c l morgan cs 4594 data communications pdh= plesiochronous digital hierarchy

C L Morgan

CS 4594 CS 4594 Data CommunicationsData Communications

PDH= Plesiochronous Digital HierarchyPDH= Plesiochronous Digital Hierarchy

C L Morgan

T-Carrier MultiplexingT-Carrier Multiplexing

• Plesiochronous multiplexing – (nearly Plesiochronous multiplexing – (nearly synchronous) synchronous) multiplexing in which two or more multiplexing in which two or more signals are transmitted at nominally the same digital rate signals are transmitted at nominally the same digital rate and their significant instances occur at nominally the same and their significant instances occur at nominally the same timetime

• Carry composite signals that contain 24, 48, Carry composite signals that contain 24, 48, 96,672, 2016, and 4032 digital voice signals96,672, 2016, and 4032 digital voice signals

• DS (Digital Signal) is signal format and T is DS (Digital Signal) is signal format and T is the carrier designationthe carrier designation

C L Morgan


• Many different formats – even within DS-1Many different formats – even within DS-1• now DS-1 and DS-3 dominatenow DS-1 and DS-3 dominate

• DS-0 = 64,000 bits/sec PCM signalDS-0 = 64,000 bits/sec PCM signal• DS-1 = 24 DS-0, operates at 1.544 Mbits/secDS-1 = 24 DS-0, operates at 1.544 Mbits/sec

• 193 bits, 8000 times a second193 bits, 8000 times a second

• DS-3 = 672 DS-0, operates at 44.736 Mbits/secDS-3 = 672 DS-0, operates at 44.736 Mbits/sec• 4760 bits, 8000 times a second4760 bits, 8000 times a second

C L Morgan


• T-1 original - 24 DS-0 signals are octet multiplexed T-1 original - 24 DS-0 signals are octet multiplexed with a single framing bit at the endwith a single framing bit at the end

Framebit

OctetCh #24

OctetCh #3

OctetCh #2

. . .

OctetCh #1

Framebit

OctetCh #24

OctetCh #23

DS-1 Frame

C L Morgan

T-1 SuperframeT-1 Superframe

T-1 Superframe (see overhead) carries 12 frames of DS-1. T-1 Superframe (see overhead) carries 12 frames of DS-1. Successive framing bits carry a sync pattern Successive framing bits carry a sync pattern 100011011100. The 6th and 12th frames are bit-robbed to 100011011100. The 6th and 12th frames are bit-robbed to form a signaling channel.form a signaling channel.

1 8-bits ch24 8-bits ch23 . . . 8-bits ch2 8-bits ch1





1 7-bits ch1+A 7-bits ch23+A . . . 7-bits ch2+A 7-bits ch1+A






0 7-bits ch24+A 7-bits ch23+A . . . 7-bits ch2+A 7-bits ch1+A

C L Morgan

T-1 Extended SuperframeT-1 Extended Superframe

T-1 Extended Superframe (see overhead) carries 24 frames T-1 Extended Superframe (see overhead) carries 24 frames of DS-1. Successive framing bits contain framing, a data of DS-1. Successive framing bits contain framing, a data link, and CRC. Frames 6, 12, 18, and 24 are bit robbed for link, and CRC. Frames 6, 12, 18, and 24 are bit robbed for 2 signaling channels.2 signaling channels.

C L Morgan

D 8-bits ch24 8-bits ch23 . . . 8-bits ch2 8-bits ch1

C 8-bits ch24 8-bits ch23 . . . 8-bits ch2 8-bits ch1


F 8-bits ch24 8-bits ch23 . . . 8-bits ch2 8-bits ch1


C 7-bits ch24+A 7-bits ch23+A . . . 7-bits ch2+A 7-bits ch1+A






F 7-bits ch24+B 7-bits ch23+B . . . 7-bits ch2+B 7-bits ch1+B






C 7-bits ch24+A 7-bits ch23+A . . . 7-bits ch2+A 7-bits ch1+A






F 7-bits ch24+B 7-bits ch23+B . . . 7-bits ch2+B 7-bits ch1+B

T-1 SuperframeT-1 Superframe

C L Morgan

T3 CarrierT3 Carrier

• T-3 has 672 voice channels - bit-interleaving T-3 has 672 voice channels - bit-interleaving groups of four DS-1 to create 7 DS-2 signals; in groups of four DS-1 to create 7 DS-2 signals; in turn the DS-2 are bit-interleaved to form one DS-turn the DS-2 are bit-interleaved to form one DS-3; (see overhead)3; (see overhead)

• Control bits are added: Control bits are added:

C L Morgan

Bit encoding for T-1Bit encoding for T-1

• AMI = Alternate Mark InversionAMI = Alternate Mark Inversion• 1s are represented by return-to-zero pulses that 1s are represented by return-to-zero pulses that

alternate between positive and negative levels alternate between positive and negative levels and zeros are represented by the absence of and zeros are represented by the absence of pulses.pulses.

• On T-carriers, should never send a long string On T-carriers, should never send a long string of zeros - one 1 in eight bits on average - no of zeros - one 1 in eight bits on average - no more than 15 consecutive 0smore than 15 consecutive 0s

C L Morgan

DS0 DS1 DS2 DS3 DS4

bits/sec 64000 1544000 6312000 44736000 274176000

#subchannels 1 24 4 7

#subframes/frame 1 1 4 7

#stuffing groups/subframe 1 1 6 8

data bits/stuffing group 1 192 48 84

overhead bits/stuffing group 0 1 1 1

total bits/stuffing group=data bits/stuffing group + overhead-bits/stuffing group 8 193 49 85

data bits/subframe=data bits/stuffing group * #stuffing groups/subframe 1 192 288 672

overhead bits/subframe=overhead bits/stuffing group * #stuffing groups/subframe 0 1 6 8

bits/subframe=data bits/subgroup * #subgroups/subframe 8 193 294 680

data bits/frame=data bits/subframe *#subframes/frame 1 192 1152 4704

overhead bits/frame=overhead bits/subframes * #subframes/frame 0 1 24 56

total bits/frame=bits/subframe * #subframes/frame 8 193 1176 4760

frames/sec=bits/sec * bits/frame 5367.346939 9398.3193

overhead bits/sec=overhead bits/frame * frames/sec 128816.3265 526305.88

max rate per sub channel=(bits/sec - oh bits/sec)/#subchannels 1545795.918 6315670.6

max stuff bits/sec for each subchannel=frames/sec 5367.346939 9398.3193

min rate per sub channel=max rate per channel - max stuff rate per channel 1540428.571 6306272.3

c l morgan cs 4594 data communications pdh= plesiochronous digital hierarchy

Documents