Formiddagsseminar12. april 2002-Transparenter

Voice Services over an IP Network

By

Dr. James G. Williams

4 Basic Technologies for VoIP

• Signaling - Call Setup

• Encoding - A/D and Quantising

• Transport - Transmission and Switching/Routing

• Gateway Control - Media Device Control – Application Software– Session Software

Standards

• Signaling - H.323 (ITU) AND SIP (IETF)• Encoding - G.711 PCM (64000 kbps), G.722

(ADPCM), G.726, G.727, etc.• Transport - RTP (Real-Time Transport Protocol

= transport voice samples), RTCP (Real-Time Transport Control Protocol = feedback on Quality), RTSP (Real-Time Streaming Protocol)

• Gateway Control - MGCP (Media Gateway Control Protocol), H.GCP, IPDC

2 Major Scenarios

• Private Network, No PSTN but with or without Internet

• Private Network with PSTN

Basic Components for VoIP

H.232Terminal(Telephone or PC)

H.323Gatewaye.g.Cisco 3600

PrivateNetwork

H.323Gatewaye.g.Cisco 3600

H.232Terminal(Telephone or PC)

Internet

Call Processing

• Caller goes off hook-detected by gateway application• Session issues dial tone• Session waits for dialed digits• Session matches dial plan pattern• Session maps called number to an IP host to route to

destination (may be itself)• Session runs the H.323 protocol to establish a

transmission and reception channel over the IP network• If RSVP used, RSVP reservations are attempted to

achieve QoS

Call Processing

• The CODECS (Coders and Decoders) are activated with parameters (Samples analog voices converts to digital - G.711 samples 8000 times per second and produces 8000 8 bit bytes = 64000 bits)

• If duration of voice in a packet is 20ms, then 50 (1280 bit) payload packets per second

• Protocol stack is RTP - UDP - IP

Call Processing

• Any Call Progress indicators are cut through the voice path as soon as audio channel established

• Signaling detected by voice ports after call setup are trapped by session layer and carried over the IP network by RTCP

• When either end hangs up, connection is torn down (any RSVP resources)

The Business Plan

• What Offerings (services, products)?• Who are the customers?• Who is the competition?• How will the services be delivered?• What technologies can be utilized?• What is the cost of delivering service?• What resources are required to deliver

and support the services?

The Business Plan

• What system architecture is required?

• What processes, functions, procedures, etc. are needed?

• What are the capacities and volumes of the resources needed?

• What Financial Resources are Needed?

• The Economic Model

Company Background

• Competitive Local Exchange Carrier (CLEC)/(Telephone Company)

• 3 Venture Capitalists - $62 Million

• 1 Finance Company - $ 120 Million

• 16 markets (cities) East Coast USA

• 8 Founders

• Estimated 400 employees

Company Background

• New Generation Network– Broadband Services to Businesses

• Small to Medium (6 – 50 employees)• Underserved Markets

– DSL to the Premise (VoIP)– ATM backbone (VoATM)– All Digital Packet Switched Network to the

PSTN– Offices in each city fully staffed

• Sales (15), Customer Care(3), Technicians(3)

Technology Architecture

LSO with a 720 Port DSLAM

(Digital Subscriber Line Access Multiplexer)

4 – 16 port IAD atCustomer Premise

Local LoopILEC Central Office

Telephone

Fax

PC/ Hub/ Router

45 – 155 Mbps

PSAXATM

Router

ATM

Digital SwitchPathstar/5-ESS

Springtide Router

1Central Office per market

Internet

PSTN

911 Center

Voice

Data

GR303

LSO

ILEC Central Office

NOCNetwork Alarms and

SNMP Packets

Other MarketPSAX

NOC Data

Services• Voice Services

– Local– Long Distance– Voice Mail– Features (Call Forward, Caller ID, etc.)– PBX and Keyset Support– Calling Cards

• Data Services– Internet Access (386 kbps to 2.3 mbps)– VPN– Email Web Hosting

Voice Requirements• 7X24 service availability

– IAD must have UPS– DSLAM must have UPS– PSAX must have UPS– Switch 7RE (5ESS) must have UPS– Need fault tolerant devices

