Megastream Repair

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Megastream Repair

• By
• Martin Sadler

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What is a Megastream?

• A point to point private leased circuit
• Usually provided at a data rate of 2megabites
• But can also be provided at 8 meg and 34 meg
• Circuits are presented at customer at either
• G703 BNC type connectors
• I421 telephone socket type plug
• X21 21 way socket
• Demarcation between BT and customer is this
• Point of connection

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What is a megastream used for?

• Point to point data traffic
• i.e. connecting lans together,connection to
• ISP ,computer networks video conferencing.
• Point to point speech traffic
• i.e. Connecting switchboards together/connecting
  remote sites to host switchboard etc.
• Mixture of data and speech

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Technology

• Megastreams are carried to the customer from the
  local exchange (serving section)
• Via
• Copper
• Optical
• Radio
• SDH
• A/SDH

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Copper 1st/2nd.gen.

• The serving section is made up of a transverse
  screened cable
• Where the go and receive pairs are separated by
  an aluminum foil screen
• to prevent cross talk.
• 1st. Generation Are relatively rare .
• The alarms scheme is very poor. Unable to apply
  loops either remotely or from the exchange.
• 2nd Generation known as 2lte on INS.
• Relatively common.
• Delivered at G703 only
• Unable to remote loop via WOOSH but able to
• Remotely loop from exchange .

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1st/2ndgen.Copper/Direct 2 and 42 Optical alarms

• Alarms
• Cat A indicates a fault on the serving section
• Cat B indicates a network fault i.e. AIS
• Cat C not used
• Cat D indicates customer equipment fault
• A 2Mbit Optic Fibre Serving Sect Fault
• B AIS Recd at local CP from Exch
• D CPs Fault - Customer Resp
• A Serving Section Alarm- BT Resp

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1st. Generation Optical

• Direct 2
• known at 2ote on INS
• Single 2 meg carried via optical serving section
• Relatively common.
• Delivered at G703 only
• Unable to remote loop via WOOSH but able to
• Remotely loop from exchange
• Similar alarms scheme to 2nd gen. copper

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1st. Generation Optical

• 42
• Known as Lx2 on INS
• Four 2 meg tribs carried over an 8 meg serving
  section
• Relatively common.
• Delivered at G703 only
• Unable to remote loop via WOOSH but able to
• Remotely loop from exchange
• Similar alarms scheme to 2nd gen. copper

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DWSS

• Digital Wideband Serving Section (DWSS)
• This is the next generation of megastream
  delivery and the
• majority on megastreams are carried via this
  technology.
• The serving section is made up of a go and a
  receive fibre
• But depending on the type of LTE/NTE fitted the
  band width
• Of the serving section can be either
• 2 Meg i.e. OX1 (1 2meg circuit)
• 8 Meg i.e. OX2 (4 2meg tribs. or 1 8 meg trib)
• 34 Meg i.e. OX13 (16 2 meg tribs. mixture of
  2meg 8meg
• tribs. or 1 16 meg trib. )

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DWSS

• On INS if equipment type is shown to be either
• OX1 ,OX2 or OX13 this indicates that the
  equipment is
• Of the 1st phase of DWSS equipment type
• And so can only be presented to customer at G703
  or I421
• All DWSS equipment types can in theory be remote
  looped
• Via WOOSH/TNS

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DWSS

• On INS if equipment type is shown to be either
• OX1 ,OX2 or OX13 this indicates that the
  equipment is
• Of the 2nd phase of DWSS equipment type
• And so can be presented to customer not only at
  G703 and
• I421 but also at X21
• As previously stated all DWSS equipment types can
  in theory
• be remote looped via WOOSH/TNS
• B,C or D

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DWSS ALARMSas seen on woosh

• 2-8MBIT/S MULDEX CARD REMOVED (TRIBS 1-4)
• indicates customer power fail
• TRIBUTARY 4 TRAFFIC IN FAIL LV/BOO OX2B 24
• indicates ais seen at LV/BOO(ie from network)
• TRIBUTARY 4 TRAFFIC IN FAIL LV/BOO OX2B 24 (NTE)
• loss of customer signal or ais from customer
• 
  

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CWSS

• Copper Wideband Serving Section (CWSS)
• Unlike 2nd. Gen. copper serving sections CWSS
  uses
• normal copper local pairs.
• Usually 2 twisted locals are used but over a
  certain distance
• 3 pairs are used.The 2 meg signal is divided by
  either 2 or
• 3 and sent over each pair or wires and then
  reconstituted at
• exchange for the xmit and customer for the
  receive. Although
• officially denied the CWSS section is generally
  the weakest
• link in a megastream and probably a good place
  to start when
• faulting a circuit

