t1 e1 overview

T1/E1/PRITechnology Overview

Connections,Frames &Signaling

5/11/01 Confidential The InterNetwork 2

Topics Covered

=Physicals, Frames and Formats=T1 - AMI/B8ZS=E1 - AMI/HDB3

=Call Control Signaling=Channel Associate Signaling (CAS)

=Robbed Bit / Wink=MFCR2 / TS16 MultiFrame

=Common Channel Signaling (CCS)= Q.921 / Q.931 ISDN PRI


T1

= North American T1 facilities operate at 1.544 MBPS. Framing may beeither Superframe (D4) or Extended Superframe (ESF).

= These facilities are deployed in the United States, Canada, Korea, Taiwan,and Hong Kong (Hong Kong also employs International G.732interconnectivity).

= Related Specifications= AT&T Pub 62411 (D4, Line Characteristics)= AT&T Pub 54016 (ESF)= ANSI T1.403 (DS1 Metallic Interface)


The Digital Hierarchy

=DS1 - Information rate of 1.544 mbps=Single frame is 193 bits wide

=Single bit for framing=24 timeslots (DS0 s)

=Each DSO is 8 bits wide (64K rate per second)=Frames occur 8,000 times a second (125 microseconds)

=8K is the magic number

=Maximum user rate is 1.536 mbps=8 kbps is used for framing/synchronization=24 Channels x 8kbps per channel


24 timeslots (DS0 s)

Each DSO is 8 bits wide(64K rate per second)

Frame Format T1


T1 Physicals

=T1 is the physical delivery mechanism of DS1

=T1 generally used to mean any 1.544 mbps service

=Copper delivery on 4 wires=one pair for RX (1+2) For CPE this is data FROM the network=one pair for TX (4+5) For CPE this is data TO the network

=T1 is a very specific type of service=Repeaters every 6,000 ft=Pulse/Waveform shape=Jitter


T1 Line Encoding=Establishes how bits are put onto the wire

=AMI - Alternate Mark Inversion=Every other 1 is a different polarity=Does not maintain ones density

=56K data service - forces the LSB to 1


T1 Line Encoding cont’d...=B8ZS - Binary 8 Zero Substitution

=Uses intentional Bi-Polar Violations to transparently maintainones density=Bi-Polar Violations are two 1 s of the same polarity=64K data service now possible - Clear Channel


T1 Framing

=Two types of framing formats; Both use theFraming Bit to establish groups=D4

=Group of 12 Frames=Used to align equipment for framing

=ESF=Group of 24 Frames=Used to align equipment for framing=Uses 4K for a maintenance channel (Facilities Data Link)=Uses 2K for CRC-6 checksum=Uses 2K for framing/synchronization


D4 Frame


ESF Datalink

= AT&T TR 54016 calls for used of a simplified X.25 Level 2structure, known as Telemetry Asynchronous Block SerialProtocol (TABS). This protocol consists of the following fields:

=Flag (hex "7E")=Address (single byte)=Control (single fixed byte: 00001000)=Information Field (variable length)=FCS (Frame Check Sequence)


ESF Datalink= The ANSI T1.403 specification can use Bit-Oriented-Signals (consisting of two bytes each) on

the datalink OR Message-Oriented-Signals. Bit-Oriented-Signals consist of an all-ones byte,followed by a ZERO BIT, followed by a six bit identifier, and the last bit set to a ZERO. Anexample of a Bit-Oriented-Signal is the 00000000 11111111 code used by ESF as a YellowAlarm condition. However, ANSI has also defined 16-bit words to indicate Payload/Lineloopback Activation/Deactivation, Automatic Protection Switching (APS) Line SwitchCommands, APS Line Switch Acknowledgements, and APS Line Release commands.

