WO2001015486A1 - Method and apparatus for improved call setup in a multimedia packet network - Google Patents

Abstract

Events and optional signals are added to the protocol that is used by a media gateway controller (MGC) (301, 302, 401, 402) to control a media gateway (309, 310, 414, 415). These events and signals allow call setup to be monitored by an MGC without actively waiting for call setup, thus avoiding the overhead involved with processing a wait state. The invention can be used to control call processing exclusively, or it can be used in conjunction with transaction pending messages.

Description

METHOD AND APPARATUS FOR IMPROVED CALL SETUP IN A

MULTIMEDIA PACKET NETWORK

DESCRIPTION

Technical Field

This invention is related to multimedia packet networks. Specifically,

this invention relates to a mechanism to allow such a packet network to

more effectively carry telephony messages, and to more efficiently interface

with the public switched telephone network (PSTN).

Background Art

Evolution of the PSTN has accelerated in recent years; however,

most of the PSTN still operates on circuit switched, time division multiplexed

(TDM) connections. Integrated services digital network (ISDN) bearer

channels often provide transport. In parallel with the PSTN, a packet based

data network has evolved. This data network has largely been used for

Internet traffic and data networking. Although these networks have been

mostly separate until recently, the two networks are starting to merge. The

merger of these networks requires that voice traffic be carried over packet

networks, and further that such packet networks be able to seamlessly integrate with traditional circuit switched networks, as the two types of

networks may carry different call legs of the same call.

FIG. 1 illustrates a typical TDM, PSTN call. Caller 101 places a call

to callee 105. The call goes through end office A, 102, over some type of

trunk bearer channel to toll office 103, then to end office B, 105, and finally

to the callee. Such calls may pass through multiple toll offices, or may be

connected directly from one end office to another. In any case, a path of

circuits for the call is maintained throughout the call. Signaling between

offices is typically provided by an ISUP (ISDN user part) connection. ISUP

signaling is well understood and is standard in the telecommunications

industry. For more information on ISUP signaling, see the various Interna¬

tional Telecommunications Union (ITU) Recommendations pertaining to

telephone signaling, including Q.761 , Q.764 and Q.931 , the most recent

versions of which at the time of filing this application are incorporated herein

by reference.

FIG. 2 illustrates a call which is similar to the TDM call of FIG. 1 ;

however, in this case, the call is transported from one end office to another

(called switch offices, 202 and 204, in this case) via a packet switched

network 203. This fact is, in theory, transparent to caller 201 and callee 205.

ISUP+ or SIP+ provides signaling in this case. ISUP+ is essentially the

same as ISUP except that ISUP+ signals contain extra fields for packet or

cell based network information. An International Telecommunications Union (ITU) recommendation was proposed for ISUP+ as of the filing date of this

application as ITU Q.BICC. SIP stands for "session initiation protocol" and is

a well-known standard. SIP and SIP+ are described in document RFC

2543, published by the Internet Engineering Task Force (IETF), March, 1999

which is incorporated herein by reference. SIP and SIP+ provide the same

type of signaling for control of calls, but are more oriented towards packet

based networks.

The network of FIG. 2 has been conceptualized for some time, and

standards groups and conference groups have written extensively about

how to make such a network work in everyday use. In order for the call leg

which is handled by the packet network to seamlessly connect with the call

legs handled by TDM switching offices, media provided by one type of

network must be converted into media provided by the other. This conver¬

sion is referred to as circuit emulation services (CES) in an ATM network.

The device that provides this conversion is called a media gateway (MG). In

the network of FIG. 2, a media gateway handles each end of the bearer

connection through packet network 203. The media gateway terminates

bearer media streams from both the switched circuit TDM network, and the

packet network. The media gateway and the network it serves may be

capable of processing audio and video (hence the term "multimedia packet

network"). The media gateway is capable of full duplex media translations.

It may also provide other features such as conferencing. Each media gateway is associated with a media gateway controller

(MGC). The media gateway is "dumb" in that it does not have call process¬

ing capabilities. The call processing capabilities for the network reside in the

MGC. An MGC provides the signaling for call control and controls the call

state of a media gateway. The protocol used by the MGC to control the MG

is called the media gateway control protocol (or the "Megaco" protocol).

Megaco is an application layer protocol which is also described in ITU

Recommendation H.248, which shares a common text with the IETF Internet

Draft "Megaco Protocol," and which is incorporated herein by reference.

The "Megaco Protocol" Internet Draft first became an IETF working docu-

ment in March, 1999. Within the Megaco protocol, session description

protocol (SDP) can be used to describe bearer channel terminations, which

are being controlled by the MGC's. SDP is described in document RFC

2327, published by the IETF, April, 1998, which is incorporated herein by

reference. Throughout the rest of this disclosure we will refer to Megaco as

"Megaco/H.248."

Despite the fact that the theoretical workings of a network like that

shown in FIG. 2 have been widely explored, such networks have seen

relatively little everyday use. The reason is that there are still problems to

be overcome before such networks exhibit the same very high quality of

service for voice traffic that users of the PSTN have come to expect. Once

such problem stems from the fact that there is no dedicated physical path for a call through a packet network, and therefore a wait state must be provided

so that each node in the network waits for an entire bearer path to be estab¬

lished before timing out.

A packet switched network, used for transport of audio and video

media streams, is typically based on asynchronous transfer mode (ATM)

frame relay (FR), and Internet protocol (IP) technologies. Public ATM

networks generally operate according to the user network interface (UNI).

