Data Communication and Internet Technology

Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Organization
Exercises to the lecture
•
•
•
•
Data Communication
and Internet Technology
More or less fortnightly
Thursday 15:30 – 17:00 h
Lecture hall AH 5
Presence exercise
Note: exercise dates are oriented at lecture
content! No fixed dates, only
announcements in the lecture.
First exercise date: November, 10th
Material (Slide copies, exercise sheets, video recordings)
Lehrstuhl für Informatik 4
RWTH Aachen
http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/datkom/WS05-06/index.html
Written exam
At the end of winter term, February 24th
Dr. rer. nat. Dirk Thißen
Contact information
Dirk Thißen
Lehrstuhl für Informatik 4, Room 4226 (Building part E1)
Phone: 0241 / 80 - 21450
E-Mail: [email protected]
Prof. Dr. Otto Spaniol
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Content
Literature and Related Courses
1. Introduction
• A.S. Tanenbaum: Computer Networks. 4th Edition, Prentice Hall, 2002.
• Networks and Network Topologies
• Communication Protocols
2. Computer Networks
• Network principles
• Network Components (Cables, Repeaters, Hubs, Bridges, Switches, Routers)
• Local Area Networks (Ethernet, Token Ring, FDDI, DQDB)
• Wide Area Networks (Frame Relay, ATM, SDH)
3. Internet Protocols
• Internet/Intranet: the TCP/IP Reference Model
• Network protocols (the Internet Protocol IP)
• Next Generation Internet
• Transport protocols (TCP and UDP)
• J.F. Kurose, K.W. Ross: Computer Networking: A Top-Down Approach
Featuring the Internet. Addison-Wesley, 2002.
• Cisco Systems: Internetworking Technologies Handbook. 3rd Edition, Cisco
Press, 2001.
Related courses:
• Mobile Communications (starting Wednesday, 26th)
4. Application Protocols in the Internet
• Higher protocols (FTP, HTTP, E-Mail, ...)
Chapter 1: Introduction
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Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Data Communication
Evolution of Data Communication
Data communication is the processing and the transport of digital
data over connections between computers and/or other devices
(generally over large distances)
The „driving power“ for the enormous growing importance of data
communications:
• Continuously decreasing costs for hardware...
• ... while computing power is increasing.
Data communication comprises two topical areas:
Computer Networks
→ How to connect several computers?
→ Which media can be used for data transport?
Example for comparison:
→ How to represent digital data on the medium?
•
•
•
•
→ How to coordinate the access of several computers to the medium?
Communication Protocols (Internet Technology)
→ Design of uniform data units for transfer
→ How to achieve a reliable and efficient transfer?
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
A PC today costs less than € 1.000,It has more computing power than a 10 years old mainframe
It contains more than 100 Million transistors
A comparable number of other components would be
prohibitively expensive – e.g. 100 Million sheets of paper
would cost more than € 50,000,-.
Computing
power is nearly
for free
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Applications
Reducing Costs
Sharing resources lowers costs
Increasing computing power leads to new possibilities in data processing:
• Speech processing
• Image processing
• Multimedia authoring
• Video conferencing
• ......
• Access to foreign resources by communication networks to achieve
reasonable usage
• Essential:
Efficient methods to share data between the components of a
distributed system
• Procedures for efficient interworking
(CSCW = Computer Supported Cooperative Work)
• Agreements for shared usage of devices which are too expensive to buy for
one single organization and/or have no use for the total capacity
Increasing system diversity
Increasing number of applications and
users
Wide range of usage: offices, factories,
at home, …
Chapter 1: Introduction
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Example for interworking of two parties: Client/Server principle
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
The Client/Server Principle
Client/Server Systems
Client
Server
Client
Process
Server
Process
Server
Program (process) which offers a service over a network.
Servers receive requests and return a result to the inquiring party. The services
offered include simple operations (e.g. name server) or a complex set of operations
(e.g. web server).
Client
Program (process) which uses a service offered by a server.
