資管 Lee Lesson 9 Transmission Control Protocol (TCP)

資管 Lee <Lesson 9-1>

Lesson 9

Transmission Control Protocol (TCP)


UDP

TCP/IP protocol suite specifies two protocols for the transport layer:UDP and TCP

ICMPIP

ARP RARP

TCP UDP

IGMP

SMTP

FTP TFTP DNS SNMP

BOOTPApplicationlayer

Transportlayer

Networklayer

Data linklayer

Physicallayer

Underlying LAN or WANtechnology


InternetInternet

Process(Running application program)

Process(Running application program)

Domain of IP protocol

Domain of TCP protocol

Port Numbers are integers between 0 and 65,535


IP header

193.14.26.7

23

…

23

TCP header

Port numberselects the process

Processes

193.14.26.7

Port Protocol Description

7 Echo Echoes a received datagram back to the sender

9 Discard Discards any datagram that is received

11 Users Active users

13 Daytime Returns the date and the time

17 Quote Returns a quote of the day

19 Chargen Returns a string of characters

20 FTP, Data FTP, data connection

21 FTP, Control FTP, control connection

23 TELNET Terminal Network

25 SMTP Simple Mail Transfer Protocol

53 DNS Domain Name Server

67 BOOTP Bootstrap protocol

79 Finger Finger

80 HTTP Hypertext Transfer Protocol

111 RPC Remote Procedure Call

193.14.26.7

23Socket address

TCP Services• Stream Data Service• Full-Duplex Service• Reliable Service


Segment in TCP unit of data

Source port number (16 bits)

Destination port number (16 bits)

Sequence number32 bits

Acknowledge number32 bits

HLEN + Reserved(4 +6)bits

Window size16 bits

Checksum16 bits

Urgent pointer16 bits

Options & padding

Header Data

TCP Segment format

Seq. number: 32 bits tells the dest. Which byte in this sequence comprises the first byte in the segment.ACK number: defines the byte number that the source of the segment is expecting to receive from the other party.Header length (4bits): 20 to 60 bytes, value is 5 to 15.Reserved(6 bits): future use.Control: six control bits or flags. Windows size: defines the size of window in bytes.Checksum: 16 bits Urgent pointer: defines the number that must be added to the sequence number to obtain the number of the last urgent byte.

Flag Description

URG The value of the urgent pointer field is valid

ACK The value of the acknowledge field is valid

PSH Push the data

RST The connection must be reset

SYN Synchronize sequence numbers during connection

FIN Terminate the connection


Options in TCP Header

Up to 40 bytes of optional information. Five options: end of option, no operation, Maximum segment size, window scale factor, and timestamp. Code: 0

00000000Code: 100000001

End of option Max. segment size option: define the max size of data, determined by the destination, default is 536.

Code: 2 00000010

Length:400000100 Maximum segment size

No option

1 byte 1 byte 2 bytes


Options in TCP Header

Window scale factor: 16 bits means from 0 to 65535 bytes. For a high channel (fiber-optic). Need a big window size. New = defined x 2 window size factor

Code: 3 00000011

Length:300000011

Scale factor

1 byte 1 byte 1 byte

Code: 8 00001000

Length:1000001010

Timestamp value

Timestamp echo reply

Timestamp: 10-byte option. The timestamp field is filled by the source when segment leaves. The destination receives the segment and stores the timestamp value. When the destination sends an acknowledgement for the bytes, it enters the previously stored value in the echo reply field. The source checks the current time versus this value. The difference is the round-trip time.


資管

Checksum field in TCP packet32-bit source IP address

32-bit destination IP address

All 0s 8-bit protocol (6) 16-bit TCP total length

Source port number (16 bits)

Destination port number (16 bits)

Sequence number32 bits

Acknowledge number32 bits

HLEN4 bits

Window size16 bits

Checksum16 bits

Urgent pointer16 bits

Options & padding

Data

Pseudoheader

Header + options

Data


Flow Control

Sliding Window for flow control

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Sliding window

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Sliding window

Pointer

Bytes 4 to 7have been sent

Bytes 8 to 13can be sent

Bytes 14~cannot be sent

TCP uses two buffers and one window to control the flow of data.

The sending part has a buffer and the size of the window.

The size of the window in the sending TCP is determined by the receiver and is announced in the ACK segments.


