[CN]Chapter                  7



[CT]Softswitch


Introduction..............................................................
Figure 7-12 Class 5 replacement Softswitch ..................................................................................
[BT A HD]

You will recall that the PSTN (Public Switched Telephone Network) performs the following functions;

access, sw...
[A HD]The Softswitch


[BT A HD]


A Softswitch is a device used to control connections between circuit switched and packe...
as provides choices of hardware without requiring changes in the switching structure. This architecture

provides opportun...
Feature Server



                   MGCP



                              SGCP                                   Signalin...
[A HD]Access
[BT A HD]
Softswitch and PSTN architectures each address three key functions:


[BEG BL]

   •   Access - how...
recall from an earlier chapter, (see Figure 7-2) for a graphic of the PC to PC and the PC to telephone

design. The primar...
PC as a phone. From there the IP handset was born. The IP handset includes the necessary computer

hardware to make an IP ...
[FIG]Figure 7-3 IP Phones on an IP Network




                                            IP
                            ...
In the PSTN voice network, service providers would have to purchase and maintain large Class 4 or 5

switches. In a VoIP n...
IP phones today are yet very expensive (~$500) compared to a conventional business handset (~$150).

That high cost is ver...
network and the PSTN). Gateways can be provisioned as standalone devices or they can be

provisioned to integrate to other...
the network to their destination.



Initially, in the early VoIP days, the gateway had to contain a lot of intelligence t...
Telephone Telephone               Telephone                         Telephone        Telephone




                       ...
connect to the line side of the gateway.




educes or eliminates interoffice phone bills The advantage is that the compan...
[B HD]Carrier Grade Gateways
[BT B HD]
Initially VoIP gateways were used for international long-distance as a bypass and e...
•   NEBS 3 compliance, yet another requirement is that the switches must be certified NEBS 3, a

       firm requirement f...
•   Backup and disaster recovery strategies,

   •   and UPS (uninterruptible power supply) to prevent network outages due...
[BEG BL]

   •   recognizing that a party has gone off hook and that a dial tone should be provided

   •   interpreting t...
As the VoIP network grows larger and larger they become more complex and management solutions

with higher intelligence be...
proprietary. Hardware and software compatibility is an issue with PSTN components, hardware or

software, from one vendor ...
IP
                                                            Telephone

 IP PBX
                     IP Network




    ...
[B HD]Class 5 Exchange
[BT B HD]

Class 5 exchanges, also known as central offices, house the Class 5 switch. The Class 5 ...
GR-303(Generic Requirement-303) is a Telcordia standard interface to a Class 5 telephone switch

from a DLC (digital loop ...
IP Centrex can replace the Class 5 switch with a softswitch (Compare Figure 7-9 to Figure 7-8). A

softswitch actually is ...
V
                                                                  PBX
 Data                                             ...
was occurring with the gateways that controlled these gateways they too were limited in their

capability to handle increa...
V

                                                Voice               Class 4        Class 5
                            ...
[B HD]Softswitch Replacing Class 5 Switches
[BT B HD]
Softswitch technologies next targeted the Class 5 switch for replace...
Obviously there are concerns and even objections to replacing a Class 5 switch with a softswitch.

These concerns include ...
Scale refers to their processing power and is measured in calls per second, the number of busy-hour

call attempts handled...
[FIG]Figure 7-13 Legacy network: data, voice &SS7 networks




                                       Data Network




   ...
[FIG]Figure 7-14 Converging networks: combined circuit and packet switched networks




                      Softswitch
 ...
[FIG]Figure 7-15 A converged network data and voice on same network




                     Softswitch


                ...
VoIP was introduced and the telecommunications industry began to concentrate on converging voice

and data networks. TDM w...
applications. With IP as core there is an opportunity to link voice and data networks by a combination

of public and priv...
associated with VoIP. It should be noted that comparable architecture is possible with a TDM network.

Instead of the main...
ensure that the QoS mandate from the sending device will be accommodated on a network wide basis.

Many incumbent service ...
Softswitch is troublesome to legacy networks (RBOCS and IXCs) and equipment vendors (makers of

PBXs and Class 4 and Class...
It was shown that a customer does not have to go cold turkey when moving from PSTN to an IP network.

Since the migration ...
Call Agent - Intelligent entity in an IP telephony network that handles call control in an MGCP model

voice over IP netwo...
Gateways are very similar to Media Gateways, but are scaled and configured to meet the needs of the

enterprise rather tha...
Media Gateway - Software that acts as a "call agent" to control telecommunications equipment in

order to bridge call tran...
Softswitch - also called a Proxy Gatekeeper, Call Server, Call Agent, Media Gateway Controller, or

Switch Controller. Sof...
d. It provides transport.



2.   What is the device called that takes care of billing, call routing, and signaling in a

...
5.   What device is located between a VoIP network and a legacy telephony network and acts as

     an interface between t...
b. Call setup

      c. Call teardown

      d. Call connection control



9.    What coordinates routing between networks...
12.   The RBOC’s offer a(n) ____________________ to provide a set of business solution

      primarily for voice service ...
13.   A converged network typically contains a mix of _____________ and _______________.

      (Choose all that are corre...
Thinking Questions



   1. Many of the CLECs (Competitive Local Exchange Carriers) of the telecom boom of the late

     ...
4. The Hale Corporation likes to regularly move its employees from place to place within the

     corporation to promote ...
Convergence+ Guide To Convergence Technologies ISBN# 0619131179

