Hss Megaco in 3g Core Network

8/14/2019 Hss Megaco in 3g Core Network

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HSS MEGACO In 3G Core Network


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COPYRIGHT INFORMATION

Copyright Hughes Software Systems, 2004

All information included in this document is under a license agreement. This publication and its contentsare proprietary to Hughes Software Systems. No part of this publication may be reproduced in any form orby any means without the written permission of

Hughes Software Systems Ltd.Plot 31, Electronic CitySector 18, Gurgaon 122015Haryana (INDIA)Tel: +91-124-2346666/2455555Fax: +91-124-2455100/2455101E-mail: [email protected]

Visit us at: http://www.hssworld.com

TRADEMARKS

All the brand names and other products or services mentioned in this document are identified by thetrademarks or service marks of their respective owners.

DISCLAIMER

The information in this document is subject to change without notice and should not be construed as

commitment by Hughes Software Systems. Hughes Software Systems assumes no responsibility ormakes no warranties for any errors that may appear in this document and disclaims any implied warrantyof merchantability or fitness for a particular purpose.


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Cont ent s

1 . 3 G W i r e l e s s N e t w o r k s 51.1. Benefits 51.2. Architecture 5

2 . D e c o m p o s e d A r c h i t e c t u r e f o r 3 G C o r e N e t w o r k 72.1. MEGACO: A preferred choice for CBC Interface in BICC Decomposed Model 92.2. Decomposed MSC Architecture as per 3G Specifications 92.3. Summary 11

3 . H S S S o l u t i o n F o r M E G A C O i n 3 G 1 23.1. HSS MEGACO Stack Features 123.2. HSS MEGACO Stack Specifications Conformance 14

4 . C o n c l u s i o n 1 7

5 . R e f e r e n c e s 1 8


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F i g u r e s

F i g u r e 1 : 3 G N e t w o r k A r c h i t e c t u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

F i g u r e 2 : D e c o m p o s e d B I C C A r c h i t e c t u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

F i g u r e 3 : M S C N e t w o r k D i a g r a m . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 0


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1. 3 G Wireless Networks

In 1998, the International Telecommunications

Union (ITU) called for Radio Transmission Technology

(RTT) proposals for IMT-2000 (originally called Future

Public Land Mobile Telecommunications Systems

(FPLMTS)), the formal name for the Third Generation

standard. Many different proposals were submitted.

The DECT and TDMA/ Universal Wireless

Communications organizations submitted plans for the

RTT to be TDMA-based, whilst all other proposals for

non-satellite based solutions were based on wideband

CDMA. The main submissions were Wideband CDMA(WCDMA) and cdma2000. The ETSI/ GSM players

including infrastructure vendors such as Nokia and

Ericsson backed WCDMA while the North American

CDMA community, led by the CDMA Development

Group (CDG) including infrastructure vendors such as

Qualcomm and Lucent Technologies, backed

CDMA2000.

The proposed IMT-2000 standard for third

generation mobile networks (or 3G) globally is a

CDMA-based standard that encompasses the

interfaces - wideband CDMA, CDMA2000 and the

Universal Wireless Communication (UWC-136)

interfaces. This will ensure a globally available wide

range of services including telephony, paging,

messaging, Internet and broadband data.

Universal Mobile Telephone System (UMTS) is the

widely used European name for 3G. UMTS is being

implemented in various phases:

! 3GPP Rel 1999: Basically an evolution of the GSM

voice services that benefit from 3G technologies.

! 3GPP Rel 4: Provides a migration for operators

from Rel 1999 circuit switched domain to an IP-

based core network infrastructure.

! 3GPP Rel 5: It specifies voice and multimedia

services on an end-to-end IP transport provided

by an enhanced General Packet Radio Service

(GPRS) in the packet-switched domain.

3G Systems are intended to provide a global

mobility with wide range of services including

telephony, paging, messaging, Internet and

broadband data. Third Generation (3G) mobile devices

and services will transform wireless communications

into on-line, real-time connectivity. 3G wireless

technology will allow an individual to have immediate

access to location-specific services that offer

information on demand. Because of its potential to

provide high-speed data services, 3G is likely to

emerge as an alternative to existing broadband access

technologies such as ADSL and cable.

