Transcript Convergence

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 circuitswitched public networks
• Voice over IP expected to grow
• Being deployed by corporations for internal
calling domestically and internationally
• Sales today done on wholesale level