Optical Fiber Questions

1		Describe what bend loss is and steps that can be taken to minimise it in the context of optical fibre.

2		Describe what type of fibre cable (loose tube or tight jacket) would usually be used in an outdoor cabling installation stating a reason why.

3		An indoor fibre cable is to be used to connect two floors of a building and is to be installed vertically in a congested maintenance shaft. What types of protection would you expect the cable to have?

4		Discuss in detail the advantages / disadvantages of the three main types of fibre connection, fusion splice, mechanical splice and connectorisation.

5		Give two advantages or disadvantages of a singlemode fibre over a multimode fibre.

6		Describe what type of fibre cable (loose tube or tight jacket) would usually be used in a building cabling installation stating a reason why.

7		An outdoor fibre cable is to be used to connect two buildings on a campus and is to be directly buried, what types of protection you would expect the cable to have.

8		Optical fibre cables use two main techniques to protect the optical fibres within them, describe one of them.

10		List 6 advantages and disadvantages of optical fibre and briefly describe.

11		In optical fibre telecommunications systems three wavelength windows are typically used. What are they and in what advantages and disadvantages do they bring to their respective systems.

12		Show how a loss measurement is taken between two patch panels. Use diagrams to support your answer.

13		Describe 3 safety issues in relation to optical fibre systems.

14		850nm and 1330nm light sources are typically used in optical fibre building cabling systems. Why are 1550nm sources typically not used?

15		Name three common areas that optical communications are used.

16		Describe in brief how ‘Total internal reflection’ allows light to be guided down an optical fibre.

17		The refractive index of the glass in an optical fibre is an important parameter. What does refractive index mean?

18		If the input power of an optical fibre link is 3mW and the output power is 0.01mw, what in the attenuation of the fibre link in dB?

20		Name one type of fibre attenuation processes and discuss how it works.

21		What steps can be taken to reduce Absorption loss in an optical fibre link?

22		What types of protection will an optical fibre cable have, to protect the fibres enclosed from moisture?

23		Describe the typical steps required to terminate an optical connector to an optical fibre.

24		What is Fresnel loss?

25		Describe one form of fibre core misalignment.

26		What advantages do ‘high density’ building cabling connectors bring to an installation?

27		How is an optical fibre cleaved? Use diagrams to support your answer.

28		What is the main difference between a high end (expensive) cleaver and a low end (cheap) cleaver?

29		Describe the steps in detail in carrying out a fusion splice.

30		What is the purpose in a V-groove in a fusion splicer?

31		Discuss the advantages and disadvantages between a fusion splice and a mechanical splice.

32		Describe in brief using a diagram to support your answer how an OTDR operates.

33		What safety precaution should be taken when working with scrap fibre?

2	(a)	A loose tube cable would usually be used in an outdoor installation. Loose tube cables allow a cable to stretch without damaging the fibre within. Also loose tube cables usually have a water blocking gel in the tube that will pour out in a vertical installation.
[10 Marks]

3	(a)	Any 2 Tensile strength – A strength member to stop the cable being stretched while installed Moisture ingress – maintenance shaft could have water systems or be humid. No water blocking gel. Crush resistance – Weight if other cables. Protection from cable ties.

4	(a)	Essay type comparison of details in table below. Advantages Disadvantages Splice Low loss Initial high cost of fusion splicer Low cost per splice Permanent Mechanical splice Semi permanent Higher loss than fusion splice Lower loss than connector Higher cost per splice Low equipment cost Connector Removable Highest loss High cost per connector
[10 Marks]

5	(a)	Any two of the below. Advantages -Higher bandwidth -Lower dispersion -Better upgrade potential Disadvantages -Difficult to couple light -Connectorisation, splicing more difficult and expensive -Connecting equipment more expensive

6	(a)	A tight jacket cable would usually be used in a building installation. Tight jacket cables are capable of tighter bend radii than loose tube cables. Also loose tube cables usually have a water blocking gel in the tube that will pour out in a vertical installation.

7	(a)	Tensile strength – A strength member to stop the cable being stretched while installed Crush resistance – To stop the weight of the soil damaging the fibre. Moisture ingress – To stop water coming in contact with the fibre and causing it to fail.

8	(a)	Loose tube or tight jacket.