1.1. Benefits

3G systems are designed for multimedia

communication between mobile users. Third

Generation (3G) provides a new network architecture

that will offer mobile users high-speed connectivity of

the order of 2 Mbps. These systems provide the

following benefits:

! High degree of commonality in design worldwide.

! Enhanced Bit rate as ATM is used as the core

technology.

! Variable bit rate to offer bandwidth-on-demand.

(Again an ATM feature).

! Multiplexing of different services (e.g. Voice,

video, data etc) with different QoS requirements

on a single connection

! Support for asymmetric up-link and down-link

traffic rate

! Worldwide roaming capability.

! Provides better power control so that UE has to

consume less power

1.2. Architecture

3G wireless networks consist of a Radio Access

Network (RAN) and a core network.

The core network consists of a packet-switched

domain and a circuit-switched domain. The PDN

includes 3G SGSNs and GGSNs, which provide the


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same functionality that they provide in a GPRS

system, and the CSN includes 3G MSC for switching of

voice calls. RAN functionality is independent from the

core network functionality. The access networkprovides a core network technology independent

access for mobile terminals to different types of core

networks and network services.

The Radio Access Network consists of new

network elements, known as Node B and Radio

Network Controllers (RNCs). Node B is comparable to

the Base Transceiver Station in 2G wireless networks.

RNC replaces the Base Station Controller. It manages

radio resources, handover control and providessupport for the connections to circuit-switched and

packet-switched domains. The interconnection of the

network elements in RAN and between RAN and core

network is over Iub, Iur and Iu interfaces based on

ATM as a layer 2 switching technology.

Data services run from the terminal device over

IP, which in turn uses ATM as a reliable transport with

QoS. Voice is embedded into ATM from the edge of

the network (Node B) and is transported over ATM

out of the RNC.

The Iu interface is split into 2 parts: circuit

switched and packet-switched. The Iu interface is

based on ATM with voice traffic embedded on virtual

circuits using AAL2 technology and IP-over-ATM for

data traffic using AAL5 technology. These traffic types

are switched independently to either 3G SGSN fordata or 3G MSC for voice.

Figure 1: 3G Network Architecture


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2. DecomposedArchitecture for 3G Core

Network

One of the main features of the Release 4 of

UMTS specification was to evolve the R99 circuit

switched domain (CS domain) in a transport network

independent manner to allow the use of different

transport resources (ATM, IP). It provides the

flexibility for PLMN internal transport that allows IP

based transport mechanisms. In the case of ATM or IP

transport, the passage of compressed speech at

variable bit rates is possible through the CS core

network.

Transport and control functions of the CS domain

network are separated to enable service provision by

different means of transport resources (ATM, IP) for

better transport resource efficiency and convergence

with the PS domain transport. ITU-T Q1902 "Bearer

Independent Call Control" (BICC) architecture has

been the basis of all the 3G Core Network

standardization efforts in the CS domain.

BICC has following logical elements:

! Call Serving Function (CSF): CSF provides

services associated with the narrowband service.

It provides the interworking functionality for

incoming and outgoing call signals, indicates the

call characteristics to the peer CSF, and invokes

the Bearer Control Nodal Functions (BCF)

necessary to transport the narrowband bearer

service across the backbone network.

! Bearer InterWorking Function (BIWF): This

functional entity provides bearer control functions

(BCF) and media mapping/switching functions

within the scope of a Serving Node (SN). A BIWF

contains BCF and MMSF. These are described

next.

! Bearer Control Function (BCF): BCF provides

common control of the bearer switching function,

the communication capability with its associated

CSF, and the signaling capability necessary for

the establishment and release of the bearer to its

peer. The Call Bearer Control (CBC) signaling is

used between the CSF an BCF entities in case

these are physically separate. The CBC protocol is

specified in ITU-T Q.1950.

! Media M apping/ Switching Function (MMSF):

This entity provides for controlled interconnection

between two bearers and optionally the

conversion of the bearer from one technology

and adaptation/encoding technique to another.

! Media Control Function (MCF): This functional

entity interacts with the BCF to provide the

control of the bearer and MMSF. The BICC

architecture allows for the interface between the

BCF and MCF to be open (the BMC interface),

but the splitting of the bearer interworkingfunctionality split into the BCF and MMSF is not

considered to be the responsibility of the BICC

standardization group.

