SigTRAN White Board Session v1.1

Version No: 12345 / Status: Live © 2008 Acision BV. All rights reserved.

SIGTRAN Victor Scripcaru – November 2008

Version No: 12345 / Status: Live

Agenda

• SS7 & IP Worlds

• SIGTRAN Protocol Stack

• SCTP

• M2PA / M2UA

• SUA / M3UA

• SMSCv5 Sigtran Implementation

• Conclusions / Q&A


Collaborating Worlds (SS7 & IP)

• SS7 is based on OSI, ITU based

• SIGTRAN (Signalling Transport) is developed by IETF

• Goal is to use underlying IP infrastructure for SS7 networking

• Formerly, IP was used in telecom backbones only for management

• New protocols specifities needed


Collaborating Result

• SS7 protocols are being supported on IP

• Is TCP dead?– A new transport protocol has been created: SCTP – Signal Transport Control Protocol (RFC 2960)

• SCTP usage– Lots of protocols / services use SCTP now


SigTRAN Protocols

• SCTP (Stream Control Transmission Protocol) – transport layer that provides reliable data transfer.

• M2PA (MTP2-User Peer-to-Peer Adaptation) used between STPs and SS7 Gateways – provides MTP3 with equivalent transport layer services as MTP2.

• M3UA (MTP3-User Adaptation) used between network elements - client/server protocol providing a gateway to legacy SS7 network for IP-based applications that interface at the MTP3 layer.

• SUA (SCCP-User Adaptation) – specifically for SMS messaging – client/server protocol providing a gateway to legacy SS7 network for IP-based applications that interface at the SCCP layer.

http://www.ietf.org/html.charters/sigtran-charter.htmlhttp://www.protocols.com/pbook/

http://www.ietf.org/html.charters/sigtran-charter.html

http://www.protocols.com/pbook/


Protocol Stacks

PDUs

ITU/ANSI/CHINA SCCP

ITU TCAP

MTP2

SUA

M2PA

SCTP

MTP1

GSM MAP

M3UA

SCTP

IP

SCTP

I/A/C MTP3 / 3b

ANSI TCAP

ANSI-41 MAP

CDMA TDMAGSM

SigtranSS7

TDM

SCCOP

AAL5

SSCF-NNI

ATM


SCTP Presentation

• Main protocol used for Sigtran

• Solves issues with TCP– Denial of Service– Reliability– Multihoming– Progressive degradation

• Designed with security in mind– Lessons learned from TCP

• Already usable and stable


SCTP - Stream Control Transmission Protocol

• SCTP was introduced to make signaling over IP reliable.

• It offers acknowledged error-free non-duplicated transfer of MSUs.

• Detection of data corruption, loss of data, and detection of duplicate data are achieved by using checksums and sequence numbers.

• A selective retransmission mechanism is applied to correct loss or corruption of data.

• SCTP provides the function and measurements in an architecturally identical manner to MTP2.


SCTP Advantages 1

• Resilience to DoS attack– 4 way handshake

• Multi-streaming (chunking)– Allows for multiple virtual connections on the same physical line

• Multi-homing– Ability of an association to support multiple IP addresses or

interfaces at a given end

• Sequenced Delivery– Allows for messages to be delivered in the order in which there

were sent.


SCTP Advantages 2

• Block-Level– Unlike TCP in which transmission is viewed as a continuous

stream of data, SCTP transmits blocks.

• Bundling multiple user message into single SCTP packet• Message retransmission does not block other streams• Heart-Beat

– SCTP uses periodic heart-beat messages to confirm the status of each end point.

• Scales well – Used for high-performance computing networks and highspeed

optical links


SCTP Terminology

• SCTP endpoint– One or more IP addresses in combination with one SCTP

port

• SCTP association– Connection between two SCTP endpoints


SCTP Multihoming

Host A Network Host B

Interface_11.2

Interface_2 2.2

Interface_13.2

Interface_14.2

gateway 2.1

gateway 1.1

gateway 3.1

gateway 4.1

Routing table host A Destination Gateway ---------------------------- 3.0 1.1 4.0 2.1

Routing table host B Destination Gateway ---------------------------- 1.0 3.1 2.0 4.1

Source = 1.2 Destination = 3.2 Data

IP packet Source = 3.2 Destination = 1.2 Data


M2PA (MTP2 User Peer-to-Peer Adaptation Layer)

• M2PA is designed for peer-to-peer signaling gateway (SG) communications. (The analogy in legacy network is STP-to-STP communications ).

• M2PA offers a protocol high availability similar to an STP C-link.• The MTP3 implementation layer in an M2PA SG is unaware of whether a

link is TDM or IP. Therefore, all MTP3 high-availability features run equally over TDM or IP links.

• Congestion, Layer2 failure detection, changeover, change-back, load balancing via SLS, screening and other MTP3 features are preserved.


