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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
Fortnightly
Thursday 15:45 – 17:15 h
Lecture hall AH 5
Presence exercise
Note: first exercise date: November, 8th
The dates for the following exercise hours
are announced in the first exercise hour
resp. on the lecture‘s web page
Material (Slide copies, exercise sheets)
http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/datkom/WS07-08/index.html
Lehrstuhl für Informatik 4
RWTH Aachen
Written exam
At the end of winter term
Contact information
Prof. Dr. Otto Spaniol
Otto Spaniol / Dirk Thißen
Lehrstuhl für Informatik 4
Phone: 0241 – 8021400 / 8021450
E-Mail: {spaniol, thissen}@informatik.rwth-aachen.de
Dr. Dirk Thißen
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.
• Communication Protocols
• Computer Networks
2. Computer Networks
• Network principles
• Network topologies and components
• Local Area Networks (Ethernet, Token Ring, Token Bus, FDDI, DQDB)
• Wide Area Networks (Frame Relay, ATM, SDH, ISDN/DSL)
3. Internet Protocols
• Internet/Intranet: the TCP/IP Reference Model
• Network protocols (the Internet Protocol IP, Routing protocols)
• Quality of Service in the Internet
• Transport protocols (TCP and UDP)
• J.F. Kurose, K.W. Ross: Computer Networking: A Top-Down Approach
Featuring the Internet. 3rd Edition, Addison-Wesley, 2005.
• Cisco Systems: Internetworking Technologies Handbook. 3rd Edition, Cisco
Press, 2001.
Related courses:
• Mobile Communications (starting Monday, 22th, 16:30 in AH 5)
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
Computing Power is cheap...
Data communication is the processing and the transport of digital
data over connections between computers and/or other devices
(generally over large distances)
Data communication comprises two topical areas:
• Today, “everybody” has a computer (at work as well as privately)
• Possible applications: file sharing, efficient interworking
(CSCW = Computer Supported Cooperative Work)
• And: Sharing resources lowers costs
Computer Networks
Access to foreign resources by communication networks to achieve
reasonable usage
→ How to connect several computers?
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
→ Which media can be used for data transport?
→ How to represent digital data on the communication medium?
• Essential:
→ How to coordinate the access of several computers to the medium?
Efficient methods to share/transfer data between the
components of a system of interconnected devices
Communication Protocols (Internet Technology)
→ Design of uniform data units for transfer
→ How to achieve a reliable and efficient transfer?
Example for interworking of two parties: Client/Server principle
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Chapter 1: Introduction
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
Chapter 1: Introduction
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Chapter 1: Introduction
→ Cost reduction
→ Better usage of resources
→ Modular extensions
→ Reliability by redundancy
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Chapter 1: Introduction
Client
Server
WWW Browser
WWW Server
eMail Program
Domain Name System
(DNS)
FTP Client
FTP Server
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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, ethical, cultural,
juridical, ... side effects.
• Eventually dubious or forbidden contents
• Responsibility
• Juridical aspects (legislation)
• Potential censorship?
• Control over the productivity of employees,
of the whereabouts of people
• Annoyance through anonymous or unwanted messages (SPAM)
• ......
• Equal partners, no fixed client and server roles
• Connections between any pair of computers
• Establishment of a whole network of connections
• Best example: File Sharing, e.g. Gnutella, BitTorrent
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Chapter 1: Introduction
Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Why 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
Data Communication
=
Protocols
A protocol is defined as the whole set of agreements between
application processes with the purpose of a common communication
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
Implementation of Protocols
Philosopher A
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
Language: Chinese
additionally: English
Language: Spanish
additionally: English
Technical Expert B
Technical Expert A
Recognizes single
characters and sends
them in Morse
Uninterpreted characters
Recognizes single
characters and sends
them in Morse
in correct order
Electrical signals
Network
The implementation takes place in layer models
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Standards Organizations - ISO
The ISO/OSI Reference Model
Necessary for world-wide usage of common protocols: standardization
Reduce the complexity of a communication process
(all details to be considered) through layers.
