2. Agenda
Brief Current SS7 Network Overview
Why SS7oIP?
Technologies
Sigtran Protocol
Deployment Strategy/ Interim Architecture
IP Core Requirements
SS7oIP Architecture for full scale Deployment
Q & A
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3. SS7 Network Today
• A-Links: Connect SSPs/ SCPs (end office switches/
databases) to STPs via 56K TDM/DS0
• B-Links: Connect STPs to STPs on the SS7 network via
56K TDM/DS0
• C-Links: Connect mated STP pairs together for
management messaging and emergency re-routing over
56K TDM/DS0
• D-Links: Connect STPs to other carriers’ STPs for
messaging off-net, 56K TDM/DS0
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4. SS7 Protocol Stack
• MTP consist of 3 levels, its purpose is to reliably transfer
messaging across the SS7 network
• MTP1-Physical interface (v.35 serial interface running at
56K or 64K)
• MTP2-ensures that messages are delivered in sequence &
error free (CRC-16)
• MTP3-provides the message routing & failure handling
(adds DPC/OPC, performs Changeover/ Changeback, tries to
restore failed links
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5. SS7 Protocol Stack Cont.
MTP1
SCCP
Network
T
U
P
Physical
Data Link
ASP
TCAP
B
I
S
U
P
I
S
U
P
MTP MTP2
MTP3
• SCCP-provides enhanced features to
support circuit-related (GTT) & non-
circuit-related signaling information
(TCAP queries). SCCP is able to
reach destination in the network by
using SSN/DPC combos
• TCAP-used for query/retrieval of
information from databases, uses
SCCP transport, puts in request for
data & waits for result
• ISUP-provides call set up & tear
down, identifies circuits for voice
path
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6. Why SS7oIP?
• *Cost Savings-
Packet networks are less expensive than leased circuit networks
Reduction of infrastructure costs on leased lines & signaling ports
• Flexibility-
Creates a many-to-many ratio for signaling
Multiple signaling points via one network link
• Infrastructure Performance-
Takes advantage of high speed & intelligent routing offered by IP transport networks
• Convergence-
Offload or migrate legacy TDM-based signaling traffic to the IP backbone
Access IP or SS7 databases & nodes from same network
• New Business Opportunities-
As SS7 & IP networks converge so do their businesses. SS7/IP is a key enabling technology for new business
opportunities in new markets
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7. SS7oIP Technologies
• 2 distinctly different technologies:
*Sigtran Protocol
Conversion of SS7 to Sigtran for transport over the IP
network (Sigtran has built-in fail safes to aid the IP core)
*TDMoIP Circuit Emulation
Encapsulation of TDM circuit for signaling transport over
the IP network without manipulating the SS7 protocol (this
technology heavily relies on the stability of the IP core)
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9. IETF Sigtran Working Group
• Group of SS7 and SS7/IP infrastructure vendors
designing SS7 over IP standards
• http://www.ietf.org/html.charters/sigtran-charter.html
• Tasked to create Transport and Stacks for reliable SS7oIP
protocol suite
• SCTP (RFC2960): Protocol for reliable and sequenced
delivery of SS7 MSUs
• Adaptation Layers: M2UA,M2PA,M3UA,SUA
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10. Sigtran Protocols
• SCTP (Stream Control Transmission Protocol, RFC2960)- transport layer that
provides reliable data transfer
• M2PA (MTP2-User Peer to Peer Adaptation, draft status)- provides MTP3
with equivalent transport layer services as MTP2
• M2UA (MTP2-User Adaptation, RFC3331)- client/server protocol providing
a gateway to legacy SS7 network for IP-based applications that interface at the
MTP2 layer
• M3UA (MTP3-User Adaptation, RFC3332)- client/server protocol providing
a gateway to legacy SS7 network for IP-based applications that interface at the
MTP3 layer
• SUA (SCCP-User Adaptation, draft status)- client/server protocol providing a
gateway to legacy SS7 network for IP-based applications that interface at the
SCCP layer
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11. SCTP vs TCP
• SCTP provides reliable transport, ensuring that data is transported across a
network without error and in sequence, like TCP
• Unlike TCP, the retransmission by SCTP of a lost message in one stream
does not block the delivery of messages in other streams. The use of multiple
streams within SCTP resolves the head of line blocking you see with the use
of TCP
• Unlike TCP, SCTP ensures the sequenced delivery of user messages within a
single stream
• Unlike TCP, SCTP supports Multi-Homing for added redundancy and faster
retransmission of non-acknowledged packets
• Unlike TCP, SCTP supports built-in heartbeat (destination check)
• Unlike TCP, SCTP supports a security cookie against SYN flood attack
• SCTP supports Selective Acknowledgements (SACK)
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12. SCTP Peer-to-Peer SS7 (M2PA) Protocol
Architecture
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SSP STP
SS7oIP Device SS7oIP Device
13. M3UA/SUA Signaling Gateway IP SS7
End Nodes
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MTP3MTP3 M3UAM3UA
SCTPSCTP
IPIP
MTP2MTP2
MTP1MTP1
MTP3MTP3
MTP2MTP2
MTP1MTP1
SCCPSCCP
TCAPTCAP
T
U
P
I
S
U
P
IS-41
IP
Network
NN
II
FF
SCCPSCCP
GTT
M3UAM3UA
SCTPSCTP
IPIP
SCCPSCCP
TCAPTCAP
T
U
P
I
S
U
P
MAP IS-41
SCTP/IPSSP/STPSSP/STP ASP/DBASP/DB
SS7
MAP
IP
Network
SUASUA
SCTPSCTP
IPIP
TCAPTCAP
MAP
MTP3MTP3
MTP2MTP2
MTP1MTP1
SCCPSCCP
TCAPTCAP
MAP
MTP3MTP3
SCTPSCTP
IPIP
MTP2MTP2
MTP1MTP1
SCCPSCCP
SUASUA
NN
II
FF
GTT
14. SS7 Stack Comparison to Sigtran
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•SS7 stack compared with Sigtran adaptation layers
•Note that the MTP3 layer remains unchanged with transport
•M2PA allows TWTC to keep the existing SS7 topology and use IP to
transport SS7 messages i.e. signaling links become virtual
•SUA is optimized to carry transactional content signaling (TCAP). M3UA can
also transport SCCP/TCAP, SUA eliminates more of the SS7 stack,makes
better use of IP routing,requires less SS7 network overhead
15. M3UA/SUA Standard Features
• Flexible Routing configuration
M3UA-DPC,OPC,SIO,ISUP,CIC range,GTT
SUA-DPC,OPC,SI=SCCP,SSN,GTT
• Fully compliant traffic mode operation
• Fully compliant signaling network management operation
• Fully compliant ASP state & traffic maintenance operation
• Fully compliant point-code sharing
• Acknowledgement of heartbeat
• Signal-Gateway Mate Protocol-used to exchange necessary state
information to act as mated pair
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16. SS7 over IP Network Design
Resilience
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Level 1:
• IP routing protocols can detect path outages and re-route
Level 2:
• When SCTP Multi-homing detects unresponsiveness in the current IP path, it
changes the IP path used for the session by changing the source and/or
destination IP address of the session. During this process, the SCTP session
remains active and MTP3 is unaware of the path change.