                               Page 1-53                 ...
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  1. 1. [CN]Chapter 7 [CT]Softswitch Introduction...............................................................................................................................................2 The Softswitch...........................................................................................................................................4 A Distributed Architecture........................................................................................................................4 Access........................................................................................................................................................7 PC to PC and PC to Phone....................................................................................................................7 Phone-to-Phone VoIP............................................................................................................................8 VoIP Gateways........................................................................................................................................12 Enterprise Gateways............................................................................................................................15 Carrier Grade Gateways......................................................................................................................17 Softswitch Technology............................................................................................................................19 Applications Server.............................................................................................................................21 Softswitch Applications.......................................................................................................................22 IP Centrex ...........................................................................................................................................23 Class 5 Exchange.................................................................................................................................24 Softswitch Replacing Class 4 Switches ..............................................................................................27 Softswitch Replacing Class 5 Switches...............................................................................................30 Transport..................................................................................................................................................32 Converged and Converging Architectures..........................................................................................32 IP Networks.........................................................................................................................................35 TDM....................................................................................................................................................37 ATM....................................................................................................................................................38 Figure 7-1 Softswitch Components...........................................................................................................5 Figure 7-2 PC to PC and PC to Phone.......................................................................................................8 Figure 7-3 IP Phones on an IP Network..................................................................................................10 Figure 7-4 SOHO grade gateway............................................................................................................14 Figure 7-5 Enterprise gateways on a VoIP network................................................................................16 Figure 7-6 IP Centrex using a Class 5 switch .........................................................................................17 Figure 7-7 IP PBX also known as soft PBX............................................................................................22 Figure 7-8 IP Centrex using a Class 5 switch..........................................................................................25 Figure 7-9 IP Centrex with Softswitch....................................................................................................26 Figure 7-10 Architecture of Class 4 and Class 5 switches with VoIP gateways....................................28 Figure 7-11 Class 4 replacement Softswitch Note: Class 4 TDM switches are absent...........................29 Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-1 5/6/2010
  2. 2. Figure 7-12 Class 5 replacement Softswitch ..........................................................................................30 Figure 7-13 Legacy network: data, voice &SS7 networks......................................................................33 Figure 7-14 Converging networks: combined circuit and packet switched networks ............................34 Figure 7-15 A converged network data and voice on same network......................................................35 [OBJ HD] After reading this chapter and completing the exercises you will be able to: [BEG OBJ]  Understand and describe the concept of softswitch and why it is the next generation technology  Describe differences between the PSTN and IP networks relative to distributed and centralized switching systems  Discuss VoIP gateways and describe their functions  Explain the relationship between; gatekeeper and media gateway controller, and softswitch and the media gateway.  Understand a signaling gateway  Compare and explain how the softswitch can replacement a PSTN class 4 switch  Compare and explain how the softswitch can replacement a PSTN class 5 switch  Understand the components and functions of a packet switched network and contrast them with the circuit switched network components and functions. [END OBJ] [A HD]Introduction Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-2 5/6/2010
  3. 3. [BT A HD] You will recall that the PSTN (Public Switched Telephone Network) performs the following functions; access, switching, and transport. The softswitch network performs the very same functions. If they perform the same functions, what distinguishes one from the other? Primarily the two networks differ only in their architectures. The softswitch architecture is a distributed architecture whereas the PSTN is a centralized architecture. You will explore the architecture for softswitch solutions and the components that comprise this new and flexible architecture. Many of the rules change between the two architectures to accommodate the shift from circuit switched to packet-switched client-server architecture, but the basic functions remain the same. The current softswitch architecture must accommodate the need to protect the current investments in legacy equipment and support. The softswitch bridges the legacy PSTN technology to the next level known as the next generation technologies. The legacy equipment will only be replaced by softswitch architectures, when the economics of the legacy equipment become favorable for the next generation of technology. New installations have the advantage from the start without the weight of integrating with the older technology. Those who are deep into old technology will delay in purchasing and installing architecture that is cheaper, simpler, smaller, and more convenient to use. Many will not be quick to change until the economics show acceptable cost savings. Economic factors; equipment depreciation cost of service, and growth will be heavily considered before migration to the softswitch architecture will take place. You will discover that migration to softswitch can be accomplished slowly, since the softswitch has been designed to integrate with the legacy PSTN. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-3 5/6/2010
  4. 4. [A HD]The Softswitch [BT A HD] A Softswitch is a device used to control connections between circuit switched and packet switched networks. A device that contains both the switching logic and fabric is used. It is common that the device is treated today as two parts; a Media Gateway, and a Call Agent Gateway. The Call Agent manages functions like; call routing, signaling, and billing so on and acts as a control center. A single Call Agent can control a number of Media Gateways in geographically isolated areas over a TCP/IP network. The Media Gateway connects various types of digital media creating an end-to-end path. The media gateway can have interfaces connecting to PSTN using DS1 or DS3 ports, it can interface to ATM networks and it has Ethernet interfaces to connect VoIP calls. The call agent controls and instructs the media gateways to connect media between these interfaces to complete the call. [A HD]A Distributed Architecture [BT A HD] Softswitch unlike the PSTN is a distributed architecture as shown in Figure 7-1. This network model separates the packet-switching hardware from the call control, service logic, and service creation used in the PSTN model. The distributed architecture enables flexibility when adding new services as well Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-4 5/6/2010
