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Information andCommunication Networks
© Siemens Atea
SUA tutorial
SCCP User Adaptation Layer tutorial
Authors: Lode Coene
Gery Verwimp
13.04.23SUA tutorial2 © Siemens Atea
Information andCommunication Networks
SCCP user adaptation layer(SUA)
- replaces the functionality of SCCP and M3UA over SCTP in an IP network- required for 3G mobile networks (from Release 5 onwards) -> Nokia, Ericsson- also applicable for IN (TCAP over IP)- runs on top of SCTP- standardization in stable mode- Transport Independent SCCP is a direct competitor (ITU-T)
IP
SCTP
M3UAadapts MTP 3 User Parts to SCTP
SUAadapts SCCP Users to SCTP
Application (+TCAP)
ISUP, SCCP classic SS7
13.04.23SUA tutorial3 © Siemens Atea
Information andCommunication Networks
SUA status in IETF & outside
• new draft 09 (November)• Applicability of SUA:
Mobility Management in Wireless 3G systems (MAP) IN services for fixed and wireless systems (INAP, CAP) in
circuit switched and VOIP systems SMS offloading Iu interface (UTRAN/GERAN: between radio access and
core network) Corporate GSM Signaling Gateways Signaling Relays
13.04.23SUA tutorial4 © Siemens Atea
Information andCommunication Networks
Basic SUA Network architecture
A1
B1
B2
C1
D1
D2
E1gt
gt
gt’
gt’
gt’’
relayNodeEntitySet
gt’’’
13.04.23SUA tutorial5 © Siemens Atea
Information andCommunication Networks
SUA network architectures
• Basic SCCP/SUA architecture: to have end-to-end communication between different entities (SGSN, HLR, SMSC…) independent from the underlying technology used (TDM, IP, ATM…)
PSTN – IP interworking all IP network
• How should Global Title Translation be done Distributed : use of local GT databases Central : remote database accessed via LDAP… Hierarchical : remote database accessed via DNS…
13.04.23SUA tutorial6 © Siemens Atea
Information andCommunication Networks
PSTN – IP interworking
mm
SS7
SwitchSwitch
Switch
Circuit switchedPOTS/ISDN
SCPLNP
IN
MSC
IP/MPLSCore Network
Global SS7 overlay network
Circuit switched network Next Generation Network
SS7
SS7
SS7
SS7
SS7SS7
SS7
SS7 over TDM
SS7 over IP
SS7
13.04.23SUA tutorial7 © Siemens Atea
Information andCommunication Networks
PSTN – IP Protocol Interworking
HLR or SCP within an IP network
IP-based NetworkPSTN
MSC (or SSP)
SignallingGateway
SUA
SCCP Interw.
SCTP
IP
MTP1-3
HLR(or SCP)
MTP1-3
MAP/INAP
SCCPTCAP
SUA
SCTP
IP
MAP/INAP
TCAP
13.04.23SUA tutorial8 © Siemens Atea
Information andCommunication Networks
SGSN
HLR
SMSC
SRP
SRP SRP
Association:
Protocol Stack:
SRP
.
.
.
.
SCTPIP
AAL5/Ether
., ...
SUA SUA
AAL5/Ether
IPSCTP
SUA
SCTPIP
AAL5/Ether
MAP, IN, RANAP...
Network border
13.04.23SUA tutorial9 © Siemens Atea
Information andCommunication Networks
SUA implementation architecture
• SUA runs as a User plane implementation in Linux• makes use of the Siemens SCTP implementation (www.sctp.de )• uses the SCTP “function callback” mechanism
13.04.23SUA tutorial10 © Siemens Atea
Information andCommunication Networks
SUA : supported featuresRouting Options for Connectionless Services
routed on IP address & SSN Supply the origination an destination IP address Supply the application Subsystem Number(SSN) Message will be routed onto the correct SCTP association towards the destination IP
address (= direct associated routing) It might turn out that there is no direct SCTP association between the local SUA node
and the destination SUA node, then SUA will use quasi-associated routing (wow route via intermediate SUA nodes based on IP address)
routed on Pointcode & SSN: same as IP address & SSN, but different address syntax (32/128 versus 14/24 bit)
routed on GT & SSN Supply the origination (= calling party) and destination (= called party) Global Title (or
Hostname in case of extended AMF) address Supply the optional application SSN Message will be routed onto the correct SCTP association towards the destination IP
address derived via Global Title Translation (GTT). If no direct association exists , then SUA will route via intermediate SUA nodes based on
the IP address.
