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Computer Network - Network Applications

Access Network Application Types​

C/S Client/Server

P2P Peer-to-Peer Application. Scenario: File sharing. Characteristics: Highly scalable, difficult to manage.

Hybrid Structure: Napster uses P2P for file transfer, C/S for file searching.

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Network Application Requirements for Transmission

  • Reliability
  • Delay
  • Bandwidth
  • Security

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Web: Http 1.0 Http1.1

Email: SMTP MIME POP3 IMAP (IMAP is a stateful protocol)

Domain Name System DNS​

  • Distributed database composed of multi-layer naming servers

  • Application layer protocol: completes name resolution

  • DNS Services

    Domain name translation Host aliasing Mail server aliasing Load balancing

Local DNS (e.g., provided by ISP)

Root DNS

TLD DNS (Authoritative Name Server)

Recursive Query (Only once)

Iterative Query (Multiple times)

Caching, Updating (TTL expiration update)

DNS Records (RR)​

RR format: (name, value, ttl)

  • Type=A Name: Host domain name Value: IP address
  • Type=NS Name: Domain (e.g., edu.com) Value: Host domain name of the authoritative name server for that domain
  • Type=CNAME Name: Alias of a real domain name Value: Real domain name
  • Type=MX Value is the mail server corresponding to Name

Q: How to register a domain name?

A: NS, A, NS (requires email) RR

P2P Applications​

Overlay Network​

Flooding Query: Overlay Network

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Hierarchical Overlay Network​

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Socket Programming​

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Identify communication endpoint (External): IP PORT

Handle/Process (Internal): Socket descriptor, is an integer index within the process

# Query which sockets connect to port 80
netstat -ano | findstr ":80"
# Query which program owns the PID 
tasklist /FI "PID eq 6016"

tasklist  | findstr 6016

Winsocket example

socketaddr_in

socket​

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closesocket​

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bind​

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listen(server)​

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connect(client)

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If TCP calls connect successfully, communication is guaranteed. UDP is not necessarily.

accept(server)​

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send sendto​

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recv recvfrom​

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setsockopt getsokopt

Network Byte Order​

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Inet_addr converts decimal IP address to 32-bit IP address.

Socket API (TCP) Call Basic Process​

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Server: Parse IP, Port, Protocol Number

TCP Client:

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UDP Client:

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