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Bài giảng Computer Networks 1 (Mạng máy tính 1) - Lecture 8: Transport Layer and Socket Programming with Java - Phạm Trần Vũ

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Computer Networks 1  
(Mạng Máy Tính 1)  
Lectured by: Dr. Phạm Trần Vũ  
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Lecture 8: Transport Layer and  
Socket Programming with Java  
Reference:  
Chapter 6 - “Computer Networks”,  
Andrew S. Tanenbaum, 4th Edition, Prentice Hall, 2003.  
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The Transport Service  
• Services Provided to the Upper Layers  
• Transport Service Primitives  
• Berkeley Sockets  
• An Example of Socket Programming:  
ꢀ An Internet File Server  
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Services Provided to the Upper  
Layers  
The network, transport, and application layers.  
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Transport Service Primitives  
The primitives for a simple transport service.  
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Transport Service Primitives (2)  
The nesting of TPDUs, packets, and frames.  
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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  
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the server's state sequence.  
Berkeley Sockets  
The socket primitives for TCP.  
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Elements of Transport Protocols  
• Addressing  
• Connection Establishment  
• Connec
• Flow Control and Buffering  
• Multiplexing  
• Crash Re
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Addressing  
• Application addresses on a host: Ports  
TSAPs, NSAPs and transport connections.  
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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.  
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Connection Release  
Abrupt disconnection with loss of data.  
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Connection Release (2)  
The two-army problem.  
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Connection Release (3)  
Four protocol scenarios for releasing a connection. (a) Normal  
case of a three-way handshake. (b) final ACK lost.  
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The Internet Transport Protocols  
ꢁ UDP – User Datagram Protocol  
•
Connection-less service  
•
Useful in client-server situations: Remote  
Procedure Call, real-time AV streaming  
ꢁ TCP – Transmission Control Protocol  
•
Connection oriented service  
•
Reliable byte stream services over unreliable  
network  
•
Most widely used in Internet  
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UDP Header  
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TCP Service Model  
ꢁ Sender and receiver need to create  
connection end-points first, called sockets  
ꢁ Each socket is addressed by the host IP  
address and a port number  
ꢁ Port numbers < 1024 are reserved  
ꢁ TCP connections are full-duplex  
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Typical TCP Applications and Ports  
Port  
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Protocol  
FTP  
Use  
File transfer  
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25  
69  
Remote login  
E-mail  
Telnet  
SMTP  
TFTP  
Finger  
Trivial File Transfer Protocol  
Lookup info about a user  
World Wide Web  
Remote e-mail access  
USENET news  
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80  
HTTP  
POP-3  
110  
119  
NNTP  
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The TCP Segment Header  
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TCP Connection Establishment  
(a) TCP connection establishment in the normal case.  
(b) Call collision.  
20  
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