SOFTSWITCH 3 Softswitch Softswitch Architecture International Softswitch Consortium ISC Reference

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SOFTSWITCH 3 Softswitch Softswitch Architecture International Softswitch Consortium ISC Reference Powered By Docstoc
 International Softswitch
Consortium (ISC) Reference
Softswitch Defining and Relationship to NGN
Source : Study on Application of Softswitch in Wireless Network
         page 128
ISC Reference Softswitch Architecture
Functional Plane
                                                                Service & Application Plane
  Management                                                     Application/Feature Server
     Plane                                                   (SCP, Service Logic, LDAP Server)                                 IN/AIN
                     Application Signaling (SIP)

                                                         Open APIs & Protocols (JAIN, Parlay, XML, SIP)

                                                              Call Control & Signaling Plane
                                                                                                            SIP-T; H.323
                                                              Call Agent, MGC, Softswitch, GK                               Inter-Network
  Subscriber &
  Network                                                          Signaling (MGCP, H.248, SIP)
  Operation                                                           Transport Plane
  Support, Billing
  Support                                                                                   Interworking                   PSTN/SS7/ATM
                     Media                         IP Transport Domain:                                                       Networks
                                                   IP Backbone, Routers, Switches, BGs
                     Server                                                                 TG (MG), SG,
                                                   QoS Mechanism (RSVP, Diffserve,
                                                   MPLS...), MS (Bearer Portion)            Interworking
                                                                                                                             other VoIP
                                                                     Non-IP Access Domain:
                                                                     Wireline Access (AG, Access Proxies)
                                                                     Mobile Access (RAN AG)
                                                                     Broadband Access (IADs, MTAs)

                                                   IP Phones (H.323, SIP,
                                                   MGCP, ...),                    Non-IP Terminals/
                                                   IP Terminals,                  Mobile Networks
                                                   IP PBX
1. Transport Plane
•   Responsible transport of messages (call signaling, call and media
    setup, or media) across the VoIP network.
•   Transport mechanism(s) for these messages based on any technology that
    satisfies the requirements for carrying these types of traffic.
•   Provides access for signaling and media with external
    networks, or terminals to VoIP networks.
•   Transport Plane devices and functions are controlled by Call Control &
    Signaling Plane.
•   The transport plane is further divided into three domains:
     • IP Transport Domain :
     • Interworking Domain;
     • Non-IP Access Domain
    a. IP Transport Domain
     • Provides the transport backbone and routing/
       switching fabric for transporting packets across the
       VoIP network. Devices like routers and switches belong to this
        domain. Devices that provide Quality of Service (QoS) mechanisms and
        policies for the transport also belong to this domain.
b. Interworking Domain
•   Domain are primarily responsible for the transformation of
    signaling or media received from external networks into a
    form that can be sent among the various entities in the
    VoIP network and vice versa.
•   Consists of devices like :
     • Signaling Gateways (signaling transport conversion between
       different transport layers),
    • Media Gateways (media conversion between different transport
       networks and/or different media),
    • Interworking Gateways (signaling interworking on the same
       transport layer but with different protocols).

c. Non-IP Access Domain
•   Domain that applies to non-IP terminals and wireless radio
    networks that access the VoIP network.
•   Consists of :
     • Access Gateways or Residential Gateways for non-IP
       terminals or phones.
           •    ISDN terminals,
           •    Integrated Access Devices (IADs) for DSL
           •    Cable Modem/Multimedia Terminal Adaptors
                (MTAs) for HFC networks, and
           •    Media Gateways for a GSM/3G mobile radio
                access network (RAN).
      Note : that the IP terminals, like a SIP phone, will directly connect to the IP
          Transport Domain, without going through an Access Gateway.

2. Call Control & Signaling Plane
 •   It controls the major elements of the VoIP network,
     especially in the Transport Plane.
 •   Carry out call control based on signaling messages
     received from the Transport Plane, handle establishment
     and teardown of media connections across the VoIP
     network by controlling components in the Transport
    • Consists of devices like :
       • Media Gateway Controller (a.k.a. Call Agent or Call
       • Gatekeepers and
       • LDAP servers.

