Lecture Topic: Network Core

Resource Sharing with circuit switching:
- Network resources divided into pieces allocated to connections 
- Frequency division multiplexing (FDM). Dividing over bandwidth, and each end user gets a portion of the bandwidth for the entire portion of time.
- Time division multiplexing (TDM). Dividing over time, and each end user gets the full bandwidth for a portion of allocated time. Similar to round robin.

Table of some information of cellular network technologies:
CS: Circuit Switching

1G (FDMA)
2G (TDMA) (GSM/CS)
3G (CDMA) (CS/PS)
4G (PS)
5G (millimeter wave)

With circuit switching you can guarantee a certain level of performance, while with packet switching there is no/less of a guarantee of performance, which is why circuit switching was important for mobile networks as emergency calls need a certain level of performance to be guaranteed.

Packet Switching:
- Internet is based on packet switching
- ARPANET was the first packet-switched network and is an ancestor of the internet
- A sending host breaks a message into packets (numbered sequentially) and sends them into the network one by one
- Packets are transmitted individually through the network and reassembled at the receiving host to recover the original message

Packet switching is a very adaptive to changing network conditions. Due to packet chunking, packets in transit can be routed through different routes depending on the used bandwidth of other nodes on the network, and this can occur between two packets of the same chunk of data. This is because packets are numbered and are reordered at the destination.

A packet follows a path:
- First hop router: This is the first router that inspects the packet and forwards it to the next hop
- Then next router does the same, and so on
- The packets eventually arrives at the destination and are decoded

Packets follow a protocol called "store and forward" 

Resource sharing with packet switching:
- Is very easy, as you can just send all packets over a link, according to different priorities

Multiplexing comparison:
- With circuit switching, if you allocate bandwidth to two services, it may end up unused and wasted, as the format of data is fixed and if service A is not using any traffic service B cannot use that other bandwidth
- Statistical multiplexing: Packet switching is on demand, so no bandwidth is explicitly allocated, and bandwidth is dynamically allocated based on current network usage

There are some downsides to packet switching to be aware of however:
-  In next lecture