Tài liệu PBX Networking Standard Telephony pdf

Module Objectives Upon completion of this chapter, you will be able to: • Describe typical PBX network applications • Identify the types of signaling used in PBX networks • Define the pr

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PBX Networking

Standard Telephony

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Module Objectives

Upon completion of this chapter, you will be able to:

• Describe typical PBX network applications

• Identify the types of signaling used in PBX networks

• Define the proprietary PBX protocols from Lucent & Nortel

• Identify design issues related with integrating PBX traffic over

data networks for both Lucent and Nortel PBXs

Upon completion of this chapter, you will be able to:

• Describe typical PBX network applications

• Identify the types of signaling used in PBX networks

• Define the proprietary PBX protocols from Lucent & Nortel

• Identify design issues related with integrating PBX-traffic over data

networks for both Lucent and Nortel PBXs

III General Design Implications

More specifically, this module focuses on a review of PBX

–Lowest cost and other policy-based routing

–Manipulation of outgoing and incoming digits

–Park, etc.

• Provides for sophisticated selection of route, i.e., saves on toll costs

• Provides detailed use records

There are many benefits of PBX

•It allows many phones in an office to share a fewer number of

outside lines, which helps to control cost growth

•It supports many different features, including:

• Short-numbering extensions

• Conferencing

• Forwarding

• Security restrictions

• Lowest cost and other policy-based routing

• Manipulation of outgoing and incoming digits

A private branch exchange (PBX) cabinet is a metal housing designed to hold the electronic components that make the PBX work Each cabinet

contains one or more shelves, or carriers with slots Each shelf in the PBX accepts a certain number of circuit boards There are different types of

circuit boards within a PBX, including the following:

• Both-way trunk circuit boards—Supports both-way trunks or

combination trunks that receive incoming calls or place outgoingcalls

• DID trunk circuit boards—Support a special type of trunk used for

incoming direct inward dialing (DID) calls only

• Universal trunk circuit boards—Mix both-way trunks, DID trunks,

loop-start tie trunks on the same board Also support Recorded ANnouncement (RAN), overhead paging, and music-on-hold

Extra Text

• Tie trunk circuit boards—Support point-to-point lines connecting two PBXs

so that the users of both systems may communicate with each other

without per-minute toll charges Most analog Ear and Mouth (E&M)

tie-trunk circuit boards handle two or four tie tie-trunks

• T1/E1 circuit boards—Multiplexers that support a high-capacity T1 or E1 circuit, enabling up to 24 (T1) or 30 (E1) voice conversations at one time Recall that T1 is the term used for a DS-1 signal carried over two copper pairs T1 is a type of line that is not a signaling type

• Digital telephone circuit boards—Support digital telephones The analog voice signal converts to a digital form at the telephone and goes back to the PBX as pulse code modulated (PCM) encoded bytes

• Analog telephone circuit boards—Support analog telephones, as well as fax machines, computer modems, and any other device which utilizes a plain old telephone service (POTS)-type loop start analog interface

• DTMF receiver circuit boards—Contain dual tone multifrequency (DTMF) receivers

• MF receiver circuit boards -Contain multifrequency (MF) receivers

• Tone sender boards -Generate all the tones for a system, including dial

tone, busy tone, DTMF, MF, and CLASS

• Common control circuit boards—Central processing unit of the PBX

When two PBXs communicate over non-ISDN tie trunks, they can use E&M

10s 100s

Switch

LA

CO Trunks Tie Trunks

CO Trunks Tie Trunks

PSTN

FX

416 526–1234

Switch

PSTN IXC

This graphic depicts typical legacy PBX-to-PBX connectivity connecting two PBXs in different local access and transport areas (LATAs)

The actual connections are from the PBX to the local exchange carrier

(LEC), for example, the central office (CO) switch then to a LEC tandem switch From there the connection is made to an inter exchange carrier’s (IXC) point-of-presence (POP), then into the IXC network cloud The

connections at the other end follow the reverse path

Tie-trunks are generally cross-connected (hard-wired) instead of switched at the LEC (CO) and IXC level If they are configured to go into a LEC/IXC switch, they are configured as dedicated nailed-up circuits

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10s 100s 10s 100s

10s 100s 10s 100s

LA

CO Trunks Tie Trunks

CO Trunks Tie Trunks

QoS WAN Internet/Intranet

FX

(212) 526–1234

PBX Supported Applications

Hold Forward Park Conference Building Page Networking Local Extensions

CCS,CAS, QSIG, Digital (PBX-to-PBX) E&M, Proprietary Digital (PBX-phone)

Tie trunks

CO trunks DID trunks

FX trunks RAN trunks Subscriber lines

Analog/Digital

IVR ACD Voice Mail Msg on Hold Call Center

Loop-type analog, T1,E1,n-wire, PRI, BRI Physical Line Type

The PBX stack is a representation of the various layers of functionality

supported by a PBX The lists of items for each layer are illustrative and not complete

You may also think about other components that provide line and trunk

supervision and signaling methods:

For analog and channel associated signaling (CAS):

• Seizure and disconnect supervision: loop-start, ground start, E&M, loop dial repeating

