BT NETWORK
INTERCONNECTION
PROVISIONING
MANUAL
SECTION 9 – STP WORKING
BT NETWORK INTERCONNECTION PROVISIONING MANUAL
Section 9 –STP Working
CONTENTS
CONTENTS ................................................................................... 2
9.1 INTRODUCTION ................................................................................... 3
9.2 STP Architecture .................................................................................. 3
9.2.1 BT STP to CP STP Architecture .......................................................................4
9.2.2 BT STP to CP End Point Architecture .............................................................6
9.2.2 BT STP to CP End Point Architecture .............................................................7
9.3 STP Signalling Link Physical Realisation ........................................ 8
9.3.1 Option 1 ..................................................................................................................9
9.3.2 Option 2 ..................................................................................................................9
9.3.3 Option 3 ..................................................................................................................9
9.3.4 Identification of physical realisation .....................................................................9
9.4 Planning and dimensioning restrictions .......................................... 10
9.5 Technical issues for Operators to address .................................. 10
9.6 STP working documentation ............................................................ 11
9.7 DOCUMENT HISTORY ..................................................................... 11
ANNEX A - STAGES AND KEY ACTIVITIES .................... 13
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Section 9 –STP Working
9.1 INTRODUCTION
STP working is designed to allow SS7 messages that are related
to:
a). a traffic route between an Operator Switch and a BT DLE to
be passed between the two end point switches, that terminate the
traffic route, without the need for dedicated signalling links between
these two end point switches. Instead of the SS7 messages passing
directly between the two end point switches, the messages are
delivered via intermediate signal points which are known as Signal
Transfer Points (STPs).
b). a traffic route between an Operator Next Generation Network
and a NGS type BT DMSU, or NGS type BT DJSU, to be passed
between the two end points, that terminate the traffic route (or the
relevant call control element), without the need for dedicated
signalling links between these two end points. Instead of the SS7
messages passing directly between the two end points, the
messages are delivered via intermediate signal points which are
known as Signal Transfer Points (STPs).
This section describes the Architecture that may be employed, the
planning and dimensioning restrictions that apply and documentation
required when STP working is to be used.
The scenarios where STP working may be applicable are set out in
Paragraph 5.2.13
and Appendix E of Annex A (Planning and
Operations Annex) to the BT Standard Interconnect Agreement.
9.2 STP Architecture
As stated above the scenarios where STP working may be applied
are detailed in the SIA and the BT STP Network has been
designed accordingly. The BT STP Network will allow STP working
in support of:
a). C7 Datadial routes at DLEs (including Restricted NTS Voice
traffic),
b). FRIACO Routes at DLEs and
c). Restricted NTS Voice traffic routes at DLEs.
d). Traffic Routes between an Operator Next Generation Network
and a NGS type BT DMSU, or NGS type BT DJSU, for all Traffic
Types.
STP working is not to be used for any other purpose.
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Section 9 –STP Working
There are two possible architectures that may be employed for STP
working in support of the DLE interconnect routes, these are shown
in the following sections.
9.2.1 BT STP to CP STP Architecture
The first architecture is where the Operator employs dedicated STP
units within their own Network and it is to these units that the
signalling links to/from the BT STP Units will terminate. The
messages being passed from either:
a). BT DLE - BT STP - CP STP - CP End Point or
b). BT NGS - BT STP - CP STP - CP End Point
There are a number of points to note concerning the structure of
the BT STP Network with regard to this STP interconnect
architecture.

BT have 6 STP Units operating in 3 pairs

The 3 pairs are Alpha - RG/P/UA & LS/WGT/L, Beta - L/ES/UW
& GR/UM and Gamma - GW/UD & NG/UM

All BT DLEs will be connected to one of these pairs of BT
STPs as their parent STPs

All BT NGSs may be connected to each of these pairs as
requirements drive such connection.

