NETWORK TL LAYER SECURITY

1. 23.1
UNIT III
Transport and Application
Layer
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2. 23-1 PROCESS-TO-PROCESSDELIVERY
The transport layer is responsible for process-to-
process delivery—the delivery of a packet, part of a
message, from one process to another. Two processes
communicate in a client/server relationship, as we will
see later.
Topics discussed in this section:
Client/Server Paradigm
Multiplexing and Demultiplexing
Connectionless Versus Connection-Oriented Service
Reliable Versus Unreliable
Three Protocols
23.2

3. Figure 23.6 Multiplexing and demultiplexing
23.3

4. Figure 23.8 Position of UDP, TCP, and SCTP in TCP/IP suite
23.4

5. The transport layer is responsible for
process-to-process delivery.
Note
23.5

6. Transport Service Primitives (2)
The nesting of TPDUs, packets, and frames.

7. Transport Service Primitives (3)
A state diagram for a simple connection management scheme.
Transitions labelled in italics are caused by packet arrivals. The
solid lines show the client's state sequence. The dashed lines show
the server's state sequence.

8. Elements of Transport Protocols
a)Addressing
b)Connection Establishment
c)Connection Release
d)Flow Control and Buffering
e)Multiplexing
f)Crash Recovery

9. Transport Protocol
(a) Environment of the data link layer.
(b) Environment of the transport layer.
Both data link layer and transport layer do error control, flow control,
sequencing. The differences are:
1. Storage capacity in subnet. Frames must arrive sequentially,
TPDUs can arrive in any sequence.
2. Frames are delivered to hosts, TPDUs need to be delivered to
users, so per user addressing and flow control within the hosts is
necessary.

10. Addressing
TSAPs (Transport Service Access Point) , NSAPs (Network SAP).
TCP calls TSAP s ... ports
ATM calls TSAPs ... AAL-SAP

11. Connection Establishment (1)
How a user process in host 1
establishes a connection with a

12. Connection Establishment (2)
Three protocol scenarios for establishing a connection using a
three-way handshake. CR denotes CONNECTION REQUEST.
(a) Normal operation,
(b) Old CONNECTION REQUEST appearing out of nowhere.
(c) Duplicate CONNECTION REQUEST and duplicate ACK.

13. Connection Release
Abrupt disconnection with loss of data.

14. Connection Release (3)
Four protocol scenarios for releasing a connection. (a) Normal case of a
three-way handshake. (b) final ACK lost.
6-14, a, b

15. Connection Release (4)
(c) Response lost. (d) Response lost
and subsequent DRs lost.
6-14, c,d

16. Multiplexing
(a)Upward multiplexing.
(b)Downward multiplexing. Used to increase the bandwidth,
e.g., two ISDN connections of 64 kbps each yield 128 kbps
bandwidth.

17. The Internet Transport Protocols: UDP
•Introduction to UDP
•Remote Procedure Call
•The Real-Time Transport Protocol

18. 23-2 USERDATAGRAM PROTOCOL(UDP)
The User Datagram Protocol (UDP) is called a
connectionless, unreliable transport protocol. It does
not add anything to the services of IP except to provide
process-to-process communication instead of host-to-
host communication.
Topics discussed in this section:
Well-Known Ports for UDP
User Datagram
Checksum
UDP
Operation Use
of UDP
23.18

19. Table 23.1 Well-known ports used with UDP
23.19

20. Figure 23.9 User datagram
format
23.20

21. UDP length
= IP length – IP header’s
length
Note
23.21

22. Figure 23.10 Pseudoheader for checksum calculation
23.22

23. Figure 23.12 Queues in
UDP
23.23

24. Remote Procedure Call
Steps in making a remote procedure call.
The stubs are shaded.

25. The Real-Time Transport Protocol
(a) The position of RTP in the protocol
stack. (b) Packet nesting.

26. The Real-Time Transport Protocol (2)
The RTP header. X indicated the presence of an extension header.
CC says how many contributing sources are present (0 to 15).
Syn. Source Id. tells which stream the packet belongs to.
For feedback information is used an associated protocol called
RTCP (Real Time Control Protocol)

27. 23-3 TCP
TCP is a connection-oriented protocol; it creates a
virtual connection between two TCPs to send data. In
addition, TCP uses flow and error control mechanisms
at the transport level.
Topics discussed in this section:
TCP Services
TCP
Features
Segment
A TCP
Connection Flow
Control Error
23.27

28. Table 23.2 Well-known ports used by TCP
23.28

29. Figure 23.13 Stream delivery
23.29

30. The bytes of data being transferred in
each connection are numbered by TCP.
The numbering starts with a randomly
generated number.
Note
23.30

31. The value in the sequence number field
of a segment defines the
number of the first data byte
contained in that segment.
Note
23.31

32. The value of the acknowledgment field
in a segment defines
the number of the next byte a party
expects to receive.
The acknowledgment number is
cumulative.
Note
23.32

33. Figure 23.16 TCP segment
format
23.33

34. Figure 23.17 Control field
23.34

35. Table 23.3 Description of flags in the control field
23.35

36. Figure 23.18 Connection establishment using three-way handshaking
23.36

37. A SYN segment cannot carry data, but it
consumes one sequence number.
Note
23.37

38. A SYN + ACK segment cannot
carry data, but does consume one
sequence number.
Note
23.38

39. An ACK segment, if carrying no data,
consumes no sequence number.
Note
23.39

40. Figure 23.19 Data transfer
23.40

41. Figure 23.20 Connection termination using three-way handshaking
23.41

42. The FIN segment consumes one
sequence number if it does
not carry data.
Note
23.42

43. The FIN + ACK segment consumes
one sequence number if it
does not carry data.
Note
23.43

44. Figure 23.21 Half-close
23.44

45. A sliding window is used to make
transmission more efficient as well as
to control the flow of data so that the
destination does not become
overwhelmed with data.
TCP sliding windows are byte-
oriented.
Note
23.45

46. Figure 23.25 Lost segment
23.46

47. The receiver TCP delivers only ordered
data to the process.
Note
23.47

48. Figure 23.26 Fast retransmission
23.48