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OSI Model
OSI stands for Open Systems Interconnection. It has 7 layers Physical layer, Data Link layer, Network layer, Transport layer, Session layer, Presentation layer, and Application layer. Each layer performs its task independently. It was developed in 1984 by the International Organization for Standardization (ISO).
OSI Model
Advantages
Both connection-oriented services and connectionless services are supported. It is quite flexible. All the layers work independently.
Disadvantages
Setting up a model is a challenging task.
Sometimes, it becomes difficult to fit a new protocol into this model. It is only used as a reference model.
TCP/IP Model
TCP/IP stands for Transmission Control Protocol/Internet Protocol. It has 4 layers named as Physical layer, Network layer, Transport layer, and Application layer. It also can be used as a communications protocol in a private computer network. It was designed by Vint Cerf and Bob Kahn in the 1970s.
Advantages
Many Routing protocols are supported. It is highly scalable and uses a client-server architecture. It is lightweight.
Disadvantages
Little difficult to set up. Delivery of packets is not guaranteed by the transport layer. Vulnerable to a synchronization attack.
Similarities between OSI Model and TCP/IP Model
OSI and TCP/IP both are logical models. One of the main similarities between the OSI and TCP/IP models is that they both describe how information is transmitted between two devices across a network. Both models define a set of layers. Each layer performs a specific set of functions to enable the transmission of data. Another similarity between the two models is that they both use the concept of encapsulation, in which data is packaged into a series of headers and trailers
dedicated to the communication for the duration of the session, and no other devices can use it
while the session is in progress. Circuit switching is commonly used in voice communication and
some types of data communication.
Advantages of Circuit Switching:
Guaranteed bandwidth: Circuit switching provides a dedicated path for communication, ensuring that bandwidth is guaranteed for the duration of the call. Low latency: Circuit switching provides low latency because the path is predetermined, and there is no need to establish a connection for each packet. Predictable performance: Circuit switching provides predictable performance because the bandwidth is reserved, and there is no competition for resources. Suitable for real-time communication: Circuit switching is suitable for real-time communication, such as voice and video, because it provides low latency and predictable performance.
Disadvantages of Circuit Switching:
Inefficient use of bandwidth: Circuit switching is inefficient because the bandwidth is reserved for the entire duration of the call, even when no data is being transmitted. Limited scalability: Circuit switching is limited in its scalability because the number of circuits that can be established is finite, which can limit the number of simultaneous calls that can be made. High cost: Circuit switching is expensive because it requires dedicated resources, such as hardware and bandwidth, for the duration of the call.
Packet Switching
Packet switching is a communication method where data is divided into smaller units called
packets and transmitted over the network. Each packet contains the source and destination
addresses, as well as other information needed for routing. The packets may take different paths
to reach their destination, and they may be transmitted out of order or delayed due to network
congestion.
Advantages of Packet Switching:
Efficient use of bandwidth: Packet switching is efficient because bandwidth is shared among multiple users, and resources are allocated only when data needs to be transmitted. Flexible: Packet switching is flexible and can handle a wide range of data rates and packet sizes. Scalable: Packet switching is highly scalable and can handle large amounts of traffic on a network. Lower cost: Packet switching is less expensive than circuit switching because resources are shared among multiple users.
Disadvantages of Packet Switching:
Higher latency: Packet switching has higher latency than circuit switching because packets must be routed through multiple nodes, which can cause delay. Limited QoS: Packet switching provides limited QoS guarantees, meaning that different types of traffic may be treated equally. Packet loss: Packet switching can result in packet loss due to congestion on the network or errors in transmission.
Unsuitable for real-time communication: Packet switching is not suitable for real-time communication, such as voice and video, because of the potential for latency and packet loss.
Similarities:
Both methods involve the transmission of data over a network. Both methods use a physical layer of the OSI model for transmission of data. Both methods can be used to transmit voice, video, and data. Both methods can be used in the same network infrastructure. Both methods can be used for both wired and wireless networks.
Difference between Circuit Switching and Packet Switching:
Circuit Switching Packet Switching In-circuit switching has there are 3 phases: i) Connection Establishment. ii) Data Transfer. iii) Connection Released. In Packet switching directly data transfer takes place. In-circuit switching, each data unit knows the entire path address which is provided by the source. In Packet switching, each data unit just knows the final destination address intermediate path is decided by the routers. In-Circuit switching, data is processed at the source system only In Packet switching, data is processed at all intermediate nodes including the source system. The delay between data units in circuit switching is uniform. The delay between data units in packet switching is not uniform. Resource reservation is the feature of circuit switching because the path is fixed for data transmission. There is no resource reservation because bandwidth is shared among users. Circuit switching is more reliable. Packet switching is less reliable. Wastage of resources is more in Circuit Switching Less wastage of resources as compared to Circuit Switching It is not a store and forward technique. It is a store and forward technique.
Circuit Switching Packet Switching protocols for delivery. 3
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Stop and Wait ARQ
Characteristics
Used in Connection-oriented communication. It offers error and flows control It is used in Data Link and Transport Layers Stop and Wait for ARQ mainly implements the Sliding Window Protocol concept with Window Size 1
Useful Terms:
Propagation Delay: Amount of time taken by a packet to make a physical journey from one router to another router.
Propagation Delay = (Distance between routers) / (Velocity of propagation)
RoundTripTime ( RTT ) = Amount of time taken by a packet to reach the receiver + Time taken by the Acknowledgement to reach the sender TimeOut ( TO ) = 2* RTT Time To Live ( TTL ) = 2* TimeOut. (Maximum TTL is 255 seconds)
Simple Stop and Wait
Sender:
Rule 1) Send one data packet at a time.
Rule 2) Send the next packet only after receiving acknowledgement for the previous.
Receiver:
Rule 1) Send acknowledgement after receiving and consuming a data packet.
Rule 2) After consuming packet acknowledgement need to be sent (Flow Control)
Problems :
1. Lost Data
3. Delayed Acknowledgement/Data: After a timeout on the sender side, a long-delayed
acknowledgement might be wrongly considered as acknowledgement of some other recent
packet.
Stop and Wait for ARQ (Automatic Repeat Request)
The above 3 problems are resolved by Stop and Wait for ARQ (Automatic Repeat Request) that
does both error control and flow control.
1. Time Out:
2. Sequence Number (Data)
Low Efficiency: Stop and Wait ARQ has low efficiency as it requires the sender to wait for an acknowledgment from the receiver before sending the next data packet. This results in a low data transmission rate, especially for large data sets. High Latency: Stop and Wait ARQ introduces additional latency in the transmission of data, as the sender must wait for an acknowledgment before sending the next packet. This can be a problem for real-time applications such as video streaming or online gaming. Limited Bandwidth Utilization: Stop and Wait ARQ does not utilize the available bandwidth efficiently, as the sender can transmit only one data packet at a time. This results in underutilization of the channel, which can be a problem in situations where the available bandwidth is limited. Limited Error Recovery: Stop and Wait ARQ has limited error recovery capabilities. If a data packet is lost or corrupted, the sender must retransmit the entire packet, which can be time- consuming and can result in further delays. Vulnerable to Channel Noise: Stop and Wait ARQ is vulnerable to channel noise, which can cause errors in the transmitted data. This can result in frequent retransmissions and can impact the overall efficiency of the protocol.
