Test your knowledge of Synchronous Digital Hierarchy with this 10-question quiz for beginners
Synchronous Digital Hierarchy (SDH) is a standardized technology that transfers multiple digital bit streams over optical fiber. Test your knowledge with these 10 fundamental questions!
1
What does SDH stand for in telecommunications?
Synchronous Data Hierarchy
Synchronous Digital Hierarchy
Serial Digital Hierarchy
Standard Digital Header
SDH stands for Synchronous Digital Hierarchy. It's an international standard for high-speed telecommunication over optical networks.
2
What is the fundamental building block of SDH transmission?
STM-0
STM-1
STM-4
VC-12
STM-1 (Synchronous Transport Module level 1) is the base-level SDH signal with a transmission rate of 155.52 Mbps.
3
What is the transmission rate of an STM-1 signal?
51.84 Mbps
155.52 Mbps
622.08 Mbps
2.488 Gbps
An STM-1 signal has a transmission rate of 155.52 Mbps. Higher rates are multiples of this base rate.
4
Which of these is NOT a common SDH network element?
Terminal Multiplexer (TM)
Add/Drop Multiplexer (ADM)
Digital Cross-Connect (DXC)
Channel Service Unit (CSU)
The Channel Service Unit (CSU) is a device used in digital leased lines, but it's not a core SDH network element.
5
What is the purpose of pointers in SDH frames?
To indicate the start of the frame
To compensate for frequency and phase variations
To carry error detection information
To identify the payload type
Pointers in SDH frames compensate for frequency and phase variations between the frame rate and payload rate.
6
How many E1 signals can be carried in an STM-1 frame?
16
32
63
64
An STM-1 frame can carry 63 E1 signals, each at 2.048 Mbps.
7
Which SDH layer is responsible for end-to-end connection monitoring?
Regenerator Section
Multiplex Section
Higher-Order Path
Lower-Order Path
The Path layer (both Higher-Order and Lower-Order) is responsible for end-to-end connection monitoring.
8
What is the primary function of an SDH Add/Drop Multiplexer (ADM)?
To convert electrical signals to optical signals
To amplify optical signals without reshaping
To insert and extract lower-rate signals from an SDH stream
To terminate SDH circuits at the network edge
The primary function of an ADM is to insert and extract lower-rate signals from a high-speed SDH stream without demultiplexing the entire signal.
9
What is the equivalent of SDH's STM-1 in the SONET standard?
STS-1
STS-3
STS-12
OC-48
SDH's STM-1 (155.52 Mbps) is equivalent to SONET's STS-3 (also 155.52 Mbps). SONET's STS-1 is 51.84 Mbps.
10
Which protection mechanism uses two fiber rings with traffic traveling in opposite directions?
Unidirectional Path Switched Ring (UPSR)
Bidirectional Line Switched Ring (BLSR)
Subnetwork Connection Protection (SNCP)
Multiplex Section Protection (MSP)
Bidirectional Line Switched Ring (BLSR) uses two fiber rings with traffic traveling in opposite directions, providing efficient protection switching.
Answers & Explanations
Question 1: What does SDH stand for in telecommunications?
Correct Answer:
b) Synchronous Digital Hierarchy
SDH stands for Synchronous Digital Hierarchy. It's an international standard (ITU-T) for synchronous data transmission over optical fiber that provides faster and more efficient network interconnection than traditional PDH (Plesiochronous Digital Hierarchy) systems.
Question 2: What is the fundamental building block of SDH transmission?
Correct Answer:
b) STM-1
STM-1 (Synchronous Transport Module level 1) is the base-level SDH signal with a transmission rate of 155.52 Mbps. Higher-level signals (STM-4, STM-16, etc.) are multiples of this base rate.
Question 3: What is the transmission rate of an STM-1 signal?
Correct Answer:
b) 155.52 Mbps
The STM-1 frame operates at 155.52 Mbps. This rate was chosen to carry a wide variety of signals including 63 E1s (2.048 Mbps each), or a single E4 (139.264 Mbps) signal.
Question 4: Which of these is NOT a common SDH network element?
Correct Answer:
d) Channel Service Unit (CSU)
The Channel Service Unit (CSU) is a device used in digital leased lines (like T1/E1), but it's not a core SDH network element. The main SDH network elements are Terminal Multiplexers (TM), Add/Drop Multiplexers (ADM), Digital Cross-Connects (DXC), and Regenerators.
Question 5: What is the purpose of pointers in SDH frames?
Correct Answer:
b) To compensate for frequency and phase variations
Pointers in SDH frames indicate the start position of the Virtual Container (VC) within the frame. This allows compensation for frequency and phase variations between the frame rate and payload rate, which is one of SDH's key advantages over earlier PDH systems.
Question 6: How many E1 signals can be carried in an STM-1 frame?
Correct Answer:
c) 63
An STM-1 frame can carry 63 E1 signals. Each E1 operates at 2.048 Mbps, and 63 × 2.048 = 129.024 Mbps, which fits within the STM-1 payload capacity of approximately 150.336 Mbps after accounting for overhead.
Question 7: Which SDH layer is responsible for end-to-end connection monitoring?
Correct Answer:
c) Higher-Order Path
The Path layer (both Higher-Order and Lower-Order) is responsible for end-to-end connection monitoring. The Higher-Order Path handles VC-3/VC-4 level connections, while Lower-Order Path handles VC-11/VC-12 level connections.
Question 8: What is the primary function of an SDH Add/Drop Multiplexer (ADM)?
Correct Answer:
c) To insert and extract lower-rate signals from an SDH stream
The primary function of an ADM is to add (insert) or drop (extract) lower-rate signals from a high-speed SDH stream without having to demultiplex the entire signal. This makes SDH networks more efficient and flexible.
Question 9: What is the equivalent of SDH's STM-1 in the SONET standard?
Correct Answer:
b) STS-3
SDH's STM-1 (155.52 Mbps) is equivalent to SONET's STS-3 (3 × 51.84 Mbps = 155.52 Mbps). While they are fundamentally compatible, there are minor differences in terminology and overhead byte allocation between the two standards.
Question 10: Which protection mechanism uses two fiber rings with traffic traveling in opposite directions?
Correct Answer:
b) Bidirectional Line Switched Ring (BLSR)
Bidirectional Line Switched Ring (BLSR) uses two fiber rings (working and protection) with traffic traveling in opposite directions. In case of a failure, traffic is switched to the protection fiber, typically within 50ms. BLSR/2 uses two fibers while BLSR/4 uses four fibers for greater capacity.