Window managementSender

Seq: 1001, 4000 bytes

ack: 5001 win:

0

ack: 5001

win:1000Seq: 5001, 1000 bytes

Receiver

4000

4000

Buffer

1000

Buffer

The sending TCP sends 4K of data in its first segment. The buffer of the receiver windows becomes full. The receiver TCP ACK the receipt of the segment, but announces a window size of zero. The sending TP can not send any more data. It must wait for ack advertising a nonzero window size.


Silly Window Syndrome

Sending application creates data slowly or the receiving application consumes data slowly. If TCP contain only 1 byte of data. It means that we are sending a 41-byte that transfer only 1 byte. Meaning that using the capacity of the network very inefficiently.

Syndrome Created by the sender: Nagle’s Algorithm◦ The sending TCP sends the first piece of data it receives from the sending application program

even if it is only one byte.

◦ After sending the first segment, the sending TCP accumulates data in the output buffer and waits until either the receiver TCP sends an ack or until enough data has accumulated to fill a max. segment.

◦ The above procedure is repeated.

Syndrome created by the receiver: Clark’s solution and delayed Acknowledgement.◦ Clark’s solution is to send an ack as soon as the data arrives, but to announce a window size of

zero until either there is enough space to accommodate a segment of max-size or until half of the buffer is empty.

◦ Delayed ack is to delay sending the ack. This means that when a segment arrives, it is not ack immediately. The receiver waits until there is a decent amount of space in its incoming buffer before ack the arrived segments. Delayed ack bring another advantage, it reduces traffic. Yet, there also is a disadvantage that it may force the sender to retransmit the unpacked segment.


Error Control TCP is a reliable transport layer protocol. Reliable means segments in order,

without error, and without any part lost or duplicated. TCP provides reliability using error control. Error control includes mechanisms

for detecting corrupted segments, lost segments, out-of-order segments, and duplicated segments.

Error detection in TCP is achieved through the use of three simple tools: checksum, acknowledge, and time-out.

Case 1: Corrupted Segment: Sender resend the corrupted segment after time-out, the receiver discarded the corrupted segment.

Case 2: Lost Segment: Sender resend the corrupted segment after time-out.

Case 3: Duplicate Segment: sender resend the segment after time-out but the ACK is only delayed. The receiver simply discard the duplicate segment.

Case 4: Out-of-Order Segment: the segment that receiver before its previous segment would not ACK immediately instead they are buffer until its previous segments are all received and the ACK is resend.

Case 5: Lost ACK: TCP uses an accumulative ACK system. Any ACK confirm everything up to the byte specified by the ACK number. So, if ACK 1601 is lost, but ACK 1801 is received, there is a confirmation up to 1801.


Error Detection and Correction

Sender

Seq: 1201, 200 bytes

ack: 1601

Receiver



Seq: 1401, 200 bytesSeq: 1601, 200 bytes


Time-out

ack: 1801

OKOK

OK

Data corrupted


TCP Timers TCP uses the four timers: retransmission timer, Persistence timer,

Keepalive Timer, and Time-Waited Timer.

retransmission timer: handles the waiting time for an acknowledgement of a segment. Retransmission time = 2 x RTT (round-trip time)

RTT = x previous RTT + (1- ) x current RTT

Persistence timer: when face with the zero window-size advertisement, TCP need this timer to solve the might deadlock problem if the receive resume to send the ack, but lost in the transmit.

Keepalive timer: prevent a long idle connection between two TCPs. Suppose that a client opens a TCP connection to a server, transfers some data, and becomes silent.

Time-waited timer: used during connection termination. When TCP closes a connection, it doesn’t consider the connection really closed. The connection is held in limbo for a time-waited period.


Connection_Three way handshaking

Sender


Seq: 4800, ack:1201

Receiver

Seq: 1200, ack: --

TCP is a connection-oriented protocol which establishes a virtual path between the source and destination. Three-way Handshaking

Seq: 1201, ack=4801

Segment 1: SYN

Segment 3: ACK

Segment 2: SYN+

ACK

Step 1: the client sends the first segment, a SYN segment. The segment includes the source and destination port numbers,…Step 2: the server sends the second segment, a SYN and ACK segment. This segment has a dual propose. First, it acknowledges the receipt of the first segment using the ACK flag and ack number. Second, the segment is used as the initialization segment for the server.Step 3: The client sends the third segment. This is just an ACK segment.


