Transcript What is IP?

A primer on the network
Dennis Couture
Director – Rural Markets
[email protected]
Congressional staff briefing June 7, 2005
The Telecommunications Network
> Our telecommunications network allows us to transmit
“information” electronically virtually anywhere.
> “Information” takes many forms, each with different
characteristics
•
•
•
•
•
Voice
Email
Broadcast video
Real-time video
Gaming
Mixing traffic requires solid engineering
2
Traffic types and characteristics
Bandwidth
Voice
Low
Delay
Tolerance
Low
Error
Tolerance
Medium
Email
Low / Medium
High
Zero
Broadcast video
High
High
Medium
Real-time video
Medium / High
Low
Medium
Gaming
Low / Medium
Low
Low
The more stringent the demands,
the more expensive the network is to build and
to maintain.
3
What is voice?
> Voice is audible human communication
• Content is concentrated at frequencies below 1KHz
• Nuance and voice uniqueness reside above 1KHz
• Traditional telephony transmits a maximum of 4KHz (NOT Hi-Fi)
> Other characteristics of voice:
• Voice communication is usually half duplex (“wasteful”)
• Voice is sensitive to delay
• Echo
• Delayed “half duplex” speech (“Over to you, Bill!)
• Voice is tolerant of interference
• The human ear/brain combination is a great receiver
• Analog noise is filtered out and ignored
• Digital bit errors have virtually no impact on intelligibility
4
Sound Waves
5
A real speech signal
6
Analog Telephony
•
•
•
•
Electrical signal mirrors the voice signal
Objective is to accurately transport this signal
4KHz signal allows speaker recognition
Common impairments include:
– Loss
A
– Noise
– Distortion
– Delay
• Impairments can accumulate
7
t
Digital Telephony
> Analog signal is “sampled”
• 8,000 samples of 8 bits every second
• 64Kbps required to carry normal voice
> Samples are transmitted digitally
> Signal is reconstructed by connecting the dots
> Impairments are minimized
• Loss
• Noise
• Distortion
• Delay
A
> Impairments do not accumulate
At this point, the voice has become a stream of
data!!!
8
t
Digital Formats
> This 64 Kb format is called Pulse Code Modulation (PCM)
• 64 Kb is a slow bit rate
> Multiple 64 Kb channels can be combined
•
•
•
•
This is called Time Domain Multiplexing (TDM)
Typically 24 channels are sequenced in a 1.544 Mb signal
These are called DS-1 or T-1 circuits
Think of loading a conveyor belt into pre-assigned slots
> Multiple DS-1 channels can then be combined
• DS-3 carries 28 DS-1 channels or 672 voice channels
• Optical systems go much higher
• OC-192 carries 129,024 voice channels
9
Let’s talk about transport
> Transmission facilities carry communications from
point to point
• Access facilities reach out to end users
• Interoffice facilities (trunks) connect internal parts of the
network
> A tremendous amount of telephone company
investment lies in transport (much more than
switching)
• Procurement and installation of cable facilities
• Terminal equipment at each end of the facility
• Ongoing maintenance costs
> These facilities deliver high bandwidths in a
reasonably secure manner
10
Fiber Transmission
11
Fiber Optics
> Light is pulsed on and off very rapidly
• Think naval flashing lights!!!
> Fiber optic systems provide:
• Very high capacity
• FASTER - Bit rates are very high
• LONGER - Distance between repeaters is increasing
• WIDER - Multiple “colors” can ride on the same fiber
• Secure transmission
• Excellent reliability
• Excellent economics
Fiber optic systems carry the vast majority of long
distance voice and data traffic
12
Increasing optical bandwidth with
Wave Division Multiplexing (WDM)
TDM
WDM
Exploits
Higher Speed
Similar to
Adding Lanes
Up to 72 “colors” of light share the same fiber
capable of 9,289,728 simultaneous calls!
13
Add more lanes to the highway
• DWDM Upgrade (Dense Wave Division Multiplexing)
•Supports OC-48 and/or 192 line rates
•Provides “effective” line rates of Terabits per second.
Channel 1
Optical
Fiber
Channel 2
DWDM
Channel 3
Channel n
14
Coupler
Enough of the preliminaries…..
How does the network work?
15
Network topology
> The network architecture physically resembles a
highway or train system
• It consists of network nodes (cities and towns) interconnected
with transport facilities (roads or tracks)
16
A SONET Network in the D.C. area
Synchronous Optical NETwork
Looks a lot like
the highway
system!!!
17
Meanwhile at the edge of the network…..
