♦ The Lucent Technologies Softswitch—
`Realizing the Promise of Convergence
`Ramnath A. Lakshmi-Ratan
`
`The Lucent Technologies Softswitch was created as a result of Project Saras, which
`was initiated by two Bell Labs researchers. The purpose of Project Saras was to
`develop a software system that solves several major problems that providers of tele-
`phony services now face. Today’s public switched communications infrastructure con-
`sists of a variety of different networks, technologies and systems, most of which are
`still based on the wireline circuit-switched structure. The technology, however, is
`evolving to packet-based networks, and service providers need the ability to inter-
`connect their customers with these flexible and cost-effective networks without
`losing the reliability, convenience, and functionality of the public switched tele-
`phone network. The Lucent Softswitch, formerly known as the PacketStar†
`IP Services Platform, resulted from a focus on these needs. This Softswitch was
`initially marketed as a signaling-interoperability and services-creation platform
`under the umbrella brand name PacketStar for Lucent data networking products. It
`was renamed in light of the recognition that it represented an emerging concept in
`the industry called a “softswitch,” referring to a software-based distributed switching-
`and-control platform. This paper provides a high-level description of the Lucent
`Softswitch and its application to building next-generation converged networks.
`
`Introduction and Background
`The demand for communications services contin-
`ues to explode and grow at an unprecedented rate. It
`is widely accepted that in just the next 15 to 20 years
`we will see the level of growth in communications
`that was seen in the entire last 100 years. Today voice
`and data networks coexist, with approximately equal
`amounts of traffic; however, data traffic rates are
`growing 10 to 15 times faster than voice, driven by an
`explosion in the use of the Internet. In 1999, one-
`third of all homes in the United States will be on line.
`The International Data Corporation predicts that the
`level of electronic commerce will increase to $400 bil-
`lion in the year 2000, up from $12.5 billion in 1997.
`Add to these indicators the fact that less than one out
`of four people in the world have ever made a phone
`call and also that all the countries of the globe are rac-
`
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`Bell Labs Technical Journal ◆ April–June 1999
`
`ing to develop the communications infrastructures
`that fuel their economies as they prepare to meet the
`next millennium.
`Global deregulation, privatization, and drastic
`restructuring of the communications services industry
`are fueling this demand further. The U.S. Telecom-
`munications Act of 1996 led a worldwide sea change
`in telecom deregulation. As a consequence of the act,
`there was an explosion in the emergence of new com-
`petitive service providers launching new communica-
`tion service enterprises, based either on reselling
`unbundled elements of the incumbent carriers’ infra-
`structures or on building facilities of their own. While
`the earlier competitive carriers focused on the resale
`model, the current landscape is dominated by the
`acquisition and construction of competitive network
`
`Bright House Networks - Ex. 1148, Page 1
`
`

`
`Panel 1. Abbreviations, Acronyms, and Terms
`AAL—ATM adaptation layer
`AIN—advanced intelligent network
`A-link—physical termination for SS7
`interconnectivity
`API—application programming interface
`ATM—asynchronous transfer mode
`CAS—channel-associated signaling
`CCS—common channel signaling
`CLEC—competitive local exchange carrier
`DS0—Digital signal level 0; transmission rate of
`64 kb/s (1 channel) in time division multiplex
`hierarchy
`DS1—Digital signal level 1; transmission rate of
`1.544 Mb/s (24 64-kb/s channels) in TDM
`hierarchy
`DS3—Digital signal level 3; transmission rate of
`44.736 Mb/s (672 64-kb/s channels) in TDM
`hierarchy
`DSL—digital subscriber line
`e&m—“ear” and “mouth” leads from customer
`to central office
`IMT—intermachine trunk
`IN—intelligent network
`INAP—intelligent network application protocol
`IP—Internet protocol