  5. 5. as provides choices of hardware without requiring changes in the switching structure. This architecture provides opportunities for developers to innovate market niche products and services. The lower layer physically transports both voice and data traffic. This layer is serviced by media gateways. SGCP (Simple Gateway Control Protocol) controls VoIP gateways by a call control component known as a call-agent. [FIG]Figure 7-1 Softswitch Components Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-5 5/6/2010
  6. 6. Feature Server MGCP SGCP Signaling Gateway Softswitch SIP Universal MGCP (Media Gateway Control Protocol) SGCP (Simple Gateway Control Protocol) call agent Media SIP ( Session Initiation Protocol) Gateway This is client-server architecture and is what provides developer opportunities. The distributive architecture is what enables a service provider to start out small and grow with the economic demand as opposed to putting out a huge upfront investment in Class 4 switches. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-6 5/6/2010 MGCP (Media Gateway Control Protocol) SGCP (Simple Gateway Control Protocol) call agent SIP ( Session Initiation Protocol)
  7. 7. [A HD]Access [BT A HD] Softswitch and PSTN architectures each address three key functions: [BEG BL] • Access - how a subscriber becomes attached to the network • Switching - how a call is controlled across the network • Transport - how a call is moved across the network [END BL] In the case of accessing a VoIP (Voice over IP) network, access can be gained from an IP source by either a PC or IP phone, or from an analog handset through a media gateway. In a residential setting your ordinary analog phones using the existing internal wiring can be attached to a very inexpensive ATA (analog terminal access) device which is attached to your broadband DSL or cable service. [B HD]PC to PC and PC to Phone [BT B HD] Early on, the QoS (quality of service) on the IP network left much to be desired. As a result this form of access, PC voice to PC voice, did not catch on immediately in the market place. The first VoIP applications used PCs equipped with speakers and microphones to access a VoIP network. It is now also possible to complete phone calls PC to telephone using a softphone application on the PC. PC-to- PC and PC to telephone applications are now used most widely for long-distance bypasses as you Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-7 5/6/2010
  8. 8. recall from an earlier chapter, (see Figure 7-2) for a graphic of the PC to PC and the PC to telephone design. The primary users of access have been saving money on long distance calling, in particular on international long distance. Some of the applications like Skype allow you to make long distance calls world wide for free PC to PC. SkypeOut provides a PC to PSTN phone service to most countries for a very small per minute fee like .017 € per minute. Today 10 € equals about 12 U.S. dollars. [FIG]Figure 7-2 PC to PC and PC to Phone PC IP Network PC Voice V Gateway Class 4 Telephone Switch [B HD]Phone-to-Phone VoIP [BT B HD] As the voice quality of VoIP improved it was not long before the industry recognized the benefits of a Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-8 5/6/2010
  9. 9. PC as a phone. From there the IP handset was born. The IP handset includes the necessary computer hardware to make an IP phone call possible. The IP phone certainly removes cultural objections to VoIP calls using the computer as a phone. The IP handset looks and functions like an ordinary telephone instead of a PC. IP handsets are stand-alone devices and provide the option for an IP desktop-to-desktop solution. A GUI (graphic user interface) on the enterprise IP phone enables numerous features much easier than with a 12-key conventional telephone handset with its long list of codes to memorize. The key advantage of an IP phone to an enterprise is that the phone requires a minimum of network configuration and management compared to a PBX. Each employee equipped with an IP phone can move their own phone anywhere that they can get onto the network with possibly no manual reconfiguration of the phone or the network. Wherever an IP handset is connected on an IP network (see Figure 7-3) the phone is recognized through its own IP and MAC addresses. In an enterprise setting, a worker can disconnect their IP phone and move to another cubicle, building, or state, or even a hotel (may require an ATA device or an 800 number to connect into the company network) and the phone will function with no reprogramming necessary. With a circuit-switched PBX (private branch exchange), tools for managing moves, adds, or changes are very time consuming and difficult to say the least. And IP networks ease of use makes it very expensive to administer. According to some estimates, it may cost from $300 to $400 per phone on a PBX to; move, add, or change it in any way. It can occasionally take a number of days for a change to be implemented on a PSTN Centrex by the telephone company. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-9 5/6/2010
  10. 10. [FIG]Figure 7-3 IP Phones on an IP Network IP Telephone IP Telephone IP Network IP Telephone Data Softswitch Server Two VoIP Protocols will be discussed in a later chapter; SIP (Session Initiation Protocol), and H.323. An IP phone connects to the network via an Ethernet connection (RJ-45). In a business environment, an Ethernet switch serves to concentrate VoIP phone lines. This makes the VoIP service provider very happy since the SP (service provider) does not need to maintain a Class 4 or 5 switch or even a VoIP gateway. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-10 5/6/2010
  11. 11. In the PSTN voice network, service providers would have to purchase and maintain large Class 4 or 5 switches. In a VoIP network, it is generally assumed that the subscriber will purchase their own CPE (customer premises equipment), therefore, the cost per DS0 (a single 64 kbps port) for the service provider is zero dollars. SIP and Java programs on an IP network enable possibilities for future applications that would not be feasible with circuit-switched architectures. These applications can be separated into three categories: [BEG BL] • WTI (web-telephony integration) applications. • Occupation specific and industry specific applications • personal productivity applications [END BL] The LCD (liquid crystal display) screens with GUIs on IP phones provide numerous expanded functions when compared to the analog handset. Using a conventional POTS handset, the user must memorize a long list of numbered codes to perform functions like as call transfer, call forwarding, camp on, conferencing, voice mail retrieval, and so on. Most users limited their list to only a handful of the possible features available on a PBX. When needed they may know the feature exists but do not know the code to activate it. This barred them from being as efficient in their communications as they could be. An IP phone with a GUI enables access to all the phone features. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-11 5/6/2010
  12. 12. IP phones today are yet very expensive (~$500) compared to a conventional business handset (~$150). That high cost is very unattractive to the residential market, but remember that in a residential setting they have the option of using their legacy analog phones using an ATA to interface then to the IP network. Price competition historically has driven the price of new technologies, it is expected the same will happen with IP phones bringing the prices into an affordable range. In review of the distributed architecture, the leading advantage of IP phones to a service provider is that they do not need to invest in a switch or gateway. From the SP’s point of view the subscriber will cover the phone investment by purchasing their own IP phones. Service providers’ profits are earned today on high margins from service feature offerings. Many new features not possible via circuit switched telephone networks will become new market niches. And the expectation is very high for many new features that the consumer will buy into. The IP phone GUI interfaces make services easier to use, resulting in a greater marketability of those new services. It is evident that the future voice network will consist of IP phones that connect to IP networks where the intelligence for that service is provided by softswitches located throughout the network instead of only on centralized computer offices. [A HD]VoIP Gateways [BT A HD] The commercial type of IP access is via VoIP gateways. A gateway provides a connection between an endpoint on a data network to the edge of the PSTN, switched-circuit network. The gateway’s job is to translate transmission formats and communication procedures that are used on each side (the data Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-12 5/6/2010
