Download - SS7 over IP Brown Bag
SS7 and SIGTRAN
Stephanie Williams
Agenda
Brief Current SS7 Network OverviewWhy SS7oIP? TechnologiesSigtran ProtocolDeployment Strategy/ Interim ArchitectureIP Core RequirementsSS7oIP Architecture for full scale DeploymentQ & A
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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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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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SS7 Protocol Stack Cont.
MTP1
SCCP
Network
TUP
Physical
Data Link
ASP
TCAP
BISUP
ISUP
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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Why SS7oIP? • *Cost Savings-
Packet networks are less expensive than leased circuit networksReduction of infrastructure costs on leased lines & signaling ports
• Flexibility-Creates a many-to-many ratio for signalingMultiple 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 backboneAccess 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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SS7oIP Technologies• 2 distinctly different technologies:
*Sigtran ProtocolConversion of SS7 to Sigtran for transport over the IP network (Sigtran has built-in fail safes to aid the IP core)*TDMoIP Circuit EmulationEncapsulation 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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IETF Sigtran
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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,SUAS. Williams 9
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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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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SCTP Peer-to-Peer SS7 (M2PA) Protocol Architecture
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SS7SS7ApplAppl
MTP3MTP3
MTP2MTP2
MTP1MTP1
MTP2MTP2
MTP1MTP1
Link Protocol
Link Protocol
SS7SS7ApplAppl
MTP3MTP3
MTP2MTP2
MTP1MTP1
MTP2MTP2
MTP1MTP1
MTP2MTP2
MTP1MTP1
MTP3MTP3
MTP2MTP2
MTP3MTP3
MTP1MTP1
SCCPSCCPGTTGTT
SCCPSCCPGTTGTT
SS7SS7 SS7SS7
M2PAM2PA
SCTPSCTP
M2PAM2PA
SCTPSCTPTransport
Peer
IPIP IPIP
IPIP
SCCPSCCPGTTGTT
SCCPSCCPGTTGTT
SSP STP
SS7oIP Device SS7oIP Device
M3UA/SUA Signaling Gateway IP SS7 End Nodes
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MTP3MTP3 M3UAM3UA
SCTPSCTP
IPIP
MTP2MTP2
MTP1MTP1
MTP3MTP3
MTP2MTP2
MTP1MTP1
SCCPSCCPTCAPTCAP
TUP
ISUP
IS-41
IPNetwork
NNIIFF
SCCPSCCPGTT
M3UAM3UA
SCTPSCTP
IPIP
SCCPSCCPTCAPTCAP
TUP
ISUP
MAP IS-41
SCTP/IPSSP/STPSSP/STP ASP/DBASP/DBSS7
MAP
IPNetwork
SUASUA
SCTPSCTP
IPIP
TCAPTCAPMAP
MTP3MTP3
MTP2MTP2
MTP1MTP1
SCCPSCCPTCAPTCAP
MAP
MTP3MTP3SCTPSCTP
IPIP
MTP2MTP2
MTP1MTP1
SCCPSCCP SUASUANNIIFF
GTT
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
M3UA/SUA Standard Features
• Flexible Routing configurationM3UA-DPC,OPC,SIO,ISUP,CIC range,GTTSUA-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 pairS. Williams 15
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
SCTP Multi-Homing Examples
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208.4.2 208.4.4
208.4.2 208.4.4ACTIVE SCTP SRC-DEST Combo
M2PA/SCTP link 0
STANDBY SCTP SRC-DEST Combo
local-peer 5000
10.120.122.6
10.120.123.6
local-peer 5000
10.120.122.22
10.120.123.22
10.120.122.6
10.120.123.6
10.120.122.22
10.120.123.22
MTP2Link 0
MTP2Link 0
Redundant Path IP Network
MTP2Link 0
MTP2Link 0
SS7/IP Device SS7/IP Device
SS7/IP Device SS7/IP Device
Deployment Strategy/ Interim Architecture
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Deployment Strategy-City
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5E
Sonus
SS7/IP
SS7/IP
TDMMigrate links ontoSS7/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
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
Interim Architecture• A-Link Strategy
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5ESS
SS7oIP ConversionDevice
SS7oIP ConversionDevice
IP Core
Sonus
TDM
TDMLocalLoop
LocalLoop
56K Circuit
DS1 Circuit
QOS implemented withinIP Core
latigid
Mux
latigid
latigid
Mux
Mux
Sample City with Link Costs
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DRM
SS7oIP ConversionDevice
SS7oIP ConversionDevice
LocalLoop
LocalLoop
latigid
latigid
Mux
Mux
IP Core
QOS implementedwithin IP Core
SS7oIP ConversionDevice
SS7oIP ConversionDevice
STP
STPlatigid
latigid
latigid
latigid
Mux
Mux
Mux
Mux
PTLD
PHNX
$117MRC
$1540.95 MRC
T1 ENT. FAC.$117 MRC
$490.78 MRC
$200MRC
T1 ENT. FAC.$117 MRC
Interim Architecture• STP City Interim
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SSP
SSP
SSP
SS7oIP Devices
SS7oIP Devices
SS7oIP Devices
A/B/C-LinksSS7 DS0s muxeddown from DS1s
SS7oIP Device
SS7oIP Device
SS7oIP Device
SS7oIP Device
A-LinksDedicated DS0s
DS0s muxedup to DS1sAll links depicted: half of each SS7 location links on IP
IP BackboneNetwork
IP BackboneNetwork
TDM Device
TDM Device
TDM Device
TDM Device
TDM Device TDM Device
TDM Device
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
failuresS. Williams 24
SS7oIP Full Scale Deployment
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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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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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Q & A
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