• Network Operations Center (NOC)– Access to every component via IP network– Uses SNMP (Simple Network Management Protocol) to

configure and reconfigure devices via the MIB (Management Information Base)

– Receives Alarm messages from devices based on threshold settings for triggers

– Ability to test circuits (Lucent’s LoopCare)

Voice Requirements

• Quality of Service (QoS)– Latency is critical for voice, not data– Local loop bandwidth considerations

• Voice without compression requires 128Kb (64Kb for each direction)

• Maximum bandwidth is determined by length of loop from LSO (SDSL = 18,000 ft. Max) and quality of the loop

• No load coils and bridged taps permitted

• Reliability– Dial Tone always there– Same actions, same results

Customer Path

IAD

ILEC Circuit (IDs, Vendor)

IP Addresses,Voice VPI/VCI,Data VPI/VCI,Telephone Numbers,Host IP Addresses

Host PC Telephone

Stinger-DSLAMShelf, Slot, Port,Voice VPI/VCI,Data VPI/VCI

IOF CircuitTerminations,IDs,Type,Channels

LSO Facility

CustomerPremise

PSAXSlot, Port,

Voice VPI/VCI,Data VPI/VCI

PathstarPort

Voice VPI/VCIIP Addresses

SpringtidePort

IP Address

3-COMID

Mail Accounts

Central Office

Other Players

• ILEC (Incumbent Local Exchange Carrier)– Own local loops– Own Telephone Numbers– Own the Customer

• IXC – Inter-exchange Carriers (Long Distance)• 911 – Emergency Management Interface• CMDS (national database)• Caller ID (LIDB – national database)• Ported Numbers (national database)• 800 Numbers (national database)

04/10/23 DRAFT - For Discussion Purposes Only

19

CLEC TO BALOCAL

Call Direction

CLEC

EO

BA

EO

Usage Billing Concept• Reciprocal Compensation

BA Bills CLEC - Usage• Local charges for MOUs TANDEM

or END OFFICE

Factors Exchange RequiredCLEC to BA• PLU Factor

Record Exchange Required NONE

LOCAL/TOLL TRUNKS

or

BA Bills CLEC - FacilitiesTandem Switched Transport (TST)• Entrance Facility or Cross ConnectDirect Trunked Transport (DT)• Entrance Facility or Cross Connect• Channel Milage (EO to EO)

TST

DT

04/10/23 DRAFT - For Discussion Purposes Only

20

Call Direction

CLEC

EO

BA

EO

Usage Billing Concept• Switched Access

BA Bills CLEC - Usage Tandem Connection• Local Switching• Tandem Switching• Tandem Transport

• Fixed• Per Mile

• RIC• CCL End Office Connection• Local Switching• RIC• CCL

Factors Exchange Required CLEC to BA• PLU Factor

Record Exchange Required NONE

or

LOCAL/TOLL TRUNKS

TST

DT

BA Bills CLEC - FacilitiesTandem Switched Transport (TST)• Entrance Facility or Cross ConnectDirect Trunked Transport (DT)• Entrance Facility or Cross Connect• Channel Milage (EO to EO)

CLEC TO BAINTRALATA TOLL

04/10/23 DRAFT - For Discussion Purposes Only

21

BA TO CLECLOCAL

Call Direction

CLEC

EO

BA

EO

Usage Billing Concept• Reciprocal Compensation

CLEC Bills BA - Usage• Local Termination charges for MOUs in accordance with CLEC tariff/agreement.

Factors Exchange Required BA TO CLEC• PLU Factor

Record Exchange Required NONE

or

LOCAL/TOLL TRUNKS

TST

DT

CLEC Bills BA - FacilitiesTandem Switched Transport (TST)• Entrance Facility Direct Trunked Transport (DT)• Entrance Facility

04/10/23 DRAFT - For Discussion Purposes Only

22

Call Direction

CLEC

EO

BA

EO

Usage Billing Concept• Switched Access

CLEC Bills BA - Usage• Switched Access Charges for MOUs in accordance with CLEC Tariff/Agreement.

