Method and apparatus for distributed MTP Level 2 architecture

Details Method and apparatus for distributed MTP Level 2 architecture Method and apparatus for distributed MTP Level 2 architecture

1999-12-08

2004-02-03

Ngo, Ricky (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S410000, C370S467000

Reexamination Certificate

active

06687251

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to SS7 signalling and more particularly to a method and apparatus for distributing the Message Transfer Part (MTP) Level 2 functionality between a Signalling Gateway and a Media Gateway.
BACKGROUND TO THE INVENTION
The following acronyms will be used throughout this document:
AERM
Alignment Error Rate Monitor
ACK
Acknowledge
ACM
Address Complete Message
AM
AERM Monitoring
ANSI
American National Standards Institute
ATM
Asynchronous Transfer Mode
BERT
Bit Error Rate Testing
CC
Congestion Control
CCS
Common Channel Signalling
CRC
Cyclic Redundancy Check
DAEDR
Delimitation, Alignment, Error Detection Rcceive
DAEDT
Delimitation, Alignment, Error Detection Transmit
DL2P
Distributed L2 Protocol
DPS
Distributed Protocol Stack
EM
Emergency Monitoring
FISU
Fill-In Signal Unit, a signalling unit complying with
MTPL2
HDLC
High-Level Data Link Control
IAC
Initial Alignment Control
IAM
Initial Address Message
IN
Intelligent Network
INH
Inhibit
ISUP
ISDN User Part
ITU
International Telecommunication Union
LSC
Link State Control
LNP
Local Number Portability
LSSU
Link Status Signal Unit, a signalling unit complying
with MTPL2
LL-MTPL2
Lower Level - Message Transfer Part Level 2, a portion
of the Distributed MTP Level 2 Architecture
Mb/s
Megabit-per-second
MG
Media Gateway
MSU
Message Signal Unit, a signalling unit complying
with MTPL2
MTP
Message Transfer Part
MTPL1
MTP Level 1
MTPL2
MTP Level 2
MTPL3
MTP Level 3
OM
Operational Measurement (OM-MG Operational
Measurement located at the Media Gateway, OM-SG
Operational Measurement located at the
Signalling Gateway)
OSI
Open Standards Interconnect
PSTN
Public Switched Telephone Network
RC
Receive Control (RC-SG Receive Control located at
Signalling Gateway, RC-MG Receive Control located
at Media Gateway)
REM
Remote
RTB
Re-Transmission Buffer
RTP
Reliable Transport Protocol
SCPs
Service Control Points
SG
Signalling Gateway
SIB
Status Indicator Busy (used by LSSUs)
SIE
Status Indicator Emergency (used by LSSUs)
SIF
Signalling Information Field
SIN
Status Indicator Normal (used by LSSUs)
SIO
Status Indicator Out of Alignment (used by LSSUs)
SIOS
Status Indicator Out of Service (used by LSSUs)
SIPO
Status Indicator Processor Outage (used by LSSUs)
SS7
Signalling System 7
SSPs
Service Switching Points
STPs
Signalling Transfer Points
SU
Signalling Unit
SUERM
Signalling Unit Error Rate Monitor
TB
Transmission Buffer
TDM
Time Division Multiplexed
TXC
Transmit Control (TCX-SG Transmit Control located at
Signalling Gateway; TCX-MG Transmit Control
located at Media Gateway)
UL-MTPL2
Upper Level - Message Transfer Part Level 2, a portion
of the Distributed MTP Level 2 Architecture
UDP
User Datagram Protocol
UNI
Un-Inhibit
VoIP
Voice over IP
A Public Switched Telephone Network (PSTN) is, conventionally, comprised of two networks—a voice/data network and a signalling network. The signalling network carries information for call set-up and tear down. The Common Channel Signalling System #7 (CC-SS7) protocol is used for call set-up and tear down.
As is known in the art, the PSTN provides users with a dedicated, end-to-end circuit connection for the duration of each call. The circuits are reserved between the originating call, tandem switches (if any), and the terminating switch based on the called party number. In a typical Intelligent Network (IN), such as the North American SS7 network, to set-up a basic call circuit between a calling party at a first Service Switching Point (SSP), and a called party, having an out-of-switch number (i.e., the called party is at a second SSP), SS7 messages are exchanged between the two SSPs using the SS7 network.
Recent developments, notably the popularity of the Internet, have increased the use of Voice over IP (VoIP) communication. Voice over IP switches need to interface to the existing PSTN networks (voice and signalling) to allow PSTN phones to use the VoIP network. A VoIP switch would interface to the PSTN Voice network using a Media Gateway. The Media Gateway provides the translation between Time Division Multiplexed (TDM) data and IP packet data. This VoIP switch would interface to the PSTN Signalling network using a Signalling Gateway. The Signalling Gateway provides the translation between SS7 and IP.
In a quasi-associated SS7 signalling network, the Signalling Gateway would connect to the local STP mated pair using A-links. In a fully associated SS7 Signalling network, the signalling gateway would connect directly with the SSPs using F-links. In the fully associated network signalling case, the SS7 signalling link is usually carried over the same facilities as the voice trunks. Since these voice trunks terminate on the media gateway, external circuitry (e.g. channel banks) are required to extract the signalling channel and route it to the signalling gateway. Moreover, since the media and signalling gateways are typically geographically quite dispersed, the equipment associated with transmitted the extracted signalling channel to the signalling gateway is expensive.
Accordingly, it is desired to provide a system which addresses some of these shortcomings.
SUMMARY OF THE INVENTION
This invention distributes the MTP Level 2 functionality between the Signaling Gateway and the Media Gateway. It allows F-links in a fully associated SS7 signaling network to be terminated on the Media Gateway and the SS7 messages to be passed between the Media Gateway and the Signaling Gateway over IP.
According to one aspect of the invention, there is provided a method providing distributed Message Transfer Part (MTP) functionality over an Internet Protocol (IP) network, said method comprising: at a first media gateway: receiving conventional MTP signalling units from a first network element; removing repeated MTP signalling units from said MTP signalling units received; either before or after said removing, encapsulating received MTP signalling units into data packets to form a reduced signalling unit packet stream; transmitting said reduced signalling unit packet stream to a signalling gateway; receiving at said signalling gateway said reduced packet stream at said signalling gateway; transmitting packets encapsulating MTP signalling units to one of said first media gateway and a second media gateway, said transmitted packets being responsive to said received reduced signalling unit packet stream; receiving at said one of said first media gateway and said second media gateway said packets transmitted by said signalling gateway; and at said one of said first media gateway and said second media gateway, re-creating conventional MTP signalling units based on said routed packets and transmitting said re-created conventional MTP signalling units to one of said first network element and a second network element.
According to a further aspect of the invention there is provided a Voice over Internet Protocol (VoIP) switch providing a distributed Message Transfer Part Level 2 (MTPL2) protocol, said VoIP switch comprising: a plurality of media gateways, each of said media gateways in communication with a conventional SS7 physical link, said conventional SS7 physical link in communication with a network element; a signalling gateway; an IP network providing IP communication between said plurality of media gateways and said signalling gateway.
According to a still further aspect of the invention there is provided a media gateway comprising: a receiver for receiving a contiguous stream of signalling units from a network element; a filter for discarding repeated signalling units in said received stream; an encapsulated data transmitter adapted to transmit data encapsulating said signalling units over a packet switched network; an encapsulated data receiver adapted to receive encapsulated data encapsulating signalling units from a packet switched network; a processor adapted to: encapsulate signalling units forming said stream of signalling units either before or after said discarding by said filter; and de-encapsulate signalling units received by said encapsulated data receiver and gene

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