SigTran

SIGTRANZTE University univ.zte.com.cn
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NGN Course Team
ZTE University univ.zte.com.cn
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Objectives
Upon the completion of this chapter, you will be able to:
Understand the history and components of SIGTRAN protocol stack
Understand the concept of SCTP
Understand the concept of M3UA
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SIGTRAN protocol Suite
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Upon completion of this chapter, you should be able to:
Understand the function of SIGTRAN protocol suite
Understand the structure of SIGTRAN protocol suite
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Fault-tolerant network
Physical separate overlay network
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VPN or firewall solutions for security
QoS for time-critical SS7 messages
SS7 for standard voice call (ISUP) is a time-critical application
Ensure sufficient bandwidth available for SS7
Public internet not recommended for SS7 over IP
Reliable?
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IP
M2UA
M2PA
M3UA
SUA
IUA
SIGTRAN adaptation and peer protocols specifically designed to handle ss7 stack over IP
M3UA
M2UA
M2PA
SUA
IUA
MTP3
ISDN
TUP/ISUP
SCCP
TCAP
SCTP
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SCTP is adoptedprovide reliable information transportation over IP network.
User adaption layer
Here are many adapting modules, provide the software interfaces for the different upper modules of SS7 ,and encapsulate the signaling of upper layer in SCTP .
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Understand the concept of SCTP
Understand the message of SCTP
Understand the communication flow of SCTP
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VOIP:cheap local calls + cheap long distance IP transport
Want to reduce additional infrastructure costs
Combine circuit-switched telephone signaling networks (PSTN) and packet-switched IP-based networks
Need to establish,monitor and terminate calls
Signaling more delay sensitive, best effort is not QoS
Need gateways between different technologies
Need a general-purpose reliable transport protocol for message-oriented applications to carry data and voice
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TCP
Limitations
Byte-stream
Oriented
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UDP
Limitations
Unreliable
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SCTP End Point: Identified by IP +port, just like TCP
Association (SCTP link ):A logic connection set up through 4-way hand shake, C/S mode.
Stream: there could be multi streams in one Association. Stream is a logic channel from one point to another point.
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Stream Sequence Nbr. n
E – Ending fragments
xx – if unknown,then
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EndpointA
EndpointB
START =2 END = 3
SACK
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SACK
4
3
5
4
4
DATA
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Abort AssociationABORT
Shutdown AssociationSHUTDOWN
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The theory of DoS Attack:
The basic Dos attack is to occupy service resource as more as possible by normal service request, so that the normal user can not get response.
To avoid being attacked, SCTP adopt :tag, cookie
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EndpointA
EndpointB
SYN Flooding: the client sends out a lot of SYN message, and the server can not get the ACK (the third message ) after it sends out “SYN +ACK” (the second message ).The three-way handshake can not be finished, so the server will use much memory resource for the half-connection, and send “SYN +ACK” again and again.
In this example ,the client use a phony IP address.
SYN seq=x
ACK y+1
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IPv4 or IPv6 or mixed
Tolerant for physical failure
May by-pass congestion points
a.a.a.1
a.a.a.2
b.b.b.1
b.b.b.2
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Data transfer
Packet no longer than the path MTU Multiple chunk in a packet
Two sequence numbers in each chunk
‘global’TSN for the association
Separate sequence numbers for each stream
U = unordered
Stream Sequence Nbr. n
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Selective ACK
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Get and set parameters (e.g. timers, thresholds)
Heartbeat control
Socket based API
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Multi-homing
No head-of-line blocking
Short transaction (e-commerce)
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Understand the concept of M3UA
Understand the messages in M3UA
Understand the signaling message flow of M3UA
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ASP: A process instance of an application server
Routing key: A routing key describes a set of SS7 parameters and parameter values that uniquely define the range of signaling traffic to be handled by a particular AS.
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ASP State Maintenance (ASPSM) Messages
ASP Traffic Maintenance (ASPTM) Messages
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1 Invalid Version
6 Unexpected Message
7 Protocol Error
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AS state altered
Alternative ASP active
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6 Heatbeat Ack (BEAT ACK)
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ASP ACTIVE ACK
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ALTERNATE ASP TAKEOVER
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Tr Trigger at least one ASP in INACT
Tr Trigger no ASP in INACT state
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SigTran

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Transcript of SigTran