Network Management

1
Network Management

• Networking Concepts

2
What is communication?

• Moving Information from place to place.
• It need not be two way e.g. TV, Radio etc.
• It need not be between two people, e.g. a person
  using a WWW info. site.
• Lots of forms of communication face to face,
  FAX, Email, Telephone etc.

3
The paradox of communication

• In face to face communication there is body
  language, intonation, inflection, context etc.
  that add to the communication process.
• In all other forms of communication, the means of
  keeping in touch actually reinforces the feeling
  of separation.
• Most forms of telecommunication are
  impoverished and affect business and personal
  relationships - the medium is the message
  (McLuhan)

4
Fragmentation Fusion

• The more channels of communication there are the
  more fragmented the market becomes - consider the
  problems of promotional marketing with over 300
  TV channels.
• In terms of technology we see fusion or
  convergence taking place - fewer devices are
  being made but these devices have much greater
  functionality e.g. a mobile phone which also
  provides Internet access.

5
A Basic Communication System

• The transmitter sends symbols which represent
  information.The channel relays them.The receiver
  may get them.
• The channel is subject to noise and interference,
  the receiver may get distorted /incomplete info.
• The more symbols a system has, the more quickly
  it can convey information. - this is a key
  concept!

6
Users Designers

• A system user wishes to convey the full meaning
  of a message without error.
• A system designer wishes to extract the essential
  information so as to transmit it efficiently -
  this saves time/money.
• Neither is concerned with the physical reality of
  the message.

7
Synchronous Asynchronous Applications

• Synchronous applications are here and now e.g.
  video conferencing in which delays and
  interruptions are not acceptable.
• Asynchronous applications are delay tolerant e.g.
  a file transfer, email etc.
• While most business applications are asynchronous
  in nature the trend is toward synchronous.

8
Signalling Basics
1
0.4v
0.2v
0
Reference
Zero Voltage

• Digital signalling is easy to understand - the
  signal is the data, one voltage level for a 1
  another for 0 - it is only possible when a
  voltage can be applied directly to a cable.
  Usually termed pulse code modulation

9
Bits Bauds

• Bit rate number of bits per second
• Baud rate number of signals per second.
• Could have multiple bits per Baud, e.g. 4 levels
  instead of 2 - we could then send twice as many
  bits in the same time.
• This gives the communication system more symbols
  and hence makes it more efficient. This applies
  to digital and analog signalling.

10
Analog Signalling

• Analog signalling involves modifying a carrier
  wave - the signal is a representation or analog
  of the data
• There are three basic methods of modulation,
  amplitude, frequency and phase.
• Fast data rates require high frequencies, but
  high frequency waves are prone to attenuation
  (weakening) - key concept.

11
Bandwidth

• The range of frequencies that a medium can
  support is called bandwidth e.g. the bandwidth of
  the telephone system is 3,000Hz or 3.3 kHz
• The bandwidth of the telephone system has not
  changed much in 80 years yet modem speeds have
  increased enormously.
• Modems use combinations of phase/frequency and
  amplitude modulation to increase throughput - the
  baud rate has scarcely changed but the bit rate
  has increased - more bits per signal.

12
Important Points

• There is no relationship between data type and
  signal type, digital data can be sent using
  analog signals vice versa.
• Digital transmission is simpler, faster and
  cheaper than analog - we deal with one frequency
  instead of several.
• While digital is widely used in localised
  settings, most long distance transmission is
  analog.

13
Digital Communication

• If the data and/or the signal are digital - the
  communication is said to be digital.
• A digital mobile phone uses a restricted form of
  analog signalling as do ADSL and IDSN - they
  provide a digital service.
• Most digital services use analog signalling -
  remember digital signalling requires a voltage to
  be applied to a cable.

14
Networking Terminology

• A network is a set of independent interconnected
  devices which may exchange information.
• The key word is independent, this implies that no
  single computer is in control of the
  communication process. Devices and information
  are more inclusive terms than computer and data
• A protocol is the set of rules governing the
  exchange of information between devices - it
  covers who may transmit first, what to do in case
  of error etc.

