Data communications and Computer Networks

UNIT 4: TRANSPORT LAYER

PRESENTATION BY
Mrs. C. Kalpana, AP/CSE
Mrs. P. Bhavani, AP/CSE
Dr. A. Ramachandiran, Assoc.Prof./CSE
TRANSPORT LAYER SERVICES
 The Transport Service
• Services Provided to the Upper Layers
• Transport Service Primitives
• Berkeley Sockets
• An Example of Socket Programming:
– An Internet File Server
Services Provided to the Upper Layers

The network, transport, and application layers.

 Transport Service Primitives

The primitives for a simple transport service.

Transport Service Primitives (2)

The nesting of TPDUs, packets, and frames.

Transport Service Primitives (3)
 Berkeley Sockets

The socket primitives for TCP.

Elements of Transport Protocols

• Addressing
• Connection Establishment
• Connection Release
• Flow Control and Buffering
• Multiplexing
• Crash Recovery
 Transport Protocol

(a) Environment of the data link layer.

(b) Environment of the transport layer.
 Addressing

TSAPs, NSAPs and transport

connections.\
 Connection Establishment

How a user process in host 1 establishes a connection

with a time-of-day server in host 2.
 Connection Establishment

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.
Connection Release(Asymmetric)

Abrupt disconnection with loss of data.

Connection Release (symmetric)

The two-army problem.

 Connection Release (3)

6-14, a, b

Four protocol scenarios for releasing a connection. (a) Normal case of a

three-way handshake. (b) final ACK lost.
 Connection Release (4)

6-14, c,d

(c) Response lost. (d) Response lost and subsequent DRs lost.
 Flow Control and Buffering

(a) Chained fixed-size buffers. (b) Chained variable-sized buffers.

(c) One large circular buffer per connection.
 Multiplexing

(a) Upward multiplexing. (b) Downward multiplexing.

 Crash Recovery

Different combinations of client and server strategy.

 A Simple Transport Protocol

• The Example Service Primitives

• The Example Transport Entity
• The Example as a Finite State Machine
 The Example Transport Entity

The network layer packets used in our example.

 The Example Transport Entity (2)
Each connection is in one of seven states:
1. Idle – Connection not established yet.
2. Waiting – CONNECT has been executed, CALL REQUEST sent.
3. Queued – A CALL REQUEST has arrived; no LISTEN yet.
4. Established – The connection has been established.
5. Sending – The user is waiting for permission to send a packet.
6. Receiving – A RECEIVE has been done.
7. DISCONNECTING – a DISCONNECT has been done locally.
THANK YOU!!!
The Example Transport Entity (3)
The Example Transport Entity (4)
The Example Transport Entity (5)
The Example Transport Entity (6)
The Example Transport Entity (7)
The Example Transport Entity (8)
The Example Transport Entity (9)
The Example Transport Entity (10)
 The Example as a Finite State Machine
The example protocol as a
finite state machine. Each
entry has an optional
predicate, an optional action,
and the new state. The tilde
indicates that no major action
is taken. An overbar above a
predicate indicate the negation
of the predicate. Blank
entries correspond to
 The Example as a Finite State
Machine (2)

The example protocol in graphical form. Transitions that leave

the connection state unchanged have been omitted for simplicity.
The Internet Transport Protocols: UDP

• Introduction to UDP
• Remote Procedure Call
• The Real-Time Transport Protocol
Introduction to
UDP

The UDP header.

 Remote Procedure Call

Steps in making a remote procedure call. The stubs are shaded.

 The Real-Time Transport Protocol

(a) The position of RTP in the protocol stack. (b) Packet nesting.
The Real-Time Transport Protocol (2)

The RTP header.

The Internet Transport Protocols: TCP
• Introduction to TCP
• The TCP Service Model
• The TCP Protocol
• The TCP Segment Header
• TCP Connection Establishment
• TCP Connection Release
• TCP Connection Management Modeling
• TCP Transmission Policy
• TCP Congestion Control
• TCP Timer Management
 The TCP Service Model

Port Protocol Use

21 FTP File transfer
23 Telnet Remote login
25 SMTP E-mail
69 TFTP Trivial File Transfer Protocol
79 Finger Lookup info about a user
80 HTTP World Wide Web
110 POP-3 Remote e-mail access
119 NNTP USENET news

Some assigned ports.

 The TCP Service Model (2)

(a) Four 512-byte segments sent as separate IP datagrams.

(b) The 2048 bytes of data delivered to the application in a single
READ CALL.
The TCP Segment Header

TCP Header.
 The TCP Segment Header (2)

The pseudoheader included in the TCP checksum.

 TCP Connection Establishment

6-31

(a) TCP connection establishment in the normal case.

(b) Call collision.
 TCP Connection Management
Modeling

The states used in the TCP connection management finite state machine.
 TCP Connection Management Modeling
(2)
TCP connection
management finite state
machine. The heavy solid
line is the normal path for a
client. The heavy dashed
line is the normal path for a
server. The light lines are
unusual events. Each
transition is labeled by the
event causing it and the
action resulting from it,
TCP Transmission Policy

Window management in TCP.

TCP Transmission Policy (2)

Silly window syndrome.

 TCP Congestion Control

(a) A fast network feeding a low capacity receiver.

(b) A slow network feeding a high-capacity receiver.
 TCP Congestion Control (2)

An example of the Internet congestion algorithm.

 TCP Timer Management

(a) Probability density of ACK arrival times in the data link layer.
(b) Probability density of ACK arrival times for TCP.
 Wireless TCP and UDP

Splitting a TCP connection into two connections.

 Transitional TCP

(a) RPC using normal TPC.

