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Networking fundamentals
Part 1 – Basic concepts for data communication
Paul Brandt
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Paul Brandt, TNO-ICT
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Take home
Now
April 2nd,
15:30
• “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, it’s particulars
Then
April 16th,
17:15
• “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!
time
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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
“ service ”
between
• Coherent, related tasks are grouped into a single layer
=
“ functionality ”
• 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
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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
but abstracts the
ex.: adoes,
postoffice
details of implementation
from higher levels in the protocol stack.
• Do you know how your letter is routed, by what vehicles and
• Interfaces: The interface
makes the layer available to higher layers.
at what time, from the mailbox to grandmother’s home?
It defines the conventions
of communication
- what to send and what
• Do you need
to know?
to expect, but also
does
deal
with implementation details.
• Do
younot
want
to know?
• 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).
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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 (IBM’s 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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network layers – the TCP/IP approach (1/2)
•
It does what it needs to do – interconnect, and that’s
TCP/IP represents the factual all
reality
there is to it. It provides barebone functionality
as required by that moment and there are no
• with the objective to provide internetworking
provisions
for future use.
• i.e. glueing inherently incompatible networks
together
And that’s already complex enough!
• 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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Networking fundamentals
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ex.: mailbox
Network layers – the TCP/IP
approach
(2/2)
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network layers – the OSI stack (1/2)
application
• The applications & processes, controlled by the
end-user (or other system processes)
email
• provides services to user-defined application
processes, and not to the end user
Service interfaces
• Data syntax conversion (EBcDIC  ASCII)
• cryptographic encoding rules
• Setup, manage & ends the connections & sessions
• Provides for simplex, half-duplex, full-duplex
• Provides reliable data transfer services
• Controls the reliability of a network path (flow ctrl)
• Provides network routing services
• Fragmentation, reassembly & delivery errors
• Interactions of 2 devices with a shared medium
• Detect and possibly correct errors from layer 1
• Media Access Control address resolution
• Represents bits to physical quantities
• layout of pins, voltages, cable specifications …
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network layers – the OSI stack (2/2)
• Each layer prepends protocol-specific
control information to the data
• The combined data & control information
is considered the next layer’s 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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Networking fundamentals
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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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Networking fundamentals
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Network layers – the TCP/IP stack (2/2)
TCP: Transmission Control Protocol
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UDP: User Datagram Protocol
Reliable - TCP manages message
acknowledgment, retransmission and
timeout.
Unreliable - When a message is sent,
it cannot be known if it will reach its
destination
Ordered - Arrived in the wrong order,
data is hold until rearranged.
Not ordered - If two messages are
sent to the same recipient, the order in
which they arrive cannot be predicted.
Heavyweight – To handle connections,
reliability and congestion control makes
it a large protocol (overhead).
Lightweight - It is a small transport
protocol since there is little control.
Streaming - Data is read as a "stream,"
with nothing distinguishing where one
packet ends and another begins.
Packets may be split or merged into
bigger or smaller data streams
arbitrarily.
Datagrams - Packets are sent
individually and are guaranteed to be
whole if they arrive. Packets have
definite bounds and no split or merge
into data streams may exist.
Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network layers – connected hosts
medium
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Networking fundamentals
medium
medium
TNO-ICT, Delft, dinsdag 1 april 2008
2. Network buzz words
• Connectionless & connection-oriented
• Circuit-switched & packet-switched
• Unicast / broadcast / multicast / anycast / point-2-point
• Network segmentation
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Connectionless & connection-oriented
Connection-oriented
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Connectionless
Communicate with prior arrangements (i.e.
“over a connection”)
Communicate without prior arrangement: do
not establish a connection between devices
Protocol prescribes specific set of rules that
specify how
• a connection should be initiated
• a connection should be negotiated
• a connection should be managed
• a connection should be terminated
Swift flow more important than errorless
transfer:
• Fire & forget, send & pray
• As soon as a device has data to send to
another, it just sends it
Persistent network path
• Agreed during setup
• pre-computed & reserved by intermediate
nodes
• Fixed during session
Variable network path
• Break message into packets (datagrams)
• Network path differ between consecutive
packets
Unicast (point-to-point) only
Facilitates broadcast & multicast
Hence:
• Guaranteed QoS
• Delivery in order
Hence
• packet loss
• out-of-sequence delivery
• packet duplication
Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Packet-switched & circuit-switched (1/2)
circuit-switched
• A route is reserved in advance from source to destination
• Reservation depends on what's available at that time in the network
• A route is used for whole communication
• The circuit (route) is maintained by the network until released
• inefficient because capacity is wasted on connections which are not in continuous use
• connection is immediately available and capacity is guaranteed
Ex.: Telephony system
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Packet-switched & circuit-switched (2/2)
Packet-switched
A physical communication channel is effectively divided into an arbitrary number of logical variable bitrate channels or data streams
Route is packet dependent
•break information into packets
•packets are routed, combined or fragmented as network deems necessary
•receive individual packets (out-of-sequence) and re-assemble them into original information
Packet switching provides:
• optimal use of channel & network capacity and minimal transmission latency
• increased robustness of communication
• allows many pairs of nodes to communicate simultaneously over the same channel
Ex.: Swarm of pigeons
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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 packetswitched networks when applications require a connection.
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Transmission methods (1/3)
Unicast: 1-to-1
Multicast: 1-to-many
Broadcast: 1 to all
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
3. Network topology
•
•
•
•
•
•
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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
Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network topologies – types (1/3)
• Line
Also 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
• Ring
Each 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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network topologies – types (2/3)
• Star
Connects 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
• Bus
All 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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network topologies – types (3/3)
• Mesh
At 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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
4. Network equipment
•
•
•
•
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Devices
Wired & wireless media
Power over ethernet
Structured cabling
Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
Network equipment – devices (2/2)
• Bridge: layer 2
• Provides switch functionality, and
• Layer 2 protocol translator (ethernet <-> 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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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
•
•
•
•
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Twisted pair
Coaxial
Fiber
Power lines
Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008
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.
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Networking fundamentals
TNO-ICT, Delft, dinsdag 1 april 2008