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Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

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Module 5 VoIP Signaling Protocols
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Page 1: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Module 5 VoIP Signaling Protocols

Page 2: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

VoIP Call Signaling

Telephones1780482182417804821825

Telephones1403471844314034718444

FortMc.Murray

Calgary

PSTN

FXS FXS

IP NetworkVOIP CALL SIGNALING

OCCURS HERE

192.168.2.1/24192.168.2.2/24

PBX PBX

Page 3: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323• The first call control standard for VoIP

was H.323, which was adopted by the ITU-T in 1996

• An umbrella standard that covers specification for transmitting audio, video and data across an IP network including the Internet

• H.323 recommendations also included a standard called T.120 which is used by Microsoft’ Netmeeting

Page 4: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Components and protocols

Call Signaling: H.225 Media Control: H.245 Audio Codecs: G.711, G.722,

G.723, G.728, G.729 Video Codecs: H.261, H.263 Data Sharing: T.120 Media Transport: RTP/RTCP

Page 5: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Elements

Page 6: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 ComponentsH.323 Gateways• Provides interoperability between H.323 and

non H.323 Switched Circuit Networks (such as PSTN). Gateways not needed unless interconnection with the SCN required. It translates between audio, video, and data transmission formats and communication systems and protocols.

• H.323 Gatekeepers Optional component of H.323 Perform Call

processing, address translation, and distributed application manager functions

Page 7: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Components H.323 terminals: Are end devices and can

either be PC or other stand-alone devices running multimedia applications.

Multi-point Control Units (MCU’s) : MCU’s provide support for conferences of 3 or more terminals. All terminals participating in a conference establish a connection with the MCU.

Note: Gatekeepers, Gateways and MCU’s are logically different components of a H.323 network but can be implemented on one device.

Page 8: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Gatekeeper Zones A zone is the collection of H.323 nodes

such as gateways, terminals, and MCUs registered with the gatekeeper.

There can only be one active gatekeeper per zone.

Page 9: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Gatekeeper Zones

Page 10: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Gatekeeper Functions- Mandatory Address Translation - Translates

H.323 IDs (such as [email protected]) and E.164 numbers (standard telephone numbers) to endpoint IP addresses.

Page 11: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Gatekeeper Functions - Mandatory Admission Control - Controls endpoint

admission into the H.323 network. To achieve this, the gatekeeper uses the following:

- H.225 Registration, Admission, and Status (RAS) messages

- Admission Request (ARQ)

- Admission Confirm (ACF)

- Admission Reject (ARJ)

Page 12: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Gatekeeper Functions - Mandatory Bandwidth Control - Consist of managing

endpoint bandwidth requirements. To achieve this, the gatekeeper uses the following H.225 RAS messages:

- Bandwidth Request (BRQ) - Bandwidth Confirm (BCF) - Bandwidth Reject (BRJ) Zone Management - The gatekeeper provides

zone management for all registered endpoints in the zone. For example controlling the endpoint registration process.

Page 13: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Optional Gatekeeper Functions Call Authorization - With this option, the

gatekeeper can restrict access to certain terminals or gateways and/or have time-of-day policies restrict access.

Call Management - With this option, the gatekeeper maintains active call information and uses it to indicate busy endpoints or redirect calls.

Page 14: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Optional Gatekeeper Functions Call Control Signaling - With this

option, the gatekeeper can route call-signaling messages between H.323 endpoints using the Gatekeeper-Routed Call Signaling (GKRCS) model. Alternatively, it allows endpoints to send H.225 call-signaling messages directly to each other.

Page 15: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Gatekeeper-Routed Call Signaling Vs Direct Endpoint Signaling

There are two types of gatekeeper call signaling methods:

Direct Endpoint Signaling - With this method, call setup messages are directed to the terminating gateway or endpoint.

Gatekeeper-Routed Call Signaling (GKRCS) - With this method, the call setup messages are directed through the gatekeeper.

