are services provided by application layer.

3.     This layer mainly holds application programs to act upon the received and to be sent data.

Question 3 what are the five layers of internet protocol stack? what are the respectability of each layer?

5 Layers in Internet protocol stack:-

1.Application Layer

2.Transport Layer

3.Network Layer

4.Link Layer

5.Physical Layer

1.Application Layer

· Applications with appropriate requirement for user.

· It is reserved for network applications and their application protocols such as HTTP, SMTP, and FTP etc.

 · Its protocol uses transport layer protocols for establishing host-to-host connection.

2.Transport Layer

 · It is responsible for End-to-Communication

 · Transport layer transports messages from application layer between client and server of application

 · It uses two protocol for transporting messages: TCP and UDP.TCP provides reliable connection oriented services, while UDP provides connection-less service 

 

3.Network Layer

· Network Layer moves packets from one host to destination.

· It has two principal component: IP protocol:-It defines the datagrams and decide how the end system and router will work Routing protocols: these protocols decide the routing path between source and destination.

4.Link Layer

· It is responsible for link-level communication

· Link layer receives the data gram from network layer at each node and delivers it to next node, the next node passes the datagram to network layer. so This layer moves entire frames from one network element to adjacent one.

· The service provided by link layer is protocol dependent

5.Physical Layer

· It provides Physical media

· At each node, it moves individual bits of frames to next node.

  Question 4 What are the benefits of the laying approach in OSI model?

Dividing the network into the seven layers provides following advantage:

1.     It prevents changes in one layer from affecting other layers.

2.     It describes what functions occur at each layer of the model that encourages industry standardization.

3.     Dividing network communication process in smaller component makes software development, design, and troubleshooting easier.

4.     Standardization of network components allows multiple-vendor development.

5.     It allows different types of network hardware and software to communicate.

6.     Dividing network in layers make network administrators life easier. They can troubleshoot issue more quickly and effectually by looking in layer that is causing issue rather than finding it entire network. It also makes learning easier.

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