13.04.23SUA tutorial11 © Siemens Atea
Information andCommunication Networks
SUA : supported featuresConnection Oriented Services
• Connection oriented service only protocol class 2 association of connection sections is not supported
• Same routing options for CORE (COnnection REquest) as for the connectionless messages.
• Routing for subsequent msgs of a SUA connection is done using the stored association Id in the SCOC TCB, thus routing based on IP address or GT is not done.
13.04.23SUA tutorial12 © Siemens Atea
Information andCommunication Networks
SUA : supported featuresASP Management
• reachability of endnodes/ application servers : ASP management ASP : application server process AS : application server: An Application Server contain at least one ASP. The ASP within the Application server
can be processing traffic or can be in standby. The way in which traffic is shared over the ASP of a AS is implementation dependent. However traffic that needs the same server (such as TCAP msgs belonging to the same transaction) must be sent to the same ASP, if possible.
An ASP can belong to different Application Servers If a ASP would fail then internal mechanisms have to provide for the transfer of state
(example state of TCAP/application transaction.) within the AS. A more global solution will be provided using Rserpool technology.
• comparison with M3UA ASP management is identical for all UAs
13.04.23SUA tutorial13 © Siemens Atea
Information andCommunication Networks
SUA : supported featuresASP Management
• Difference between SS7 management and ASP management ASP management only deals with adjacent nodes SS7 management indicates statuses from non-adjacent nodes or routes (STP) Indicates to a ASP to start/stop sending traffic to the SG for a specified DPC and SSN Also congestion levels may be exchanged with the ASP SS7 management is in principle only used for interworking between a PSTN and a IP
network, but is also extendable to an all-IP infrastructure (single node = combined SG and AS)
Still requires the use of a pointcode overlay of the all IP network SS7 management gives the impression that the SG+ASP’s is a SS7 node(end/relay)
towards the SS7 network.• Error and notify msg
Use is still not very clear, e.g. their effect on ASPSM/ASPTM procedures.• Dynamic registration of ASP to a SG
Should be treated as extremely dangerous, especially if this is extended to the peer-to-peer IPSP - IPSP case (double-ended registration). Interop seems very doubtful here.
13.04.23SUA tutorial14 © Siemens Atea
Information andCommunication Networks
SPCx
SCMG
SSy
SPC1
SG
SPC2
ASP1
SPC3
ASP2 SSz
SSb
SSb
AS
SS7 network orSG + AS(P)
IP network
13.04.23SUA tutorial15 © Siemens Atea
Information andCommunication Networks
IP network Operator 1 IP network operator 3
IP network operator 2SUA uses a digit pattern which is translated from node to node until the final destination is reached -> Global title (e.g. MSISDN number : CC + NDC + SN)
Global title aspects Global title aspects
13.04.23SUA tutorial16 © Siemens Atea
Information andCommunication Networks
SUA : supported featuresRelay service : provide GTT (AMF ?) service
Useful for NAT crossing : no unknown NAT middlebox needed. The relay point is the box and it is explicitly visible towards other SUA relay points or SUA endpoints in both the normal internet and the NAT.Can be used as a firewall for SUA traffic : example removal of SMS spam traffic, enforcement of roaming agreements, ...If relay point is used for transitioning into the NAT then IPSEC can be used. Expands the addressing capabilities
E164 to E212 E164 to hostname Hostname to hostname hostname to E164 IPv4 - IPv6 network or NAT border crossing Pseudo end-to-end :network architecture hiding
Allow for loadsharing across a pool of relay points (using Rserpool or own SUA built in protocol)•
13.04.23SUA tutorial17 © Siemens Atea
Information andCommunication Networks
Use of ENUM in SUA
A1
B1
B2
C1
D1
D2
E1gt
gt
gt’
gt’
gt’’
relayNodeEntitySet
gt’’’
DNS ADNS X
DNS B
DNS DNS
DNS root
13.04.23SUA tutorial18 © Siemens Atea
Information andCommunication Networks
SUA: supported features Building the GT tree of the relaying service via DNS(ENUM)
• Normal way of using DNS is to invoke GetHostname for every message that passes: More negative points than positive
would create a DNS message flood in the DNS system as all connectionless msgs use E164/E212 numbers(if numbers gets cached, this problem may be reduced , but raises other issues)
the response time from the DNS is unpredictable due to its hierarchical architecture. Would produce a WWW(world wide Wait) effect on SS7 traffic
Using the Time-to-live(TTL) from the DNS records is quite useless as SUA would have a direct connection with the remote SUA node(and thus know far much better if the remote side is active or not). That would mean that SUA should not be caching the DNS info but always have the up-to-date info of all its adjacent SUA peers.
