TCP connection release, connection management, Tx. Policy, congestion control, Timer management, DNS, Resource Records

1. Dr. C. Sreedhar
COMPUTER
NETWORKS

2. Topics
 TCP Connection Release
 TCP connection Management
 TCP Transmission Policy
 TCP Congestion control, TCP Timer
Management
 DNS, Resource Records,
 Nameservers

3. TCP Connection Release
 Each simplex connection is released independently of its sibling.
 To release a connection, either party can send a TCP segment
with
FIN bit set, which means that it has no more data to transmit.
 When the FIN is acknowledged, that direction is shut down for new
data.
 Data may continue to flow indefinitely in the other direction,
however. When both directions have been shut down, the
connection is released.

4. TCP Connection Management Modeling (1)

5. TCP Connection Management Modeling

6. TCP Transmission
Policy
•receiver has a 4096-byte buffer
•sender transmits a 2048-byte segment
•now has only 2048 bytes of buffer
space, advertise a window of 2048
•sender transmits another 2048 bytes
•Receiver, advertises with window as 0
•Disadvantage
•Consider telnet connection to an
interactive editor that reacts on every
keystroke
•TCP creates a 21-byte TCP segment,
which it gives to IP to send as a 41-byte
IP datagram
•In all, 162 bytes of bandwidth are used
and four segments are sent for each

7. Nagle’s Algorithm
 Nagle tries to solve the problem caused by the sending
application delivering data to TCP a byte at a time.
 When data come into sender one byte at a time, send first
byte and buffer the rest until outstanding byte is
acknowledged. Then send all buffered characters in one TCP
segment and start buffering again until they are all
acknowledged.
 Allows a new packet to be sent if enough data (fills half the
window or a maximum segment) is present.

8. Silly Window Syndrome
 This problem occurs when data are passed to
sending TCP entity in large blocks, but an interactive
application on receiving side reads data 1 byte at a
time.
 Then the interactive application reads one character
from the TCP stream

9. Silly window syndrome

10. Clark's solution
 Clark's solution is to prevent receiver from sending a
window update for 1 byte. Instead it is forced to wait
until it has a decent amount of space available and
advertise that instead.
 Specifically, receiver should not send a window
update until it can handle maximum segment size it
advertised when connection was established or until
its buffer is half empty, whichever is smaller.

11. Nagle and Clark
 Nagle tries to solve the problem caused by
sending application delivering data to TCP a
byte at a time.
 Clark tries to solve the problem of receiving
application consuming the data up from TCP a
byte at a time.

12. TCP Congestion Control
(a) A fast network feeding a low capacity receiver.
(b) A slow network feeding a high-capacity receiver.
Outstanding data must be limited by both the network AND the receiver

14. TCP Timer Management
(a) Probability density of acknowledgment arrival
times in data link layer. (b) … for TCP

15. The DNS Name Space (1)
A portion of the Internet domain name space.

16. The DNS Name Space
Generic top-level domains

17. Domain Resource Records (1)
The principal DNS resource record types

18. Domain Resource Records (2)
A portion of a possible DNS database for cs.vu.nl.

19. Name Servers (1)
Part of the DNS name space divided into zones
(which are circled).

20. Name Servers (2)
Example of a resolver looking up a remote name in
10 steps.