SIGTRAN Overview Training

SIGTRAN OverviewIntroduction to SigTran
Last update: May 1, 2007
All Rights Reserved © Alcatel-Lucent 2007, Plano, TX, USA
What is SIGTRAN ?
SIGTRAN is a set of protocols defined to transport SS7 messages over IP networks
SIGTRAN allows IP networks to inter-work with Switches Circuit Network (SCN)
MGC – Media Gateway Controller
Controlling Access (IP PSTN)
MG – Media Gateway
SIGTRAN
SIGTRAN Stack
Adaptation layer, i.e. M2PA, M2UA, M3UA, etc
Stream Control Transmission Protocol (SCTP)
Standard IP stack
About Adaptation Layers
M2UA – MTP2 User Adaptation layer. MTP2-MTP3 communication is remote and are M2UA messages. They are non-primitives sent over IP. SG is not an SS7 node as there is no MTP3 [RFC3331]
M3UA - MTP3 User Adaptation layer supports MTP3 functions and provides transport of MTP3-User signaling over IP [RFC4666]
M2PA – MTP2 Peer-to-Peer Adaptation layer provides peer-to-peer communication between two endpoints. MTP2-MTP3 communication is local and uses std primitives [RFC4165]
SUA - SCCP User Adaptation layer supports the transport of SCCP signaling over IP using SCTP without MTP3 [RFC3868]
IUA - ISDN User Adaptation layer supports the transport of ISDN signaling directly between SG-MGC over IP [RFC3057]
Differences between M2UA and M2PA
A: M2UA: MTP2/MTP3 (remote) communication is defined as M2UA messages and sent over the IP connection.
M2PA: IPSP processes MTP2/MTP3 primitives.
B: M2UA: SG-MGC connection is not an SS7 link. It is an extension of MTP to a remote entity.
M2PA: SG-IPSP connection is an SS7 link.
C: M2UA: SG is not an SS7 node and has no point code.
M2PA: SG is an SS7 node with a point code.
D: M2UA: SG does not have upper SS7 layers since it has no MTP3.
M2PA: SG can have upper SS7 layers, e.g., SCCP.
E: M2UA: uses M2UA management procedures.
M2PA: relies on MTP3 for management procedures.
M2UA
M2PA
Why M3UA is chosen for mobile applications ?
M2UA is not suitable
designed for MTP2 backhauling (invocation of remote MTP2 layer)
no full IP peer to peer mode, only IP-SS7 legacy interworking
example : relay of legacy SS7 associated signalling terminated at a MGW toward a MGC through IP
SUA is not suitable
IUA is not suitable
M2PA could have been suitable
only peer to peer mode, a legacy SS7 link is replaced by an “SS7 IP link” (an SCTP association)
MTP3 management is kept unchanged
M2PA enabled STP (which is not popular) needed in networks
All Rights Reserved © Alcatel-Lucent 2007, #####
SCTP
Motivation – Why SCTP, but not TCP?
The Problem with TCP:
TCP is byte-streamed. It provides a single stream of data and guarantees that data to be delivered in byte-sequence order
TCP is sensitive to delays caused by network errors (loss of bytes, messages or sequence violation)
In case error occurs, TCP will hold up delivery of all data
For example: If TCP were used for delivering ISUP messages, the loss of one message relevant to one telephone call would result in the delay of all other ISUP messages
The Solution
SCTP Functional Overview
Acknowledged error-free non-duplicated transfer of signaling information
In-sequence delivery of messages within multiple streams
Message oriented, rather than bytes oriented as in TCP
Capable of bundling multiple messages into a single SCTP packet
Data fragmentation as required
Network-level fault tolerance through support of multi-homing at either or both ends of an association
Congestion avoidance and resistance to flooding (denial-of-service) and masquerade attacks
Key SCTP Features:
Support multi-stream capability, i.e. transmit data through multiple streams, each with independent sequenced delivery. The number of incoming and outgoing streams is negotiated when association is established
Support multi-homing, i.e. each SCTP endpoint may be known by multiple IP addresses. If one route becomes unavailable, another will be used.
SCTP: Multi-Stream
To deliver ISUP messages there is a need to decouple messages based on the calls (such as CIC) so that messages associated with different calls can be delivered independently
With multi-stream Calls 2 & Call 3 are processed normally.
