A new SS7-SIGTRAN protocol interchanger software ... - IEEE Xplore

5th International Conference on Electrical and Computer Engineering ICECE 2008, 20-22 December 2008, Dhaka, Bangladesh

A new SS7-SIGTRAN protocol interchanger software operated with modified USB E1 for nationwide IP backbone – Necessity for BTCL PSTN M. S. Munir¹, K. Ahmed¹, ASM Shihavuddin¹, Tahmid Latif¹ and Md. Saifur Rahman² ¹Department of Electrical and Electronic Engineering, Islamic University of Technology (IUT), Bangladesh. ²Electrical and Electronic Engineering Department, Bangladesh University of Engineering and Technology (BUET), Mailing Address: 16/9 North Circular Road, Vuter Goli, Dhanmondi, Dhaka, Bangladesh. E-mail: {smunir, kabir_89}@iut-dhaka.edu, {shihav407, tahmidlatif, saif672}@yahoo.com,

Abstract – This paper presents a new Signaling System no. 7 (SS7) and IP based Signaling Transport (SIGTRAN) protocol interchanger software and related hardware for Bangladesh Telecommunications Company Ltd. (BTCL) to expand its existing network using IP backbone. As the demand of wireline phone of BTCL is increasing day by day, it has become a necessity for BTCL to expand its network. At this point, BTCL can expand its network by establishing IP backbone and connecting it with the existing SS7 network using the new SS7-SIGTRAN interchanger software. This will be a good utilization of the newly arrived IP based transport and switching technologies which is reducing the cost of delivering different services. Again, compared to voice, packet data is becoming more significant proportion of traffic for BTCL. It has become essential to find ways of consolidating voice, data traffic, platforms and services to reduce the operational, maintenance and initial cost of BTCL. IP network is the best solution to this problem. This makes network expansion through IP backbone while keeping connection to the existing SS7 network a necessity for BTCL which is possible by using the proposed software and hardware.

I.

Introduction

Considering the success of mobile communications, it may appear that wireline phones are going to be obsolete. But the global wireline operator revenues are estimated to grow at a compound annual rate of 4% between now and 2009[1]. The index of fixed telephone lines per 100 population for major world regions during 1994-2006 shows a significant growth of the total number of the fixed telephone connection (Table-1) [2]. Table 1: Index of fixed telephone line of the world per 100 population. 1995 2000 2005 2006 Fixed telephone 0.3 0.4 0.8 0.88 Cellular subscribers 0.2 6.4 13.3 Mobile phone as share of total phone 36.2 89.4 94.4 lines

So, BTCL invariably will have to expand its network in future. As the competition in the telecommunication market is intense due to the presence of the mobile operators, the cost of network expansion of BTCL will play a significant role while taking the decision. Again the various value added services provided by the other operators will put pressure on BTCL to introduce those services too. Moreover data traffic is increasingly becoming a significant proportion of the total traffic [4]. All IP network seems to be a perfect solution of this problem. But the most cost effective and easiest way to meet these challenges will be to expand the network using IP backbone while keeping connection with the existing SS7 network. This situation makes it essential to expand the network using IP backbone and use SS7-IP protocol interchanger to connect it with the existing SS7 network. At this point we have proposed a new SS7 and IP based SIGTRAN protocol interchanger software and related software to perform the task.

II. Proposed System

Similar to the global demand for the fixed telephone line, BTCL also has a lot of pending demand which shows that

978-1-4244-2015-5/08/$25.00 (c)2008 IEEE

its customer base is still to be grown in future (Table-2) [1][3]. Table 1: Pending demand of BTCL. Pending Region Capacity Connection demand Dhaka 54,211 609,350 542,265 Chittagong 237,295 138,145 26,028 Khulna 129,005 75,168 2,560 Rajshahi 61,296 34,693 1,311 Rangpur 76,119 38,210 686 Sylhet 75,01 39,721 8,692 Country Total 11,13,065 8,68,202 93488

