Lecture 11

Lecture 11

Convergence

Switching

• Circuit Switching– designed to support voice network

– set up a complete path before connecting calls

– path saved for entire duration of call

• Packet Switching– only uses network capacity when data to be transported

– data broken into packets, multiple computers share same path

Circuit Switching

• Based on voice traffic

• Today data traffic increasing

• Not necessary to reserve entire path for a connection when sending data

• Waste of capacity when adding up silences on the circuit

Packet Switching

• Internet Protocol does not save a path in the network for the entire duration of the call

• During pauses and silences, conversations from multiple sources are transmitted over shared facilities

• These variable lengths of data are called packets

Increases in Data Traffic

• Caused by:– Internet usage from individual homes– increased email usage

IP-Based Networks

• Will increasingly be built due to:– increased level of data traffic– increased demand for VPNs

• VPNs are managed by carriers that provide links between corporate sites, and between corporate sites and their customers

• Will dramatically change the design and structure of the public network

Structure of Telecom Networks

• Is changing– Increases in competition

• causes lower long distance prices

• lower profit margins on long-distance

• may disappear

• Less costly to build due to increases in efficiency in equipment and multiplexing

Overlay Networks

• Separate network for a particular service covering most of the same geographical locations as the basic telephone network, but operating independently

• Elimination of these is a cost saver• Run on their own equipment• Everything duplicated when you have an overlay

network

Technical Advances

• Leading to improvements in IP networks:– improvements in switching routers– faster digital signal processors or DSPs– dense wavelength division multiplexing– lower, cost, programmable switches– new protocols improving the quality of voice

and video over packet networks

Switching Routers

• Enhance the quality of voice and video carried on IP networks– establish a path in network for high priority services

such as voice and video

– addressing stored on silicon cards

– multi-protocol label switching enable router to process calls faster

Digital Signal Processors

• DSPs are special purpose micro-processors

• execute instructions

• good at performing small number of repetitive tasks such as:– converting analog voice into digital– compressing voice– packetizing voice

Voice Compression

• Key capability of DSPs

• uses mathematical algorithms to make voice smaller so it can be sent at lower speeds

DWDM

• Fiber optic multiplexing technique

• Enable one strand of fiber to carry up to 96 channels of data

• Makes networks faster and lower in cost to construct– need fewer amplifiers to boost signal

– need less fiber

– need fewer multiplexers

Programmable Switches

• Non-proprietary telephone switches

• Work with enhanced services in the public switched network– calling card services– debit cards– voice messaging– fax services– international callback

Programmable Switches

• Connect central office switches with enhanced services

• Can transport calls

• Cost less than traditional central office switches

• Costly switching programmed into router

• Can be used to aggregate calls

Converged Networks

• Free calling over the Internet– proprietary software

– soundcard

– headset, microphone, or telephone plugged into computer

• H.323– standard way for users to make voice calls from

PCs connected the Internet

Calls from PCs to the Telephones

• Carriers include:– IDT

– Delta Three• offer long distance to consumers from PC or phone• software available from the IDT Web site• users abroad can make calls to US 10-15 cents p/min• users place local call to IDT switch, voice translated to

digital, compresses, packetized, routed over Internet

Calls over Internet to Telephones

• Carriers: IDT, ATT Worldnet, Delta Three– sell service routed from customer’s phones to Internet

– customers dial a local telephone number and PIN number

– local telephone provider routes call to the Internet Telephony Service Provider (ITSP) POP

– digitized, compressed, packetized

– routed over the Internet

– deconverted to analog

– billing tracked

Carriers with Facilities

• Constructing new networks too expensive

• Switches are now connected to networks

• Carriers with switches buy exclusive access to fiber optic channels– Indefeasible Right to Use (IRU)– carrier purchases the rights to a set number of

fiber strands from owners of fiber network

Converged Networks

• Calls over Internet from PC to telephones

• Calls over the Internet from telephones

• Carriers with their own facilities

• Data-only networks using IP and ATM

Applications for Convergence

• Prepaid Debit Cards

• Document Sharing

• VPNs between corporate sites, E-commerce– Security issues

– tunneling

– network-based address filtering

– authentication

– authorization

Tunneling

• Way to provide security on VPNs

• VPNs are shared services: security an issue– traffic from multiple organizations carried on

same transportation media– tunnels surround customer packets with an

extra header on each packet to provide security– encryption also important component to

tunneling

Tunneling

• A local area network term– Means:

• to temporarily change the destination of a packet

• to traverse one or more routers that are unable to route to the real destination

Network Based Address Filtering

• Alternative to tunneling

• Address contains security information

• Software looks up information contained in IP address to accept or reject information

• Frequently used on security software located in organizations’ premises

Authentication

• Authorizes you as the individual you claim to be on the system

• CHAP popular authentication protocol– Challenge Handshake Authentication Protocol

• Every time a remote user attempts to log onto the VPN the remote computer will be challenged by the security server

• Remote computer responds with value calculated by CHAP software

Authorization

• Ability to allow or deny an individual access to databases or services

• Done– by the carrier– again at the customer site

Voice and Data Using IP on Dedicate Lines

• VPN can be created by leasing dedicated lines

• IP used on these dedicated lines to send email, data, voice

• Requires use of:• security software

• routers

• multiplexers

Connecting Phone Systems to IP Networks

• Used to connect two or more locations

• Accomplished by connecting existing phone system to on-site routers– to send voice and fax over spare capacity in

VPN or private lines using IP– voice digitized, packetized, compress then

formatted for phone system, packets reordered, and decompressed

Call Center Connections to Internet

IP-Based Telephone Systems

Summary

• IP for voice telephony still in its infancy

• most voice traffic still carried of circuit-switched public networks

• Voice over IP expected to grow

• Being deployed by corporations for internal calling domestically and internationally

• Sales today done on wholesale level