  13. 13. network and the PSTN). Gateways can be provisioned as standalone devices or they can be provisioned to integrate to other systems. An existing telephone handset interfaces to a gateway via; a direct connection, a PBX, or a Class 5 switch. The gateway is responsible for packetizing the voice and routing it over the IP network. Located on the edge of a network is the media gateway, it interfaces between TDM (Time Division Multiplexing) and IP networks. Here is where analog or digital signals from a handset (PBX or Class 4 or Class 5 switch) are digitized (if analog), packetized, and compressed for transmission over an IP network. The mechanism that accomplishes this is called a codec (in this case a speech coder/decoder). The media gateway is capable of interfacing directly with a TDM switch (PBX or Class 4 or Class 5 switch). A gateway includes three elements: [BEG BL] • an interface for the TDM side of the network (described in terms of DS0s or T1s) • an interface for the packet side of the network (usually an Ethernet connection) • the necessary signal processing between these two sides. [END BL] Signal processing is done using a DSP (digital signal processors) on a circuit board designed to support voice. Signal processing functions include echo cancellation, coding/decoding of the analog signals adapting the digitally encoded information into a series of IP datagrams that are then transmitted over Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-13 5/6/2010
  14. 14. the network to their destination. Initially, in the early VoIP days, the gateway had to contain a lot of intelligence to make voice calls possible. A media gateway can be a part of the switching and routing depending on the intelligence contained in the gateway. The advancement of gatekeeper technology into a carrier-grade softswitch has moved the intelligence from the gateway onto the softswitch. The trend is toward placing more intelligence in the softswitch and less intelligence in the media gateways. Of all its capabilities, scalability is the most important factor for media gateways. The number of ports, DS0s, in one chassis determines its classification. Depending on its density, the number of DS0s, a media gateway fits into one of these classifications: [BEG BL] • residential or SOHO gateway • enterprise gateway • carrier grade gateway [END BL] SOHO stands for (Small office Home office). Figure 7-4 Illustrates a residential or SOHO grade VoIP gateway. [FIG]Figure 7-4 SOHO grade gateway Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-14 5/6/2010
  15. 15. Telephone Telephone Telephone Telephone Telephone IP Network Data Softswitch Server [B HD]Enterprise Gateways [BT B HD] Enterprise gateways can combine legacy telephony to interface with VoIP networks (see Figure 7-5). This is done by connecting a gateway to the trunk side of a PBX. This will allow the users will retain their existing handsets. The company will not have to require new training to utilize their existing telephone handsets. This will provide businesses with the option to retain its expensive PBX and the PBX handsets while moving toward or converting to IP networking technology. Enterprise gateways are usually configured with multiple T1 or El cards in a single chassis that interface on the trunk side of the PBX. On the trunk side of the gateway is an Ethernet connection to a router. The T1 trunks Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-15 5/6/2010
  16. 16. connect to the line side of the gateway. educes or eliminates interoffice phone bills The advantage is that the company. [FIG]Figure 7-5 Enterprise gateways on a VoIP network V PBX Digital Data Voice Telephone IP Network Gateway Server Softswitch V PBX Voice Digital Gateway Telephone Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-16 5/6/2010
  17. 17. [B HD]Carrier Grade Gateways [BT B HD] Initially VoIP gateways were used for international long-distance as a bypass and enterprise interoffice long distance. These applications began to show value and that has led to a demand for larger (greater capacity) gateways. This translates into more ports per gateway, for the carrier operations. (see Figure 7-6). These gateways needed to have enough DSOs to allow Application Servers to interface with Class 4 and Class 5 switches. The numbers here are upward of 100,000 DS0s in a single node with an OC-3 trunk-side interface. These gateways absolutely have to offer PSTN five 9s reliability to interface with circuit switches. [FIG]Figure 7-6 IP Centrex using a Class 5 switch V Class 4/5 Voice Switch Telephone IP Network Data Gatewa Softswitch Server V Class 4/5 Voice Switch Telephone Gatewa Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-17 5/6/2010
  18. 18. • NEBS 3 compliance, yet another requirement is that the switches must be certified NEBS 3, a firm requirement for any platform to be installed in a central office. NEBS (Network Equipment Building Standards) address the switches physical reliability. All carriers in North America require that equipment in their switching locations go through rigorous NEBS testing. The tests include evaluations for; • electrical safety • bonding and grounding • immunity from electromagnetic emissions • lightning • power failure recovery. Equipment must also meet physical standards which includes; • fire resistance • earthquake resistance • altitude testing • temperature • humidity • battery of other rigid tests Other Strategies required to become NEBS compliant: Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-18 5/6/2010
  19. 19. • Backup and disaster recovery strategies, • and UPS (uninterruptible power supply) to prevent network outages due to power failure, • ensuring access to mirror sites, • fire and waterproof storage facilities for critical databases and configuration backup information Softswitching, an advanced technology, has empowered VoIP to darken TDM as the telephony technology. Until the development of the softswitch, VoIP was in a stall lacking intelligence necessary to route calls across the network. The progress to an IP alternative for the PSTN would likely not have happened in the absence softswitch technology. Two very important requirements for softswitch are reliability and scalability. The service must be available and work when needed and it must be able to scale small to medium to large environments without disruption to ongoing services, and downscale as well. [A HD]Softswitch Technology [BT A HD] The intelligence in a network is provided by the softswitch. It has to coordinate; call control, signaling, and the other features that manage a call across networks. Call controls first and foremost responsibility is to manage call setups and teardowns this is the softswitches principally. When a call is established, connection control is responsible to control that the call stays up until it is released by either the calling party or called party. Call control and service logic are the functions that process a call and provide telephone features. Examples of call control and service logic functions include: Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-19 5/6/2010
  20. 20. [BEG BL] • recognizing that a party has gone off hook and that a dial tone should be provided • interpreting the dialed digits to determine where the call is to be terminated • determining if the called party is available or busy • recognizing when the called party answers the phone • recognizing when either party subsequently goes on-hook • and lastly records the above actions for billing. [END BL] In order to set up a call, a common protocol must be used that is understandable at each end of the network and throughout disparate networks. A softswitch uses peer to peer for call control, and softswitch for media control. Signaling protocols are SIP, H.323, and SS7 (Signaling System 7). Out of H.323 technology evolved gatekeeper technology. H.323 was designed for local area networks an H.323 gatekeeper manages activities in a zone. A zone is a group of one or more gateways managed by a single gatekeeper. Think of a gatekeeper as a logical function and not a physical function. Its functions are: [BEG BL] • address translation - a name or email address for a terminal or gateway and a transport • address admissions control - authorizing access to the network. [END NL] Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-20 5/6/2010
  21. 21. As the VoIP network grows larger and larger they become more complex and management solutions with higher intelligence became necessary. As the network grows, greater call-processing power became necessary. To interface signaling between IP networks and the PSTN requires VoIP to support signaling protocols to SS7. The need to integrate features across the PSTN the IP network using disparate voice over protocols became a key softswitch obligation. The softswitch controls the number and type of features provided to the network. It interfaces with an application server coordinating; conferencing, call forwarding, and other call features. Softswitch software hosted on a server includes call control applications. The greater the demand the larger the server required. An SS7 signaling gateway serves as a protocol intermediary, and a translator between the PSTN and IP networks when a call originates in an IP network. A translation from the H.323 signaling protocol to SS7 is necessary in order to set up the call. Signaling gateways are used to terminate signaling links from PSTN networks or other signaling points. Billing, administrative, and tracking functions are available from usage statistics, important management features of the softswitch. [B HD]Applications Server [BT B HD] The application server provides call forwarding, conferencing, voice mail, forward on busy, camp on, call transfer, and so on. The softswitch provides these application programs to the appropriate subscribers as requested. A softswitch is designed on open standards, whereas the Class 4 or Class 5 switch offers only Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-21 5/6/2010
