1. A Course-End Conclusions
Dr. Rocky K. C. Chang

2. The internetworking problem
Different data-link protocols
Different MAC address spaces
Different MTUs
An hour-glass model (end-to-end argument)
IP as the glue
IP addresses
IP fragmentation and reassembly
IP over anything and everything

3. All boil down to the design goals
Best effort IP service
Reliability requirement: trusting states to the end hosts
Requirement for supporting a variety of TOS
Requirement for accommodating a variety of networks
End-to-end argument
Keep the network simple: IP packets go in and IP packets come out.
Implement applications at the network edge.

4. The forwarding problem
Main issues of concerns
Who knows what
Speed (forwarding table size and lookup)
Not responsible for the correctness of the routes
Hop-by-hop forwarding as a result of the best-effort approach.
Source routing and tunnels
Virtual circuit switching
IP switching
From classful to classless routing

5. The routing problem THE intelligence of the IP layer
Use a hop-by-hop protocol to deliver packets end-to- end.
Main issues of concerns
Speed of convergence
Prone to routing loops
Efficiency
Two main approaches (in midst of many other differences and variations)
Distance vector and link state

6. A tale of two routing problems
All routing protocols concern delivering packets from one point to another.
An intradomain routing additionally concerns optimizing certain costs of a route.
An interdomain routing additionally concerns satisfying certain policies of an AS.
Current Internet characteristics
Asymmetric routes
Packet reordering
Packet losses
Nonfriendly intermediaries

7. The end-to-end problems
TCP adds the following services to IP:
Multiplexing (through the port number)
Inordering (through the TCP SN)
At-most-one-copy (through the TCP SN)
Arbitrarily large application messages (through the wraparound TCP SN space)
Flow control (through advertised window)
End-to-end reliability (through the sliding window protocol and retransmission)
Congestion control (through ACK clocking, congestion window, slow start, etc)

8. The congestion control problem
Congestion control and/or resource allocation hold one of the keys to the Internet stability.
A TCP sender interprets packet losses (without receiving ACKs) as a sign of congestion.
Slow starting to trigger packet losses (reaching the network capacity)
Next time, perform congestion avoidance when approaching to the congestion point.
Other approaches do not induce packet losses.
TCP/Vegas, Explicit Congestion Notification

9. Two Internet applications
DNS provides
a distributed database for domain names and
protocols to obtain their resource records.
Web provides
A global naming system to identify resources
A text-based language to facilitate a navigation across various related resources, and
A protocol for requesting and responding
Interaction between TCP and HTTP
Web proxies: not longer end-to-end

10. Coverage in terms of protocols