PARTIAL PRIVATE CIRCUITS
PPC ISH DUAL FIBRE WORKING/SINGLE FIBRE WORKING CONVERSION - SERVICE
DESCRIPTION
1. Outline of the Service
This is an enhancement of the current PPC product set, and BTW will be offering the following options:
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ISH/ISH extension dual fibre to single fibre working conversion
ISH/ISH extension single fibre to dual fibre working conversion
2. Key Features and Availability
Conversion of ISH and ISH Extension Fibres.
Conversion from Dual Fibre Working to Single Fibre Working will allow Communication Providers to
utilise more of their existing fibre Infrastructure. This is achieved by inserting a device called a “coupler”
into the into the Transmit/Receive path of the system (see diagram below). A coupler is a piece of
equipment that joins separate transmit and receive fibres into a single physical fibre path. Insertion of a
coupler has to be performed intrusively, although from a service perspective traffic can be placed onto
the second leg (either the transmit or receive path) during the change process. Therefore, service is
not lost, but is ‘at risk’ during the procedure.
Similarly, conversion from Single Fibre Working to Dual Fibre working will require Intrusive work to be
carried out and there will be a need for the customer to ensure that there is suitable fibre and
infrastructure available to make these changes.
It will also be noted that the change from Dual Fibre Working to Single Fibre Working (and vice versa)
will need to be highly collaborative between BT and the relevant CP, to ensure minimum downtime of
the service protection and to agree that performance is acceptable after the change, before re-instating
into traffic carrying.
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Dual Fibre Working
Rx
Tx
East I/F
West I/F
Customer
Core
ADM
ADM
West I/F
East I/F
Rx
Tx
Coupler
Coupler
Single Fibre Working
The Section layer protection mechanism is not affected by this change and will operate normally when
one or both legs are changed.
For BT to determine the acceptability of conversion from DFW to SFW, BT needs to understand the
distance of the In Span section. With this information, BT can calculate the ‘End of Life’ performance of
this section and determine whether the additional loses of SFW couplers compromise this value.
Therefore BT reserve the right to refuse a conversion on the grounds of compromising ‘End of Life’
capability (i.e. cable ageing). It will also be necessary to agree the end to end dB levels prior to the
change in order to agree whether any existing added attenuators need removing or reducing. BT will
require the customer to supply their current Receive level reading (measured in dB) for BT to take into
account with the BT end Receive levels. This will enable BT to calculate the available power budget and
consequent affects on SFW. BT could make all this information available to the customer if desired.
Technical information for ISH/ISH Extension Dual Fibre Working /Single Fibre Working
conversion.
STM-1 infrastructure
BT deploys only Single wavelength couplers in these builds.
supported in process or procedure.
Dual Wavelength is not currently
The 1310nm single wavelength coupler (i.e. uses 1310nm interface at each end of a section) introduces
10.9dB attenuation penalty per section. This includes an additional penalty to avoid same wavelength
reflections from the coupler for sections where line losses approach the tolerance of the available power
budget (BT does not use filters for this purpose).
When considered in conjunction with the BT standard fibre factor of 0.5dB/km at 1310nm, SFW on
STM-1 builds, this reduces the available reach of a section by almost 22km. This will preclude some
builds from conversion.
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STM-4 and STM-16 infrastructure
BT deploys dual wavelength couplers (1310nm and 1550nm bands) and relies on the ADM interface
having a Wideband receive tolerance.
The dual wavelength coupler introduces an attenuation penalty of 2.6dB per section. Since 1310nm is
used in one direction, BT use the standard fibre factor of 0.5dB/km and this equates to a reduction in
reach of 5km. This will preclude some builds from conversion.
Where Long Haul interfaces are deployed over short distances, it will be necessary to introduce
additional attenuation at the time of conversion, and cost will be incurred for attenuators on a bespoke
basis.
The figures of 10.9dB and 2.6dB are BT calculated planning parameters used by BT; they ensure 'End
of Life' compatibility and tolerance to fibre characteristics. The customer may use different values in
their own networks for their Coupler characteristics from their chosen supplier.
All SFW in BT employs a pre-defined Section Trace format. This is used on STM-1, 4, & 16 SFW
sections for diagnostic purposes when a fibre break is encountered. The Section Trace Mismatch alarm
is used to override any reflections from an ADMs' own end transmitter
The customer should advise BT of their Section Trace value to be recorded by BT as the expected
value from the customer. BT will advise the customer of the BT Section Trace value for recoding and
setting on the customers’ network.
