CSCE 515: Computer Network Programming

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CSCE 515Computer Network Programming

• Chin-Tser Huang
• huangct_at_cse.sc.edu
• University of South Carolina

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Layer 7 Application
Each Layer 7 protocol specifies how one
particular application uses a network. Each
protocol specifies how an application on one
machine makes request and how the application on
another machine responds.
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 6 Presentation
Layer 6 protocols specify how to represent data.
They are used to translate from the
representation on one computer to the
representation on another computer.
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 5 Session
Layer 5 protocols specify how to establish a
communication session with a remote system,
including specifications for security details
such as authentication using passwords.
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 4 Transport
Layer 4 protocols specify how to provide reliable
data transfer for different applications.
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 3 Network
Layer 3 protocols specify how addresses are
assigned and how packets are forwarded between
networks.
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 2 Data Link
Layer 2 protocols specify how to organize data
into frames and how to transmit frames over a
network.
Application
Presentation
Session
Transport
Network
Data link
Physical
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Layer 1 Physical
Application
Layer 1 protocols specify details of interacting
with network hardware.
Presentation
Session
Transport
Network
Data link
Physical
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Origin of Internet

• In the 60s, US DoD funded ARPANET for testing
  new network technologies
• ARPANET was later extended to the Internet
• Protocol suite used with Internet is Transmission
  Control Protocol/Internet Protocol (TCP/IP)

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TCP/IP Model in Internet
OSI model
TCP/IP model
Application
Application
Presentation
Session
Transport
Transport
Network
Network
Data link
Link
Physical
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Transport Layer

• Protocol TCP, UDP
• TCP provides a reliable flow of data between two
  hosts including mechanism of connection setup,
  congestion control, and retransmission
• UDP provides a simpler service which is unreliable

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Client-Server Model

• Assume one side of communication is client, and
  the other side is server
• Server waits for a client request to arrive
• Server processes the client request and sends the
  response back to the client
• Iterative or concurrent

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Port Number

• TCP and UDP identify applications by 16-bit port
  numbers
• Some servers are assigned well-known port number
• For example, ftp is port 21 and telnet is port 23
• Clients usually use ephemeral port numbers
  between 1024 and 5000

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Network Layer

• Protocol IP, ICMP, IGMP
• Assign addresses to hosts on the Internet
• Determine how to forward messages over the
  Internet

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Internet Address

• Every interface on the Internet has a unique
  address
• In IPv4 every address is 32-bit, while in IPv6
  every address is 128-bit
• Usually specified with dotted-decimal notation
  written as 4 decimal numbers, one for each byte
• hadar.cse.sc.edu 129.252.130.109

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Classes of Network

• Every network belongs to one of five classes,
  based on first byte in its address

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24
hostid
0
netid
Class A
14
16
hostid
1
0
netid
Class B
21
8
hostid
1
1
0
netid
Class C
28
1
1
1
0
multicast group ID
Class D
1
1
1
1
reserved
Class E
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Ranges for Different Classes

• Class A 0.0.0.0 to 127.255.255.255
• Class B 128.0.0.0 to 191.255.255.255
• Class C 192.0.0.0 to 223.255.255.255
• Class D 224.0.0.0 to 239.255.255.255
• Class E 240.0.0.0 to 255.255.255.255

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Domain Name System (DNS)

• Dotted-decimal addresses are both hard to
  remember and meaningless
• Use a structured name for each host
• For example, hadar.cse.sc.edu
• DNS is a distributed database providing mapping
  between IP addresses and hostnames

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Header Encapsulation

• An application sends messages down the protocol
  stack
• Each layer adds information to a message by
  prepending an extra header

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Header Encapsulation
Application
User data
Transport layer header
Network layer header
Transport
Network
Link layer header
Link
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Application Programming Interface (API)

• A set of operations available to an application
  programmer
• Two popular APIs
• Sockets developed at Berkeley
• X/Open Transport Interface (XTI) developed by
  ATT
• We will focus on sockets

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What Is a Socket?

• An API between applications and network protocol
  software provided by the OS
• Provide following functions
• Define an abstract endpoint for communication
• Initiate and accept a connection
• Send and receive data
• Terminate a connection gracefully

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Elements of a Socket

• Each socket can be uniquely identified by
• Source IP address
• Source port number
• Destination IP address
• Destination port number
• An end-to-end protocol (TCP or UDP)

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Types of Sockets

• Two different types of sockets
• Stream sockets
• Datagram sockets

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Stream Sockets

• Also known as connection-oriented socket
• Use TCP
• Provide reliable, connected networking service
• Error free no out-of-order packets
• Applications telnet, ssh, http

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Datagram Sockets

• Also known as connectionless socket
• Use UDP
• Provide unreliable, best-effort networking
  service
• Packets may be lost may arrive out of order
• Applications streaming audio/video

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Next Class

• Socket programming in Java
• Read JNP Ch. 14, 16