Examples for Client/Server systems
Request
Network
Network
Reply
Advantages
→ Cost reduction
→ Better usage of resources
→ Modular extensions
→ Reliability by redundancy
Chapter 1: Introduction
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Client
Server
WWW Browser
WWW Server
eMail Program
Domain Name System
(DNS)
FTP Client
FTP Server
Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Another principle: Peer-to-Peer
Non-technical Aspects
Communication networks enable a faster and cheaper exchange/distribution
of information. There is however a large number of social, ethnical, cultural,
juridical, ... side effects.
• Eventually dubious or forbidden contents
• Responsibility
• Juridical aspects (legislation)
• Potential censorship?
• Control over the productivity of employees,
• Equal partners, no fixed client and server roles
of the whereabouts of people
• Connections between any pair of computers
• Annoyance through anonymous or unwanted messages (SPAM)
• Establishment of a whole network of connections
• ......
• Best example: File Sharing, e.g. Napster, Gnutella
Chapter 1: Introduction
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Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
First Generation Computer Networks
Computing Center
Operator
Rest of
the world
Mainframe
Telephone lines
Computer Networks
Demultiplexer
Multiplexer
Terminals
Terminals
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Peripherals
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Introduction of Local Area Networks
Global Networking
Building A
Building A
Rest of
the world
Rest of the
world
(Internet)
Clients
Local
Server
Fixed lines,
ISDN, Provider ...
Fixed lines
Switch
Building B
Computing Center
Operator
Computing Center
Router
Mainframe
Router
Server
Network and system
administrator
Router
Backbone
Building B
Router
Clients
Building C
Local
Server
Switch
Peripherals
Terminals
Peripherals
Switch
Mainframe
Router
Chapter 1: Introduction
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Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Classification of Networks
Classification of Networks
Point-to-Point Network
• A pair of computers is directly connected by one cable
Classification by Distance
1m
Broadcast Network
• One-to-all (e.g.: radio, television)
• All connected stations are sharing one transmission channel
• For ensuring that the data are sent the correct receiver, they have to
marked with the destination address of the receiving computer
• Data are being packed into packets with the Unicast Address of the
receiver
• Every computer connected controls each received packet for its destination
address. Only the addressed computer processes the data, all others are
simply deleting them.
• To address all connected stations at once, so-called Broadcast
Addresses are used
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Chapter 1: Introduction
Personal Area Network (PAN)
10 m
Room
100 m
Building
1 km
Campus
Local Area Network (LAN)
Metropolitan Area Network (MAN)
10 km
Town
100 km
Country
1000 km
Continent
10000 km
Planet
Wide Area Network (WAN)
Internet
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Local Area Networks
LANs: Bus
• Communication infrastructure for a restricted geographical area
(10 m up to some km)
B
Terminating
resistor
• Usually maintained by one local organization
Example: Ethernet
Ω
• Linked are PCs/Workstations/...., for exchanging information and sharing
peripherals and resources
Ω
A
• Transmission capacity up to 1,000 Mbit/s
• Transmission delay of a message in the range of milliseconds (~10 ms)
Bus
• Simple connection structures (“Simple is beautiful”)
• Broadcast Network: if station A intends to send data to station B, the message
reaches all connected stations. Only station B processes the data, all other
stations are ignoring it.