`IPDC—Internet protocol device control
`ISDN—integrated services digital network
`ISP—Internet service provider
`ISUP—ISDN user part
`ISV—independent software vendor
`ITU-T—International Telecommunication
`Union—Telecommunication Standardization
`Sector
`JVM—Java* virtual machine (Sun Microsystems)
`LCDS—Lucent Communication Directory Server
`LDAP—lightweight directory access protocol
`Mantra—Lucent proprietary canonical multi-
`party call model
`MGCP—media gateway control protocol
`MTP—message transfer part
`
`OA&M—operations, administration, and
`maintenance
`OC-3—optical carrier digital signal rate of
`155 Mb/s in a SONET system
`PBX—private branch exchange
`PDL—policy description language
`PEP—policy enforcement point
`PIP—packet intelligent peripheral
`POTS—“plain old telephone service”
`PRI—primary rate interface (ISDN)
`PSTN—public switched telephone network
`RADIUS—remote authentication dial-in user
`service
`RAS—remote access server/service
`RDBMS—relational database management system
`RTP—real-time transport protocol
`Sapphire—Lucent gateway control protocol
`SCCP—signaling section and control part
`SCP—service control point
`SDK—software development kit
`SIP—session-initiation protocol
`SNMP—simple network-management protocol
`SPS—service provider servlet
`SS7—Signaling System 7
`SSP—service switching point
`STP—signal transfer point
`T1—terrestrial facility (North America) to
`transport primary rate of 1.544 Mb/s
`(24 64-kb/s channels)
`TCAP—transaction capabilities applications part
`(SS7 protocol)
`TCP—transmission control protocol
`TDM—time division multiplexed
`UDP—user datagram protocol
`UFA—user feature applet
`UNI—user network interface
`VTOA—voice and telephony over ATM
`VoIP—voice over IP
`VPN—virtual private network
`
`facilities, driven by a huge influx of investment capital.
`The post–U.S. Telecom Act landscape of the com-
`munications service-provider marketplace is going
`through significant restructuring. Technology
`advances in software, transport, and interconnection
`are rapidly making it feasible for service providers to
`
`bundle and create so-called converged service offer-
`ings. These are little more than the packaging of dis-
`parate services such as local, cellular, and long distance
`telephony with paging and Internet-access services
`into one billing and customer-service bundle.
`Alternatively, some carriers are attempting to build
`
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`
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`
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`
`

`
`Business drivers
`
`Competition
`Depreciation
`Labor unions
`Regulation
`
`Branding, bundling,
`marketing, sales
`Applications talent,
`software/servers, speed
`Right-of-way, capacity,
`reliability, capital
`
`Integrated service providers
`
`Divergence of business models
`
`Packet data
`
`Cable
`
`Wireless
`
`Wireline
`
`Convergence of technologies
`
`Business models
`
`Business
`Service
`Network
`Elements
`
`Service bundling
`and retail
`Applications
`creation, delivery
`Network access
`and bandwidth
`
`Cable
`
`Data
`
`Wireless
`
`Wireline
`
`Regulated monopolies and
`oligopolies (circa 1996)
`
`Business layer
`
`Service layer
`
`Network layer
`
`Element layer
`
`Figure 1.
`Telecommunications industry structure evolution.
`
`truly converged infrastructures that provide voice,
`data, and multimedia services over the same network
`using packet-based technologies in backbone net-
`works. This convergence of network infrastructure
`technologies is being accompanied by a divergence of
`business models, with specialized carriers emerging in
`many different niches (Figure 1). On the one hand,
`some of the major carriers are still building fully verti-
`cally integrated service businesses. On the other hand,
`there is an emergence of three new types of business
`models: (1) the infrastructure provider model, which
`leverages of rights of way and investment capital for
`construction; (2) the service applications provider
`model, which leverages speed in creating new service
`applications, together with the modern data-based
`infrastructures to deliver them; and (3) the service
`retailer and marketer model, which leverages brand
`image, marketing, and customer franchises.