Protocol can be defined as the rules governing the syntax and synchronization of communication. We have worked with two protocols: SS7 and SIGTRAN. Signaling System no. 7 (SS7) is a set of telephony signaling protocols [5], which are used to set up the vast majority of the world's public switched telephone network telephone calls. SS7 provides a universal structure for telephony network signaling, messaging, interfacing and

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network maintenance [6]. SIGTRAN is the name given to an IETF working group that produced specifications [7] for a family of protocols that provide reliable datagram service and user layer adaptations for SS7 and ISDN communications protocols. Our developed software along with our designed hardware is capable of taking signaling channel data from PSTN network and analyzes that according to SS7 and SIGTRAN protocol structure defined by ITU-T [5][6][8]. Performance evaluation of SIGTRAN-based Signaling Links Deployed in Mobile Networks [9] is very important and with our software, the incorrect data can also be detected. Our developed software takes SS7 protocol data from SS7 network through designed USB E1 card and SIGTRAN data from SIGTRAN network through Ethernet port using “Data reader” window of the software. Then the data is processed according to the protocol stack selected by the “Stack selector” window of our software. Then the data of a selected protocol is exchanged with the other protocol using the “Protocol exchanger” window of our software. The working principle of our developed hardware and software is like, SS7 Network

E1 card

Hardware Part

Ethernet port

Software part

Data reader

addressing and routing. TUP is a link-by-link signaling system used to connect calls. ISUP provides a circuitbased protocol to establish, maintain and end the connections for calls. TCAP is used to create database queries and invoke advanced network functionality mobile services (MAP), etc. [11] OSI Model

TCAP

Layer 7 Layer 4, 5 6

Stack selector

Protocol exchanger

T U P

ASP

B I S U P

I S U P

Level 4

SCCP Layer 3 Network Layer 2

Data Link

Layer 1

Physical

Level 3 MTP

Level 2 Level 1

Fig. 2 SS7 Protocol Stack [12] Each SS7 data is transmitted in MTP (Message Transfer Part). Each MTP contains different SS7 layers, which are well defined by ITU-T. The MTP structure for SS7 data used in our software is like,

IP Network

MTP F CK

Data reader

SS7 Level

Application Entity

SIF

SIO

LI

FIB

FSN

BIB

BSN

F

First bit transmitted

Stack selector

TUP

TUP Message information elements

ISUP

ISUP Message information elements

SCCP EOP

User message / Data

Fig. 1 Working principle of our developed software and hardware

Message type

Message group

Message Type

SCCP message Header

Message Type

Label B Label C Label D

Includes called and calling party address TCAP

III. Software Architecture

Component portion Component n

Component 2

Component 1

Transaction portion

Fig. 3 MTP structure of SS7 data [13]

A. Protocol Stack The first part of the development of our software was to develop the protocol stack of SS7 and SIGTRAN protocol.

A.1. SS7 Stack The SS7 protocol stack borrows partially from the OSI Model of a packetized digital protocol stack. OSI layers 1 to 3 are provided by the Message Transfer Part (MTP) of the SS7 protocol; for circuit related signaling, such as the Telephone User Part (TUP) or the ISDN User Part (ISUP), the User Part provides layers 4 to 7, whereas for non-circuit related signaling the Signaling Connection and Control Part (SCCP) provides layer 4 capabilities to the SCCP user [10]. The MTP covers the transport protocols including network interface, information transfer, message handling and routing to the higher levels. SCCP is a sub-part of other L4 protocols, together with MTP 3 it can be called the Network Service Part (NSP), it provides end-to-end

Using these structures we have developed the SS7 protocol stack of our software.

A.2. SIGTRAN Stack The SIGTRAN protocols specify the means by which SS7 messages can be reliably transported over IP networks. The architecture identifies two components: 1. A common transport protocol for the SS7 protocol layer being carried and 2. An adaptation module to emulate lower layers of the protocol. For example, if the native protocol is MTP (Message Transport Layer) Level 3, the sigtran protocols provide the equivalent functionality of MTP Level 2. If the native protocol is ISUP or SCCP, the sigtran protocols provide the same functionality as MTP Levels 2 and 3. If the native protocol is TCAP, the SIGTRAN protocols provide the functionality of SCCP (connectionless classes) & MTP Levels 2 & 3.