The UNI is described in the book, "ATM User Network Interface (UNI)

Specification Version 3.1 " by the ATM Forum, published by Prentice Hall

PTR, June, 1995, which is incorporated herein by reference. An update to

the UNI version 3.1 , "ATM User-Network Interface (UNI) Signaling Specifi¬

cation 4.0" was published by the ATM Forum in July, 1996, and is incorpo¬

rated herein by reference. For private ATM networks, the private network to

network interface (PNNI) describes the ATM interface. PNNI is covered in

the ATM forum document "PNNI addendum for the network call correlation

identifier" published by the ATM forum in July 1999, which is incorporated

herein by reference.

In ATM, fixed-length cell carry packetized data. Each cell that is sent

through the network has a virtual channel identifier, and other addressing

information; however, each node in the network handles many cells that are

associated with different media streams. Therefore, there is no provision for

a node to control cells for a call throughout a call path. Media gateways and other nodes in the path must actively wait for call setup throughout the

network, consuming processing power and making it difficult to maintain an

appropriate level of quality of service. What is needed is a way to more

directly monitor the status of a connection, so that valuable processing

power is not used to process wait states.

Disclosure of Invention

The present invention solves the above described problem by pro¬

viding new signals and events to be used in call setup of a connection

oriented bearer path so that no wait state is required during the path setup.

These signals and events allow processors in the network to switch to other

tasks instead of actively waiting for connections to be completed. The

signals and events also provide for simpler and more efficient network

implementation. The invention can be used exclusively to control call setup.

Or it can be used in combination with transaction pending messages.

A media gateway and its MGC at either or both ends of a bearer path

can make use of the invention. In describing the invention, we use "originat¬

ing" and "terminating" to refer to the calling and called ends of the call path,

respectively. We use the terms "near-end" and "far-end" to refer to the end

of the path relative to where the particular process being discussed is taking

place, usually relative to where key messages are being exchanged by a

media gateway and an MGC. The terms "near-end" and "far-end" are used independently of the terms "originating" and "terminating." In connection

with call setup, the terms "forward" and "backward" refer to which end

initiates the bearer connection through the packet network. "Forward" refers

to a process where the originating end sets up the connection, and "back¬

ward" refers to a process where the terminating end sets up the connection.

In the Megaco/H.248 protocol, a signal is a request from the MGC to

the media gateway to apply some process to network terminations. In the

case of TDM terminations, the signals can be in-band signals, such as

tones, or out-of-band signals such as those specified by ISUP. In any case,

these signals are relayed from the media gateway to the MGC where they

are processed. In the case of ATM terminations, most signals are UNI

signals or messages. An event is a notification sent from the media gate¬

way to the MGC when a requested state is reached. In the preferred em¬

bodiment, the invention is implemented with new events and signals to be

used in the Megaco/H.248 protocol. However, the fundamental operation of

these events and signals is independent of the underlying bearer network.

The signals and events can be mapped to any underlying network such as

ATM or frame relay.

According to the invention, a media gateway receives a command

from its MGC to add a connection for the bearer path and the command

specifies a connection available signal for notifying the MGC if and when the

connection is available. We abbreviate "connection available" as "coav." Coav is both a signal and an event. When an ATM network is used for

transport, the command from the MGC triggers the media gateway to send

an ATM UNI setup message to the far-end media gateway. The media

gateway then initializes the connection with the far-end media gateway. If

there is no connection at all for the call, this initialization step involves setup

and connect messages being exchanged. In most cases an "add" command

is used to direct a media gateway to establish a bearer path, however, some

other command, for example, a "move" command can be used. Also, as will

be explained in more detail later, there could be a connection which has

already been established by the far-end media gateway, in which case, the

initialization step simply involves identifying the connection and correlating it

with the current call. Once the bearer path has been established, the coav

event is sent to the MGC.

If the connection cannot be established, a "connection not available"

or "cont" signal is specified. Like coav, cont is both a signal and an event.

The MGC can also send cont to the media gateway to disconnect or release

the path. The media gateway in this case can respond with the connection

not available event. The media gateway will notify the MGC when the

connection is disconnected at any time during the call, even if the discon¬

nection occurs because of a network failure. In this case, a notice of failure

event may also be sent from the media gateway to the MGC. As part of the process described above, an optional continuity check

can be performed across the bearer path. This check involves one of the

media gateways sending a continuity check message to the other media

gateway. The media gateway receiving the continuity check then responds

with a continuity response. In this way, a bearer path can be confirmed at

the end of the setup process to ensure the reliability of the call being han¬

dled.

The invention is implemented by software in combination with the

hardware of the media gateway and media gateway controller. The software

which implements many aspects of the present invention can be stored on a

media. The media can be magnetic such as diskette, tape or fixed disk, or

optical such as a CD-ROM. Additionally, the software can be supplied via a

network. A media gateway is essentially a switching system containing

switching fabrics, a computing module, network interfaces, and other re¬

sources. The network interfaces are implemented by adapters which are

connected to switching fabrics to allow access to the system from the net¬

works. Input/output modules or adapters allow software to be loaded and

various maintenance functions to be performed. A computing module

contains a processor and memory that execute the software and provide the

means to control the operation of the media gateway to implement the

invention. The media gateway controller can also be a switching system, but

would more typically be a type of workstation containing a bus such a

personal computer interconnect (PCI) bus. A workstation that typically

implements the invention includes a plurality of input/output devices and

adapters for connection to the necessary networks. A system unit includes

both hardware (a central processing unit and memory) and software which

together provide the means to implement the media gateway controller.

The invention operates in a network in which media gateways act as

endpoints to a call leg being carried on a bearer channel through the net¬

work. Each media gateway is controlled by and connected to a media

gateway controller. An MGC uses the previously mentioned Megaco/H.248

protocol to control its media gateway, and the invention provides an exten¬

sion to the Megaco/H.248 protocol.

Brief Description of Drawings

FIG. 1 conceptually illustrates a prior-art telephone connection

through the public switched telephone network.

