SS7 Whitepaper Ver 1.41

\* CMG

SMSC White Paper

SMSC connectivity and the SS7 Network

1999 CMG Telecommunications & Utilities B.V.

1Version History

Version Date Details of Changes Author(s)

0.1 22/08/00 Initial version MOC

0.2 29/08/00 2nd Draft MOC0.3 29/08/00 3rd Draft MOC

0.4 08/09/00 4th Draft MOC/AR/NK

0.5 08/09/00 5th Draft MOC/AR/AL

Approval Record

Version Date Approved by Signature

1.4 22/04/23 Steven van Zanen

SMSC connectivity and the SS7 Network Version 1.4 1

The information in this document is subject to change without notice and should not be construed as a commitment by CMG. CMG assumes no responsibility for any errors that may appear in this document.

The information given in this document is strictly confidential.

2 Version 1.4 SMSC connectivity and the SS7 Network

2Table of contents

1 Introduction.......................................................................................................3

2 Standard E1/T1 Connectivity...........................................................................4

2.1 Introduction.................................................................................................................... 4

3 Multiple Point Codes.........................................................................................7

3.1 Introduction.................................................................................................................... 7

3.2 Concept.......................................................................................................................... 8

3.2.1 Maximum Capacity when using Multiple Point Codes......................................................9

3.2.2 Advantages of using Multiple Point Codes.......................................................................9

3.2.3 Disadvantages of using Multiple Point Codes................................................................10

3.3 Supporting STP/MSC vendors......................................................................................10

4 SS7 over ATM..................................................................................................11

4.1 Introduction..................................................................................................................11

4.2 Concept........................................................................................................................ 11

4.2.1 Advantages..................................................................................................................12

4.2.2 Disadvantages..............................................................................................................12

4.3 Customer Questionnaire...............................................................................................12

4.3.1 Operations:................................................................................................................... 12

4.3.2 Technical...................................................................................................................... 12

4.3.3 Planing......................................................................................................................... 13

5 SS7 over IP.......................................................................................................14

5.1 Introduction..................................................................................................................14

5.2 Issues........................................................................................................................... 14

Appendix A...............................................................................................................15


1 Introduction

After the introduction of SMS at the beginning of the nineties, SMS has gone through a huge evolution from a behavioural point of view. It started as a voice mail notification service that triggered mobile users that a voice mail message was waiting for them to invoke call completion. A few years later operator started to use the mobile terminated SMS for the introduction of Value Added Services and in the mid-nineties operators started to enable mobile originated SMS. Since this happened, interactive Value Added Services were being introduced to the customers and the mobile users started to use SMS as a medium to communicate with each other.

Today mobile originated SMS is responsible for 70 to 80% of the total SMS traffic and messages volumes are increasing explosively. The GSM Association reported that Global SMS has reached 5 billion SMS per month in the first half of 2000, which is an increase of 75% from the end 1999 figures. The forecast for the end of 2000 is 10 billion and 100 billion SMS per month is predicted by the end of 2002! Telecom Italy Mobile reported that SMS contributed for 4% of the total revenue in the first quarter of 2000, while Sonera reported that SMS contributed even for more, 9%!

CMG had foreseen this market evolution and was able to provide a high performance SMSC with a capacity of 500 SMS per second in 1999. A single SMSC platform currently supports up to 2500 Short Messages per second. CMG is and has been the market leader for capacity SMSC platforms because of its product vision that the number of SMSCs in an operator’s network should be limited. Many operators are sharing this vision especially regarding network configuration, operation & maintenance and cost of ownership.

In order to provide a capacity of 2500 Short Messages per second commercially in the network, a large number of SS7 connections are required. Due to the fact that a maximum of 16 signalling links between two adjacent nodes of a SS7 network can be established (ITU Specification), the number of network elements required to transport messages to the network is becoming a bottleneck. This document describes how to overcome this bottleneck within the network by introducing a multiple point-code configuration or other new technologies. The described alternatives will enable the operator to increase the SMS capacity and to benefit from the revenue that this market expansion will bring.

This paper gives a description of the SS7 options currently available to Operators as well as new technologies that will be incorporated into the current SMSC Standard Telecom Platform. It is intended that this whitepaper will aid operators to choose from the available SS7 connectivity options one that will provide for Operators current and future needs in a clear and open manner.

