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
$(P \times \tau) + 1$ ?

# 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
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