Note: Cisco IOS gatekeepers are Direct Endpoint signaling based and do not support GKRCS.

Page 16: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.
Page 17: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Signaling

Page 18: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 SignalingThree main areas of control:• Registration Admission and Status (RAS)

signaling• Call Control Signaling• Media Control and Transport signalingSignaling can occur between: - Endpoints and Gatekeepers - Gatekeepers - Endpoints directly, without gatekeepers (In

this case, no RAS messages exchanged).

Page 19: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

RAS Signaling RAS is the signaling protocol used between

gateways and gatekeepers. The RAS channel is opened before any other channel and is independent of the call setup and media transport channels.

Gatekeeper Discovery: Automatic or manual. The Gatekeeper discovery multicast address is 224.0.1.41, UDP ports 1719 (gatekeeper registration and status port) and 1718 (gatekeeper discovery port).

Page 20: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Gatekeeper Autodiscovery RAS Messages Gatekeeper Request (GRQ): A multicast

message sent by an endpoint looking for the gatekeeper

Gatekeeper Confirm (GCF): The reply to an endpoint GRQ indicating the transport address of the gatekeeper’s channel

Gatekeeper reject (GRJ): Advises the endpoint that the gatekeeper does not want to accept it’s registration. Usually due to a configuration error on the gateway or gatekeeper

Page 21: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Registration

Occurs after the discovery process but before you can place any calls

Registration Request (RRQ) Registration Confirm (RCF) Registration Reject (RRJ) Unregister Request (URQ) Unregister Confirm (UCF) Unregister Reject (URJ)

Page 22: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

AdmissionsAdmissions messages between endpoints

and gatekeepers provide the basis for call admissions and bandwidth control

Admissions Request (ARQ): An attempt by an endpoint to initiate a call

Admissions Confirmation (ACF): An authorization by the gatekeeper to admit the call

Admissions Reject (ARJ): Denies the endpoint’s request to gain access to the network for this particular call

Page 23: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Endpoint Location Location Request (LRQ) : Sent to request

the endpoint or gatekeeper contact information for one or more E.164 addresses

Location Confirmation (LCF): Sent by gatekeeper to the endpoint indicating location address

Location Reject (LRJ): Sent by gatekeepers that receive an LRQ for which the requested endpoint is not registered or has unavailable resources.

Page 24: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Status Information

The GK can use the RAS channel to obtain status info. Typical polling period for status messages is 10 seconds

Information Request (IRQ) Information Request Response (IRR) Status Enquiry: GK typically uses this

message to verify call state

Page 25: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Bandwidth ControlBandwidth is initially managed through the

ARQ/ACF/ARJ but bandwidth can change during the call

Bandwidth Request (BRQ): Sent by an endpoint to the gatekeeper requesting an increase or decrease in call bandwidth

Bandwidth Confirmation (BCF): Sent by the gatekeeper confirming acceptance of the bandwidth change request

Bandwidth Reject (BRJ): Sent by the gatekeeper rejecting the bandwidth change request if the requested bandwidth is not available

Page 26: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.225 Call Control (Setup) Signaling H.225 call control signaling is used to setup

connections between H.323 endpoints. The ITU H.225 recommendation specifies the use and support of Q.931 signaling messages.

A reliable (TCP) call control channel is created across an IP network on TCP port 1720.

Setup, Call Proceeding, Alerting, Connect, Release Complete, Facility Messages

Setup message sent on the well known H.225 port 1720

The connect message can contain the transport UDP/IP address for H.245 signaling

Page 27: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.245 Media Control and Transport H.245 handles end-to-end control messages between H.323 entities. H.245 procedures establish logical channels for transmission of audio,

video, data, and control channel information. A reliable control channel is created over IP using the dynamic

assigned TCP port in the final call signaling message The exchange of capabilities, the opening and closing of logical

channels, preference modes, and message control takes place over this control channel. H.245 control also enables separate transmit and receive capability exchange as well as function negotiation, such as determining which codec to use

Fast Connect is another method besides H.245 to establish media channels between endpoints.

