cisco voice voip

7/27/2019 cisco voice VOIP

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This Voice Internetworking tutorial provides information about this rapidly emerging technology, andexplains how to set up both analog and digital voice calls over networks. In modules 1 through 4 in theasic Voice over I! tutorial, you will learn to configure and troubleshoot Voice over I! "VoI!# callsusing the $isco %&4' router and the $isco ()*%'' access router in a virtual simulated network.

Today,private branch exchanges "!+s#( !+ is a small telephone switch owned by a company ororganiation. -ithout a !+, a company would need to lease one telephone linefor every employeewho has a telephone. -ith a !+, the company only needs to lease as many lines from the telephonecompany as the maximum number of employees that will be making outside calls at one time. This isusually around 1' of the number of extensions.

( telephone switching system must perform the following functions/

0ecognie a reuest for service.

2otify the station of an incoming call.

3etect onhook or offhook status.

!rovide status information to the originator of the call, such as when the called telephone goesoff hook, or the network is busy.

5stablish a connection6really 7ust a path across the network from one endpoint to another.

)witches also act as concentrators because the number of telephones in use is usually greater than thenumber of simultaneous calls that can be made. 8or example, a company may have &'' telephone setsconnected to a !+, but may have only 1* trunksconnecting the !+ to the central office "$9#switch.
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( $9switch might service a few hundred lines or as many as 1'',''' lines.

$9 versus !+

( !+ is like a miniature $9 switching system designed for a business or a private institution.

(lthough a !+ and a $9 are closely related, there are differences between them.

( !+ is intended for private operation within a company. ( $9 is intended for public service.

( !+ usually has some type of arrangement to greet outside callers and connect them to

internal extensions.

:ost !+s do not maintain the high level of service protection that must be maintained in a

$9. (ssurance features such as processor redundancy "in the event of processor failure# andbattery backup power, which are standard in a $9, may not be a part of a !+.

$9s reuire a sevendigit local telephone number, while !+s can be more flexible and create

dialing plans to best serve their users "%, 4 *, or & digit extensions#.

( !+ can restrict individual stations or groups of stations from certain features and services,

such as access to outside lines. ( $9 usually has no interest in restricting usage because thesefeatures and services are billed to the customer. $9s normally provide unlimited access to everymember on the network.

The key components of a telecommunications network are loops, lines, trunks, and!+ trunks.

;oops

( loopis literally the physical pair of wires that connects a telephone directly to a $9 a local loop is the connection between your houseand the phone company.

Loops, Lines, and Trunks
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;ines

( lineis a communications path between a customer


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!+s and !+ Trunks

In a business using a !+, every employee


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T1 is a B4channel digital system that carries data at 1.*44 :bps through the telephone

switching network. T1 is used in 2orth (merica and Capan.

51 is a %'channel digital system that carries data at the rate of B.'4D :bps. 51 is used in

5urope, (ustralia, and ;atin (merica.

$oaxial $able

$oaxial cable, often referred to as Ecoax,E is made up of a hollow outer cylindrical conductor thatsurrounds a single inner wire conductor. Two types of coax cable are currently in use6*'ohm fordigital signaling and F*ohm for analog and highspeeddigital signaling. It is currently rare to findcoax used for telephony, but use of coax for usertonetworkconnections is becoming more common.$oax is occasionally used inside the network over short distances at the higher rate digital transportsystems6T%, T4, and5%.

T%transmits data via the telephone switching network at the rate of 44.F%& :bps. T% and T4

are used primarily in the A.).

5%is a digital transmission system used predominantly in 5urope, (ustralia, and ;atin (merica.

5% carries data at a rate of %4.%&D :bps.

0adio 8reuencies

The use of cellular services6which use radio waves6for network access is increasing in popularity,both for analog cellular services and digital !ersonal $ellular )ervice "!$)#. 0adio is also increasinglypopular for the wireless local loop. 0adio lets you avoid installing wiring in the ground to provide theservice. Inside the network, radio is usually used with microwave technology such as ;ocal :icrowave3istribution )ystem ";:3)# and :ultipoint :icrowave 3istribution )ystem "::3)# to carry higherrate digital systems on a linetosite basis between points.