Level 3:
• If SCTP/IP can not correct the issue, MTP3 is notified to initiate standard MTP3
rerouting procedures (standard SS7)
Resilience Hierarchy
IP Routing
SCTP Multi-Homing
MTP
IP Routing
19. Deployment Strategy-City
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5E
Sonus
SS7
/IP
SS7
/IP
TDMMigrate links onto
SS7/IP platform
after X months
IP CoreNew IP links
soak period
•Each A-link city will have 1 or 2
SS7/IP devices during deployment
with ½ the city’s A-links riding over
IP
•IP link soak period & TDM migration
of remaining links-TBD
•Savings are realized only after TDM
link(s) are disconnected
20. Deployment Strategy-STP City
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Portland SS7
/IP
SS7
/IP
ColumbusSS7
/IP
SS7
/IP
TDM TDM
IP Core
½ (B-links)
(A-links)
(C-links)
½ (B and C-links)
STPSTP
21. Interim Architecture
• A-Link Strategy
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5ESS
SS7oIP Conversion
Device
SS7oIP Conversion
Device
IP Core
Sonus
TDM
TDM
Local
Loop
Local
Loop
56K Circuit
DS1 Circuit
QOS implemented within
IP Core
Mux
Mux
Mux
22. Sample City with Link Costs
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DRM
SS7oIP Conversion
Device
SS7oIP Conversion
Device
Local
Loop
Local
Loop
Mux
Mux
IP Core
QOS implemented
within IP Core
SS7oIP Conversion
Device
SS7oIP Conversion
Device
AT&T DS1
MCI DS1
STP
STP
Mux
Mux
Mux
Mux
PTLD
PHNX
$117
MRC
$1540.95 MRC
T1 ENT. FAC.
$117 MRC
$490.78 MRC
$200
MRC
T1 ENT. FAC.
$117 MRC
23. Interim Architecture
• STP City Interim
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SSP
SSP
SSP
SS7oIP Devices
SS7oIP Devices
SS7oIP Devices
A/B/C-Links
SS7 DS0s muxed
down from DS1s
SS7oIP Device
SS7oIP Device
SS7oIP Device
SS7oIP Device
A-Links
Dedicated DS0s
DS0s muxed
up to DS1sAll links depicted: half of each SS7 location links on IP
IP Backbone
Network
IP Backbone
Network
TDM Device
TDM Device
TDM Device
TDM Device
TDM Device TDM Device
TDM Device
24. IP Core Requirements
• COS implemented throughout IP core to guarantee bandwidth for SS7
messaging
• Physically diverse/ redundant access paths into the core for each link
• Latency from furthest SP on SS7 network to STP-IP core cannot inject > 50
msecs (WC) of latency on roundtrip
• Security
• QOS measurements required for signaling traffic
• Router outages must meet MTTR on service affecting SS7 outages
• Network congestion must give SS7 signaling priority
• Dropping MSU packets is unacceptable
• Sub-Second reroute in the core must be in place for IP network failures
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26. Full Scale Deployment
• Once all trials and “soak periods” have completed-the goal is to
migrate all A,B, & C-links to IP network
• Savings realization on TDM link costs can happen only after the
TDM links have been disconnected (30-45 day window for discos)
• NOC personnel (SS7 group) must be thoroughly trained on the
new equipment
• IP Maintenance/ Transport group must be kept in loop and
available to aid the SS7 support team in the NOC (24X7-if issue
has been isolated to underlying IP transport )
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27. Key Areas for Testing
• SCTP (Sigtran) association management & config
• IP vs. SS7 traffic priority & contention
• Link & link set failure
• Reroute capabilities
• Coexistence of SS7 & IP-based links within a common linkset
• QoS/ COS capabilities
• Troubleshooting & debug capabilities
• Vendor interoperability
• Latency measurements
*Requires either module in INET/ NeTracker (lab) for monitoring capability (if TWTC
chooses to look at the Sigtran protocol/ SS7 monitoring still valid on TDM end of
SS7/IP circuit
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