Packet switching | Packet switched network | Switching technology | TechTerms

Summary

This script explores the concept of network applications and packet switching, detailing how data is divided into packets and transmitted over the internet via routers. It explains the process of Store-and-Forward transmission, end-to-end delay calculations, and the potential for queuing delays and packet loss. The role of IP addresses and forwarding tables in directing packets to their destination is also highlighted, along with the automatic updating of forwarding tables through routing protocols, providing a comprehensive overview of data transmission in computer networks.

Takeaways

• 🌐 Network applications like Google Chrome, Skype, and Outlook require an Internet connection to operate and exchange data such as images, audio, video, or text files.
• 📦 Data is divided into small units called packets, typically 1 MB in size, for transmission over the Internet.
• 🔄 Packet switching is the method where data packets are transmitted over a network of packet switches, which can be routers or link-layer switches.
• 🚀 Store-and-Forward transmission involves storing the entire packet at the switch before forwarding it to the next destination.
• ⏱️ Propagation delay is the time it takes for a bit to travel from the sender to the receiver, which is 3 ms in the example provided.
• 🕒 The total end-to-end delay for transmitting a packet includes the time taken to send the packet and any additional delays due to the number of links.
• 🔗 The delay for receiving the first packet is 2L/R seconds, and for multiple packets, the formula is (N+(P-1))L/R seconds, where N is the number of links and P is the number of packets.
• 📈 Queuing delay occurs when packets wait in a buffer due to the router's transmission rate being exceeded or other packets being sent.
• 🚫 Packet loss happens when the buffer is full, and incoming packets cannot be stored, leading to data being dropped.
• 📍 IP addresses are unique identifiers for devices on the Internet, and routers use forwarding tables to determine where to send incoming packets.
• 🔄 Forwarding tables are updated automatically through routing protocols to ensure efficient packet routing.

Q & A

What are network applications and why do they require the Internet?

Network applications, such as Google Chrome, Skype, and Outlook, are programs that rely on the Internet to function. They require the Internet because they need to send data, such as images, audio, video, or text files, between end systems or hosts over the network.

What is the purpose of dividing data into packets in network applications?

Data is divided into packets to efficiently manage the transmission over the network. This method allows for the data to be sent in small, manageable units, improving the overall network performance and reliability.

Can you explain the concept of packet switching?

Packet switching is a method of data transmission over a network where data is broken down into small packets. These packets are then routed through a network of packet switches, such as routers or link-layer switches, to reach their destination.

What is Store-and-Forward transmission and why is it used?

Store-and-Forward transmission is a technique where a packet switch, such as a router, must receive the entire packet before it can forward it to the next destination. It is used to ensure that the integrity of the data is maintained during transmission.

How is the propagation delay defined and what factors affect it?

Propagation delay is the time it takes for a signal to travel from the sender to the receiver over a communication link. It is affected by the distance the signal travels and the speed of light in the medium.

What is the formula for calculating the total end-to-end delay for transmitting packets?

The total end-to-end delay for transmitting packets is calculated using the formula {N+(P-1)}L/R, where N is the number of links, P is the number of packets, L is the number of bits in each packet, and R is the transmission rate in bits per second.

What causes queuing delay and how does it affect packet transmission?

Queuing delay occurs when packets must wait in a buffer at a router before being transmitted, due to the router being busy with other transmissions. It affects packet transmission by introducing additional waiting time, which can lead to delays in data delivery.

What is packet loss and how does it occur in a network?

Packet loss occurs when a packet is dropped either because the buffer in the router is full or due to other network issues. It can disrupt the flow of data and lead to incomplete or corrupted transmissions.

How do routers determine the correct communication link to forward a packet?

Routers use forwarding tables to determine the correct communication link to forward a packet. These tables map the destination address prefix to the router's link interface, allowing the router to match the packet's destination address and forward it appropriately.

What is the role of IP addresses in packet switching?

IP addresses are unique identifiers for devices on the Internet. They are used in packet switching to maintain the destination address in the packet header, which helps routers determine the correct path for the packet to reach its destination.

How are forwarding tables in routers updated?

Forwarding tables in routers are updated automatically with the help of routing protocols. These protocols enable routers to exchange information about network topology and update their tables accordingly to ensure efficient routing of packets.

Outlines

00:00

🌐 Understanding Network Applications and Packet Switching

This paragraph explains the concept of network applications such as Google Chrome, Skype, and Outlook that rely on the Internet. It delves into the process of packet switching, where data is divided into packets and transmitted over a network of packet switches, which can be routers or link-layer switches. The paragraph discusses the Store-and-Forward transmission method, where packets are stored before being forwarded, and introduces the concepts of propagation delay, end-to-end delay, and queuing delay. It also touches on packet loss due to buffer limitations and the impact of transmission rates on queuing. The summary highlights the technical aspects of data transmission in network applications and the challenges faced in packet switching.