8iberThe transmission format for fiber in 2orth (merica is typically )ynchronous 9ptical 2etwork, or)925T. )925T was designed to run at very high speeds "up to B.* Gbps#. The backbones of mostcarrier networks today are based on )925T. )ynchronous Transport )ignal level 1 ")T)1# is the basicbuilding block signal for )925T, with faster rates defined as )T)n, where nis a multiple of the )T)1rate "*1.D4 :bps#. )925T was approved as an international standard in 1@DD.

$able TV companies generally do not use )925T because they have already converted much of theirnetworks to fiber, at least into residential neighborhoods. To avoid digging up lawns to lay cable,copper is still typically used for the last section into the customer


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$oaxial$able

$able TV T%, T45%

44.F%& ?%4.%&D :bps

0adio $ellular -;;, ;:3), and ::3)

T%, T45%

44.F% :bps%4.%&D :bps

8iber )925T$able Television

)925T B.* Gbps

There are two fundamental types of signaling/ in-bandand out-of-band.(n inband signal istransmitted within the freuencyrange normally used for information transmission6the same channelthat you talk over or send data over. (n outofband signal is communicated outside those freuenciesor channels normally used for information transfer. The other freuency or channel could be on thesame physical interface but not inside the same bandwidth being used for voice or data. 8or example,on a freuency division system, the signal could be out of band because it is transmitted at a higherfreuency than the voice freuencies. 9n a timedivision system, it could be out of band because it is ina different time slot from the other freuencies.

etween the user and the network, inband signaling is generally used. ut if you ever use I)32 toplace voice calls, then you


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H

-ith the telephone network, as with any large network, the numbering scheme is one of the mostimportant issues. 5very telephone has a uniue number, or address, analogous to a network address. In2orth (merica, the 2orth (merican 2umbering !lan "2(2!# is used> it consists of a threedigit area

code, a threedigit office code, and a fourdigitstation code. (rea codes are assigned geographically,office codes are assigned to specific switches, and station codes identify a specific port on that switch.The format used is 12xx2++++++, with 2 B J @ and + ' J @. -hen you place a call, beforethe call can be switched to its final destination, the telephone network uses signaling to identify thefinal address.

These numbering plansnormally conform to the ITAT 5.1&4 recommendations, which cover theinternational dialing plan as well as many other recommendations. 8or an international calling plan,each country is assigned a one to threedigit country code> each country


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( typical telephone does the following/

0euests service from the network

!erforms dialing functions

!erforms a notification function "it rings#

!rovides answer and disconnect supervision

$onverts outgoing speech to electrical signals, and vice versa

(utomatically ad7usts to the supplied power

8or a telephone call to perform these functions and complete the call, several forms ofsignalingmustoccur/

(ccess signaling

)tation loop signaling

(ddress signaling

The purpose of signaling in a voice network is to establish a connection. =ou typically begin a phonecall by taking a phone off hook, which sends an access signal. The line is seied, a path establishedacross the network, and on the other end, the call is acknowledged.

The following Vo3 describes how a call is made in greater detail.C lick Her eto L a u c h VoD

The next section describes the call process and signaling in more detail.

(lthough various types of signaling are used in telecommunications today, this tutorial coversonly those that directly apply to $isco voice implementations. :odules 1 and B cover the most


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common analog signaling techniues supported by the $isco %&4'6loop start, ground start, and 5L:>digital signaling is covered later.

The following Vo3, provides a good introduction to telephone signaling. (ccess this Vo3 beforeproceeding with this section.

C lick Her eto L a u c h VoD

(ccess )ignaling

The first type of signaling involves access signaling, which determines when a line is off hook or onhook. -hen the handset is on its cradle, the phone is referred to as being on hook. -hen a telephone ison hook, the two wires do not touch, so the circuit "loop# is open and no current flows. -hen thehandset is out of its cradle, it goes off hook. The wires touch, closing the loop, allowing current to flowthrough the two conductors that connect the phone to the network, sending an EoffhookE signal to theswitch. To place a call, the phone must be off hook. To receive a call it must be on hook.

When the phone is on hook, no current flows

When the phone is off hook, current flows through

the conductors, and a signal is sent to the network.

