Introduction. TDM Techniques. Agenda. Point-To-Point Channels

Transcription

1 atenkommunikation SS 2007 atenkommunikation SS 2007 Introduction TM Techniques Time ivision Multiplexing (synchronous, statistical) igital Voice Transmission, PH, SH line protocol techniques (data link procedures) were developed for communication between two devices on one physical point-to-point link bandwidth of physical link is used exclusively by the two stations in case multiple communication channels are necessary between two locations multiple physical point-to-point are needed expensive solution in order to use one physical link for multiple channels multiplexing techniques were developed TM Techniques, v45 3 genda Introduction Synchronous (eterministic) TM synchronous (Statistical) TM igital Voice Transmission PH SH Point-To-Point hannels 1 B1 1 2 B2 2 1 Location point-to-point communication channels carried on multiple physical links 2 Location B TM Techniques, v45 2 TM Techniques, v45 4 Page 03-1 Page 03-2

2 atenkommunikation SS 2007 atenkommunikation SS 2007 Multiplexing / emultiplexing multiplexer is a device which can take a number of input channels and, by interleaving them, output them as one data stream on one physical trunk line 1 2 Types of TM depending on timing behavior two methods synchronous TM timeslots have constant length (capacity) and can be used in a synchronous, periodical manner asynchronous (statistical) TM timeslots have variable length and are used on demand (depending on the statistics of channel communication) B1 1 1 P1 P2 P3 P4 T Mux Trunk Line T Mux P1 P2 P3 P4 B2 2 2 TM Techniques, v45 5 TM Techniques, v45 7 Time ivision Multiplexing (TM) time division multiplexer allocates each input channel a period of time or timeslot controls bandwidth of trunk line among input channels individual time slots are assembled into frames to form a single high-speed digital data stream available transmission capacity of the trunk is time shared between various channels at the destination demultiplexer reconstructs individual channel data streams Synchronous TM Standards TM framing on the trunk line can be vendor dependent proprietary TM products can be standard based two main architectures for standardizing synchronous TM for trunk lines PH Plesiochronous igital Hierarchy eg E1 (2Mbit/s), E3 (34Mbit/s), E4, T1 (1,544Mbit/s), T3 SH - Synchronous igital Hierarchy eg STM-1 (155Mbit/s), STM-4 (622Mbit/s), STM-16 TM Techniques, v45 6 TM Techniques, v45 8 Page 03-3 Page 03-4

3 atenkommunikation SS 2007 atenkommunikation SS 2007 genda Synchronous Time ivision Multiplexing Introduction Synchronous (eterministic) TM synchronous (Statistical) TM Voice Transmission PH SH 1 B1 1 low bit rate P1 P2 P3 P4 T sync Mux high bit rate T sync Mux P1 P2 P3 P4 2 B Flag 8 bit bit B1 - B2 8 bit bit 1-2 Flag 8 bit 1-2 constant time interval TM Techniques, v45 9 TM Techniques, v45 11 Synchronous Time ivision Multiplexing synchronous TM periodically generates a frame consisting of a constant number of timeslots each timeslot of constant length timeslots can be identified by position in the frame timeslot 0, timeslot 1, frame synchronization achieved by extra flag field every input channel is assigned a reserved timeslot eg timeslot numbers refer to port numbers of a multiplexer traffic of port P1 in timeslot 1 for 1-2 channel traffic of port P2 in timeslot 2 for B1- B2 channel Trunk Speed with Synchronous TM User 1 User B1 User 1 User 1 B B Framing B B 4 64 kbit/s + F 256 kbit/s Trunk speed = Number of slots User access rate Each user gets a constant timeslot of the trunk 64 kbit/s User 2 B 64 kbit/s User B2 64 kbit/s User 2 64 kbit/s User 2 TM Techniques, v45 10 TM Techniques, v45 12 Page 03-5 Page 03-6