05:01

🔍 The Role of Forwarding Tables and Routing Protocols

The second paragraph explores how packet switches determine the appropriate communication link for forwarding packets. It explains the use of unique IP addresses and forwarding tables within routers to direct packets to their destinations. The paragraph uses an analogy of a person asking for directions to illustrate how packets navigate through a network with the help of routers and their forwarding tables. It concludes with an explanation of how forwarding tables are automatically updated using routing protocols, ensuring efficient data transmission across the Internet.

Keywords

💡Network Applications

Network applications refer to software programs like Google Chrome, Skype, and Outlook that require an Internet connection to operate. These applications facilitate various online activities such as browsing, communication, and email management. In the script, network applications are essential for understanding how data is transmitted over the Internet, highlighting their role in modern digital communication.

💡Packets

Packets are small units of data that result from the division of larger files into manageable pieces for efficient transmission over a network. The script explains that instead of sending an entire file at once, it is broken down into packets, typically 1 MB in size, to ensure smooth data transfer. This concept is central to the functioning of packet switching networks.

💡Packet Switching

Packet switching is a method of data transmission where data is sent in the form of packets over a network of interconnected devices, such as routers or switches. The script describes this process as fundamental to how information travels across the Internet, with packets moving from one switch to another until they reach their destination.

💡Store-and-Forward Transmission

Store-and-Forward transmission is a technique where a packet switch, such as a router, receives an entire packet before forwarding it to the next destination. The script illustrates this concept by explaining that the router must store all bits of a packet before it can begin transmission to the next host, ensuring reliable data transfer.

💡Propagation Delay

Propagation delay is the time it takes for a signal to travel from the sender to the receiver over a communication medium. The script uses the example of a bit sent from host A to the router, taking 3 milliseconds to arrive, to explain how propagation delay affects the overall transmission time in a network.

💡End-to-End Delay

End-to-End delay refers to the total time taken for a packet to travel from the source host to the destination host in a network. The script calculates this delay by considering the time to send a packet and the number of links in the path, using the formula NL/R, where N is the number of links and L/R is the time to send one packet.

💡Queuing Delay

Queuing delay occurs when packets must wait in a buffer before being transmitted due to network congestion or other packets being sent. The script explains that if host A's transmission rate exceeds the router's capacity, packets will experience queuing delay, waiting in line to be forwarded.

💡Packet Loss

Packet loss happens when packets are dropped due to a full buffer in the router or other network issues. The script describes packet loss as a potential problem in data transmission, where either incoming packets or those already in the queue are discarded when the buffer is full.

💡Forwarding Table

A forwarding table is a data structure within a router that maps destination IP addresses to specific outbound links. The script explains that routers use these tables to determine the correct path for forwarding packets towards their destination, based on the network address contained in the packet header.

💡IP Address

An IP address is a unique identifier assigned to devices on a network, allowing them to communicate with each other. The script mentions IP addresses as essential for routing packets, with examples like 192.168.1.2, to illustrate how routers use these addresses to forward packets to the correct destination.

💡Routing Protocols

Routing protocols are sets of rules that enable routers to dynamically update their forwarding tables to reflect changes in the network. The script explains that these protocols help routers to automatically update their tables, ensuring efficient packet routing even as network conditions change.

Highlights

Network applications like Google Chrome, Skype, and Outlook require Internet connectivity to function.

Data in network applications is sent over the Internet in small units called packets.

Packet switching is the method of data transmission over a network of packet switches.

Store-and-Forward transmission involves storing all bits of a packet before forwarding it.

Propagation delay is the time it takes for bits to travel from the sender to the router.

The total end-to-end delay for packet transmission can be calculated using the formula 2L/R seconds for the first packet.

Queuing delay occurs when packets wait in the router's buffer for transmission.

Packet loss happens when the router's buffer is full and incoming packets cannot be stored.

Forwarding tables in routers determine the appropriate communication link for forwarding packets.

IP addresses are unique identifiers for devices on the Internet.

Routers use forwarding tables to match the destination address prefix and forward packets accordingly.

Routing protocols automatically update forwarding tables in routers.

An analogy compares packet switching to asking for directions when traveling to a new place.

The process of data packets reaching their destination is similar to asking for directions from multiple people.

End-to-end delay, queuing delay, and packet loss are important considerations in packet switching networks.

The transmission rate of the sender and the router's capacity can impact queuing delay.