  22. 22. proprietary. Hardware and software compatibility is an issue with PSTN components, hardware or software, from one vendor are not compatible with products from another vendor. The softswitch open standards are deliberate to free service providers from vendor dependences. Softswitch enables service providers to provide integrate third-party applications or the opportunity to write their own applications. This is the ultimate sales point for a service provider that is offered by the softswitch technology. [B HD]Softswitch Applications [BT B HD]We will explore how softswitch measures up with the various levels of PSTN switches. IP PBX - a VoIP gateway can be placed on the trunk side of a PBX. The gateway packetizes the voice and routes it over an IP network which can save the business in long-distance costs. This solution uses the existing PBX's set of features like; call forwarding, conferencing, and so on. It provides investment protection by leveraging the legacy PBX with a VoIP solution. The intelligence for this solution is provided by software known as gatekeeper. The gatekeeper is the predecessor of the softswitch. This design is illustrated in Figure 7-5. Developers have designed a soft PBX, which can replace the legacy PBX (illustrated in Figure 7-7). These soft PBXs known as IP PBXs are significantly lower priced than a hardware. The IP PBX may be called an enterprise-grade softswitch. [FIG]Figure 7-7 IP PBX also known as soft PBX Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-22 5/6/2010
  23. 23. IP Telephone IP PBX IP Network IP Telephone [B HD]IP Centrex [BT B HD] IP Centrex - The RBOCs (Regional Bell Operating Companies) realized the threat softswitches was to on their circuit switched Centrex. Should large companies route their interoffice voice traffic over a corporate WAN (wide area network) using an IP PBX, that would diminish the need for the RBOC’s circuit switched Centrex services. Although lagging a bit behind the the IP PBX the IP Centrex services became available. Centrex is a specialized business solutions for voice service. The equipment is owned by the service provider and is located in the service provider's premises. Centrex service caters to removing the burden of cost and responsibility of telephony equipment ownership for a business. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-23 5/6/2010
  24. 24. [B HD]Class 5 Exchange [BT B HD] Class 5 exchanges, also known as central offices, house the Class 5 switch. The Class 5 switch is concerned with subscriber type of activities; generation of dial-tone, comfort sounds like ring echo and touch tone sounds, handling of network services such as advice of call duration, charges, etc. A single Class 5 can serve up to 10,000 subscribers it can cover an area of a small city of less than 10,000, a a group of small towns, or support several villages. IP provides improved utilization of access by carrying simultaneous calls over a single broadband service. For an analog Centrex, one pair of copper wires is needed to serve each analog telephone, regardless of whether the phone is active or not. When phone goes on hook, the bandwidth of those wires is unused. IP Centrex service can support an IP network when using a Class 5 Switch platform, and support traditional POTS (Plain Old Telephone Service) and ISDN lines. This works using a CPE media gateway and a GR-303 gateway which is co-located with the Class 5 switch (see Figure 7-8). The media gateway size can range from an IP phone to a large carrier-grade media gateway. The GR-303 gateway translates all signaling information it receives from the customer's media gateway, depacketizes the voice for delivery to the switch translating signaling messages from the switch into the appropriate IP telephony protocols; H.323, SIP, or MGCP, packetizing the voice for delivery to the customer's media gateway. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-24 5/6/2010
  25. 25. GR-303(Generic Requirement-303) is a Telcordia standard interface to a Class 5 telephone switch from a DLC (digital loop carrier). In order to connect directly to the PSTN, IP phones and IP telephony gateways must adhere to the GR-303 standard. [FIG]Figure 7-8 IP Centrex using a Class 5 switch V V IP Network GR303 Voice Gateway Gateway Class 5 Switch Telephone Telephone The customer's media gateway, the GR-303 gateway, and the IP network connected together appear to the Class 5 switch as a DLC (Digital Loop Carrier) system. And the telephone sets connected to the customer gateway appear as ordinary phone lines. The IP Centrex appears as a DLC system to the Class 5 switch, it can deliver the same features to the IP Centrex users that it delivers to an analog or an ISDN Centrex user. As a result PSTN features are available to IP Centrex users without an upgrade to the Class 5 switch. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-25 5/6/2010
  26. 26. IP Centrex can replace the Class 5 switch with a softswitch (Compare Figure 7-9 to Figure 7-8). A softswitch actually is an application specific to telephony running on a large network server. The softswitch provides call control and service logic just as a Class 5 switch does. Class 5 switches are responsible for transport or switching of the packetized voice, but the softswitch in not. Because these functions are now performed by a Gateway. Softswitch and IP Centrex signal each other using IP telephony protocols like SIP or H.323. The call setup information is gathered and the softswitch figures out where the called party resides. If the called party is a member of the Centrex group, then the softswitch will inform the originating media gateway or IP phone, and the terminating media gateway or IP phone to route the call directly from one to another. If the called party not a member of the Centrex group, but is served by the PSTN, then the softswitch will inform the originating media gateway or IP phone to route the call to a trunking gateway connecting it to the PSTN. [FIG]Figure 7-9 IP Centrex with Softswitch Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-26 5/6/2010
  27. 27. V PBX Data Voice Telephone IP Network Gateway Softswitch Server V Voice PBX Gateway Telephone Here the trunking gateway’s codec packetizes and compresses the voice so that it can be transmitted over a circuit-switched facilities. The trunking gateway must work with a signaling gateway that is used to exchange SS7 signals with the PSTN. The signaling and the trunking gateways receive their instructions from a softswitch. [B HD]Softswitch Replacing Class 4 Switches [BT B HD]Class 4 replacement by softswitch began with the long-distance bypass industry. Long distance bypass operators use VoIP gateways for international transport. This technology enabled bypass to be competitive with the incumbent long-distance companies. Technical challenges for these operators grew as demand for service grew. With growth it was soon discovered that the media gateways were not dense enough for the levels of traffic they were handling. A similar growth situation Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-27 5/6/2010
  28. 28. was occurring with the gateways that controlled these gateways they too were limited in their capability to handle increasing traffic. And a most challenging situation was that the international traffic required interfacing to different country variations of SS7 signaling, all countries do not have exactly the same rules governing SS7. Necessity, scalability and intelligence in the bypass network, became the mother of invention which came in the form of a Class 4 replacement softswitch. This softswitch is made up of more densely populated gateways and manages with more intelligence. This involved installing a dense gateway on the trunk side of a Class 4 switch. Similar to the PBX solution, the media gateway packetized the voice from the Class 4 switch and routed it over an IP network. This resulted in the service provider saving money on its long distance transport. Subsequently the circuit-switched Class 4 switch would be removed from that architecture altogether. Now the Class 5 switch connected directly to a media gateway to route the call over an IP network. The call control, signaling, and features were now controlled by a softswitch. It would follow that the softswitch, as a Class 4 replacement switch, would now compete directly with the Class 4 switch. Figures 7-10 and 7-11 make obvious this evolution in architecture. [FIG]Figure 7-10 Architecture of Class 4 and Class 5 switches with VoIP gateways Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-28 5/6/2010