The BT STP pairs are connected with each other, although this
cannot be utilised when the Operator is using STP Units as
only 2 STP units are allowed in a signalling path

An STP Route between the CP STPs and a BT STP Pair
consists of 2 Linksets, each of which consists of at least 2
Signalling Links

An STP Route between the CP STPs and a BT STP Pair will
have; 1 Linkset connecting one of the CP STPs and one of the
BT STPs in the pair, with the other Linkset connecting the
second CP STP to the second BT STP in the pair

To reach a BT DLE dependant on a BT STP Pair the Operator
STPs must have an STP Route to that BT STP Pair and send
the signalling for the dependant BT DLE via its parent BT STP
Pair.
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Section 9 –STP Working
BT DLE - BT STP - CP STP - CP End Point
In the diagram; The signalling for the traffic route shown must go
via an STP Route with Linksets provided between CP STP A - BT
STP B and CP STP B - BT STP D
BT
Node
STP E
STP Route 3 =
STPs E & F = Gamma Pair DLEs
only
BT
Node
BT
Node
STP F
CP
CP
STP A
NODE
STP A
STP B
STP C
STP D
BT
Node
Speech/Data Circuits
STP Route 1 =
STPs A & C = Alpha Pair DLEs
only
STP Route 2 =
STPs B & D = Beta Pair DLEs only
BT
Node
CP
STP B
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Section 9 –STP Working
BT NGS - BT STP - CP STP - CP End Point
In the diagram; The signalling for the traffic route shown goes via
an STP Route with Linksets provided between CP STP A - BT
STP B and CP STP B - BT STP D (i.e. CP STPs connected to
BT Beta pair STPs). However, if the CP STPs were connected to
BT STPs A and C (i.e. BT Gamma pair STPs) then BT will
connect the relevant NGS to BT STPs A and C.
STPs A & C = Alpha Pair
STP E
STP F
CP
CP
STP A
STPs E & F = Gamma Pair
NODE
STP A
STP B
STP C
STP D
Speech/Data Circuits
STPs B & D = Beta Pair
STP Linkset =
BT
NGS
CP
STP B
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Section 9 –STP Working
9.2.2 BT STP to CP End Point Architecture
The second architecture is where the Operator does not employ
dedicated STP units within their own Network and it is the
Operator’s End Point units that the signalling links to/from the BT
STP Units will terminate. The messages being passed from BT DLE
- BT STP - CP End Point Switch.
STP Route 1 =
STPs A & C = Alpha Pair DLEs &
non-dependant DLEs if necessary
STP Route 2 =
STPs B & D = Beta Pair DLEs &
non-dependant DLEs if necessary
BT
Node
STP E
STP F
STP A
STP B
STP C
STP D
STP Route 3 =
STPs E & F = Gamma Pair DLEs &
non-dependant DLEs if necessary
BT
Node
BT
Node
BT
Node
BT
Node
CP
NODE
Speech/Data Circuits
Speech/Data Circuits
There are a number of points to note concerning the structure of
the BT STP Network with regard to this STP interconnect
architecture.

BT have 6 STP Units operating in 3 pairs

The 3 pairs are Alpha - RG/P/UA & LS/WGT/L, Beta - L/ES/UW
& GR/UM and Gamma - GW/UD & NG/UM

All BT DLEs will be connected to one of these pairs of BT
STPs as their parent STPs

The BT STP pairs are connected with each other

An STP Route between the CP End Point and a BT STP Pair
consists of 2 Linksets, each of which consists of at least 2
Signalling Links
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Section 9 –STP Working

An
will
the
CP

To reach a BT DLE dependant on a BT STP Pair the Operator
does not have to have an STP Route to that BT STP Pair, as
the signalling for the dependant BT DLE may go via a nonparent BT STP Pair to reach its parent BT STP Pair. However,
if an STP Route exists between the CP End Point and the
parent BT STP Pair then it is desirable to send the signalling
via the parent STP Pair