FIG. 2 conceptually illustrates a telephone connection similar to that

of FIG. 1 , except that one call leg goes through a packet switched network.

FIG. 3 is a block diagram of one network in which the present inven-

tion is used. FIG. 4 is a block diagram of a different network in which the present

invention is used.

FIG. 5 is a flowchart illustrating the method of the present invention.

FIG. 6 is a flowchart illustrating the method of the present invention in

which a transaction pending message is used.

FIG. 7 is an example message flow diagram that illustrates an exam¬

ple of how the present invention is used.

FIG. 8 is another example message flow diagram that illustrates an

example of how the present invention is used..

FIG. 9 is another example message flow diagram that illustrates how

the present invention is used.

FIG. 10 is another example message flow diagram that illustrates the

use of the present invention.

FIG. 11 is another example message flow diagram that illustrates the

use of the present invention.

FIG. 12 is another example message flow diagram that illustrates the

use of the present invention.

FIG. 13 is a block diagram of a media gateway that implements the

present invention.

FIG. 14 is drawing of one implementation of a media gateway con-

trailer that is used with the present invention. FIG. 15 shows an example of a media which stores software that

implements the present invention.

Mode(s) for Carrying Out the Invention

FIG. 3 illustrates one architecture in which the present invention can

be used. According to FIG. 3, telephone 304 is where a call originates.

Telephone 303 is where a call terminates. Telephones 303 and 304 are

shown as illustrations only. In reality, they can be directly connected to the

media gateways or can be connected through extensive TDM networks. In

the latter case, lines going into the media gateways would actually be TDM

trunks. Media gateway A, 310, is the originating media gateway and media

gateway B, 309 is the terminating media gateway. The media gateways of

FIG. 3 convert voice to ATM. We therefore refer to this network architecture

as voice and telephony over ATM, or "VTOA" architecture, however, the

same architecture can be used for Internet protocol (IP) telephony. Media

gateway controller A, 301 , controls media gateway A. Media gateway

controller B, 302, controls media gateway B. Alternatively both media

gateways can be controlled by a single MGC. Media gateway A includes

TDM endpoint 305 and packet endpoint 306. Media gateway B includes

TDM endpoint 308 and packet endpoint 307. Packet network 311 serves as

the transport network through which bearer channels are established to

interconnect calls between the two media gateways. This network and the endpoints to which it is connected can be frame relay, ATM, IP, or some

other type of packet network. For illustrative purposes, most of the discus¬

sion refers to an ATM network. The media gateway controllers communi¬

cate with each other via ISUP+, SIP, or SIP+. It is also possible to use a

nonstandard protocol, specific to the manufacturer of the media gateway

controllers and media gateways.

Either a media gateway or a media gateway controller can generate

the end-to-end call identifier (EECID), as determined by the network de¬

signer. The EECID is used to identify a call leg uniquely across the ATM

network, regardless of the number of nodes used in completing the network

path. The EECID allows the MGC's, the media gateways, and any nodes in

the bearer path to identify the call uniquely. Note that media gateway

controller A, 301 , controls media gateway A, 310, using the Megaco/H.248

protocol, an application layer protocol for media gateway control. Likewise,

media gateway controller B, 302, controls media gateway B, 309, using the

same Megaco/H.248 protocol. The media gateway or media gateway

controller at either end can generate the EECID, regardless of which end is

the originating end for the call and which end is the terminating end for the

call.

FIG. 4 illustrates a slightly different architecture in which the invention

is used. According to FIG. 4, media gateway controller A, 401 , controls

media gateway A, 415, using the Megaco/H.248 protocol and media gate- way controller B, 402, controls media gateway B, 414, using the

Megaco/H.248 protocol. In FIG. 4, 403 is the originating telephone and 404

is the terminating telephone. ATM network 411 serves as the transport

network. Again, any of the media gateway controllers or media gateways

can generate an EECID to identify calls being handled by the network. The

main difference between the network of FIG. 4 and the network of FIG. 3 is

that the network of FIG. 4 supports digital subscriber loop, or DSL. DSL

comes in various types such as aDSL, sDSL and hDSL, and so "xDSL" is

used to designate DSL in FIG. 4. In this case each media gateway includes

a splitter; 405 in the case of media gateway 415 and 410 in the case of

media gateway 414. TDM terminations 406 and 408 and ATM endpoints

407 and 409 each reside in their respective media gateways and allow both

data and TDM voice to be transported across the ATM network 411. The

splitters 405 and 410 split the voice from the data. The data connection

from user terminal 412 is completed through splitter 405 to ATM termination

407 in the case of media gateway A. The data connection from user termi¬

nal 413 is completed through splitter 410 to ATM termination 409 in the case

of media gateway B. Otherwise, the operation of the network in FIG. 4 is

essentially the same as the operation of the network of FIG. 3.

Many aspects of the invention are implemented through enhance-

ments to the previously mentioned Megaco/H.248 protocol. The connection

model for the protocol describes logical entities, or objects, within the media gateway that can be controlled by the media gateway controller. The model

relies on extractions, primarily terminations and contexts. A termination

sources and/or sinks one or more media streams. A context is an associa¬

tion between a collection of terminations.

In general, an "add" command is used to add terminations to con-

texts. A termination may be moved from one context to another with a

"move" command. A termination exists in, at most, one context at a time. A

non-packet termination can exist outside of a context. Property values can

be set for terminations by including appropriate descriptors as parameters to

the various commands in the Megaco/H.248 protocol. A termination in a

context may have its value changed by the "modify" command. Other

commands that are important to the implementation of the invention will be

discussed later.