`The Lucent Technologies Softswitch is particularly
`useful to the business model involving infrastructure
`providers. The next section of this paper “The
`Evolution of Public Communications Networks,” char-
`acterizes the public switched telecommunications
`
`infrastructure, its movement toward packet-based
`technology, and the challenges network service
`providers face as it moves in that direction. The following
`section, “Lucent Technologies Softswitch Technology,”
`presents Lucent’s Softswitch as an approach to meet-
`ing these challenges. That section discusses the tech-
`nology design philosophy, the network architectures,
`and the systems architectures of the Lucent Softswitch.
`
`The Evolution of Public Communications Networks
`Today’s public switched telecommunications
`infrastructure consists of a variety of different net-
`works, technologies, and systems. Most of this is still
`the wireline circuit-switched infrastructure, repre-
`sented in Figure 2. Analog local loops, usually after
`being aggregated by a subscriber loop carrier, are con-
`nected to a local (Class 5) switch where the connec-
`tion carries both media and control signaling for all of
`the aggregated loops. The local switch is connected
`through two separate networks to other toll/tandem
`and local switches. One network of intermachine
`trunks (IMTs) carries the media in the form of 64-kb/s
`time division multiplexed (TDM) streams. All of the
`associated control information is carried on a separate
`
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`Bright House Networks - Ex. 1148, Page 3
`
`

`
`Network
`
`SCP
`
`SCP
`
`SCP
`
`SCP
`
`SS7 network
`(ISUP/MTP)
`
`IMTs
`(TDM-G.711)
`
`Local
`switch
`
`Toll/tandem
`switch
`
`Toll/tandem
`switch
`
`Toll/tandem
`switch
`
`SS7 network
`(ISUP/MTP)
`
`IMTs
`(TDM-G.711)
`
`Local
`switch
`
`ISDN PRI/CAS
`(TDM-G.711)
`
`Enterprise
`PBX
`
`POTS
`phone
`
`POTS
`phone
`
`PBX feature
`phone
`
`POTS
`phone
`
`Customer premises
`
`CAS – Channel-associated signaling
`G.711 – ITU-T Recommendation G.711
`IMT – Intermachine trunk
`ISDN – Integrated services digital network
`ISUP – ISDN User Part
`ITU-T – International Telecommunication Union—
` Telecommunication Standardization Sector
`
`MTP – Message transfer part
`PBX – Private branch exchange
`POTS – “Plain old telephone service”
`PRI – Primary rate interface
`SCP – Service control point
`SS7 – Signaling System 7
`TDM – Time division multiplexed
`
`Figure 2.
`Today’s public switched telephone network (PSTN).
`
`packet-based signaling-and-control network (typically
`using ITU-T Signaling System 7 [SS7]1,2 or Common
`Channel Signaling System 7 [CCS7]).
`The SS7 network basically consists of three kinds
`of signaling points—service switching points (SSPs),
`signal transfer points (STPs), and service control points
`(SCPs). Each signaling point is identified by a unique
`numeric point code, analogous to an Internet protocol
`(IP) address in an IP network.
`SSPs are switches that originate, terminate, or tan-
`dem calls. STPs are packet switches that interconnect
`and route traffic in the SS7 network. An STP’s role is
`similar to that of an IP router but it has significant dif-
`
`ferences. SCPs are centralized database servers for such
`functions as 800-number translation and personalized
`information.
`PRI trunks refer usually to DS1 lines or, more pop-
`ularly, T1 lines that have one channel reserved for pri-
`mary rate interface (PRI) signaling. Prominent variants
`include fractional T1s and non-facility associated
`signaling trunks. Channel-associated signaling trunks, or
`CAS trunks, refer to in-band signaling variants that can
`run on DS1 or T1 trunks.
`Much of the logic needed for establishment of
`connections and routes for the media through the net-
`work are resident in the switches. Additional logic and
`
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`
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`
`Bright House Networks - Ex. 1148, Page 4
`
`

`
`information for enhanced services (such as
`800/900/700 national/personal number services) are
`drawn from SCPs, which are connected through the
`SS7 network to the switches. In some cases other
`adjuncts called intelligent peripherals provide media
`resources such as dual-tone multiple-frequency digit
`recognition, spoken announcements, speech recogni-
`tion, and synthesized (text-to-speech) announcements
`as part of these enhanced services. In general, a circuit
`intelligent peripheral refers to an external media-
`processing engine capable of terminating TDM audio
`streams and performing some processing on those
`streams.