  29. 29. V Voice Class 4 Class 5 Gateway Switch Switch Data IP Network Telephone Softswitch V Server Class 4 Voice Switch Class 5 Gateway Switch Telephone [FIG]Figure 7-11 Class 4 replacement Softswitch Note: Class 4 TDM switches are absent V Class 5 Telephone Data Voice IP Network Gateway Switch Softswitch V Telephone Server Voice Class 5 Gateway Switch Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-29 5/6/2010
  30. 30. [B HD]Softswitch Replacing Class 5 Switches [BT B HD] Softswitch technologies next targeted the Class 5 switch for replacement (see Figure 7-12). The ability of the softswitch industry to replace the Class 5 provides the finality of the legacy telecommunication PSTN infrastructure. A Class 5 switch cost millions of dollars and requires at large chunk of real estate. A Class 5 replacement softswitch can provide incredible positive financial implications for the local telephone service providers. [FIG]Figure 7-12 Class 5 replacement Softswitch V Telephone Data Voice IP Network Gateway Softswitch Server V Telephone Voice Gateway Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-30 5/6/2010
  31. 31. Obviously there are concerns and even objections to replacing a Class 5 switch with a softswitch. These concerns include E911 and CALEA (Communication Assistance for law Enforcement Act) of 1994. Another concern is the perception that softswitch will not be able to match Class 5 switch features. One Class 5 manufacturer is reported to have some 3,500 features that have been developed over a 20+ year time frame. A number of successful Class 5 replacement softswitch installations have taken place and this segment of the industry by all counts is growing rapidly. E911 (Enhanced 911 service) is a North American telephone network feature that automatically associates the physical address with the calling party's telephone number. This provides emergency responders with the location of the emergency without the person calling for help having to provide it. Enhanced 911 have been deployed in most metropolitan areas in the United States. One of the 911 issues relates to phone mobility, physically moving the phone from one geographic location to another (a different address). If you move your phone from one geographic location to another even just to a different floor in a building, 911 will think that you are at the previous location. The U.S. Congress passed the CALEA (Communications Assistance for Law Enforcement Act) to aid law enforcement in its effort to conduct surveillance of digital telephone networks. The act obligates telephone companies to make it possible for appropriate law enforcement agencies to tap phone conversations carried out over its networks, as well as making call records available. The act also stipulates that it must not be possible for a user to detect that his conversation is being monitored. The softswitches that replace PBXs, Centrex, Class 4 and Class 5 switches are very diverse in scale. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-31 5/6/2010
  32. 32. Scale refers to their processing power and is measured in calls per second, the number of busy-hour call attempts handled. The capability to handle features from a feature server and interface different signaling protocols are additional diversities. A softswitch is actually software that resides on a server. The limitations are the processing power of the server and the complexity of the software. The softswitch concept which is fundamentally the separation of call agents and applications from the underlying media transport is what will make it possible for AOL (America Online Inc.) or Yahoo or Microsoft or others to one day be your full-service Telco. [A HD]Transport [BT A HD] [B HD]Converged and Converging Architectures [BT B HD] There are three modes of voice transport in use today: IP, TDM, and ATM (Asynchronous Transfer Mode). IP networks bypassing TDM and ATM networks long-distance service providers dramatically reduced their costs of long-distance transport. This allowed them to be more profitable than their TDM and ATM competitors. Softswitch and VoIP made their debut on the transport side of the network. Long distance service providers badly needed an intelligence that would provide call control over an IP network used for transport. And the softswitch needed a SS7 interface into the IP network. Lastly it had to control the transmission of features across an IP network. Accomplishing this gave birth to the Class 4 replacement softswitch. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-32 5/6/2010
  33. 33. [FIG]Figure 7-13 Legacy network: data, voice &SS7 networks Data Network voice Network Class 5 Class 4 SS7 Switch Switch Class 4 Switch Class 5 Switch Telephone Telephone Convergence technology is the integration of voice, data, video and other broadband services provided over a single network based on IP. The subscriber as a result enjoys highly efficient IP services desktop to desktop. This can be referred to as a converged network. The Class 4 and Class 5 switch was designed when voice and data were distributed over separate channels. These are known as legacy networks (see Figure 7-13), the legacy infrastructure of Class 4 and 5 switches remains at the periphery of the network while the core of the network is IP which provides proficient voice transport. A converged network is where voice and data are handled on one network (see Figure 7-15). Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-33 5/6/2010
  34. 34. [FIG]Figure 7-14 Converging networks: combined circuit and packet switched networks Softswitch SS7 IP Network Universal Media Gateway Telephone Server Universal Media Gateway Class 4 Class 5 Switch Switch Class 5 Switch Telephone Telephone In the converged environment, voice switching is performed by Class-less switches (meaning no Class 4 or Class 5 switches). The limitations of geography defined a Class 5 switch as providing local service and a Class 4 switch as providing long distance service. If geography is not relevant, then a Class designation must also be described the same. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-34 5/6/2010
  35. 35. [FIG]Figure 7-15 A converged network data and voice on same network Softswitch IP SOHO Media Gateway Telephone IP IP Network IP IP IP Enterprise Media Server Gateway IP Telephon Carrier Grade Media Gateway Telephone Telephone [B HD]IP Networks [BT B HD] Because of its wide availability IP is becoming the preferred means of transport for data and the preferred means of transport for voice. Originally designed for DARPANET, IP became the protocol for the Internet as well as the transport medium of choice for most data networks. In the late 1990s Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-35 5/6/2010
  36. 36. VoIP was introduced and the telecommunications industry began to concentrate on converging voice and data networks. TDM was designed specifically for voice and does not handle data as well as IP. New demands for email, instant messaging, video conferencing, and World Wide Web applications were indicators of a growing demand for IP data based communications, as opposed to circuit switched communications. The cost of the PSTN dual systems to handle communications seems grossly inefficient. Advantages of converging voice and data networks: [BEG BL] • IP offers a world wide universal addressing scheme • the integration of voice and data applications • less bandwidth • lower equipment costs • lower operations and maintenance costs [END BL] Large service providers operate; the PSTN, the ATM network, the Frame Relay network, the IP network, the ISDN and DSL overlay networks, wireless and X.25 networks. Each of these networks requires their own OAM&P (Operations, Administration, Maintenance, and Provisioning) to provide the facilities and personnel required to manage each network. And IP strongly appears to be the approach for replacing these dissimilar systems with an efficient networking technology. TCP/IP is omnipresent throughout the world. IP is supported by all personal computers, LANs and WANs, dial-up Internet access, handheld devices, wireless web, and other next-generation Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-36 5/6/2010
  37. 37. applications. With IP as core there is an opportunity to link voice and data networks by a combination of public and private infrastructures. IP has the advantage of offering a world wide universal addressing scheme. The integration of technology devices and software, and the convergence of voice and data services as well as multimedia are accelerating rapidly. Service providers now offer an ever expanding repertoire of high-margin services that separate them from circuit-switched service providers. Examples include: [BEG BL] • “follow me” services - (like a cell phone, your number follows you, not fixed to a single geographic location – a challenge for 911. • meet me – net meeting and instant messenger, VoIP conferencing, and so on. [END BL] , email address as substitute for telephone numbers, and video conferencing over IP. These are all benefits of converged voice and data networks. The anticipation of nearly unlimited demand for IP based services in the late 1990s initiated the creation of IP backbone providers. But the anticipated level of demand did not materialize, but instead resulted in over delivery of IP backbone capacity. The winners of this were the IP consumers as well as the VoIP service providers. [B HD]TDM [BT B HD] Time division multiplexing is circuit-switched legacy PSTN telephony. The TDM softswitch is Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-37 5/6/2010
