Chapter 1: Introduction Computer Networks
Maccabe
Computer Science Department The University of New Mexico
August 2002 Topics
Uses of Computer Networks
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Chapter 1 – p.2/66 Uses of Computer Networks
Business Applications
Home Applications
Mobile Users
Social Issues
Chapter 1 – p.3/66 Business Applications
A network with two clients and one server
Client
Server
Network
Chapter 1 – p.4/66 Business Applications (2)
The client-server model involves requests and replies
Client machine Server machine Request
Network
Reply
Client process Server process
Chapter 1 – p.5/66 Home Applications
Access to remote information
Person-to-person communication
Interactive entertainment
Electronic commerce
Chapter 1 – p.6/66 Home Applications Peer-to-Peer Networks
No fixed clients and servers
Chapter 1 – p.7/66 Home Applications Examples of E-commerce
Chapter 1 – p.8/66 Mobile Network Users
Chapter 1 – p.9/66 Social Issues
No problem when primary use is technical suing ISP for content available businesses versus employees (email content) government versus citizen (Carnivore – email) cookies spam good (easier communication) and bad (easier flow of sensitive information)
Chapter 1 – p.10/66 Topics
Uses of Computer Networks
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Chapter 1 – p.11/66 Network Hardware
Local Area Networks
Metropolitan Area Networks
Wide Area Networks
Wireless Networks
Home Networks
Internetworks
Chapter 1 – p.12/66 Broadcast Networks
Types of transmission technology
Broadcast links
Point-to-point links
Chapter 1 – p.13/66 Broadcast Networks(2)
Classification based on scale Interprocessor Processors Example distance located in same
1 m Square meter Personal area network
10 m Room
100 m Building Local area network
1 km Campus
10 km City Metropolitan area network
100 km Country Wide area network 1000 km Continent
10,000 km Planet The Internet
Chapter 1 – p.14/66 Local Area Networks
Computer
Cable Computer
(a) (b) Two types of broadcast networks
(a) bus (b) ring
Chapter 1 – p.15/66 Metropolitan Networks
A metropolitan area network based on cable TV
Junction box
Antenna
Head end
Internet
Chapter 1 – p.16/66 Wide Area Networks
Relation between hosts on LANs and the subnet
Subnet Router
Host
LAN
Chapter 1 – p.17/66 Wide Area Networks (2)
Stream of packets from sender to receiver
Router Subnet Sending host Receiving host B D A E
C Packet Router C makes a Sending process Receiving process choice to forward packets to E and not to D
Chapter 1 – p.18/66 Wireless Networks
Categories of wireless networks:
System interconnection
Wireless LANs
Wireless WANs
Chapter 1 – p.19/66 Wireless Networks (2)
Base To wired network station
(a) (b)
(a) bluetooth configuration (b) wireless LAN
Chapter 1 – p.20/66 Wireless Networks (3)
Flying router
Portable Wired computer LAN One telephone call per computer (a) (b)
(a) individual mobile computers
(b) a flying LAN
Chapter 1 – p.21/66 Home Network Categories
Computers (desktop PC, PDA, shared peripherals)
Entertainment (TV, DVD, VCR, camera, stereo, MP3)
Telecomm (telephone, cell phone, intercom, FAX)
Appliances (microwave, fridge, clock, furnace)
Telemetry (utility, burglar alarm, babycam)
Chapter 1 – p.22/66 Topics
Uses of Computer Networks
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Chapter 1 – p.23/66 Network Software
Protocol Hierarchies
Design Issues for the Layers
Connection-Oriented and Connectionless Services
Service Primitives
The Relationship of Services to Protocols
Chapter 1 – p.24/66 Network Software Protocol Hierarchies
Layers, Protocols, and Interfaces
Host 1 Host 2 Layer 5 protocol Layer 5 Layer 5
Layer 4/5 interface Layer 4 protocol Layer 4 Layer 4
Layer 3/4 interface Layer 3 protocol Layer 3 Layer 3
Layer 2/3 interface Layer 2 protocol Layer 2 Layer 2
Layer 1/2 interface Layer 1 protocol Layer 1 Layer 1
Physical medium
Chapter 1 – p.25/66 Protocol Hierarchies(2)
Philosopher-translator-secretary architecture
Location A Location B
I like J'aime Message Philosopher rabbits bien les lapins 3 3