3. Service & Application Plane
• Provides the control, logic and execution of one or more
  services or applications in a VoIP network.
• Control the flow of a call based on the service execution
  logic. They achieve this by communication with devices in
  the Call Control & Signaling Plane.
• Service & App Plane consists of devices like :
   • Application Servers and
   • Feature Servers.
   Service & App Plane may control specialized bearer components, such
    Media Servers, that perform functions like conferencing, IVR, tone
       processing, and so on.
4. Management Plane
It functions such as :
 • Subscriber and service provisioning,
 • Operational support,
 • Billing and
 • Other network management tasks are handled.
It can interact with any or all of the other three planes through
industry standard (e.g. SNMP) or proprietary protocols and
  Functional Entities

The diagram above shows 12 different functions. Understanding the autonomy of
all 12 functions is an important characteristic of the ISC Reference Architecture.
1). Media Gateway Controller Function
   (MGC-F) a.k.a. Call Agent or Call Controller
Provides the call state machine for endpoints. Its primary role
is to provide the call logic and call control signaling for one
or more media gateways.
    • Maintains call state for every call on a media gateway
    • May maintain bearer states for bearer interfaces on the
    • Communicates bearer messages between two MG-Fs,
       as well as with IP phones or terminals
    • Acts as conduit for media parameter negotiation
    • Originates/terminates signaling messages from
       endpoints, other MGC-Fs and external networks
    • May interact with the AS-F for the purposes of
       providing a service or feature to the user
    • May manage some network resources (e.g. MG-F ports,
       bandwidth etc.)
•   May provide policy functions for endpoints
•   Interfaces to R-F/A-F for call routing, authentication and
•   May participate in management tasks in a mobile
    environment (mobility management is generally part of
    the CA-F)
•   Applicable protocols include H.248 and MGCP
2). Call Agent Function (CA-F) and 3) Interworking
   Function (IW-F)
CA-F and IW-F are subsets of the MGC-F.
 • CA-F exists when the MGC-F handles call control and call
   state maintenance. Examples of CA-F protocols and APIs include :
      • SIP, SIP-T, BICC, H.323, Q.931, Q.SIG, INAP, ISUP, TCAP, BSSAP,
        RANAP, MAP and CAP (mobile)
      • Open APIs (JAIN, Parlay, etc.)
•   IW-F exists when the MGC-F performs signaling
    interaction between different signaling networks (e.g. SS7
    and SIP). Examples of IW-F protocols include H.323/SIP
4). Call Routing and 5). Accounting Functions
• R-F provides call routing information to the MGC-F, while the
• A-F :
     • collects call accounting information for billing
        purposes. A-F can also
     • have a broader role embodied by the common AAA
        functionality (authentication, authorization and
        accounting) in remote access networks.

Primary role of both functions is to respond to requests from
one or more MGC-Fs, directing the call or its accounting to
terminating endpoints (other MGC-Fs) or services (AS-Fs)
R-F/A-F Characteristics :
•   Provides routing function for intra- and inter-network call
    routing (R-F)
•   Produces details of each session for billing and planning
    purposes (A-F)
•   Provides session management and mobility management
•   May learn routing information from external sources
•   May interact with the AS-F for the purposes of providing a
    service or feature to the user
•   May operate transparently to the other entities in the
    signaling path
•   Many R-Fs and A-Fs can be chained together in a
    sequential or hierarchical manner
•   The R-F/A-F is often integrated with the MGC-F. However,
    just as is the case with the ASF,
•   An integrated R-F/A-F/MGC-F can also request services of
    an external R-F/A-F.
    • The A-F collects and emits per-call accounting
      information. The AS-F emits accounting information for
      enhanced services, such as conferences and premium
      information services.
    • Applicable protocols for the R-F include ENUM and
    • Applicable protocols for the A-F include RADIUS and
      AuC (for mobile networks)