Call 1
Call 2
Call 3
Call 2
Call 3
SCTP: Multi-Stream
An SCTP packet may be composed of multiple chunks (contains SS7 messages) which belong to multiple streams
Chunks are queued if necessary and then delivered to SCTP User Part in sequence per stream
Multi-homing
Only one path is active at a given time
Paths are monitored to detect failures via exchanging “Heartbeat”
Active Path
inactive Path
Data & Acks
Heartbeats / Acks
SCTP Key Terms
Chunk
A unit of information within an SCTP packet, consisting of a chunk header and chunk-specific content (Init, Ack, Data,…).
SCTP Packet
The unit of data delivery across the interface between SCTP and the connectionless packet network (e.g., IP). An SCTP packet includes (i) common SCTP header, (ii) possible SCTP control chunks, and (iii) user data encapsulated within SCTP DATA chunks.
Transmission Sequence Numbers (TSN)
A 32-bit sequence number used internally by SCTP. One TSN is attached to each chunk containing user data to permit the receiving SCTP endpoint to acknowledge its receipt and detect duplicate deliveries.
Signalling Endpoint (SEP)
The logical sender/receiver of SCTP packets. On a multi-homed host, an SCTP endpoint is represented to its peers as a combination of a set of eligible destination transport addresses to which SCTP packets can be sent and a set of eligible source transport addresses from which SCTP packets can be received. All transport addresses used by an SCTP endpoint must use the same port number, but can use multiple IP addresses. A transport address used by an SCTP endpoint must not be used by another SCTP endpoint. In other words, a transport address is unique to an SCTP endpoint.
Association
A protocol relationship between SCTP endpoints, composed of the (i) two SCTP endpoints and (ii) protocol state information including Verification Tags and the currently active set of Transmission Sequence Numbers (TSNs), etc. An association can be uniquely identified by the transport addresses used by the endpoints in the association. Two SCTP endpoints MUST NOT have more than one SCTP association between them at any given time.
Stream
A uni-directional logical channel established from one to another associated SCTP endpoint, within which all user messages are delivered in sequence except for those submitted to the unordered delivery service
Illustration of SCTP Association Path and Stream
IP
Association
Path
Port
Illustration of SCTP Streams, Packets and Chunks
SS7 Network Element
SCTP Packet Format
SCTP packet is composed of a common header and chunks. A chunk contains either control or user data
Multiple chunks can be bundled into one SCTP packet up to the MTU size, except for INIT, INIT-ACK, and SHUNTDOWN COMPLETE chunks.
If user data message does not fit into one SCTP packet, it can be fragmented into multiple packets
MTU – Max Transmission Unit
SCTP Chunk Format
Data
Bits 0 - 7
Transmission Sequence Number (TSN) is attached to each chunk in an increasing order in a pkt. It is used for per-association reliability
ID Value Chunk Type
10 - COOKIE ECHO
11 - COOKIE ACK
14 - SHUTDOWN COMPLETE
Stream Sequence Number (SSN) is the current chunk number of the piece inside the specific stream. It is for per-stream ordering
TSN
SSN
Four-WAY Association Establishment
set asso w/ Z
build temp TCB
authenticate
MAC : Message Authentication Code
TCB : Transmission Control Block
Cookie : A subset of association info required to re-create TCB and its resultant MAC
MOS : Max # of OG Stream
MIS : Max # of IN Stream
How can SCTP protect against denial of service attacks?
A cookie is in the INIT-ACK sent from server to client.
Server does not allocate TCB and resource or after INIT.
TCB is derived from the cookie sent back from the client in COOKIE-ECHO.
The server has no knowledge of the association until the client responds with a COOKIE-ECHO, it becomes resilient to DoS attacks.
COOKIE-ACK (SAK)
Selective Acknowledgement (SACK)
Every chunk in a packet sent out by STCP must be acknowledged
If acknowledge chunk X is not received (GAP is detected), retransmission of the chunk X is performed
Acknowledges can be cumulated and sent out within one SACK message
Multiple GAPs can be reported in one SACK message
Criteria of retransmission
Retransmission occurs when
(2) (2)
(4) (5)
The actual value is the offset to the next received chunk
The offset to the end of received block
IP header
M3UA
What is M3UA and What is not?
What is M3UA?
M3UA stands for MTP3 User Adaptation Layer and is defined in RFC4666
M3UA provides transport of MTP3-User signaling, e.g., ISUP, TUP and SCCP messages, over IP using SCTP.
M3UA protocol can be used between SG and MGC or between two MGCs.
