Lecture Topic: Delay and Internet Layering

# Single Packet over Same Rate Links
If each node has the same rate, and you consider only transmission delay, what is the end to end delay to send one packet of length L?

# 4 Packets over 2 Same Rate Links
$d_{trans} = (L/R) = \tau$
$d_{e2e} = 5\tau$
Visual in slides

Two phases:
- Phase 1 has transmitted P-1 packets out
- Phase 2 has 1 Packet left
$$(P + N) \times \tau = d_{e2e}$$

# 4 Packets over 2 Links of different rates
$$d_{e2e} \approx \frac{\text{Total package size}}{\text{E2E throughput}}$$
So, estimating
$d_{e2e} \approx \frac{4 \times L}{R} = 4\tau$
while the real end to end delay is $5\tau$

# Internet Layering
Also called TCP/IP model
## Layers (inverse order due to markdown)
1. Application
2. Transport
3. Network
4. Link
5. Physical
## Applications
- SMTP 
- HTTP 
- DNS
## Transport
- UDP
- TCP
## Network
- IP
- Routing protocols
## Link
- Ethernet
- WiFi
## Physical
- Moving individual bits from one node to the next

Terms:
- Router (Operates on network layer)
- Switch (Operates on link layer)
- Modem (Modulation, converting mediums and modes)
- Access Point (WiFi access)

## Protocols
Define how peers communicate and exchange information over the network including rules, procedures, and message formats

Application layer protocols:
- Web server to web client (HTTP)

(More examples for each layer in slides)

### Encapsulation
Messages get passed down between each layer, and information gets appended to the header that gets delivered as the payload