1.3 The network core

Summary

This video provides an overview of the network core, focusing on packet switching and circuit switching. It explains how data packets are forwarded through routers using forwarding tables and routing algorithms, highlighting concepts like queuing delays and packet loss. The differences between packet and circuit switching are illustrated with real-world analogies, showcasing the efficiency of packet switching for bursty data. The video concludes with an explanation of the internet's structure as a network of networks, emphasizing the roles of access ISPs, regional networks, and tier-1 ISPs, ultimately setting the stage for discussions on network performance.

Takeaways

• 😀 The network core is a set of interconnected routers and communication links that facilitate data transmission.
• 😀 Packet switching is the primary method of data transmission, where application messages are divided into packets.
• 😀 Forwarding and routing are two essential functions in network core, with forwarding focusing on moving packets and routing determining the paths.
• 😀 Queuing delays occur when packet arrival rates exceed transmission capacity, similar to queues in everyday situations.
• 😀 Circuit switching allocates resources in advance to ensure no queuing occurs but can lead to inefficiency due to idle resources.
• 😀 Packet switching allows for greater user capacity compared to circuit switching by leveraging statistical multiplexing.
• 😀 The example of link speed and user bandwidth illustrates the differences in user capacity under circuit and packet switching.
• 😀 TCP protocols help manage congestion effectively in packet-switched networks.
• 😀 The internet is structured as a network of networks, including access networks, transit ISPs, and content provider networks.
• 😀 Understanding the principles of packet forwarding, queuing, and network structure is crucial for grasping internet performance and efficiency.

Q & A

What are the main functions performed inside the network core?

The main functions are forwarding (or switching) and routing. Forwarding involves moving packets from the router's input link to the appropriate output link, while routing determines the paths taken by packets from source to destination.

How does packet switching operate?

Packet switching operates by taking application-level messages, dividing them into smaller chunks called packets, and sending these packets through the network to reach their destination nodes. Routers forward these packets based on destination addresses.

What is the significance of the forwarding table in a router?

The forwarding table is crucial for the router's operation as it contains the mapping of destination addresses to output links. When a packet arrives, the router uses this table to determine where to send the packet next.

What is the difference between forwarding and routing?

Forwarding is a local action that occurs within a router, involving the transfer of packets to the appropriate output link. Routing is a global action that involves determining the best paths for packets across the entire network.

What is queuing delay in the context of networking?

Queuing delay occurs when packets arrive at a router faster than they can be transmitted on the outgoing link, causing packets to wait in a queue. This can lead to increased latency and potential packet loss if the queue exceeds the router's memory capacity.

How does circuit switching differ from packet switching?

Circuit switching involves establishing a dedicated communication path with reserved resources for the duration of a call, ensuring no delays or packet loss. In contrast, packet switching shares network resources dynamically, allowing for more efficient use but potentially resulting in queuing and packet loss.

What are the two methods of circuit switching?

The two methods of circuit switching are Frequency Division Multiplexing (FDM), which allocates narrow frequency bands to calls, and Time Division Multiplexing (TDM), which divides time into slots allocated to different calls.

What is statistical multiplexing gain in packet switching?

Statistical multiplexing gain refers to the increased efficiency of packet switching, allowing more users to be supported simultaneously due to the bursty nature of data transmission. It contrasts with circuit switching, where resources are reserved even when not in use.

What challenges can packet delays and loss present in networking?

Packet delays and loss can complicate communication protocols, necessitating mechanisms like retransmission and congestion control to ensure data integrity and performance.

What does the phrase 'the internet is a network of networks' mean?

This phrase describes the structure of the internet, where millions of individual access networks (like home and institutional networks) connect to each other through regional and global networks, creating a vast interconnected system.