Download SCCP user adaptation layer(SUA)

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SUA tutorial
SCCP User Adaptation Layer tutorial
Authors:
Lode Coene
Gery Verwimp
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SCCP user adaptation layer(SUA)
Application (+TCAP)
SUA
ISUP, SCCP classic SS7
adapts SCCP Users to
SCTP
M3UA
adapts MTP 3 User
Parts to SCTP
SCTP
- 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
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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
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Basic SUA Network architecture
gt’
B1
A1
D1
gt
E1
gt’’’
gt
C1
B2
D2
gt’’
gt’
relayNodeEntitySet
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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…)
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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…
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PSTN – IP interworking
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PSTN – IP Protocol Interworking
HLR or SCP within an IP network
PSTN
MSC
(or SSP)
IP-based Network
HLR
(or SCP)
Signalling
Gateway
MAP/INAP
MAP/INAP
TCAP
SCCP
MTP
1-3
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TCAP
SCCP Interw.
SUA
MTP
SCTP
1-3
IP
SUA
SCTP
IP
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Network border
SGSN
SRP
SRP
., ...
HLR
SRP
.
.
.
Association:
.
SMSC
Protocol Stack
SRP
:
MAP, IN, RANAP...
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SUA
SUA
SCTP
IP
AAL5/Ether
SCTP
IP
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SUA
SCTP
IP
AAL5/Ether
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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
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SUA : supported features
Routing Options for Connectionless Services
routed on IP address & SSN
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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:
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same as IP address & SSN, but different address syntax (32/128 versus 14/24 bit)
routed on GT & SSN
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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.
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SUA : supported features
Connection Oriented Services
• Connection oriented service

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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.
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SUA : supported features
ASP Management
• reachability of endnodes/ application servers : ASP management
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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
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ASP management is identical for all UAs
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SUA : supported features
ASP Management
• Difference between SS7 management and ASP management
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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
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Should be treated as extremely dangerous, especially if this is extended to the peer-topeer IPSP - IPSP case (double-ended registration). Interop seems very doubtful here.
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IP network
SS7 network or
SG + AS(P)
ASP1
SPC2
SSb
AS
SG
SCMG
SPC1
SPCx
ASP2
SSz
SSy
SPC3
SSb
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Global title aspects
IP network operator 2
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)
IP network Operator 1
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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
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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)
•
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DNS root
DNS
Use of ENUM in SUA
DNS
DNS X
DNS A
DNS B
gt’
B1
A1
D1
gt
E1
gt’’’
gt
C1
B2
D2
gt’’
gt’
relayNodeEntitySet
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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
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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)
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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.
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
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
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Comparison with other stacks (1)
• SUA <-> SCCP+M3UA
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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 ...
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Comparison with other stacks (2)
• SUA <-> transport independent SCCP
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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)
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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

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this advantage depends of course on applications using the extended addressing
capabilities
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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.
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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
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... And now for something completely different...
GSM goes around the world
SS7 makes it work
http://www.sctp.be/sua
http://www.sctp.de
..And SMS is the mobile data revolution..
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