There are two common methods of providing the basic access signal/ loop startandground start.

Loop start. This is the most common techniue for access signaling in a standard !ublic

)witched Telephone 2etwork "!)T2#. :ost residential telephones are analog loopstarttelephones, based upon the concept of the subscriber loop, or local loop. The loop is anelectrical communications path consisting of two wires, one for transmitting and one forreceiving voice signals. The twowire circuit is still referred to as the tip and ring, with the tip
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being tied to the ground and the ring tied to the negative side of the battery. -hen the phonehandset is picked up "goes off hook#, this action closes the circuit, establishing a loop betweenthe !+and the phone. $urrent is drawn from the battery of the !+, indicating a change instatus. This change in status signals the current detector in the !+ to provide dial tone. (nincoming call is signaled to the handset by a standard on?off pattern, which causes the telephoneto ring.

To give you a more graphic representation of how loop startworks, review the following2etit.

round start.Ground start is another access signaling method used on on trunk linesor tie

linesbetween !+s to indicate onhook?offhook status to the $9. In groundstart signaling,one side of the twowire trunk "typically the ringin the tip and ring configuration# is

momentarily grounded to create dial tone.

To give you a more graphic representation of how ground startworks, review the following2etit.

The tip is tied to the ground! the ring

is tied to the negati"e side of the #attery.

(s you can see, the seiure of the line reuires the cooperation of both parties to the call. ( failureon either side stops the progress of the call. Therefore, both parties terminate service upondisconnecting "either an open tip or ring lead#. This setup averts the disconnect supervision problemthat might occur on the loopstart circuit, when a given line can be released only by the party whooriginated the phone call. 8or this reason, !+s work best on groundstart trunks.

In a normal loopstart circuit, when you pick up the handset, you hear a dial tone indicating that acircuit is ready. 9n a groundstart circuit, however, the euipment at the userMs end should sense theflow of electrical current on the EtipE lead and interpret that the !+ is ready, so a dial tone from a!+ is not necessary, and its presence is optional. This setup allows the network to indicate offhookstatus, or seiure of an incoming call independent of the ringing signal.
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-hen the trunk is seied simultaneously from both ends, the resulting condition is known asglare. Glare makes loop start a poor solution for highvolume trunks such as those found in a

workplace. Ground start corrects for glare by providing current detection at both ends.

8+9 and 8+) )ignaling

(foreign exchange (FX)is a term applied to a trunk that has access to a distant $9. 8+ trunk signalingcan be provided over either analog or T1 links and which utilie either loopstart or groundstart offhook signaling techniues.

$oreign e%change Station &$%S'( )tandard residential phone lines are configured for 8+)

signaling. (n 8+) interface can be used to connect basic devices such as phones, modems, andfaxes and must provide voltage, ring generation, offhook detection, and call progressindicators.

$oreign e%change )ffice &$%)'(8+9 signaling is used primarily to communicate with $9

switching euipment or !+s. ecause an 8+9 port on a router communicates directly withthe !)T2 or a !+, it reuires that a dialtone, ring indication, and call progress indicators beprovided to it.

The basic design of 8+) and 8+9 is simple but can cause problems, including disconnect supervision,probably the most common one. This problem can be fixed by implementing either disconnect

supervision or using ground start.

5L: )ignaling

(nother analog signaling techniue, used mainly between !+s or othernetworktonetworktelephony switches, is known as 5L:, which stands for Eear and mouthE "or for Erec5ive andtrans:itE#. There are five 5L: signaling types, as well as two different wiring methods. $isco 5L: interfaces and configuration are covered in the next module of this course.

)tation ;oop )ignaling

-hen the !+ receives the offhook signal, it responds with an audible signal indicating that it is readyfor a call6the dial tone. This twoway exchange between the !+ and the telephone is known asstation loop signaling.
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(ddress )ignaling

In response to the audible prompt of the dial tone, the caller can reuest connection to anothertelephone by transmitting the address "telephone number# of the reuested telephone "sometimesreferred to as the called party identification number# to the !+. This is known as address signaling.