.


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CSF

BCFMCF

BCF

MMSF

BIWF

CBC

BMC

BICCCS2

Bearer ControlProtocol

Bearer

Figure 2: Decomposed BICC Architecture


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2.1. MEGACO: A preferred choice forCBC Interface in BICCDecomposed Model

The, the H.248 Media Gateway Control Protocol

(MEGACO) was found to be a strong contender for the

protocol to be used as the CBC interface during the

course of development of BICC CS2 for the following

reasons:

! The MEGACO connection/context model is generic

in nature and provides explicit control to MGC

(CSF in SN) to control both the incoming and the

outgoing sides of the connection. CSF also has

the flexibility to monitor the internal through-

connection between incoming and the outgoing

bearers. This flexible connection handling allows

support of different call models and different

media processing purposes.

! The generic connection framework of MEGACO is

easily extensible through the concept of

packages, which define the necessary attributes

(events/signals/properties/statistics) Procedural

guidelines with reference to the specific need for

any particular package have also been defined.

! MEGACO caters to advanced and feature specific

needs via the rich capability set of the protocol,

supporting multi-media terminations, providing

support for varied media interconnection

scenarios in supplementary services, multi-party

conferencing and electronic surveillance

requirements.

! Megaco supports the concept of Virtual MGs thatallows dynamic sharing of MGW physical node

resources. A physical MGW can be partitioned

into logically separate virtual MGWs/domains

consisting of a set of statically allocated

Terminations. .

2.2. Decomposed MSC Architectureas per 3G Specifications

As mentioned above 3GPP uses BICC as the base

architecture and this BICC suite in turn refers to

MEGACO for interfacing MSC server (CSF functionality)

with the MGW (BIWF/BCF functionality).

The CS core network shall employ the MSC

server, GMSC server and Media gateways

MSC Server

The MSC server mainly comprises the call control

and mobility control parts of a GSM/UMTS MSC as

described in 3GPP TS 23.002. It is also integrated with

a VLR to hold the mobile subscriber's service data and

CAMEL related data. The MSC server terminates the

user-network signaling (see 3GPP TS 24.008) and

translates it into the signaling over the Nc interface. It

also terminates the signaling over the Mc interface

with the media gateway. The MSC server controls the

parts of the call state model that pertain to connection

control for media channels in an MGW. It also

provides the 'Call Control Function' in the BICC model.

GMSC Server

The GMSC server mainly comprises the call

control and mobility control parts of a GSM/UMTS

GMSC as described in 3GPP TS 23.002. The GMSC

server terminates the signaling over the Nc interface

and the call control interfaces to the external

networks. It also terminates the signaling over the Mc

interface towards the media gateway. The GMSC

server controls parts of the call state model that

pertain to connection control for media channels in an

MGW. It also contains the 'Call Control Function' in the

BICC model

Media Gateway

The media gateway terminates the signaling over

the Mc interface from the (G)MSC servers. It also

terminates the bearer part of the signaling over the Iu

interface and the Nb interface. The bearer signaling

from RNC to Media gateway over the Iu interface is

defined by ALCAP signaling procedures. The media

gateway contains bearer terminations and media


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manipulation equipment (e.g. transcoders, echo

cancellers, or tone senders). It may perform media

conversion and framing protocol conversion.

The network diagram shown below represents

the MSC, which is distributed into MSC Server and

Media Gateway

MediaGateway

MediaGatewayN

b

MSCServer

GMSCServerN

c

McMc

UTRAN

PSTN

Iu

(Sign

alling

)PSTN

(Sign

alling

)

PSTN

(Bea

rer)Iu

(Bea

rer)

Figure 3: MSC Network Diagram

The Mc reference point describes the interfaces

between a MSC server and a Media Gateway which as

mentioned above is based on Megaco.

The 3GPP document TS 29.232 describes the Mc

interface. The Media Gateway Controllers covered in

this specification are the MSC server and the GMSC

server. The BICC architecture as described in 3GPP TS

23.205 and 3GPP 29.205 defines the usage of this

protocol.