International Standards Organization - ISO
7 layers:
•
•
•
•
Organisation, which is working on a volunteer basis (since 1946)
Members: standards organizations in more than 150 countries
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 International Telecommunication Union (ITU-T)
regarding telecommunication standards
• Pioneering work of ISO regarding data communication: the
ISO/OSI reference model (OSI: Open Systems Interconnection)
• Notice: only the concept is pioneering – not the products
developed from those concepts!
Chapter 1: Introduction
Interpreter B
Uninterpreted sentences,
i.e. no knowledge about politics
Accepted today: solution 2.
www.iso.ch
protocols
Interpreter A
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
Philosopher B
Language: Spanish
service
Language: Chinese
Chapter 1: Introduction
Thoughts about world politics
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7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
Standard interfaces for
commonly used
communication services
Network-independent
end-to-end data transfer
Addressing and
routing of “packets”
Protection of “frames”;
Flow Control
Criticism of the model:
Layer 5 and 6 are rarely
being implemented
Generally too much
overhead – some details
are unnecessary, some
are overloaded
Signal representation,
character transmission
Transmission medium (“Layer 0”)
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), data
rate, …
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
4. Transport Layer
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 to detect missing or wrong ordered data units. In
this flow control, the current network state is considered to not only adapt to the
receiver, but to the network capacities as well.
Again, addressing is a topic here as well. While on layer 3 the receiving host is
addressed, here a single communication process on this host is addressed.
Chapter 1: Introduction
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Layer Tasks
Layer Tasks
5. Session Layer
This layer offers the possibility for dialogue control, i.e. it can be defined which data
streams on layer 4 together are forming a dialogue, in which pattern communication
partners are allowed to send data, and (in case of a half-duplex communication
medium) at which time data can be transferred in which direction.
Part of this is the so-called token management. During the transmission tokens can
be exchanged. With certain operations only the communication partner which owns
the token is allowed to conduct the operation. That means, a set of tokens exists 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
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
(so-called routers) manage tables with path information and use the uniform
addresses to make a decision about the best path to the receiver.
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6. Presentation Layer
The task of this layer is to display the data to be transmitted in a 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 a
specific abstract data format before the transmission and are being translated back
by the receiver into its own personal data format.
7. Application Layer
In this layer standardized interfaces are being provided for commonly used
application services. One example is file transfer. On the application layer a
universally valid protocol including an interface for 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 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 of 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).
Session Layer
Layer n
service
received from
Data Link Layer
Layer (n-1)
H
Data
H
Application Layer
Chapter 1: Introduction
Transport Layer
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, a n-PDU can be segmented into several (n-1)-PDUs
before transmission (or vice versa):
Application
process
Application
process
Application Protocol
Application Layer
Presentation
Layer
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
Data
A-PDU
H
Transport Layer
Application
process
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Chapter 1: Introduction
Application Layer
Presentation Protocol
Session Protocol
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
Application-oriented
service
request
H
Data
Network Layer
Physical Layer
Network/transmission-oriented
n-PDU
H
Presentation
Layer
• For layer (n-1), these PDUs are the data to be transmitted.
Layer n
Application
process
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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
(= Layer 1&2, also partly layer 3)
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
Network and system
administrator
Router
Backbone
Building B
Router
Server
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
Important Terms
Classification of Networks
Switch
A switch has several connectors, from each connector a cable can be
drawn to a computer. These computers then are linked to a small
network. The switch knows which computer is plugged in at which
connector (address of the network interface card) and forwards data to a
destination computer.
Router
A switch only knows which computers are connected to it directly; if
someone wants to send data to a computer far away, some instance is
needed which knows the way to the destination over several other
computers or switches. Routers are used to manage global address
information and forward data through complex networks.
