Jacek Ilow

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OSI

• Jacek Ilow
• j.ilow_at_dal.ca

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Overview

• Wide Area Networking and Telecommunications
• Standard Organizations
• OSI Model
• WAN Technologies
• Digital Telephony
• QoS
• Summary

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WANs and LANs

• Wide Area Networks
• machines are spread over a wide geographical
  region
• comm channels are furnished by a third party
  (telephone company, public data networks)
• channels are of relatively low capacity (tens
  kbs)
• channels are error prone, BER10 E-5

• Local Area Networks
• machines are spread over a small geographical
  region
• comm channels are privatly owned
• channels are relatively high capacity (Mbs)
• channels are relatively error-free, BER10 E-9

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The Telephone Network

• The customer premise equipment
• telephone handsets, modems, PBX
• transmission facilities
• the local (subscriber) loop and the trunk lines
• switching facilities
• the main function is to interconnect and route
• local switching systems (central office)
• tandem switches connect trunks to trunks
• a toll switch that serves the long distance
  network

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Virtual Circuits vs Datagrams
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Packet vs. Circuit Switching

• Packet switching allows multiple users to share
  data-network facilities and bandwidth, rather
  than providing specific amounts of dedicated
  bandwidth to each user.
• Traffic passed by packed-switched networks is
  bursty and can be aggregated statisticall to
  maximize the use of on-demand bandwidth
  resources.
• There is much more overhead associated with
  packet switching as compared to circuit
  switching.
• Conncetionless character of packet switching in
  contradistinction to connection-oriented circuit
  switching allows routing around failed links,
  whereas in circuit switching the entire circuit
  would need to be switched

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Driving force for WAN

• More powerful applications have an impact on
  human productivity
• Bandwidth is becoming available to support these
  applications
• Decreased costs to use this bandwidth
• Increased computing power
• Decreased costs of telecomputing will make
  gigabit-based applications cost effective

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Bandwidth requirements of different media types
CIF Common Intermediate Format MPEG Moving
Pictures Expert Group
QCIF Quarter CIF JPEG Joint photographic experts
group
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WAN Technologies

• Synchronous Optical Network (SONET) or
  Synchronous Digital Hierarchy (SDH)
• a high-speed synchronous carrier system, based on
  the use of optical fiber technology and a defined
  digital multiplexing hierrarchy
• Frame Relay
• a fast relay service, with minimal network
  support offering bandwidth on demand
• Wireless Systems
• a wide array of wireless systems designed to
  support primarilly voice and low-speed data

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• Broadband Signaling
• a second-generation signaling technology (based
  on ISDN and SS7) used to setup and tear down
  virtual circuits
• Asynchronous Transfer Mode
• a high speed virtual circuit with cell relay
  technology
• Residential Broadband
• video on demand, client-server applications,
  Internet browsing on the local loop

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Standards

• Standards are required to govern
• the physical
• electrical
• procedural
• characteristics of communication equipment
• The principal disadvantage of standards is that
  they tend to freeze technology
• Standards and Regulation
• Voluntary standards (CCITT and OSI)
• Regulatory standards (FCC and Industry Canada)
• Regulatory use of voluntary standards

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Terms of Reference

• Telecommunications
• the technology of communication-at-a-distancethat
  permits information to be created anywhere and
  used everywhere
• Communication
• the transfer of information according to agreed
  conventions
• Standard
• a prescribed set of rules, conditions, or
  requirements concerning definition of terms
  classification of components specification of
  materials, performance, or operations
  delineation of procedures or measurement of
  quality describing products and materials
• Communication network
• set of devices, mechanisms, and procedures by
  which end-user equipment attached to the network
  can exchange meaningful information

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• OSI Standard
• provides conceptual and functional framework
  which allows international teams of experts to
  work productively and independently on standards
  for each layer of the Ref Model
• Bearer services
• means to convey information between users without
  alteration of the content of the message
• Connection
• a concatenation of transmission channels or
  telecommunication circuits, switching and other
  functional units set up to provide for the
  transfer of signals between two or more points in
  a telecommunication network, to support a single
  communication

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Standards Organizations

• CCITT - International Telegraph and Telephone
  Consultive Committee
• committee of the International Telecommunications
  Union (ITU) which itself is a United Nations
  treaty organization
• Study groupsNetwork organization Tariff and
  accounting principles Data communications
  networks Terminals for telematic services
  Switching and signaling Transmission performance
  of telephone network and terminals Transmission
  systems and equipment Data transmission over the
  telephone network ISDN
• As of 1993, CCITT is ITU-TSS (Telecommuni-cation
  Standardization Sector) in Geneva

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• IOS - International Organization for
  Standardization
• international agancy for the development of
  standards on the wide range of subject
• voluntary, non-treaty organization whose members
  are designated bodies of participating nations
• CCITT has primarily been concerned with data
  transmission and communication network issues
• the lower three layers of the OSI architecture.
• ISO has traditionally been concerned with
  computer communications and distributed
  processing issues,
• layers 4 through 7.
• The merger of the fields of data processing and
  data communications has resulted in considerable
  overlap in the areas of concern of these two
  organizations.

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Communications Architecture

• A communications architecture is a structured set
  of software modules that implement the
  communications function.
• The model provides a framework within which
  standards at each layer can be developed
  systematically and in parallel.
• Communications standards assure a large market
  and therefore promote lower costs through
  competition and mass production.
• Standards promote interoperability that is,
  standards promote the ability for products from
  different vendors to work together.
  Interoperability gives purchasers more
  flexibility in equipment selection and promotes
  distributed applications between and among
  different organizations.

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OSI Reference Model
Application Presentation Session Transport Network
Data Link Physical
AH
User Data
AH
User Data
PH
AH
User Data
PH
SH
AH
User Data
PH
SH
TH
AH
User Data
PH
SH
TH
NH
AH
User Data
PH
SH
TH
NH
LH
LT
AH
User Data
LT
PH
SH
TH
NH
LH
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OSI Reference Model..
Application Presentation Session Transport Network
Data Link Physical
Application Presentation Session Transport Network
Data Link Physical
Service to layer (N1)
Protocol with peer layer (N)
Layer (N)
Service to layer (N-1)
Comm Path
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OSI Network Service

• Independence of the underlying communications
  facility
• Network users need not be aware of the details
  of the subnetwork facilities used.
• End-to-end transfer
• All routing and relaying are performed by the
  network-service provider and are not of concern
  to the network-service user.
• Transparency
• The network service does not restrict the
  content, format, or coding of user data.

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OSI Network Service...

• Quality of service selection
• The network-service user has some ability to
  request a given quality of service.
• User addressing
• A system of addressing (NSAP addressing) is used
  that allows network-service users to refer
  unambiguously to one another.
• The essential requirement for internetworking is
  that the two communicating end users are
  presented with the same network service that is,
  they employ the same set of network-service
  primitives and parameters.