2-Architecture and Principles

Question 1

What is networking today?

Answer 1

An eclectic mix of theory and practice

Question 2

What is the ARPANET

Answer 2

Created in 1966 to connect big academic computers together. The first operational APRPANET nodes came on line in 1969 at UCLA, SRI, UCSB and Utah.

Question 3

What is National Physical Laboratory or NPL Net?

Answer 3

Came online around 1969 as well in the UK (connected to ARPANET by) 1974

Question 4

Fun fact about ARPANET

Answer 4

In 1971 there were about 20 ARPANET nodes and the first host to host protocol. There were 2 cross country links at 50 kbps.

Question 5

There were other Networks

Answer 5

SAT net, Packet radio, Ethernet LAN

Question 6

TCP/IP was standardized

Answer 6

1978-1981.

Question 7

Flag Day

Answer 7

Jan 1, 1983 - ARPANET transitioned to TCP/IP

Question 8

Domain Name System (DNS)

Answer 8

Rollout in 1982 replaced hosts.txt file

Question 9

TCP congestion control

Answer 9

1988

Question 10

NFS net and BGP

Answer 10

1989

Question 11

Audio and video

Answer 11

1992

Question 12

First major search engine

Answer 12

Alta Vista

Question 13

What are the “Problems and growing pains” -> All issues would require changes to the basic infrastructure.

Answer 13

1) Running out of addresses -> only 2^32 addresses -> IPv4
2) Congestion Control -> insufficient dynamic range
3) Routing - No security, easily mis-configured, poor convergence, non-determinism
4) Security -> bad at key management, secure software deployment
5) Denial of Service -> too easy and common place

Question 14

Internet original design principles

Answer 14

Design Philosophy of the DARPA Internet Protocols, Dave Clark 1988 (study notes on this paper)

Question 15

Goal of internet?

Answer 15

“Multiplexed utilization of existing interconnected networks.” Sharing (statistical multiplexing/Packet switching) and interconnection (narrow waist)

Question 16

Packet Switching

Answer 16

Information for forwarding traffic is contained in destination address of every data gram or packet. (Best effort Service) Sharing resources here. drawbacks are potential for delay or loss/dropped packets

Question 17

Packet Switching vs Circuit Switching

Answer 17

PS: Variable delay
CS: Busy Signals
PS: Sharing of Network resources
CS: Dedicated resources between sender and receiver

Question 18

Interconnection: achieved due to Narrow Waist

Answer 18

Goal: Interconnect many existing networks and to hide underlying technology from applications (IP is at the center - the network layer)

Question 19

Narrow waist layers

Answer 19

Application layer -> http, smtp
Transport layer -> tcp, udp
3) Network layer -> IP (Difficult to change at this level)
2) Link layer -> ethernet 
1) Physical layer -> Soner

Question 20

Design goal: Survivability

Answer 20

• Network works even if some devices fail
  1) replication
  2) fate sharing - acceptable to loose state info for entity if that entity itself is lost if that (easier to withstand complex failures - easier engineering)

Question 21

Design goal: Heterogeneity

Answer 21

1) IP

2) “best effort” service model (makes debugging hard though)

Question 22

Design goal: Distributed Management

Answer 22

Addressing (ARIN, RIPE, etc)
Naming(DNS)
Routing(BGP)

Question 23

3 more design goals:

Answer 23

1) Cost
2) Ease of attachment
3) Accountability

Question 24

What’s missing in Clark’s paper?

Answer 24

Security, Availability, Mobility and Scaling

Question 25

Mentioned in Clark’s design goal paper

Answer 25

Heterogeneity, Interconnection and Sharing

Question 26

End to End argument

Answer 26

Saltzer, Reed and Clark in 1988:
In a system that includes communications, one usually draws a modular boundary around the communication subsystem and defines a firm interface between it and the rest of the system. When doing so, it becomes apparent that there is a list of functions each of which might be implemented in any of several ways: by the communication subsystem, by its client, as a joint venture, or perhaps redundantly, each doing its own version. In reasoning about this choice, the requirements of the application provide the basis for the following class of arguments: The function in question can completely and correctly be implemented only with the knowledge and help of the application standing at the endpoints of the communication system. Therefore, providing that questioned function as a feature of the communication system itself is not possible, and moreover, produces a performance penalty for all clients of the communication system. (Sometimes an incomplete version of the function provided by the communication system may be useful as a performance enhancement.) 

Basically that the middle should be dumb and the endpoints should be intelligent

1) Error handling in file tranfer
2) end to end encryption
3) tcp/ip split in error handling

Question 27

End to end argument violations

Answer 27

• Network Address Translators (NAT)
• VPN Tunnels
• TCP Splitting
• Spam (in some sense)
• p2p systems
• caches
• Routing
• multicast
• Qos

Question 28

Violation NAT part

Answer 28

(private) Home network -> NAT -> (public) Internet
192. 168.0.0/16 68.211.6.120

Mapping IP address and port numbers from private to public