ManagingSIGTRAN Networks

Graham ByarsProduct ManagerASD

SIGTRAN growth is being fuelled by two key factors:• CAPACITY - Link and STP capacity running

out as new services (SMS, VoIP, IMS) and their associated nodes and signalling load are introduced

• COSTS - Increasing operational, maintenance and cost of network

Legacy C7 Architecture

HLR

HLR

BSC

GGSN

SGSN STP

STP

MSC

VLR

MSC

VLR

BSC

Call Control

Access

Media

SMSC

SCP

Services

STP

STP

SIGTRAN Drivers

SIGTRAN is being introduced as:• SMS offload as TDM based SS7 network reach capacity

• Replacement of TDM links and STPs which are a costly infrastructure

• Migrations to VoIP and IMS services infrastructure (Rel4 and Rel5 3GPP Architectures)

The benefits of SIGTRAN include:• CAPACITY - Higher network efficiency by providing increased signalling capacity to

reduce network congestion as subscribers adopt new, multimedia services

• COSTS - Reduced transport costs by up to 70 percent;

– Significant Opex reductions for Operators if the SIGTRAN route is taken. Estimates are up to 50% savings.

GSM SIGTRAN ArchitectureOptions – Signalling Gateway

HLR

HLR

BSC

STP

STP

MSC

VLR

MSC

VLR

BSC

Call Control

Access

SMSC

SCPServices

BSC

MSC

VLR

ITP

HLR

ITP

Signalling Gateway Network• Signalling transported over legacy TDM and

IP network• ITP (IP transfer point) gateway act as

gateways points (often implemented as part of new iSTPs)

Drawbacks• CAPACITY – depending on STP architecture

ITP could become new bottleneck

SIGTRAN

GSM SIGTRAN ArchitectureOptions Dual Stacking

HLR

HLR

BSC

STP

STP

MSC

VLR

MSC

VLR

BSC

Call Control

Access

SMSC

SCP

Services HLRDual Stacking Network• Signalling transported over legacy TDM

and IP network• SIGTRAN enables by ‘Dual stacking’

key nodes – MSC, HLR

Drawbacks• Some nodes will never migrate and

some node may only have SIGTRAN So, you still may need Signalling Gateway function

SIGTRAN

BSC

MSC

VLR

HLR

MAP

ISUP

CAP

CAPMAP

MPLSVPN

SCTP

C7

C7

STP

STP

C7 SIGTRAN

M3UA

SCCP

TC

MAP/INAP

MTP3

IPIP

MTP2

MTP1 16 16

MSC/HLR

100BaseT

2.5 SIGTRAN Architecture

2.5G and 3G SIGTRAN Network• Migration of 2.5G Signalling Links to

SIGTRAN (Gb and Gr)• SIGTRAN connection by SS7 over IP

enabled BSC and SGSN

HLR

GGSN

SGSN STP

STP

MSC

VLR

BSCCall Control

Access

SMSC

SCP

Services

SIGTRAN

Gr

Gb

Gn

BSC

MSC

VLRBSC

MSC

VLR

HLR

MAP

ISUP

CAP

HLR

HLR

SIGTRAN

SIGTRAN

SIGTRAN User Adaptation Layer Protocols

SIGTRAN a working group setup by the IETF developed a new family of adaptation layer protocols to support Signalling Transport of circuit-switched signalling over IP networks

The adaptation layer protocols introduce new protocol messages and protocol inter-working scenarios

MTP3

IP

SCTP

M3UASUA

ISUP

M2PAM2UA

TCAP

MTP1

MTP2

MTP3

SCCP

SIGTRAN

MTP1

MTP2

MTP1

MTP2

M3UA – Protocol Inter-working

IPIP

MTP3

SCTP

M3UA

SCCP

SCTP

M3UA

SCCP

MTP3

SCCP

Signaling Gateway

SS7Network

IPNetwork

ITPHLRMSC

VLR

SIGTRAN Congestion Control

Transfer Controlled (TFC) SCON (Signalling Congestion)

Signalling Point Congestion Application Server Congestion

M3UAMTP3

TFC

SP

MTP1MTP2MTP3

IPSCTPM3UA

SignallingGateway/STP

SP

SPMSU

SCON

SP

TFC

SP

MTP1MTP2MTP3

IPSCTPM3UA

SignallingGateway/STP

SP

SPMSU

SCON

SP

TFC

MSUcongestion

SPcongestion

SP

Customer Requirements• Ensure that routing algorithms have been setup correctly to balance the

load across the network and bottlenecks are not occurring

• Understand the logical connection loads for planning purposes

• Identify and resolve Protocol interworking problems as messages traverse from TDM to IP stacks through new nodes (ITF, Dual stack nodes, etc) or between new IP enabled nodes (IP HLR, IP MSC)

