Mitchell Technical Institute Telecommunications

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Mitchell Technical InstituteTelecommunications

• EC 249
• Outside Plant
• An Overview of
• Outside Plant

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Work Environment

• Telephone companies divided into two major
  divisions.
• 1. ISP
• Inside Plant
• 2. OSP
• Outside Plant
• Cable splicers must have full understanding of
  outside plant.

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OSP Terms

• Refer to Handout figure 2.1
• Trunk Cable
• Pedestal
• Subscriber
• BSW Buried Service Wire
• Distribution Cable
• Feeder Cable

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• Entrance Cable
• Junction Splice
• Arial Pole
• Aerial Terminal
• Central Office A B

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MDF

• Main Distribution Frame
• Handout figure 2.2
• Outside plant starts here
• Demarcation point
• The interconnection between telephone company
  communications facilities and the terminal
  equipment, protective apparatus, or wiring at a
  subscribers premises.

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MDF terms

• Connector blocks the termination point for all
  outside plant cable pairs onto the MDF.
• All equipment wire, from the protector units on
  the MDF inward toward the switching equipment, is
  considered the inside plant.

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• All wiring, cable fixtures, and terminal
  equipment from the protector unit outward toward
  the subscriber or field are considered to be OSP.
• The outside plant begins at the MDF protector
  block.
• The MDF connector block with its removable module
  units, provides protection from overvoltage and
  excess current.
• As well as a tie down point for the CO switching
  equipment jumpers.

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• Should lightning strike an OSP cable or should
  electric power lines come in contact with the
  telephone circuits, the MDF modules are designed
  to go open.
• This disconnects the cable pair from the
  switching equipment in an effort to protect the
  switch from electrical damage.
• Most CO circuits operate at 5 or -5 volts,
  higher voltage will cause damage to the delicate
  circuit packs within the switch.

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Tip Cables to the Vault

• OSP cables that terminate on the MDF connector
  are called Tip Cables.
• These tip cables are multiple paired cables with
  extra pairs to replace pairs that may go bad.
• Generally 22 24 gauge insulated copper wire.

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Vault Splice

• May be found overhead or under the MDF or mounted
  on the wall in the CO.
• The vault splice is defined as the point where
  the outside plant entrance cable is spliced to
  the MDF tip cables.
• Entrance cables are generally the largest size
  cable in OSP varying from 300 to 4200 pairs.
• Vault splices may be very large.

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• Vault splices use airtight closure to prevent
  corrosion of the internal connections.
• Vault splices will be grounded to the CEGB.
• Cable Entrance Ground Bar
• The purpose of this is to stop any lightning
  strike or power surge from passing through the
  vault splice and onto the MDF and associated
  equipment.

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Entrance Cables Go Outside

• The entrance cable leaves the vault and proceeds
  toward the field to the first manhole, the 1st
  major pedestal, or a riser pole.
• Where it enters the junction splice.
• Here the large entrance cable is spliced and then
  splits into trunk cables, feeder cables, etc.

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• Trunk cables contain pairs that connect directly
  to another central office or that connect to a
  remote office or foreign exchange (FX) circuits,
  tie lines, alarm circuits, and long distance
  trunks.
• Occasionally trunk cables will contain some
  subscriber circuits.
• Repeaters and amplifiers are common on trunk
  cables.

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Feeder Cables

• Also come out of the riser (junction) splice.
• These feeder cables are medium sized cables, 75
  600 pairs.
• And are used to feed into distribution cables for
  subscriber access.
• Feeder cables often contain load coils to improve
  transmission.

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Distributing Dial Tone

• Distribution cables distribute copper pairs to
  the subscriber terminals.
• Are hard spliced into or cross-connected onto
  feeder cables.
• Vary in size from 3 to 300 pairs.
• These cables are fitted with terminal blocks,
  which provide a connection point for the
  subscriber drop wire.

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• Occasionally, BSW
• Buried Service Wire is spliced directly to the
  cable pair without the use of a terminal block.
• From the distribution cable a drop (service)
  wire extends to the subscribers premises.
• The drop wire is the final link from the CO to
  the customer.

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• There it terminates in a demarcation jack of some
  type, often referred to as a Network Interface
  Device (NID), Subscriber Network Interface (SNI),
  or simply a protector.
• This demarcation jack is mounted on the house and
  provides protection against lightning strikes and
  power surges.
• The NID also provides a disconnect point where
  the subscriber or the telephone technician can
  test the line circuit.

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• OSP cables are often placed on poles Aerial
  cables, buried in the earth (direct buried or
  buried cable) or sometimes placed in conduit
  passing from manhole to manhole (underground
  cable).
• No matter the architecture they all serve the
  same purpose.
• To provide a singular and discrete circuit from
  the MDF to the subscribers demarcation point.
• Also providing electrical and physical protection
  from the elements.

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Summary - Terms to Know

• ISP
• Inside Plant
• MDF
• Main Distribution Frame
• OSP
• Outside Plant
• NID
• Network Interface Device

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• SNI
• Subscriber Network Interface
• Entrance Cable
• Trunk Cable
• Feeder Cable
• Distribution Cable
• Tip Cable
• Cross Connect Box
• BSW
• Buried Service Wire

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• Drop Wire
• Vault Splice
• Junction Splice
• Central Office
• Load Coil
• Aerial Cable
• Buried Cable
• Underground Cable
• Protector