Transcript TDC 463-98-501/502, Summer II 2002 1-3

Unit 1: Introduction. Layering
  What is a (communications) network?
• An interconnected structure that allows attached devices to communicate with each
other
 
Network Applications
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Client/Server Model
Example Applications: WWW etc.
Protocols and Standardizations
Network Classifications
 
 
LAN, MAN, WAN etc.
Internetwork
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 
Internetworking devices
The Internet as an example
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Brief history
Structure of the Internet
RFC (Request for Comments)
Network Architectures
 
 
Protocol v.s. Services
OSI and TCP/IP
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Request Service
Provide Service
v.s. peer-to-peer model
Network Protocols =
agreed-upon ways in which computers exchange information
Syntax: structure or format of the data
Semantics: meanings
Timing/Procedrue: when data should be sent and how fast it can
be sent.
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LAN
MAN
WAN
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Internetwork
Internetworking devices: bridges, routers, brouters, gateways
Figure 1-4 The Internet
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The Internet:
A collection of networks and routers that span many countries and uses the
TCP/IP protocols to form a single, cooperative virtual network.
Intranet: connection of different LANs within an organization.
Main players in the Internet:
Started by U.S. research/military organizations:
(D)ARPA: (Defense) Advanced Research Projects Agency
 funds technology with military usefulness
DoD: U.S. Department of Defense
 early adaptor of Internet technology
NSF: National Science Foundations
 funds university research
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Today:
National backbone providers (NBPs)
interconnected through exchange points:
NAPs (Network Access Points) and MAEs
(Metropolitan
Area Exchanges)
Regional ISPs connects to the NBPs
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Brief History of the Internet
1830: telegraph
1876: telephone (circuit-switching)
Development of Early Packet Switching Principles:
early 1960's concept of packet switching (Paul Baran)
1965: MIT's Lincoln Laboratory commissions Thomas Marill to study computer
networking
1968: ARPAnet contract awarded to Bolt Beranek and Newman (BBN)
1969: ARPAnet has 4 nodes (UCLA, SRI, UCSB, U. Utah), connected by IMPs
(Interface message processors); connected by 50 kbps lines
1971: 15 nodes and 23 hosts
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Internetworking, and New and Proprietary Networks
1973: TCP/IP design.
First satellite link from California to Hawaii
First international connections to the ARPANET:England and Norway
1979: ARPAnet had about 100 nodes
1980s: DARPA funded Berkeley Unix, with TCP/IP
1980-81: BITNET (IBM protocols) and CSNET (NSF-funded)
Early 1980's: split ARPnet (research), MILNET (Military)
Proliferation of Networks:
1984: Domain Name Services (Mapping Domain names into IP addresses)
1986: NSFNET created (56kbps backbone)
1989: Internet passes 100,000 nodes
First proposal for World Wide Web
NSFNET backbone upgraded to T1 (1.544 Mbps)
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Commercialization and the Web:
1990: Original ARPAnet disbanded
Fall 1991: CSNET discontinued
1991: Gopher released by University of Minnesota
1992: NSFNET backbone upgraded to T3 (44.736 Mbps)
March 1992: First MBONE (Multicast Backbone) video multicast
November 1992: First MBONE video multicast
Februray 1993: 1,776,000 hosts
May 1993: NSF solicited for bids and designated a series of NAPs (e.g. Chicago NAP
is run by Ameritech)
April 30, 1995: NSFNet backbone disbanded
(See http://www.navigators.com/isp.html for excellent information and links about the
architecture of the Internet)
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Some Internet-related organizations
ISOC: http://www.isoc.org
The Internet SOCiety (ISOC) is a professional membership society with more than 150 organizational and
6,000 individual members in over 100 countries. It provides leadership in addressing issues that confront the
future of the Internet, and is the organization home for the groups responsible for Internet infrastructure
standards, including the Internet Engineering Task Force (IETF) and the Internet Architecture Board (IAB).
IAB: http://www.iab.org
The IAB (Internet Architecture Board) is the Internet Society overseer of the technical evolution of the
Internet. The IAB supervises the Internet Engineering Task Force (IETF), which oversees the evolution of
TCP/IP, and the Internet Research Task Force (IRTF), which works on network technology.
IETF: http://www.ietf.org
The Internet Engineering Task Force
(IETF) is a large open international community of network designers,
operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth
operation of the Internet. It is open to any interested individual.
Responsible for RFCs (Request for Comments, Internet Standards/drafts) which can be located at
http://www.ietf.org/rfc.html
ICANN: http://www.icann.org
The Internet Corporation for Assigned Names and Numbers (ICANN) is the non-profit corporation that was
formed to assume responsibility for the IP address space allocation, protocol parameter assignment, domain
name system management, and root server system management function previously performed under U.S.
Government contract by IANA (Internet Assigned Numbers Authority) and other entities.
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Figure 1-1 Maturity levels
of an RFC
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Analogy:
Application = boss
Transport = secretary
Network Access = post office
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ISO OSI Model
(ISO = International Standard Organization, OSI = Open Systems Interconnection)
Also data compression
and encryption
• Synchronization –
mechanism for inserting
check points
• Dialog control – halfduplex or full-duplex
Packets
Frames
End-to-end Error and
Flow Control
Error and Flow Control
over a single link
Bits
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Figure 2-2 OSI Layers
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Figure 2-3 An exchange using the OSI model
Layer 5 PDU (Protocol Data Unit) =
Layer 6 PDU + Layer 5 header
Encapsulation
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Virtual
communication
between layer 5
entities (software
implementation)
Decapsulation
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Figure 2-7 Transport Layer
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Figure 2-8 Session Layer
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Figure 2-10 Application Layer
Directory Service
File transfer and
management
email
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Service: What is provided?
Protocol: How is the service provided?
Layer N+1 entity
Interface. Passing
Service Primitives (e.g.
request and parameters)
Layer N entity
Layer N+1 entity
Layer N entity
Exchange Layer N PDUs
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Services
• A connection is set up first Full addresses
needed to set up.
• May use connection number for exchanging data
and connection release
• Data delivered in sequence.
• Full addresses with all data units
• Data may be delivered out of sequence.
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1.
= connection.request
7.
= disconnection.request
2.
= connection.indication
8.
= disconnection.indication
3.
= connection.response
4.
= connection.confirm
5.
= data.request
6.
= data.indication
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Figure 2-11 TCP/IP and OSI Model
Connection-oriented
Connectionless
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Figure 2-13 Relationship of layers and addresses in TCP/IP
Example: web browser
implementing HTTP
Interface. Eg. WINSOCK on PCs
Implemented in TCP and
UDP software.
HTTP uses TCP.
Implemented in IP
software
Eg. Ethernet Medium
Access Control (MAC)
implemented in NIC card
(Network Interface Card)
and driver software
Eg. TCP port 80
for web server
Eg. 140.192.33.37 (32bit)
Eg. Ethernet address
(48-bit)
Eg. Ethernet PHY layer.
Implemented in NIC card
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Figure 2-14 Physical addresses: identify and interface card (Link address, MAC address)
• Usually contains a checksum/Frame check sequence for detecting
errors.
• Calculated based on the rest of the frame.
• CRC (Cyclic redundancy check) is commonly used.
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Figure 2-15 IP addresses (A logical address necessary for universal communication over the internet,
and is independent of the underlying physical networks)
Note: We commonly uses
names such as
www.cs.depaul.edu (called
Domain Names). To
translate from names to IP
addresses, needs to use
DNS (Domain Name
Service) implemented at
the Application level.
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Figure 2-16 Port addresses (Different processes communicate through different ports)
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