= The ANSI T1.403 Message-Oriented-Signals conform to the LAPD, Q.921 HDLC format:= Flag (hex "7E")= Address (2-Bytes used to express SAPI, TEI information)= Control (single fixed byte: 00000011)= Information Field (variable length)= FCS (Frame Check Sequence)

= ANSI T1.403 terminal equipment (CSU) transmit Performance Report messages towards thenetwork every second. The following Error Events are reported in the Performance ReportMessage (PRM).


T-Carrier D4 and ESF Alarms= AIS (Alarm Indication Signal) CFA

= The AIS is also known as a "Keep Alive" or "Blue Alarm" signal. This consists of an UNFRAMED all-ones signal sentto maintain transmission continuity. The AIS CFA signal is declared when both the AIS state and RED CFApersist simultaneously.

= OOF (Out-Of-Frame) Condition = Occurs whenever Network or DTE equipment senses errors in the incoming framing pattern. Depending upon the

equipment, this can occur when 2 of 4, 2 of 5, or 3 of 5 framing bits are in error. A reframe clears the OOF condition.

= Red CFA (Carrier Failure Alarm)= Occurs after detection of CONTINUOUS OOF condition for 2.5 seconds. This alarm state is cleared when no OOF

conditions occur for AT LEAST 1 second. Some applications (AT&T DACS services) may not clear the CFA state forUP TO 15 seconds of NO Out-Of-Frame occurrences.

= Yellow CFA (Carrier Failure Alarm)= When a Terminal/Network equipment enters a RED CFA state, it transmits a "Yellow Alarm" in the opposite direction.

A Yellow Alarm is transmitted by setting Bit #2 of each timeslot to a 0 (zero), SPACE state for D4Framed facilities. For ESF facilities, a Yellow Alarm is transmitted by sending a repetitive 16-bitpattern consisting of 8 MARKS (1) followed by 8 SPACES (0) in the Datalink bits. This is transmittedfor a MINIMUM of 1 second.

= LOS (Loss Of Signal)= A LOS condition is declared when no pulses have been detected in a 175 +/- 75 pulse window (100 to 250 bit times).


Digital Voice=Analog <=> Digital Conversion

=Analog signal is sampled 8,000 per second=Nyquist Theorem

=With a sampling rate of two times the frequency, an analogsignal can be faithfully represented.

=Each sample is a snapshot best guess=Quantizing error

=Difference between actual sample and digital value


Pulse Code Modulation

=Samples take 8K per second=Sample values are converted to pulses (PAM)

=Heights of pulses are measured (PCM)=Analog to Digital Conversion=Digital value is an 8-Bit code word=256 Possible Codes=Reference for Toll Quality voice=G.711 audio


Analog to PCM Conversion


Companding

= Non-Linear coding uses more values torepresent lower volume levels and less values forhigher volume levels

= Captures the subtleties of conversation= Not many value differences when someone is screaming= µ-LAW - typically used on T1 facilities

= A-LAW - typically used on E1 facilities


PCM Word Makeup

Softer volumes are have morevariations than loud Volumes.In other words, you don t needmany values to accuratelyrepresent someone yelling.


E1 Standards= The International CCITT framing format is adopted by most

countries (Europe, Central/South America, etc.). Thesefacilities operate at 2.048 MBPS.

= This framing format is actually defined in CCITTRecommendation G.704, although Recommendation G.732supplements G.704.

= G.704: Synchronous Frame Structure= Used and Primary and Secondary= Hierarchical Levels

= G.732: Characteristics of Primary PCM= Multiplex Equipment Operating at= 2048 KBPS.


G.703/G.704 Framing

= The standard frame is 32 timeslots, with each timeslot consisting of an 8-bit byte. A MultiFrame consists of 16 frames, numbered zero to fifteen.

= The timeslots are numbered 0 to 31. Timeslot 0 is used for:=Synchronization=Alarm Transport= International Carrier use

= Timeslot 16 may be used to transmit Channel Associated Signaling (CAS)information. Note that G.732 DOES NOT define the signaling states, onlythe transport of the states through the G.732 frame.