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Part 2: “Stack Manager” window of our software lets the user to choose which message in the SS7 data is to be exchanged. It is very useful operation when the SS7 data length is very high. By choosing specific message, then user can reduce the number of exchanged messages so that only the desired message is transmitted. The is particularly important to maintain the various value added services easily. The software window of “Stack Manager” is shown bellow:

TC A P SC C P M TP 3 M 3U A

M 2U A

IS D N

M 2PA

SU A

IU A

S C TP IP

Fig. 4 SIGTRAN Protocol Stack [14]

B. SS7 and SIGTRAN Protocol Interchanger The task of the data exchange between SS7 and SIGTRAN protocol is performed according to the following structure, SS7 TCAP SCCP

STP

SIGTRAN

TCAP/RANAP Applications

I S U P

TCAP

SCCP SCCP

NIF ISUP

MTP3

MTP3

M3UA

M3UA

MTP2

MTP2

SCTP

SCTP

MTP1

MTP1

IP

SS7

IP

I S U P

S I P

IP

Fig. 7 “Stack Manager” window of our developed software

IP

Fig. 5 SS7 and SIGTRAN protocol interconnection structure [15] Our software exchanges SS7 protocol data via our designed USB E1 card and SIGTRAN protocol data from Ethernet port. This exchange of data between two different protocols takes place by analyzing the data [16] and maintaining the structure mentioned in figure 5. There are three part of the software which performs the data exchange operation. They are, 1. Data reader 2. Stack selector and 3. Data exchanger Part 1: “Data Reader” window of our software is used to take SS7 data via E1 card or SIGTRAN data via Ethernet port. At first, the user has to specify the source to extract data for exchange. The selected source will be used as the base protocol which will be converted to the other protocol data. The software view for performing this task is shown bellow,

Part 3: “Data Exchanger” is the last part of our software with which the selected portion of the base protocol data is exchanged to the other protocol data. During this exchange process, the exchanged data can be saved for analysis. Our exchanger also has an analyzer mode with the following features which meets almost all the features of current available protocol analyzers: • Summary View displays MTP2, MTP3 information and SS7 Message types, Called and Calling number, SCCP message type, SSN, INAP information, and more • Hex/Binary view displays the frame information in HEX and ASCII format • Exports detailed and summary information to a comma delimited file for subsequent import into a database or spreadsheet • Supports filtering and search features based on Frame length, FSN, BSN, SSN and so on • Hex Dump View displays the frame information in HEX and BINARY format. • View of duration of completed call, OPC, DPC, CIC, Called and Calling Party Numbers, and more. [17] The data read from the Ethernet port or E1 card using the selected source by the Data Reader window of the software and according to the selected stack using the Stack Manager window of the software. This data is then converted into the other protocol data and routed. The software window performing data exchanging from SS7 to SIGTRAN protocol is shown bellow,

Fig. 6 “Data reader” window of our developed software

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architecture, which achieves throughputs approaching 1 MIPS per MHz allowing optimization of power consumption. [19] FT245BM: The FT245BM is the 2nd generation of FTDI’s popular Single Chip USB Parallel FIFO bidirectional Data Transfer I.C. The FT245BM provides an easy cost-effective method of transferring data to / from a peripheral and a host P.C. at up to 8 Million bits (1 Megabyte) per second. [20] 74HC244: These octal buffers and line drivers are designed specifically to improve both the performance and density of 3-state memory address drivers, clock drivers, and bus-oriented receivers and transmitters.

Fig. 8 “Data Exchanger” window of our developed software.

