1. SCCP User Adaptation Layer tutorial Authors: Lode Coene Gery Verwimp
SUA tutorial
SCCP User Adaptation Layer tutorial
Authors:
Lode Coene
Gery Verwimp

2. SCCP user adaptation layer(SUA)
Application (+TCAP)
- 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)
ISUP, SCCP classic SS7
SUA
adapts SCCP Users to SCTP
M3UA
adapts MTP 3 User Parts to SCTP
SCTP IP
SUA tutorial

3. 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
SUA tutorial

4. Basic SUA Network architecture
gt’ B1 D1 gt
gt’’’ E1 A1 gt C1
gt’’ D2 B2
gt’
relayNodeEntitySet
SUA tutorial

5. 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…
SUA tutorial

6. PSTN – IP interworking SUA tutorial Kalte Farben Warme Farben
Vorzugsfarben
4 × Grau (aus 216)
SUA tutorial

7. PSTN – IP Protocol Interworking
Kalte Farben
PSTN – IP Protocol Interworking
Warme Farben
HLR or SCP within an IP network
Vorzugsfarben
PSTN
IP-based Network
4 × Grau (aus 216)
MSC
(or SSP)
HLR
(or SCP)
Signalling
Gateway
MAP/INAP
SCCP
TCAP
MAP/INAP
TCAP
SCCP Interw.
MTP
1-3
MTP
1-3
SUA
SUA
SCTP IP
SCTP IP
SUA tutorial

8. SGSN SRP SRP HLR SRP SMSC SRP Network border Protocol Stack : ., ...
Association: . . .
SMSC
SRP
Protocol Stack :
MAP, IN, RANAP...
SUA
SUA
SUA
SCTP
SCTP
SCTP IP IP IP
AAL5/Ether
AAL5/Ether
AAL5/Ether
SUA tutorial

9. SUA implementation architecture
SUA runs as a User plane implementation in Linux
makes use of the Siemens SCTP implementation ( )
uses the SCTP “function callback” mechanism
SUA tutorial

10. SUA : supported features Routing 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.
SUA tutorial

11. SUA : supported features Connection Oriented Services
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.
SUA tutorial

12. SUA : supported features ASP 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
SUA tutorial

13. SUA : supported features ASP 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.
SUA tutorial

14. IP network SS7 network or SG + AS(P) ASP1 SPC2 SSb AS SG SCMG SPC1
SPCx
SSz
SSy
ASP2
SPC3
SSb
SUA tutorial

15. Global title aspects IP network Operator 1 IP network operator 3
SUA 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)
SUA tutorial

16. SUA : supported features Relay 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)
IPSEC does not work if the SCTP association is terminated within the NAT, IPSEC works only till the NAT border. A NAT box has to change addresses and portnumbers in the IP and transport header. IPSEC has authenticated or encrypted at least the transport header so changing this would break the association. This can be circonvented by tunneling.
SUA tutorial

17. Use of ENUM in SUA B1 D1 E1 A1 C1 B2 D2 DNS root DNS DNS DNS X DNS A
DNS B
gt’ B1 D1 gt
gt’’’ E1 A1 gt C1 B2
gt’’ D2
gt’
relayNodeEntitySet
SUA tutorial

18. 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)
SUA tutorial

19. 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
SUA tutorial

20. 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 ...
SUA tutorial

21. 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)
SUA tutorial

22. 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
SUA tutorial

23. 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.
SUA tutorial

24. Bug reports, suggestions, support can be directed to:
Conclusion
Bug reports, suggestions, support can be directed to:
Lode Coene: phone:
Gery Verwimp : phone:
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:
Thank you
SUA tutorial

25. ... And now for something completely different...
GSM goes around the world
SS7 makes it work
..And SMS is the mobile data revolution..
SUA tutorial