Fast Connect enables media connection establishment for basic point to point calls with one round-trip message exchange. These procedures dictate that the calling endpoint include the faststart element in the initial setup message. Preferred by some vendors.

Page 28: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Protocol Suite Overview

                                                                                                                                                                                               

Page 29: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

H.323 Products In Cisco AVVID IP Telephony, H.323

Gateways and Gatekeepers are implemented in Cisco IOS gateways and routers.

Page 30: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Session Initiation Protocol (SIP)Alternative to H.323:• Session Initiation Protocol (SIP): IETF standard

based on RFC 2543, which is obsoleted by RFC 3261

• Application layer signaling-control protocol used to establish, maintain, and terminate multimedia sessions

• SIP invitations can establish sessions and carry session descriptions

• SIP supports unicast and multicast sessions as well as point-to-point and multipoint calls

• SIP can operate in conjunction with other signaling protocols such as H.323

Page 31: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

SIP ElementsSIP is a peer-to-peer protocol as each node

can be a client and server. Two main components: User agents and network servers

User Agents (UA): Client end-system applications that contain both a user-agent client (UAC) and a user-agent Server (UAS), otherwise known as client and server

Network Servers: Proxy Server, Redirect Server, and Registrar Server

Page 32: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Proxy, Redirect Servers, Registrar Servers Acts on behalf of other clients and contains both client

and server functions A proxy server interprets and can re-write request

headers before passing them on to the other servers Rewriting the headers identifies the proxy as the

initiator of the request and ensures that replies follow the same path back to the proxy instead of the client

Redirect Server: Accepts SIP requests and sends a redirect response back to the client containing the address of the next server. Redirect Servers do not accept calls, nor do they process or forward SIP requests

Registrar Server: Keeps a registration database of the SIP endpoints on the network

Page 33: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Addressing Also called SIP Universal Resource

Locators (URLs) Similar to email addresses identified by

user@host The user portion can be a user name or

telephone number, and the host portion can be a domain name or network address

E.g sip:[email protected] [email protected]

Page 34: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Locating a Server A client can send a SIP request either

directly, to a locally configured proxy server, or to the IP address and port of the corresponding SIP URL

Sending the request to the proxy server is easy but sending it to the SIP URL is a bit complicated. Look at the textbook section Chapter 11.

Page 35: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

SIP Message RequestsSix kinds of message requests: Invite: Indicates that the user or service is invited to

participate in a session ACK: Represent the final confirmation from the end

system and conclude the transaction initiated by the INVITE command.

OPTIONS: Enables you to query and collect user agents and network server capabilities

BYE: This method is used by calling and called parties to release a call.

CANCEL: This request enables user agents and network servers to cancel any in progress request

REGISTER: used by clients to register location information with SIP Servers

Page 36: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Message Responses SIP message responses are based upon the

receipt and interpretation of a corresponding request

Some common responses: 100 – Trying, 180 – Ringing, 200 – OK, 301 – Moved Permanently, 305 – Use Proxy, 400- Bad Request, 404 – Not found, 500 – Internal Server Error, 600 – Busy everywhere

Many more in Chapter 11. Please go through.

Page 37: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

SIP Operation – Proxy Server Example

Page 38: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

SIP Redirect Server Example

Page 39: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

SIP Future Increase in adoption among vendors

and service providers 3GPP has chosen SIP as the standard for

multimedia communication Closely tied with IMS (Internet

Multimedia System), which is the 3GPP standard for merging the Internet and Cellular Worlds

Will likely not completely replace H.323 SIP and H.323 likely to co-exist in future

for a while

Page 40: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Required Reading Chapter 10 and 11 of textbook

Page 41: Module 5 VoIP Signaling Protocols. VoIP Call Signaling.

Additional References www.sipforum.org for latest

developments in SIP technology http://www.cs.columbia.edu/sip/ http://www.3gpp.org/


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