= However, G.704 recognizes the requirement for Common ChannelSignaling and also allows the TRANSPARENT End-To-End transport ofTimeslot 16.


E1 Physicals=Rate of 2.048 mbps

=Single frame is 256 bits wide (125 microseconds)=32 timeslots (DS0 s)

=Each DSO is 8 bits wide (64K rate per second)=Timeslot 0 used for Synchronization

=Two types of physical delivery=Unbalance 120 Ω

=Copper delivery on 4 wires=one pair for RX (1+2)=one pair for TX (4+5)

=Balanced 75 Ω=Coax with BNC connectors

=one cable for RX=one cable for TX


E1 Line Encoding

=Establishes how bits are put onto the wire=AMI - Alternate Mark Inversion

=Every other 1 is a different polarity=Does not maintain ones density

=56K data service - always forced the LSB to 1

=HDB3 - High Density Bipolar 3=Every other 1 is a different polarity=Uses Bi-Polar Violations to automatically maintain one

density=64K data service now possible


E1 Frame Structure

=32 Timeslots Total=Each channel holds 8 Bits

=Each channel repeats 64,000 times a second (64 Kbps)

=30 Timeslots for voice calls

=Two Special Timeslots=TS0

=Framing and Synchronization

=TS16=Signaling


E1 Framing

=Two types of framing formats=Double Frame

=Uses bits in TS0

=CRC-4=Submultiframe

=TS 16 MultiFrame is independent fromDouble frame and CRC-4!!!


Timeslot 0 Operation

= In NORMAL applications, there is NO ERRORCHECKING capability provided within the G.704specification. In such cases, Timeslot 0 provides theability to transport International and National bits.

= However, G.704 does describe an OPTIONALimplementation where a CRC-4 checksum can be usedto provide ERROR DETECTION for Frames 0 through 7,and Frames 8 through 15. When this OPTIONAL formatis used, the EVEN FRAME’s International bit is replacedwith a CRC-4 bit. The National Bits are relabeled asSPARE BITS.


TS0 Operation without CRC-4

= The meaning of the information contained in the Timeslot 0 bytedepends upon whether the Frame number is EVEN or ODD:


TS0 with CRC-4 - Odd Frames

= The CRC bits in Frames 0, 2, 4, and 6 provide error detection for thepreviously transmitted/received SUB-MULTIFRAME for Frames 0through 7. The CRC bits in Frames 8, 10, 12, and 14 provide errordetection for the previously transmitted/received SUB-SULTIFRAMEFrames 8 through 15:


TS0 with CRC-4 - Even Frames


TS16 MultiFrame Alignment

= When Timeslot 16 of the E1 frame is used for Channel AssociatedSignaling purposes, Frame 0 contains information that is used by thereceiver to identify the incoming frame. Specifically, this pattern inTimeslot 0, Frame 0 is called the MultiFrame Alignment Signal (MFAS).

|Bit 1 |Bit 2 |Bit 3 |Bit 4 |Bit 5 |Bit 6 |Bit 7 |Bit 8 |Frame 0 |------|------|------|------|------|------|------|------|

| 0 | 0 | 0 | 0 | X | Y | X | X |

= X = Spare Bits, set to 1 if not used.= Y = Yellow Alarm (Loss of MultiFrame Alignment Signal) (0 = Normal | 1 = Loss of MFAS)

= The ABCD state of 0000 is not allowed. If all bits in Timeslot 16 are 0, aLoss of MultiFrame Alignment Signal can be assumed.