BICC tailored the MEGACO H.248 protocol by

adding a few packages (Q.1950) and Annex C native

tags. 3GPP further tailored it for MSC-MGW by adding

the following 3G specific packages for handling 3G

specific features.

! 3GUP (User Plane) package

The MGC uses this package to indicate to the

MGW that the Iu (or Nb) User Plane is used

between the RNC (or distant MGW) and theMGW. The package is sent in the Establish

bearer, Modify Bearer Characteristics and Prepare

bearer procedures.

! Circuit Switched Data package and

Enhanced Circuit Switched Data package

These packages contain the information needed

to be able to support GSM and UMTS Circuit

Switched Data from the media gateway. When

the Media Gateway Controller initiates the

"Establish Bearer" procedure, the "Prepare

Bearer" procedure, the "Modify Bearer" procedure

or the "Reserve Circuit" procedure, it shall

provide the PLMN BC ("plmnbc" property above)

for the termination on the mobile side and the


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ISDN BC for the termination on the fixed side. For

a mobile-to-mobile call, it shall provide the PLMN

BC on both terminations. The presence of the

PLMN BC property may trigger the use of the

IWF.

! TFO package

Tandem Free Operation (TFO) is intended to

avoid the traditional double speech

encoding/decoding in MS to MS (GSM), MS to UE

(GSM/3G) or UE to UE (3G) call configurations.

The key advantages of Tandem Free Operation

are

! Improvement in speech quality by avoidingthe double transcoding in the network;

! Possible savings on the inter-PLMNtransmission links, which are carrying

compressed speech compatible with either

32/16/8 kbps sub-multiplexing schemes,

including packet switched transmission;

! Possible savings in processing power in thenetwork equipment since the transcoding

functions in the Transcoder Units are

bypassed;

! Possible reduction in the end-to-endtransmission delay.

This package defines events and properties for

Tandem Free Operation (TFO) control.

! 3G Expanded Call P rogress Tones Generator

Package and Flexible Tone Generator

Package

These packages extend "Expanded Call Progress

Tones Generator Package. These packages add

a new toneId for CAMEL prepaid warning tone to

inform the party that the Max Call Period

Duration is about to expire.

! Modification Of Link Characteristics Bearer

Capability Package

This package contains an event, which when

requested by the MGC, will cause the MG to

notify the MGC that modification of the link

characteristics is allowed. This notification is

typically generated when the bearer has been

established.

! Cellular Text telephone Modem Text

Transport Package

The CTM text transport package is intended for

enabling robust real time text conversation

through a voice channel primarily intended for

communication over mobile networks. This

package includes the mechanisms needed to

transport T.140 text conversation streams [19] in

a voice channel environment, using the CTM

Cellular Text Telephone Modem. The transport

mechanism allows for alternating transmission of

voice and text.

! IP transport package

This package contains the information needed to

be able to support IP transport from RAN to the

media gateway.

2.3. Summary

As 3G networks are migrating to use packet-

based transport mechanisms for data within the

network, transmission of voice media is also migrating

over to this Packet Network. With the introduction ofthe Softswitch-based Architecture, where the Mobile

Switching Center (MSC) is disintegrated into a call

control MSC Server (Softswitch) and switching Media

Gateway(s) interfacing through the MEGACO protocol

, network operators worldwide stand to gain many

benefits .


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3. HSS Solution ForMEGACO in 3G

HSS was an early adopter of MEGACO and

demonstrated MEGACO based applications as early as

September 1999 (Fall Interop, Atlanta). HSS

MEGACO-based solutions were released in March

2000 and have been integrated by customers to build

Media Gateway and Media Gateway Controller

applications

3.1. HSS MEGACO Stack Features

Based on HSS Advanced Architecturefor Protocol Engineering (AAPE )Framework

! Scalable Implementation of:

! Stack dimensioning at init-time or compile-time as per user requirements

! Number of Associations! Number of Transactions! Number of Commands requests and

responses.

! Platform independence:

! Suited to Single and distributed targetenvironments

! Portable on any Operating System withminimum efforts. Sample Ports provided for

Solaris, WinNT, Linux and VxWorks platforms

! Software Architecture Independence:

! Suited to horizontal/vertical architectures! Flexible Function or Message-based (C-

structure or Octet based) interface between

the client application and the core stack.