As previously mentioned, according to one aspect of the invention an

end-to-end call identifier (EECID) is associated with a call, and with a bearer

path through the packet network, which completes a call leg. When we say

the EECID is associated with a call or a path, we mean that all of the nodes

and devices involved in maintaining a call leg are aware of which call to

which specific Directory Numbers (DN's), or other user address are associ¬

ated with each packet of information which flows through the relevant part of

the network. Depending on the type of underlying networks and/or protocols the EECID can be carried across the network in various ways. Details of

some possible signaling will be discussed later.

It is preferable to include the EECID in the Megaco/H.248 protocol as

part of the stream descriptor in addition to the local control descriptor, local

descriptor, and remote descriptor. These descriptors are all part of the

stream parameter, a known part of the Megaco/H.248 protocol. It is also

possible to include the EECID in the Megaco/H.248 protocol as part of a

session descriptor protocol (SDP) term. SDP is a well-known protocol,

described in the previously cited IETF RFC 2327, which is used to describe

packet terminations, such as IP and ATM terminations within the

Megaco/H.248 protocol.

In addition to including the EECID in the Megaco/H.248 protocol, it

must be included in other protocols and/or data streams that allow the

network to communicate. It is especially important to include the EECID in

the ATM cell structure used in the ATM transport network, since the media

gateways on the ends of the ATM networks form the ends of the bearer

channel carrying the part of the call leg which passes through the packet

network. Assuming the packet network shown in FIG. 3 and FIG. 4 is an

ATM network implemented according to the UNI standard promulgated by

the ATM forum, there is a choice of possible places in an ATM cell where

the EECID can be placed. The network prefix is a fixed, required part of the

cell, used for routing. The EECID could be placed in the ATM user part. ATM network routing only uses the first thirteen-byte network prefix of the

ATM address. The following 7 bytes of the user part can be used to trans¬

port the EECID. Another possible place for the EECID is the ATM subad-

dressing. The subaddressing field usually only has local significance and

can be dropped if it is unused. It can be adapted to implement the EECID of

the present invention. Most non-UNI 4.0 compliant ATM networks are

currently implemented without using a generic information trans¬

port/information element (GIT IE) field; however, the GIT IE field will proba¬

bly be the best place for the EECID as that field becomes more widely used.

The EECID must also be included in ISUP+ messages, if ISUP+ is

used between the two gateway media controllers. FIG. 8 shows an ISUP+

message. Field 801 contains the ISUP information and 802 contains the

ISUP+ information, which is essentially directed towards packet based

networks, and includes an application transport mechanism field. The

EECID is preferably included in the transport mechanism field.

If SIP+ is used between the two media gateway controllers, the

EECID is carried as a term in the session description protocol (SDP).

Syntax for the session description protocol, which includes the EECID, is

"c=eecid: (eecid value)" or "a=eecid: (eecid value)." Note that the terms

"c=eecid: (eecid value)" or "a=eecid: (eecid value)" need not be used if the

stream descriptor is used to specify the EECID in the Megaco/H.248 proto¬

col. As previously discussed, either an MGC or a media gateway some¬

where in the network selects the EECID, that is, determines a value for the

EECID, before it can be associated with a call leg. The EECID can be any

arbitrary number that is unique so as to allow correlation of the end-to-end

network path between the two media gateways. The choice of the value for

the EECID has implications for the call flow. In some cases, the value can

only be derived by the network, as with the NCCI as discussed above.

Preferably, the value of the EECID is not dependent on the underlying

network architecture. A simple way to create an EECID is to simply have

the device that is determining the EECID, generate a random number. It is

also possible to use a number that is already associated with some part of

the network.

A possible value to use for the EECID is a session-ID or call-ID. The

session-ID is a random number passed from the MGC to the media gate¬

way. The media gateway can then pass the session-ID to the far end media

gateway as an EECID with its initial setup message. The session-ID can

also be passed through ISUP+ messages. The session-ID would not be

able to be used if the media gateway is to generate the EECID. The call-ID

is similar to the session-ID. Both are specified to identify a call solely within

an MGC or media gateway.

Finally, the most preferable value for the EECID, assuming a numeri¬

cal value, which is associated with the network, is used, is the ATM sup- ported backward network connection identifier (BNC-ID). The BNC-ID is

four bytes long and is generated by the media gateway. The media gateway

sends the BNC-ID to its media gateway controller for forwarding to the far-

end. The BNC-ID is included in the setup command between media gate¬

ways to correlate the call.

According to our invention, a package with a signal, called a "connec¬

tion available" (coav) signal, that explicitly requests the establishment of the

packet network path, an event, called a "connection available" (coav) event,

that explicitly reports the successful completion of the path, and an event,

called "connection not available" (cont), that explicitly reports the failure to

establish the requested path can be added to any protocol that is used for

call control in any packet-based network. Similarly, the package would

include a signal, called a "connection not available" (cont) signal, that explic¬

itly requests the release of the packet network path, and an event, called a

"connection not available" (cont) event, that explicitly reports the successful

release of the path. If the invention is used with the Megaco/H.248 protocol,

these signals and events can be used alone, or with an existing provisional

response mechanism implemented through the "transaction pending" com¬

mand. The events and signals that are used with Megaco/H.248 in both of

these alternatives are shown in the following table. The signals and events

symbolized by the "coav" and the "cont" symbols are new according to the

invention. The EECID, previously discussed, is an optional parameter for the coav and cont events, hence it is denoted with the letter O. If a media

gateway fails to release a packet network path, the media gateway sends a

"report failure" (of) event to the media gateway controller. The continuity

check, continuity response, and report failure are also part of this package,

which we call the "packet pipe" event package:

Symbol Definition R S Parameter(s)

coav bearer connection available X BR EECID (O) cont bearer connection not available X BR EECID (O) col continuity check X TO co2 continuity response X TO Duration of report failure X Duration

R specifies that each symbol is part of an event report. BR indicates a brief

tone. TO indicates a timeout tone that stops after the amount of time speci¬

fied by the duration parameter has passed. Note that the col and co2

signal/events are shown for illustrative purposes only to demonstrate the

optional use of continuity testing in conjunction with the process of setting up

a bearer path. These signals are not required to implement the present

invention in Megaco/H.248.