M3UA provides a equivalent set of primitives at its upper layers as provided by MTP3 to its local users.
What is M3UA not?
M3UA is not an MTP3 over IP. M3UA does not provide some of the services in MTP3.
For example, M3UA on SG does not support MTP3 network management messages, such as TFA, TFP, etc.
M3UA Protocol Architecture
NIF
NIF is the interface between MTP3 and M3UA. It provides seamless mapping between MTP3 and M3UA on Signalling Gateway. It performs protocol termination, translation and user part protocol encapsulations.
SEP - SS7 Signalling Endpoint
SG - Signalling Gateway
Exchange data messages between SS7 and IP networks
Relay IP or SS7 messages back to the originator in the same format
Provide global network management services in support of data flows between MTP3 and M3UA layers
M3UA
M3UA Network Entities
SG - Signalling Gateway
AS – Application Server
IPS – IP Server
M3UA Terms
Application Server (AS):
AS is a logical entity, such as virtual switch or database element capable of handling call processing / transaction for a specific routing key
AS is identified by a routing key, which is a set of SS7 parameters, such as SIO/OPC/DPC/SSN.
AS is modelled as one or more Application Server Processes (ASP), Signalling Gateway Process (SGP) or IP Server Process (IPSP)
ASP1
ASP2
AS
Signalling Gateway (SG):
SG is a signalling agent capable of sending / receiving Switched Circuit Network (SCN) native messages at the edge of the SS7 / IP networks.
SG contains one or more Signalling Gateway Process (SGP) providing serves as an active, backup, load-sharing or broadcast process
SG
SGP1
SGP2
IP
IPSP1
IPSP2
AS
AS
IPSP1
IPSP2
IP
SS7
IP
Signalling Peer Processes
Application Server Process (ASP):
A process instance of an Application Server, such as MGC, IP SCP, or IP HLR.
An Application Server Process serves as an active or backup process of an Application Server
An ASP contains an SCTP endpoint and may be configured to process signalling traffic for more than one Application Servers.
IP Server Process (IPSP):
A process instance of an IP-based application. An IPSP is essentially the same as an ASP, except that it uses M3UA in a point-to-point fashion. Conceptually, an IPSP does not use (interface with) the services of a Signalling Gateway node.
Signalling Gateway Process (SGP):
An Application Process instance running on SG. It is identified by a unique SCTP endpoint.
Illustration of AS, ASP, SGP, IPSP, Routing Key and Routing Context
ASP 1
SGP 1
SGP n
IPSP 2
IPSP n
NGN NODE
ASP n
Signaling Gateway
IP networks
NGN NODE
IPSP 1
RC – Routing Context. A value that uniquely identifies a Routing Key to represent Application Server (AS).
SCTP endpoint
SCTP associations
M3UA SS7/IP Network Architecture
NOTES:
AS1 is processing MAP protocol for the point code A in SS7 network 1
AS2 is processing ISUP protocol for the point code A in SS7 network 1
n x ASP serve the AS1 & AS2 in a load-sharing manner
Signaling Gateway SG1 gives access to SS7 network 1 & 3
Signaling Gateway SG2 gives access to SS7 network 1 & 2
From SS7 network 1, SG1 & SG2 are seen as STPs
ASPs load share traffic between SGs and between SGPs in SG1 and SG2
IP node
M3UA modes
Backhauling mode
Internally MG and MGC share the same Signalling Point Code (SPC)
M3UA is used to transfer MTP3 primitives between SG and MGC.
The link between SG-MSC is not an SS7 link
M3UA is transparent to MTP3 User layers, such as ISUP/BICC/SCCP.
SS7 network
MG and MGC have different SS7 Point Codes.