Factors Exchange Required BA to CLEC• PLU Factor

Record Exchange Required NONE

or

TST

LOCAL/TOLL TRUNKS

DT

CLEC Bills BA - FacilitiesTandem Switched Transport (TST)• Entrance Facility Direct Trunked Transport (DT)• Entrance Facility

BA TO CLECINTRALATA TOLL

04/10/23 DRAFT - For Discussion Purposes Only

23

Call Direction

CLEC

EO

Usage Billing Concept• Switched Access• Meet Point Billing• Multiple Bill/Multiple Tariff

BA Bills IXC - Usage• Tandem Switching• Portion of Transport CLEC Bills IXC - Usage• Switched Access Charges for MOUs in accordance with CLEC tariff/agreement.

CLEC Bills BA - Usage• Not Applicable

Factors Exchange RequiredIXC to CLEC - FGD Factors

Record Exchange RequiredCLEC makes originatingrecordCLEC to BA• EMR 115002

IXC SUBTENDINGOZZ/CIC FGD/B

BA Bills CLEC - FacilitiesTandem Switched Transport (TST)• Entrance Facility or Cross Connect

CLEC TO AN IXC

04/10/23 DRAFT - For Discussion Purposes Only

24

Call Direction

CLEC

EO

Factors Exchange RequiredIXC to CLEC - FGD Factors

Usage Billing Concept• Switched Access • Meet Point Billing• Multiple Bill/Multiple Tariff

BA Bills IXC - Usage• Tandem Switching• Portion of Transport

CLEC Bills IXC - Usage• Switched Access Charges for MOUs in accordance with CLEC tariff/agreement.

CLEC Bills BA - Usage• Not Applicable

Record Exchange RequiredBA to CLEC• EMR 110101CLEC to BA• EMR 115002

FGD/BIXC SUBTENDING

OZZ/CIC

BA Bills CLEC - FacilitiesTandem Switched Transport (TST)• Entrance Facility or Cross Connect

IXC TO A CLEC

04/10/23 DRAFT - For Discussion Purposes Only

25

Call Direction

CLEC

EO

CLEC

EO

Factors Exchange Required

Record Exchange Required11-01-01 to NYSPNYSP bills OriginiatingCLEC for Transit ServiceCharges

BA Bills Originating CLEC - Usage• Transit Service Charges• Recovery of Local Termination charges for MOUs paid by BA to Terminating CLEC.

Terminating CLEC Bills BA - Usage• Local Termination charges for MOUs in accordance with Terminating CLEC tariff/agreement

Usage Billing Concept• Transit Service

LOCAL/TOLL TRUNKS

(Originating) (Terminating)

CLEC TO CLECLOCAL

04/10/23 DRAFT - For Discussion Purposes Only

26

Call Direction

ITC

EO

CLEC

EO

Factors Exchange RequiredNONE

Record Exchange Required• BA to ITC- 110101• ITC to BA- 115002

LOCAL/TOLL TRUNKS

ITC subtends a BA Access Tandem

FGC-LIKE TRUNKS

MP

CLEC TO ITCLOCAL/INTRALATA

Usage Billing Concept• Transit Service• Meet Point Billing

BA Bills CLEC - Usage• Tandem Switching• Tandem Transport - Fixed - Per mile from SWC to MP

Independent Bills CLEC - Usage• Charges for MOUs in accordance with tariff/agreement.

CLEC and Independentmust have billing agreement.

04/10/23 DRAFT - For Discussion Purposes Only

27

Call Direction

ITC

EO

CLEC

EO

Usage Billing Concept• Special Access

BA Bills CLEC - Usage• Channel Termination• Channel Mileage - Fixed - Per mile from SWC to MP

ITC Bills CLEC - Usage• Charges for MOUs in accordance with CLEC tariff/agreement.

Factors Exchange RequiredNONE

Record Exchange RequiredNONE

MP

Direct Trunk - ITC and CLECcould utilize 2-way.

CLEC and Independent must have billing agreement.