The explicit request alternative has desirable characteristics. In par¬

ticular, the use of explicit signals and events eliminates the need for the

media gateway to maintain the state of an add transaction request. The

explicit embodiment also reduces the transaction request state monitoring in

the MGC, and eliminates the need for the media gateway to potentially send multiple transaction pending replies. The explicit signals and events also

reduce complexity when multiple add commands are used in a single trans¬

action.

When requesting establishment of a network path, an add command

is sent to the media gateway, which then explicitly specifies the "connection

available" (coav) signal and event. When requesting release of a network

path, a subtract command is sent to the media gateway, which then explic¬

itly specifies the "connection not available" (cont) signal and event. The

coav signal is sent only to the ATM termination, which is responsible for the

origination of the setup sequence of the network path. The transaction,

which specifies these requests, is acknowledged on receipt. The media

gateway manifests the coav signal for an ATM network. A notify message of

the coav or the "of event is sent from the media gateway to the MGC upon

a connection becoming available or upon failure to establish the connection,

respectively. Note that the use of the coav and cont signals are optional. If

they are not used, the initiation of the establishment or release of the path is

implied by the add or subtract command, respectively.

The continuity check and response can be used automatically by the

media gateway without an instruction from the MGC. However, these two

events/signals can also be requested by the MGC during call processing.

An additional characteristic of this approach is that embedded signals and events can be used to allow for additional processing to be invoked auto¬

matically for such things as continuity checking of the network path.

An alternative way of making a connection request is based on the

Megaco/H.248 provisional response "transaction pending" reply wait state.

This command is used when a command is received but pending for com-

pletion of processing. The media gateway can respond to the MGC with a

command "transaction pending" response, so that the MGC won't be

blocked for the completion response. When the media gateway finishes

executing the command, it can then send the "transaction reply" message to

acknowledge that the original command has been successfully completed or

has failed. In addition to using the coav signal explicitly, the connection

request is expressed implicitly by the add command. The rationale behind

this approach is that the packet connection does not exist until it is added to

the context. Therefore, the add command implies setting up the bearer

connection.

The EECID is present in either the stream descriptor or the termina¬

tion descriptor for the network path. The media gateway must use the

EECID to determine if it needs to initiate the network path setup. The media

gateway will keep a record of all requests received from other media gate¬

ways for setup of a network path. When the add command is received, the

media gateway will determine if a bearer path setup request with the speci¬

fied EECID has been received. If a network path associated with the EECID exists, then the network path bearer connection already exists and the

correlation is reported back to the MGC via a transaction reply. If no pend¬

ing network path is found with the same EECID, then the path initialization is

invoked. In this approach, there won't be a coav signal and bearer connec¬

tion available event notification. If the media gateway determines that there

will be sufficient delay setting up the bearer connection to cause the trans¬

action request to time out, the media gateway will respond to the media

gateway controller with a transaction pending response. Upon completing

the bearer connection, the media gateway will respond to the MGC with a

transaction reply indicating success or failure of the attempt.

The method described immediately above can incur processing over¬

head in determining whether or not network path setup is required. Another

negative consideration is that there is no mechanism to use embedded

signals and events to allow for automatic processing of subsequent actions

such as continuity checking of the network bearer path. The MGC has to

issue a separate message for continuity checking and response. This

combination at least eliminates the need for the media gateway to search

through pending network path requests to determine if a network path setup

is required. If the coav signal is present, the setup will begin immediately. If

the two embodiments are used simultaneously, accommodations have to be

made to eliminate redundant messaging to report the completion of the add

command and the coav or cont event. Figures 5 and 6 illustrate the overall method of the invention. FIG. 5

is a flowchart that shows the explicit call setup method. At 501 the add

command is sent from the MGC to the media gateway. The add command

can specify any signal and response that the media gateway will under¬

stand. In this case, the signal and response is coav for connection avail-

able, and/or cont for connection not available. At 502 the add command is

confirmed. In this embodiment, the confirmation takes the form of an imme¬

diate transaction reply message to the MGC. At 503 the bearer connection

is initialized.

The bearer connection can be initialized either by the media gateway

setting up the bearer connection, called a forward setup, or the media

gateway simply identifying an existing bearer connection, which has been

set up by a far-end media gateway, called a backward setup. In either case,

the media gateway waits until the bearer path is completely established at

504, and responds with a coav event at 505. The MGC will typically notify

the far-end MGC of this occurrence at 506. An optional continuity check is

shown as being performed at 507. This continuity check consists of a

continuity check message being sent to the far-end media gateway, and a

response being received. If the connection is not available in FIG. 5, a cont

event is sent to the MGC at 508, and the far end is notified at 509. The

process then ends at 510. The flowchart of FIG. 6 illustrates the implicit call setup method used

with the new signals and events of the invention. At 601 an add command

is given by the MGC to the media gateway as before. This time, however,

the media gateway responds with a transaction pending message at 602,

which forces the MGC to wait until it receives further instructions from the

media gateway. At 603, the media gateway again initializes the bearer path.

Only after the bearer path is fully established is the transaction reply sent to

the MGC at 608. A coav event is returned to the MGC at 609. The far-end

is notified at 610. Again, a continuity check is optionally performed at 611.

In FIG. 6, if the bearer path has not been established at 604 after a

time-out at 605, the cont event is returned to the MGC at 606. The far end

is notified at 607. In this case, a continuity check can still be performed at

611 to further check the status of the network.