Process requirements
The process will be highly collaborative between BT and the CP, in order to be executed reliably and
efficiently. There will be a number of steps in the process, which will take in to account:
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Compatibility between couplers; only approved manufacturers will be accepted for this work.
Testing will be undertaken BEFORE decommissioning to ensure suitability. BT reserves the
right to reject a conversion in the event that the circuit is not considered suitable.
Testing will be undertaken after change of couplers.
Section layer performance analysis will be undertaken after re-commissioning and insertion of
the couplers.
BT stresses the criticality of collaborative working, since engineers must be simultaneously at both ends
before, during, and immediately after the entire process. BT reserves the right to charge for time lost
through missed appointments.
It is imperative that customers check with their equipment supplier to ensure that the Interfaces they
deploy are compatible with this method of Single Fibre Working.
3. Order Handling and Provision
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These conversions will be ordered & delivered in the same way as the PPC Circuits, and will
use existing processes, systems and operational resource.
Conversions out of hours will occur at a time defined by mutual agreement between BT & the
customer.
Standard Lead Time for this product will be 50 day’s dependant on availability of attenuators &
couplers.
Compatibility between couplers; only approved manufacturers will be accepted for this work.
Testing will be undertaken BEFORE decommissioning to ensure suitability. BT reserves the
right to reject a conversion in the event that the circuit is not considered suitable.
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Testing will be undertaken after change of couplers.
Section layer performance analysis will be undertaken after re-commissioning and insertion of
the couplers.
BT reserves the right to refuse to carry out any conversion owing to technical and distance
constraints.
SFW on STM4 or STM 16 systems requires dual wavelength couplers to be installed. This
requires a 1310nm interface to be installed at one end of the Mux section and 1550 nm on the
other. Consequently, if the interface on both ends of the fibre is 1310 nm, either BT or the CP
will have to change its interface. In this instance the CP will be required to change the interface
at its end, as the process of changing the BT end could result in a loss of service for all circuits
on that system, and will be prohibitively expensive.
On STM-1 infrastructures BT uses 1310/1310nm couplers. If the infrastructure exists at
1550nm, BT will not offer the option to change to SFW because it is likely that the 1550nm
band has been used due to reach and SFW will take it out of distance limits.
At STM-4 and STM-16 infrastructures which were installed at 1550nm, BT requires that the CP
changes its end of the fibre to 1330nm in order to ensure that distance limits are not exceeded.
BT will reserve the right to turn down the change if there is insufficient power budget.
BT stresses the criticality of collaborative working, since engineers must be present
simultaneously at both ends before, during and immediately after the entire process. BT
reserves the right to charge for time lost through missed appointments.
This collaboration minimises the out of service time. BT will strive to keep this as short as
possible but can offer no warranties with respect to service being affected during the changeover.
4. Associated Documents
Title
BT Wholesale Carrier Price List
DSL In span Handover and PPC Provisioning Manual
PPC Operations & Maintenance Manual
Location
www.btinterconnect.com
www.btinterconnect.com
www.btinterconnect.com
5. Glossary
BT
BTW
CP
CSH
IP
ISH
STM
TISBO
PPC’s
CPE
TDM
MSH
PECN
PoH
ACO
ADM
British Telecom PLC
BT Wholesale
Communications Provider
Customer Sited Handover
Internet Protocol
In Span Handover
Synchronous Transport Mode
Traditional Interface Symmetric Broadband Origination
Partial Private Circuits
Customer Premises Equipment
Time Division Multiplexing
Marconi Synchronous Hierarchy
Public Electronic Communications Network
Point of Handover
Advanced Capacity Order
Add/Drop Multiplex
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CMC
CPL
CRF
CSH
ACO
ADM
CMC
NTU
PECN
PPC
PSI
QoS
SDH
SLA
STM
URL
Customer Management Centre
Carrier Price List
Customer Requirements Form
Customer Sited Handover
Advanced Capacity Order
Add/Drop Multiplex
Customer Management Centre
Network Terminating Unit
Public Electronic Communications Network
Partial Private Circuit
Product & Service Instance
Quality of Service
Synchronous Digital Hierarchy
Service Level Agreement
Synchronous Transfer Mode
Unique Resource Location
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