COMP514 – Advanced
Communications
Lecture 2: SDH
Matthew Luckie
mluckie@cs.waikato.ac.nz
Lecture Outline
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SDH : Synchronous digital hierarchy
Self-healing rings
OAM
Fault location
Synchronous Digital Hierarchy (SDH)
• Dominant standard for digital
telecommunications networks
SONET
STS-1 / OC-1
STS-3 / OC-3
STS-12 / OC-12
STS-48 / OC-48
STS-192 / OC-192
STS-768 / OC-768
SDH
Data Rate (Mbps)
51.84
STM-1
155.52
STM-4
622.08
STM-16
2488.32
STM-64
9953.28
STM-256
39813.12
STM-1
• STM-1 frame rate 8000/second
– 125 microseconds
• STM-1 frame 270 columns by 9 rows
– 2430 bytes / 19440 bits
• 19440 * 8000 = 155.52 Mbps
STM-1 Frame
9 Rows
Regenerator
Section
Overhead
(RSOH)
AU Pointer
Multiplexer
Section
Overhead
(MSOH)
Section
Overhead
(9 bytes)
Path
Overhead
Information
Payload
Payload
(261 bytes)
STM-1 / STM-n
• STM-1 frames begin with A1/A2 frame
alignment bytes.
– Receiver can watch for this sequence every
125us to gain synchronisation
• STM-n is formed by byte-multiplexing
STM-1 frames.
– STM-4 frame begins with
A1 A1 A1 A1 A2 A2 A2 A2
SDH Networks
DXC
Backbone
DXC
DXC
DXC
ADM
ADM
ADM
ADM
ADM
ADM
DXC
ADM
Regional
Networks
ADM
ADM
DXC
DXC
DXC
Local Metro
Networks
ADM
ADM
DXC
ADM
ADM
ADM
ADM
Customers
C
C
C
C
SDH Multiplexers
• Add-drop multiplexers allow individual
streams to be added or removed from the
STM-1
STM-n
STM-n
ADM
SDH Multiplexers
• Digital Cross Connects (DXC) demux the entire
stream and switch channels to other SDH
circuits
– Core equipment will break down to STM-n rate
– Edge equipment will break down entire stream
DXC
STM-n
STM-n
STM-n
SDH Repeater
• A repeater regenerates the optical signal
Self Healing Rings
Bidirectional links between nodes
Self Healing Rings
Bidirectional links between nodes
Self Healing Rings
Bidirectional links between nodes
Operations and Maintenance (OAM)
• Goals of OAM are
– Performance monitoring
– Fault detection
– Fault notification
– System protection
– Point-of-fault identification
OAM
• Hierarchical structure
– F1: Repeater section
– F2: Digital section
– F3: Transmission path
– F4: Virtual Path (VP)
– F5: Virtual Channel (VC)
OAM for ATM
• If the first two
bits of payload
type field are
1 and 0
– OAM cell
– 100 : segment
– 101 : end-to-end
8
7
6
5
4
3
2
1
Virtual Path Identifier (VPI)
Virtual Channel Identifier (VCI)
Payload Type CLP
CRC