Part 1 Basic concepts for data communication

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Part 1 Basic concepts for data communication

• Networking fundamentals

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Paul Brandt, TNO-ICT

• If you have any questions or suggestions, do not
  hesitate to get in contact
• e paul.brandt_at_tno.nl
• t 015-2857056
• whttp//www.linkedin.com/in/paulbrandt

Questions cant be stupid. Only answers can.
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Objective

• Technical foundation to
• sift the wheat from the chaff
• know about possibilities and impossibilities
• familiarise with the buzz words
• Get a perspective on the blur of data
  communications

it's not the definitions that decide what
technology to use, but rather the technology that
indicates what kind of network you have!
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Take home

• What is it and what is it used for
• connection-oriented vs. connectionless
  communications
• circuit-switched vs. packet-switched networks
• network equipment (gateways, routers, switches,
  )
• protocols
• topologies
• standards
• proprietary, de-facto, dejure openness
• actuals related to domotics
• telecommunication, its particulars
• Home networking technologies overview
  analysis, TU/e TNO, December 2003
• it's not the definitions that decide what
  technology to use, but rather the technology that
  indicates what kind of network you have!

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1. Network layers
To understand any complex system is to break it
down into modular components and then analyze
what they do and how they interact
Networks are most often compartmentalized by
dividing their functions into layers
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Network layers what are they

• Each layer is responsible for performing a
  particular type of tasks
• Tasks can create very elementary functionality
  (buffering bits), very abstract functionality
  (stream video data) and everything in between
• Coherent, related tasks are grouped into a single
  layer
• Layers are conceptually arranged into a vertical
  stack
• Each layer only interacts with the layers above
  it and below it
• Each layer provides services to the higher
  layers
• Lower layers are charged with more elementary
  tasks such as hardware signalling, converting
  from bits to electrical signal and vice versa
• The middle layers in turn use these services to
  implement more abstract functions such as
  transporting data
• The highest layer uses these abstract services to
  implement user applications (email, web browsing)
• Layers use protocols to implement the actual
  communication

service functionality
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Network protocols what are they (1/2)

• A protocol often refers to a code of conduct, or
  a form of etiquette as observed by, for instance,
  diplomats.
• Diplomats must follow certain rules of ceremony
  and form
• to ensure that they communicate effectively
• to ensure that they communicate without coming
  into conflict
• to understand what is expected of them when they
  interact, which can be different for different
  conversation partners

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Network protocols what are they (2/2)

• Networking protocols define
• a language ( a logical 1 is represented with
  5 VDC, HTML )
• and a set of rules ( I will only read messages
  addressed to me )
• and procedures ( every receipt of a message will
  be acknowledged, except the ACK-msg itself )
• that enable devices / systems / applications to
  communicate
• In the context of the OSI Reference Model, a
  protocol is formally defined as a set of rules
  governing communication between entities at the
  same layer
• In the context of the TCP/IP model, a protocol is
  loosely defined as being similar to a
  communication service

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Network layers the OSI approach (1/2)

• Principle of abstraction
• Define services on a functional level, not how it
  is implemented
• Protocols are therefore transparent to higher
  layers
• OSI's major contribution to networking theory is
  in its distinct separation between three
  fundamental concepts
• Services A service defines what a layer does,
  but abstracts the details of implementation from
  higher levels in the protocol stack.
• Interfaces The interface makes the layer
  available to higher layers. It defines the
  conventions of communication - what to send and
  what to expect, but also does not deal with
  implementation details.
• Protocols These are private methods of
  implementation which the higher layers have no
  access to or knowledge of. Thus, they can be
  changed (i.e. to allow adding support for new or
  improved technology) without compromising
  integrity (i.e. altering the basic functioning of
  higher layers).

• ex. a postoffice
• Do you know how your letter is routed, by what
  vehicles and at what time, from the mailbox to
  grandmothers home?
• Do you need to know?
• Do you want to know?

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Network layers the OSI approach (2/2)

• Principle of abstraction was a good idea, and
  still is!
• Unfortunately
• the designers of the OSI model built the
  reference model before the protocols existed
• and did not understand from an engineering
  perspective where various pieces would optimally
  fit
• and had to deal with politics (IBMs SNA model)
• Hence the OSI Reference Model should be
  considered as
• an excellent educational tool, which terminology
  is widely-used to describe behavior and design of
  networks
• a crappy communication stack that you don't,
  really don't, want to implement as such!

!! Never, ever try to completely fit actual
protocols to the OSI layers !! ? use OSI as a
model, not as a factual reality
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Network layers the TCP/IP approach (1/2)
It does what it needs to do interconnect, and
thats all there is to it. It provides barebone
functionality as required by that moment and
there are no provisions for future use. And
thats already complex enough!