4 atenkommunikation SS 2007 atenkommunikation SS 2007 Idle Timeslots with Synchronous TM User 1 User B1 User 1 User 1 Timeslot with Idle Pattern 4 64 kbit/s + F 256 kbit/s If a communication channel has nothing to transmit -> Idle timeslots -> Waste of bandwidth 64 kbit/s User 2 64 kbit/s User B2 64 kbit/s User 2 64 kbit/s User 2 isadvantages bitrate on trunk line T sum of all port bitrates (P1-P4) plus frame synchronization (flag) high bitrate is required hence expensive if no data is to be sent on a channel special idle pattern will be inserted by the multiplexer in that particular timeslot waste of bandwidth of trunk line asynchronous (statistic) time division multiplex avoids both disadvantages making use of communication statistics between devices TM Techniques, v45 13 TM Techniques, v45 15 dvantages compared to pure point-to-point physical links synchronous multiplexing adds only minimal delays time necessary to packetize and depacketize a byte transmission/propagation delay on trunk the delay for transporting a byte is constant the time between two bytes to be transported is constant hence optimal for synchronous transmission requirements like traditional digital voice any line protocol could be used between devices method is protocol-transparent to endsystems channel looks like a single physical point-to-point line genda Introduction Synchronous (eterministic) TM synchronous (Statistical) TM Voice Transmission PH SH TM Techniques, v45 14 TM Techniques, v45 16 Page 03-7 Page 03-8

5 atenkommunikation SS 2007 atenkommunikation SS 2007 synchronous Time ivision Multiplexing usually devices communicate in a statistical manner not all devices have data to transmit at the same time therefore it is sufficient to calculate necessary bitrate of the multiplexer trunk line according to the average bitrates caused by device communication if devices transmit simultaneously only one channel can occupy trunk line data must be buffered inside multiplexer until trunk is available again statistics must guarantee that trunk will not be monopolized by a single channel TM Techniques, v45 17 TM Operation multiplexer only generates a transmission frame if data octets are present at input ports source of data must be explicitly identified in transmission frames addressing reason for addressing there exists no constant relationship between timeslot and portnumber as with synchronous TM Note: addressing in synchronous TM is implicit by recognizing the flag of the frame and hence the position of a certain timeslot port identifier is used as address of source and sent across the trunk TM Techniques, v45 19 synchronous Time ivision Multiplexing TM Operation / Facts 1 B1 1 1 P1 P2 P3 P4 buffer T stat Mux variable time interval low bit rate buffer T stat Mux P1 P2 P3 P4 Flag P2 8 bit B1 - B2 P4 8 bit 1-2 Flag P2 8 bit B1 - B2 P3 8 bit 1-2 Flag Flag low bit rate Portidentifier P2 8 bit B1 - B2 8 bit B1 - B2 8 bit B1 - B2 Flag P4 8 bit bit B2 2 2 transmission frame can be assembled using either a single channel octet by frame suitable for character oriented terminal sessions or multiple channel octets per frame suitable for block oriented computer sessions in case of congestion buffering causes additional delays compared to synchronous TM delays are variable because of statistical behavior hence not optimal for synchronous transmission requirements like traditional digital voice sufficient for transmission requirements of bursty data transfers TM Techniques, v45 18 TM Techniques, v45 20 Page 03-9 Page 03-10

6 atenkommunikation SS 2007 atenkommunikation SS 2007 synchronous / Statistical TM TM Facts User 1 64 kbit/s User B1 64 kbit/s User 1 64 kbit/s User 1 64 kbit/s 64 kbit/s verage data rates 16 kbit/s 64 kbit/s User 2 B 64 kbit/s User B2 64 kbit/s User 2 64 kbit/s User 2 Trunk speed dimensioned for average usage Each user can send packets whenever he wants Buffering necessary if trunk already occupied B TM can be used protocol transparent however in case of buffer overflow transmission errors will be seen by devices FS errors to avoid FS errors a kind of flow control between multiplexer and device (end system) should be used which is a new element in data communication methods this is different from flow control between end systems learned so far in module about line protocols examples for flow control HW flow control based on handshake signals (eg RTS, TS) SW flow control (eg XON/XOFF) Protocol based flow control such as known in connection oriented line protocols like HL (eg RR and RNR) end system and TM have to speak the same protocol language TM Techniques, v45 21 TM Techniques, v45 23 synchronous / Statistical TM genda User 1 64 kbit/s User B1 64 kbit/s User 1 64 kbit/s 64 kbit/s 64 kbit/s User 2 64 kbit/s User B2 64 kbit/s User 2 Introduction Synchronous (eterministic) TM synchronous (Statistical) TM Voice Transmission PH SH User 1 64 kbit/s 64 kbit/s User 2 If other users are silent, one user can fully utilize his access rate TM Techniques, v45 22 TM Techniques, v45 24 Page Page 03-12