18
Telephone Loops
Twisted Pairs
> Loops connect your telephone to the network
> Analog transmission
> Long loops (> 18 Kft.) deteriorate the signal
• Loss, Frequency Distortion, Noise
> Load coils can correct this distortion
• Cut off high frequencies
• Preclude use of DSL
A
Increasing loop
length
^
4 Khz
19
f
Carrier Serving Areas
> Short loops (no load coils) are now standard
• Less costly to build and maintain
• Allows higher frequencies, so as to carry data
• DSL can be provisioned in a CSA
> High speed links connect the Digital Loop Carrier
(DLC) to the central office
• May be copper or fiber fed
Local
Serving
Area
Central
Office
DLC
DLC
20
Carrier
Serving
Areas
Mixed Service Delivery With a typical DLC
> No VoIP in this picture
$$
> Common facilities to the remote unit
• Mixed TDM and IP traffic
> Loop carries analog voice plus IP
> Could add Broadband Voice via the PC or an IP Phone
> Analog phone service survives power outages
Today’s investment supports
future services.
IP
DSL
DSLAM
IP
TDM GR-303
TDM
Switch
PSTN
21
NG
DLC
Analog
Voice
RTP/IP
TCP/IP
Mixed Service Delivery With BBDLC
and a TDM switch
>
>
>
>
>
Common facilities to the remote unit carry only IP traffic
Loop carries analog voice plus IP
BBDLC converts analog voice to IP
Could add Broadband Voice via the PC or an IP Phone
Analog phone service survives power outages
IP
RTP/IP
IP
Gateway
IP
DSL
BB
DLC
TDM
Switch
PSTN
VoIP
22
TCP/IP
MGCP
MEGACO/H.248
Analog
Voice
Triple Play
>
Why do Triple Play????
•
One method of extracting more revenue from a DSL line
•
•
>
A significant defensive move against the cable threat
Triple play is a big step
•
•
•
>
Content acquisition is an important issue
Own or share a head end?
Buildout of access network can be costly
Impact of HDTV must be considered
•
•
>
Trying to improve a marginal business case for Internet Access
Bandwidth requirements / channel capacity
MPEG-4 equipment
Video on Demand is a significant revenue opportunity
The demand for more advanced video-related
capabilities will continue to rise.
23
Ah, but where do the roads go?
> Roads interconnect towns and cities
> Access facilities connect users to their local central
office
> Trunk facilities connect central offices to each other
24
Switching Systems
> A digital switch:
• Converts voice into a digital format
• Interprets the dialed digits
• Routes the call to its destination by:
• Completing local calls
• Transferring all other calls to another switch for completion
Central
Office
Trunks
Central
Office
DLC
25
North American Numbering Plan
26
Numbering Issues
> In the wireline world, an area code defines a
geographic area
• Mobile phones and some VoIP services break this model
• This is the source of the E911 problem for both VoIP and
cellular
> Geographic and Overlay area codes
• 7 vs. 10 digit dialing
> Toll free increase (888, 877 etc.)
> Depletion of number inventory
• Explosion of cell phones, pagers, fax machines, 2nd lines
• Recovery program underway (000’s block pooling)
> Local Number Portability
• Support of a competitive marketplace
27
Signaling
> The method of controlling the routing of a call
• Uses in-band tones and computer communications
> Dual Tone Multifrequency (DTMF)
i.e. TouchTone® in-band signaling
> SS7 (Signaling System 7) (out of band)
• Very fast and reliable
• Sets up calls via Signal Transfer Points
• Performs special data retrieval
SCP
SCP
STP
STP
From service Control Points
• 800 number translation
> Call Progress Tones
• Busy (60 IPM)
• Reorder (120 IPM)
• Special Information Tones (SIT)
> VoIP essentially uses in-band signaling
• Security and reliability issue
28
Central
Office
Central
Office
Old-Fashioned long distance
1
2
AT&T
Long Lines
Tandem
Offices
End
Offices
29
5
...
1
2
2
...
2
3
...
3
3
...
3
4
...
4
4
...
4
...
5
5
...
5
5
...
5
5
...
5
Modern long distance
> The network is “flatter”, with multiple LD Carriers
> The Local Access and Transport Area defines a Bell Company’s
operating area.
> Rural telephone companies may connect directly to LD carriers
but often connect to the closest Bell tandem switch
LATA
5
5
4
AT&T
... 5
MCI
:
Sprint
30
LATA
4
5
... 5
Operator Services
> Human intervention assists in call processing
•
•
•
•
•
Collect calls
Bill to 3rd party
International calling assistance
Directory Assistance
Emergency call transfer
> Dial “O” for local operators
TOPS*
Tandem
End
Office
End
Office
> Dial “OO” for LD operators
* TOPS – Traffic Operator Position System – a Nortel product
31
Let’s talk Wireless!!!!
> Wireless communications are booming
> Most of the world utilizes the GSM radio format
> In North America, multiple radio formats in use:
• CDMA, GSM, AMPS, TDMA
• Impacts the development of wireless devices
• GSM and CDMA formats are incompatible
(((
)))
(((
Mobility
Switching
System
Base
Station
Controller
)))
Cell sites
Only a small portion of the call is carried over wireless
32
(((
Why is it called “cellular”?