• TCP/IP represents the factual reality
• with the objective to provide internetworking
• i.e. glueing inherently incompatible networks
  together
• TCP/IP major contribution was that it was
  engineered, meaning
• it simply described the existing situation from
  an engineer's perspective and gave little thought
  to ensuring the model made sense
• it is pragmatic relatively simple
• it was required to be open
• it was for free and since it worked it became
  succesful

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Network layers the TCP/IP approach (2/2)
ex. mailbox Mailbox has got 2 entrances, one for
local mail and one for non-local mail. You
need to know the scope of local

• t was nice TCP/IP actually worked, and still
  does!
• Unfortunately, it only speaks its own language,
  i.e.
• common problems are not solved by a generic
  foundation
• protocols are not really transparent
• can't be used to intelligently describe another
  type of protocol stack
• Hence the TCP/IP reference model should be
  considered as
• an incomplete, best-effort to provide an
  (inter)networking solution that, without any
  guarantees, actually works out quite nicely most
  of the times
• really very difficult to explain how it's working
  in the first place

ex. experts disagree on whether TCP/IP should be
modelled with 2, 4 or 5 layers. ex. internet is
TCP/IP need I say more?
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Network layers the OSI stack (1/2)
application
email
Service interfaces
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Network layers the OSI stack (2/2)

• Each layer prepends protocol-specificcontrol
  information to the data
• The combined data control informationis
  considered the next layers data

• That data is offered to the service interface
• Data transfer is therefore vertical
• Protocols communicate horizontal(through
  protocol-specific control information)

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Network layers the TCP/IP stack (1/2)

• Similar services exist at different layers, ex.
  Address translation by DNS ARP
• Interconnection of multiple networks
• No formal or informal agreement about mapping of
  OSI TCP/IP stacks can be found in literature
• TCP connection-oriented
• UDP connection-less

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Network layers the TCP/IP stack (2/2)
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Network layers connected hosts
medium
medium
medium
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2. Network buzz words

• Connectionless connection-oriented
• Circuit-switched packet-switched
• Unicast / broadcast / multicast / anycast /
  point-2-point
• Network segmentation

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Connectionless connection-oriented
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Packet-switched circuit-switched (1/2)
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Packet-switched circuit-switched (2/2)
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Connections versus circuits

• A Connection is a logical thing whilst a circuit
  is a physical thing
• A connection implies peers are conscious of
  having established a communication, a circuit
  implies a physical route on layer 2
• ex. BBC radio broadcast connectionless over
  circuit
• A circuit is not a prerequisite for a connection
• Connection-oriented protocols will be used over
  packet-switched networks when applications
  require a connection.

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Transmission methods (1/3)

• Unicast 1-to-1
• Multicast 1-to-many
• Broadcast 1 to all

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Transmission methods (2/3)

• Unicast
• Messages that are sent from one device to another
  device they are not intended for others
• Eavesdropping! Unicast doesn't guarantee that
  others won't also read it, just that they
  normally will not do so
• This is the most common type of messaging, so
  this addressing capability is present in almost
  all protocols
• Broadcast
• These messages are sent to every device on a
  network
• Used for a variety of purposes, including finding
  the locations of particular stations or the
  devices that manage different services
• Broadcasts are normally implemented via a special
  address that is reserved for that function

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Transmission methods (3/3)

• Multicast
• Messages are sent to a group of stations that
  meet a particular set of criteria
• The most complex type of message because they
  require a means of identifying a set of specific
  devices to receive a message
• Anycast
• A message that should be sent to the closest
  member of a group of devices
• IPv6 only
• Point to point
• Only two devices are connected together
  everything sent by one device is implicitly
  intended for the other, and vice-versa
• Thus, no addressing of messages on a
  point-to-point link is strictly necessary
• ex. RS-232 protocol

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Network segmentation (1/2)

• subnetwork (subnet)
• A subnetwork is a portion of a network or a
  network that is part of a larger internetwork
• The abbreviated term subnet also has a specific
  meaning in the context of TCP/IP addressing
• Segment (Network Segment)
• A segment is a small section of a network
• In some contexts, a segment is the same as a
  subnetwork
• More often it implies something smaller than a
  subnetwork
• Earlier ethernet
• the coax cable itself was called a segment
• segment was shared by all devices connected to
  it, it became the collision domain for the
  network
• Totally unrelated TCP meaning Segment is the
  name of the messages sent in TCP

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Network segmentation (2/2)

• Internetwork (or Internet)
• refers to a larger networking structure that is
  formed by connecting together smaller ones
• In others, a network is differentiated from an
  internetwork based on how the devices are
  connected together
• where a network usually refers to a collection of
  machines that are linked at layer two of the OSI
  Reference Model
• using technologies like Ethernet or Token Ring
• and interconnection devices such as hubs and
  switches
• An internetwork is formed when these networks are
  linked together at layer three using routers that
  pass Internet Protocol datagrams between networks
• intranet vs. extranet
• intranet internal network that uses TCP/IP
  technologies
• extranet is an intranet that is extended to
  individuals or organizations outside the company
  boundaries

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3. Network topology

• Line daisy chain
• Ring is Line with identical start end point
• Mesh no particular structure, either partial or
  Fully Connected
• Bus implies single shared medium (ex. ether)
• Tree Extended Star
• Hybrids

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Network topologies types (1/3)

