Signaling System #7, Sixth Edition / Edition 6 available in Hardcover, eBook
Signaling System #7, Sixth Edition / Edition 6
- ISBN-10:
- 0071822143
- ISBN-13:
- 9780071822145
- Pub. Date:
- 08/28/2014
- Publisher:
- McGraw Hill LLC
- ISBN-10:
- 0071822143
- ISBN-13:
- 9780071822145
- Pub. Date:
- 08/28/2014
- Publisher:
- McGraw Hill LLC
Signaling System #7, Sixth Edition / Edition 6
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Overview
THE MOST COMPLETE, CURRENT GUIDE TO SIGNALING SYSTEM #7 (SS7)
Thoroughly updated to cover the latest advances in the telecommunications industry, Signaling System # 7, Sixth Edition, addresses the impact of emerging technologies and applications, such as Long Term Evolution (LTE) and 4G networks, on SS7. An all-new chapter onDiameter discusses how to successfully implement SS7-to-Diameter interfaces to bridge 3G and 4G networks. Real-world examples, protocol message details, call flows, and effective migration strategies are included in this practical guide.
Comprehensive coverage includes:
- The SS7 network—international and national planes
- The OSI model
- SS7 protocols and the protocol stack
- Signal units
- Message Transfer Part (MTP), including level 3
- Signaling Transport (SIGTRAN)
- ISDN User Part (ISUP)
- Signaling Connection Control Part (SCCP)
- Transaction Capabilities Application Part (TCAP)
- The evolution to Diameter
Product Details
| ISBN-13: | 9780071822145 |
|---|---|
| Publisher: | McGraw Hill LLC |
| Publication date: | 08/28/2014 |
| Edition description: | New Edition |
| Pages: | 640 |
| Product dimensions: | 7.50(w) x 9.30(h) x 1.50(d) |
About the Author
Read an Excerpt
1 Signaling System #7
Early telephone networks were the result of years of evolution, with little thought about future technology. Based around analog equipment, the telephone network of the early telephone company was not well suited for services such as data and video. Many individual technology service providers began popping up during the 1960s, providing packet-switching networks and data communications services the telephone companies were just not equipped to provide.
The international telephone network was facing the same problems. In many countries, just getting telephone service was a feat in itself. As international bodies began investigating alternative technologies for providing telephone service to the masses (such as cellular), the need for an all-digital network became apparent. Thus arose the beginnings of an all-digital network with intelligence.
Why intelligence? To understand the answer to this question, you must first understand the mechanics of a telephone call. When a subscriber picks up a telephone receiver, an electrical signal is sent over a wire to a telephone switch. The telephone switch detects electrical current on this wire and interprets this "signal" as a request for dialtone.
But let's say the subscriber wants to transmit data over this same line using packet switching rather than an analog modem. The information sent to the telephone switch has to define the transmission as digital, as well as data and not voice, before the switch can deter-mine how to handle the call. This is only one portion of the call.
To transmit the data to another network, the switch must deter-mine first how the data is to be routed (to whatdestination), and what circuits to use to reach the destination. After this has been determined, some form of request must be sent to the telephone switch on the other end of the circuit to request a connection. This continues all the way through the network, with the same requirements at each leg of the call. Telephone switches need the ability to signal one another and share information regarding the type of transmission, how the transmission is to be routed (call destination), and what the contents of the transmission are (audio, video, data, and so on).
If there is to be special handling or routing for a call, the telephone switches involved in routing the call must be able to obtain these instructions. Rather than store routing instructions for every single telephone number in the world within each and every telephone switch, each network is responsible for their own network database. The telephone switches then need the ability to connect and communicate with these databases to obtain the special instructions.
This is a high level view of what signaling networks really do. They allow telephone switches (and now packet switches) to communicate directly with one another, and share information needed to process any type of a call autonomously. Signaling System #7 (SS7) was originally designed for the analog telephone network, but has continually undergone enhancements and changes to accommodate the ever-changing world of telecommunications. Today, SS7 is used for data, video, voice, audio, and even Voice over IP (VoIP) networks.
The International Telecommunications Union (ITU) commissioned the then CCITT to study the possibility of an all-digital intelligent network. The result was a series of standards known now in the United States as Signaling System #7 (SS7). These standards have paved the way for the Intelligent Network (IN) and, with it, a variety of services, many yet to be unveiled.