CLEC TO ITCLOCAL/INTRALATA TOLL

Internet, Intranet,Extranet

Pre-SaleSystem

(BroadStreet)

Order Management

System(Arbor/OM)

Provisioning(Dset, BA)

Billing(Arbor/BP)

FinancialAccounting

System

Payroll(Payroll One)

Human ResourceSystem

(Employease)

Web Site

E911,PIC/CARE

Number PortabilityOther Interfaces

(Arbor/BP)

CustomerCare

(Arbor/BP)

Help DeskTrouble Ticket

(Remedy)

System Components

Arbor/BPCustomer Care

CustomerInquiry

CustomerAccount

Maintenance

Pre-SaleSystem

Analysis

Prospects, LSOs, Employees,Inventory, Maps, Regulatory,

Competition, etc.

Financial Accounting

System

GL, AR, AP, Assets,Purchasing, etc.

ILEC, IXCRevenue and Payments

ServicesRatesDiscountsFormats

Arbor//BPBilling

Payroll

Human Resources

Sales SystemOrder Data

Arbor/OM

InstallationConfiguration

ProvisionE-Bonding

ILECs, CLECS,IXCs

Contract, Letter

NotificationsCustomer,Sales

CustomerUsage

ILEC, IXC

BillDatsSoftware

Databases

CustomerIntelligence

Commissions

NetworkMonitoring

FaultManagement

Arbor/OMRemedy

Trouble Ticket

MaintenanceTools

LoopCare

Charges,Inventory,Times

Back Office System Flow03/16/2000

SU

N S

OL

AR

IS O

.S.

OM Arbor/BP

BillDatsSybase DB

Presale & Sales

ILEC Provisioning ILEC & Quintessent

Network Fault Management (NFM)

HP

UX

O.S

.

LoopCare

Window

s 2000 O.S

.

Remedy Help Desk

Remedy Trouble Ticketing

Financial & Asset Management

Web Server (IIS)

Mail Server (Exchange)

Trading PartnersSystem Interface (EDI,

CORBA)

Desktop Applications

Gis System

BroadStreet Employees

BroadStreet Customers

Public

Validation Quintessent

Oracle DBMS

Informix DBMS

Oracle DBMS

Web Server

iPlanet

DSL line Qualification

Software Architecture

SQLServer

BackOffice Support Architecture

Windows 2000 Servers

Web Server Mail Server

Remedy Help Desk

FinancialsDesk Top

Apps

E911

Internet Intranet Extranet

Arbor/OM and Arbor/BP Servers

Ordering and Provisioning Data Capture

GatewayServer

Oracle DBMS

Customer Care

Order EntryProduct

Configuration

ILEC/LSR PIC/Care Pre-Order

Journals

Payments

Invoicing NOC andProvisioning

Servers

Oracle DBMS NFMLoopCare

Navis

Remedy TroubleTicket

CajunView

Remote NetworkDevices

LNP

LIDB

Sprint Mgt

911 ServiceRequests

MediationServers

ILECsVerizon, Etc.

5ESSSwitches

MSAGData Updates

InventoryIPs, Tele No.IADs, Stinger

Circuits

SprintLD

3COMMessaging

CMDS

SQL Server DBMS

DBMS

Provisioning Support

Order Management

Order Queue

Provisioning InterfaceFor Stinger,PSAX and Switch

Stinger TableData –w-

Pre-configured Path Data

Update PSAXTable

Update Circuits Table

UpdateSwitch TableUpdate

3-COM TableUpdate

Calling Cards

ProvisioningInterface for

The IAD

Update IAD Table

Database

Intranet/Extranet VoIP

• Voice/IP is not expensive, but the initial outlay will depend largely on where and to what extent the technology is deployed.

• Some sites only want voice/IP for local telephony with all externals calls still going over the public switched telephone network (PSTN) or over a private voice network.

• But more commonly, voice/IP is deployed externally with the existing on-site telephone infrastructure left intact. In this case, a gateway is needed to route a call over a wide area IP network.

Voice Over IP

• A major technical question is where and how best to deploy the gateway function. This will depend on factors such as the size of the site, number of sites, location of sites, etc.

• While there are serious questions over voice/IP reliability and quality, analyst Gartner Group predicts that these are likely to fade this year.

Voice over IP

• At present, the quality of voice/IP almost never exceeds the PSTN and suffers from variability, even over private IP networks.