To illustrate the detail of the invention, Figures 7-12 present detailed

signal flows showing the setup of bearer path connections in a multimedia

packet network. There are literally dozens of possible signal flows, which

could be implemented to make use of the invention. The signal flows pre¬

sented here should be considered as examples only. When we refer to

implicit versus explicit setup, we are using the terminology discussed above

for explicit versus implicit signaling and events. When we refer to forward

setup versus backward setup we are referring to which end of the network is

performing the bearer path setup relative to the originating end of the net- work. If the originating end of the network is also setting up the bearer

connection we have a forward setup. If the originating end of the network is

passing information to the terminating end and the terminating end is setting

up the bearer connection, we have a backward setup. In reference to FIG.

9, all messages are discussed. For the other message flow diagrams, only

new messages, which are important to illustrating the differences between

those examples and previous examples, are discussed. The letters A and B

correspond to the ends of the network path as shown in the network dia¬

grams of Figures 3 and 4.

In Figures 7-12, the TDM termination is a logical representation of a

TDM line and an ATM termination is a logical representation of an ATM

network connection. Although an ATM termination is illustrated in all cases,

the invention is not limited to use of an ATM network for the bearer connec¬

tion. The invention is also applicable with other connection-oriented net¬

works such as frame relay networks.

Turning to FIG. 7, an explicit forward setup is illustrated. At 710, a

notify message indicating an offhook condition is sent from media gateway A

to MGC A. At 711 , MGC A responds with an add command. At 716, media

gateway A replies with a transaction reply. At 713 and 701 , the two media

gateway controllers negotiate connection parameters. At 714, MGC A

sends a pipe connect request to MGC B. In this case, at 702, MGC B sends

an add command to media gateway B with explicit instructions for setting up the bearer path with the connection signal coav and the event coav when

the connection is available. At 703, media gateway B immediately responds

to MGC B with a transaction reply signal; the transaction reply signal is in

response to an add command. This transaction reply does not mean that

the add command is completed. Rather, the transaction reply simply means

that media gateway B is working on adding the ATM termination. Media

gateway B chooses an EECID at 702 and sends the EECID back to MGC B

at 703. MGC B passes the EECID to MGC A at 707. At 715, MGC A sends

the add command with the EECID and explicit event and signal coav. Media

gateway A immediately replies to MGC A with a transaction reply at 717. At

704, the UNI setup message is sent from media gateway A through the ATM

network to media gateway B. A connect message is sent from media gate¬

way B to media gateway A to indicate the bearer path is accepted at 705.

Media gateway B uses the EECID to associate the call and the bearer path.

This prevents an unauthorized bearer connection from being set up. Then

MGC B notifies media gateway B at 706.

After receiving a UNI connect message from media gateway B, media

gateway A notifies MGC A that the coav event has occurred at 708. In the

above example, the MGC B cannot add the ATM termination until the UNI

service has been set up. This limitation comes about because the EECID is

needed to create the ATM termination. At 718, MGC B is notified by MGC A

through ISUP+ or other means that the bearer path (packet pipe) has been established. The process is completed with the pipe connect complete ack

message at 712.

FIG. 8 illustrates the signal flows for explicit backward setup. At 801 ,

MGC A chooses the EECID and passes it to media gateway A. There is an

embedded continuity check applied after the coav event occurs and there is

a return continuity check associated with the continuity check event. At 812,

MGC A passes the EECID to MGC B. At 802, media gateway A sends a

transaction reply to the add command to acknowledge that the transaction is

accepted. Once again, the add command has not been fully executed. At

81 1 , MGC B sends an add command to MG B. This command asks for a

bearer path to be set up using signal=coav. At 803, media gateway B sends

the ATM UNI setup message with an EECID to media gateway A. An event

notification on coav with embedded event col and signal co2 is explicitly

requested. Upon receipt of continuity check col response co2 will be given.

This command also asks for a bearer path to be set up using signal=coav.

After the connection is set up, media gateway B responds at 805 with a coav

event. At 809 MG A also notifies MGC A that event=coav has occurred. At

806, the continuity check signal is applied by media gateway A since the

coav has occurred. At 807, media gateway B applies the continuity check

response signal since it receives the continuity check event. At 808, media

gateway B notifies its media gateway controller that the continuity check

event has occurred. Similarly, media gateway A notifies its media gateway controller that the coav and the continuity check return events have both

occurred at 810.

FIG. 9 illustrates the message flows for implicit backward setup. In

this case, the EECID is assigned by the media gateway. At 901 , media

gateway A chooses the EECID and sends a transaction pending response

with the EECID to its media gateway controller so that the media gateway

controller waits for the setup. At 902, media gateway B passes the EECID

in the UNI setup message to media gateway A. At 903, when the connec¬

tion setup is complete, media gateway A sends a transaction reply to the

add command and the EECID to media gateway controller A. Media gate-

way B immediately sends a transaction reply to the add command to MGC

B.

FIG. 10 also illustrates an implicit forward setup. In this case a media

gateway controller creates the EECID. Also, the col and co2 continuity

checking messages are used. At 1001 , an add command with the EECID is

sent from media gateway controller A to media gateway A. At 1002, media

gateway A responds to its MGC with a transaction pending command. Note

that media gateway A still uses the EECID for establishing the connection

with media gateway B. 1003 and 1004 illustrate the continuity check and

continuity check response, respectively.

Figures 1 1 and 12 illustrate what happens when a failure occurs. In

FIG. 11 , at 1101 , MG B can't accept the UNI setup due to an error. Any number of things could cause the error. One possibility is that there is no

EECID known at MG B that matches the one in the UNI setup message. At

1 104, MG B reports failure (of) to MGC B. At 1102 MG A times out or

receives a reject message from MG B. MG A reports failure (of) to MGC A

at 1103. At 1105, and 1106, MGC a and MGC B exchange messages to

disconnect the pipe connection. Messages like that shown at 1105 and

1106 can come from either MGC A or MGC B.