> A cellular radio has limited range
> As a user moves out of range, the call
transfers to a different tower (a ‘handoff”
that is often the source of dropped calls)
> The area served by a tower is a “cell”
> Cells are laid out in a honeycomb
pattern and can be subdivided into new
cells as traffic increases
> Adjacent cells use unique frequencies to
avoid interference requiring the phone to
change channels
> Cells can also be “sectorized” to
increase capacity
33
(((
)))
)))
Wireless to the world
> Mobile calls are wireless only at the edge
> The remainder is handled exactly like a wireline call
Today’s network
…
:
Wireless network
Mobility
Switching
System
Base
Station
Controller
LATA
5
5
4
LD #1
... 5
LD #2
LD #3
34
Cell sites
Wireless Communications
> More than just PCS/Cellular Service
> Wireless data is becoming more and more important
•
•
•
•
•
WiFi technology is spreading rapidly
Spokane and Philadelphia city-wide
Walla Walla rural network (1500 square miles)
Small hot spots (McDonald’s, Starbucks)
Home networking
> WiMax will emerge to compete with WiFi
• More than just range extension
• Adds Quality of Service (QoS) assurance
• Terminal pricing will be critical
> Security is an issue – war chalking
Convergence of wired and wireless on an IP
network is the future!
35
What is the Internet?
> The Internet is a large computer network
• Originally designed to allow communications in times of
nuclear war – DARPA design
• Largely a self-healing network
> All data transmission is packetized
• Utilizes IP (Internet Protocol) routing
• Packets are switched by routers
> The most popular applications are:
• Email
• The World Wide Web
• Access the web using Modems, LANs, xDSL, cable etc.
• Web content is stored in servers at web sites
36
What is IP?
• Internet Protocol is the grammar of the Internet
• A standard method of computer communication
• Utilizes a unique 4-byte addressing scheme (e.g.
47.11.97.255)
• Sends variable length packets
• Packets are delivered on a “best efforts” basis
• Packets are often lost
• Packet delivery times are relatively slow and quite
variable
• Error detection and correction are the
responsibility of end users
• TCP (Transmission Control Protocol) does this
• Error correction is accomplished by retransmitting
missing or damaged packets
• Real-time applications typically do not correct errors
37
The Internet’s dirty little secrets
> The Internet was never designed as a real-time
delivery system.
• The transit time for individual packets can vary substantially
• This variance is called jitter and effectively adds delay to realtime applications – e.g. VOICE
> Traffic capacity is relatively poorly engineered,
particularly at the edges
• IP doesn’t handle congestion well
• Delay increases the jitter limits
• IP will drop packets under congested conditions
Delay and packet loss are the two major causes of
voice quality deterioration in VoIP calls
38
Packetizing voice (VoIP)
> The format for carrying voice is changing to a
packetized format, primarily using IP
• Voice can be transmitted much like data is over the Internet
> Maintaining voice quality is a big issue
• Control of delay is essential
• Packet loss must be minimized
• Compression has some disadvantages
> “Voice over packet” and “Voice over the Internet”
are not exactly the same
> Traditional TDM voice will be around for years
> Interworking of VoIP and TDM is mandatory
39
The role of VoIP
> VoIP is many things to many people
> To the Enterprise:
• A vehicle for major expense reduction
• A key to improving productivity through feature integration
> To the Carrier:
• A vehicle to lower LD costs, enhance CLEC reach and build unique
customer networks
• Eventually, the means to operate one network, eliminating TDM
> To the Consumer:
• Today, primarily a method of buying cheaper telephone service
It will take many years for VoIP to totally replace
TDM; but high value subscribers will adopt the
technology sooner.
40
How does IP telephony work?
(IP in the middle)
SS7
Gateway
“Gatekeeper”
“Gatekeeper”
IP
TDM
TDM
Gateway
Gateway
PSTN Local
Exchange
New York
PSTN Local
Exchange
Legend
SS7 Protocol
Bearer Path
Interworking Protocol
IP Control Protocol
41
Paris
How does IP telephony work?
(Totally IP)
SS7
Gateway
Telco
provides
the link to
the Internet
“Gatekeeper”
“Gatekeeper”
Telco
provides
the link to
the Internet
IP
TDM
PSTN Local
Exchange
42
PSTN Local
Exchange
Gateway
Gateway
DSL over
existing
copper
loops
VoIP line
TDM
Legend
SS7 Protocol
Bearer Path
Interworking Protocol
IP Control Protocol
DSL over
existing
copper
loops
VoIP line
How does IP telephony work?
(IP to PSTN)
SS7
Gateway
Telco
provides
the link to
the Internet
“Gatekeeper”
Sydney
“Gatekeeper”
Telephone
company
terminates
the call
IP
TDM
PSTN Local
Exchange
Gateway
43
PSTN Local
Exchange
Gateway
Common
Transport
VoIP line
TDM
Legend
SS7 Protocol
Bearer Path
Interworking Protocol
IP Control Protocol
VoIP line
An architecture for evolution
(((
(((
Application
Server
)))
(((
)))
)))
SIP
TA
IP
RTP/IP
Hybrid Switch
IP
Gateway
IP
DSL
TCP/IP
BB
DLC
Analog
Voice
PSTN
Legacy
lines
Eventually the hybrid becomes a softswitch.
44
45