  38. 38. associated with VoIP. It should be noted that comparable architecture is possible with a TDM network. Instead of the mainframe computer architecture encompassing the Class 4 and Class 5 switches, a TDM softswitch uses client-server architecture. Instead of VoIP gateways, it uses TDM gateways, which can be just as scalable as a Class 4 or Class 5 switches. [B HD]ATM [BT B HD] ATM is the principal long-distance voice transport in North America. It replaced TDM due to its superior efficiency and has yet to be outdated by IP due to its reputation for excellent QoS, a capability built into its adaptation layer. The ATM adaptation layer examines customer traffic as it arrives at the switch. Next, based on the type of traffic, the ATM adaptation layer classifies the traffic on its QoS requirements. These requirements are based on three parameters: [BEG BL] • whether the traffic is connectionless or connection-oriented • whether it requires a fixed or variable bit rate • whether an explicit timing relationship exists between the sending and receiving devices [END BL] Following that process, ATM assigns a class to the cells that make up the traffic stream. It then delivers the cells to the network, knowing that ATM's highly reliable connection oriented transport will Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-38 5/6/2010
  39. 39. ensure that the QoS mandate from the sending device will be accommodated on a network wide basis. Many incumbent service providers are faced with the challenge of interworking their ATM and IP networks as they shift traffic to the efficient IP networks. [EOC A HD]Summary From earlier chapters and reinforced here you discovered that the PSTN is made up of three main essentials: access, switching, and transport. IP also manages these three essential functions. Softswitch technologies have enabled the telecommunications market to open the switching aspect of the business to competition. Softswitch makes it possible for a service provider to economically bypass the central office and Class 5 and Class 4 switches. The only path to competition in telecommunications markets is for each service provider to own and operate their own switching facilities. Softswitch, given its lower costs of ownership and operation coupled with its distributed architecture, makes it possible for new market entrants to compete favorably with incumbent service providers. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-39 5/6/2010
  40. 40. Softswitch is troublesome to legacy networks (RBOCS and IXCs) and equipment vendors (makers of PBXs and Class 4 and Class 5 switches) because elements of softswitch are grossly cheaper, simpler, smaller, and more convenient to use in the network than their predecessors. You have learned how the economics and of softswitch will reduce telephony costs and provide communications features that otherwise could not be possible with the centralized PSTN system. You are now familiar with the differences between distributed [PSTN] and distributive [IP networks]. Gatekeepers and gateways have evolved and taken on various functions over time. The softswitch has become more and more intelligent as the earlier intelligence in the gateways has been moved to the softswitch to provide more efficiency in the overall network. The importance of a Media Gateway (call agent) is to control telecommunications equipment in order to bridge call transmission between circuit-based networks and IP-based networks. You have explored how the PSTN Class 4 switch and Class 5 switch can be replaced with softswitches. The components of a packet switched network and the circuit switched network components have been discussed emphasizing the efficiencies gained by exploiting a distributed packet switched IP networks. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-40 5/6/2010
  41. 41. It was shown that a customer does not have to go cold turkey when moving from PSTN to an IP network. Since the migration path using softswitches allows both systems to co-exist allowing a gradual migration. [EOC A HD]Key Terms [BEG KT] Application Server - is a server computer in a computer network dedicated to running certain software applications. ATA (analog terminal adapter) is a device used to allow analog phones to be connected to an IP network. Voyage and other VoIP residential service providers use CPE ATAs to connect analog phones to a broadband IP network. Broadband is typically provided by DSL or Cable services. ATM - This is the international standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixed-length (53-byte) cells. Fixed-length cells allow cell processing to occur in hardware, thereby reducing transit delays CALEA - The U.S. Congress passed the Communications Assistance for Law Enforcement Act (CALEA) to aid law enforcement in its effort to conduct surveillance of digital telephone networks. The act obliges telephone companies to make it possible for appropriate law enforcement agencies to tap phone conversations carried out over its networks, as well as making call records available. The act also stipulates that it must not be possible for a user to detect that his conversation is being monitored. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-41 5/6/2010
  42. 42. Call Agent - Intelligent entity in an IP telephony network that handles call control in an MGCP model voice over IP network. Call agent is known as a MGC (Media Gateway Controller). Carrier-Grade Gateways – are gateways that uphold the PSTN carrier reliability standards 99.999% uptime availability. CPE – is communication equipment residing on the end user's side, demark, of the network interface boundary . DLC – is a multiplexing/de-multiplexing system that typically has a high bandwidth fiber connection to a Central Office out one side, and provides copper interfaces to many residences out the other side. DLC's are deployed where there is fiber installed to a neighborhood, but copper to the homes. DLC's are less expensive to deploy than Fiber to the Home or Fiber to the Curb because there's only one optoelectric conversion required. DS0 - In T-carrier systems Digital signal 0 (DS0) is a basic digital signaling rate of 64 kb/s, corresponding to the capacity of one voice-frequency-equivalent channel. E911 - Enhanced 911 services or E911 service is a North American telephone network feature that automatically associates the physical address with the calling party's telephone number. This is generally done by a form of reverse telephone directory that is supplied by the telephone company. This provides emergency responders with the location of the emergency without the person calling for help having to provide it. Enhanced 911 has been deployed in most metropolitan areas in the United States. enterprise gateways - are customer premises equipment that provides conversion between the audio signals carried on telephone circuits and data packets carried over the Local Area Network. Enterprise Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-42 5/6/2010
  43. 43. Gateways are very similar to Media Gateways, but are scaled and configured to meet the needs of the enterprise rather than a carrier. gatekeepers – along with MGCs (media gateway controllers) were precursors to the softswitch. GR-303 - A set of technical specifications from Bellcore that define the interface between the Digital Loop Carrier (DLC) and a Class 5 switch. GUI - A computer terminal interface, such as Windows that is based on graphics instead of text. H.323 - is an umbrella recommendation from the ITU-T that defines the protocols to provide audio- visual communication sessions on any packet network. IP Centrex - is a set of specialized business solutions where the equipment providing the call control and service logic functions is owned and operated by the service provider and is located on the service provider's premises. IP Network - a network in which transmission of information is done using IP protocol. IP PBX - The Internet Protocol Private Branch eXchange (IP PBX) is telephone switching equipment that resides in a private business instead of the telephone company. An IP PBX delivers employees dial-tone, the ability to conference, transfer, and dial other employees by extension number as well as many other features. Voice transmissions are sent via data packets over a data network instead of the traditional phone network. LCD (Liquid Crystal Display) - is a display that consists of two polarizing transparent panels and a liquid crystal surface sandwiched in between. Voltage is applied to certain areas, causing the crystal to turn dark. A light source behind the panel transmits through transparent crystals and is mostly blocked by the dark crystals. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-43 5/6/2010