In FIG. 12, the EECID is created and sent from MG A to MGC A at

1201. MG A sends the UNI setup message at 1202, but it is rejected at

1206. After the add command is confirmed at 1205, a report of failure (of) is

sent from MG A to MGC A at 1208. A report of failure is also sent from MG

B to MGC B at 1207.

FIG. 13 illustrates a conceptual, functional block diagram of a switch¬

ing system, which can be used to implement a media gateway, which in turn

implements the invention. Computing module 1301 includes a central

processing unit, memory, and supporting circuitry. This computing module,

together with any computer program code stored in the memory, is the

means for controlling the overall operation of the switching system to per¬

form the method of the invention. TDM switching fabric 1302 is for switching

TDM channels and is controlled by the computing module. Input output (I/O)

module 1304 is also connected to the processor of computing module 1301

and includes media devices to load computer program code as well as connections for workstations or other equipment for control and mainte¬

nance of the switching system. TDM network access module 1303 serves

as a TDM network interface and is connected to TDM switching fabric 1302,

both of which are managed by the computing module 1301. Circuit emula¬

tion system 1305 provides circuit emulation services, converting TDM voice

to packets such as ATM cells. Packet switching fabric 1306 sends and

receives packets on the packet network through packet network interface

1307.

FIG. 14 illustrates a workstation, which can be used to implement a

media gateway controller according to the present invention. I/O devices

such as keyboard 1402, mouse 1403 and display 1404 are used to control

the system. One or more of these devices may not be present in normal

operation. System unit 1401 is connected to all devices and contains

memory, media devices, and a central processing unit (CPU) all of which

together form the means to implement the present invention. Network

interfaces are normally implemented via adapter cards plugged into a bus,

however, for the sake of simplicity they are shown graphically as interface

1405.

As previously mentioned, appropriate computer program code in

combination with appropriate hardware implements most of the elements of

the present invention. This computer program code is often stored on

storage media. This media can be a diskette, hard disk, CD-ROM, or tape. The media can also be a memory storage device or collection of memory

storage devices such as read-only memory (ROM) or random access mem¬

ory (RAM). Additionally, the computer code can be transferred to the work¬

station over the Internet or some other type of network. FIG. 15 illustrates

one example of a media. FIG. 15 shows a diskette of the type where

magnetic media 1502 is enclosed in a protective jacket 1501. Magnetic field

changes over the surface of the magnetic media 1502 are used to encode

the computer program code. In this way the computer program code is

stored for later retrieval.

We have described specific embodiments of our invention, which pro-

vides an end-to-end call identifier (EECID) to uniquely identify a call leg

across a packet network, regardless of the number of nodes used in com¬

pleting the network path. One of ordinary skill in the networking and com¬

puting arts will quickly recognize that the invention has other applications in

other environments. In fact, many embodiments and implementations are

possible. The following claims are in no way intended to limit the scope of

the invention to the specific embodiments described.

We claim:

Claims

1. In a media gateway, a method of establishing a bearer path

through a multimedia packet network, the method comprising the steps of:

receiving (501) a command from a media gateway controller

(MGC) to establish a connection for the bearer path;

confirming (502) the command with the MGC;

initializing (503) the connection with a far-end media gateway;

and sending (505) a connection available event to the MGC if and

when the bearer path has been established so that call setup can be

completed without processing a wait state.

2. The method of claim 1 wherein the command specifies a connec-

tion available signal and a request for notification of connection available

and connection not available events.

3. The method of claim 1 , further comprising the step of sending

(508) a connection not available event to the MGC if and when a determina-

tion has been made that the bearer path cannot be established.

4. The method of claim 2 further comprising the step of sending

(508) a connection not available event to the MGC if and when a determina-

tion has been made that the bearer path cannot be established.

5. In a media gateway, a method of releasing a bearer path through

a multimedia packet network, the method comprising the steps of:

receiving a command from a media gateway controller (MGC)

to release a connection for the bearer path;

confirming the command with the MGC;

releasing the connection with a far-end media gateway; and

sending a connection not available event to the MGC if and

when a determination has been made that the bearer path has been

released.

6. The method of claim 5 wherein the command specifies a connec-

tion not available signal and a request for notification of a connection not

available event.

7. In a media gateway controller (MGC), a method of directing a me-

dia gateway to establish a bearer path through a multimedia packet network,

the method comprising the steps of:

sending (601) a command to the media gateway to establish a

connection for the bearer path;

confirming the command with the media gateway; and

receiving (609) a connection available event from the media

gateway if and when the bearer path has been established so that

call setup can be completed without processing a wait state.

8. The method of claim 7 wherein the command specifies a connec-

tion available signal and a request for notification of connection available

and connection not available events.

9. The method of claim 7, further comprising the step of receiving a

connection not available event from the media gateway if and when a

determination has been made that the bearer path cannot be established.

10. The method of claim 8 further comprising the step of receiving a

connection not available event from the media gateway if and when a

determination has been made that the bearer path cannot be established.

7 11. In a media gateway controller (MGC), a method of directing a

media gateway to release a bearer path through a multimedia packet net-

work, the method comprising the steps of:

sending a command to the media gateway to release a con-

nection for the bearer path;

confirming the command with the media gateway; and

receiving a connection not available event from the media

gateway if and when a determination has been made that the bearer

path has been released.

12. The method of claim 11 wherein the command specifies a con-

nection not available signal and a request for notification of a connection not

available event.