Telephones generally use two basic types of address signaling/ pulse and tone. *ulse dial "rotary dialing#

0otary dial phones represent the digit being dialed by momentarily stopping the current flowwhen the user turns the circular dial. 8or example, the circuit is broken three times, whichcreates three pulses in the current, to dial the digit E%.E

In general, the repetition rate of the pulses must be between D and 11 pulses per second "pps#.The percent of the time that a break state is maintained within a pulse must be approximately &1percent of the pulse length. This setup is depicted in the following diagram.

*ulse +ialing

( complete explanation of pulse dialing is beyond the scope of this tutorial. 0efer to 5I(standard 5I(?TI( 4F' for the technical details about pulse dialing.

Tone dial "dual tone multifreuency, or 3T:8> the method used by pushbutton telephones#.

3T:8 is the most commonly used signaling system today. The keypad on a pushbutton phonehas 1B keys. 5ach key press generates both a lowfreuency and a highfreuency tone "theDual Tone# that is specific to each individual key. The tones are then picked up and interpretedby telephone switches. The tones were selected to easily pass through the phone network withminimum interaction with each other and little attenuation.

The following table describes the 3T:8 tone pairs.

+TM$ Tone *airs

$reuency

in -ert&-'

/012 - /334 - /566 - /433 -

426 - 1 ($B

358%

"89#N(O

661 - GKI CP; :29 "8#
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4 * & NO

780 - !0)F

TAVD

-+=@

"I#N$O

780 - Q 9!50

'

R "!#

N3O

8or most 3T:8 systems, there are 1B possible signaling states. "9nly the values incolumns 1J% are typically used. =ou can see that these correspond to the buttons on a standardpushbutton telephone. The fourth column contains additional values used by the A.).Government


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a path to the remote $9 could not befound. (ll trunks were busy.

$ongestion 4D' S &B' '.B '.% )imilar to fast busy.

0eorder 4D' S &B' '.% '.B The transmission paths to the office or

euipment serving the called customerare busy. :ay indicate a condition suchas a timedout sender or unassigned codedialed.

0ingback"normal#

44' S 4D' B.' 4.' The audible ring that the caller hearsthrough the receiver.

0ingback"!+#

4D' S 4D' 1.' %.' )ame as above, but note the differentinterval.

Kandset

offhook

14'' S

B'&' SB4*' SB&''

'.1 '.1 Ased to cause offhook customers to

replace the receiver onhook on apermanent signal call and to signal anon!+ offhook line when ringing keyis operated by a switchboard operator

Invalidnumber

B'' 6 4'' $ontinuous,freuencymodulated at 1 K

(lerts the calling party to hang up, checkthe called number, and dial again. Inmodern systems, calls to unassigned ordiscontinued numbers are routed to amachine announcement system thatverbally supplies a message. In some

older $9s, you could be routed to anintercepting operator. 0eorder tone mayalso be returned for this condition.

In countries outside 2orth (merica, the call progress tones you hear while placing a call maysound uite different from the ones represented in the table. The call progress tones in this table and thesound samples that you hear in this tutorial are based on 2orth (merican standards. The call progress

tones could be configured differently so that the freuencies and on and off times will vary.

-hen the !+ receives the 3T:8 digits that indicate the number to call, the !+ decides how toroute the call/ to the local telco


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(ssuming the call can be established, signaling would then occur at the remote end of the network. The$9 seies a line to the !+ and forwards the digits. The !+ selects the appropriate station, andsignals an alert. The call proceeds, and the switch generates ring voltageto the phone. -hen the phonedetects the voltage, it rings. The caller also hears an audible ring through the receiver> this signal is theringback signal that is generated by the switch.

To ensure proper call handling and voicemail routing,answer supervisionsignaling is particularly

important. 8or example, if a phone is not answered after a specified number of rings, a call can bererouted to voice mail based upon the lack of an answer supervision signal.

The methods of signaling discussed here are not the only available methods. 8or a more detaileddiscussion of signaling, including descriptions of supervision, address, callprogress, and networkmanagement signaling, read )ignaling, which is included with this tutorial. =ou can also search $isco$onnection 9nline "$$9# for more information on this and other voicerelated topics.
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cisco voice voip

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