6). SIP Proxy Server Function (SPS-F)
The most common embodiment of the R-F and A-F is as a SIP
Proxy Server. For this reason, the ISC recognizes a separate SIP
Proxy Server Function (SPS-F).
7). Signaling Gateway Function (SG-F) and
8). AccessGatewaySignaling Function (AGS-F)
•   SG-F provides a gateway for signaling between a VoIP
    network and the PSTN, whether SS7/TDM- or BICC/ATM-
    based. For wireless mobile networks, the SG-F also provides
    a gateway for signaling between an IP-based mobile core
    network and PLMN that is based on either SS7/TDM or
    The primary role of the SG-F is to encapsulate and
    transport PSTN (ISUP or INAP) or PLMN (MAP or CAP)
    signaling protocols over IP.
•   AGS-F provides a gateway for signaling between a VoIP
    network and circuit-switched access network, whether V5-
    or ISDN-based.
•   For wireless mobile networks, the AGS-F also provides a
    gateway for signaling between an IP-based mobile core
    network and PLMN that is based on either TDM or ATM.
AS-F Characteristics:
•     May request the MGC-F to terminate calls/sessions for certain
      applications (e.g. voice mail or conference bridge)
•     May request the MGC-F to re-initiate call features (e.g. find
      me/follow me or pre-paid calling card)
•     May modify media descriptions using SDP
•     May control an MS-F for media handling functions
•     May be linked to Web applications or have Web interfaces
•     May have an API for service creation
•     May have policy, billing and session log back-end interfaces
•     May interface with MGC-Fs or MS-Fs
•     May invoke another AS-F for additional services or to build
      complex, component-oriented applications
•     May use the services of an MGC-F to control external resources
•     Applicable protocols include SIP, MGCP, H.248, LDAP, HTTP, CPL
      and XML
•     Applicable open APIs include JAIN and Parlay
Note : Often the combination of the AS-F and the MGC-F provides enhanced call control services, such as network
announcements, 3-way calling, call waiting and so on. Rather than connecting the AS-F and MGC-F with a protocol,
vendors often use an API between the AS-F and MGC-F when they are implemented in a single system. In this
embodiment, the AS-F is known as a “Feature Server.”
AGS-F Characteristics :
•   Encapsulates and transports V5 or ISDN signaling
    protocols (e.g. SS7) using The interface from the AGS-F to the
    other entities is a protocol interface when the AGF-F and
    MGC-F or other AGF-F are not co-located (e.g. SIGTRAN)
•   SIGTRAN to the MGC-F
•   For mobile networks, encapsulates & transports BSSAP or
    RANAP signaling protocols (e.g. SS7) using SIGTRAN to the MGC-F
•   One MGC-F may serve many AGS-Fs
•   Applicable protocols include SIGTRAN, M3UA, IUA and
    V5UA over SCTP

9). Application Server Function (AS-F)
The AS-F is the application execution entity. Its primary role is
to provide the service logic and execution for one or more
applications and/or services.
The primary role of the AGS-F is to encapsulate and transport
V5 or ISDN (wireline), or BSSAP or RANAP (wireless) signaling
protocols over IP.

R-F/A-F Characteristics :
•   Encapsulates and transports PSTN signaling protocols (e.g.
    SS7) using SIGTRAN to the MGC-F or another SG-F
•   For mobile networks, encapsulates and transports PSTN/
    PLMN signaling protocols (e.g. SS7) using SIGTRAN to the
    MGC-F or another SG-F
•   The interface from the SG-F to the other entities is a
    protocol interface when the SG-F and MGC-F or other SG-
    F are not co-located (e.g. SIGTRAN)
•   One SG-F can serve multiple MGC-Fs
•   Applicable protocols include SIGTRAN, TUA, SUA and
    M3UA over SCTP
•   May perform signaling and media event detection
    functions such as DTMF detection,
•   on/off-hook detection, voice activity detection, etc.
•   Manages its own the media processing resources required
    to provide the functionality mentioned above
•   May have the ability to perform digit analysis based on a
    map downloaded from the MGC-F
•   Provides a mechanism for the MGC-F to audit the state and
    capabilities of the endpoints
•   Is not required to maintain the call state of calls passing
    through the MG-F; the MG-F only maintains the connection
    state of the calls it supports
•   A SIP phone is an MG-F and MGC-F in a single box
•   A SIP-capable gateway is an MG-F and MGC-F in a single
•   “Hair pinning” of a call by the MG-F directed toward the
    source network may occur under control of the MGC-F
•   Applicable protocols include RTP/RTCP, TDM, H.248 and
10). Service Control Function (SC-F)
•   SC-F exists when the AS-F controls the service logic of a
•   For this reason, the ISC recognizes a separate SC-F.
    Examples of SC-F protocols include : INAP, CAP and MAP;
    open APIs include JAIN and Parlay.