This book outlines the technologies related to the SS7 protocols and details how the protocols work within the IN.
Introduction to SS7
The ITU-TS (once known as the CCITT) developed a digital signaling standard in the mid-60s called Common Channel Interoffice Signaling System #6 (CCIS6) that would revolutionize the telephone industry. Based upon a proprietary, high-speed data communications network, CCIS6 later evolved into C7 (known as Signaling System #7 (SS7) in the U.S.), which has now become the signaling standard for the entire world.
The secret to its success lies in the message structure of the protocol and the network topology. The protocol uses messages, much like X.25 and other message-based protocols, to request services from other entities. These messages travel from one network entity to another, independent of the actual voice and data they pertain to, in an envelope called a packet.
CCS was first introduced in the United States in the 1960s as CCIS6. Developed by the International Telecommunications Union -Telecommunications Standards Society (ITU-TS), CCIS6 used a separate facility for sending signaling information to distant telephone offices.
The first deployment of CCIS6 in the US. used 2.4-kbps data links. These were later upgraded to 4.8 kbps. Messages were sent in the form of data packets and were used to request connections on voice trunks between two central offices. This became the first use of packet switching in the Public Switched Telephone Network (PSTN). The packets were assembled by placing 12 signal units of 28 bits each into a data block. This is similar to the method used in SS7 today.
SS7 was derived from the earlier CCIS6, which explains the similarities. SS7 provides much more capability than CCIS6. Where CCIS6 used fixed-length signal units, SS7 uses variable-length signal units (with a maximum sized length), providing more versatility and flexibility. SS7 also uses higher speed data links (56 kbps). This makes the signaling network much faster than CCIS6. In international networks, the data links operate at 64 kbps. Recently, high speed links (HSL) operating at 1.544 Mbps have been deployed in the US, conforming to a Telcordia (formerly Bellcore) standard. TCP/IP has also been introduced as a transport for SS7 providing 100 Mbps facilities.
As of 1983, CCIS6 was still being deployed throughout the U.S. telephone network, even though SS7 was being introduced. As SS7 began deployment in the mid-1980s, CCIS6 was phased out of the network. SS7 was used in the interoffice network and was not immediately deployed in the local offices until many years later.
In fact, the first usage of SS7 in the U.S. was not for call setup and teardown, but for accessing remote databases. The opposite is true of Europe and other International communities, where C7 is still used today for call setup and teardown, but the concept of centralized databases for custom call routing is still new. In the 1980s, the US. telephone companies offered a new service called Wide Area Telephone Service (WATS), which used a common 800 area code regardless of the destination of the call. This posed a problem for telephone-switching equipment, which uses the area code to determine how to route a call through the PSTN.
To overcome this problem, a second number was assigned to every 800 number. This second number is used by the switching equipment to actually route the call through the voice network. But number had to be placed in a centralized database where all central offices could access it. This database became a popular commodity for all telephone companies and still exists today.
When an 800 number is dialed, the telephone company switching equipment uses a data communications link to access this remote database and look up the actual routing number. The access is in the form of a message packet, which queries the network for the Humber. The database then responds with a response message packet, providing the routing telephone number as well as billing information for the 800 number. The switching equipment can then route the call using conventional signaling methods.
SS7 provides that data communications link between switching equipment and telephone company databases. Shortly after the 800 1 1 umber implementation, the SS7 network was expanded to provide of her services, including call setup and teardown. Still, the dataImse access capability has proven to be the biggest advantage behind SS7 and is widely used today to provide routing and billing information for all telephone services including 800 numbers, 900 ii umbers, 911 services, custom calling features, caller identification, and many new services yet to be offered.
800 numbers at one time belonged to one service provider. If subscribers wanted to change service providers, they had to surrender their 800 number. This was due to the location of the routing information. All routing information for 800 numbers is located in a central database within the carrier's network and accessed via the SS7 network. SS7 is now used to allow 800 numbers to become transportable and to provide subscribers the option of keeping their 800 numbers even when they change service providers.
When someone dials an 800 number today, the telephone switch sends a query to the network database to first determine to which carrier the 800 number belongs. After the switch receives this information, it can direct a query to the network of the carrier owning the 800 number and translate the 800 number into an actual routing number. This concept was later extended to support number portability.
