EEC-484/584 Computer Networks

1
EEC-484/584Computer Networks

• Lecture 3
• Wenbing Zhao
• wenbingz_at_gmail.com
• (Part of the slides are based on Drs. Kurose
  Rosss slides for their Computer Networking book)

2
Outline

• Protocol layers, reference models
• Network standards
• Internet history
• Application layer
• Principles of networked applications

3
Protocol Layers

• Networks are complex!
• many pieces
• hosts
• routers
• links of various media
• applications
• protocols
• hardware, software

• Question
• Is there any hope of organizing structure of
  network?
• Or at least our discussion of networks?

4
Organization of Air Travel

• A series of steps

5
Layering of Airline Functionality

• Layers each layer implements a service
• Via its own internal-layer actions
• Relying on services provided by layer below

6
Why Layering?

• Dealing with complex systems
• Explicit structure allows identification,
  relationship of complex systems pieces
• Layered reference model for discussion
• Modularization eases maintenance, updating of
  system
• Change of implementation of layers service
  transparent to rest of system
• E.g., change in gate procedure doesnt affect
  rest of system

7
Internet Protocol Stack

• Application supporting network applications
• HTTP, DNS, SMTP
• Transport process-process data transfer
• TCP, UDP
• Network routing of datagrams from source to
  destination
• IP, routing protocols
• Link data transfer between neighboring network
  elements
• PPP, Ethernet
• Physical bits on the wire

8
ISO/OSI Reference Model

• Presentation allow applications to interpret
  meaning of data, e.g., encryption, compression,
  machine-specific conventions
• Session synchronization, checkpointing, recovery
  of data exchange
• Internet stack missing these layers!
• these services, if needed, must be implemented in
  application

9
Encapsulation
source
message
application transport network link physical
segment
datagram
frame
switch
destination
application transport network link physical
router
10
Network Standardization

• Why standard?
• Only way to achieve interoperability
• Standards also increase the market for products
  adhering to them
• Two kinds of standards
• De facto from the fact (standards that just
  happened)
• De jure by law (formal, legal standards adopted
  by authorized organization)

11
Treaty Organization between Nations
12
Voluntary, Nontreaty Organization
13
IEEE 802 Standards
14
Internet Standard Body

• Internet Society (used to be Internet
  Architecture Board)
• Internet Research Task Force (IRTF)
• Concentrate on long term research
• Internet Engineering Task Force (IETF)
• Deal with short term engineering issues
• Standardization process
• Proposed standard request for comments (RFCs)
• Draft standard after gt 4 month test by gt 2
  sites
• Internet standard if convinced the idea is sound

15
Internet History
1961-1972 Early packet-switching principles

• 1972
• ARPAnet public demonstration
• NCP (Network Control Protocol) first host-host
  protocol
• first e-mail program
• ARPAnet has 15 nodes

• 1961 Kleinrock - queueing theory shows
  effectiveness of packet-switching
• 1964 Baran - packet-switching in military nets
• 1967 ARPAnet conceived by Advanced Research
  Projects Agency
• 1969 first ARPAnet node operational

16
Internet History
1972-1980 Internetworking, new and proprietary
nets

• 1970 ALOHAnet satellite network in Hawaii
• 1974 Cerf and Kahn - architecture for
  interconnecting networks
• 1976 Ethernet at Xerox PARC
• late70s proprietary architectures DECnet, SNA,
  XNA
• late 70s switching fixed length packets (ATM
  precursor)
• 1979 ARPAnet has 200 nodes

• Cerf and Kahns internetworking principles
• Minimalism, autonomy - no internal changes
  required to interconnect networks
• Best effort service model
• Stateless routers
• Decentralized control
• Define todays internet architecture

17
Internet History
1980-1990 new protocols, a proliferation of
networks

• 1983 deployment of TCP/IP
• 1982 SMTP e-mail protocol defined
• 1983 DNS defined for name-to-IP-address
  translation
• 1985 FTP protocol defined
• 1988 TCP congestion control

• New national networks Csnet, BITnet, NSFnet,
  Minitel
• 100,000 hosts connected to confederation of
  networks

18
Internet History
1990, 2000s commercialization, the Web, new apps

• Early 1990s ARPAnet decommissioned
• 1991 NSF lifts restrictions on commercial use of
  NSFnet (decommissioned, 1995)
• Early 1990s Web
• Hypertext Bush 1945, Nelson 1960s
• HTML, HTTP Berners-Lee
• 1994 Mosaic, later Netscape
• Late 1990s commercialization of the Web

• Late 1990s 2000s
• More killer apps instant messaging, P2P file
  sharing
• Network security to forefront
• Est. 50 million host, 100 million users
• Backbone links running at Gbps

19
Internet History

• 2007
• 500 million hosts
• Voice, Video over IP
• P2P applications BitTorrent (file sharing),
  Skype (VoIP), PPLive (video)
• More applications youtube, gaming
• Wireless, mobility

20
Introduction Summary

• Covered a ton of material!
• Internet overview
• Whats a protocol?
• Network edge, core, access network
• Packet-switching versus circuit-switching
• Internet structure
• Performance loss, delay, throughput
• Layering, reference models
• Networking standards
• History

• You now have
• Context, overview, feel of networking
• More depth, detail to follow!

21
Application Layer Protocols

• Principles of networked applications
• Client server model
• Sockets
• Addressing
• Protocol
• What do we need from transport layer?

22
Creating a Network Application

• Write programs that
• run on different end systems and
• communicate over a network
• No need to write code for devices in subnet
• Subnet devices do not run user application code
• application on end systems allows for rapid app
  development, propagation

23
Inter-Process Communications

• Process program running within a host
• Processes in different hosts communicate by
  exchanging messages

• Client process process that initiates
  communication
• Server process process that waits to be
  contacted

More accurately, client and server should be
regarded as the roles played by a process. A
process can be both a client and a server
24
Sockets

• Process sends/receives messages to/from its
  socket
• For each point-to-point connection, there are two
  sockets, one on each side
• API (Application Programming Interface) (1)
  choice of transport protocol (2) ability to fix
  a few parameters

Controlled by app developer
Internet
Controlled by OS
25
Addressing

• To receive messages, a process must have an
  identifier
• Each host device has a unique 32-bit IP address
• Question Does the IP address of the host on
  which the process runs suffice for identifying
  the process?

26
Addressing

• Identifier includes both IP address and port
  numbers (16-bit) associated with process on host
• Example port numbers
• HTTP server 80
• SSH server 22
• To send HTTP request to academic.csuohio.edu Web
  server
• IP address 137.148.49.46
• Port number 80

27
Application Layer Protocol Defines

• Types of messages exchanged
• e.g., request, response
• Message syntax
• what fields in messages how fields are
  delineated
• Message semantics
• meaning of information in fields
• Rules for when and how processes send respond
  to messages

• Public-domain protocols
• defined in RFCs
• allows for interoperability
• e.g., HTTP, SMTP
• Proprietary protocols
• e.g., KaZaA

28
What Transport Service Does an Application Need?

• Data loss
• some apps (e.g., audio) can tolerate some loss
• other apps (e.g., file transfer, telnet) require
  100 reliable data transfer

• Bandwidth
• some apps (e.g., multimedia) require minimum
  amount of bandwidth to be effective
• other apps (elastic apps) make use of whatever
  bandwidth they get

• Timing
• some apps (e.g., Internet telephony, interactive
  games) require low delay to be effective

29
Exercise

• A system has an n-layer protocol hierarchy.
  Applications generate messages of length M bytes.
  At each of the layers, an h-byte header is added.
  What fraction of the network bandwidth is filled
  with headers?