voice services
TRANSCRIPT
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)
04/12/23 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
04/12/23 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
04/12/23 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
04/12/23 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
04/12/23 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
04/12/23 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
04/12/23 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
04/12/23 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.
04/12/23 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.