Internetworking, Protocols

calvesnorthNetworking and Communications

Oct 24, 2013 (3 years and 7 months ago)


Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 1
© Arto Karila
Tik-110.250 Fundamentals of Network Media (3 cr)
Spring 2000
Professor Arto Karila
Helsinki University of Technology
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 2
© Arto Karila
General properties of protocols
A protocol shall be:
• Completely and unambiguously defined
• Free of dead-locks and live-locks
• Able to recover from all error conditions
Some possible functions of protocols:
• Addressing
• Connections
• Error detection
• Error correction
• Flow control
• Prioritization
• Multiplexing / splitting
• Segmentation / concatenation
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 3
© Arto Karila
Different types of network services
Circuit switched services
• Connect, communicate, disconnect
• Fixed capacity reserved from the network for each connection
• Based on Time Division Multiplexing (TDM)
• E.g. the Public Switched Telecommunications Network
(PSTN) and the Nordic Public Data Network (X.21 Datex)
Packet switched services
• Based on virtual connections which are set up and discon-
nected but do not reserve fixed capacity from the network
• Enable statistical multiplexing and more efficient use of
network capacity
• E.g. X.25 type networks
Connectionless (datagram) services
• No connection
• Each datagram is routed separately through the network
• For example the Internet and most local area networks (LANs)
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 4
© Arto Karila
Interconnecting networks
• The main trend of internetworking continues to be the
interconnection of ever faster LANs at ever higher speeds
• Devices used in interconnection of networks (esp. LANs)
• Repeater – physical layer, handles bits
(and possibly non-data symbols)
• Bridge – data link layer, handles frames
• Switch – data link layer, handles frames
• Router – network layer, handles packets
• Gateway – upper layers, used to interconnect totally
different systems (such as a DECNet-SNA gateway)
• Internetworking is based on routers and network layer
addresses (IP addresses)
• All the devices connected into the network must use the
same network protocol - the Internet Protocol (IP)
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 5
© Arto Karila
• The main trend in telecommunications since 1980
• Increasing capacities in the local and wide area
• Internet = network of networks
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 6
© Arto Karila
• Internetworking = the interconnection of separate
(and often different) communications networks into an
internetwork (or internet, a network of networks)
• An internetwork typically consists of a large number of Local
Area Networks (LAN), Metropolitan Area Networks (MAN) and
Wide Area Networks (WAN) interconnected via routers
• The Internet = a global open internetwork
• Internet technology can also be used to implement closed
corporate networks known as intranets
• Two or more interconnected intranets are called an extranet
• An internetwork provides only an unreliable connectionless
datagram service between any two computers
• It is the services and applications implemented in the
computers that make the internetwork interesting
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 7
© Arto Karila
The internet abstraction
• For the connected machines an internetwork appears to be a
uniform network with each host identified by its IP address
• Any machine can directly communicate with any other
Work station
IP addresses
130. 233.3.3
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 8
© Arto Karila
Real structure of an internet
• An internetwork consists of different physical (sub)networks
interconnected via routers as illustrated by the example below
130. 233.3.3
Physical network
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 9
© Arto Karila
Internet architecture
• In an internetwork separate networks are interconnected into
a larger virtual network
• All networks are treated as “equal”, such as:
• LANs
• Frame Relay connections
• Leased lines
• Routing is based on Internet Protocol (IP) and its addresses
• An IP address consists of a network prefix and the number of
the node in the network
• A routers forwards packets from one network into another
based on the recipient’s IP address
router 1
router 2
network 1
network 2
network 3
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 10
© Arto Karila
Critique of the OSI model
• Too heavy - too many layers with overlapping functionality
• Too connection oriented
• Overly heavy and slow standardization process
• The standards produced tend to be rather theoretical and
rarely provide solution to real-life problems
• The standardization of OSI protocols (such as X.400 and
FTAM) and OSI profiles (such as GOSIP) has been a complete
• The main function of the OSI model today is to server as a
generic framework and terminology, not as a protocol family
• The TCP/IP protocol suite has fulfilled all the promises made
by OSI when it was conceived
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 11
© Arto Karila
Internet layer model
The Internet model only has four layers:
higher-level protocols
Internet Protocol
communication networks
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 12
© Arto Karila
Internet and OSI layer structures
• The figure below shows the layers of Internet and those of OSI
• In some cases (such as X.25) the ”physical network” of
Internet reaches up to the network layer of OSI
• The Internet Protocol (IP) can be run on virtually any network,
e.g. LAN, leased line, ATM, Frame Relay, X.25 or packet radio
1. Physical layer
2. Data link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation layer
7. Application layer
Application level protocols:
IEEE 802.3, FDDI, E1, ATM, Frame Relay etc.
application processes
OSI Internet
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 13
© Arto Karila
Internet standardization
• The Internet standardization process has always been very
pragmatic aiming at ”a rough consensus and working code”
• This has led into a considerably faster standardization
process than is possible at for example ISO, ITU-T or ETSI
• All Internet standards are RFCs but not all RFCs are standards
• Some bodies participating in Internet standardization:
• Internet Engineering Task Force (IETF) is divided into
working groups developing RFCs
• Internet Architecture Board (IAB) is responsible for defining
the overall architecture of the Internet and providing
guidance for IETF
• Internet Engineering Steering Group (IESG) is responsible
for technical management of IETF activities and the Internet
standardization process
• Internet Society (ISOC) is a professional membership orga-
nization commenting on policies and overseeing activities
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 14
© Arto Karila
Development of the Internet
• Internet in its approximately current form has been in use
since 1981
• For 19 years in a row its growth rate has been about 100% p.a.