Backbone A backbone is a set of computers (usually routers) which are connected
by point-to-point links over large distances. A backbone serves for
covering a large region with a communication network which can
interconnect small, local networks of single institutions.
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Point-to-Point Network
• A pair of computers is directly connected by one cable
Broadcast Network
• One-to-all: when one station sends, all others receive
• All connected stations are sharing only 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
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Classification of Networks
Networks
Connection
to a WAN
Better classification scheme:
Classification by Distance
1m
Personal Area Network (PAN)
10 m
Room
100 m
Building
1 km
Campus
10 km
Town
100 km
Country
1000 km
Continent
10000 km
Planet
Chapter 1: Introduction
Switch
Router
Local Area Network (LAN)
Metropolitan Area Network (MAN)
Local Networks (LANs)
Wide Area Network (WAN)
Metropolitan
Network (MAN),
backbone for a
town or a region
Internet
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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
Networks
Networks
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Networks
“Dark Fiber”
rented wavelength
GRE
KIE
HAM
AWI
ROS
DES
Central node Frankfurt
– connection to the
European research
network Géant.
EWE
BRE
POT
HAN
Surfnet
BIE
MUE
BRA
DUI
KAS
MAG
TUB
FFO
HUB
ZIB
ADH
GOE
LEI
FZJ
DRE
MAR
JEN
BIR
AAC
CHE
GIE
• Connection to other backbone
networks (international as well as to
other German backbone networks)
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Networks
• German research network X-WIN –
backbone based on optical fiber, for
universities and research institutes
with a data rate of 10 GBit/s
• Additionally: DWDM (Dense
Wavelength Division Multiplexing):
up to 160 simultaneous
transmissions on different
wavelengths:
1.6 TBit/s capacity!
Chapter 1: Introduction
Geant2
FRA
ILM
BAY
GSI
WUE
HEI
SAA
Renater
Also in Frankfurt and
Hamburg:
intercontinental
connections.
ESF
ERL
REG
FZK
AUG
KEH
STU
GAR
Switch/GARR
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
Standards Organizations - IEEE
IEEE 802.11 Variants
Institute of Electrical and Electronic Engineers - IEEE
• Standardization e.g. of the IEEE 802.XStandards for Local Area Networks
•
•
•
•
•
•
•
802.1
802.2
802.3
802.4
802.5
802.6
802.7
Overview and Architecture of LANs
Logical Link Control (LLC)
CSMA/CD („Ethernet“)
Token Bus
Token Ring
DQDB (Distributed Queue Dual Bus)
Broadband Technical Advisory
Group (BBTAG)
• 802.8 Fiber Optic Technical Advisory
Group (FOTAG)
• 802.9 Integrated Services LAN
(ISLAN) Interface
• 802.10 Standard for Interoperable
LAN Security (SILS)
• 802.11 Wireless LAN (WLAN)
Chapter 1: Introduction
Each IEEE standard has lots of variants – e.g. here for Wireless LAN:
www.ieee.org
802.11a
• 802.12 Demand Priority
(HP’s AnyLAN)
• 802.14 Cable modems
• 802.15 Personal Area Networks
(Bluetooth)
• 802.16 WirelessMAN (WiMAX)
• 802.17 Resilient Packet Ring
• 802.18 Radio Regulatory Technical
Advisory Group (RRTAG)
• 802.19 Coexistence Technical
Advisory Group
• 802.20 Mobile Broadband Wireless
Access (MBWA)
• 802.21 Media Independent Handover
• 802.22 Wireless Regional Area
Networks (WRAN)
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
54 MBit/s WLAN in the 5 GHz band
802.11b
11 MBit/s WLAN in the 2,4 GHz band
802.11c
Wireless Bridging between Access Points
802.11d
"World Mode", Adaptation to regional regulations (e.g. used frequency ranges)
802.11e
QoS und streaming enhancement for 802.11a/g/h
802.11f
Roaming for 802.11a/g/h (Inter Access Point Protocol IAPP) between Access Points
of different vendors
802.11g
54 MBit/s WLAN in the 2,4 GHz band
802.11h
54 MBit/s WLAN in the 5 GHz band with dynamic adaptation of channel and
frequency choice as well as automatic adaptation of transmission power
(enhancement of IEEE 802.11a for Europe)
802.11i
Authentication/encryption for 802.11a/b/g/h
802.11j
Japanese variant of 802.11a for the frequency range of 4,9 GHz - 5 GHz
802.11k
Improved measurement/evaluation/management of radio parameters (e.g. signal