Without SS7, number portability would be impossible. Local Number Portability (LNP) is a service mandated by the FCC in 1996 which requires telephone companies to support the porting of a telephone number. If customers wish to change their service from Plain Old Telephone Service (POTS) to ISDN, they would normally be forced to change telephone numbers. This is because of the way telephone numbers are assigned in switching equipment, with switches assigned ranges of numbers...
Table of Contents
Chapter 1: Signaling System #7Chapter 2: The SS7 NetworkChapter 3: Overview of a ProtocolChapter 4: Overview of Signal Units Chapter 5: Message Transfer Part (MTP)Chapter 6: Message Transfer Part (MTP) Level 3Chapter 7: Signaling Transport (SIGTRAN)Chapter 8: ISDN User Part (ISUP)Chapter 9: General Description of SCCP FunctionsChapter 10: Overview of TCAPChapter 11: Mobile Application Part (MAP)Chapter 12: SS7 and the IP Multimedia Subsystem (IMS)Appendix A: ITU-TSS SS7 PublicationsAppendix B: American National Standards Institute (ANSI) SS7 PublicationsAppendix C: Cause Codes Appendix D: Acronym ListBibliographyIndexIntroduction
But during all of these discussions, nothing (or at least very little) has been mentioned about how all of this is possible. How is it possible that many networks can communicate with one another, and what control mechanism is used to maintain the connections and data communications?
Behind the scenes is a quiet, highly reliable, fault-tolerant data communications network that links the world's telephone networks together and allows them to share vital signaling and control information. This one network, which controls telecommunications networks around the world, is being prepared to control the broadband networks that will form the framework for tomorrow's "Information Highway"
This data communications network is so robust, so sophisticated, that few really know much about it. Only recently has anything been written about this network, and what information does exist has been sparse and ambiguous. The very standards that define the network are written to answer the needs of so many different audiences that they remain vague and reliant on reader interpretation.
This network, often dubbed the world's largest data communications network, is known as Signaling System #7 (SS7). It started as a way to access 800 databases here in the U.S., although its functions provide much more. Soon SS7 was being used to send signaling information from exchange to exchange. Today,the same network is being used to control central office switching equipment from remote locations.
SS7 is really a control network, as well as a signaling network. This is important to understand, because as the Information Highway rolls out, and as the Advanced Intelligent Network (AIN) is implemented, SS7 will be relied on almost exclusively as a means for telephone companies and other service providers to share database information and switching control without human intervention.
Already we are seeing SS7 play an important role in Local Number Portability (LNP), a new requirement for all telephone service providers (both wireline and wireless) defined in the Telecommunications Act of 1996. SS7 continues to grow in use and function, as tile industry discovers new uses for this powerful technology.
Without SS7, AIN is not possible. Cellular roaming is not seamless. 800 numbers are not portable. And the many features and services we take for granted today (such as caller ID) would not be feasible.
When someone asks me how to break into the telecommunications field, I provide one suggestion: Learn SS7. Every telephone company needs it. Every manufacturer develops around it, yet there is a lack of expertise in SS7 in this country. That is what this book is all about.
As I began studying SS7 protocols and began providing seminars around the country, I came to the conclusion that there is no reference material available that provides a comprehensive view of SST nothing to explain the various acronyms and the true applications of this network.
Hence the reason for this book. If you are looking for more than a reference book-a tutorial on SS7, a text book which provides realworld applications, and a futuristic look at the telephone networks-read on.
The intent of this book is to provide a comprehensive introduction to this fascinating network and its protocols, as well as a reference for those already familiar with SS7. Although the various standards are always the best source for specific details, this book provides something the standards do not: explanations as to when and why procedures are used and what they mean to the network, the subscriber, and the service provider.
Although it is based on ANSI and Bellcore standards, the text is of value to anyone seeking knowledge about SS7 networks. Although the message types and the protocol parameters may be different between countries, the principles and applications are universal.
I hope you find this to be as fascinating as I did while writing this book. Truly, we are at an exciting period for the telecommunications industry, as new services and applications are defined almost monthly. Keeping up with all of the new technologies and advances can be a dizzying experience. Yet the future is today, and this technology is a key player in making it all happen.
Travis Russell