11). Media Gateway Function: (MG-F)
•   MG-F interfaces the IP network with an access endpoint or
    network trunk, or a collection of endpoints and/or trunks.
•   MG-F serves as the gateway between the packet and
    external networks, such as the PSTN, mobile network, etc.
•   For example, the MG-F could provide the gateway
    between :
      • an IP and circuit network (e.g. IP to PSTN),
      • or between two packet networks (e.g. IP to 3G or
Its primary role is to transform media from one transmission
format to another, most often between :
 • circuits and packets,
 • ATM packets and IP packets, or
 • analog/ISDN circuits and packets as in a residential

MG-F Characteristics:
• Always has a master/slave relationship with the MGC- F
  that is achieved through a control protocol such as MGCP
• May perform media processing functions such as media
  transcoding, media packetization, echo cancellation, jitter
  buffer management, packet loss compensation, etc.
• May perform media insertion functions such as call
  progress tone generation, DTMF generation, comfort noise
  generation, etc.
12. Media Server Function (MS-F)
The MS-F provides media manipulation and treatment of a
packetized media stream on behalf of any applications. Its
primary role is to operate as a server that handles requests
from the AS-F or MGC-F for performing media processing on
packetized media streams.

MS-F Characteristic:
•   Support for multiple codecs and transcoding
•   Support for control by multiple AS-Fs or MGC-Fs
•   Support for multiple concurrent capabilities:
      o digit detection
      o streaming of tones and announcements (any
         multimedia file)
      o algorithmic tone generation
      o recording of multimedia streams
      o speech recognition
      o speech generation from text
       o speech generation from text
       o mixing (conference bridge)
       o fax processing
       o voice activity detection and loudness reporting
       o scripted combinations of the above
•   Performs under the control of an AS-F or MGC-F through a
    control protocol, with either :
•   tight coupling (resource control) or loose coupling
    (function invocation or scripts)
•   Applicable protocols include SIP, MGCP and H.248
MGC Building Blocks
         Network Example
• Wireline
• All-IP Network
• VoIP Tandem Switching
• POTS Carried over
• Access Network (V5/ISDN) over IP
• Cable Network (e.g. PacketCable™) over IP
• VoDSL and IAD over IP
• Wireless (3GPP R99 Special Case NGN)
• Wireless (3GPP R2000 General Case all IP)
• WCDMA Mobile Network
3G Third Generation
3GPP 3G Partnership Project (UMTS)
AAA Authentication, Authorization and Accounting (IETF)
A-F (Call) Accounting Function (ISC)
ADSL Asymmetric Digital Subscriber Line
AG Access Gateway
AGS-F Access Gateway Signaling Function (ISC)
AIN Advanced Intelligent Network
AN Access Network
API Application Programming Interface
AS Application Server
AS-F Application Server Function (ISC)
ATM Asynchronous Transfer Mode
ATU-R ADSL Terminal Unit-Remote
AuC Authentication Center (GSM)
BG Border Gateway
BICC Bearer Independent Call Control (ITU Q.1901)
BSSAP Base Station Subsystem Application Part (GSM, 3GPP)
CA Call Agent
CA-F Call Agent Function (ISC)
CAMEL Customized Applications for Mobile Network Enhanced Logic (GSM)
CAP CAMEL Application Part (GSM, 3GPP)
CLI Common Language Infrastructure
CM Cable Modem
CMTS Cable Modem Termination System (DOCSIS, PacketCable)
COPS Common Open Policy Protocol (IEFT RFC 2748)
CPL Call Processing Language
DiffServ Differentiated Services