7 atenkommunikation SS 2007 atenkommunikation SS 2007 Voice Transmission digital voice transmission based on Nyquist s Theorem analogous voice can be digitized using pulse-codemodulation (PM) technique requiring a 64kbit/s digital channel voice is sampled every 125usec (8000 times per second) every sample is encoded in 8 bits used nowadays in the backbone of our telephone network today analogous transmission only between home and local office -> so called local loop synchronous TM originated from digital voice transmission Linear Quantization mplitude + mplitude - Quantization Error Time TM Techniques, v45 25 TM Techniques, v45 27 Sampling of Voice Nyquist s Theorem any analogue signal with limited bandwidth f B can be sampled and reconstructed properly when the sampling frequency is 2 f B transmission of sampling pulses allows reconstruction of original analogous signal sampling pulses are quantized resulting in binary code word which is actually transmitted Improving SNR (Signal Noise Ratio) to improve the SNR of speech signals lower amplitudes receive a finer resolution than greater amplitudes a nonlinear function (logarithmic) is used for quantization US: μ-law (Bell) Europe: -law (ITU) Power R = 2 * B * log 2 V Quantization levels Telephone channel: Hz 8000 Hz x 8 bit resolution = 64 kbit/s Frequency 300 Hz 3400 Hz TM Techniques, v45 26 nalogue input signal TM Techniques, v45 28 Page Page 03-14

8 atenkommunikation SS 2007 atenkommunikation SS 2007 Log Quantization Voice ompression Segment 3 Segment 2 Segment 1 Segment 0 mplitude Finer sampling steps at low amplitude levels, hence better SNR for silent "voice parts" Time Waveform oders Non-linear approximation of analog waveform PM (no compression), PM Vocoders speech is analyzed and compared to a codebook only codebook values are transmitted and speed synthesizer at the receiver Hybrid coders ombination of waveform coders and vocoders 48 kbps to 16 kbps Used for mobile phones ELP, GSM TM Techniques, v45 29 TM Techniques, v45 31 Encoding (PM) Standardized odec's Putting digital values in a defined form for transmission Segment 3 Segment 2 Segment 1 Segment 0 mplitude Polarity 8 bit PM sample P Se Se Se St St St Segment Step Time St PM G711 (64 kbps) daptive ifferential Pulse ode Modulation (PM) only the difference from one sample pulse to the next will be transmitted fewer bits used for encoding the difference value G726 (16, 24, 32, 40 kbps) Low elay ode Excited Linear Predictor (L-ELP) G728 (16 kbps) onjugate Structure lgebraic ode Excited Linear Predictor (S- ELP) G729 (8 kbps) ual Rate Speech oding Standard G723 is the basic standard for voice transmission in IP networks basis is the ELP-Technique of GSM uses minimal data rate of 5,3K at fair quality or 6,3K with good quality TM Techniques, v45 30 TM Techniques, v45 32 Page Page 03-16

9 atenkommunikation SS 2007 atenkommunikation SS 2007 igital voice channel S0 = igital Signal, Level 0 1 timeslot in multiplexing frames Base for hierarchical digital communication systems Equals one PM coded voice channel 64 kbit/s Each samples (byte) must arrive within 125 μs To receive 8000 samples (bytes) per second Higher order frames must ensure the same byte-rate per user(!) Multiplexing Basics S0: 1 Byte E1: 32 Byte E2: 132 Byte F 1 digital voice channel 31 digital voice channels 131 digital voice channel 125 μs 64 kbit/s 2048 kbit/s 8448 kbit/s note: S0 and higher rates can be used for any transport digital information -> data transmission TM Techniques, v45 33 TM Techniques, v45 35 Multiplexing Basics S0 8 bits of PM sample 8 bits of next PM sample eg S1/E1 time 125 μsec = 1/8000 = 1 frame timeslots genda Introduction Synchronous (eterministic) TM synchronous (Statistical) TM Voice Transmission PH SH frame rate is always 8000 frame per second at all levels of the hierarchy byte interleaved multiplexing TM Techniques, v45 34 TM Techniques, v45 36 Page Page 03-18