  44. 44. Media Gateway - Software that acts as a "call agent" to control telecommunications equipment in order to bridge call transmission between circuit-based networks and IP-based networks. A Media Gateway acts as a translation unit between disparate telecommunications networks such as PSTN; Next Generation Networks; 2G, 2.5G and 3G radio access networks or PBX. Media Gateways enable multimedia communications across Next Generation Networks over multiple transport protocols such as ATM and IP. MGCP (Media Gateway Control Protocol) was developed by Telcordia and Level 3 Communications, is one of a few proposed control and signal standards to compete with the older H.323 standard for the conversion of audio signals carried on telephone circuits (PSTN) to data packets carried over the Internet or other packet networks. QoS - Short for Quality of Service, a networking term that specifies a guaranteed throughput level. One of the biggest advantages of ATM over competing technologies such as Frame Relay and Fast Ethernet is that it supports QoS levels. This allows ATM providers to guarantee to their customers that end-to-end latency will not exceed a specified level. RBOCs (Regional Bell Operating Companies) - Originally seven local telephone companies formed upon the divestiture of AT&T in 1984. The seven were: NYNEX, Bell Atlantic, BellSouth, Southwestern Bell, US WEST, Ameritech, and Pacific Telesis. Today there are only four: VERIZON, SBC, BELL SOUTH, and QWEST SGCP - Controls Voice over IP gateways by an external call control element (called a call-agent). SIP - is a multimedia and telephony protocol that provides services including call forwarding, number delivery, authentication and other telecoms applications. The protocol can set up, control and tear down sessions including internet telephone calls and multimedia conferences. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-44 5/6/2010
  45. 45. Softswitch - also called a Proxy Gatekeeper, Call Server, Call Agent, Media Gateway Controller, or Switch Controller. Software used to bridge a public switched telephone network and voice over Internet by separating the call control functions of a phone call from the media gateway (transport layer). Softswitch performs call control functions such as protocol conversion, authorization, accounting, and administration operations. SOHO (Small Office/Home Office) - is the fastest growing market for computer hardware and software. So-called SOHO products are specifically designed to meet the needs of professionals who work at home or in small offices. TDM (Time Division Multiplexing) - is a communication system technique that interleaves information from several channel inputs onto a carrier in specific time slots. [END KT] [EOC A HD]Review Questions [BEG RQ] 1. Which of the following is an architectural feature of a softswitch network that is not a feature of a Public Switched Telephone Network? a. It provides access. b. It provides switching c. It is a distributed architecture Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-45 5/6/2010
  46. 46. d. It provides transport. 2. What is the device called that takes care of billing, call routing, and signaling in a softswitch network? a. Media gateway b. Softswitch gateway c. Call agent d. Soft agent 3. Which of the following are possibilities for completing a Voice over IP telephone call? (Choose all that are correct.) a. PC to Phone b. PC to PC c. Phone to PC d. PC to softswitch 4. What is the chief advantage of IP phone to the service provider? a. They can move their points of presence without reprogramming b. They do not have to purchase a Class 4 or 5switch c. They do not have to provide customer service d. They have to provide a special switch that is inexpensive. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-46 5/6/2010
  47. 47. 5. What device is located between a VoIP network and a legacy telephony network and acts as an interface between the two networks? a. Media gateway b. Data base c. Transformer d. GUI receivers 6. Switching equipment for major carries must be tested by ___________. a. National Security Agency b. Network Equipment Building Standards c. International Standards Organization d. Cisco 7. A(n)_______________________ aggregates several business legacy telephony lines for interface with a Voice over IP network. a. Enterprise gateway b. SOHO gateway c. PSTN gateway d. Trunk consolidator 8. ______________ is the phrase used for establishing a telephone connection. a. Call switch Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-47 5/6/2010
  48. 48. b. Call setup c. Call teardown d. Call connection control 9. What coordinates routing between networks of signaling messages? a. PSTN switch b. Analog/digital converter c. A hub d. A softswitch 10. What is the function of an H.323 gateway? (Choose all that are correct) a. Address translation b. Authorization of access c. SS7 signaling d. Manages activities in a zone 11. A(n) ________________________________ provides for call forwarding, conferencing, voice mail, and forward on busy. a. Application server b. Client c. MGCP d. NEBS Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-48 5/6/2010
  49. 49. 12. The RBOC’s offer a(n) ____________________ to provide a set of business solution primarily for voice service to their customers a. IP PBX b. Media gateway c. IP Centrex d. Class 5 switch 13. Which of the following is (are) voice over IP signaling protocols? (Choose all that are correct) a. SIP b. H.323 c. SS6 d. SS7 12. A(n) ________________________ packetizes/depacketizes voice so that it can be transmitted over circuit-switched facilities. a. Trunking gateway b. IP PBX c. Hub d. Class 3 switch Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-49 5/6/2010
  50. 50. 13. A converged network typically contains a mix of _____________ and _______________. (Choose all that are correct.) a. IP equipment, PSTN equipment b. Voice, data c. IP traffic, TDM traffic d. CALEA, SIP 14. Which of the following is an advantage of a converged network? (Choose all that are correct.) a. Lower equipment costs b. Integration of voice and data applications c. No legacy telephone equipment is used d. Lower maintenance costs 15. _______________ is the principal long-distance voice transport in North America. a. ATM b. TDM c. NEBS d. QoS Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-50 5/6/2010
  51. 51. Thinking Questions 1. Many of the CLECs (Competitive Local Exchange Carriers) of the telecom boom of the late 1990s failed because they were forced to compete with incumbent carriers by having to deploy the same expensive PSTN switches as the incumbents. What do you think would have been the CLECs fate had softswitches been available to them? Why? 2. The deployment of softswitch services to the last mile will have a strong positive impact on local economic development while expanding people's quality of life through improved education, entertainment, and communication. Do you agree? Explain why or why not. Provide examples. 3. Sam has been supporting telephony switch equipment for over 30 yours. He has had training on his legacy telephony equipment as new equipment has been added, and he is considered “the best in the business.” His company now wants to move into implementing a Voice over IP solution in one of their offices, and they want Sam to do the work. What should Sam do to prepare? Do you think that taking Voice over IP training will provide him enough information to accomplish the job? In reality, how different is the new system going to be? Should he push for hiring a Voice over IP expert? Support your conclusions with evidence that your have found in the library or on the web. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-51 5/6/2010
  52. 52. 4. The Hale Corporation likes to regularly move its employees from place to place within the corporation to promote camaraderie. Three people have been supporting the legacy PSTN telephony network within the corporation, but one is scheduled to retire in a 6 months. The president of the company has retained you as telephone consultant to determine whether it would make more sense to change to a voice over IP system so that he doesn’t have to place the retiring employee. What sorts of things would you need to consider in making this determination? 5. Given the cost of a Voice over IP telephone handset, how are service providers offering telephone service over cable modem from the home at a cost-effective price point? Does the home-owner have to purchase Voice over IP handset for each extension in the home? Why or why not? 6. In light of advances in Voice over IP telephone devices, describe the type of computer and telephony equipment possibilities for future workers. Will workers need both a voice handset and a computer? 7. What are the advantages and disadvantages of CALEA? [END RQ] Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-52 5/6/2010
  53. 53. Convergence+ Guide To Convergence Technologies ISBN# 0619131179 Page 1-53 5/6/2010

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