Connection Termination_ Four-way Handshaking Four-way Handshaking to terminate the connection.

Sender


Seq: 7000, ack:2501

Receiver

Seq: 2500, ack: --

Seq: 2501, ack=7002

Segment 1: FIN

Segment 4: ACK

Segment 2: ACK

Seq: 7001, ack:2501Segment 3: FIN

Step 1: the client sends the first segment, a FIN segment. Step 2: the server sends the second segment, a ACK segment to confirm the receipt of the FIN segment. Step 3: the server TCP can continue sending data in the server-client direction. When it does not have any more data to send, it sends the third segment. FIN segment.Step 4: the client TCP sends the fourth segment an ACK segment to confirm the receipt of the FIN segment.


TCP Operation

Message from process

TCPheader TCP data

IPheader IP data

Frameheader Frame data

Process

a. Encapsulationb. Decapsulation

Message from process

TCPheader TCP data

IPheader IP data

Frameheader Frame data

Process


TCP Operation

TCP

TELNETclient

Port 52000

Incomingqueue

Outgoingqueue

TCP

TELNETserver

Port 23

Incomingqueue

Outgoingqueue

Use of TCP• TCP uses a buffer to store the stream of data coming from the sending application program, the sending TCP has the choice to create segments of any size from the stream.•The receiving TCP also buffers the data when they arrive and delivers them to the application program when the application program is ready or when receiving is o.k.•Push operation is used when a keystore in the interactive way.


TCP design_state transition diagram

Urgent Data TCP uses a buffer to store the stream of data coming from the sending application program. It wants to abort the process, but it has already sent a huge amount of data. If it issues a abort command (control+C), these two characters will be stored at the end of the receiving TCP buffer. The solution is to send a segment with the URG bit set. The sending application tells the sending TCP that the piece of data is urgent. The sending TCP creates a segment and inserts the urgent data at the beginning of the segment.

state description

CLOSED There is no connection

LISTEN The server is waiting for calls from the client

SYN-SENT A connection request is sent; waiting for ack

SYN-RCVD A connection request is received

ESTABLISHED Connection is established

FIN-WAIT-1 The application has requested the closing of the connection

FIN-WAIT-2 The other side has accepted the closing of the connection

CLOSING Both sides have decided to close simultaneously

TIME-WAIT Waiting for retransmitted segments to die

CLOSE-WAIT The server is waiting for the application to close

LAST-ACK The server is waiting for the last ack


CLOSED

LISTEN

SYN-SENT

ESTABLISHED

CLOSINGFIN WAIT-1

CLOSEWAIT

SYN-RCVD

FIN WAIT-2

TIME- WAIT

Active open/SYN

SYN /SYN+ACK

SYN+ACK/ACKClose /FIN

ACK /-

FIN/ACK

(Time-out)

passive open/-

SYN/SYN+ACK

ACK/-

FIN/ACK

Close /ACKLASTACK

ACK/-

FIN /ACK

ACK/-

Send /SYNRST /-

FIN+ACK/ACK

Close or time-out/-

time-out/RST

Green line for ClientRed line for serverDot line for unusual situations

States shown in ovals. Directed lines defines transition.Each line has two strings separated by a slash. The first is the input, what TCP receives, the second is the output, what TCP sends.


Client Diagram

Initiations:◦ The client TCP starts in the CLOSED state.

Connection establishment:◦ While in this state, the client TCP can receive an active open reuest from the client

application. It sends s SYN segment to the server TCP and goes to the SYN-SENT state.

◦ In this state, the client TCP can receive an SYN+ACK segment from the other TCP. It sends an ACK segment to the other TCP and goes to the ESTABLISHED state.

Data transfer state.◦ In the ESTABLISHED state, data transfers. The client remains in this state as long as it is

sending and receiving data.

Connection termination:◦ While in this state, the client TCP can receive a close request from the client application. It

sends a FIN segment to the other TCP and goes to the FIN-WAIT-1 state.

◦ While in this state, the client TCP waits to receive an ACK from the server TCP. When the ACK is received, it goes to the FIN-WAIT-2 state. It does not send anything. Now the connection is closed in one direction.

◦ The client remains in this state for the server to close the connection from the other end. If the client receives a FIN segment from the other end, it sends an ACK segment and goes to the TIME-WAIT state.