Topologies
- (+) Passive coupling of stations
• Bus
• Star
- Restriction of the extension and number of stations to connected
LAN
• Ring
+ Simple, cheap, easy to connect new stations
• Tree
+ No choose of path to target (= routing) necessary
• Meshed network
Chapter 1: Introduction
+ The breakdown of a station does not influence the rest of the network
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Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
LANs: Star
LANs: Tree
Branch 1
Branch 2
Star
A
• Designated computer as central station:
a message of station A is forwarded to
station B via the central station
B
B
• Broadcast network (Hub) or point-topoint connections (Switch)
Repeater
Example: Fast Ethernet
Router
Backbone
– Expensive central station
A
C
D
– Vulnerability through central station
(Redundancy possible)
Tree
+ Definite path, no routing
• Branching elements can be active (Router) or passive (Repeater)
+ N connections for N stations
+ Bridging of large distances
+ Easy connection of new stations
+ Adaptation to given geographical structure
• Topology: Connection of several busses or stars
+ Minimization of the cable length necessary
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
LANs: Ring
LANs: Meshed Networks
Fully Meshed Network
Ring
• Point-to-Point connections between all
stations
• Broadcast Network
B
• Chain of point-to-point connections
– For N stations,
needed
• Active stations: messages are regenerated
by the stations (Repeater)
A
connections are
– Breakdown of the whole network in case of
failure of one single station or connection
– Connecting a new station is a costly
process
+ Large extent possible
+ No routing
+ Easy connection of new stations
+ Redundant paths
+ Only N connections for N stations
+ Maximal connection availability through
routing integration
• Variant: bidirectional ring
Example: Token Ring, FDDI
N ( N − 1)
2
stations are connected by two opposed
rings
Partly meshed network: cheaper, but routing, flow control
and congestion control become necessary (Wide Area Networks)
Chapter 1: Introduction
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Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
LANs: Examples
Metropolitan Area Network (MAN)
Ethernet (IEEE 802.3, 10 MBit/s)
- originally the standard network
- available in an „immense number“ of variants
• Designed for larger distances than a LAN,
usage e.g. in a whole town
• Similar technologies as in a LAN
• In general, only 1 or 2 cables without additional
components
• Main difference to LANs: Time slots
Token Ring (IEEE 802.5, 4/16/100 MBit/s)
- for a long time the Ethernet competitor
- extended to FDDI (Fiber Distributed Data Interface)
MAN
Fast Ethernet (IEEE 802.3u, 100 MBit/s)
- at the moment the most widely spread network
- extension of Ethernet for small distances
Gigabit Ethernet (IEEE 802.3z, 1,000 MBit/s)
- very popular at the moment; 10 GBit/s are already in the
planning phase at the moment
Example: Distributed Queue Dual Bus (DQDB, IEEE 802.6)
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Wireless Networks
•
•
•
•
Bridging of any distance
Connects LANs and MANs over large distances
Irregular topology, based on current needs
Consists out of stations (routers) which are connected through point-to-point
with each other
• Mostly quite complex interconnection of subnetworks which are owned by
independent organizations
WAN
Router
Host
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Wide Area Network (WAN)
LAN
Chapter 1: Introduction
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• System Interconnections (PANs)
• direct connection between the components
of a computer (Example: Bluetooth)
• Wireless LANs
• Communication of computers connected by a base
station (Access Point) in a local area, or direct
connection between computers
(Example: IEEE 802.11 Wireless LAN, WLAN)
• Range of 10 – 100 meters
• Transmission capacity of up to 100 MBit/s
• Wireless MANs/WANs
• E.g. common telecommunication networks like GSM
• Range of several kilometers (“worldwide”)
• Transmission capacity below 1 MBit/s
• IEEE WirelessMAN (IEEE 802.16) as MAN for data transmission
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Standards Organizations - IEEE
Institute of Electrical and Electronic Engineers - IEEE
• Standardization e.g. of the IEEE 802.XStandards for Local Area Networks
• 802.1 Overview and Architecture of LANs
• 802.2 Logical Link Control (LLC)
• 802.3 CSMA/CD („Ethernet“)
• 802.4 Token Bus
• 802.5 Token Ring
• 802.6 DQDB
(Distributed Queue Dual Bus)
• 802.7 Broadband Technical Advisory
Group (BBTAG)
• 802.8 Fiber Optic Technical Advisory
Group (FOTAG)
www.ieee.org
• 802.9 Integrated Services LAN
(ISLAN) Interface
• 802.10 Standard for Interoperable
LAN Security (SILS)
Communication Protocols
• 802.11 Wireless LAN (WLAN)
• 802.12 Demand Priority
(HP’s AnyLAN)
• 802.14 Cable modems
• 802.15 Personal Area Networks
(Bluetooth)
• 802.16 WirelessMAN
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Why Protocols?
Implementation of Protocols
To enable understanding in communication, all communication partners have to
speak the same „language“.
→
→
→
→
→
→
→
Data formats and their semantics
Control over media access
Priorities
Handling of transmission errors
Sequence control
Flow control mechanisms
Segmentation and composition of long
messages
→ Multiplexing
→ Routing
Solution 1:
Write one large „Communication Program“ which fulfills all requirements needed
to establish a communication process.
