统计时分复用

Time slots allocated even if no data
11
Time Division Multiplexing
12
★ 2. Synchronous TDM and Statistical TDM 同步时分复用和统计时分复用
Synchronous
用户 时分复用
A
B C
a b b c c
Key Points
FDM, TDM FDM system synchronous TDM and statistical TDM ADSL
2
Multiplexing
复用，多路复用
The two common forms of multiplexing : frequency-division multiplexing (FDM) Time-division multiplexing (TDM)
Each requires a certain bandwidth centered around the carrier frequency-channel The channels are separated by guard bands
e.g. broadcast radio and cable TV
Address information is required to assure proper delivery
18
8.4 Asymmetrical Digital Subscriber Line
P267
★ 3. ADSL（非对称用户数字线路）
t t ③ #1 ④ 3 个 STDM 帧
t
#2
#3
TDM System
DS-1 Transmission Format
Each frame contains 24 channels; 8 bits per channel ; plus a framing bit 24×8＋1＝193bits/frame
17
8.3 Statistical TDM
统计时分复用
P260
In Synchronous TDM many slots are wasted Allocates time slots dynamically based on demand
n I/O lines, but only k (k<n) time slots available on the TDM frame.
Data Rate: 193bits×8000帧= 1.544Mbps Data Rate of each channel: 8bits×8000帧/s=64kbps
16
Sonet/SDH
Compatible 兼容
P257
SONET：Synchronous Optical Network (ANSI)同步光纤网络 STS_1 一级:51.84Mb/s STS_3 3×51.84Mb/s=155.52Mb/s SDH: Synchronous Digital Hierarchy (ITU-T)同步数字系列 STM-1 155.52Mb/s STM-4 4×155.52=622.08Mb/s
10
8.2 Synchronous Time Division Multiplexing
TDM Used for digital signals
P250
Multiple digital signals interleaved（交替） in time Time slots （时隙）preassigned to sources and fixed
5
Frequency Division Multiplexing Diagram
6
FDM of Three Voice band Signals
7
FDM System
8
(USA)
9
Wavelength Division Multiplexing波分复用
Multiple beams of light at different frequency Carried 百度文库y optical fiber Each color of light (wavelength) carries separate data channel 1997 Bell Labs Commercial systems of 160 channels of 10 Gbps now available
Data and Computer Communications
Part Two Data communications
Chapter 8 Multiplexing
1
Main Contents
8.1 8.2 8.3 8.4 frequency-division multiplexing FDM 频分复用 Synchronous Time Division Multiplexing 同步时分复用 Statistical Time Division Multiplexing 统计时分复用 Asymmetrical Digital Subscriber Line ADSL 不对称数字用户线路
3
★1. FDM and TDM frequency-division
频分复用和时分复用
Time-division
a b b c c a d t
8.1 Frequency Division Multiplexing
P243
FDM Used for analog signals Each signal is modulated to a different carrier frequency
a
t
①
t ②
ab
t ③ ④ d t #1
bc
#2
c
#3
a
#4
d
t
D
4 个时分复用帧
★ 2. Synchronous TDM and Statistical TDM 同步时分复用和统计时分复用
Statistical
用户 统计时分复用 A a b b c c d a t
①
B
C D
t ②
a b b c c d a