• Ensure that quality metrics of C7 network are maintained when migrated to SIGTRAN

• RTT = 80±20 ms • Bit Error Rate < 1 in 1010

• Availability > 99.998%• Maintain consistent KPIs (e.g. ASR) and monitoring capabilities (e.g. Call

Tracing) provided today by passive monitoring solutions to ensure customer service and support does not degrade

Customer Use Case – IP node configurationWith in a few weeks of installing QoSA SIGTRAN into their live network a large North American operator was receiving value from the solution

A new IP-MSC was turned up with a poorly configured trunk group to a LEC (inbound and outbound traffic). The trunk group’s search pattern was incorrect causing glare. The MSC serves as a gateway, taking traffic from 4 other MSCs so a large amount of voice traffic would be carried by this node. QoSA SIGTRAN saw 5000 abnormal releases every 5 minutes.

• QoSA SIGTRAN identified the problem• QoSA SIGTRAN showed when the problem started

Value Proposition5000 abnormal releases every 5 minutes

(Average at Peak times)

• Total number of abnormal releaseper day = ¼ * 5000 * 288 = 360,000

• Remove retries ÷5 = 72,000• Average Cost per call $2.25 (5minutes)• Lost revenue per day = $162,000

Saving $162,000 per day

Customer Use Case – Route ConfigurationWith in a few hours of installing QoSA SIGTRAN into their live network a large European operator was receiving value from the solution.

QoSA SIGTRAN showed that the load distribution of SS7 signalling was not as expected and two logical connection that should be carrying half the traffic were only carrying heart beat messages. Whilst not a problem at this stage of the deployment as traffic rates increased on the SIGTRAN network or a connection failure occurred this could have a dramatic effect on the ability of the SIGTRAN network to handle the traffic.

• QoSA SIGTRAN identified the problem• QoSA SIGTRAN showed when the problem started

3rd and 4th logicalconnection thatshould have beencarrying half theload only showsa heart beat

2 out of six logical connection carrying traffic

SSP

SSP

iSTP iSTP

Customer Use Case – Real time alertof network outages

With in a few weeks of installing QoSA SIGTRAN into their live network a large North American operator was receiving value from the solution.QoSA SIGTRAN Top N logical link loads indicated that an iSTP quad was imbalanced. Two of the links load dropped and two increased. A Protocol Analysis session on the C links showed what traffic was being re-routed. Back to QoSA and it shows 2 SSPs with a drop in traffic confirming they had lost one of their SIGTRAN logical links to the iSTP. The NOC was informed of the outage and with their existing Network Management tools they had a ticket open on one of the SSPs but had missed the other.

iSTP

SIGTRANSIGTRAN

iSTP

C

B

A

SSP

Customer Use Case – IP Performance

Switch Site South West

R

MSC

VLR

HLR

R

R

SCTP Retransmission Timer

R

Switch SiteNorth East

Switch Site North West

R

MSC

VLR

HLR

iSTP

iSTP

• Normal route between North West HLR and South West MSC fails.

• IP network re-routes via router in North East.

• Round trip time increases such that the SCTP retransmission time is exceeded and the HLR starts to retransmit messages

• This leads to duplicate SS7 message being sent across the network and an increased load on the STP starts to cause congestion problems

• Monitoring of the SACK message and the SACK chunks will indicate duplicate data and gaps

SS7

SIGTRAN Troubleshooting

IuCS

TDM

ISUPBICC

MAP o IP

MAP TDM

UMTS, GPRS, ISUP, MAP, CAMEL Troubleshooting Over TDM and IP using:SESSION TRACE

SIGTRANGCP

TDM

TDM

MATD

TDM

ISUP o IP

ISUP TDM

GboIPIuPS

MSC

VLR

SMSC

STP

STP ITPITP

STP

STP

MSC

VLR

SMSC

HLRSMSC

BSC

SGSN

MSCServer

MGW

MSCServer

RNC

SMSC

SIGTRAN Monitoring

UMTS, GPRS, ISUP* and MAPBusiness Analytics Over TDM and IP using:DMT

UMTS, GPRS, ISUP* and MAP QoS Over TDM and IP using:QoS ANALYZER

Load (Link and Node), SNM and Call Based Measurements, For SCTP, M3UA, etc using: QoSA SIGTRAN

* Available as a Service Pack on C.05

IuCS

TDM

ISUPBICC

MAP o IP

MAP TDM

SIGTRANGCP

TDM

TDM

TDM

ISUP o IP

ISUP TDM

GboIPIuPS

MSC

VLR

STP

STP ITPITP

STP

STP

MSC

VLR

SMSC

HLRSMSC

BSC

SGSN

MSCServer

MGW

MSCServer

RNC

SMSC

QUESTIONS