1.2. The 4 Layer Internet Model

Layering is core concept to boost reusability and modularity in network design”

“Each layer doesn’t have to regard how the right below layer worked, it is Abstraction

I. Link Layer

carry the data(called frame) over one link at a time, hop-by-hop.

i.e. Ethernet(wired), Wi-Fi(wireless)

II. Network Layer

deliver data(called datagram) end-to-end, from src to des

*IP(Internet Protocol): Network Layer must use IP: not reliable, ordering, error-check

III. Transport Layer: TCP / UDP

deliver data(called packet) from src application to des application

A. TCP(Transmission Control Protocol):

1. Reliability: re-transmit until received successfully

2. In-Order: guarantee correct in-order delivery

i.e. web client, e-mail client

B. UDP(User Datagram Protocol):

no reliable, no ordering

i.e. video conferencing

IV. Application Layer:

have their-own protocol parsing semantics of byte-stream served by Transport Layer

i.e. http, ftp, www, ssh, telnet, dns, dhcp, sip

“Layer can use the service provided layer right below by well-defined API”

V. Terminology

A. Packet = data + header

header is meta-data describing what data is, where it is going, it comes from

[OSI 7-layer to 4-layer Internet Model]

Unit 5. Applications and NATs

5.0. Applications and NATs

5.1. Network Address Translation

5.2. NATs – Types

5.3. NATs -Implications

5.4. NATs – Operation

5.5. HTTP

5.6. HTTP / 1.1 keep-alive

5.7. BitTorrent

5.8. DNS 1

5.9. DNS 2

5.10. DNS 3

5.11. DHCP

5.12. Application and NATs(recap)