CEN 4500 Network Fundamentals

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CEN 4500 - Network Fundamentals

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• Part 8
• Network Properties

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Network Characteristics

• Ownership
• Private
• Owned by individual or Corporation
• Restricted to owners use
• Typically used by large corporations
• Public
• Owned by a common carrier
• Individuals or corporations can subscribe
• Public refers to availability, not access to
  data

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Network Characteristics

• Advantages Disadvantages
• Private
• Complete Control ?
• Installation and operating costs ?
• Public
• No need for dedicated staff ?
• Dependent on carrier ?
• Subscription fee ?

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Public Network Connections

• One connection per subscriber
• Typical for small company or individual
• Communicate with another subscriber
• Multiple Connections per Subscriber
• Typically large, multi-site corporations
• Communicate among multiple sites as well as with
  another subscriber

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Virtual Private Networks

• A service offered by common carriers
• Service provided over public network
• Usually used to interconnect sites of single
  corporation
• Acts like a private network
• No data sent to other subscribers
• No data received from other subscribers
• Data encrypted during transmission

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Network Service

• Two basic Types of networks
• Connectionless
• User generates packet which contains address of
  intended recipient
• Network takes over from that point
• Connection-Oriented
• Formally requests connection to receiver
• Waits for network to form connection
• Formally terminates connection when no longer
  needed

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Connectionless Networks

• Characteristics
• Packet must contain full identification of
  destination
• Each packet handled independently
• No setup required before transmitting
• No cleanup required after transmission
• Analogous to sending a postcard via USPS

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Connection-Oriented Networks

• Characteristics
• Network receives connection request
• Forms path to specified destination
• Dedicates path throughout transmission
• Shuts down path upon senders request
• Packets need not contain recipients full address
  after connection established - lowers overheads
• Analogous to a telephone call

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Service Paradigms
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Network Performance

• Two Primary Metrics Used
• Delay
• Time required for 1 bit to travel through the
  network
• Conceptually like the length of a pipe
• Throughput
• Number of bits-per-second that can be transmitted
• Conceptually like the width of a pipe

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Network Performance

• Delay
• Four types
• Propagation
• Switching
• Access (LANs)
• Queuing (WANs)

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Network Performance

• Components of Delay
• Fixed (nearly constant) Delays
• Propagation
• Switching delays
• Variable Delays
• Queuing

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Network Performance

• Throughput
• Usually specified as bps
• Two types often considered
• Bandwidth - the physical capabilities of the
  hardware comprising the network
• Effective Throughput - what really gets down the
  wire in a fixed amount of time.

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Network Performance

• Relationship Between the Two
• In theory, no relationship between delay and
  throughput - wrong
• All relative to traffic load load acerbates
  inherent delays, introduces other delays and
  consequently reduces throughput
• Load defined as ratio of throughput to capacity
• aka Utilization
• High utilization congestion

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Network Performance

• Newer Metric - Jitter
• Becoming more common as real-time video and audio
  become commonplace on digital networks
• Any delay in network corrupts end result
• Two different approaches to the problem
• Isochronous Networks
• Asynchronous Networks

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Network Performance

• Isochronous networks used by telephony-based
  common carriers
• Guarantees that each packet transmission will
  experience the exact delay over a network
• Regardless of number or quality of paths used,
  delay will be constant

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Network Performance

• Asynchronous networks used by data-only carriers
• Do not guarantee delay length
• Newer protocols (network-specific software) have
  been developed to counter jitter-related
  problems ie buffering

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Required Reading

• Comer, chapter 15