• Advantage: efficient data exchange for a given application.
• Disadvantage: No flexibility! Adoptions require large efforts.
Solution 2:
Write a set of small programs specialized to special tasks of the communication
process. For each application, the needed programs can be combined.
• Advantage: Very flexible, since single components can be exchanged.
• Disadvantage: Fixed structures of program interworking; adds more complexity
and overhead.
A protocol is defined as the whole set of agreements between
Accepted today: solution 2.
application processes with the purpose of a common communication
The implementation takes place in layer models.
Chapter 1: Introduction
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Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Example: Exchange of Ideas between
Philosophers
Philosopher A
Standardization
Philosopher B
Thoughts about world politics
Language: Chinese
Standardization
Interpreter B
Interpreter A
Language: Chinese
Indispensable for the area-wide practical use of communication systems:
Language: Spanish
Uninterpreted sentences,
Language: Spanish
i.e. no knowledge about politics
additionally: English
additionally: English
Technical Expert B
Technical Expert A
Recognizes single
characters and sends
them in Morse
• On the national as well as the international level!
• Successful standardization is quite difficult due to:
Complex technical problems have to be solved
The involved parties, e.g. companies are often working against each other
Confidentially restrictions hinder the information flow
Uninterpreted characters
in correct order
Electrical signals
Recognizes single
characters and sends
them in Morse
Network
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Chapter 1: Introduction
• Consequence:
Standardization processes are very slow (due to many, often non-technical
reasons).
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Standards Organizations - ISO
The ISO/OSI Reference Model
International Standards Organization - ISO
• Organisation, which is working on a volunteer basis (since 1946).
• Members: standards organizations in approx. 90 countries
www.iso.ch
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Chapter 1: Introduction
• Deals with a very broad range of standards
• 200 Technical Committees (TC) for specific tasks (e.g. TC97 for
computer and information processing)
• TCs consist of subcommittees comprising in turn several working
groups
• Interworking with ITU-T regarding telecommunication standards,
(ISO is a member of ITU-T).
• Pioneering work of ISO regarding data communication: the
ISO/OSI reference model
• Notice: only the concept is pioneering – not the products
developed from those concepts!
Reduce the complexity of a communication process
(all details to be considered) through layers.
7 layers:
7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
Common services for the
end user
Criticism of the model:
Network-independent
end-to-end data transfer
Layer 5 and 6 are rarely
being implemented
Addressing and
routing of “packets”
Generally to much
overhead – some details
are unnecessary, some
are overloaded
Securing of “frames”;
Flow Control
Signal representation,
character transmission
Transmission medium („Layer 0”)
(OSI: Open Systems Interconnection)
Chapter 1: Introduction
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Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Layer Tasks
Layer Tasks
1. Physical layer
This layer is responsible for transmitting single bits over the medium. Signal
representation is defined here to ensure that a sent „1“ is understood by the
receiver as „1“. For this, e.g. on a copper cable it is defined, which voltage is used
to represent a „1“ resp. a „0“ and how long this voltage has to be for one bit.
Moreover details are being defined like the type of cables, meaning of pins of
network connectors, transmission direction on the cable (uni-/bidirectional), …
2. Data Link Layer
Ensures an error-free data transmission between two neighbored hosts (e.g. in a
sub-network). Therefore the incoming data are segmented into so-called frames
which are being transmitted separately. The receiver, which identifies the start and
the end of a frame e.g. with a bit pattern, checks if the transmission has been
correct (e.g. with the help of a checksum). Additionally, flow control is used to
control the re-transmission of corrupt frames and protect the receiver from
overload.
An additional task in broadcast networks is the control of medium access, i.e. the
stations are coordinated in some way to prevent from access conflicts.
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
3. Network Layer
This layer is responsible for the data transmission over larger distances and between
heterogeneous sub-networks. The main task is (worldwide) uniform addressing of
hosts and choosing a path through the whole network (routing). A necessary prerequisite for doing so is among other things a common address range and an
agreement about a maximum size of the transferred data units. Intermediate stations
(the routers) manage tables with routing information and use the uniform addresses
to make a decision about the best path to the receiver.
