1. Enactment of segmentation
2 volunteers to act as routers
10 volunteers to act as Kbits
10 Kbit message travels via store-forward, vs
2 Kbit segments travel via store-and-forward
Gain due to pipelining!

2. Transport service reqs of apps
Application
file transfer
Web documents
real-time audio/video
stored audio/video
interactive games
instant messaging
Data loss
no loss
Bandwidth
elastic
Time Sensitive no

3. TCP or UDP Application Underlying layer protocol transport protocol
SMTP [RFC 2821]
Telnet [RFC 854]
HTTP [RFC 2616]
FTP [RFC 959]
proprietary
(e.g. RealNetworks)‏
(e.g., Vonage,Dialpad)‏
Underlying
transport protocol
Application
remote terminal access
Web
file transfer
streaming multimedia
Internet telephony

4. Stateless protocols Where did we see this stateless idea before?
What if keeping state is inevitable? (DNS)‏
Use soft-state, state that flushes itself periodically

5. How do cookies invade privacy?
How can big vendors figure out the external sites you visit?
Big vendors advertise to many web sites. When the advertisement is requested, your cookie information goes along side it to the vendors webserver.

6. Ftp is not firewall friendly. Why?
Server initiates data connection to the client
Data connections can be to arbitrary port numbers

7. S: What is your mail reader?
elm/pine
outlook
netscape/mozilla thunderbird
gmail/yahoo/hotmail
UB's webmail portal

8. Why not SMTP directly to end host?
This would require sender and receiver to be always on in anticipation of messages.
Indirection helps in several other problems.

9. Why is SMTP not P2P? The mail servers act as peers don't they?
Servers are almost always on, no peer join/leave.

10. Why not centralize DNS? single point of failure traffic volume
distant centralized database
maintenance
doesn’t scale!

11. Difference between local DNS and authoritative DNS ?
Local DNS is a cache at the client side
Authoritative DNS is the authoritative source at the server side

12. Why the random selected upload peer in Bittorrent?
To explore, and optimize, not to get fixed in a local minima.