IV. Hardware Architecture For reading data from SS7 link, we have designed an USB E1 card with which the data of signaling channel of SS7 link can be directly saved by our developed software. Our USB E1 card is an enhanced third-generation hardware that consolidates the essential pieces of industry-standard test equipment into a powerful, PCBased USB E1 solution. PEF2256: The FALC56 is the latest addition to Infineon’s FALC® family of sophisticated E1/T1/J1 framer and Line Interface Unit (LIU) transceivers which supports all standard E1/T1/J1 functions. [18] ATmega16: The ATmega16 is a low-power CMOS 8-bit microcontroller based on the AVR enhanced RISC

Using these ICs we have designed the USB E1 card. For avoiding complex PCB, we have designed the E1 card in two parts. They are, 1. Transceiver module: It includes x Transceiver IC x Synchronizing Clock x Impedance matching transformer x Transient voltage Suppressor x Connector for E1 link 2. Controlling module: It includes x Microcontroller x USB interface x Clock x Serial and Parallel interface x Power supply unit The schematics of the controlling and transceiver module are shown bellow.

Fig. 9 Transceiver module of the E1 card.

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Fig. 10 Controlling part of the E1 card.

V.

Result

The hardware designing part is completed and currently it’s working soundly.

SS7 and SIGTRAN data can be read [Fig. 6] according to the selected structure [Fig. 7] and exchanged using our hardware and software [Fig. 8] successfully. One of the major achievements of our work is the tremendous reduction of the cost. The manufacturing cost of the hardware is very minute compared to the market price of similar range hardware. A PCI slot E1 card costs about 500USD in the current market whereas our hardware costs only 55USD.

VI. Conclusion

(a)

In this paper, we have presented a new SS7 and SIGTRAN protocol exchanger software and modified USB E1 card hardware. Protocol exchanger is going to be very necessary to consolidate voice, data traffic, platforms and services to reduce the operational, maintenance and initial cost of the network. This software will enable BTCL to expand the network using IP backbone which is very cheap compared to SS7 network. Whereas, existing SS7 network can be connected with the new IP network easily. Also the different value added services will be easier to provide through the SIGTRAN network. Finally, we believe that this software and hardware will be a feasible solution for BTCL to expand its network.

References

(b) Fig. 11 (a) Top and (b) Bottom layer of the designed PCB of the E1 card

[1] Md. Anwar Hossain Masud. “Nationwide all IP network: necessity and possibility for BTTB PSTN”. ICECE 2006. [2] Global fixed and mobile connection growth status. http://www.unescap.org.

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[3] BTCL yearly report from www.btcl.gov.bd. [4] T. Yamanda. “A new public network including IP communications as a universal service”. 2000. Ritsumeikan University, Japan. [5] ITU data from http://www.itu.int/ITU-D/ [6] ITU-T Recommendations, Q.700 to Q.716. [7] Fred Halsal, Multimedia communication. [8] IETF reference document “Framework Architecture for Signaling Transport”, RFC-2719, http://www.ietf.org/rfc/rfc2719.txt. [9] Performance Technologies protocol standard document. www.pt.com. [10] Chukarin, A. Pershakov, N. Samouylov. ‘Performance of Sigtran-based Signaling Links Deployed in Mobile Networks.’ ConTel 2007. [11] Dawis, E.P. ‘Architecture of an SS7 protocol stack on a broadband switch platform using dualistic Petri nets.’ Communications, Computers and signal Processing, 2001. PACRIM. [12] ITU-T reference document Q.701, Page 5. [13] “Tutorial on Signaling System 7 (SS7)” from Performance Technologies, Page 6. www.pt.com. [14] ITU-T reference document Q.700 page 14. [15] SIGTRAN Protocol Suite by Jim Darroch, Page 8. [16] Reference document on “SS7 over IP signaling transport and SCCP” by International Engineering Consortium, Page 16. www.iec.org. [17] Signaling System # 7 protocol analyzer software. www.gl.com/ss7.html. [18] GL communication protocol analyzer software standard www.gl.com/protocol_analysis.html. [19] Falc2256 product brief of Infenion Technologies, Page 1. www.infenion.com. [20] ATmega16L Datasheet from ATMEL Corporation. Page 1. www.atmel.com. [21] FT245BM datasheet from Future technologies Ltd. Page 1. www.ftdichip.com

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