DOCSIS Data Over Cable System Interface Specification
DQoS Dynamic Quality of Service
DSL Digital Subscriber Line
DSLAM DSL Access Multiplexer
DTMF Dual Tone/Multiple Frequency
ENUM E.164 Numbering (IETF RFC 2916)
FS Feature Server
GGSN Gateway GPRS System Node (GPRS, 3GPP)
GK Gatekeeper
GMSC Gateway Mobile Services Switching Center (GSM, 3GPP)
GPRS General Packet Radio Service
GSM Global System for Mobility
HFC Hybrid Fiber/Cable
HLR Home Location Register (GSM, 3GPP)
HSS Home Subscriber System (3GPP)
HTTP Hyper Text Transport Protocol (IETF)
IAD Integrated Access Device
IETF Internet Engineering Task Force
IN Intelligent Network
INAP Intelligent Network Application Protocol
ISDN Integrated Services Digital Network
ISUP Integrated Services Digital Network User Part (SS7)
ITU International Telecommunications Union
IUA ISDN User Adaptation
IVR Interactive Voice Response
IW-F Inter-working Function (ISC)
JAIN Java Application Interface Network
LDAP Lightweight Directory Access Protocol (IEFT)
M3UA MTP3 User Adaptation (IETF SIGTRAN)
MAP Mobile Application Part (GSM, 3GPP)
MEGACO MEdia GAteway COntrol (IETF RFC 3015 or ITU H.248)
MG Media Gateway
MGC Media Gateway Controller
MGC-F Media Gateway Controller Function (ISC)
MGCP Media Gateway Control Protocol (IETF RFC 2705)
MG-F Media Gateway Function (ISC)
MMAS Mobile Multimedia Application Server (3GPP)
MMCS Mobile Multimedia Call Server (3GPP)
MPLS Multi-Protocol Label Switching
MS Media Server
MSC Mobile Services Switching Center (GSM, 3GPP)
MS-F Media Server Function (ISC)
MTA Multimedia Terminal Adaptor (PacketCable)
NCS Network Call/Control Signaling (PacketCable)
NGN Next Generation Network
OEM Original Equipment Manufacturer
OSA Open Service Access (3GPP)
OSS Operational Support System
PBX Private Branch eXchange
PLMN Public Land Mobile Network (3GPP, UMTS)
POTS Plain Old Telephone Service
PSE Personal Service Environment (3GPP)
PSTN Public Switched Telephone Network
QoS Quality of Service
RAN Radio Access Network
RANAP Radio Access Network Application Part (3GPP)
R-F (Call) Routing Function (ISC)
RFC Request For Comment (IETF)
RG Residential Gateway
RSVP Resource ReSerVation Protocol (IETF)
RTCP Real Time Transport Control Protocol (IETF)
RTP Real Time Transport Protocol (IETF RFC 1889)
SC-F Service Control Function (ISC)
SCP Service Control Point
SCTP Stream Control Transmission Protocol
SDP Session Description Protocol
SG Signaling Gateway
SG-F Signaling Gateway Function (ISC)
SGSN Serving GPRS System Node (GPRS, 3GPP)
SIGTRAN SIGnaling TRANsport (IETF M3UA, IUA, SUA, V5UA Drafts)
SIP Session Initiation Protocol (IETF)
SIP-T SIP For Telephony (IETF Draft)
SNMP Simple Network Management Protocol
SPS-F SIP Proxy Server Function (ISC)
SS7 Signaling System 7
TCAP Transaction Capability Application Part (SS7)
TDM Time Division Multiplexing
TG Trunk or Trunking Gateway
TGCP Trunking Gateway Control Protocol
TLA Three-Letter Acronym
TRIP Telephony Routing over IP (IETF RFC 2871)
UMTS Universal Mobile Telecommunications System
V5UA V5 User Adaptation (IETF SIGTRAN)
VAD Voice Activity Detection
VLR Visitor Location Register (GSM, 3GPP)
VoDSL Voice over DSL
VoIP Voice over IP
WAP Wireless Application Protocol
WCDMA Wideband Code Division Multiple Access
XML Extensible Markup Language
   •       Example of Implementation
                                                                                                            (MGC)      Application
 Analog phone
                                                           PSTN Networks                         SS7oIP
                  N ES
                  S OF


