National Communications System NCS Switching and Signaling SS7

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National Communications System (NCS)Switching
and Signaling (SS7)
David S. Finn Integrated Network Planning and
Implementation BellSouth Telecommunications David.
Finn_at_BellSouth.com 205-977-5018
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Switching and Signaling (SS7)

• This Presentation Will Focus on Central Office
  Switching and Signaling (SS7)
• However, first we will take a look at the type of
  damage inflicted on telecommunications by
  hurricanes like Katrina
• Where is BellSouths Network Most Vulnerable?
• For Hurricanes Like Katrina
• Outside Plant Facilities
• Local Loop
• T1 Carrier
• SONET Rings
• Central Offices
• Loss of Power
• Loss of Communication with other offices and with
  Customers
• Loss of Telemetry
• Loss of Signaling

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Switching and Signaling (SS7)

• Katrina Damage
• Outside Plant
• Above-ground poles and cables were wiped out in
  most areas near the eye of the hurricane
• Underground cables and manholes were flooded by
  the massive amount of water which poured into the
  area due to the levee breech
• Digital Loop Carrier Terminals were either
  destroyed or made inoperable by high water and
  loss of power

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Switching and Signaling (SS7)

• Katrina Damage
• Central Offices
• Total of about 117 central offices (including BST
  and ITCs) went out-of service immediately after
  Katrina hit
• Completely Destroyed (6-10)
• Some replaced by portable DLC systems
• Others replaced by moving remaining subscribers
  into Remotes such as EXMs
• Loss of Signaling (SS7)
• Mainly due to A-Link facilities being destroyed
• New Orleans LATA hit the hardest
• Loss of Power (-48v DC)
• Isolated Offices Emer. Power Generators ran out
  of gas
• Cell Towers
• Faced many of the same problems

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Switching and Signaling (SS7)

• TYPES OF SWITCHING ENTITIES
• Class 5 End Office (or C. O.)
• Connects subscribers telephone lines to the
  telecommunications network
• Provides BORSCHT functionality (Battery,
  Overvoltage protection, Ringing, Supervision,
  Codec, Hybrid and Testing)
• Provides line and trunk concentration
• Serves as a Host for Remote Offices
• Serves as an SSP - Connects to SS7 for
  signaling and AIN functions
• Tandem Central Office
• Serves as a hub for connecting voice trunks
  from numerous Class 5 end offices
• Provides voice trunk connections to Long Distance
  carriers and Wireless providers
• Provides E9-1-1 Routing to PSAPs
• Types include Lata/Access Tandem, Toll Tandem,
  E911 Tandem, TOPS Tandem

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Switching and Signaling (SS7)

• TYPES OF SWITCHING ENTITIES
• Signaling Transfer Points (STPs)
• Provide efficient, fast call setup and teardown
  of telephone calls
• Provide routing for database lookups (AIN, LNP,
  800, etc.)
• Are the primary switches used in a packet-based
  network as opposed to the circuit based network
• Provide Gateway Screening for Customer Access
  (IXCs, ITCs, CLECs, Wireless)
• Serve as the PSTN entry point into the VoIP
  Network

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Switching and Signaling (SS7)

• BellSouths Class 5 Central Offices
• 32 Analog 1AESS C. O.s (SSPs)
• 856 Lucent 5ESS C. O.s
• 355 5ESS Hosts and 501 Remotes
• 581 Nortel DMS C. O.s
• 285 DMS Hosts and 283 Remotes and 10 DMS-10
• 138 Siemens C. O.s (includes 85 Remotes)
• 1607 Total C. O.s with approx. 20.3 million
  NALs
• Hosts average about 24,000 lines
• Remotes average about 3,500 lines
• Other Stand-Alones average about 20,000 lines

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Switching and Signaling (SS7)

• BellSouths Tandem Central Offices
• 109 Tandems designated as Local, Access, LATA and
  TOPS
• Many of the switches that host the Tandems serve
  multiple Tandem functions
• Most of the Tandem switches are located in the
  same buildings as the Class 5 Central Offices

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Switching and Signaling (SS7)

• We are now going to look at how telephone lines
  enter a Central Office
• Then were going to see an example of how lines
  are concentrated within the CO
• After that, we will see how Central Offices are
  tied together from a signaling standpoint and
  how calls progress across the network from one
  CO to another
• And, finally, well take a look at how the
  various telephone networks across the United
  States are interconnected

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Switching and Signaling (SS7)
These are the cables carrying the copper wires
from your home into the cable vault below the
central office and up to the distribution frame.
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Switching and Signaling (SS7)
The wires are separated into the copper pairs
that provide your telephone service and run into
the back of the distribution frame.
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Switching and Signaling (SS7)
This is the front of the distribution frame where
the copper pairs are connected one-by-one to the
Central Office switch.
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Switching and Signaling (SS7)

