Metropolitan Area Networks - PowerPoint PPT Presentation


PPT – Metropolitan Area Networks PowerPoint presentation | free to view - id: 109dd9-YzZlY


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation

Metropolitan Area Networks


... to any one type. For both isochronous and delay insensitive data. ... Special frames for isochronous communication (pre-arbitrated frames every 125 microseconds) ... – PowerPoint PPT presentation

Number of Views:164
Avg rating:3.0/5.0
Slides: 9
Provided by: dudley2


Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Metropolitan Area Networks

Metropolitan Area Networks
  • Chapter 8

Why MANs?
  • Metropolitan Area Networks evolved primarily to
    permit LANs to interconnect across a metropolis
    or a country.
  • Two major technologies
  • Distributed Queue Dual Bus (DQDB).
  • Fiber Distributed Data Interface (FDDI).

  • Adopted in 1990 by IEEE 802.6.
  • It is a multiplexing method.
  • Its medium is not limited to any one type.
  • For both isochronous and delay insensitive data.
  • The transfer of data messages between stations on
    two LANs is handled to appear as if they were on
    the same LAN.

DQDB cont.
  • Two busses accessible to every node.
  • Failure of one node can not incapacitate the
  • Empty frames are generated by the two sources
    annihilated at the sinks.
  • Different dual bus implementations
  • Open dual bus.
  • Point-to-point bus.
  • Looped dual bus.

How DQDB Works
  • Empty frames travel from sources to sinks.
  • Each node may peek non-destructively at the
    frames as they go by.
  • Empty, non-reserved frames may be used.
  • To write, a node logically ORs its message
    with, and replaces the content of the empty frame.

How DQDB Works cont.
  • To reserve a frame on Bus A, a node must capture
    an empty frame on Bus B and set the reserved
  • FIFO priorities are used.
  • Special frames for isochronous communication
    (pre-arbitrated frames every 125 microseconds).
  • A flag in the header indicates a special frame.

  • Standardized by ANSI X3T9.5.
  • Similar to IEEE 802.5.
  • Motivation for implementation was not only the
    interconnection of LANs but the need for high
    speed networking.
  • Support ring with maximum circumference of 100 km.

FDDI cont.
  • Data transmission speed 100 Mbits/s.
  • NRZI coding is used.
  • Dual counter-rotating rings.
  • Inner ring is mainly for back-up.
  • The bit error rate is low 1 in 1012
  • Each station is a repeater.
  • Self-healing nature.