• (Dial) starting arrangements: Wink-start, immediate dial, delay dial

• Addressing methods: DTMF, MF, dial pulse

• Answer supervision: Battery reversal, E&M control lead signaling

For ISDN:

Tie Lines

Analog 2/4 wire type 1-5

Digital 2/4 wire

FXO interface

2

Analog

Analog trunk circuits connect automated systems (such as a PBX) and the network (such as a central office) The most common form of analog tie trunk is the E&M interface Like a serial port, E&M has a DTE/DCE type of reference In the telecom world, the “trunking” side is similar to the DCE, and is usually associated with CO functionality The Cisco 3600 acts as this side of the interface

The other side is referred to as the “signaling” side, like a DTE, and is usually a device such as a PBX There are five distinct physical configurations for the E&M interface (types 1-5), and two distinct flavors of audio interface (2-wire or 4-wire) Note that even though it may be called a 4-wire E&M circuit, it is likely to have 6 to 8 physical wires! The difference between a 2-wire and 4 -wire circuit is whether the audio path is full duplex on one pair or two pairs of wires

The foreign exchange office (FXO) interface (typically an interface card) supports the CO side loop-start line The foreign exchange station (FXS) supports the

station-side of the loop-start line Foreign exchange (FX) is the term used

historically to describe the PBX or telephone instrument connection to a remote CO Typically the “FX line” was used to get local, toll-free dialing in another LATA

Digital

Digital T1/E1trunk circuits are 4 wire In Europe, and soon in North America, ISDN BRI can be used as a trunk The BRI U-interface is 2-wire Subscriber lines may be 2- or 4-wire They support several typical analog signaling protocols, both in-band and out-of-band, ISDN, and analog emulation

III General Design Implications

The next section of this presentation is going to discuss PBX signaling

• In-band signaling

• CCS—Common channel signaling

• Out-of-band signaling

• Digital subscriber lines: 2-wire, 4-wire

• Digital trunks: 4-wire

Method of communicating telephony events: off-hook, busy, on-hook, etc.

Types of Signaling

There are two flavors of loop start lines The Station side loop start line uses

an FXS interface, while the CO side uses an FXO interface.Typically, digital lines are associated with out-of-band signaling

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Types of Telephony Signaling

Types of telephony signaling are as follows:

• Supervisory—Monitoring the status of a line or circuit to determine if it

is busy, idle or requesting service (flash-hook) Supervision is the term derived from the function of monitoring manual circuits on a

switchboard At that time, the signal was conveyed by a switchboard lamp for the line Now voltage levels, signaling tones, or bits (digital signaling) provide this function

• Addressing—The process of transmitting routing and destination

signals over the network Addressing signals include dial pulses, tone pulses, or data pulses over loops, trunks, and signaling networks

• Call progress—Signals that inform the user of the status of the call setup, for example, busy tones

III General Design Implications

The next few slides will focus on the analog side of PBX Signaling

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• Loop start signaling station side

–FXS Interface Side

• Loop start signaling CO side

–FXO interface side

• Ground start CO side

• E&M—Used for PBX dial tie trunks or carrier systems

–The best way to connect switches together using analog facilities

E&M Trunk Station

Side Loop Start Line

PBX or

CO Switch

CO Side Loop Start Line

PBX

Station Side Loop Start Line

Station Loop Signaling

PBX-to-PBX Signaling, or PBX to CO Signaling

Analog Signaling

There are three traditional types of analog signaling: E&M, station side

loop-start Signaling (FXO interface side), and CO side loop-start

signaling Stations connected to PBXs or central offices use the FXS

interface, while CO switches use the FXO interface

Consider the various interfaces available from the PBX when

interconnecting Cisco components Understand that the connection

needs to be supervised Supervision handles such things as call setup

and teardown, and monitors the actions of the connected entities

Analog is not the best approach for more than a few trunks The best way today is connecting PBXs via an ISDN PRI over a T1 circuit The

signaling used must support call supervision Without supervision, if a

caller hangs up the phone after receiving no answer, the “called” remote phone will continue to ring

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Off-hook Ground Battery Voltage

E&M Trunk Group

E

E M

M

Analog Signaling: E&M

•E&M signaling (PBXs, switches)

–Separate signaling leads for each direction

–6 to 8 physical wires

–E ("Ear" or "Earth")—Signal wire from trunking (CO) side to signaling (user) side.