! Multi-thread safe to support variedarchitectures

Conforms to MEGACO (RFC 3525 + IGMay 2003)Encoding/Decoding and Parameter

validation services! Support for ABNF based Text Encoding

! Support for ASN based Binary Encoding/decoding

! Supports encoding/decoding in both long and

short token format

Transport Management Support

! Includes complete ALF support (can optionally be

disabled through a compile time option). This

includes handling retransmissions, provisional

responses, and storage of responses for long

timer duration and three-way handshake.

! Supports multiple underlying Transport Protocols

like UDP/TCP/ATM (MTP3B, SSCOP, AAL5), SCTP

and M3UA.

! Support synchronous and asynchronous interface

with transport layer.

! Simultaneous support for various transport

!

Association Management Support

! Allows multiple associations with peer

! MG can communicate with multiple Call Agents

! Call Agent can control multiple MGs

! Executes procedures for MG-MGC control

interface as defined by the protocol.

! Initiates registration at MG (through the

ServiceChange command defined by the protocol)

! Notifies application of registration when at MGC

! Support for multiple secondary MGCs

! Protection against Restart Avalanche

! Negotiation of Protocol version

! Recovery procedures in case of peer failure

detection.

! Support for redundant switchover

! Modification of transport parameters

! Deletion of existing association


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! API provided at MGC end to change the state of

association

! Unknown MG discovery and DHCP support on IP

transport.

Transaction Management Support

! Ensures in sequence execution of commands in a

transaction

! Command collation into transactions.

! Handling of mandatory and optional commands

Flexible to be used for MG and MGC applications

ATM transport support as per draft-ietf-megaco-h248i-00. Stack supports! Transport over SSCOP, AAL5 and MTP3b.

! In case of multiple links in MTP3b, user can

specify the link Id for every transaction to be sent

to peer.

! ALF support for all the transports

Session Description Protocol Support!

IN SDP as per RFC 2327! ATM SDP as per RFC 3108

! IPBCP SDP support as per Q.1970

! T.38 SDP support as per MEGACO Annex F and

T.38 Fax Communication over IP.

Support for Packages! Support for nearly 100 packages. Tool provided

to easily add/edit/delete packages from current

Megaco Stack package database

! Support for Packages as per Q.1950: ITU-T

Q.1950 + Annex A1 changes

! Support for 3GPP Packages and stack procedures

as per TS 29.232 v5.3.0

! Support of the basic packages as per RFC 3015

Support for Statistics collection! API Statistics

! Protocol Statistics

! Internal Event Statistics

! Error Statistics

Support for Error Reporting! Multiple Error Levels (Critical, Major, Minor)

! Multiple Error Types

Descriptor Isolation! Implementations needing less code footprint can

disable descriptors through provided compile

time options if they are not required in the

profiles they use

Other Features! Flexible to be used for MG and MGC applications

! Supports MIB: draft-ietf-megaco-mib-02.txt


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3.2. HSS MEGACO Stack Specifications Conformance

TS 29.232Section #

TS 29.232MEGACOrequirements

HSS MEGACO stack implementation

4 UMTS capabilityset

It can be made part of a MEGACO profile.

The profile would go in the Service Change (registration request)towards the MGC

5 Namingconventions

The stack supports these naming conventions for both Text andASN

6 Topologydescriptor

Supported as required (for handover and lawful interception.)

7 Transaction timers All MEGACO transaction related timers are supported

8 Transport All the required transport mechanisms are supported. Rel 3.0contains transport support for IP(TCP,UDP)/SCTP/M3UA/ATM(MTP3B, SSCOP, SAAL UNI, NNI and AAL5).

9 Multiple VirtualMG.

MEGACO stack supports the Multiple Virtual MG architecture

10 Formats and

codes

All these codes are finally encoded and decoded as per the

MEGACO protocol. The HSS stack supports them.11 Mandatory

Support of SDPand H.248 AnnexC informationelements

HSS MEGACO stack is one of the very few stacks to support allthe following:

! IN SDP

! ATM SDP

! Annex C native tags

13 BICC packages Supports all the mandatory and optional packages as defined inthe ITU-T Q.1950.

The user can easily add more packages. Easy editing anddeletion also possible.