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CWSS

• As with DWSS 1st phase CWSS could only be
  delivered
• At G703 and I421.But 2nd phase can also be
  delivered at
• X21.Unfortunately we dont know how to tell the
  difference
• between the 2 on INS.
• On INS you will see CWSS2 or CWSS3 but this
  denotes the
• amount of pairs used .Local pair information is
  not on INS
• this information is held on CSS or sometimes
  CAMSS.
• When testing locals an fmo would expect to see
  120 volts
• towards the exchange and rectified loop towards
  the customer

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CWSS ALARMSas seen on woosh

• RECEIPT OF AIS (2MBIT/S) YMGS-ZEM 1 LDLS ZEM
  CWSS2
• means AIS from network.
• RECEIPT OF AIS (2MBIT/S) YMGS-ZEM 1 LDLS ZEM
  CWSS2(NTE)
• means AIS from customer
• LINE 1 BER GT 1.10-6 MAY-YEVOF 1 LDLS MAY CWSS3
  617 (NTE )
• means errors on serving section exch.-customer
  direction
• LINE 1 BER GT 1.10-6 MAY-YEVOF 1 LDLS MAY CWSS3
  617
• means errors on serving section customer to
  exch.direction
• LINE 2 NOT TRAINED BZ/D-YBGUB/E 1 LDLS BZ/D CWSS3
  110 (NTE)
• means fault on pair 2 of cwss section
• HIGH POWER FEED TO LINE L/WHI-YAFBF/D 3 LDLS
  
• means fault on local pair
  

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SDH

• More and more megastreams have an SDH element to
• them either as part of the network or as delivery
  into
• the customers premises. SDH is delivered at G703.
• It is not possible to remote loop via WOOSH but
  the SDH
• Control can apply loops at various points to
  assist testing.

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SDH Alarmsas seen on woosh

• these are examples of alarms reported by sdh
  equipment
• but do not indicate a fault on the sdh kit but on
  the signal
• going into the sdh port
• INTERMITTENT TRIB INPUT 840-20771-TRIB8/1-2
• TRIB INPUT LOSS OF SIGNAL
• HO PATH SIGNAL DEGRADE
• LO PATH EXCESSIVE BER Additional Repeats
• A common sdh alarm is COMMUNICATIONS FAILURE
  WITH NE
• this is not service affecting

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Access SDH

• A very new product providing a sdh serving
  section
• Unlike SDH this can be delivered at X21.
• Alarms are minimal although loops can be
  provided by
• SDH control.

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Megastream diagnostics and testing

• Because megastream alarm coverage is patchy
• diagnosing megastream alarms is not a precise
  science
• And course of action is decided on
• Alarms that are available
• Previous fault history
• Information from the customer
• Type of technology involved
• Guess work.
• Convenience

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AIS

• When AIS seen on a circuit always send fmo to
  opposite end to the end seeing AIS.
• If AIS seen both ends suspect network /high
  order fault.
• Or customer has removed there attachments at
  both ends

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Down With AIS Alarms

• AIS (traffic in fail ) seen at L/CLB
• Most likely to be either serving section fault at
  aend or loss
• Of customer signal at aend. Send fmo to aend
• RA(NTE) BR/C WG L/CLB
  RB(NTE)

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Down With Alarms

• AIS (traffic in fail ) seen at L/CLB (NTE)
• This indicate loss of customer signal or input
• Suggest advising customer that fault on his
  equipment
• If customer insists suggest fmo to RB and POC
  raised.
• RA(NTE) BR/C WG L/CLB
  RB(NTE)

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Using TNS to Loop circuits

• Providing the technology is correct i.e.
• DWSS or CWSS and TNS is connected and
• working megastreams can be looped from
• the circuit diagnostic tool icon on woosh
• this can be used during
• co-op with customer
• To facilitate a remote loop e2e (using only 1
  engineer)
• In an attempt to clear woosh alarms
• however you need to be aware of the implications
  of looping at the aend of an x21 delivered
  circuit.

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X21 Delivered Circuits

• X21 is a simple data transfer protocol which
  provides timing
• over the link to synchronise customers routers
• By convention the aend is always set to master
  and the bend
• to slave .
• When testing towards the aend of a looped x21
  circuit the
• fmo will see sync.loss and errors unless he sets
  his tester
• to external clock source or recover timing.
• Another way round this is to move the loop to the
  exchange
• instead of the customer but of course this
  doesn't test the
• whole circuit