◦ When the client is in this state, it starts a timer and waits until this timer goes off. the value of this timer is set to double the lifetime estimate of a segment of maximum size. The client remains in the state before totally closing to let all duplicate packets, if any, arrive at their destination to be discarded. After the time-out, the client goes to the CLOSED state, where it began.


Server Diagram Initiation:

◦ The server TCP starts in the CLOSED state.

Passive for connection:◦ While in this state, the server TCP can receive an passive open request from the server

application. it goes to the LISTEN state.

◦ In this state, the server TCP can receive an SYN segment from the client TCP. It sends an SYN+ACK segment to the client TCP and goes to the SYN-RCVD state.

◦ While in this state, the server TCP can receive an ACK segment from the client TCP. It goes to the ESTABLISHED state. This is the data transfer state.

Data transfer:◦ In the ESTABLISHED state, data transfer. The server remains in this state as long as it is

sending and receiving data.

Passive for termination:◦ While in this state, the server TCP can receive a FIN segment from the client TCP. It can send

an ACK segment to the client and goes to the CLOSE-WAIT state.

◦ While in this state, the server TCP waits until it receives a close request from the server program. It then sends a FIN segment to the client and goes to the LAST-ACK state.

◦ When the server is in this state, the server waits for the last ACK segment. It then goes to the CLOSED state.


TCP Design

OutputProcessing

module

4 components: (two data-structures plus three modules)Control-block table: keep tracks of the open ports. Four fields: the state, the Process ID, the port number, and the corresponding queue number.Input Queues: s set of input queues, one for each process.

Control-blockmodule

… …

TCBs

TCP Segment IP

TCP

InputProcessing

module

TCP Segment

Application layerMessage from application


Transmission Control Blocks (TCBs)

State Process Local IP address ….. Pointer

State: defines the state of connectionProcess: process ID and server/client, …Local IP address:Local port number:Remote IP address:Remote port number:Interface: local interfaceLocal window: comprise several subfields, holds information about the window at the local TCPRemote window:Sending sequence number:Receiving sequence number:Sending ACK number:Round-trip time: several fields holds information about the RTTTime out values: several fields hold the values of different time-out values such as retransmission time-out, persistence time-out,…Buffer size.Buffer pointer


Main Module operationReceive: a TCP segment, a message from an application or a time-out event 1. Search the TCB table 2. if (corresponding TCB is not found)

1) Create a TCB with the state CLOSED 3. find the state of the entry in the TCB table. 4. case (state)

CLOSED: 1. if (passive open” message from application received) 1. change the state to LISTEN

2. if (“active open” message from application received)1. send a SYN segment2. change the state to SYN-SENT

3. if(any segment receive)1. send an RST segment

4. if (any other message received)1. issue an error message

5. returnLISTEN:

….


Main Module operation ©SYN-SENT: 1. if (time-out) 1. change the state to CLOSED.

2. if (SYN segment received)1. send a SYN+ACK segment2. change the state to SYN-RCVD.

3. if(SYN+ACK segment receive)1. send an ACK segment2. change the state to ESTABLISHED

4. if (any others segment or message received)1. issue an error message

5. returnSYN_RCVD:

….


Quiz 1

Question 2:

The following is a dump of a TCP header in hexadecimal format.

05320017 00000001 00000000 500207FF 00000000

Q:

What is the source port number, destination port number, sequence number, ack number, length of the header, type of the segment, and the window size?

Question 1: Fill the procedures in the MAIN operation for the LISTEN

state?


Main Module operationANS 1: case (state)

LISTEN: 1. if (” send data” message from application received) 1. send a SN segment.

2. change the state to SYN-SENT.2. if (SYN segment received)

1. send a SYN+ACK segment2. change the state to SYN-RCVD

3. if (any other message received)1. issue an error message

4. return

ANS 2:


Quiz 21. Explain connection establishment procedure in TCP?

2. Explain connection termination procedure in TCP?

3. Explain flow control in TCP?

4. Explain error control in TCP?

5. Write out the Main module operation for State: SYN-SENT?

6. Compare TCP and UDP in terms of connection, flow control, and error control?

7. Compare the header between TCP and UDP?

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資 管 Lee Lesson 9 Transmission Control Protocol (TCP)

資管 Lee Lesson 9 Transmission Control Protocol (TCP)