SG functions as an STP, but not exactly
SG is required to perform “Point Code Translation”
“Pipe”
“Router”
AS-SG-SEP Model (AS/SG Model)
This model allows an IP node to dialog with legacy SS7 node through the inter-working of a signaling gateway
AS : Application Server
IPS-IPS Model
IP
SCTP
M3UA
IP
SCTP
M3UA
SCCP
TCAP
MAP
IP
IPS
SCCP
TCAP
MAP
IPS
This model allows to build a full SS7oIP network using M3UA
No extra-hop SG is needed between the IP nodes (less overhead)
It leads to a network with a flat organization and has the following consequences for large networks :
All Network Elements that have to dialog each other have to be inter-connected through a mesh of SCTP association
The number of SCTP associations increases with the number of NE in the network, if SCTP multi-homing is used to provide network path resilience, SCTP heartbeat traffic flows on inactive paths also increases, thus demanding more network bandwidth and CPU power
Depending on the NEs architecture/implementation, signaling capacity extension of one NE can lead to configuration impacts on all other NEs it is connected to
M3UA Protocol
M3UA Header
Version: 8 bits of version number
Class: 8 bits of message class
Type: 8 bits of message type (refer to section 3.1.2 RFC 4666)
Length: 32 bits of message in bytes, incl. header and parameter padding
Data: Variable length, contains parameters, if any
M3UA protocol
No Registration – RC is provisioned
SGP
ASP1
Dynamic Registration – Client sends RC and RK to server
LRC: Local Routing Key ID
RC : Routing Context
RK : Routing Key
NTFY (AS-INACTIVE) (RCn)
ASP ACTIVE (RCn)
Ready to receive ASP Sate Mgt Msg
SigTran
SigTran – An Alcatel-Lucent A5020 Solution
System Capability and Limitation:
- Max number of Peer Server Process (PSP) supported: 40 (TBD)
- Max number of Peer Application Server (PS) supported: 128 (TBD)
H/W and initial S/W Installation:
- For R4.1.12.0 load refer to “A5020 Wireless Call Server - W4.1 Software
Installation” (3HP700081016RJZZA)
- Move up until reaches Application Server (AS)
A5020 SIGTRAN Architecture
up to 3 interface cards
Daughter card
SSCF/SSCOP
AAL5/ATM
SCTP
IP
MAC
Daughter card
SSCOP - Service Specific Connection Oriented Protocol
MAC - Media Access Control address
DDM
DDM
DDM
A5020 SIGTRAN distribution principles
Out going messages:
Selection of DDM card for outgoing messages by user part (ISUP/BICC/SCCP):
First message DDM selection based on round robin
Following message : same DDM as first message
Selection of the SCTP end point is based on SLS (static table)
Incoming messages:
M3UA
M3UA
M3UA
AS
AS
ASP
AS
AS
A5020 SIGTRAN defense principles
Three levels of defense:
Multi-homing mechanism
Global traffic of the SCTP association is carried on the remaining path
SIM outage:
N+1 load sharing
After detection, at ASP level , the global traffic of the AS is handled on the remaining SCTP association present on another SIM
Static SLS table for outgoing & incoming messages are updated to take into account the new configuration
DDM outage:
N+1 load sharing
After detection, distribution mechanisms exclude the DDM for the election of the DDM for the first message to send
Static SLS table for outgoing & incoming messages are updated to take into account the new configuration
A5020 SIGTRAN Dimensioning capacities – Model C
2 SAM Netra 240+ (1+1)
8 CCM Netra 240+ (4+4)
2 SIM Netra 240 + (1+1)
2 IPM or CCM Netra 240+ (1+1)
3 DDM Netra 240 + (2+1)
A5020 SIGTRAN Dimensioning capacities – Model F
2 SAM Netra 240+ (1+1)
18 CCM Netra 240+ (9+9)
4 SIM Netra 240 + (3+1)
4 IPM or CCM Netra 240+ (1+1)
3 DDM Netra 440 + (2+1)
Netra SIM Hardware
For specifications on the iSPAN® 5539F PCI Multiprotocol T1/E1/J1 Communications Controller:
SIM Server Configuration w/ T1/E1 Cards
SIM Server Configuration w/ T1/E1 & OC-3
SIM Dimensioning (Netra)
NB SS7 (MTP3) :
BB SS7 (MTP3B)
SIGTRAN (M3UA) : IP FE (100Mbps) or GE (1000Mbps)
MTP3/MTP3B Interfaces are provided on daughter boards:
E1/T1 NSL& E1/T1 HSL & E1/T1 ATM HSL : same daughter board with 4 connections (Interphase 5539F)
OC3/STM1 ATM : daughter board with 1 connection (Interphase 5500+4532)
A Netra SIM hosts 3 daughter boards:
Feuil1
2205000
Capacity SIGTRAN msg/sec
Box Redundancy
N+1
erlangs links
List of Tables used for SCTP and M3UA in A5020 WCS
SystemConfiguration
"GTWGEN", "SGW", "SCTP", "maxNmbInStrms", "Integer", 4, "MaximumNumberofIncomingStreams", "10", "10", "10", "10", 0, "SGW_SCTP_ID“
“GTWGEN", "SGW", "SCTP", "maxNmbOutStrms", "Integer", 4, "MaximumNumberofOutgoingStreams", "10", "10", "10", "10", 0, "SGW_SCTP_ID“
d
SS7Configuration
SGWM3UAPSCONFIG - Local and Peer (remote) Application Server (AS)
SGWM3UAPSPASCONFIG - PSP Ids for (local) Application Server
SGWM3UAROUTECONFIG - Associate (remote) AS to routing Key, i.e. ISO/DPC
Configuration Sigtran on A5020 WCS (R4.1) - Configure SCTP End Points:
STEP 1: Click Signaling Gateway -> SIGTRAN -> SCTP END POINT -> ADD. TABLE: SGWSCTPCONFIG
Local IP address on SIM card
Local IP PORT Num
Must set to M3UA
Configuration Sigtran on A5020 WCS (R4.1) - Configure SCTP End Points (cont):
NOTE: USAP ID, which binds lower Service Access Point (SAP) to upper SAP in SCTP, must be unique.