• Technology and standards to provide an end-to-end connection and offer guaranteed bandwidth without interference from other network traffic are only just coming into place.

Voice over IP

• Voice/IP is being more widely deployed over private IP-based intranets

• Can save money by routing conventional calls from existing phones over the IP backbone.

• When virtual private networks are used to carry IP-based voice - the quality is similar to GSM cellular, but may not be deemed reliable enough for talking to customers.

Voice Over IP

• London-based marketing agency Rainier implemented voice/IP for toll bypass using its virtual private IP network for calls between its London office and offices in Boston and San Francisco.

• Voice/IP has cut Rainier's transatlantic voice communications bill by 75% compared with BT's rates.

• The delay, about 15 to 30 seconds, is the time it takes to set up the fixed path through the end-to-end network, including the component provided by the ISP.

Voice Over IP• One problem with using intranets or virtual private networks to carry

voice is that it can become unacceptable during peak periods. • The ideal solution would be to route calls over the PSTN at such

times, if only you could tell in advance that the quality of service available over the IP network was inadequate.

• Networking and telecoms systems vendor Nortel Networks has developed a technique for monitoring the condition of an IP network for this situation.

• A company's Meridian private branch exchanges (PBXs) can assess the likely quality of the IP network on an ongoing basis by transmitting test packets and measuring the transit delays.

• While this delay is kept within acceptable bounds, the network is deemed acceptable for voice/IP. But if the delay falls outside the bounds, calls are re-routed over the PSTN.

Voice Over IP• VoIP has the potential to deliver new applications and features not

so easy to support over the PSTN. • Web-enabled call centres, where voice/IP will enable voice calls to

be opened up within an existing Internet session. • Currently, some sites have 'call me' buttons, but the call-backs run

on a separate line over the PSTN which is not useful if only one line exists and is already busy during an Internet session.

• Voice/IP will also enrich existing telephony by making sophisticated call-handling features more readily accessible.

• Modern PBXs have for years come with a huge sophistication of features which are largely inaccessible because the LCD display on handsets is not a useful interface

Voice Over IP

• Service providers may offer caller identification as a feature

• IP signaling, perhaps combined with caller identification, can also be used to facilitate sophisticated call conferencing of the kind previously only available as a specialist service.

• Larger conferences usually require a mediator to control admissions to the conference and introduce new participants to the others.

• The use of IP signaling combined with the PC interface makes it easy to perform these functions.

VoIP Applications• On-site IP telephony allowing internal calls to be made over IP-based Lans. • Corporate toll bypass where voice calls are made over internal IP networks or

virtual private IP networks. • Voice over the Net between two multimedia-equipped PCs. • Fax over the Net. The cost is very cheap, and quality is less of an issue

because communication is not real time and loss of bandwidth simply delays transmission

• IP-based public phone services. Carriers can cut costs by consolidating voice and data over single IP core networks and can deliver new features not possible over the PSTN such as advanced conferencing

• Call-centre IP telephony. This is a variant of voice/IP, but is a distinct application

• Voice messaging over the Internet. The Net can become a medium for unified messaging.

• Video-over-IP. This field unto itself is raising a variety of unique technical issues.

Voice Over IP Gateways

VoIP Gateways Increase in Functionality

Softswitch

SoftSwitch

VoIP Quality• Bandwidth and transit delay affect voice quality during transmission

over any communications link.• Circuit-switched voice and cellular GSM, the voice is sampled and

converted into bits at the rate of 64Kbps. Each sample represents an approximation of the sound during its sampling period, in this case, 1/8000 of a second.

• On the PSTN, an end-to-end path is set up, and this imposes a slight delay which is barely noticeable except over satellite links. This delay is very consistent and has no effect on quality. As the bandwidth is fixed, quality does not vary during the conversation.

• With voice/IP , the digital bits obtained from the sampling process are first packed into IP packets before being transmitted, and this imposes a slight up-front delay. But this is not an issue unless the voice is packed and then unpacked into bit streams during transmissions.

VoIP Quality• IP networks do not normally provide a fixed end-to-end path for a whole session nor a

guaranteed bandwidth. • This is mitigated by stamping the packets with the time they were sent and using

buffers to hold them for a second or so at the receiving end, so that they can be assembled in the right order and with the right timing.