strength), e.g. for enabling location based services
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Chapter 1: Introduction
Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
IEEE 802.11 Variants
802.11m
Summary of earlier enhancements, correction of errors in former specifications
(maintenance)
802.11n
Enhancement for a future, faster WLAN with data rate of 108 – 320 MBit/s
802.11p
WAVE - Wireless Access for the Vehicular Environment (such as ambulances and
passenger cars)
802.11r
Fast roaming
802.11s
ESS Mesh Networking
802.11t
Wireless Performance Prediction (WPP) - test methods and metrics
Recommendation
802.11u
Interworking with non-802 networks (for example, cellular)
802.11v
Wireless network management
802.11w
Protected Management Frames
802.11y
3650-3700 Operation in the U.S.
Internet Protocols
(= Layer 3 – 7)
Only few standards (the grey shaded) are “standalone” standards defining data
exchange – the others are supplements for network variants, or enhancements like
security, QoS, etc.
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
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,
integrated into layer 7, if needed
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
organizations 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 beyond
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). But, several enhancements are done in the
meantime, e.g. MPLS for a connection-oriented transfer of data (see QoS chapter).
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),
or when only very small messages have to be sent.
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
4. Political reasons
1. Time
The TCP/IP protocols were already widely used before OSI had finished
the standardization activities.
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.
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.
3. Complicatedness
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
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.
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.
The TCP/IP protocols are used, from ISO/OSI only the terminology remained
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
Cross-Layer Protocol Design
Cross-Layer Protocol Design
ISO/OSI clearly defines independent layers, in the Internet protocols the layers
theoretically are also independent (in reality, there are some mix-ups between TCP
and IP)
But sometimes it makes sense to violate the layer concept and to allow inter-layer
exchange of information or even interaction:
Examples for cross-layer interaction:
• In wireless transmission, common control of data rate (layer 2) and sending
power (layer 1) is useful
• Routing protocols (layer 3) in wireless mesh networks can use information about
signal-to-noise ratio and interference (layer 1) in path decisions
Disadvantages:
• Flexibility is lost – exchange of single protocols is not longer possible
• Solutions are tailored to certain application scenarios, usage is restricted
Goal: lightweight (i.e.
simplified) protocols,
specially tailored to a
certain application
Avoid overhead of layer concept:
• Minimize energy consumption for small devices with low capabilities
• Consider characteristics of communication medium at time of protocol design
• Performance increase
Chapter 1: Introduction
5. Hurriedly product implementation
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Concept for low-capability devices / wireless communication
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Lehrstuhl für Informatik 4
Kommunikation und verteilte Systeme
And now…
1. Introduction
• Communication Protocols
• Computer Networks
2. Computer Networks
• Network principles
• Network topologies and components
• Local Area Networks (Ethernet, Token Ring, Token Bus, FDDI, DQDB)
• Wide Area Networks (Frame Relay, ATM, SDH, ISDN/DSL)
3. Internet Protocols
• Internet/Intranet: the TCP/IP Reference Model
• Network protocols (the Internet Protocol IP, Routing protocols)
• Quality of Service in the Internet
• Transport protocols (TCP and UDP)
4. Application Protocols in the Internet
• Higher protocols (FTP, HTTP, E-Mail, ...)
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