14 H.248 standard

packages

All the basic packages are supported

14.1 Call independentH.248 transactions

All the procedures in Table 2 are supported

14.1.1 MGW Out ofservice/Maintenance Locking

Supported. Use of Delay is optional


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TS 29.232Section #



14.1.2 MGWCommunicationUp

Supported

14.1.3 MGW Restoration Supported. Use of Delay is optional

14.1.4 MGW Register Supported

14.1.5 MGW Re-register Supported

14.1.6 (G)MSC ServerOrdered Re-register

Supported

14.1.7 (G)MSC ServerRestoration

Supported. Any reason can be specified

14.1.8 Termination Out-of-Service

Supported.

14.1.9 TerminationRestoration

Supported.

14.1.10 Audit Value Supported

14.1.11 Audit Capability Supported

14.1.12 MGW CapabilityChange

Supported

14.1.13 (G)MSC ServerOut of Service

Supported

14.1.14 MGW ResourceCongestionHandling Activate

Supported. Commands for both the procedures can be encodedby the respective MGC/MG

14.1.15 MGW ResourceCongestionHandling Indication

Supported. Commands for both the procedures can be encodedby the respective MGC/MG

14.2 Call related H.248transactions

All the procedures in Table 3 are supported

BICC procedures described in Q.1950 supported.

Also, supported is the note, the procedures defined in table 3can be combined with another procedure in the same action.

This means that they can share the same contextID andtermination ID(s).


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TS 29.232Section #



15 UMTS packages The following mandatory packages supported ( 3GPP TS 29.232

V5.3.0)

! 3GUP (User Plane) package! Circuit Switched Data package! TFO package! 3G Expanded Call Progress Tones Generator Package! Modification Of Link Characteristics Bearer Capability Package! Cellular Text telephone Modem Text Transport Package

! Enhanced Circuit Switched Data package

.


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4. Conclusion

MEGACO stack being a part of the HSS Next

Generation Product Portfolio can be combined with

other solutions in the VoIP and 3G domain to quickly

turn-around solutions for emerging Next Generation

3G networks.


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5. References

This document uses the following references:

1. 3GPP TS 23.292 "3rd Generation Partnership

Project; Technical Specification Group Core

Network; Media Gateway Controller (MGC)

Media Gateway (MGW) Interface

2. 3GPP TS 23.205: "3rd Generation Partnership


Network; Bearer Independent CS Core Network

Stage 2"

3. 3GPP TS 29.205: "3rd Generation Partnership


Network; Application of Q.1900 series to Bearer

Independent CS Network architecture; Stage 3"


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The comprehensive set of software building blocks from Hughes

Software Systems consists of both frameworks and protocol stacks for

the Voice over Packet domain.

Frameworks Stacks

Softswitch Framework MEGACO stack

Media Gateway Framework MGCP stack

Gatekeeper Framework SIP stack

SIP Server Framework H.323 stack

Mini Gateway Framework SIGTRAN stack

The comprehensive set of software building blocks from Hughes

Software Systems consists of both frameworks and protocol stacks for

the Voice over Packet domain.

Hughes Software Systems is a keysupplier of communication

technologies for Voice over Packet,Intelligent Networks and High-speed

Mobile Networks, and is fully focussedon the needs of its customers to build

Next Generation Networks.

HSS USA, East CoastGermantownTel: +1-240-453-2498BostonTel: +1-617-547-6377DallasTel: +1-972-517-3345

HSS USA, West CoastSan JoseTel: +1-408-436-4604Los AngelesTel: +1-323-571-0032; 571-0114

HSS EuropeMilton Keynes, UKTel: +44-1908-221122GermanyTel: +49-6155-844-274FinlandTel: +358 40 8290977

HSS IndiaGurgaonTel: +91-124-2346666/2455555BangaloreTel: +91-80-2286390

Hughes Software SystemsPlot 31, Electronic City, Sector 18, Gurgaon 122 015, Haryana, India

Tel: +91-124-2346666/2455555, Fax: +91-124-2455100/

Hss Megaco in 3g Core Network

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