hệ thống MGCP trong viễn thông

Separation of Media and Call Control Gateways switched network as a native circuit-switched system and vice versa Signaling path and media path are different in Signaling path and medi

Media Gateway Control and the Softswitch Architecture

Ng Tai Hung

Voice over IP

Reduced bandwidthReduced bandwidth

Replacing all traditional circuit-switched

networks is not feasible.

VoIP and circuit-switching networks coexist

Separation of Media and Call Control

Gateways

switched network as a native circuit-switched

system and vice versa

Signaling path and media path are different in

Signaling path and media path are different in VoIP systems.

proxies)

SS7, Signaling System 7

Separation of Media and Call Control

functions

Signaling conversion

The call-control entities use signaling to communicate.

Media conversion

A slave function (mastered by call-control entities)

and signaling from the media path

Separation of Media and Call Control

Advantages of Separation

sink

control multiple gateways

control multiple gateways

MGCP, Media Gateway Control Protocol

IETF

Softswitch Architecture [1/2]

Softswitch Architecture [2/2]

Signaling (SS7) SCP

Internet

SS7 Network

MGCP/

(SS7) Gateway

Trunking Gateway

Call Agent SCP

Residential Gateway

STP

Trunking GatewayTrunkingGateway

CO

Switch

Residential GatewayResidentialGateway

It is possible to use different network components from different vendors.

It is possible to focus on one area.

Softswitch/PSTN Interworking

the MGCs

Requirements for Media Gateway Control [1/2]

Including the capability to negotiate the media formats

media streams

specified events within the media streams, and

the corresponding actions

Requirements for Media Gateway Control [2/2]

certain QoS requirements

from an MG to an MGC

The management of associations between an MG

and an MGC

In the case of failure of a primary MGC

MGC can control different MGs

MGCs

Protocols for Media Gateway Control

The first protocol is MGCP

Relation with H.323 Standards

Internet

Signaling (SS7) Gateway

Trunking Gateway

Gatekeeper

Terminal or Gateway RTP

H.225/RAS H.225/Q931 H.245

MGCP

H323, SIP & MGCP, MEGACO

GW GK

MCU

TN

TN TN

H323, SIP & MGCP/MEGACO

signaling & media

control are coupled

MGCP Connection Establishment

Do what the CA instructs

Do what the CA instructs

A line or trunk on circuit-switched side to an RTP port on the IP side

Trunking Gateway to CO/Switches

Residential Gateway to PSTN Phones

Access Gateway

Likely to be the SIP

circuited-switched line and an RTP port on the IP side.

MGCP Endpoints [1/3]

DS0 channel

such as DS1 (1.544 Mbps) or E1 (2.048 Mbps)

Analog line

The gateway shall be required to extract the data and forward it as IP packets.

Announcement server access point

No external circuit-switched channels

Interactive voice response (IVR) access point

MGCP Endpoints [2/3]

Interactive voice response (IVR) access point

Conference bridge access point

Packet relay

networks

MGCP Endpoints [3/3]

Wiretap access point

ATM trunk-side interface

GW’s Domain Name + Local Name

The connections to be created

MGCP Calls and Connections

The connections to be created

The session descriptions to be exchanged between the connections

9 commands to handle Connection/Endpoints

All commands are acknowledged.

Separated by a single empty line

One command can be included within another

Only one level of encapsulation

E.g., when instructing a gateway to create a connection, CA can simultaneously instruct the gateway to notify the CA of certain events.

MGCP Parameters [2/6]

Connection-related statistical information

Average latency, jitter, packets sent/received/lost

GW -> CA

That an endpoint should detect during quarantine period That an endpoint should detect during quarantine period

E.g., off-hook, on-hook, hook-flash, DTMF digits…

MGCP Parameters [3/6]

In response to an audit command

A list of events associated with the current state

To indicate the maximum size MGCP packet supported by

an MG

Included in the response to an AUEP command

Included in the response to an AUEP command

Events and signals are grouped into packages

Analog line endpoint

Group events and signals into packages

with the two character “x-”

Combined NAS/VOIP GW Access GW (VOIP)

Access GW (VOIP + NAS) Residential GW

MGCP Parameters [4/6]

Events that occur during the period in which the GW is

waiting for a response to a Notify command

Process the events or discard them

When a GW deletes/restarts a connection

When a GW deletes/restarts a connection

An SDP session description

A list of events that an endpoint is to watch for

Associated with each event, the endpoint can be instructed

to perform actions

E.g., collect digits, or apply a signal

MGCP Parameters [5/6]

RequestInfo (F)

NotifiedEntity

RequestIdentifier (X)

To correlate a given notification from a GW

RestartDelay (RD)

will be brought back into service

RestartMethod (RM)

under-qualified, do nothing further

matched, send the collected digits to CA

over-qualified, send the digits to CA

MGCP Response

Header

E.g., I: A3C47F21456789F0 (ConnectionId)

E.g., I: A3C47F21456789F0 (ConnectionId)

Session Description

Call Setup Using MGCP

Call Flow for RGW to TGW

Call Flow for RGW to TGW

D: (11x|080xxxxxx|57xxxxx|002x.T)

ACK to RQNT(1)

200 1201 OK

R: RequestEvents D: DigitMap

E: Embedded Request R: Notification Request N: Notify immediately S: Signal Request

D: Digit Map

Call Flow for RGW to TGW

NTFY(2) : Notify from RGW

ACK to NTFY(2)

200 2002 OK

X: RequestIdentifier O: ObservedEvent

Call Flow for RGW to TGW

p: packetize period(ms) a: Compression Algo.

M: Mode X: RequestIdentifier R: RequestEvents

I: ConnectionId

Call Flow for RGW to TGW

ACK to CRCX(3) Session Description

G726~G732 encoded audio sample at 8 kHZ

Call Flow for RGW to TGW

Call Flow for RGW to TGW

Session Description from ACK(4)

ACK to MDCX(5)

200 1206 OK

M: Mode

Call Flow for RGW to TGW

S: SignalRequests

Call Flow for RGW to TGW

Call Flow for RGW to TGW

ACK to DLCX(8)

200 1210 OK

P: PS=1245, OS=62345, PR=780, OR=45123, PL=10, JI=27, LA=48

PS: Packets sent OS: Octets sent PR: Packets received OR: Octets received PL: Packets lost JI: Average Jitter (ms) LA: Average Latency (ms)

T

Usage of Commands

DeleteConnection()

ConnectionId in the parameter line

GW responds with Connection parameters

Only EndpontId (and CallId) in the parameter line

GW does not respond with Connection parameters

Reason-Code & Connection-Parameters in Command

Usage of Commands

{RequestedEvents

DigitMapSignalRequestsRequestIdentifier, … }

EndPointIdList is returned

Interworking between MGCP and SIP

Interworking between MGCP and SIP