• This shows an entire row of the distribution
  frame.
• Different types of frames in C. O. s
• MDF Main Distributing Frame
• TMDF Trunk MDF
• SMDF Subscriber MDF
• CMDF Combined MDF
• COSMIC Common Systems Main InterConnection
  frame

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Switching and Signaling (SS7)

• As an example, let us assume that all those
  cables entering the CO are comprised of about
  40,000 subscriber pairs
• How can a CO handle 40,000 lines?
• CONCENTRATION
• Allows Telcos to provide service to all
  subscribers while limiting the amount of CO
  equipment they must provide
• The next 2 slides show examples of
  Concentration

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A High Level View of Concentration
Switching and Signaling (SS7)
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Switching and Signaling (SS7)
ANALOG LINE CONCENTRATION
This graphic depicts a concentration ratio of
101. 640 lines enter at the left side and have
only 64 paths out of the switch into the network.

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Switching and Signaling (SS7)
This is one row of the central office switch, a
Lucent 5E. Each cabinet holds a number of cards,
or circuit packs plugged in to shelf slots.
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Switching and Signaling (SS7)
This is the multiplexing equipment for an OC 192
circuit that can carry 9.6 GB of data per second.
This equipment costs approximately 250,000.
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Switching and Signaling (SS7)
This is a fiber cross connect point where the
data from the multiplexers leaves the central
office on fiber trunks.
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Switching and Signaling (SS7)
CLECs can lease caged space for security
LECs are required by law to provide space for
CLECs (Competitive Local Exchange Carriers)
equipment inside their Central Offices
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Switching and Signaling (SS7)
Now were going to shift gears a little bit and
take a look at how a call gets from one CO (SSP)
to another SSP
SSP A-Link Diversity
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Switching and Signaling (SS7)
CALL SETUP EXAMPLE 1 Phone A calls Phone B
Caller B
Caller A
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Switching and Signaling (SS7)
NOTES FOR CALL SETUP EXAMPLE 1
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Switching and Signaling (SS7)
NOTES FOR CALL SETUP EXAMPLE 1 (CONTD)
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Switching and Signaling (SS7)
EXAMPLE OF END OFFICE CONNECTIONS
DLC
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Switching and Signaling (SS7)

• In Call Setup Example 1, the Users were
  connected to COs (SSPs) that shared the same STP.
• What happens when a call is made from a user
  assigned to an SSP connected to STP A to a user
  assigned to an SSP connected to STP B?

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Switching and Signaling (SS7)
CALL SETUP EXAMPLE 2
Signaling Network
STP Pair A
STP Pair B
B or D Links
A-Links
SSP B
SSP A
B
Voice Trunks
A
In the example above, phone A dials phone B. SSP
A sends an IAM over the A-Link to the STP. STP
A then forwards it on to STP B, which routes it
to SSP B according to the information in the IAM.
SSP B then determines the status of Phone B and
the availability of a vacant Voice Trunk before
sending signaling back to SSP A to complete the
voice portion of the call. Ringing is then
applied to the Phone B and audible ringing is
sent to Phone A.
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Switching and Signaling (SS7)

• Now were going to take a look at a typical RBOC
  (Regional Bell Operating Company) signaling
  network
• It could have multiple pairs of STPs, SCPs, SSPs
  and Tandems
• Industry Standard Rules of Signaling Links
• A and C-Links must have at a minimum 2-way
  diversity
• B and D-Links must have at a minimum 3-way
  diversity

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Switching and Signaling (SS7)
Typical Signaling Network
D
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Switching and Signaling (SS7)

• Typical RBOC SS7 Network Elements
• Six Pairs of Gateway STPs
• IXCs, ITCs, CLECs, Wireless Connected at
  Gateways
• Local SSPs
• Six Pairs of Local STPs
• Only BST End Offices (SSPs) Connected to Local
  STPs
• Eight Pairs of AIN SCPs (Caller ID, CLASS)
• Six Pairs of LNP SCPs
• Two LTF/800/LIDB Pairs of SCPs
• 5,780 Low-Speed (56kbs) SS7 Links
• 690 High-Speed (ATM, 1.536 mbs) SS7 Links

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Switching and Signaling (SS7)

• How does a call leave its home network and get
  all the way across the country?
• Next we will look at a diagram which depicts the
  signaling and voice paths that a long distance
  call might make

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Switching and Signaling (SS7)
Long Distance Carrier STP
B-Link
B-Link
STP
STP
Signaling Links
A-Link
A-Link
A-Link
A-Link
SSP
SSP
Access Tandem
Voice Trunks
Access Tandem
LD Tandem
RBOC A
RBOC B
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Switching and Signaling (SS7)

• This concludes the presentation
• Following is a list of acronyms with their
  definitions commonly used in the
  telecommunications industry

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Switching and Signaling (SS7)
ACRONYMS and DEFINITIONS
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Switching and Signaling (SS7)
ACRONYMS and DEFINITIONS
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Switching and Signaling (SS7)
ACRONYMS and DEFINITIONS
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Switching and Signaling (SS7)
ACRONYMS and DEFINITIONS