UDP /TCP, Congestion Control, Presentation Aspects
User Datagram Protocol (UDP)
It provides connectionless service and end-to-end delivery of transmission.
It is an unreliable protocol as it discovers the errors but not specify the error.
User Datagram Protocol discovers the error, and ICMP protocol reports the error to the sender that user datagram has been damaged.
UDP consists of the following fields:
1. Source port address: The source port address is the address of the application
program that has created the message.
2. Destination port address: The destination port address is the address of the
application program that receives the message.
3. Total length: It defines the total number of bytes of the user datagram in bytes.
4. Checksum: The checksum is a 16-bit field used in error detection.
Transmission Control Protocol (TCP)
It provides a full transport layer services to applications.
It creates a virtual circuit between the sender and receiver, and it is active for the duration of the transmission.
TCP is a reliable protocol as it detects the error and retransmits the damaged frames. Therefore, it ensures all the segments must be received and acknowledged before the transmission is considered to be completed and a virtual circuit is discarded.
At the sending end, TCP divides the whole message into smaller units known as segment, and each segment contains a sequence number which is required for reordering the frames to form an original message.
At the receiving end, TCP collects all the segments and reorders them based on sequence numbers.
CONGESTION CONTROL
What is Congestion?
A state occurring in network layer when the message traffic is so heavy that it slows down network response time.
Effects of Congestion
• As delay increases, performance decreases.
• If delay increases, retransmission occurs, making situation worse.
Congestion Control Algorithms
Congestion Control is a mechanism that controls the entry of data packets into the network, enabling a better use of a shared network infrastructure and avoiding congestive collapse.
There are two congestion control algorithm which are as follows:
1. Leaky Bucket Algorithm
2. Token Bucket Algorithm
Leaky Bucket Algorithm
• The leaky bucket algorithm discovers its use in the context of network traffic shaping or rate-limiting.
• A leaky bucket execution and a token bucket execution are predominantly used for traffic shaping algorithms.
• This algorithm is used to control the rate at which traffic is sent to the network and shape the burst traffic to a steady traffic stream.
• The disadvantages compared with the leaky-bucket algorithm are the inefficient use of available network resources.
• The large area of network resources such as bandwidth is not being used effectively.
Example:
Imagine a bucket with a small hole in the bottom. No matter at what rate water enters the bucket, the outflow is at constant rate. When the bucket is full with water additional water entering spills over the sides and is lost.
Similarly, each network interface contains a leaky bucket and the following steps are involved in leaky bucket algorithm:
1. When host wants to send packet, packet is thrown into the bucket.
2. The bucket leaks at a constant rate, meaning the network interface transmits packets at a constant rate.
3. Bursty traffic is converted to a uniform traffic by the leaky bucket.
4. In practice the bucket is a finite queue that outputs at a finite rate.
Token Bucket Algorithm
• The leaky bucket algorithm has a rigid output design at an average rate independent of the bursty traffic.
• In some applications, when large bursts arrive, the output is allowed to speed up. This calls for a more flexible algorithm, preferably one that never loses information. Therefore, a token bucket algorithm finds its uses in network traffic shaping or rate-limiting.
• It is a control algorithm that indicates when traffic should be sent. This order comes based on the display of tokens in the bucket.
• The bucket contains tokens. Each of the tokens defines a packet of predetermined size. Tokens in the bucket are deleted for the ability to share a packet.
• When tokens are shown, a flow to transmit traffic appears in the display of tokens.
• No token means no flow sends its packets. Hence, a flow transfers traffic up to its peak burst rate in good tokens in the bucket.
The leaky bucket algorithm enforces output pattern at the average rate, no matter how busty the traffic is. So in order to deal with the bursty traffic we need a flexible algorithm so that the data is not lost.
One such algorithm is token bucket algorithm.
Steps of this algorithm can be described as follows:
1. In regular intervals tokens are thrown into the bucket.
2. The bucket has a maximum capacity.
3. If there is a ready packet, a token is removed from the bucket, and the packet is sent.
4. If there is no token in the bucket, the packet cannot be sent.
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