Is less flexible than the standard Global Title Translation function: a DNS name when distributed in DNS will always map to the same set of IP addresses (= SUA nodes) independent from the place where the resolving is requested, which would lead to a SUA hierarchical network design, something that is very BAD for reliability and contrary to any SS7 network design up till now(SS7 favors greatly a peer-to-peer network design and SS7-over-IP should benefit from that)
A name in the DNS can return many IP addresses and not all those address may belong to the same. node -> DNS is sometimes used for loadbalancing across multiple nodes and it is impossible to make a difference between a truly multihomed (SUA)node and a a bunch of replicated (SUA) nodes(with no multihoming attached to each single node naturally) (Except if you start finding it out for yourself by setting up association with each of the addresses)
13.04.23SUA tutorial19 © Siemens Atea
Information andCommunication Networks
Use of SUA with SCTP
• Association setup, release, mapping (distribute traffic over different associations according to addressing info), SSN, portnumber• Difference between end and relay point.
static associations dynamic associations (pure end-to-end)
• ASP issues -> relation to Rserpool • TESTIP: Basic tester for testing the capabilities of SUA• Not compatible (yet) with the EWSD based TEST User part
13.04.23SUA tutorial20 © Siemens Atea
Information andCommunication Networks
Comparison with other stacks (1)
• SUA <-> SCCP+M3UA SUA has better knowledge of the underlying network than SCCP on top of M3UA,
I.e. the Routing Contexts can be more fine-tuned. Management should be simpler as only one layer (SUA ASP management) has to
be administered versus 2 (M3UA ASP management + SCCP management). Can use extended addressing capabilities which are not included in SCCP (use of
IP address and of hostname/DNS names) yet. SUA does NOT require SS7 pointcodes (administrative) in principle, but the
traditional SCCP users may still require PC or SSN status indications ...
13.04.23SUA tutorial21 © Siemens Atea
Information andCommunication Networks
Comparison with other stacks (2)
• SUA <-> transport independent SCCP Just as SUA, TI-SCCP would lack the MTP3 transfer functionality and point code
overlay to support traditional management procedures, if run directly over SCTP. TI-SCCP can be run over M3UA as well, via the appropriate STC. TI-SCCP doesn’t have extended addressing capabilities yet. This may change but
is up to TI-SCCP standardisation (example IP address/hostname/DNS name)
13.04.23SUA tutorial22 © Siemens Atea
Information andCommunication Networks
SUA applicability
• SUA can transport bigger SMS messages (nr of char >> 160) however, this would also be true for traditional SCCP and TI-SCCP, but requires
adaptations to MAP protocol and raises interworking issues
• SUA can transport bigger messages for all its applications particularly useful in all-IP, where segmenting/reassembly can be left to SCTP
• SUA is less complex than M3UA+SCCP, but has extended features … because it can be fine-tuned to SCCP applications
• SUA supports the basic IP addressing architecture and DNS naming this advantage depends of course on applications using the extended addressing
capabilities
13.04.23SUA tutorial23 © Siemens Atea
Information andCommunication Networks
1st SUA bakeoff 5 – 9 November 2001
• Done at Siemens atea, Herentals Belgium• 5 Companies attended: Performance Technologies(PTI), Radisys, Hughes Software Systems(HSS), Cisco and Siemens• No big problems detected with spec• Most implementations only supported Connectionless and were acting as Signalling gateway• Connection-oriented worked also -> to be used in 3GPP??• Basic SUA Management worked.
13.04.23SUA tutorial24 © Siemens Atea
Information andCommunication Networks
Conclusion
Bug reports, suggestions, support can be directed to:Lode Coene: Email: [email protected], phone: +32-14-252081
Gery Verwimp : Email: [email protected], phone: +32-14-253424
Implementation is open source , may be used, changed, whatever. If you have a great idea to be used in SUA,
let us know, we ‘ll consider it for a next version.
Source is to be released under the GPL on the web: www.sctp.be/sua
Thank you
13.04.23SUA tutorial25 © Siemens Atea
Information andCommunication Networks
... And now for something completely different...
GSM goes around the world
SS7 makes it work
..And SMS is the mobile data revolution..
http://www.sctp.be/sua http://www.sctp.de