ISDN Terminals                                               Switch         STP                                                Management
                                                                      SS7                                                        System
                                S ES

                                       S OF
                                       N ES

       xDSL Terminals                                                                             Trunk
Analog phone                                               Access

           N ES
           S OF
           IX R

ISDN Terminals                                                                    IP Customer
                                                                                  Premises                  IP Core Networks
                         N ES
                         S OF
                         IXR                                                           S ES
                                                                                        IEM N
                                                                                        IXDO F
                                                                                       N R

  xDSL Terminals                                                                      IP Clients and

   [2] Sumber : Siemens, Surpass                          Packet Local Switch

Sun MicroSystem version
Softswitch Components
1. Media Gateway Controller (MGC) / Call Agent
   (CA) / Softswitch
   • Hold call processing rules by controls SG & MG
     (to perform the job) : call set up & tear down.
   • Interfaces to the OSS
   • Interworking with other networks

2. Signaling Gateway (SG)
   • Gateway between SS7 network and the nodes
     managed by the Softswitch
3. Media Gateway (MG)
    • Handels the media data payload including
    • Supports legacy telephony (PSTN) : CAS/ISDN
3. Media Server

  • Perform peripheral functions such as DSP, IVR

4. Feature Server)
  • Provide all the revenue generating features and
    services like billing, multi-party conferencing etc.
  • It uses the resources and related services located
    on other components of the Softswitch
  • It may also support certain services to meet
    certain implementation necessity e.g.:
    Functional Requirement and
        System Charactiristic
1. Softswitch (MGC/CA)
 • Responsible for bridging with different characteristics,
   including the PSTN/SS7, and IP networks :
     –   Validation and initiation before establishing phone connections
     –   Managing voice and data traffic throughout the various networks
 • It is often referred to as a ―Call Agent‖ (because of its Call
   control messaging functions).
 • Also is referred to as a ―Media Gateway Controller‖
   (because of its Media Gateway Control functions). These
   names are used interchangeably.
 • MGC, MG and SG represents the minimum configuration of a
a. Functional Requirements
•   Call control engine
•   Voice call establishment protocols : H.323, SIP
•   Media control protocols : MGCP, Megaco/H.248
•   Class of service and quality of service control
•   SS7 control protocol: SIGTRAN (SS7 over IP)
•   SS7 processing (when using SigTran)
•   QoS related protocol message handling such as RTCP
•   Routing, including :
     –   Routing component : local dial plan (E164 to port mapping)
     –   Digit analysis overlap and/or enblock signaling
     –   Digit translation support for IP, FR, ATM and other networks
• Call Detail Records (CDR) for billing
• Bandwidth management control
• Provisioning for Media Gateways:
     –   Assignment and real time configuration of DSP resources
     –   DS0 channel assignments
     –   Voice transmission (coding, compression, and packetization)
• Provisioning for Signaling Gateways:
    –   SS7 variants
    –   Process Timers
    –   Linkset configuration
    –   Point code or routing configuration
• Gatekeeper registration

b. System Characteristic
 • It is CPU intensive. A multi-processor system is most
 • A large in-memory database required. It’s enable multiple
   processes to live in memory.
 • It deals mostly with IP traffic. A sufficient amount of high-
   speed connectivity may be required.
 • A dual-redundancy approach for network connectivity is
   normally required.
• It requires support for a variety protocols.
• Disk storage is primarily used for logging.
• It must be highly available. There are several methods for
  achieving this.

2. Signaling Gateway (SG)
 Creates a bridge between the SS7 network and an IP
 Under the control of the Gateway Controller a Signaling
  Gateway causes a Softswitch to appear like an ordinary
  SS7 point code (SS7 node) in an SS7 network.
 The Signaling Gateway only handles SS7 signaling;
 Media Gateway handles the voice circuits established by
  the SS7 signaling mechanism.
 SIGTRAN defines a suite of protocols and User Adaptation
  layers for ransporting signaling information over IP-based
 If SigTran is used as the protocol between the Gateway
  Controller and the Signaling Gateway, then only MTP1,
  MTP2, and SigTran reside on the Signaling Gateway. In this
  case, MTP3 and higher protocol stacks will reside on the
  Gateway Controller.
A Signaling Gateway usually supports the following layers :
• SCTP, which is responsible for reliable signaling
  transport, streaming, congestion avoidance and control
• M3UA, which supports the transport of ISUP, SCCP, and
  TUP messages over IP
• M2UA, which supports congestion control and the
  transport of MTP3 messages
• IUA, which supports the Q.931/Q.921 interface
• M2Peer, which supports the MTP3-to-MTP2 interface
  • If a proprietary event interface is used between the
    Gateway Controller and the Signaling Gateway, then the
    entire SS7 protocol stack resides on the Signaling
    Gateway (including MTP3, ISUP, SCCP, and TCAP).
  • A signaling gateway establishes the protocol, timing, and
    message-framing requirement of the SS7 network, as well
    as the functional equivalents within the IP network.
  • Refer to Appendix B for background details on Signaling
    and SS7.

