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ring down circuit
no dialing of numbers, just physical connection
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Alexander Graham Bell
inventor of ring down circuit
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switch ( end office switch)
the cable from the telephone( your home) to centralized switch office whats the device
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PSTN
the telephone system of an enterprise company
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POTS – Plain Old Telephone System / Service
Term for traditional single residental line
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line noise
the static onto the voice network by electrical appliances
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accumulated noice
process of going through several amplifers with one voice signal
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repeater ( digital amplifer)
not only clean it but amplify the signal to its original condition with 1s and 0's
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7 times
max number you cna clean up a signal
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Pulse Code Modulation (PCM)
most common method of encoding an analog voice signal into a digital stream of 1s and 0s.
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voice frequency filter
what filters out anything greater then 4000 hz
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Nyquist theorem
if you sample at twice the highest frequency on a voice line, you achieve good-quality voice transmission. 8000 times per sec
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voice frequency filter
filter out anything greater than 4000 Hz
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quantization
wave is then coverted into a discrete digital form
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8 bits
PCM uses how many bits for code and logaritm compression
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64,000bps(bits per second) or 64 kbps
telephone structure is based what speed
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µ-law
: the standard used in North America and Japan
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u-law
the standard in europe
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u-law
what contry is responsibe for long distance calls from u-law to a-law
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Local loop (or Class 5 switch or endoffice switch)
connects home telephone to the central office switch
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tandem switches (class 4 switches)
end office switches interconnect through trunks to
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Trunk
communication path between several central office switches
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class 5 switch
switch services include basic dial-tone, calling features, and additional digital and data services to subscribers using the local loop.
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user to network signaling
How an end user communicates with the PSTN.
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Network-to-network signaling
How the switches in the PSTN intercommunicate
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analog,** Integrated Services Digital Network (ISDN) **or T1
when using twisted coper the user connects through
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Dual Tone Multi-Frequency (DTMF)
The most common signaling method for user-to-network analog communication
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DTMF
is known as in-band signaling because the tones are carried through the voice path.
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ISND
- uses out of band signaling
- the signal is transported on a channel separated from the voice (D-Channel)
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is faster
glare reduced
set up the line faster
benefits of out of band signaling
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glare
when two people are on the same circuit at the same time. (both dialing at the same time)
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bearer (B channel)
the channel on which voice data and fax is carried on
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data or control channel (D channel)
the channel on which the signal is carried
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Basic Rate Interface (BRI)
2 64 kbps B channels and one 16kbps D channel
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Primary Rate Interface (PRI)
23 64 kbps B channels and one 64kbps D channellarge enterprise
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network to network
network to network
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T1/E1, and SONET
Network to network communication is carried on
-
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T1 carrier over twisted pair
is a 1.544-Mbps digital transmission link normally used in North America and Japan
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T4 handles
168 T1 circuits or 4032 4-kbps connections and is 274.176 Mbps
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circuit based
what type of system is a wast of bandwidth
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50%
percentage of a call that is silent overhead
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Multi-Frequency (MF)
Robbed Bit Signaling (RBS)
what are the 2 in-band signaling methods
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SS7
what network to network also use out of band signaling
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out of band signaling
interconnect to the Intelligent Network (IN)
Makes the PSTN to offer CLASS (custon local Area signaling services) services
why is SS7 beneficial
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set up telephone calls between switches
open standard
what are the benefits of SS7
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Local Numbe Portability (LNP)
Reduced post-dialing delay- faster
Increased call completion- singal pckets that contain all the information are fast then tones.
Additional services (ANI, call blocking, etc.)
Services can be transparent across multiple vendors’ switching equipment
Connection to the IN enables the PSTN to offer Custom Local Area Signaling Services (CLASS) services such as
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regular busy signal
the end user is busy ( person is on the line but wont answer)
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all the circuits are full. ( when all the lines are full and it cant dedicate a 64bit channel)
fast busy
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custom calling
rely on the end office switch not the entire pstn to carry into from circuit switch to circuit switch
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CLASS features
require ss7 connecticity to carry features to from end to end PSTN
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North American Numbering Plan (NANP)
- 11 digit plan
- 1-NPA-NXX(central office code)-XXXX
- N= 2-9
- x=0-9
- ◦3 parts NPA-NXX-XXXX (traditional)
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statation number
the last 4 digets (extension)
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overlay
when you have to dial 1+ 10 digets because of diff area codes
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Local Exchange Carrier (LEC)
keeps track of long distance providers in a static table on the CO switch.( gives us the dial tone)
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North AmericanNumbering Plan Association (NANPA)
who gives the long distance code
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IXC – Inter-Exchange Carrier
is routed to the proper long distance network carrier
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ITU-T International Numbering Plan
- Recommendation E.164 specifies the following be used to route a call
- Country Code (CC)- 1,2 or 3 digits. First digit defines world numbering zones
- National DestinationCode (NDC)- Less than or equal
- to 15 digits
- Subscriber Number (SN)- Less than or equal
- to 15 digits
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Data has overtaken voice as the primary traffic on many networks built for voice.
The PSTN cannot create and deploy features quickly enough.
Data/Voice/Video (D/V/V) cannot converge on the PSTN as currently built.
The architecture built for voice is not flexible enough to carry data.
Circuit-switched calls require a permanent 64-kbps dedicated circuit between the two telephones.
Key *voice is made for reliabilty and over lost conversation*
Drawbacks to the PSTN
-
the layers are open standard
security is good
why use circuit switched
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payload
ip simpley transports data end to end with no real interest in
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Real-time Transport Protocol (RTP)
- Is utilized in addition to a User Datagram Protocol (UDP)/IP header to provide timestamping.
- Currently the cornerstone for carrying real-time traffic across IP networks.
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RTP
- runs atop UDP and IP and is commonly noted as RTP/UDP/ IP
- one-way delay of no more than 150 ms.
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jitter and delay
UDP check for
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delay and jitter
rtp is sensity to
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H.323
ITU-T recomendation for Voip call ( how multimedia traffic is carried over packet networks)
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VoIP Call-Control Protocols
As of this writing, the main VoIP call-control protocols are SIP, H.323, MGCP, and H.248/MEGACO
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SIP
a media-based protocol that will enable end devices (endpoints or gateways) to be more intelligent
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Open Service Application Layer
Thousands of new enhanced applications can be specifically developed for packet infrastructures (great for call centers)
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Reliability
Network stability
Guaranteed bandwidth per call, call quality
More feature-rich PBX environment
No “viruses” or other user-induced problems
Reasons to choose traditional PSTN
-
cheaper in long run
maintance is better
more application
reduce load and biandwidth
but security not as good
why choose voip
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a fax machine
what are ATA's for
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