 |
| TRAINING
MATERIAL | Optical Multiplexing |
|
In the early years fibre optics being used to transport data
for voice or LAN traffic it was never invisaged that one day
the need would out strip capacity but that situation is now
facing LAN users and Metro Telcos alike. In major cities bans
have been placed on Telcos digging new infrastructure in and
so the need has arisen to better utilise what is installed.
This, together with new Gigabit technologies and applications,
has driven the need for fibre expand the existing capacity
of installed fibre to be massively expanded, hence WDM,CWDM
& DWDM
|
|
|
 |
TDM
(Time Division Multiplexing) onto a wavelength
This technologies allow low speed copper base data stream to
be multiplexed, converted from electrical to optical signals
and transmitted into an optical fibre at a specific wavelength.
TDM (Time Division Multiplexing) is the traditional method of
allowing multiple data streams to be transmitted via time slicing
and synchronising. This has been the norm for voice traffic
for many years. WDM (Wavelength Division Multiplexing) is analogous
to broadband systems by allowing multiple wavelengths (like
frequencies in coax) to exist in a fibre core. |
|
|
|
WDM
(Course Wavelength Division Multiplexing)
WDM technology allows 2 wavelengths to coexist with in the fibre's
core so making a fibre pair (Transmit and Receive) become a
single fibre with 1310nm wavelength the transmitter and 1550nm
the receiver or vice versa, on single mode fibre. This halves
the number of fibres used and so doubling the existing fibre
capacity. This technology allows two wavelengths to co-existing
with in a single fibre using 850/1310 or 1310/1550nm wavelengths.
It offers a cost effective method of generating new fibre links
with out the need to lay more fibres. |
|
|
|
CWDM
(Course Wavelength Division Multiplexing)
Fibre carrying capacity can further be doubled with CDWM and
and multiplied again with TDM (Time Division Multiplexing).
CWDM allows up to eight wavelengths to co exist in a single
fibre core, doubling data capacity. TDM (Time Division Multiplexing)
may further electrically multiplex multiple low speed data channels
into a single wavelength and thus multiple wavelength into a
single core. Transmission distance are only limited to the dynamic
range or loss budgets of the proposed fibre route which may
be from 10Km to 200Km. |
|
|
|
DWDM
(Dense Wavelength Division Mux.)
The next generation of wavelength multiplexers offer 16 and
32 wavelength multiplexing The wavelengths used in DWDM are
specified in the ITU grid, which state laser wavelength and
channel separation. These, DFB, special lasers are very coherent
(narrow) allowing 16 or 32 channels to coexist in the 1550nm
wavelength window. All data is transparent when optically multiplexed
because each data-stream is a separate wavelength. The maximum
transmission rate is at present 2.5Gbps per wavelength (l) multiplied
by the total number of wavelengths give 80Gbps (32 x 2.5Gbps).
Systems are managed either via SNMP, IP or VT100 and have the
ability to test and monitor fibre activity and dial out on fibre
failure |
|
|
 |