a. Functional Requirements
   A Signaling Gateway must support the following functions :
   • It must provide physical connectivity to the SS7 network
     via a TI/El or Tl/V.35 physical connection
   • It must be able to transport SS7 information between
     Gateway Controller and Signaling Gateway via an IP
  • It must provide a transmission path for voice, video, and
    optionally data. (Data transmission may be supported
    within the Media Gateway)
  • Provide Highly Available SS7 operation for
    telecommunication services

b. System Characteristic
 A Signaling Gateway has the following system characteristics:
 • It is I/O intensive, but not very CPU intensive.
 • A maximum amount of memory should be available to hold
    state information, configuration information, the point code
    map, alternate routes, etc.
 • A disk storage is primarily used for logging; a small
    capacity may be adequate.
•   The Ethernet interface (to the IP network) may require dual
•   It may interface with the SS7 network by using a T1/E1,
    with a minimum 2 D-channels, and a maximum 16 D-
•   Performance and flexibility can be increased using a H.110
    or H.100 bus.
•   High Availability is a requirement, multiple Signalling
    Gateways or signalling links are available. Redundancy is
    built into SS7 networks by design.
3. Media Gateway (MG)
      Provides transport media (voice, data, fax, and video)
       between the IP packet network and the PSTN.
      Typically, DSP perform :
         analog-to-digital conversion
         voice/audio code compression
         echo cancellation
         silence detection
         suppression
         comfort noise generation
         out-of-band DTMF signal transport, etc.
      DSPs control the translation of voice into packets for the
       IP network
      Appendix C has more details on Media encoding of
       digitized audio.
 a. Functional Requirements

A Media Gateway should support the following :
• Transmission of voice data using the RTP transmission
• DSP resource and T1 timeslot allocation under control of
   the Gateway Controller, as a result of MGCP or MEGACO
   messages. SIP is preferred, although optional.
• Manage DSP resources to provide voice and packet
   functions for the services mentioned above.
• Support for legacy protocols such as loop-start, ground-
   start, E&M, CAS, QSIG, and ISDN over T1.
• Support of T1 clear channel configuration for transferring
   voice traffic payload in SS7 networks.
• Managing T1 resources and links.
• Hot plug of DSP and Tl cards.
 •     Redundancy and HA strategies for Media Gateway
 •     Ability to scale the Media Gateway including the ports,
       cards, and nodes without impacting other Softswitch

b. System Characteristic
     A Media Gateway has the following system characteristics:
     • It is I/O intensive; I/O scalability is required.
     • The maximum amount of memory may be necessary to
        hold state information, configuration information, MGCP
        messages, DSP libraries, etc.
     • A disk storage is primarily used for logging; a small
        capacity may be adequate.
• The Ethernet interface (to the IP network) may require
• The interface to the TDM network may need to span several
  T1/E1 interfaces.
• Densities of 120 ports (DS0’s) are normal. Typically these
  interfaces incorporate onboard DSPs to perform several
  types of compression.
• H.110 bus can be leveraged for localized system flexibility.
• A High Availability configuration may scale the user density.
4. Media Server
    • Usually separately from the Feature Server because
      Media Server applications involve specialized media
      processing (must support high-performance DSP hw).

  a. Functional Requirements
    A Media Server may have the following functional
    • Basic voicemail functionality
    • Integrated fax mailbox, notification may use e-mail or pre-
      recorded message.
    • Voice recognition capability if provided, e.g voice activity
      dialing can route a voice-activated call by using database
      lookups, and then route the call.
    • Video conferencing capability including video conference
      setup and transmission via H.323 or SIP.
   • Video conferencing capability including video
     conference setup and transmission via H.323 or SIP.
   • Speech-to-text capability to send text to a person’s
     email account or pager device by using voice input.
   • Speech-to-Web feature converts key words into text
     strings, which can be used for Web lookup or Web
   • Unified messaging is the ability to read voice, fax, and
     email messages via the same user interface.

b. System Characteristic
   A Media Server has the following system characteristics:
   • It is CPU intensive, as it may handle a lot of MGCP
      message traffic.
   • Several implementation options exists with local or co-
      located DSP resources or native CPU
• The maximum amount of memory may be required for in-
  memory databases, large local caching buffers,
  extensive libraries, and so forth.
• A disk storage used for logging can be of small capacity.
  If DSP libraries, speech patterns are stored, adequate
  storage is needed on Disk.
• It handles mostly IP traffic, if DSP resources are used for
  speech processing.
• It typically can be clustered (n+m type) for high
5. Feature Server
    • Feature Server is defined as an application-level
      server that hosts, a set of business services.
    • This may be also referred to as a Business Application
    • Since most feature servers host business services and
      communicate over IP networks, there are no
      softswitch-specific constraints on how to divide or
      group application components.