The following topics are discussed

Standard E1/T1 SS7 Connectivity including link selection

Multiple Point Codes per SMSC

SS7 over ATM

SS7 over IP


2 Standard E1/T1 Connectivity

2.1 Introduction

This section describes the current manner that a CMG SMSC is connected into the SS7 network.

Currently the SMSC interfaces either with STP's (Signalling Transfer Points) or directly to MSC's (Mobile Switching Centre's) and HLR's (Home Location Registers). Over these interfaces the MAP (Mobile Application Part) commands are transmitted in order to originate and complete SMS messaging.

The diagram below shows a possible SS7 network topology consistent with current network deployments.

As can be seen from the above the number of adjacent signalling points has a direct effect on the capacity that the network may receive from a CMG SMSC. The limitation of 16 links is based on the ITU SS7 connectivity standard. For ANSI SS7 there is a limit of 32 SS7 links between two network elements.

Note: There is currently development being undertaken by the telecommunications industry to improve the ANSI SS7 protocol, one of the enhancements is the ability to support up to 256 SS7 links between two network elements.


Below is a diagram indicating the number of signalling links required in order to support a number of messaging rates.

These figures are based on ITU-T SS7 links (64 Kbit), global title routing, and phase 2 messaging in a non-number portability environment. SMDA/sec (Short message delivery attempts per second) is taken to be terminating message attempts, originating messages is takes to be 50% of terminating messages. A message length of 55 octets (62 characters) per message is assumed of which 5% are greater then 100 octets (114 characters). Alerts are taken to be <25% of terminating messages. All links are assumed to be balanced.

Recommended Not Recommended

Erlang 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

SMDA/sec

22 11 8 6 5 4 4 3 3 350

100 44 22 15 11 9 8 7 6 5 5

250 109 55 37 28 22 19 16 14 13 11

500 217 109 73 55 44 37 31 28 25 22

750 326 163 109 82 66 55 47 41 37 33

1000 435 218 145 109 87 73 63 55 49 44

Therefore the following would be the number of adjacent signalling points required to support such messaging at 0.3 Erlang during normal operation.

SMDA/sec 50 100 250 500 750 1000

STP's required

1 1 3 4 7 10

As can be seen once messaging rates above 500 message attempts are required the number of Adjacent Signalling Points may become unmanageable to the operator.


With an ANSI SS7 stack (56 Kbit) with global title routing in a non-number portability environment SMDA/sec (Short message delivery attempts per second) is taken to be terminating message attempts, originating messages is takes to be 50% of terminating messages. A message length of 55 octets (62 characters) per message is assumed of which 5% are greater then 100 octets (114 characters). Alerts are taken to be <25% of terminating messages. All links are assumed to be balanced. Phase 1 messaging is assumed.

Recommended Not Recommended

Erlang 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

SMDA/sec

50 19 10 7 5 4 4 3 3 3 2

100 37 19 13 10 8 7 6 5 5 4

250 92 46 31 23 19 16 14 12 11 10

500 183 92 61 46 37 31 27 23 21 19

750 274 137 92 69 55 46 40 35 31 28

1000 365 183 122 92 73 61 53 46 41 37

Therefore the following would be the number of adjacent signalling points required to support such messaging at 0.3 Erlang during normal operation.

SMDA/sec 50 100 250 500 750 1000

STP's required

1 1 1 2 3 4


3 Multiple Point Codes

3.1 Introduction

This feature is of interest to Operators with a limited number of STP's (Signalling Transfer Points). SS7 currently has the limitation due to ITU & ANSI standards of a maximum of 16 links / 32 links respectively between any two adjacent nodes in a SS7 network. This means that by having one SMSC and two STP's in a network, a total of 32/64 links (ITU-T / ANSI) can be connected to the SMSC. This has an obvious impact in that the throughput of the SMSC can not exceed the capacity of signalling links available. As certain STP vendors only allow a percentage of the bandwidth of a link to be used to prevent congestion of the STP and provide capacity for redundancy in the event of link failure, this can quickly become a bottleneck in the network. Please note that OPTION 15 must be enabled on the SMSC to support this option.

E.g. Using 2 STP's, with MAP phase 2, and a 0.3 erlang line capacity, the network is only capable of receiving 216 SM./sec from the SMSC with an ITU-T SS7 stack.

