What’s the difference between SONET and SDH?
SONET vs SDH provide similarities and difference between SONET and SDH technologies,data rates,voice channels supported for various designations(OC. May 5, Development of this international counterpart to SONET began a few years after SONET. The diﬀerences between SONET and SDH are based. Synchronous optical networking (SONET) and synchronous digital hierarchy ( SDH) are . With a few exceptions, SDH can be thought of as a superset of SONET. SONET is a set of .. digital traffic. Every SDH/SONET connection on the optical physical layer uses two optical fibers, regardless of the transmission speed.
Part of the overhead is transmitted, then part of the payload, then the next part of the overhead, then the next part of the payload, until the entire frame has been transmitted. For STS-1, the frame is transmitted as three octets of overhead, followed by 87 octets of payload. This representation aligns all the overhead columns, so the overhead appears as a contiguous block, as does the payload.
Synchronous optical networking - Wikipedia
The internal structure of the overhead and payload within the frame differs slightly between SONET and SDH, and different terms are used in the standards to describe these structures. In practice, the terms STS-1 and OC-1 are sometimes used interchangeably, though the OC designation refers to the signal in its optical form. It is therefore incorrect to say that an OC-3 contains 3 OC-1s: The first nine columns contain the overhead and the pointers.
For the sake of simplicity, the frame is shown as a rectangular structure of columns and nine rows but the protocol does not transmit the bytes in this order. For the sake of simplicity, the frame is shown as a rectangular structure of columns and nine rows. The first three rows and nine columns contain regenerator section overhead RSOH and the last five rows and nine columns contain multiplex section overhead MSOH.
The diﬀerences between SDH and SONET
The fourth row from the top contains pointers. The STM-1 frame consists of overhead and pointers plus information payload. The first nine columns of each frame make up the Section Overhead and Administrative Unit Pointers, and the last columns make up the Information Payload.
Thus, an OC-3 circuit can carry Carried within the information payload, which has its own frame structure of nine rows and columns, are administrative units identified by pointers. Also within the administrative unit are one or more virtual containers VCs.
VCs contain path overhead and VC payload. The first column is for path overhead; it is followed by the payload container, which can itself carry other containers. Administrative units can have any phase alignment within the STM frame, and this alignment is indicated by the pointer in row four. The overheads contain information from the transmission system itself, which is used for a wide range of management functions, such as monitoring transmission quality, detecting failures, managing alarms, data communication channels, service channels, etc.
The STM frame is continuous and is transmitted in a serial fashion: Transport overhead The transport overhead is used for signaling and measuring transmission error rates, and is composed as follows: AU Pointer Points to the location of the J1 byte in the payload the first byte in the virtual container.
Path virtual envelope Data transmitted from end to end is referred to as path data. Nevertheless, as network architectures have remained relatively constant, even newer equipment including multi-service provisioning platforms can be examined in light of the architectures they will support.
Thus, there is value in viewing new, as well as traditional, equipment in terms of the older categories.
Regenerator[ edit ] Traditional regenerators terminate the section overhead, but not the line or path. Regenerators extend long-haul routes in a way similar to most regenerators, by converting an optical signal that has already traveled a long distance into electrical format and then retransmitting a regenerated high-power signal. Since the late s, regenerators have been largely replaced by optical amplifiers.
Also, some of the functionality of regenerators has been absorbed by the transponders of wavelength-division multiplexing systems.
SONET / SDH Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH)
STS multiplexer and demultiplexer[ edit ] STS multiplexer and demultiplexer provide the interface between an electrical tributary network and the optical network. Add-drop multiplexer[ edit ] Add-drop multiplexers ADMs are the most common type of network elements. Traditional ADMs were designed to support one of the network architectures, though new generation systems can often support several architectures, sometimes simultaneously.
ADMs traditionally have a high-speed side where the full line rate signal is supportedand a low-speed side, which can consist of electrical as well as optical interfaces.
The low-speed side takes in low-speed signals, which are multiplexed by the network element and sent out from the high-speed side, or vice versa. Advanced DCSs can support numerous subtending rings simultaneously. These architectures allow for efficient bandwidth usage as well as protection i. Switching is based on the line state, and may be unidirectional with each direction switching independentlyor bidirectional where the network elements at each end negotiate so that both directions are generally carried on the same pair of fibers.
Unidirectional path-switched ring[ edit ] In unidirectional path-switched rings UPSRstwo redundant path-level copies of protected traffic are sent in either direction around a ring.
A selector at the egress node determines which copy has the highest quality, and uses that copy, thus coping if one copy deteriorates due to a broken fiber or other failure. UPSRs tend to sit nearer to the edge of a network, and as such are sometimes called collector rings.
Any other nodes on the ring could only act as pass-through nodes. Bidirectional line-switched ring[ edit ] Bidirectional line-switched ring BLSR comes in two varieties: BLSRs switch at the line layer. Rather, the ring nodes adjacent to the failure reroute the traffic "the long way" around the ring on the protection fibers.
BLSRs trade cost and complexity for bandwidth efficiency, as well as the ability to support "extra traffic" that can be pre-empted when a protection switching event occurs. In four-fiber ring, either single node failures, or multiple line failures can be supported, since a failure or maintenance action on one line causes the protection fiber connecting two nodes to be used rather than looping it around the ring.
BLSRs can operate within a metropolitan region or, often, will move traffic between municipalities.
What’s the difference between SONET and SDH?
Because a BLSR does not send redundant copies from ingress to egress, the total bandwidth that a BLSR can support is not limited to the line rate N of the OC-N ring, and can actually be larger than N depending upon the traffic pattern on the ring. The worst case is when all traffic on the ring egresses from a single node, i. In this case, the bandwidth that the ring can support is equal to the line rate N of the OC-N ring.
This is why BLSRs are seldom, if ever, deployed in collector rings, but often deployed in inter-office rings. Synchronization[ edit ] Clock sources used for synchronization in telecommunications networks are rated by quality, commonly called a stratum.
Synchronization sources available to a network element are: The interface is often a DS1, with sync-status messages supplied by the clock and placed into the DS1 overhead.
Line-derived timing A network element can choose or be configured to derive its timing from the line-level, by monitoring the S1 sync-status bytes to ensure quality. Holdover As a last resort, in the absence of higher quality timing, a network element can go into a holdover mode until higher-quality external timing becomes available again.
In this mode, the network element uses its own timing circuits as a reference.