    • These value-added services can either be part of the
      call agent, or they can be deployed separately.
    • The applications communicate with the Call Agent
      through protocols such as SIP, H.323 and others.
    • These applications are usually hardware-independent
      but they may require extensive databaseaccess.
Examples of feature services:
• 800 number service—This service provides lower call
  charges for high levels of incoming calls.
  Translation of the 800 number to an actual target
  telephone number is provided by the 800 number
  database. The called party pays for these calls.
• 900 number service—This service provides
  information, contest call-in, and public opinion polls.
  The caller pays for these calls.
• Billing service—Call detail records (CDRs) are created
  by the call agent. The CDR program has many billing
  features, such as the ability to apply rates based on
  line type, time-of-day, etc.
  This service may offer the customer access to their
  billing record on demand via a voice call or a Web
• H.323 GateKeeper—This service supports routing
  across domains. Each domain (which is handled by a
  Softswitch) can register its phone numbers and trunk
  access numbers with the GateKeeper via H.323. The
  GateKeeper provides the call routing service (and digit
  translation) for each H.323 endpoint.
  The GateKeeper may provide billing and bandwidth
  management control to the Softswitch.
• Calling card services—This service allows a caller to
  access long distance service via a traditional
  Billing, PIN authentication, and routing support are
  provided by the service.
• Call authorization—This service establishes Virtual
  Private Network (VPN) using a PIN authorization.
• VPN—This service establishes virtual private (voice)
  networks. These are private networks which can offer the
  following features:
   • Dedicated bandwidth (via leased high-speed networks)
   • Guaranteed Quality of Service (QoS)
   • Enhanced features that do not necessarily adhere to
   • Private dialing plans
   • Secure encrypted voice transmission
• Centrex services—With this service, the service provider
  offers features usually found only in large central offices and
  PBX systems, such as:
   • Basic features: call waiting, forward, transfer, park, hunt,
       and voicemail
   • Convenience features: autodial, speed dial, calling line ID
   • Customized private dialing plans
   • Secure encrypted voice transmission
• Call center services:
   • Automatic call distribution, which efficiently routes
      incoming calls to multiple destinations
   • Answering agents based on a configured policy
      management scheme
System Characteristic
A Feature Server has the following system characteristics:
• It typically requires moderate to high CPU utilization. This is
  dependent upon the specific application.
• A large onboard memory is desirable for low latency.
• It may require CPU scalability to scale with traffic and
  application enhancements.
• Several databases may be located at the Feature server.
• Adequate disk storage may be budgeted for the application
  needs depending on the nature of the application. 100GB to
  2TB range for a typical voice mail bank.
• The Ethernet interface (to the IP network) may be
  implemented with dual redundancy.
        Call Progression – Events, Messages,
                       Protocols                                       Long Distance Carrier
                                                                           IP Networks
                                                                 Softswitch                Softswitch
                    PSTN                                           (MGC)                     (MGC)                                                PSTN
                                 Networks                                                                                         SS7
                                               SG       TG                                                  TG          SG      Networks                   Analog
         phone                                                                                                                                             phone
                      Switch      STP                                                                                                STP        LE
                     Switch      STP                                                                                                STP        LE

             Dial Tone

                                                                                                                                                               < 700 ms
                                                              Reply           SIP Invite
                                                                                                 Reply                        IAM
                                                                                                                                           ACM      Ringing

                                                                                                                                                               to answer

                                                                              SIP 183                                                               Off-hook
                                        ACM             ACM                                                                                ANM
             Ring Tone     ACM                                                                              ANM              ANM

                                                                              SIP 200            Modify

                                                                                                                                                               < 105 ms
                                                              Modify                             Reply
                                        ANM                   Reply
                                                                          RTP Stream

              On-hook      REL
                                                          Substract             Bye
                                                            Reply                               Substract
                                                                                                 Reply                       REL
                                                                                                                             RELC          RELC
                                                                              SIP ACK                     RELC
                                        RELC           RELC
                                                SIgTran                        SIP-T                          SIgTran
                                  SS7                      Megaco                              Megaco                               SS7
[4] Sumber : Sun Microsystems, The Softswitch, January 2002
Example of Implementation :
Soffswitch Integration using Compact PCI Technology (cPCI)

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