Transport Protocols and Distributed Applications

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• Transport Protocols and Distributed Applications

2G1316 2G1317Data Communications and Computer
Networks
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Illustrations in this material are collected from
Behrouz A Forouzan, Data Communications and
Networking, 3rd edition, McGraw-Hill.
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Todays Lecture

• Transport Protocols
• End-to-end packet transmission
• TCPconnection-oriented transmission
• UDPdatagram transmission
• Distributed Applications
• the Client-Server communication model
• DNS, Mail, FTP, WWW, SNMP
• DHCP

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Transport Protocols

• End-to-end (process-to-process) transport service
  for applications

LAN1
LAN2
Host1
Host2
Router
TCP
TCP
IP
IP
IP
MAC1
MAC1
MAC2
MAC2
PHY
PHY
PHY
PHY
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Application Addressing
UDP/TCP Port
IP Protocol
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Client-Server Model

• Server uses a well known port number
• IANAInternet Assigned Numbers Authority
• Client port numbers are assigned dynamically
• Ephemeral ports

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Some Well Known Port Numbers
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User Datagram Protocol (UDP)

• Connectionless datagram service

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Why Datagrams?

• Application doesnt need a reliable service
• Periodic updates, statistics, etc
• Connection-oriented service too costly
• Overhead with connection management
• Application does flow and error control itself
• Retransmissions are useless
• When a packet is lost, its lost

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Transmission Control Protocol (TCP)
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Round Trip Time Estimation
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Network Congestion

• More packets than the network can handle
• Throughput decreases
• Delay becomes infinite

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How Much Data in Each Burst?
sender window min(receiver window, congestion
window)

• Receiver windowadvertised by receiver
• Congestion windowTCP congestion control

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TCP Congestion Window Size
Transmission round
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TCP Summary

• Connection-oriented
• Point-to-point
• Stream-oriented
• Byte sequence numbers
• Sliding window
• Go-back-N
• Adaptive retransmission timer
• Round-trip time estimates based on measurements
• Congestion control
• Packet loss indicates congestion

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Applications

• Domain Name System (DNS)
• to allow symbolic names instead of numeric IP
  addresses
• Simple Message Transfer Protocol (SMTP)
• the basic protocol of e-mail communication
• File Transfer Protocol (FTP)
• Hypertext Transfer Protocol (HTTP) for Web
  browsing
• Simple Network Management Protocol (SNMP)
• To manage network devices
• Dynamic Host Configuration Protocol (DHCP)
• Autoconfiguration

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Domain Name System (DNS)

• Translate host name to IP address
• www.imit.kth.se ? 130.237.203.50
• 3 generations of translations
• HOSTS.TXT
• DNS
• Dynamic DNS

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Hierarchical Name Space

• www.imit.kth.se, ftp.internic.net, google.com, ...

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Hierarchy of Name Servers

• Root servers (13, currently)
• List of addresses available from ftp.internic.net

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Name Lookup (Resolution)

• Request/response
• A client is assigned a set of DNS servers
• Through configuration
• DNS servers remember previous lookups
• Caching

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Simple Mail Transfer Protocol (SMTP)

• SMTP delivers mail to a users mailbox
• Normally via an outgoing SMTP mail server

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SMTP Mail Format

• Plain text
• MIME encoding of non-text data
• Multipurpose Internet Mail Extension

Mail From alice_at_red.orgRCPT TO bob_at_blue.com
From AliceTo BobDate 2004-02-19
0801Subject Important mail Please read
carefully!
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User Mail Delivery
POP, IMAP, WWW, ...
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File Transfer Protocol (FTP)

• File transfers between computers
• TCP
• Normally two connections
• Data and control (ports 20 and 21)

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World Wide Web

• Distributed system
• CERN 1989
• Hypertext
• HTMLHypertext Markup Language

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Hypertext Transfer Protocol (HTTP)
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Non-Static Pages

• Run a program on the server to create the page
• Dynamic pages
• CGI, PHP, ASP, ...
• Get a program from the server and run it on the
  client
• Active pages
• Java, JavaScript, ...

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Network Management

• Simple Network Management Protocol (SNMP)
• To monitor and control network devices (interface
  cards, routers, etc.)
• Elements
• manager machine with special software (client)
• agents small software in each managed device
  (server)
• management information base (MIB) the set of
  managable objects in each device
• Processes
• the manager gets and sets parameters from the MIB
• agents notify the manager of significant events
• UDP, port 161

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Dynamic Host Configuration Protocol
Internet
Default router
Subnet
DNS server

• IP address
• Static or dynamic (leasing)
• Subnet mask
• IP address of default router
• IP address of DNS server

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Summary

• Transport protocols
• TCP how to achieve reliable transfer over IP
• retransmission
• congestion control
• UDP an unreliable transport protocol

• Distributed applications
• the client-server model
• Applications
• DNS
• SMTP
• FTP
• SNMP
• HTTP
• DHCP

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Reading Instructions

• Behrouz A. Forouzan, Data Communications and
  Networking, third edition
• 21 Transport Layer
• 22 Process-to-Process Delivery UDP and TCP
• 22.1 Process-to-process delivery
• 22.2 User Datagram Protocol (UDP)
• 22.3 Transmission Control Protocol (TCP)
• 23 Congestion Control and Quality of Service
• 23.2 Congestion
• 23.4 Two examples
• (Congestion control in TCP)
• 24 Client-Server Model Socket Interfaces
• 21.1 Client-server model
• 25 Domain Name System (DNS)
• 26 Electronic Mail (SMTP) and File Transfer (FTP)
• 27 HTTP and WWW