15
Why Network?

• Networks evolved to meet two categories of need
  sharing resources and communication per se.
• Local area networks (LANs) - emphasis on
  sharing.(e.g. sharing printers, servers etc.)
• Wide area networks (WANs) - emphasis on
  communication
• Networks may be thought of as the glue that holds
  systems together and a means of providing
  failsoft services.

16
LANs WANs

• LANs have simple efficient protocols which deal
  with high speed communication over short
  distances and evolved to allow sharing of
  resources.
• WANs have complicated, inefficient protocols
  which deal with slow communication over long
  distances. They evolved to support communication.

17
LANs WANs

• However, as software has become network intrinsic
  we find LANs being used to provide an information
  infrastructure for entire organisations.
• Also with the advent of optic fibres (which
  provide high speed, almost error free
  communication over long distances) we can use
  efficient LAN like protocols over longer
  distances, Metropolitan Area Networks (MANs)
  interconnect business LANs within city limits.

18
Terminology

• Host or station a computer in the network
  running applications software, a station is a
  desktop machine while a host usually runs
  applications for lots of users.
• Subnet that which connects the hosts, i.e.
  switching elements and transmission lines.
• IMP (interface message processor) or Node a
  switching element in the network i.e. these
  handle the delivery of information through the
  network. (These terms apply to WANs, other terms
  are used in LAN contexts)

19
A Network
Host
Stations
Hosts
20
Topologies

• Star Network
• Reliant on central node, old fashioned mainframe
  thinking.
• Tolerant of link failure
• Many modern networks are multistar topology.
• The investment on the central node is wasted in
  part if it is handling communications as well as
  processing - dumb or X terminals

21
Topologies

• Tree Network - fewer links but more nodes.
• Control less central.
• Front end processors (concentrators) take load
  off central node (possibly a mainframe) saving
  upgrade costs
• FEPs can also be used in client server systems

FEP
Hosts
Hosts
22
Topologies

• Bus System or (Common Medium) All Stations use
  the same mediumcoaxial cable, RF etc.
• Central control possible but unusual - the
  Broadcast system gives some failsoft potential
• The interface would be inside the station
  (network interface card - NIC)
• Ethernet would be the best known example.

23
Topologies

• Ring Systems
• Simple, fast protocols
• Links could be simplex
• (most common) or full
• duplex
• most common

24
Topologies

• Arbitrarily connected (mesh) - connected as
  required, very good failsoft.(almost like the
  telephone network)
• Routing decisions made by local nodes.

25
Topologies

• Totally connected each node has a direct path to
  every other node
• High performance, no routing, good failsoft but
  very costly
• Suited to small, high speed networks.

26
Standards Architectures

• So far we have considered networks to be flat
  but we need to make a distinction between the
  application and the communication.
• Communications software takes the input - output
  needs of the application and translates them into
  a form the hardware can understand. This software
  is also distinct from the communication process.

27
Layered Architectures

• Clear division of functionality gives modular
  approach to development and ease of
  standardisation.
• Application independence - software assumes that
  services are available - no need to know about
  implementation details.
• Facilitates maintenance - it is easy to
  replace/omit or nominally implement a layer

28
Layered Architectures

• ISO Seven layer model provides a theoretical
  framework and an International Standard
• The model has been a great success but its
  protocols have not, they were just too
  complicated. TCP/IP won the protocol war.
• TCP/IP uses a four layer model, the principles
  are the same but the structure is simpler for the
  sake of efficiency.
• The text uses a 5 layer model ...

29
Standards

• In order to make technology manageable we must
  reduce complexity and diversity.
• Adopting widely used standards give use the means
  to do this.
• Additionally, standards help to reduce risk and
  cost.
• Remember standards may not be the best
  standards (e.g. VHS vs. Beta) but they are
  workable!