`Next-Generation Networks
`The direction that the industry is taking in con-
`ceiving and building next-generation networks and in
`evolving the current public switched telephone net-
`work (PSTN) is largely premised on replacing much of
`the TDM-based circuit-switched infrastructure with an
`Internet-protocol (IP)–based or asynchronous-
`transfer-mode (ATM)–based packet-switched infra-
`structure. Figure 3 describes the replacement of the
`toll/tandem or long distance part of the PSTN with a
`packet backbone. The packet backbone is essentially
`thought of as carrying the media traffic. The signaling-
`and-control traffic can be carried, as before, on a sepa-
`rate packet-based network, or else can be carried in
`secure and protected bandwidth flows within the
`packet backbone network.
`Drivers of Packet-Based Technology
`As carriers attempt to marshal investment capital
`to fund network construction, their business cases are
`strongly influenced by the time value of investments,
`which in turn are driven by the rate of innovation and
`economic learning effects in the core technologies cho-
`sen for the networks. These learning-curve effects are
`best characterized by the length of the period observed
`in which the performance/price ratio doubles
`(Table I). The period for commercial computing is the
`shortest at about 18 months. It is driven by the learn-
`ing curve for semiconductors (often referred to as
`Moore’s Law, named after Intel co-founder Gordon
`Moore). The performance-doubling period for TDM
`circuit-switching technology is the longest of those
`shown, at about 60 to 80 months. Packet-based IP and
`
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`
`Bell Labs Technical Journal ◆ April–June 1999
`
`Table I. Technology innovation periods.
`
`Networking technology
`platforms
`
`Performance/price ratio
`doubling period
`
`Commercial computing
`
`IP technology
`
`ATM technology
`
`18 months
`
`20 months
`
`40 months
`
`TDM-circuit switching
`
`60–80 months
`
`ATM technologies have displayed intervals of 20 and
`40 months, respectively.
`In addition to their more rapid rate of develop-
`ment, it is estimated that the simpler topologies of
`packet-based networks would lead to significant
`reduction in operations and administration costs. It is
`no wonder that there is an increasing focus on IP and
`ATM technologies by network operators. However,
`severe challenges face operators building out new net-
`works or extending/replacing existing circuit-switched
`networks with packet-based infrastructures.
`Challenges of Network Service Providers
`Carriers looking to create new service businesses
`or to evolve existing ones face the immediate problem
`that they must, at a minimum, provide services over
`their new/evolved networks with the same composi-
`tion, convenience, and quality as the PSTN services to
`which the markets are accustomed. This implies that
`they must build new IP-based or ATM-based packet
`networks that interconnect with the existing wired or
`wireless PSTN, as well as other networks such as cable
`networks, in order to provide ubiquitous interconnec-
`tivity and seamless services.