Information L: Dutch for the remote Translator L: Dutch Ik vind translator Ik vind konijnen konijnen 2 2 leuk leuk
Information Fax #--- for the remote Fax #--- L: Dutch secretary Secretary L: Dutch Ik vind Ik vind 1 1 konijnen konijnen leuk leuk
Chapter 1 – p.26/66 Protocol Hierarchies(3)
Example information flow supporting virtual communication in layer 5 Layer Layer 5 protocol 5 M M
Layer 4 protocol 4 H4 M H4 M
Layer 3 protocol 3 H3 H4 M1 H3 M2 H3 H4 M1 H3 M2
Layer 2 protocol 2 H2 H3 H4 M1 T2 H2 H3 M2 T2 H2 H3 H4 M1 T2 H2 H3 M2 T2
1
Source machine Destination machine Chapter 1 – p.27/66 Design Issues for the Layers
Addressing
Error control
Flow control
Multiplexing
Routing
Chapter 1 – p.28/66
Connection-Oriented and Connectionless Services
Service Example
Reliable message stream Sequence of pages Connection- oriented Reliable byte stream Remote login
Unreliable connection Digitized voice
Unreliable datagram Electronic junk mail Connection- less Acknowledged datagram Registered mail Request-reply Database query
Chapter 1 – p.29/66 Service Primitives
Five service primitives for implementing a simple connection-oriented service
Chapter 1 – p.30/66 Service Primitives (2)
Packets sent in a simple client-server interaction on a connection-oriented network
Client machine Server machine (1) Connect request Client (2) ACK process Server (3) Request for data process System (4) Reply calls (5) Disconnect Operating Kernel Protocol Drivers Kernel Protocol Drivers system stack (6) Disconnect stack
Chapter 1 – p.31/66 Relationship Between Services and Protocols
Layer k + 1 Layer k + 1
Service provided by layer k
Protocol Layer k Layer k
Layer k - 1 Layer k - 1
Chapter 1 – p.32/66 Topics
Uses of Computer Networks
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Chapter 1 – p.33/66 Reference Models
The OSI (Open Standards Interconnection) Reference Model
The TCP/IP Reference Model
A Comparison of OSI and TCP/IP
A Critique of the OSI Model and Protocols
A Critique of the TCP/IP Reference Model
Chapter 1 – p.34/66 OSI Layering Principles
Layers should be created where different abstraction is needed. Each layer performs a well defined function The function of each layer should be chosen with an eye toward defining an international standard. The layer boundaries should be chosen to minimize the information flow across boundaries. The number of layers should be large enough that distinct functions need not be thrown together in the same layer out of necessity and small enough that the architecture does not become unwieldy.
Chapter 1 – p.35/66 Reference Models OSI
Layer Name of unit exchanged Application protocol 7 Application Application APDU
Interface Presentation protocol 6 Presentation Presentation PPDU
Session protocol 5 Session Session SPDU
Transport protocol 4 Transport Transport TPDU Communication subnet boundary Internal subnet protocol
3 Network Network Network Network Packet
2 Data link Data link Data link Data link Frame
1 Physical Physical Physical Physical Bit Host A Router Router Host B
Network layer host-router protocol Data link layer host-router protocol Physical layer host-router protocol Chapter 1 – p.36/66 OSI Layers
Application applications, e.g., HTTP Presentation syntax and semantics of information (encoding) Session dialog control, token management, synchronization Transport packetization Network packet routing Data Link free of undetected transmission errors Physical moving bits
Chapter 1 – p.37/66 Reference Models (2) TCP and OSI
OSI TCP/IP
7 Application Application
6 Presentation Not present in the model 5 Session
4 Transport Transport
3 Network Internet
2 Data link Host-to-network
1 Physical
Chapter 1 – p.38/66 Network Models (3) Protocols and Networks in TCP/IP
Layer (OSI names)
TELNET FTP SMTP DNS Application
Protocols TCP UDP Transport
IP Network
Packet Physical + Networks ARPANET SATNET radio LAN data link
Chapter 1 – p.39/66 Comparing the OSI and TCP/IP Models
Concepts central to the OSI model:
Services
Interfaces
Protocols
Nice, layered design.
TCP/IP is a collection of protocols; services and interfaces are an afterthought.