• But the delay can only be minimal or else the packet will be too late to be of any use. Even when there are no serious delays and IP packets have a fixed path, bandwidth can be reduced when there is a surge in traffic leading to degraded quality.

• Instead, everything slows down, and some packets have to be discarded to ensure that at least a reduced number can arrive on time. The result is that there are fewer bits to represent the sound at the receiving end and quality degrades.

• The only way to solve these problems is to set up fixed paths through the network for the duration of a conversation and allocate a fixed amount of bandwidth to it. You create a tunnel through the network shielded from other traffic.

• This reduces the efficiency of the IP network because this tunnel is then reserved purely for the voice and cannot be re-allocated to other traffic even during periods of silence, until the parties hang up.

VoIP Security

• Security - a high priority for and company or university who relies on its computer networks for quick access to private or sensitive materials. – Currently encryption and authentication of user access is only a

recommendation by H.323. What this means is that any H.323 aware user can tap into any conversation on the system. And an employee or any outside person can monitor every conversation with access without ever having to leave his or her desk.

• Another security issue arises if a corporation uses VoIP technology for a remote access location. – This is one of the main uses for partial VoIP implementation

today, but it is also a serious security risk because of problems with firewalls. Currently H.323’s firewall negotiation mechanisms require direct access into the corporate network. A blatant violation of most corporations’ security requirements is the call-set up of H.323.

Making VoIP Work• Making Voice over IP function efficiently in a corporate enterprise

network requires adequate bandwidth allocation and management.– For each call to be sent across an IP network, 17Kbps is needed of the

total bandwidth. If properly designed and operated a company’s network can use a 56 or 64 KBPS link to simultaneously share several voice calls and data traffic without any delays or problems.

• Whereas when using the Internet, Providers such as America on Line (AOL) handle too much Internet traffic and rout transmissions too many times to provide a clear and precise connection.

• In larger organizations where a large amount of data is carried across a network, Voice over IP would need a separate infrastructure in order to be utilized. – Especially in companies where up to 50 phone lines can be used

simultaneously an Intranet type of infrastructure will be needed to process the calls with PSPN quality.

VoIP and Convergence

• Voice, fax, data and multimedia traffic are transmitted over a single multipurpose network

• These advantages include:– lower recurring transmission charges, – reduced long-term network ownership costs, and– the ability to deploy a wide range of powerful voice enabled applications.

• The disadvantages are:– technology professionals are concerned with the quality of voice calls on the

data network– the stability of voice-over-IP (VoIP) solutions, and – the consequences of being prematurely "locked-in" to a given vendor’s

architecture.– A lack of expertise and experience with VoIP technology

• By using an intelligent multi-path gateway switch that links the PBX, the data network and the public switched telephone network (PSTN), companies can effectively "hedge their bets" even as they move ahead with their initial VoIP deployments.

VoIP Implementations• PBX-based gateways

– The leading manufacturers of PBX equipment are all introducing their own solutions to the VoIP challenge.

– These vendors have minimal experience in IP-centric data networking.– Without strong expertise in connectionless, non-determinate protocols, it

is unclear if they will be able to address the issues of voice signal quality in the IP world.

– A drawback to this approach is that it is tied to highly proprietary PBX platforms with no real record in open technical standards.

• Router-based gateways– Manufacturers of routers and other data networking hardware are also

attacking the VoIP market and have healthy marketshare. – Their expertise in IP technology should also help them in solving voice

quality problems using the IP quality-of-service (QoS) techniques.– Their unfamiliarity with voice technology and call management hamper

their ability to deliver corporate-class telephony solutions.

VoIp Implementations

• PC-based gateways– Several vendors are bringing stand-alone gateways to

market. These products offer a router- and PBX-independent solution, since they are not tied to a particular manufacturer’s platform. These smaller, more nimble vendors exhibit a greater ability to rapidly adopt – and even help define – emerging standards.

• Alternative to the above– The multi-path switch. These devices are specifically

designed to address the issues unanswered by the product categories described above – including voice quality, network reliability, and vendor independence

VoIP SLA• Service level agreements (SLAs) are also a major hindrance for

uptake as they tend to be immature, making it harder for vendors and carriers to overcome potential customers' quality of service and security concerns.