`To begin with, there are many different protocols
`used in the packet-circuit gateways that interconnect
`circuit and packet networks and in the devices and
`client appliances used on those networks. These
`include, for example, H.323 and its subsidiary protocols
`(an ITU-T packet-telephony protocol suite),3-9 Internet-
`protocol device control (IPDC), session-initiation proto-
`col (SIP),10 Microsoft’s NetMeeting*, and media-
`gateway–control protocol (MGCP).11 Even if the protocol
`choices were made, there are many vendors of the gate-
`ways and devices, and one vendor’s implementation of
`a protocol is not guaranteed to interwork with
`another’s. Any implementation must, of course, trans-
`parently handle both PSTN and IP clients and must
`
`Bright House Networks - Ex. 1148, Page 5
`
`

`
`SCP
`
`Local
`switch
`
`SS7 network
`(ISUP/MTP)
`
`IMTs
`(TDM-G.711)
`
`SCP
`
`VolP/VTOA-based LD packet backbone network
`
`Network
`Customer premises
`
`ISDN PRI/CAS
`(TDM-G.711)
`
`SCP
`
`Local
`switch
`
`SS7 network
`(ISUP/MTP)
`
`IMTs
`(TDM-G.711)
`
`VolP/VTOA
`(RTP/UDP/IP or
`AAL1/AAL2)
`
`Enterprise
`PBX
`
`Enterprise
`PBX
`
`POTS
`phone
`
`POTS
`phone
`
`PBX feature
`phone
`
`POTS
`phone
`
`PBX feature
`phone/POTS
`phone
`
`POTS
`phone
`
`AAL – ATM adaptation layer
`ATM – Asynchronous transfer mode
`CAS – Channel-associated signaling
`G.711 – ITU-T Recommendation G.711
`IMT – Intermachine trunk
`IP – Internet protocol
`ISDN – Integrated services digital network
`ISUP – ISDN User Part
`ITU-T – International Telecommunication Union—
` Telecommunication Standardization Sector
`LD – Long distance
`
`MTP – Message transfer part
`PBX – Private branch exchange
`POTS – “Plain old telephone service”
`PRI – Primary rate interface
`RTP – Real time transport protocol
`SCP – Service control point
`SS7 – Signaling System 7
`TDM – Time division multiplexed
`UDP – User datagram protocol
`VoIP – Voice over IP
`VTOA – Voice and telephony over ATM
`
`Figure 3.
`Next-generation packet-based long distance networks.
`
`utilize multiple existing directories and databases, such
`as the SCP and relational database management system
`(RDBMS) in the PSTN, and lightweight-directory-access
`protocol (LDAP), remote-access service (RAS), and
`remote-authentication dial-in user service (RADIUS) in
`the packet world.
`Service providers must recoup their investments
`in legacy networks by reusing existing services, such as
`intelligent network (IN) services, while being able to
`innovate and offer new Internet services. While doing
`all this, they have to systematically grow their business
`by being able to manage and scale these converged
`networks. Additionally, there is the problem of
`
`adapting/integrating new services. With the telephony
`marketplace becoming more competitive, next-
`generation networks must provide the ability to inte-
`grate new services from any source—local or remote—
`to meet the market demands of the ever changing
`workplace. These networks must also provide a method
`of differentiating one service provider from another.
`
`Project Saras
`To solve these challenges, Lucent Technologies
`has developed the Lucent Softswitch in an effort called
`Project Saras.12 The basic approach is premised on the
`unbundling of the core functionality of a conventional
`circuit switch and the distribution of this functionality
`
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`
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`Bright House Networks - Ex. 1148, Page 6
`
`

`
`Traditional circuit
`switch model
`
`Softswitch model
`
`SS7
`network
`
`Management
`system
`
`New
`services
`
`Controller
`
`Billing
`system
`
`Lucent
`Technologies
`Softswitch
`
`TDM
`
`Line
`card
`
`Time slot
`interchange
`
`Trunk
`card
`
`TDM
`
`Gateway control
`protocol
`
`SCP
`
`SS7
`network
`
`Gateway control
`protocol
`
`TDM
`
`IP
`ATM
`
`IP/ATM
`backbone
`
`IP
`ATM
`
`TDM
`
`Access/trunking
`media gateway
`
`Access/trunking
`media gateway
`
`ATM – Asynchronous transfer mode
`IP – Internet protocol
`ITU-T – International Telecommunication Union—
` Telecommunication Standardization Sector
`
`SCP – Service control point
`SS7 – Signaling System 7
`TDM – Time division multiplexed
`
`Figure 4.
`Unbundling services and control from media transport.
`
`across the backbone of a packet network in the form
`of software components that run on commercial stan-
`dard computers. This unbundled and distributed archi-
`tecture must be open and programmable, both for the
`service provider and for any third-party feature devel-
`oper, to create and provide new services. All this has
`to be capable of providing the scalability and reliability
`that the market demands.