Below is a diagram of a seven node SMSC connected to two STP's according to ITU-T SS7 standards. As all the FEP's (front-end processors) share the same point code (2202) (the FEP's also share the same Global Title), there can only be a maximum of 16 links between the SMSC and STP 1. The same is true for connectivity to STP 2. Therefore the SMSC has a maximum capacity of 32 SS7 links in a two STP configuration.

Fig 1: Seven node SMSC connectivity to two STP's using a single point code.


3.2 Concept

By configuring the SMSC to have more then one point code and global title, the number of links that can be connected increases proportionally.

Once FEP's have unique point codes rather then sharing a single point code the SS7 capacity of the system increases dramatically. This can be seen in the diagram below where a maximum of 128 links under ITU-T and 256 links under ANSI are now technically possible due to the SMSC having 4 point codes. (See note 1).

Each FEP should have a unique global title and point code. The SMSC also has a Virtual Global Title configured in the network, which is known to the subscriber base. Introducing a Virtual Global Title in the network will enable the Operator to support a multiple SMSC configuration in a distributed environment at the same time.

Upon receiving a message from a subscriber, the STP (Signalling Transfer Point) should translate this virtual global title to one of the available FEP point codes. This is typically done based on a round robin algorithm.

Note 1: CMG's current high performance Seven node SMSC is licensed for 96 links. Should more links be required then a hardware and license upgrade would be required. This would most likely be provided by CMG on a project basis.

Note 2: This concept is not designed to reduce downtime during a SMSC upgrade.

Fig 2: Seven node SMSC connectivity to two STP's using multiple point codes.

In order to enable such a configuration the operator must update the global title tables with new global titles to map to the SMSC's FEP's. The STP's should load share all messages sent to the Virtual Global Title address using global title translation to the FEP's.


The following Diagram should aid the Operator in the way a STP can transfer a message to the relevant FEP. (Applies to ITU-T only).

Fig 3: Example of message routing by the STP to the relevant FEP of the SMSC

3.2.1 Maximum Capacity when using Multiple Point Codes.

The maximum commercial capacity of STP (Standard Telecom Platform) 4.0 has not increased with the introduction of Multiple Point Codes due to the fact that the maximum number of links that the current STP supports has not increased. This functionality allows operators previously limited by the ITU-T 16-link rule or by the ANSI 32-link rule the ability to support more links from their infrastructure to the SMSC.

3.2.2 Advantages of using Multiple Point Codes

The maximum number of SS7 links is increased therefore increasing the potential throughput of the SMSC.

Network traffic between FEP's reduced dramatically therefore reducing load on intersystem communication facilitating higher SMSC throughput.

SS7 traffic between FEP's eliminated therefore increasing SS7 stability

The SS7 stack on a FEP may be restarted without affecting other FEP's \ links which increases the availability of the system

3.2.3 Disadvantages of using Multiple Point Codes

STP / Network functionality and configuration required to enable this functionality


Greater Operator expertise required for SS7 maintenance as well as SS7 configuration such as STP configuration, multiple FEP configuration and SS7 load-sharing configuration

A node failure appears as a complete signalling point failure (*)

Should a FEP fail all transactions being processed is lost and will not be redirected to an alternate FEP. A STP (Signalling Transfer Point) will redirect only new transactions to an alternate FEP.

* Note: Should a node fail, the network may generate an alarm to indicate a complete signalling point failure. However as the SMSC is using multiple point codes full service capacity is available. Operators are required to make note of this point in order to understand that the availability of the SMSC is not compromised.

3.3 Supporting STP/MSC vendors

Please verify with your STP/MSC vendor as to capabilities/restrictions on SCCP load sharing.

Questions that Operators should/may ask their Infrastructure providers

How many sub addresses (MSISDN's) can the STP translate the SMSC's Global Title into? (There is currently a requirement of 4 addresses for STP 4.0)

What is the algorithm used for message distribution (round robin is preferred by CMG due to its load-sharing characteristics)?

Is there any restriction on signalling link selection that could affect the number of links between two signalling points? (Certain vendors do not support the maximum number of links between two network elements).

CMG currently has information on the following infrastructure vendors with relation to this concept.

AlcatelCMG has successfully implemented a multiple point-code solution in a live Operator site that uses Alcatel as their primary infrastructure vendor.

