Differences between SONET and SDH

The hierarchy of the standard SDH corresponds to that of SONET for ATM interfaces.
The hierarchy of flows is different on three continents (USA, EC, Japan) is a rate of 51.84 Mbps, which was chosen for form the first level of SONET: STS-1 (Synchronous Transport Signal, level 1). The other levels are called SONET OC-n (Optical Carrier level n). So there is just a gap between the levels of SDH and SONET: Level 1 SDH (155.52 Mb / s) is level 3 and level SONET 2 of SDH (622.08 Mb / s) is the level 12 of SONET.

The virtual containers and types

To carry signals, using virtual containers (VC: Virtual Container). In the VC that are sections overload (POH: Path Overhead), which are used by pointers. The transport of containers on STM 1 STM 16 done by TDM. The couple VC-pointer, called AU (Administrative Unit) can therefore to carry both synchronous signals. Depending on the speed, the units are two levels Possible AU3 and AU4. Containers are managed in the SDH transmission network, regardless of the signals they carry. This packaging is called adaptation.

Types

There are two types of virtual containers:

• The virtual containers of lower order (VC-11 VC-12, VC-2
and VC-3) which are carried in virtual containers
higher order.
• The virtual containers of higher order (VC-3 and VC-4)
are multiplexed to form the resulting signal.

The principle of SONET / SDH

The arrival of SDH

SDH offers significant advantages over the PDH. SDH based
on a digital frame that provides high level, in addition to the top
speed (higher than PDH):
• Greater flexibility as to the possibility of extracting or
to insert directly a component of said multiplex
• Ease of operation and maintenance (Flow
important for these functions)
• An opportunity to move towards high speed (frames
synchronous broadband are built by multiplexing
phase the basic entity. This entity defines the basic
implicitly all frames high speed, the limitation
is more than technological)

• An interconnection of broadband systems facilitated by the
normalization of the frame line and optical interfaces
corresponding
• The network architectures providing security against
the line faults or equipment
• The modularity of SDH equipment is more suited to
advances in technology.



The SDH frames

There are different frames in SDH. The base frame is called
STM-1 (Synchronous Transport Module level 1).
STM-1 to a length of 2430 bytes. Frequency transmission
is 125ns, which gives us a rate of:
2430 * 8 / 125 = 155.52 Mbit / s.
In this frame, 9 bytes are reserved for the management and
addressing, leaving a payload of 150.336 Mbit / s.

OBJECTIVE OF TRAFFIC GROOMING

1.To combine low-speed traffic streams onto high-capacity wavelengths
2.Improve bandwidth utilization
3.Optimize network throughput
4.Minimize the network cost (transmitter, receiver, fiber link, OXC, ADM, amplifier,wavelength converter etc)

TRAFFIC GROOMING

Traffic-grooming is a kind of multiplexing in optical signal by packing low speed traffic streams into higher-speed streams.

There is a significant advantage to groom the traffic.
1.Reduction of wavelengths : If each demand requires a light-path exclusively, we need a lot of wavelengths to be allocated.
2.Reduction of costs for installing WDMs and operating networks