ICSA 745 Transmission Systems Foundations for Emerging Technologies

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ICSA 745 Transmission SystemsFoundations for
Emerging Technologies

• Nirmala Shenoy
• Dept. of Information Technology
• Rochester Institute of Technology

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Scope

• Virtual circuits
• Connection oriented and connectionless services
• Variable and constant bit rate services
• Flow control and congestion management

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Scope

• User payload integrity management
• Address and identification schemes
• Multiplexing methodologies
• Switching, routing and relaying

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Virtual Circuits

• Physical circuit
• two users communicate directly with each other
  through a circuit
• Virtual circuit
• User unaware of sharing
• Intermediate systems relay information as they
  arrive

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Types of Virtual Circuits

• Permanent Virtual Circuit - PVC Allocated by
  contract
• Switched Virtual Circuits - SVCallocated on
  demand
• Semi-Permanent Virtual Circuits SPVC
• Not guaranteed continuous service

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Permanent Virtual Circuits

• Requires a contract agreement
• Provisioned on a continuous basis
• Entries stored at intermediate nodes for
  appropriate handling
• Payloads should carry assigned identifier
• Quality of service - throughput, delay, security,
  error-rates, etc. specified

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Switched Virtual Circuit

• Not pre-provisioned
• Call setup essential
• Connection request -virtual circuit number
  allocation, connection tear down
• Virtual circuit number is used during the session
  to route information
• Resources released when session is over

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Semi-permanent Virtual Circuits

• Pre-provisioned similar to PVC
• Does not guarantee that users will obtain level
  of requested service

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Connection-Oriented System

• Systems using virtual circuits
• Connection setup, connection tear down
• Forwarding nodes maintain connection information
  for packet handling
• Processing overheads
• Normally in-sequence delivery

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Connectionless Systems

• Does not employ virtual circuits
• No information maintained by intermediate nodes
• Ad hoc processing
• Known as datagram networks

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Comparison

• Connection-Oriented
• more control over traffic and servicing users
  QOS
• Faster payload processing
• Low end-to-end delays

• Connectionless
• No Qos guarantees
• Robust
• forwarding decisions to be made

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Coexistence

• Telephone networks throughout connection
  oriented
• TCP/IP based transfers end-to-end connection
  oriented, within the network connection less
• UDP/IP connectionless throughout
• Protocol Layer based

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Traffic Characteristics

• Different applications have different patterns of
  traffic
• Continuous
• Bursty
• Highly Bursty

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Variable Bit Rate

• Service preferred by bursty traffic
• Periods of lull and periods of heavy traffic
• Transmit and receive traffic asynchronously
• Loose timing and synchronisation between sender
  and receiver
• Traffic may be queued during bursts
• Non-real-time, Real time
• Example email, client-server apps, video(?)

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Constant Bit Rate

• Can be used by services requiring continuous
  bandwidth
• Predictable and bound delay, low jitter
• Normally preferred by real-time services
• Example voice, video, video-conferencing (?)

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Virtual Multiple Networks

• Integrated VBR and CBR service support
• All traffic is digitized
• Manage the different traffic and provide fair and
  suitable service for all traffic
• User perspective one network

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Flow Control

• Network QoS Requirement
• traffic should not saturate a network
• Should not exceed the networks capacity
• Methods of flow control
• Explicit
• Implicit
• None

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Explicit Flow Control

• Network explicitly informs end systems via
  explicit messages on the amount of traffic the
  end systems can send
• Users can increase traffic on congestion clearance

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Implicit Flow Control

• Informs user about congestion
• Packet dropping, messages
• User should reduce traffic, else data will be
  dropped
• Control messages
• user is violating service contract
• network is congested

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No Flow Control

• Network discards any traffic that is creating
  congestion
• Simple for network to implement
• User service requirements not met
• Connectionless networks have traffic regulation
  mechanisms
• carrier-sense collision
• issuance of tokens

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User Payload Integrity Mgmt

• All payload correctly received
• Network responsibility?
• End system responsibility?
• Do all applications need this feature?
• EFT, voice, video, data service based?

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Addresses Labels

• Connectionless systems Explicit Address
• each PDU uses explicit addresses for routing
• IP address - network/subnetwork/device
• Connection-oriented systems - Labels
• uses a short label or Virtual Circuit Identifier
• label used to index into state tables to
  determine the explicit location or forwarding
  information

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Multiplexing

• Frequency Division Multiplexing (FDM)
• each user has fixed portion of freq. spectrum
• Time Division Multiplexing (TDM)
• each user is given a slot
• slots are rotated among the attached users
• Statistical TDM (STDM)
• dynamically allocate time slots
• Code Division Multiplexing
• Usage of codes

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Network Interface

• User-to-Network Interface - UNI or SNI
• protocol that governs the interface between the
  user and the network
• Network-to-Network Interface - NNI or ICI
• protocol that governs the interface between
  networks

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Switching, Routing and Relaying

• Relaying forward data as it comes
• Switching comes in at one input is switched on
  to another
• Routing decision made on which path to take
• Source routing
• Non-source routing

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Network Interfaces

• UNI or SNI
• User network interface, subscriber network
  interface
• NNI or INSI within network
• Network- network interface, intra-network
  switching interface
• NNI or ICI between networks
• inter-carrier interface

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Convergence Operations

• Performed at UNI
• Add synchronization and accommodate different
  transfer rates
• Convergence Sublayer - CS
• Application specific
• Example error detection, synchronization

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Segmentation and Reassembly

• Segmentation is performed on the user traffic
  before it enters the network
• Reassembly is performed before data reaches end
  user