SiemensSiemens STP's are restricted to resolving a global title to two point codes. Due to signalling link selection only 8 links per point code are possible. Therefore a Multiple Point Code solution is of no tangible benefit to an operator.


4 SS7 over ATM

4.1 Introduction

ATM technology as an option in the SMSC product is expected to become available in Q2 2001. ATM introduces broadband technology into the SS7 network. This helps to reduce the bottleneck between STP's in a SS7 network. SS7 over ATM allows up to 16 ATM links between 2 STP's with each ATM link having a bandwidth of a T1 or E1 line (1.544 Mbps or 2.048 Mbps).

4.2 Concept

By configuring a SMSC with ATM links, substantial throughput improvements are possible as rather than having a limitation of 16 64 Kbit links (ITU-T) between two adjacent nodes this is increased to 16 2.048 Mbps (ITU-T) between any two adjacent nodes. This is a dramatic improvement in possible bandwidth between adjacent nodes. With the ANSI SS7 Stack implementation, maximum throughput is increased to 32 1.56 Mbps between any two Adjacent nodes.


4.2.1 Advantages

SS7 bandwidth increased and as a result so is potential SMS volume between the SMSC and the SS7 network.

No change is required in SS7 network operations, topology, routing or load-sharing

Minimal impact in SMSC management for ATM entities

Traditional E1/T1 cabling is used reducing the need for expensive cabling

ATM can co exist with traditional E1/T1 in the SS7 network

4.2.2 Disadvantages

Requires specific hardware to support ATM links (new boards on the SMSC)

ATM functionality may be dependant on your STP/MSC software version (e.g. Ericsson Release 8 MSC/ TSC)

E1/T1 trunk required for each 2 Mb ATM link (although this is a normal requirement for an increase in bandwidth)

SS7 over ATM is to date not largely deployed.

It is possible to configure a SMSC to support standard and ATM SS7 links, however a single FEP may only have links of one type. This functionality enhancement is only available with Compaq's SS7 stack version 7.4.1 or higher.

4.3 Customer Questionnaire

CMG would request that Operators consider the below questionnaire and return the results to your sales representative in order that CMG meets the market demands of our customer base. Please verify with your STP/MSC vendor as to capabilities/restrictions with their ATM solution.

Questions that Operators should/may ask themselves and their Infrastructure providers

4.3.1 Operations:

Do you envisage that your SMS traffic will push your SS7 network to its performance limit?

Do you plan an SS7 over ATM migration for solving performance issues

Do you plan to use other method than SS7 over ATM to solve performance issues?

Do you plan an SS7 over ATM migration for other reasons?

What are your expected capacity requirements and timeframe for ATM dimensioning?

4.3.2 Technical

Are your STPs ATM ready?

Who is your STP manufacturer?

Do you intend to connect the SMSC directly to your STPs?


Do you intend to connect the SMSC via an ATM network to your STP?

Which ATM switches are using? (in case of ATM network connection)

Do you intend to use both E1/T1 and ATM links for your SMSC connectivity?

4.3.3 Planing

Has a decision for SS7 over ATM been already made or scheduled?

Are you planing or undergoing any field tests presently?

How long would you plan to run a field test before introducing ATM to your live environment?


5 SS7 over IP

5.1 Introduction

SS7 over IP is a necessary industry development to facilitate the huge data volumes projected for a 2.5 / 3G network.

SS7 over IP is currently undergoing the process of standardisation, however it is expected that this bearer will not be integrated into networks in the near term. CMG is monitoring developments in this area and will provide a SS7 over IP solution once standardisation is complete.

5.2 Issues

Currently there a number of issues to be resolved before SS7 over IP can be integrated into CMG's SMSC.

Physical

Connection (cable type and Connector)

Standards (ATM*, Ethernet)

Speeds (gigabit / megabit)

* Note: ATM referred to here refers to TCP/IP ATM networks and not "SS7 over ATM" as mentioned in the previous chapter.

It has also to be decided where SS7 is connected into the IP protocol. Will direct MAP commands be sent over IP or is SCCP & TCAP information to be included? CMG is working in close co-operation with STP vendors to support the development of this broadband solution.


Appendix A


Documents

SS7 Whitepaper Ver 1.41