(b) RPC using T/TCP.
 Performance Issues

• Performance Problems in Computer Networks

• Network Performance Measurement
• System Design for Better Performance
• Fast TPDU Processing
• Protocols for Gigabit Networks
 Performance Problems in Computer
Networks

The state of transmitting one megabit from San Diego to Boston

(a) At t = 0, (b) After 500 μsec, (c) After 20 msec, (d) after 40 msec.
 Network Performance Measurement

The basic loop for improving network performance.

1. Measure relevant network parameters, performance.
2. Try to understand what is going on.
3. Change one parameter.
System Design for Better Performance
Rules:
1. CPU speed is more important than network speed.
2. Reduce packet count to reduce software overhead.
3. Minimize context switches.
4. Minimize copying.
5. You can buy more bandwidth but not lower delay.
6. Avoiding congestion is better than recovering from it.
7. Avoid timeouts.
System Design for Better
Performance (2)

Response as a function of load.

System Design for Better
Performance (3)

Four context switches to handle one packet

with a user-space network manager.
 Fast TPDU Processing

The fast path from sender to receiver is shown with a heavy line.
The processing steps on this path are shaded.
 Fast TPDU Processing (2)

(a) TCP header. (b) IP header. In both cases, the shaded fields are taken
from the prototype without change.
Fast TPDU Processing (3)

A timing wheel.
 Protocols for Gigabit Networks

Time to transfer and acknowledge a 1-megabit file over a 4000-km line.

THANK YOU
Data communications and Computer Networks
UNIT 4

PRESENTATION BY
Mrs. C. Kalpana, AP/CSE
Mrs. P. Bhavani, AP/CSE
Dr. A. Ramachandiran, Assoc.Prof./CSE
 The Transport
Service
• Services Provided to the Upper Layers
• Transport Service Primitives
• Berkeley Sockets
• An Example of Socket Programming:
– An Internet File Server
Services Provided to the Upper
Layers

The network, transport, and application layers.

 Transport Service
Primitives

The primitives for a simple transport service.

Transport Service Primitives
(2)

The nesting of TPDUs, packets, and frames.

 Transport Service Primitives
(3)

A state diagram for a simple connection management scheme.

Transitions labeled 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.
 Berkeley
Sockets

The socket primitives for TCP.

Elements of Transport Protocols

• Addressing
• Connection Establishment
• Connection Release
• Flow Control and Buffering
• Multiplexing
• Crash Recovery
Transport Protocol

(a) Environment of the data link layer.

(b) Environment of the transport layer.
 Addressing

TSAPs, NSAPs and transport connections.

 Connection
Establishment

How a user process in host 1 establishes a connection

with a time-of-day server in host 2.
 Connection Establishment
(3)

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.
 Connection
Release

Abrupt disconnection with loss of data.

Connection Release
(2)

The two-army problem.

 Connection Release
(3)

6-14, a, b

Four protocol scenarios for releasing a connection. (a) Normal case of a

three-way handshake. (b) final ACK lost.
 Connection Release
(4)

6-14, c,d

(c) Response lost. (d) Response lost and subsequent DRs lost.
 Flow Control and
Buffering

(a) Chained fixed-size buffers. (b) Chained variable-sized buffers.

(c) One large circular buffer per connection.
 Multiplexing

(a) Upward multiplexing. (b) Downward multiplexing.

 Crash Recovery
To recover from server crashes…………..

If there is a transmission between a client and a server and mean

while if the server crashes, the server will send a broadcast TPDU
to all other hosts, announcing that it just crashed. Each client can
be in any of 2 states:

One TPDU outstanding, SI

No TPDUs outstanding, SO
The Internet Transport Protocols: UDP

• Introduction to UDP
• Remote Procedure Call
• The Real-Time Transport Protocol
Introduction to UDP

The UDP header.

 Remote Procedure Call

Steps in making a remote procedure call. The stubs are shaded.

The Real-Time Transport Protocol

(a) The position of RTP in the protocol stack. (b) Packet nesting.
The Real-Time Transport Protocol
(2)

The RTP header.

The Internet Transport Protocols: TCP
• Introduction to TCP
• The TCP Service Model
• The TCP Protocol
• The TCP Segment Header
• TCP Connection Establishment
• TCP Connection Release
• TCP Connection Management Modeling
• TCP Transmission Policy
• TCP Congestion Control
• TCP Timer Management
• Wireless TCP and UDP
• Transactional TCP
THE TCP SERVICE MODEL
 The TCP Service
Model

Port Protocol Use

21 FTP File transfer
23 Telnet Remote login
25 SMTP E-mail
69 TFTP Trivial File Transfer Protocol
79 Finger Lookup info about a user
80 HTTP World Wide Web
110 POP-3 Remote e-mail access
119 NNTP USENET news

Some assigned ports.

The TCP Segment
Header

TCP Header.
 TCP Connection Establishment

6-31

(a) TCP connection establishment in the normal case.

(b) Call collision.
TCP Connection Management Modeling

The states used in the TCP connection management finite state machine.
TCP Connection Management Modeling (2)
TCP Transmission Policy

Window management in TCP.

TCP Transmission Policy (2)

Silly window syndrome.

 CONGESTION CONTROL
congestion is ultimately caused by traffic sent into the
network by the transport layer. The only effective way to
control congestion is for the transport protocols to send
packets into the network more slowly.

•Desirable bandwidth allocation

•Regulating the sending rate
Principles of Congestion Control
Congestion:

• informally
• manifestations:

• a highly important problem!

 Goals of congestion control

•Throughput

•Fairness

Give different sessions “equal” share.

Maximize the minimum rate session.

Single link:
 Efficiency and power

(a) Goodput and (b) delay as a function of offered load

 TCP Congestion Control

(a) A fast network feeding a low capacity receiver.

(b) A slow network feeding a high-capacity receiver.