Chapter 1 – p.40/66 A Critique of the OSI Model and Protocols
Why OSI did not take over the world: Bad timing TCP/IP forced shortened standardization period Bad technology layers are more political than technical documentation is overly complex error and flow control duplicated in multiple layers Bad implementations complexity lead to poor implementations Bad politics TCP/IP == Unix, Unix good OSI == committee, committee bad
Chapter 1 – p.41/66 Bad Timing
David Clark’s apocalypse of the two elephants Billion dollar Research investment
Standards Activity
Time Timing of standards is critical: too early – research is incomplete too little time and they get crushed OSI standards got crushed
Chapter 1 – p.42/66 A Critique of the TCP/IP Reference Models
Problems:
service, interface and protocol not distinguished
not a general model
host-to-network “layer” not really a layer
no mention of physical and data link layers
minor protocols deeply entrenched, hard to replace
Chapter 1 – p.43/66 Hybrid Model
Chapter 1 – p.44/66 Topics
Uses of Computer Networks
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Chapter 1 – p.45/66 Example Networks
Internet
Connection-oriented networks:
X.25, Frame Relay, and ATM
Ethernet
Wireless LANs: 802.11b
Chapter 1 – p.46/66 The ARPANET
(D)ARPA – (Defense) Advanced Research Projects Agency A command and control network that could survive nuclear war Network structure
Switching office
Toll office
(a) (b) (a) the telephone network
(b) Baran's proposed distributed switching network Chapter 1 – p.47/66 The ARPANET Original Design
Host-host protocol Host Host-IMP protocol
Source IMP to destination IMP protocol
IMP-IMP protocol IMP-IMP protocol Subnet
IMP
IMP – Interface Message Processors Host-IMP pairs IMP-IMP software (56kbs, leased lines) Host-IMP software
Chapter 1 – p.48/66 Growth of the ARPANET
SRI UTAH SRI UTAH MIT SRI UTAH ILLINOIS MIT LINCOLN CASE
UCSB UCSB SDC UCSB SDC CARN STAN
UCLA UCLA RAND BBN UCLA RAND BBN HARVARD BURROUGHS (a) (b) (c)
SRI LBL MCCLELLAN UTAH ILLINOIS MIT
CCA MCCLELLAN AMES TIP BBN SRI UTAH NCAR GWC LINCOLN CASE AMES IMP HARVARD LINC X-PARC RADC ABERDEEN ILLINOIS CARN STANFORD NBS AMES USC LINC ETAC UCSB MITRE FNWC RAND MIT TINKER STAN SDC ARPA ETAC MITRE RADC UCSB UCSD SAAC UCLA RAND TINKER BBN HARVARD NBS BELVOIR CMU
UCLA SDC USC NOAA GWC CASE (d) (e) (a) December 1969, (b) July 1970, (c) March 1972, (d) April 1972, (e) September 1972
Chapter 1 – p.49/66 NFSNET 1988 Backbone
NSF Supercomputer center NSF Midlevel network Both
Chapter 1 – p.50/66 Internet Usage
Traditional applications (1970–1990)
News
Remote login
File transfer
Chapter 1 – p.51/66 Architecture of the Internet
Regional ISP Backbone
POP
NAP Telephone Client Server farm system
Corporate LAN Router
Chapter 1 – p.52/66 Connection-Oriented Networks
X.25, Frame Relay, and ATM
−Multiple routes (nuclear war)
−Connection setup
+Billing
Chapter 1 – p.53/66 ATM
Virtual circuits Router Subnet Sending host Receiving host
Sending process Virtual circuit Receiving process
Fixed sized cells (easier to route)
Bytes 5 48
Header User data
Chapter 1 – p.54/66 ATM Reference Model
Plane management
Layer management
Control plane User plane
Upper layers Upper layers CS: Convergence sublayer CS Sublayer ATM adaptation layer Sublayer SAR: Segmentation and SAR reassembly sublayer ATM layer TC: Transmission convergence sublayer Sublayer TC PMD: Physical medium Physical layer Sublayer PMD dependent sublayer
user plane: data transport, flow control, error correction control plane: connection management
Chapter 1 – p.55/66 ATM Layers and Sublayers
OSI ATM ATM layer layer sublayer Functionality
CS Providing the standard interface (convergence) 3/4 AAL SAR Segmentation and reassembly
Flow control Cell header generation/extraction 2/3 ATM Virtual circuit/path management Cell multiplexing/demultiplexing
Cell rate decoupling Header checksum generation and verification 2 TC Cell generation Packing/unpacking cells from the enclosing envelope Frame generation Physical
Bit timing 1 PMD Physical network access
Chapter 1 – p.56/66 Ethernet
ALOHANET
Original Ethernet
Transceiver Interface cable Ether
Chapter 1 – p.57/66 Wireless LANs
Base To wired network station
(a) (b)
(a) Using a base station (b) ad-hoc networking
Chapter 1 – p.58/66 Wireless LANs Issues
listen before send Range Range of A's of C's radio radio
A B C
limited radio range obstructions multipath fading (reflections, multiple receipts) mobility in higher level software (e.g., printers) base station handoff (multi-cell networks)
Ethernet Base station Portal
Cell
Chapter 1 – p.59/66 Topics
Uses of Computer Networks
Network Hardware
Network Software
Reference Models
Example Networks
Network Standardization
Chapter 1 – p.60/66 Network Standardization
De facto
De jure
Interoperability
Who’s who in the International Standards World
Who’s who in the Internet Standards World
Chapter 1 – p.61/66 Telecommunications
AT & T breakup lead to 1500 phone companies Nationalized PTT (Post, Telegraph & Telephone) move toward privatization of PTTs ITU (International Telecommunication Union) Main Sectors Radiocommunications (ITU-R) Telecommunications Standardization (ITU-T, CCITT) Development (ITU-D) Classes of Members National governments Sector members Associate members Regulatory agencies Chapter 1 – p.62/66 International Standards
ISO – International Standards Organization
ANSI – American National Standards Institute
NIST – National Institute of Standards and Technology
IEEE – Institute of Electrical and Electronic Engineers
Chapter 1 – p.63/66 IEEE 802 Standards
(*) Important standards, (↓) Hibernating, (†) Gave up
Chapter 1 – p.64/66 Internet Standards
IAB – Internet Architecture Board
RFC – Request For Comment
IRTF – Internet Research Task Force
IETF – Internet Engineering Task Force
Chapter 1 – p.65/66 Metric Units
Chapter 1 – p.66/66