–M ("Mouth" or "Magnet")—Signal wire from signaling (user) side to trunking (CO) side

–Allows independent signaling

Analog

Analog trunk circuits connect automated systems (such as a PBX) and the network (such as a central office, or CO) The most common form of analog tie trunk is the E&M interface Like a serial port, E&M has a DTE/DCE type of reference In the

telecom world, the “trunking” side is similar to the DCE, and is usually associated with

CO functionality The Cisco 3600 acts as this side of the interface

The other side is referred to as the “signaling” side, like a DTE, and is usually a device such as a PBX There are five distinct physical configurations for the signali ng part of the interface (types 1 to 5), and two distinct flavors of audio interface (2-wire or 4-wire) Note that even though it may be called a 4-wire E&M circuit, it is likely to have 6

to 8 physical wires! The difference between a 2-wire and 4-wire circuit is whether the audio path is full-duplex on one or two pairs of wires

The five E&M types are as follows:

• Type 1

• Asymmetrical: Cannot be used “back to back”

• Does not provide ground isolation between equipment, may produce noise

in audio circuits, or be susceptible to electrical transients

• Only requires six wires

• Most common interface in North America

• Type 2

• Can be used “back to back” for either trunking or signaling sides with

crossover cable

• Provides complete ground isolation

• Requires all eight wires

• Usually used on Centrex lines and Nortel PBX systems

• Type 3

• Asymmetrical: Cannot be used “ back to back”

• Provides ground isolation

• Requires all eight wires

• Mostly used on older, step-by-step CO systems

• Type 4

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State E-Lead M-Lead On-hook Open Ground Off-hook Ground Battery Voltage

E&M Trunk Group

E

E M

M

Analog Signaling: E&M (continued)

•E&M signaling (PBXs, switches)

–Separate signaling leads for each direction

–6 to 8 physical wires

–E ("Ear" or "Earth")—Signal wire from trunking (CO) side to signaling (user) side.

–M ("Mouth" or "Magnet")—Signal wire from signaling (user) side to trunking (CO) side

–Allows independent signaling

• Type 5

• Can be used “back-to-back” with crossover cable

• Does not provide ground isolation

• Only requires six wires

• Simplest to debug

• Used on some AT&T and Lucent PBX systems and widely used outsideNorth America

In the voice telephony world, the terms “lines” and “trunks” have special meaning

A trunk is a circuit which connects two pieces of a switching environment together

A trunk, DIDs excepted, is not assigned a publicly dialable directory number A line

is a circuit that connects a piece of the switching environment to a subscriber A line always has a directory number assigned to it

When a subscriber places a call to another subscriber on the same switch, the call

is a “line -to-line” call When a subscriber places a call to a subscriber on another switch, it is a “line-to-trunk” to “trunk-to-line” call

The terms line and trunk are sometimes in the eye of the beholder Circuits that PBXs use to connect to a CO switch and to place or receive calls are viewed by the PBX as “trunks." The same circuits may be considered, however, as “lines” to the

CO switch The same CO POTS circuit which has been assigned a directory

number (for example, 573-555-1212) can be used equally well by a residential

subscriber with a single line phone as it can by a PBX The circuit is connected on the CO’s line side, and on the PBX’s trunk side To the CO, the circuit is a line To the PBX, the circuit is a trunk

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Off-hook Ground Battery Voltage

E&M Trunk Group

E

E M

M

Analog Signaling: E&M (continued)

•E&M signaling (PBXs, switches)

–Separate signaling leads for each direction

–6 to 8 physical wires

–E ("Ear" or "Earth")—Signal wire from trunking (CO) side to signaling (user) side.

–M ("Mouth" or "Magnet")—Signal wire from signaling (user) side to trunking (CO) side

–Allows independent signaling

Analog Supervisory Signaling

It is possible to mix starting signaling protocols, but is is not recommended The following are three such signaling protocols:

• Immediate start signaling

• The originating switch goes off-hook, waits for a finite period of time (200

ms, for example), then sends the dial digits without regard to the far end

• An immediate start interface can usually originate a call to a wink start interface

• An immediate start interface can usually place a call to a delay dial

interface if the delay pulse is shorter than the immediate start delay

Otherwise, operation is erratic

• wink start signaling

– The originating switch goes off-hook, waits for a temporary off-hook pulse from the other end (which is interpreted as an indication to proceed), then sends the dial digits wink start was developed to minimize glare, where both ends attempt to seize the trunk at the same time

– A wink start interface can usually originate a call into a delay dial interface

if there is a delay pulse Otherwise, the call will hang, with a 50 percent chance of working or not

• Delay dial signaling

– The originating side goes off-hook and waits for about 200 ms, then

checks to see if the far end is on-hook If the far end is on-hook, it outputs dial digits If the far end is off-hook, it waits until it goes on-hook, then outputs dial digits

– This protocol was invented for use with systems that have fewer digit collectors than trunk interfaces The delay signal says, in effect “Wait—I'm not ready to receive digits.”

– A delay dial interface can, for the most part, originate a call into an

immediate start or wink start interface

Addressing via “in-band” signaling is performed by dial pulse, DTMF, and MF

These can be used over digital, for example, T1 circuits Dial p ulse is emulated with A/B bits, while DTMF is carried as PCM-encoded audio

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State E-Lead M-Lead On-hook Open Ground Off-hook Ground Battery Voltage

E&M Trunk Group

E

E M

M

Analog Signaling: E&M (continued)

•E&M signaling (PBXs, switches)

–Separate signaling leads for each direction

–6 to 8 physical wires

–E ("Ear" or "Earth")—Signal wire from trunking (CO) side to signaling (user) side.

–M ("Mouth" or "Magnet")—Signal wire from signaling (user) side to trunking (CO) side

–Allows independent signaling