`
`Lucent Technologies Softswitch Technology
`Figure 4 describes how the functionality of the
`circuit switch, represented by the model on the left,
`is unbundled and distributed across the packet back-
`bone using the Lucent Softswitch model on the right.
`The media interfaces in the circuit switch (line/trunk
`cards) are replaced by media gateways that convert
`TDM flows to IP or ATM packet flows. The time slot
`interchange, or switch matrix, is replaced by the high
`performance packet backbone itself. The switch con-
`
`troller that switches timeslots across the switch
`matrix is replaced by the Lucent Softswitch, which
`controls the switching and routing of media packets
`between media gateways across the packet backbone.
`In both cases, the switch controller implements
`service logic—as in the case of intelligent network
`application protocol (INAP) triggers in advanced
`intelligent network (AIN) 0.1. In addition, other
`services are brought into the communications flows it
`controls—for example, through its interconnection
`with the SS7 network in the case of PSTN IN services,
`or through other databases, logic or feature servers,
`and media servers.
`Trunking devices or trunking gateways are devices
`that terminate trunks associated with SS7 control
`links. These TDM trunks carry media from an adjacent
`switch in the traditional circuit-switched network. The
`adjacent switch usually belongs to a different service
`
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`
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`
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`
`

`
`provider. Depending on the agreement between the
`service providers, these trunks are also called co-carrier
`trunks or feature group D trunks.
`Access devices or access gateways are devices that ter-
`minate PSTN signaling and media. Traditional cus-
`tomer premises equipment or a Class 5 switch would
`be an appropriate example. More specifically a Lucent
`Ascend MAX family member is an example where
`DS1s or DS3s supporting in-band signaling variants or
`PRI are terminated.
`Trunking and access devices and gateways are gen-
`erally referred to as media devices and media gateways.
`Thus, the Lucent Softswitch begins by providing
`the same functionality as a circuit switch, but it does so
`in packet-based networks designed to be intercon-
`nected with PSTNs. The distinguishing characteristics
`of the Lucent Softswitch are:
`• It is a programmable call-processing system
`supporting a variety of PSTN, ATM, and IP
`protocols.
`• It runs on commercial computers and operat-
`ing systems.
`• It controls external trunking gateways, access
`gateways, and remote access servers (RASs).
`For example,
`– A Lucent Softswitch plus a trunking gate-
`way is a replacement for a toll/tandem
`switch (Class 4 switch) with voice over IP
`(VoIP) or voice and telephony over ATM
`(VTOA) in the backbone;
`– A Lucent Softswitch plus an access gateway
`is a voice virtual-private-network (VPN)/
`private-branch-exchange (PBX) tie-line
`replacement with VoIP in the backbone;
`– A Lucent Softswitch plus a RAS offers a
`managed modem service using co-carrier
`trunks (that is, modem calls signaled
`through SS7 ISDN user part [ISUP]);
`– A Lucent Softswitch plus a trunking gate-
`way and a local feature server is a replace-
`ment for a local switch (Class 5 switch) with
`VoIP/VTOA in the backbone.
`• It reuses IN services through an open and flexi-
`ble directory interface. For example, it provides
`a directory-enabled architecture with access to
`
`RDBMS, LDAP, and transaction-capabilities
`applications part (TCAP) directories.
`• It provides open application programming
`interfaces (APIs) for third-party developers to
`create next-generation services.
`• It has programmable back-office features, such as
`– Programmable event-detail recording, and
`– Call-detail events written to a service
`provider’s event-collection mechanism.
`• It has advanced policy-server–based manage-
`ment of all software components, including
`– Simple network management protocol
`(SNMP) 2.0 interfaces exposed by all com-
`ponents, and
`– Policy description language and a system for
`writing and enforcing custom policies.