10 atenkommunikation SS 2007 atenkommunikation SS 2007 Multiplexing Hierarchies igital Hierarchy of Multiplexers why hierarchy and standardization? only a hierarchical digital multiplexing infrastructure which is standardized can connect millions of (low speed) customers across the city/country/world two main architectures PH - plesiochronous digital hierarchy plesio means nearly synchronous, clock differences are compensated by bit stuffing techniques / overhead bits PH is still used for low-speed lines SH - synchronous digital hierarchy overcomes deficits of PH in North merica SONET is used telecommunication backbones move very quickly to SONET/SH 64 kbit/s E1 = 30 x 64 kbit/s + Overhead E2 = 4 x 30 x 64 kbit/s + Overhead Example: European PH E3 = 4 x 4 x 30 x 64 kbit/s + O E4 = 4 x 4 x 4 x 30 x 64 kbit/s + O Note: the actual data rates are somewhat higher because of overhead bits (O) TM Techniques, v45 37 TM Techniques, v45 39 PH Hierarchy North merica / NSI Signal arrier hannels Mbit/s Signal Europe / ITU arrier hannels Mbit/s S0 S1 S1 T1 T S0 EPT-1 EPT-2 "E0" E1 E S2 S3 T2 T EPT-3 EPT-4 E3 E S4 T EPT-5 E Incompatible rates ifferent signalling schemes ifferent overhead μ-law versus -law PH Limitations PH overhead increases dramatically with high bit rates Overhead 11% 10% 9% 8% 7% 6% % % 3% % % 052 S1 S2 S3 S4 EPT-1 EPT-2 EPT-3 EPT-4 TM Techniques, v45 38 TM Techniques, v45 40 Page Page 03-20

11 atenkommunikation SS 2007 atenkommunikation SS 2007 E1 Frame Structure R Multiframe Structure Timeslot frames per second frame frame frame frame frame frame frame timeslot 0 timeslot 1 timeslot 2 timeslot 3 timeslot or 1 N N N N N 8 bits per slot 2048 Mbit/s Frame lignment Signal (FS) (every alternating frame) Not Frame lignment Signal (NFS) (every alternating frame) TM Techniques, v45 41 frame 0 frame 1 frame 2 frame 3 frame 4 frame 5 frame 6 frame 7 frame 8 frame 9 frame 10 frame 11 frame 12 frame 13 frame 14 frame 15 timeslot 0 1 FS 0 NFS 2 FS 0 NFS 3 FS 1 NFS 4 FS 0 NFS 1 FS 1 NFS 2 FS 1 NFS 3 FS Si NFS 4 FS Si NFS timeslot 1 timeslot 31 semimultiframe 1 TM Techniques, v R Multiframe Sync - bits semimultiframe 2 E1 Frame Structure every second frame timeslot 0 contains FS used for frame synchronization (R) bit is part of an optional 4-bit R sequence provides frame checking and multiframe synchronization (larm Indication) bit so called Yellow (remote) alarm used to signal loss of signal (LOS) or out of frame (OOF) condition to the far end N (National) bits reserved for future use genda Introduction Synchronous (eterministic) TM synchronous (Statistical) TM Voice Transmission PH SH TM Techniques, v45 42 TM Techniques, v45 44 Page Page 03-22

12 atenkommunikation SS 2007 atenkommunikation SS 2007 Reasons for SONET/SH evelopment Incompatible PH standards!!! PH does not scale to very high bit rates Increasing overhead Various multiplexing procedures Switching of channels requires demultiplexing first emand for a true synchronous network No pulse stuffing between higher levels Phase shifts are compensated by floating payload and pointer technique emand for add-drop es and ring topologies Network Structure PTE Path Termination Service (Sn or En) mapping and demapping Line (Multiplex Section) Section (Regenerator Section) REG (Regen) Section termination Path (Path Section) (Regen Section) M or S Line termination ( section termination) Line (Multiplex Section) Section Section Section (Regen Section) REG (Regen) Section termination SONET(SH) Terms (Regenerator Section) PTE Path Termination Service (Sn or En) mapping and demapping TM Techniques, v45 45 TM Techniques, v45 47 SH History SONET/SH Line Rates fter divestiture of T&T Many companies -> many proprietary solutions for PH successor technology In 1984 ES (Exchange arriers Standards ssociation) started on SONET Goal: one common standard Tuned to carry US PH payloads In 1986 ITT became interested in SONET reated SH as a superset Tuned to carry European PH payloads including E4 (140 Mbit/s) SH is a world standard SONET is subset of SH Originally designed for fiber optics SONET SONET Optical Levels Electrical Level O-1 STS-1 O-3 STS-3 O-9 STS-9 O-12 STS-12 O-18 STS-18 O-24 STS-24 O-36 STS-36 O-48 STS-48 O-96 STS-96 O-192 O-768 Line Rates Mbit/s SH Levels STM-0 STM-1 STM-3 STM-4 STM-6 STM-8 STM-12 STM-16 STM-32 STS STM-64 STS STM-256 efined but later removed, and only the multiples by four were left! (oming soon) TM Techniques, v45 46 TM Techniques, v45 48 Page Page 03-24