• Phil Smith, business development director for Cisco, which is investing heavily in VoIP technologies, agreed. "It's fair comment to say that there is a lot of work to do to educate the market, and we're out there trying to do that," he said.

• "SLAs are a particularly tricky area because of the sheer number of different players involved in the process of providing VoIP services, but I'm sure that as the market evolves, these will be resolved."

• Analyst group Frost & Sullivan estimates sales of VoIP gateways at $260m in 2001, set to reach $2.9bn in 2006.

QoS Standards

• Support for QoS routing can be viewed as consisting of three major components:

• 1. Obtain the information needed to compute QoS paths and select a path capable of meeting the QoS requirements of a given request,

• 2. Establish the path selected to accommodate a new request,

• 3. Maintain the path assigned for use by a given request.

RFC 2676 – QoS Routing• QoS Routing Mechanisms and OSPF Extensions

– The assumption is that a flow with QoS requirements specifies the requirements in some fashion that is accessible to the routing protocol.

– This could correspond to the arrival of an RSVP [RZB+97] PATH message, whose TSpec is passed to routing together with the destination address.

– After processing such a request, the routing protocol returns the path that it deems the most suitable given the flow's requirements.

– Depending on the scope of the path selection process, this returned path could range from simply identifying the best next hop, i.e., a hop-by-hop path selection model, to specifying all intermediate nodes to the destination, i.e., an explicit route model.

– In addition to the problem of selecting a QoS path and possibly reserving the corresponding resources, one should note that the successful delivery of QoS guarantees requires that the packets of the associated "QoS flow" be forwarded on the selected path.

Metrics• Link available bandwidth:

– The link physical bandwidth or some fraction thereof that has been set aside for QoS flows. Since for a link to be capable of accepting a new flow with given bandwidth requirements, at least that much bandwidth must be still available on the link, the relevant link metric is, therefore, the (current) amount of available

• Link propagation delay: – This quantity is meant to identify high latency links, e.g., satellite links,

which may be unsuitable for real-time requests. – This quantity also needs to be advertised as part of extended LSAs,

although timely dissemination of this information is not critical as this parameter is unlikely to change (significantly) over time.

• Hop-count: – This quantity is used as a measure of the path cost to the network. A

path with a smaller number of hops (that can support a requested connection) is typically preferable, since it consumes fewer network resources.

VoIP Standards• H.323 suite of protocols for interworking with H.323 endpoints.

– This allows the system to seamlessly integrate H.248/Megaco-based systems with H.323-based voice-over-IP (VoIP) systems. H.323 is also used to communicate between third-party softswitches.

• SIP for interworking with SIP endpoints. – This allows the system to seamlessly integrate H.248/Megaco-based

systems with SIP-based VoIP systems. SIP is also used to communicate between third-party softswitches.

• H.248 Megaco device control protocols to support the distributed VoIP call control architecture needed to scale up for carrier-class deployments.

• SS7 ISUP for seamless PSTN signaling integration.• SS7 TCAP for seamless integration with intelligent network-based

services.

Reminder : H.323 Network Elements

PSN

CSN

V.70Terminal

H.324Terminal

SpeechTerminal

H.322Terminal

SpeechTerminal

H.320Terminal

H.321Terminal

GSTNGQOS LAN

N-ISDN B-ISDN

H.323 MCU

H.323 Terminal

H.323 Gatekeeper

H.323 Gateway

H.323 Terminal

H.323 Terminal

Media Gateway Control ProtocolMGCP

• MGCP is designed as an internal protocol within a distributed system that appears to the outside as a single VoIP gateway.

• It is composed of a Call Agent, that may or may not be distributed over several computer platforms, and of a set of gateways, including at least one "media gateway"

• Media Gateway performs the conversion of media signals between circuits and packets, and at least one "signalling gateway" when connecting to an SS7 controlled network.

• In a typical configuration, this distributed gateway system will interface on one side with one or more telephony (i.e. circuit) switches, and on the other side with H.323 conformant systems.