`Lucent Softswitch Technology Design Philosophy
`The essential design philosophy behind the Lucent
`Softswitch is based on creating a scalable, distributed
`software system that is independent of a specific
`underlying hardware/operating system and is capable
`of handling a variety of synchronous communication
`protocols—putting the infrastructure in an ideal posi-
`tion to track Moore’s curve. Such a distributed system
`can be termed a programmable synchronous communica-
`tion control network and should be capable of supporting
`the following basic requirements:
`• Protocol- and device-independent develop-
`ment of call-processing and/or synchronous-
`session-management applications;
`• Safe execution of multiple third-party applica-
`tions in the Lucent Softswitch network with-
`out any adverse effects caused by malicious or
`wrong behavior of applications;
`• The capability for third-party hardware vendors
`to add support to new devices and protocols;
`• The ability for service providers and application
`providers to add support for global system-
`wide policies without compromising perfor-
`mance and security;
`• The capability for the evolving synchronous
`communication control network to support
`diverse back-office systems including billing,
`network management, and other operation
`support systems;
`
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`
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`
`

`
`Synchronous
`communications
`protocols
`
`Media
`
`RTP, H.323 media content sections or AAL-1/AAL-2, for example
`
`Control and
`signaling
`
`Streaming
`
`RTSP, for example
`
`Interactive
`
`Peer to peer
`
`Master/slave
`
`H.323, SIP, ISUP,
`BISUP, Q.931,
`Q.2931, or CAS,
`for example
`
`IPDC, MGCP,
`H.GCP, GR-1129,
`or POTS T/R,
`for example
`
`AAL – ATM adaptation layer
`ATM – Asynchronous transfer mode
`BISUP – Broadband ISDN user part
`CAS – Channel-associated signaling
`GR-1129 – Generic Requirement 1129 (Telcordia)
`H.323 – ITU-T Recommendation H.323;
` packet telephony protocol suite
`H.GCP – ITU-T proposal under study for gateway
` control protocol
`IPDC – Internet protocol device control
`ISDN – Integrated services digital network
`
`ISUP – ISDN user part
`ITU-T – International Telecommunication Union—
` Telecommunication Standardization Sector
`MGCP – Media gateway control protocol
`POTS – “Plain old telephone service”
`Q.2931 – ITU-T Recommendation Q.2931
`Q.931– ITU-T Recommendation Q.931
`RTP – Real time transport protocol
`RTSP – Real time streaming protocol
`SIP – Session-initiation protocol
`T/R – Tip/ring
`
`Figure 5.
`Synchronous communications protocols.
`
`• Support of run-time binding or dynamic topol-
`ogy of the synchronous communication con-
`trol network that aids organic evolution;
`• Scalability from very small networks to very
`large networks (on the order of the current
`PSTN and more); and
`• Support for fault resilience from the ground up.
`These requirements enable the next-generation
`service provider to deploy a Lucent Softswitch-based
`network as the backbone for synchronous communi-
`cation control that allows rapid development and
`deployment of advanced synchronous multimedia
`applications.
`
`Signaling and Communications Protocol Agnosticism
`A basic aspect of the Lucent Softswitch design phi-
`losophy as mentioned above is the abstraction of sig-
`
`naling and synchronous communications protocols
`and their implementation details through a canonical
`model that hides these details from the core call/ses-
`sion processing and control. This canonical model
`(internally referred to as Mantra) is a generalized
`multi-party call/session model of zero or more parties.
`Existing call models, such as the Q.93113 model,
`become a special case of this model. The special case of
`a zero-party call represents pure third-party call con-
`trol. This allows for the development and evolution of
`the system in a way that is agnostic to the emergence
`and adoption of specific protocols or their varied
`implementations by different vendors.
`As in Figure 5, synchronous communication pro-
`tocols can generally be classified into two basic types.
`The first set deals with the representation, processing,
`and transmission of media content such as audio and
`
`182
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`Bell Labs Technical Journal ◆ April–June 1999
`
`Bright House Networks - Ex. 1148, Page 9
`
`

`
`video. The second set deals with control and associated
`signaling between parties, devices, and infrastructure
`systems that exchange, process, or transmit this content.