4. Transport Layer (ISO/OSI)
Layer 4 manages end-to-end communication between two processes. It is
responsible for ensuring that the received data are complete and in correct order.
For this, again flow control is used (sequence numbers, acknowledgements) to
detect missing or wrong ordered data units. Beneath this, the current network state
is considered to not only adapt to the receiver, but to the network capacities as well.
Addressing is a topic here as well. On the transport layer, a single communication
process on receiver side is addressed.
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Layer Tasks
Layer Tasks
6. Presentation Layer
5. Session Layer
This layer (like the transport layer) manages reliable data transport between the
computers. However also additional services are being offered, like e.g. the
possibility for dialogue control. I.e. it can be defined in which direction the
transmission can take place.
Closely related with this topic is the token management which also belongs to level
5. During the transmission so called tokens can be exchanged. With certain
operations only the communication partner which owns the token is allowed to
conduct the operation.
Token management is also used here for other purposes, i.e. a set of tokens exist
to coordinate several operations. One important operation is to set synchronization
points in the communication process, to restart the transmission at the point it has
ended in case of a connection loss.
Chapter 1: Introduction
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The task of this layer is to display the data to transmitted that way, that they can be
handled from a lot of different systems. So computers code a string with ASCII
characters, others use Unicode, some for integers the 1-, other the 2-complement.
Instead of defining a new transmission syntax and –semantics for every
application, it is tried to provide a universally valid solution. Specific data are
encoded in an abstract (and commonly recognized) data format before the
transmission and are being translated back by the receiver into its own personal
data format.
7. Application Layer (ISO/OSI)
In this layer (standard-) protocols are being provided which can be used from a
whole set of applications/systems. One example is file transfer. On the application
layer a universally valid protocol including an interface of file transfer is being
provided. For systems from different manufacturers only the link-up into the local
file system has to be realized. Other examples are file transfer, e-mail, remote
operations etc.
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Interplay between the Layers
The whole Communication Process
• Layer (n-1) offers its functionality to the above lying layer n as a communication
service.
• Layer n enhances the data to be sent with control information (Header) and
sends the data together with the header as Protocol Data Units (PDU).
Application Layer
• Two communication partners on layer n exchange PDUs by using the
communication service of the nearest lower lying layer (n-1).
n-PDU
H
Presentation
Layer
• For layer (n-1), these PDUs are the data to be transmitted.
Layer n
Application
process
H
Session Layer
Layer n
Data Link Layer
Layer (n-1)
H
Data
Data
Application Layer
Chapter 1: Introduction
Transport Layer
H
Network Layer
T-PDU
H
N-PDU
T
Data Link Layer
Layer (n-1)
Physical Layer
H: Header, e.g. control
information of the layer
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Bit stream
Transmission medium
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
The Communication Process
The OSI Reference Model in the Network
• Not necessarily a one-to-one mapping between layers
• Depending on the protocol, n-PDUs can be segmented into several (n-1)-PDUs
before transmission:
Application
process
Application
process
Application Protocol
Application Layer
Presentation
Layer
Application Layer
Presentation Protocol
Session Protocol
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
Host A
Chapter 1: Introduction
Session Layer
S-PDU
Physical Layer
(n-1)-PDU
Presentation
Layer
P-PDU
H
Network Layer
Application
process
A-PDU
H
Transport Layer
Data
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Chapter 1: Introduction
Transport Protocol
Presentation
Layer
Session Layer
Transport Layer
Network
Layer
Data Link
Layer
Physical
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Data Link Layer
Router A
Router B
Host B
Internal Protocols
Network Layer
Physical Layer
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Standards Organizations - IETF
The TCP/IP Reference Model
Internet Engineering Task Force - IETF
www.ietf.org
• Forum for the technical coordination of the work regarding
Arpanet, the precursor of the Internet (since 1986).
• Evolution to a large, open, and international community of
administrators, vendors and researchers.
• Works on evolution of the Internet architecture and the smooth
operation of the Internet.
• Several working groups on Internet protocols, applications,
routing, security, …
• Standard draft proposals can become a full standard only if an
implementation of the proposal is successfully tested at two
independent locations for at least four month.