Transcripts

The applications, like Google chrome, Skype, Outlook, that need Internet to function are

called network applications.

In a network application, the end systems or hosts need to send data to each other over

the Internet.

The data can be an image, audio, video or a text file.

Instead of sending the whole file at once, it is divided into small data units at the

source, say 1 MB, and are called packets.

These packets, then, move over a network of packet switches to reach the destination host.

Packet switches can be routers or link-layer switches.

This method of data transmission over a network of packet switches in the form of small data

units or packets is called packet switching.

Consider two hosts connected to each other via a network router.

Host A wants to send an image to host B. So host A divides the image file into three packets

each having L-bits and starts sending a packet at a rate of R bits/sec.

Therefore, the total time required to transmit L-bits or one packet is L/R seconds.

So at the time, less than L/R second, the router has received only a portion of first

packet P1.

By this time, the router cannot forward the received bits of packet P1 to host B. It first

needs to store all bits of the packet before it can begin the packet transmission.

It is called Store-and-Forward transmission.

Let us assume that host A sends a bit to the router at time, t=0 sec.

It reaches the router after 3 ms.

So, the delay in receiving the bits at the router is 3 ms.

It is called propagation delay.

If the propagation delay is zero, then the first bit is available to the router at the

same time host A transmits it.

In the current case, the host A completes sending the first packet at time L/R sec.

So the router receives, store, and start sending the packet P1 to the host B at the same time

L/R sec.

Now, the router is also transmitting at the same rate of R bits/second.

Since, there are L-bits in packet P1, so host B receives the packet P1 after additional

L/R seconds.

Hence, the total end-to-end delay in receiving the first packet is 2L/R seconds.

In general, it is NL/R seconds, where N is the number of links.

In our case, host A has three packets.

At time L/R seconds, the router has received the packet P1 and has started sending it to

the host B. At the same time, host A has started sending the packet P2 to the router.

So, at time 2L/R seconds, host B receives the first packet P1, and the router receives

the second packed P2.

At 3L/R seconds, the host B receives the second packet, and the router receives the third

packet P3.

At last, at 4L/R seconds, the host B receives the third packet.

In general, if there are P packets and N links, the total end-to-end delay is {N+(P-1)}L/R

seconds.

Along with this store-and-forward delay, queuing delay and packet loss may occur.

Suppose the host A is sending a file to host B via a packet switch.

The router is sending data to host B at a transmission rate of 10 Mbps.

Till the host A's transmission rate is less than or equal to 10 Mbps, no queuing will

occur.

In case, the host A's transmission rate exceeds 10 Mbps for a moment; the incoming packets

have to wait in the buffer present in the router and forms a queue.

The time till when the incoming packet wait in the queue before transmission is called

queuing delay.

Queuing delay can also occur in cases where host A is sending packets to the router, but

the router is busy is sending packets received from the host C. The packets received from

the host A will queue in the buffer till the previous transmission is over.

Since the buffer has finite space, cases may occur where the incoming packet may find the

buffer completely filled.

In such cases, either the incoming packet or the one present in the buffer is dropped

off.

It is called packet loss.

Till now, we have learned that in packet switching, the packet switches receive packets at one

communication link and forwards it to another communication link.

During this process, it may suffer store-and-forward delay, queuing delay or packet loss.

But how the packet switches know to which communication link the incoming packet should

be forwarded?

Here, forwarding tables come into picture.

On the Internet, every device has a unique address known as an IP address (192.168.1.2

and 192.168.3.8).

When host A sends a packet to host B, it maintains the IP address of host B (192.168.3.8) in

the packet header.

Every router has a forwarding table.

It maps the portion of the IP address or network address to the router's link interface.

When a router receives a packet, it matches the prefix of the packet's destination address

with the entries present in the table and forwards the packet to the corresponding outbound

link.

In the current case, the packet from host A is forwarded to link interface m1.

Finally, host B receives the packet.

Packet switching occurs in the same way as a person used to go from one place to another

if he does not know the route to the destination.

Suppose you are in a place named Manali and want to go to house number 369, BBMB Colony,

Sundernagar.

At Manali, you asked a woman for the way to Sundernagar and you reached there.

In Sundernagar, you asked a man for the way to BBMB colony.

Once you reached there, you asked a boy for house number 369.

Finally, you reached your destination.

In a network, data packets move in the same way.

Replace yourself with a packet, woman, man, and boy with routers, and house with a host.

Like you reached your destination with the help of people and the information they have,

in computer networks, the packets reach their destination with the help of routers and the

forwarding tables they have.

But how forwarding tables are updated in the routers?

They are updated automatically with

the help of routing protocols.