In the diagram; STP Routes are shown between the CP End
Point and all 3 BT STP Pairs, this is not a mandatory
requirement as the previous bullet point indicates.
STP Route between the CP End Point and a BT STP Pair
have; 1 Linkset connecting the CP End Point and one of
BT STPs in the pair, with the other Linkset connecting the
End Point to the second BT STP in the pair
9.3 STP Signalling Link Physical Realisation
2Mbit/s
Through Connected Timeslots
Option 1
STP
STP
NGS
NGS
OLO
CP
NODE
NODE
Speech Circuits
New BT DLE - STP
Signalling Linkset
OLO
CP
NODE
NODE
Option 3
BTDLE
DLE
BT
Option 2
OLO
CP
NODE
NODE
CP to BT STP
Signalling Linksets
The STP signalling links are not connected between the CP
STPs/End Points and the BT STPs directly using dedicated 2Mb/s
systems. The signalling links are 64Kb/s channels that are
transported between the CP Network and the BT Network using
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Section 9 –STP Working
previously spare 64Kb/s channels on traffic carrying interconnect
2Mb/s systems.
The diagram above illustrates the three possible methods that can
be used to transport the signalling links from the Operator’s
Network into a point within the BT Network.
9.3.1 Option 1
This shows the scenario where the STP signalling link is configured
onto a spare 64Kb/s channel within a 2Mb/s interconnect system
that is connected to an NGS that is co-sited with a BT STP unit.
This 64Kb/s channel is then connected across the NGS unit as a
Through Connected Circuit (TCC) onto a dedicated 2Mb/s system
connecting the NGS unit to the co-sited BT STP unit. The circuit is
then connected to the relevant signalling terminal equipment in the
BT STP Unit.
The signalling link may equally be delivered over a 2Mb/s
interconnect circuit that terminates on a DMSU or NGS that is not
co-sited with the BT STP Unit. In this case the TCC would extend
the 64Kb/s channel from the DMSU or NGS where the 2Mb/s
interconnect circuit is terminated on through the BT Network to the
co-sited NGS and then on to the BT STP Unit.
9.3.2 Option 2
This shows the scenario where the STP signalling link is configured
onto a spare 64Kb/s channel within a 2Mb/s interconnect system
that is connected to a BT DLE. This 64Kb/s channel is then
connected across the BT DLE as a Through Connected Circuit
(TCC) onto a dedicated 2Mb/s system connecting the BT DLE unit
to the parent BT STP unit(s). The circuit is then connected to the
relevant signalling terminal equipment in the BT STP Unit.
9.3.3 Option 3
This shows the scenario where the STP signalling link is configured
onto a spare 64Kb/s channel within a 2Mb/s interconnect system
that is connected to a BT DLE. This 64Kb/s channel is then
connected across the BT DLE as a Through Connected Circuit
(TCC) onto a spare 64Kb/s channel between the BT DLE and the
NGS that is co-sited with the BT STP Unit, this may be directly or
via other DMSU/NGS Units. The 64Kb/s channel is then connected
across the co-sited NGS unit as a Through Connected Circuit
(TCC) onto a dedicated 2Mb/s system connecting the NGS unit to
the co-sited BT STP unit. The circuit is then connected to the
relevant signalling terminal equipment in the BT STP Unit.
9.3.4 Identification of physical realisation
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Section 9 –STP Working
The Operator will identify the 2Mb/s interconnect system that is to
be used for the delivery of each STP signalling link into the BT
Network, this is then documented by the Operator within the
appendix 26 form from the Interconnection Provisioning Manual.
The BT Signalling Design Team will arrange for the allocation of
the Signalling Termination Equipment and the building of the
Through Connect Circuit in accordance with the appendix 26
requirements.
Consideration of both the Traffic carrying Interconnect 2Mb/s circuit
used to transport the STP signalling links and any switches that
the STP Signalling Links pass through (as through connected
circuits/nailed-up timeslots) must be given in order to ensure diverse
routing of the STP Signalling Links and, therefore, Network integrity
and security. This must apply to the STP Signalling Link transport
within both BT’s and the Operator’s Networks.
9.4 Planning and dimensioning restrictions
The restrictions applied to the use of STP working in support of
interconnect routes to BT DLEs, NGS type BT DMSUs and NGS
type BT DJSUs are contained within Appendix E of Annex A to
the BT Standard Interconnect Agreement.

BT will allocate the BT STPs to be used for all linksets, the
Traffic Routes to STP Routes and the Primary/Secondary STPs
within each STP Route (Appendix 26)
9.5 Technical issues for Operators to address
The following are issues with STP working that the Operator should
address.