• LineAlso known as Daisy Chain, data hops from
  one node to another
• Increases latency
• Easiest way to add nodes
• Node or line failure results in network failure
• Limited data collision (only with single line
  half-duplex mode, only between adjacent nodes)
• Needs double line for full-duplex
• RingEach of the nodes is connected to two other
  nodes, similar to Line topology, however
• with the first and last nodes being connected to
  each other, forming a ring
• data generally flows in a single direction only
  (dual-ring in two directions)
• Dual rings are less susceptible to node or line
  failures

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Network topologies types (2/3)

• StarConnects all cables to a central point of
  concentration, usually a hub or switch. Nodes
  communicate across the network by passing data
  through the hub.
• Less susceptible for network failure
• Central node is SPOF
• Extended star or tree connect central nodes of
  more stars together
• Many nodes can be connected using few hops and
  thus low latency
• BusAll nodes are connected to a common
  transmission medium which has exactly two
  endpoints.
• data is received by all nodes in the network
  virtually simultaneously
• very susceptible for data collisions
• Bus endpoints need proper termination (echo
  induced collisions)

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Network topologies types (3/3)

• MeshAt least two nodes with two or more paths
  between them to provide redundant paths
• Decentralised as opposed to stars
• Implicit redundancy provides higher network
  reliability
• Fewer hops between nodes (and hence lower
  latency) implies complexer connections, up to
  full mesh (i.e. (n-1)! connections)
• Multiple paths also implies path ambiguity

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Network topologies 3 levels of abstraction

• Physical level topologies
• Nodes of a network and the physical connections
  between them
• The layout of wiring, cables,
• The locations of nodes, and the interconnections
  between the nodes
• Level 1 abstraction
• (Signal level topologies)
• The path that the signals take when propagating
  between the nodes
• Consider this equal to Logical Level Topologies
• Logical level topologies
• Level 2 and up abstraction
• The path that the data takes between nodes
• Logical topologies are able to be dynamically
  reconfigured by special types of equipment such
  as routers and switches
• The logical topologies are generally determined
  by network protocols as opposed to being
  determined by the physical layout

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4. Network equipment

• Devices
• Wired wireless media
• Power over ethernet
• Structured cabling

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Network equipment devices (1/2)

• Repeater Hub layer 1
• segment (length) extension by signal
  strengthening Ethernet up to 5 segments
  between 2 hosts
• signal in signal out
• identical speed over all segments
• collision repeater by jamming signal
• cable breakage less dramatic (results in 2
  operational, distinct networks)
• Switch layer 2 "switched ethernet"
• isolate physical layer (packet errors
  collisions to segment only)
• Learn location of devices (MAC addresses)
• various speeds, more optimal bandwidth usage

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Network equipment devices (2/2)

• Bridge layer 2
• Provides switch functionality, and
• Layer 2 protocol translator (ethernet lt-gt
  bluetooth)
• Creates logical network from individual physical
  segments
• Router Layer 3
• Layer 3 protocol implementation translation
• performs routing based upon protocol
  prescriptions
• Gateway Layer 4 and above
• Protocol implementation translation above layer
  3
• Interconnects end-to-end systems with varying
  protocols

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Network equipment Media (1/2)

• Wired media
• Don't take it for granted
• impedance signal distortian and length
• terminators and reflections
• environmental mutual interference
• Available wired media
• Twisted pair
• Coaxial
• Fiber
• Power lines

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Network equipment Media (2/2)

• Wireless media
• Radio frequency (RF)
• Differ in frequency transmission speed
• Differ in bandwidth available channels
• Differ in emmitted power distance
• Highly regulated
• Some radiobands are very crowded (WLAN, GSM)
• Infrared (IR)
• Requires line of sight
• Restricted to Point-to-point
• Hardly used

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Network equipment Power over ethernet

• Not to be confused with ethernet over power / PLC
• Powering network devices through ethernet cables
• Defined as IEEE standard 802.3af
• 48 VDC / 400 mA / 15.4 W max
• powered pairs may also carry data
• Extension to the standard IEEE 802.3at
• All pairs may carry power
• Provide up to 56 watts of power

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Network equipment Structured cabling (1/2)

• Defined by Telecommunication Industry Association
  (TIA) as TIA-942
• Telecommunications Infrastructure Standards for
  Data Centers, april 2005
• Defines
• Site space layout requirements to buildings
• Cabling infrastructure standards for
  terminology physical organisation
• Tiered Reliability standards for achieving 4
  levels of availability
• Environmental considerations a.o. power heat
  dissimination

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Network equipment Structured cabling (2/2)

• Cabling infrastructure defines
• Entrance Facilities is where the building
  interfaces with the outside world.
• Equipment Rooms host equipment which serves the
  users inside the building.
• Telecommunications Rooms are where various
  telecommunications and data equipment resides,
  connecting the backbone and horizontal cabling
  sub-systems.
• Backbone Cabling as the name suggests carries the
  signals between the entrance facilities,
  equipment rooms and telecommunications rooms.
• Horizontal Cabling is the wiring from
  telecommunications rooms to the individual
  outlets on the floor.
• Work-Area Components connect end-user equipment
  to the outlets of the horizontal cabling system.