E1 TS16 MultiFrame


Signaling

=Signaling is used to indicate Status=Incoming Calls=Channel Status

=Available

=Out-of-Service

=Two Types of Signaling=CAS - Channel Associated

=Signaling is in-band

=CCS - Common Channel=one timeslot for signaling — D-channel

=messages signify link and call status=64 kb/s


T1 Signaling

=CAS (Common Associated)=Robbed Bit

=Ground Start=Loop Start=E&M immediate=E&M Wink Start

=CCS (Common Channel)=ISDN PRI Service

=Q.921=Q.931


T1 ISDN PRI

=Uses Timeslot 24 for communication=Allows only 23 voice channels=NFAS allows one D channel to signal multiple T1 s

=Allows other T1/PRI lines to utilize a full 24 voice channels=Generally need a back-up D channel for more than 2 PRI s

=T1 (ESF, B8ZS)=23 B + D=D-channel in TS 24


E1 ISDN PRI

=Uses TS16 for the D Channel=Allows 30 voice channels=No need for NFAS

=You don t lose a timeslot for signaling

=E1 (with or without CRC-4)=30B + D=D-channel in always in TS 16


ISDN PRI Call Setup/Teardown

=SETUP →=SETUP ACK ←=(CALL PROCEEDING ←)=(ALERTING ←)=CONNECT ←=CONNECT ACK →

=Talk=DISCONNECT →=DISCONNECT ACK ←


ISDN PRI Operation

=ISDN as it fits within the OSI Model


ISDN PRI Operation - Layer 1

=Layer 1 is either T1 or E1

=For PRA using T1 facilities=23B+D=Datalink in TS24

=For PRA using E1 facilities=30B+D=Datalink in TS16


ISDN Layer 2 - Q.921 (LAPD)=Built on HDLC (similar to X.25)=Establishes communication with a SABME=Error control — CRC, Retransmission, Flow control=Single TEI, 0=The ISDN datalink


ISDN Layer 3 Q.931

= This is known as DSS 1 (Digital Subscriber Signaling System #1) and isdetailed in ITU Recommendation Q.931. This function is responsible forthe actual setup and teardown of ISDN calls.

Q.931 Header & Information Element


ISDN PRI Operation - Layer 3

=Q.931=protocol discriminator 08=link control messages=controls call setup and tear down=assigns CRV for each call=messages comprise Information Elements (IEs)=mandatory IEs and optional IEs


Q.931 Packet Description

ProtocolLayer 3 header information. Generally always 08 , meaning Q.931 Callmaintenance

Call Reference Value (CRV)in PRI is a 15-bit value which is used to associate messages with a particularchannel connection.

Message TypeThere are four general categories of messages:

1) Call Establishment2) Call Information3) Call Clearing4) Miscellaneous


Information Elements

=There are four general categoriesof messages that might bepresent:=Call Establishment=Call Information=Call Clearing=Miscellaneous


ISDN Information Elements♦ Each type of message can contain Mandatory and Optional InformationElements. While there are few single octet (byte) Information Elements, mosthave multiple octets associated with them.

♦ When Information Elements consist of multiple octets, the byte (octet)immediately following the Information Element Identifier is used to describe howmany bytes (octets) are in the Information Element (length). This is how thereceiver knows where to start looking for the next Information Element in amessage.

Some common Information Elements are listed below:

1.Bearer Capability (identifies requirements of the requested B-Channel) 2.Cause (identifies reasons for disconnect or incomplete calls) 3.Channel Identification (identifies requested B-Channel 4.Progress Indicator (Indicates status of outgoing call) 5.Calling Party Number (identifies caller) 6.Called Party Number (destination number)


Decoding an ISDN Message02010000080200270504038090A21803A983901E028A816C0200C37005810383939

02010000 LAPD Header

08=Q93102=Call Reference Value0027=the number of this call05 SETUP

04=bearer cap03=length80=CCITT, speech90=circuit, 64KA2=layer 1, u-law

18=channel ID03=lengthA9=this interface, PRI, exclusive, not D, B183=CCITT, number, B-channels90=1 0010000=slot 16

1E=Progress indicator02=length8A=CCITT, private network servingremote user81=call is not end-to-end ISDN

6C=calling party number02=length00=type unknown, plan unknownC3=number not available due tonetwork provided screen

70=called party number05=lengthThe called party number is 0899

t1 e1 overview

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