M2UA (MTP2 User Adaptation Layer)

• M2UA is a protocol for the backhauling of SS7 MTP3 messages over IP using the services of SCTP

• With M2UA the SG functions as a transparent relay that converts SS7 messages to IP format

• M2UA allows for only one IPSP in the network

SMSC (AS)


M2PA and M2UA Compared

• Similarities:– Both transport MTP3 messages– Both present an MTP2 upper interface to MTP3

• Differencies:– M2PA: IPSP processes MTP3-to-MTP2 primitives;– M2UA: IPSP transports MTP3-to-MTP2 primitives between the SG’s MTP2 and the IPSP’s

MTP3 (via NIF) for processing;

– M2PA: SG is an SS7 node with a point code;– M2UA: SG is not an SS7 node and has no point code;

– M2PA: SG can have upper SS7 layers, e.g. SCCP;– M2UA: SG does not have upper SS7 layers since it has no MTP3;

– M2PA: may have one or more IPSPs;– M2UA: can only have one IPSP;

– M2PA: SG can route to other SPs, perform Global Title Translation as well as provide application layer services;

– M2UA: SG’s single function is to relay MTP3 messages.


SUA / M3UA (XUA) Terminology 1

• Application Server (AS)– An addressable entity

• ASP: Application Server Process– Is a processing instance of an AS– Each IP7 entity is an Application Server Process– Is an SCTP endpoint

• Association: SCTP association– Provides the transport of SCCP protocol data units and M3UA

layer peer messages


SUA / M3UA (XUA) Terminology 2

• Signalling Gateway– SCTP endpoint– Gateway between M3UA and classical SS7

• Signalling Gateway Process– A processing instance of a Signalling Gateway– For example, each ITP is a Signalling Gateway & Signalling

Gateway Process


SigTRAN Connectivity

MTP3M3UA

SCTP

IP

MTP2

MTP1

NIF

ISUP and SCCP messagesISUP and SCCP messages

SEPSEPASPASP SS7 SGSS7 SG

IPNetwork

M3UA

SCTP

IP

SCCP

TCAP

MAP IS-41 ISUP

MTP2

MTP1

SCCP

TCAP

MAP IS-41 ISUP

MTP3

SS7SCTP/IP

SCCPGTTGTT

SS7 Network


M3UA (MTP3 User Adaptation Layer)

• M3UA supports the transport of any SS7 MTP3-User signalling (i.e. ISUP or SCCP messages) to an IP signalling point (IPSP) using the services of SCTP

• M3UA is IP aware in that it translates the contents of the incoming SS7 MSU using the Routing Key to map to the relevant IP addresses

SMSC (AS)


SUA (SCCP-User Adaptation Layer)

• SUA defines a protocol for the transport of any SS7 SCCP-user signalling message such as TCAP, RANAP, or MAP over IP using SCTP services

SMSC (AS)


SUA and M3UA Comparison

• M3UA: Needs the SCCP services• SUA: Does not need SCCP services, reducing the complexity of the

node and thereby reducing cost

• M3UA: Support ISUP services• SUA: Cannot support ISUP services

• M3UA: Each IP node is required to have a point code and an IP address

• SUA: Each IP node does not require a point code

• M3UA: Messages are handled from point code to point code• SUA: Allows the IP network to route the messages using global title

information or SSN


SMSCv5 implementation: SUA and M3UA

• Existing IP7 entity is extended with M3UA and SCCP functionality

• SCCP Global Title Translation is implemented for both SUA and the new SCCP layer

• Global Title to SG(G) translation is implemented bringing more flexibility by SG selection rules and enabling so called TCAP relay

• Integrated SS7 Signalling Network Management is implemented for SUA and the new SCCP and M3UA layers

• Existing IP7 entity is extended with the network management functionality

• The current SUA user management and routing context management functionality is extended for SCCP and M3UA


SCCP – Transport Layer Functionality

TCAPSCCP

MTP3

SS7 Network

MTP2

ConnectionLess Primitives

Routing Control

SubsystemManagement

ConnectionOrientedPrimitivesUDT/UDTS

XUDT/XUDTS

GTT lib


Global Title Translation

• IP7 now supports SCCP/M3UA, so must do GTT as well• Purpose (1): identify SS7 destination signaling point

based on e.g. E.164 address– destination: point code (DPC), or point code + subsystem

number (DPC+SSN)

• Purpose (2): enable modification of the GT digits• Part of SCCP protocol layer within SS7 network

– intermediate translation: GTT yields next node (DPC) where another GTT is done

– end translation: GTT yields node and subsystem (DPC+SSN) where message is finally handled


Global Title Translation Overview

Destination

OutputAddress

InputAddress

RoutingInfo

AddressMatcher

More or less changed GTGT

SCCP Entity SetAvailability

Tester

SS7 SignalingNetwork

Management Availability Information

DPC or DPC+SSN


Questions & Answers


Documents

SigTRAN White Board Session v1.1