`The Lucent Softswitch supports various control
`and signaling protocols including master/slave control
`protocols as well as peer-to-peer protocols spanning
`the entire gamut from circuit telephony to packet tele-
`phony. Examples of the narrowband circuit-telephony
`protocols currently supported by the Lucent Softswitch
`include SS7 ISUP (including country variants), Q.931,
`and various CAS variants (with equivalent mapping
`done to Q.931 by a media gateway). Examples of
`packet-telephony VoIP protocols that are supported
`include H.323 v1/v2, SIP, IPDC, and MGCP.
`Examples of packet-telephony VTOA protocols sup-
`ported include IPDC, Sapphire (a Lucent ATM gate-
`way control protocol), and user-network interface
`(UNI) versions.
`The Lucent Softswitch supports Layer 3 (call con-
`trol signaling) for the various circuit and packet tele-
`phony protocols. Layer 2 and Layer 1 aspects of the
`signaling protocols are terminated by:
`• Hardware elements running in the same gen-
`eral purpose computer as the individual Lucent
`Softswitch components; or
`• Hardware elements external to the Lucent
`Softswitch, such as external signaling gateways
`and STPs with TCP/IP support.
`In the latter case, Layer 3 signaling is tunneled by the
`external hardware element using TCP/IP.
`Lucent Softswitch-Based Network Architectures
`The Lucent Softswitch is designed as a distributed
`software system that provides seamless interoperability
`between networks based on diverse technologies, pro-
`tocols, and devices. Figure 6 illustrates an instance of
`a Lucent Softswitch-based network architecture for
`VoIP whose functionality is similar to the current circuit-
`switched inter-exchange–carrier/long-distance
`network. In this figure, a Class 4 switch is replaced by
`a Lucent Softswitch and a set of trunking gateways.
`The Lucent Softswitch terminates ISUP signaling from
`the STPs, either by directly terminating A-links
`(shown as ISUP/MTP in the figure) or by accepting
`ISUP signaling over TCP/IP. The trunks (which are
`signaled through ISUP) from a local switch (or other
`
`circuit switches) are terminated in the trunking gate-
`way, which is capable of converting the G.71114
`TDM signal into real-time-transport-protocol
`(RTP)15-16/user-datagram-protocol (UDP)/IP packets of
`various sizes using various coding schemes (such as
`G.711 or G.72917). The circuit switches view the
`Lucent Softswitch like yet another circuit switch or
`SSP. The trunking gateway itself is controlled by the
`Lucent Softswitch using a master/slave protocol such
`as IPDC or MGCP to associate a specific time slot
`(bay/module/line/channel or circuit identification
`code) from the circuit switch with specific
`source/destination RTP/UDP/IP streams. The Lucent
`Softswitch, as part of its call processing, identifies
`the best possible egress gateway to be used for ter-
`minating the call and uses this information to com-
`mand the trunking gateways to perform specific
`functions. For example, the Lucent Softswitch can
`choose to complete most of the calls through a
`least-cost routing logic that chooses the egress gate-
`way closest to the destination phone—in which
`case, voice is typically carried mostly in the IP back-
`bone. Alternatively, the Lucent Softswitch can
`decide to use the TDM switching capabilities of the
`trunking gateway, and thus complete the call
`through just the circuit-switched network. The service
`logic that runs as part of the Lucent Softswitch and
`that makes these basic routing decisions is itself
`completely programmable.
`Figure 6 also illustrates the ability of the Lucent
`Softswitch to handle access gateways that terminate
`either integrated services digital network (ISDN) PRI
`or CAS signaling from enterprise PBXs (either on dedi-
`cated access lines or on an IP-based access line. Such
`access gateways can be controlled by the Lucent
`Softswitch in multiple ways based on the packet tele-
`phony protocol actually supported by the access gate-
`way. The Lucent Softswitch can act like an H.323
`gatekeeper for H.323-based gateways that use the
`gatekeeper-routed model, and it can act like the desti-
`nation gateway for a static/destination-routed model.
`The Lucent Softswitch can also control the access gate-
`way using a master/slave protocol such as IPDC or
`M