9	(a)	Any 2 Tensile strength – A strength member to stop the cable being stretched while installed Moisture ingress – Has an aluminium foil jacket. As it is loose tube will also have moisture blocking gel. Crush resistance – Has a wire braid jacket just below the first layer of the cables outer jacket. Source: From Google

GSM Protocols

GSM Protocol is divided into mainly three Layers:

Layer-1 Protocol:-          MTP
Layer-2 Protocol:-          LAPDm
-          LAPD
Layer-3 Protocol:-          RR
-          MM
-          CM
-          BSSMAP
-          DTAP
-          MAP

 Layer-1 Protocol:

        MTP-Message Transfer Part:

–        The Message Transfer Part (MTP) is part of the Signaling System 7(SS7) used for communication in Public Switched Telephone Networks.

–        MTP is responsible for reliable, unduplicated and in-sequence transport of SS7 messages between communication partners.

–        The MTP provides a mechanism giving reliable transfer of signaling messages

–        The Media Transfer Protocol (MTP) is an extension to the Picture Transfer Protocol (PTP) communications protocol that allows media files to be transferred atomically to and from portable devices.

 Layer-2 protocols:

LAPDm-Link Access Protocol D Channel Mobile

LAPDm:

–        LAPDm stands for Link Access Procedure on D channel (modified). This is a modified version of LAPD and is optimized for the GSM Air interface.

–        It is said to be a lightweight LAPD protocol as it does not handle error correction/detection.

–        It handles:

–        Segmentation and reassembly of data and  

–        Acknowledges/unacknowledged data transfer

–         Re-sequencing of data frames and flow control!

The LAPD protocol is used for A and A-bis interface.

LAPDm is a data link layer protocol used in GSM cellular networks. LAPDm forms Layer 2 of the Um interface between the Base Transceiver Station and Mobile station which is to say that it is used in the radio link between the cellular network and the subscriber handset

     Functions:

– Organization of Layer 3 information into frames

–        Data flow Control

–        Acknowledged/Unacknowledged data transmission

–        Segmentation

–        Data re-assembly

– Peer-to-peer transmission of signaling data in defined frame formats

– Recognition of frame formats

– Establishment, maintenance, and termination of one or more (parallel) data links on signaling channels

Layer-3 Protocols:

• A number of mechanisms needed to establish, maintain and terminate a mobile communication session
• Layer III implements the protocols needed to support these mechanisms
• A signaling protocol, the registration process, is composed of a sequence of communication events or messages

RR: Radio Resource Management

MM-Mobility Management

CM-Connection Management

BSSMAP-Base Station Subsystem Mobile Application Part

DTAP-Direct Transfer Application Part

MAP-Mobile Application Part

MM:

-          Responsible for

-           location management and

-           Security

·         Location management involves the procedures and signaling for location updating, so that the mobile’s current location is stored at the HLR, allowing incoming calls to be properly routed.

·         Security involves the authentication of the mobile, to prevent unauthorized access to the network, as well as the encryption of all radio link traffic.

·         The protocols in the MM layer involve the SIM, MSC, VLR, and the HLR, as well as the AuC (which is closely tied with the HLR).

CM:

The CM functional layer is divided into three sub layers.

             - Call Control (CC)

             - Supplementary Services

             - Short Message Service

                Call Control (CC) sub layer

- manages call routing, establishment, maintenance, and release, and is closely related to ISDN call control.

Supplementary Services sub layer

 - manages the implementation of the various supplementary services (Call Forwarding/waiting/hold), and also allows users to access and modify their service subscription.

Short Message Service sub layer

 - handles the routing and delivery of short messages, both from and to the mobile subscriber.

     BSSMAP:

–        BSSMAP Support all of the procedure between the MSC & BSS that require interpretation and processing of information related to single call and Resource management

–        BSSAP includes all messages exchanged between the BSC and the MSC that the BSC actually processes—examples include PAGING, HND_CMD, and the RESET message. More generally, BSSAP comprises all messages that are exchanged as RR messages between MSC and BSC, and messages that are used for call-control tasks between the BSC and the MSC.

–        The BSS Management Application sub-Part (BSSMAP) supports other procedures between the

MSC and the BSS related to the MS (resource management, handover control), or to a cell within the BSS, or to the whole BSS.

   DTAP:

–        The Direct Transfer part is used to transfer call control and Mobility management message between the MSC & MS.The DTAP information in these message is not interpreted by the BSS.

MAP:

•          It pprovides basic communication between HLR and other MSC

•          MAP functions:

–        Updating of location information in VLRs

–        Storing routing information in HLRs

–        Updating and supplementing user profiles in HLRs

–        Handoff of connections between MSCs

Source: From Google