• This growth is still continuing for at least several years
• Internet started as an academic network
• In 1994 Internet was brought to the attention of the corporate
world by the advent of the World Wide Web (WWW)
• Some current trends in the Internet:
• Lots of new applications based on WWW and Java
• Internet telephony is challenging the Public Switched
Telephone Network (PSTN)
• Computer Supported Collaborative Work (CSCW)
• Electronic commerce
• Distribution of digital media
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 15
© Arto Karila
Growth of the Internet
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 16
© Arto Karila
Development of Internet Technologies
• Internet technologies (both standards and products) are
developing much faster than traditional telecom
• Soon conventional techniques cannot compete with Internet
even in implementing traditional services
Rapidly growing
“technology gap”
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 17
© Arto Karila
• The Public Switched Telecommunications Network (PSTN)
has developed over the past 100 years into a network with:
• Global coverage
• High availability
• Well working and flexible billing system
• Some degree of information security
• In many countries (almost) fully digitalized
• The PSTN is circuit switched and based on TDM
• Capacity can be reserved for data (leased lines)
• The network was designed for and works best with speech
• Today most of the transatlantic traffic is data (mainly faxes)
• Among the shortcomings of the PSTN are:
• Slow standardization process
• Complicated signaling and network management
• High cost (especially in data transfer)
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 18
© Arto Karila
• The Internet has developed over some 20 years to something
that is in many ways a complement of the PSTN
• Internet is characterized by its:
• Global coverage
• Varying availability
• Primitive billing system
• No built-in information security
• Internet has always been a packet-based connectionless
network implementing datagram service
• The network was designed for data but is increasingly being
used for speech and video
• The standardization process of the Internet is fast and
• The Internet makes very efficient use of network resources
(being packet based) but does not offer real-time properties
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 19
© Arto Karila
Internet - the True B-ISDN?
• Internet has fulfilled all the promises of OSI and established
itself as the leading network technology
• We are still missing a few things in the Internet, such as:
• Differentiated quality of service
• Usage based billing
• Security
• Real multicast capability
• All of these are being developed to the Internet
• Internet technology is developing much faster than traditional
networking technologies
• It is a matter of (short) time before Internet technology will be
widely used in public networks carrying voice and video
• The Internet Protocol (IP) is the key technology of the
foreseeable future
• The main obstacles are political - not technical
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 20
© Arto Karila
Needs and Solutions
• Internet technology does not yet fulfill all the requirements
• However, there are solution well underway
• The IP security extension IPSEC is a proposed standard and
will provide generic security at the IP level
• The Differentiated Services (DiffServ) working group of the
IETF is developing service differentiation based on service
classes and the connectionless stateless paradigm
• Mobility support is provided by the existing Mobile IPv4
and the work for Mobile IPv6 is in progress
• The Internet Group Membership Protocol (IGMP) and
Protocol Independent Multicast (PIM) are available and
coming into wider use
• Management and billing still need a lot of work
• The Internet technology can be augmented to meet all of the
current and foreseeable needs
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 21
© Arto Karila
• The convergence of information technologies is already
a fact of life and making fast progress
• The convergence of information technologies consists of
several parallel trends:
• Mobile and fixed networks and services are converging
• Voice, video and data are converging
• Information processing and communications are
• Internet technologies and especially the Internet Protocol
will be central to this development
• This development will totally reform both telco and IT
• It will also have a fundamental impact on all business and
service processes
• New cross-curricular skill sets are in short supply
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 22
© Arto Karila
Convergence of Information Technologies
• A new area of technology and business called Infocom, which
is expected to be a major area of growth in the near future, is
• Telecom, datacom & IT => Infocom
• Infocom will be the biggest single business area in the world
• Today among other things the following is happening:
• Traditional telecom vendors (e.g. Nokia, Ericsson and
Siemens) are buying datacom and IT companies
• Traditional datacom and IT vendors (e.g. Cisco Systems,
3com and Microsoft) are expanding to telecom
• The prices of high-tech companies are soaring but they are
still selling fast
• The real winners will be the first companies that can
succesfully operate in the whole area of infocom
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 23
© Arto Karila
The Role of IT
• Telecommunications today is 80% software and only 20%
• In telco devices, networks, routers etc. the portion of software
is increasing and the line between software and hardware
• Intelligence is moving from the center of the network to its
edges and terminal devices
• The key question is not "how to make communications
devices?" but "how to build manageable and secure
communications systems and services and networked
• The complexity of networked applications is so great that no
good methodology for designing, implementing or testing
them exists today
• Creating telecommunications software and networked
applications are the great challenges of our time
Tik-110.250 Fundamentals of Network Media, 22.3.2000, slide 24
© Arto Karila
Cultural Differences
• Cultural differences form a big obstacle to convergence
• Telecom and IT are two completely different cultures:
• The telecom culture is characterized by slow and thorough
standardization, long-term centralized planning, heavy
infrastructure and (still today) government regulation
• The IT culture, on the other hand, has always been market-
driven, poorly standardized and fast-moving
• Datacom as a culture is something in between the two
cultures mentioned above but clearly closer to IT than to
telecom and often even more anarchist in nature than IT
• It is difficult for representatives of these three cultures to
even communicate, let alone come to a common agreement
• Mixing cultures has always been difficult - motivation, time
and favorable circumstances are needed for a new joint
culture to grow