User Service Access Point ID
Local SIM Num
Number of IP address for SCTP Association. Max is five, but limited by SIM card with 2 IP address
Configuration Sigtran on A5020 WCS (R4.1) - Peer (remote) Server Process (PSP):
STEP 2: Click Signaling Gateway -> SIGTRAN -> SCTP END POINT -> ADD. TABLE: SGWM3UAPSPCONFIG
NOTES: RX/TX ASP ID specifies if RX/TX Application Server Process ID (in Self ASP ID) is available in ASPUP and NTFY msg
Remote IP Addr
Local SIM Num
ID must be unique
Configuration Sigtran on A5020 WCS (R4.1)- Peer (remote) Server Process (PSP) (cont):
NOTES: Different remote IP addresses or port number shall be used if adding more than one PSPs to the same remote SG / AS. The same rule applies to SIM card number under SCTP association.
Choose logical network
WCS send INIT
Configuration Sigtran on A5020 WCS (R4.1) - Configure Application Server (AS): Local
STEP 3: Click Signaling Gateway -> SIGTRAN -> Gateways -> <Logical SGW> -> ADD. TABLE: SGWM3UAPSCONFIG
Local AS
Specify if the AS needs to be active for Point Code availability
Load Share or Active Stand-by (must set the same as in remote AS)
Configuration Sigtran on A5020 WCS (R4.1) - Application Server (AS): - Local (cont)
NOTE 1: Local Routing Context (RC) must be consistent with the Peer RC provisioned on the remote Application Server
Local Routing Context
Number of PSPs required to have this AS shown in available state
Select one that matches peer AS
Configuration Sigtran on A5020 WCS (R4.1) - Application Server (AS): - Local (cont)
STEP 4: After click Apply the above window is shown. Click Add Row to add PSP Ids for this AS. TABLE: SGWM3UAPSPASCONFIG
Configuration Sigtran on A5020 WCS (R4.1) - Application Server (AS): - Remote
STEP 5: The configuration is the same as provisioning local AS, except Local Flag needs to be set to “False”.
Local Flag must be set to “False”
Remote RC
Configuration Sigtran on A5020 WCS (R4.1) - Application Server (AS) Remote (cont)
STEP 6: click on the ‘Network Appearance’ and use Add Row to add the PSP Ids for this remote AS
Configuration Sigtran on A5020 WCS (R4.1) - Configure M3UA Route: - Local
STEP 7: Click Signaling Gateway -> SIGTRAN -> Gateways -> <Logical SGW> -> M3UA Route -> ADD
Set to Local
Local Point Code
Select “Not Specified”
Local AS ID
Configuration Sigtran on A5020 WCS (R4.1) - Configure M3UA Route: - Remote
STEP 8: Click Signaling Gateway -> SIGTRAN -> Gateways -> <Logical SGW> -> M3UA Route -> ADD. TBL: SGWM3UAROUTECONFIG
Set to PS
Remote Point Code
Local Point Code
Remote AS ID
Configuration Sigtran on A5020 WCS (R4.1) - Configure M3UA Route: - Properties
STEP 9: For remote there is need to specify ISUP protocol and SLS Range
Sigtran Overview, by Horst Kirschbnaum, January, 2007
Signaling backhaul using SIGTRAN by third party SG, by Xuemei Zhang, March 2007
WCS 5020 MG 7570 SIGTRAN – ALU Training Manual
Thank you !
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SIGTRAN Overview Training