Overview of the Network Core

Key Concepts

Network Core: Consists of a set of routers interconnected by communication links.
Packet Switching: Core operation of the internet where messages are divided into packets and sent from source to destination.
Circuit Switching: An alternative to packet switching, involves dedicated resources for each call.

End Hosts: Divide application-level messages into data chunks (packets).
Forwarding: Local action in routers, moving incoming packets to appropriate output links using forwarding tables.
Routing: Global action, determining paths from source to destination and establishing forwarding tables.
Store-and-Forward: Packet bits are transmitted from one router to another, complete packets are forwarded to the next hop after being fully received.

Queuing Delays: Occur when arrival rate exceeds transmission rate, leading to packet queues.
Packet Loss: Occurs when a router's memory is exhausted and packets cannot be stored.

Call Setup: Resources within the network are allocated for a call from source to destination.
No Queuing Delays or Data Loss: Due to reserved link capacity.
Inefficiency: Bandwidth is lost if not utilized by the call.
Multiplexing: Done via Frequency Division Multiplexing (FDM) or Time Division Multiplexing (TDM).

Packet Switching: Better for bursty data, no call setup. Congestion can occur, but protocols (e.g., TCP) manage sending rates to mitigate effects.
Circuit Switching: Guarantees no delay or loss, but can be inefficient due to idle resources.

Network of Networks: Internet connects millions of access networks.
Global vs Regional Networks: Global transit ISPs connect regional networks and access ISPs.
Peering: Networks interconnect at Internet Exchange Points.

Tier 1 ISPs: Large, well-connected networks with national and international coverage.
Regional Networks: Interconnect with Tier 1 ISPs and access networks.
Content Provider Networks: Run by companies like Google or Facebook, connecting data centers and services directly to users.

Introduced key network concepts such as packet forwarding, queuing, and routing.
Discussed differences between packet and circuit switching.
Examined the structure of the internet as a network of networks.
Next focus: Network performance.