• Result of such a standardization process: the resounding
success of the Internet protocols TCP/IP
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Application Layer
Presentation Layer
Don´t exist
Session Layer
Transport Layer
Transport Layer
Network Layer
Internet Layer
Data Link Layer
Host-to-Network Layer
Physical Layer
ISO/OSI
Chapter 1: Introduction
TCP/IP
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
The Tasks of the TCP/IP Layers
The Layers of TCP/IP
Host-to-Network Layer (corresponds to ISO/OSI 1-2)
Not defined exactly. The design does not matter, it is only defined that a host must
be connected to the network via a protocol in a way that it is able to send and
receive IP datagrams. The protocol design is left over to other standards to cover
heterogeneous networks of all kinds.
Internet Layer (corresponds to ISO/OSI 3)
The term Internet refers here to the interworking of different networks, therefore not
on the Internet itself. The protocol enables communication between hosts over the
own network borders. In the Internet, the transmission is connectionless, meaning
that the data are segmented into packets which are addressed and sent
independently into the network. On each network border, a router takes over the
forwarding of the packets. The choice of path can be dynamic, depending on the
current network load. As a result, single packets can get lost by overload situations
or received in wrong order. Such faults are not handled (this task is left over to the
transport layer).
In contrast to ISO, only one packet format is defined, together with a connectionless
protocol, the Internet Protocol (IP).
Chapter 1: Introduction
Application Layer
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Transport Layer (corresponds to ISO/OSI 4)
This layer covers the communication between the end systems. To adapt to
different applications, two protocols are defined.
TCP (Transmission Control Protocol) is a reliable, connection-oriented protocol
to protect the transmission of a byte stream between two hosts. The byte stream is
segmented to fit into IP packets. On the receiving side the packets are reassembled in the original order with the purpose of restoring the original data
stream. It also includes flow control to adapt to the receiver‘s capabilities and to
overcome the faults caused by the connectionless IP.
UDP (User Datagram Protocol) is an unreliable and connectionless protocol („best
effort“). No error correction is integrated, thus the transmission is used when the
speed of the data transmission is more important than the reliability (speech, video).
Application Layer (corresponds to ISO/OSI 7)
This layer defines common communication services. This comprises TELNET
(remote work on another computer), FTP (file transfer), SMTP (electronic mail),
DNS („phonebook“ for the Internet), HTTP (used for World Wide Web), etc.
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
OSI vs. TCP/IP
OSI vs. TCP/IP
1. Time
4. Political reasons
The TCP/IP protocols were already widely used before OSI had finished
the standardization activities.
2. Freedom from obligation
A „reference model“ like OSI is free from obligation. It only defines what
is to be done, but not how to do it. Result: incompatibility of products.
Very high and partly unneeded expense in the OSI specification
(thousands of pages of specification descriptions).
By the wish to consider all special cases, lots of options were included,
making the products lavish, unhandy, and for too expensive - “The
option is the enemy of the standard”!
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
And now…
1. Introduction
• Networks and Network Topologies
• Communication Protocols
2. Computer Networks
• Network principles
• Network Components (Cables, Repeaters, Hubs, Bridges, Switches, Routers)
• Local Area Networks (Ethernet, Token Ring, FDDI, DQDB)
• Wide Area Networks (Frame Relay, ATM, SDH)
3. Internet Protocols
• Internet/Intranet: the TCP/IP Reference Model
• Network protocols (the Internet Protocol IP)
• Next Generation Internet
• Transport protocols (TCP and UDP)
4. Application Protocols in the Internet
• Higher protocols (FTP, HTTP, E-Mail, ...)
Chapter 1: Introduction
5. Hurriedly product implementation
The first OSI products were implemented too fast (driven by the
success of TCP/IP protocols), were covered with faults, and had an
overall low performance.
3. Complicatedness
Chapter 1: Introduction
OSI was dominated too much by Europe – especially from the national
telecommunication companies which had lucrative monopolies. The real
market power was in the USA – nobody was interested in OSI over there.
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In contrast, the “theoretically far more unmodern“ TCP/IP protocols
were continuously modified and improved. They were of a high quality
level and successfully tested before deployment and cheap to buy due
to high production numbers.
Chapter 1: Introduction
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