Provide BT details of % signalling loads (peak and average) per
linkset (appendix 26).

Provide BT with the maximum STP signalling link loading
threshold if other than the 40% maximum loading threshold
required by BT.

Provide BT details of their Signalling routings to support BT
DLE, NGS type BT DMSU and NGS type BT DJSU interconnect
utilising STP working.

Must ensure MTP congestion control works end to end.

Network management processes are required.

BT would prefer to connect to CP STPs

Testing of STP Network configuration will be required (OTM).
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Section 9 –STP Working

Testing for each new interconnect will be required (OTM).

New Interworking Points Codes required at all interconnect points

Knowledge of CP STP signalling routing under CP STP failure is
required.

Network Management Controls will be invoked if excessive
signalling over STP path occurs.

STP working is significantly more complex than direct signalling.

Increased possibility of signalling network problems

Careful end to end design required.

Detail is dependant on the architecture of networks involved

RESULT OF STP WORKING IS A UK SIGNALLING NETWORK
9.6 STP working documentation
The BT Interconnect STP Connection and Signalling Path Profile
should be compiled using the forms contained in Appendix 26
to
this Manual.
Explanatory notes to assist with the completion of the form are
provided.
Electronic templates can be supplied to the OPERATOR by BT to
enable the information to be supplied to BT in electronic form, or
they can be obtained from the BT web site.
The Key Stages and activities in the procedure to be followed by
the OPERATOR and BT when STP working is to be employed
shown in Annex A.
9.7 DOCUMENT HISTORY
ISSUE
No.
3.1
DATE
12/01/2001
AUTHOR
Kevin Young
SUMMARY OF CHANGES
Initial issue of this new section.
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Section 9 –STP Working
3.2
12/02/2003
Kevin Young
Reviewed and updated.
3.3
17/02/2004
Kevin Young
Updated for the launch of STP for NTS
Voice.
3.4
12/09/2006
Kevin Young
Updated for launch of STP to NGSs for
Operator Next Generation Network
connection
3.5
12/02/2009
Kevin Young
Updated to include STP to NGS type BT
DJSUs for Operator Next Generation
Network connection
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Section 9 –STP Working
ANNEX A - STAGES AND KEY ACTIVITIES
FLOWCHART FOR
STP Working
required
COMPLETION OF
APPENDIX 26
No App26
required
N
Y
Operator completes; Operator STP/End Point
1141 code & IWPC and whether the units are
STPs or not, plus SS7 version Then submits the
APP26 to BT (TAM)
TAM forwards App26 to BT
Sig. Design Team
BT (Sig. Design) allocate the traffic routes from ACO onto
STP Route(s) and replicate the App26 as necessary.
BT also allocate the BT STPs for each STP Route and
assign an STP Route “N” designation to each STP
Route. App26 is returned to Operator via the TAM.
Operator completes the SS7 Message profile for each STP
Route based on the traffic routes allocated to each STP
Route. The Operator also completes the Physical delivery
section for all Sig. Links within each STP Route, stating
which 2Mb/s (ICON) is to be used for the transport of the
Sig. Links between the Operator’s Network and BT’s
Network. The Operator resubmits the App26 to BT
(TAM) . The Appendix 26 is then an order form for both
STP working on the interconnect routes plus an order
form for the STP Signalling Links that are NEW.
BT TAM amends
ACO to show correct
STP Route
allocations for each
TFC route and
forwards to
Operator and
BT CTC
TAM forwards App26 to BT
Sig. Design Team
Operator acknowledges
ACO amendment
B
A
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Section 9 –STP Working
B
A
BT (Sig. Design) assess the SS7 Message
Profile for each STP Route (App26)
Y
Changes
required to TFC
Route allocations on App26
as a result of SS7
Message
Profile.
N
BT (TAM) agrees App26(s)
and forwards to Operator.
Operator submits the completed
Appendix 26 form to the BT CTC,
as an order for STP working on the
detailed Operator-BT
interconnect Routes and as an order
for the NEW STP Signalling Links
shown.
Order progression of
STP Sig.Link orders
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