13. A computer program product (1501 , 1502) for enabling a media

gateway to establish a bearer path through a multimedia packet network, the

computer program product having a media with a computer program em-

bodied thereon, the computer program comprising:

computer program code for initializing a connection for the

bearer path in response to receiving a command from a media gate-

way controller (MGC) to establish a connection for the bearer path;

computer program code for confirming commands with the

MGC; computer program code for sending a connection available

event to the MGC if and when the bearer path has been established

so that call setup can be completed without processing a wait state;

and

computer program code for sending a connection not available

event to the MGC if and when a determination has been made that

the bearer path cannot be established.

14. The computer program product of claim 13 wherein the computer

program further comprises computer program code for releasing the con-

nection for the bearer path in response to receiving a command from the

MGC to release the connection for the bearer path and confirming that the connection has been released by sending the connection not available

event.

15. The computer program product of claim 13 wherein the com-

mand to establish a connection specifies a connection available signal and a

request for notification of the connection available and connection not

available events.

16. The computer program product of claim 14 wherein the com-

mand to establish a connection specifies a connection available signal and a

request for notification of the connection available and connection not

available events and the command to release the connection specifies a

connection not available signal and a request for notification of a connection

not available event.

17. A computer program product (1501 , 1502) for enabling a media

gateway controller (MGC) to direct a media gateway to establish a bearer

path through a multimedia packet network, the computer program product having a media with a computer program embodied thereon, the computer

program comprising:

computer program code for sending a command to the media

gateway to establish a connection for the bearer path;

computer program code for confirming commands with the

media gateway;

computer program code for receiving a connection available

event from the media gateway if and when the bearer path has been

established so that call setup can be completed without processing a

wait state and for receiving a connection not available event if and

when a determination has been made that the bearer path cannot be

established.

18. The computer program product of claim 17 wherein the computer

program further comprises computer program code for sending a command

to the media gateway to release the connection for the bearer path and for

receiving the connection not available event in response.

19. The computer program product of claim 17 wherein the com-

mand to establish a connection specifies a connection available signal and a request for notification of the connection available and connection not

available events.

20. The computer program product of claim 18 wherein the com-

mand to establish a connection specifies a connection available signal and a

request for notification of the connection available and connection not

available events and the command to release the connection specifies a

connection not available signal and a request for notification of a connection

not available event.

21. Apparatus for establishing a bearer path through a multimedia

packet network, the apparatus comprising:

means for initializing (1301, 1304, 1306, 1307) a connection

for the bearer path in response to receiving a command from a media

gateway controller (MGC) to establish a connection for the bearer

path;

means for sending (1301 , 1304) a connection available event

to the MGC if and when the bearer path has been established so that

call setup can be completed without processing a wait state; and means for sending (1301, 1304) a connection not available

event to the MGC if and when a determination has been made that

the bearer path cannot be established.

22. Apparatus for directing a media gateway to establish a bearer

path through a multimedia packet network, the apparatus comprising:

means for sending (1401, 1405) a command to the media

gateway to establish a connection for the bearer path;

means for receiving (1401 , 1405) a connection available event

from the media gateway if and when the bearer path has been estab-

lished so that call setup can be completed without processing a wait

state and for receiving a connection not available event if and when a

determination has been made that the bearer path cannot be estab-

lished.

23. A media gateway for establishing a bearer path through a multi-

media packet network under the control of a media gateway controller

(MGC), the media gateway comprising:

a switching fabric (1302, 1306); one or more network interfaces (1303, 1307) connected to the

switching fabric; and

a computing module (1301) connected to the switching fabric

for controlling the switching fabric according to a computer program to

enable the media gateway to receive commands from a media gate-

way controller (MGC) to establish and release connections for the

bearer path, and send a connection available event to the MGC if and

when the bearer path is established and a connection not available

event to the MGC if and when a bearer path is not established.

24. The media gateway of claim 23 wherein a command to establish

a connection specifies a connection available signal and a request for

notification of the connection available and connection not available events

and a command to release the connection specifies a connection not avail-

able signal and a request for notification of a connection not available event.

25. A programmed computer system (1401 , 1405) that is operable as

a media gateway controller, the programmed computer system having

connections (1405) for at least one media gateway, the programmed com-

puter system including a computer program comprising: computer program code for sending a command to the media

gateway to establish a connection for a bearer path;

computer program code for confirming commands with the

media gateway;

computer program code for receiving a connection available

event from the media gateway if and when the bearer path has been

established so that call setup can be completed without processing a

wait state and for receiving a connection not available event if and

when a determination has been made that the bearer path cannot be

established.

26. The computer system of claim 25 wherein the computer program

further comprises computer program code for sending a command to the

media gateway to release the connection for the bearer path and for receiv-

ing the connection not available event in response.

27. The computer system of claim 25 wherein the command to

establish a connection specifies a connection available signal and a request

for notification of the connection available and connection not available

events.

28. The computer system of claim 26 wherein the command to es-

tablish a connection specifies a connection available signal and a request

for notification of the connection available and connection not available

events and the command to release the connection specifies a connection

not available signal and a request for notification of a connection not avail-

able event.

29. A packet network for supplying bearer paths for multimedia calls

comprising:

at least one media gateway (309, 310, 414, 415) for initializing

and releasing bearer path connections according to commands re-

ceived, the media gateway also operable to send a connection avail-

able event if and when the bearer path is established and a

connection not available event if and when a bearer path is not es-

tablished; and

at least one media gateway controller (MGC) (301, 302, 401 ,

402) connected to the media gateway, the MGC operable to send the

commands to media gateway and to receive the connection available

event and the connection not available event.

30. The network claim 29 wherein the commands include a com-

mand to establish a connection that specifies a connection available signal

and a request for notification of the connection available and connection not

available events.

31. The network of claim 30 wherein the commands further include a

command to release the connection that specifies a connection not available

signal and a request for notification of a connection not available event.