1. Switching & Data Networks Switching and Interconnection Networks
Lecture ID: ET-IDA-067
Tutorial-2
Switching and Interconnection Networks
, v04
Prof. W. Adi

2. SS7- Review questions
Q1. What is signaling in a telecommunication system?
Signaling refers to the exchange of information between call components required to provide and maintain service.
Q2. What is in-band and out-of-band signaling?
In-band signaling: is the signaling that takes place over the same path as the conversation.
Out-band signaling: is the signaling that does not take place over the same path as the conversation.
Q3. What is a signaling link?
A digital channel established by the out-of-band signaling and used for the exchange of
Signaling information.
Q4. At which speeds do SS7 signaling links usually operate ?
At a rate of 56 or 64 kbps.
Q5 What is associated signaling ?
A simple signaling technique in which a path allocated between each interconnected pair of switches as a signaling link. All signaling traffic between the two switches could traverse this link.
Q6. Which are the essential components of SS7 network ?
-Signal Switching Points (SSPs): telephone switches used to originate,terminate or switch calls.
-Signal Transfer Points (STPs): packet switches,they receive and route the incoming Signaling
messages to the proper destination.
-Signal Control Points (SCPs): database used to provide information necessary for advanced call
processing capabilities.

3. Q7. Why are STP network elements deployed in pairs called mated pairs ?
To ensure higher reliability in case of defects in some STP nodes
Q8. Which are the link types of SS7 network ?. Describe the function of every link type
*A-links:a link that interconnect an STP and either an SSP or an SCP; it is used for the purpose of
delivering signaling to or from the signaling end points.
*C-links: interconnects mated STPs,used to enhance the reliability of the signaling network when one or
several links are unavailable.
*E-links: Additional set of links to a second STP to provide backup connectivity in case that basic A-links
fail to connect.
*F-links: “Fully-associated” links which connect two signaling end points directly, allowing associated
signaling only. These links are optional.
Q9. What is a virtual telephone number ?
Are telephone numbers (like 800 numbers) used to substitute the real telephone numbers. The real subscriber
number is found in the data base of the SS7 network unit SCP.
Q10. Which network element is responsible for translating the 800 number to its real subscriber number ?
SCP : Signal Control Points

4. Q11. What are the main protocol layers of SS7 Network (describe two of them).
MTP, SCCP, TCAP, ISUP
*MTP (Message Transfer Part): provides physical layer in MTP level 1 and link-layer in MTP level 2 responsible for error checking,flow control, sequence checking and network layer in MTP level 3 which includes node addressing, routing, alternate routing and congestion control.
*TCAP (Transaction Capabilities Application Part): is an application layer defines the messages and protocol used to communicate between applications and network nodes
*SCCP (Signaling Control Part): Interfaces MTP to higher level applications as Intelligent Network and Mobile Network applications
*ISUP (ISDN user part): manages ISDN network applications
Q12. What are the three types of SUs (Signal Units) in SS7 ? Describe their main use.
*Message Signal Units (MSUs): are the workhorses of the SS7 network. All signaling associated with setup and tear down, database query and response and SS7 network management takes place using MSUs.
*Link Status Signal Units(LSSUs): used to communicate information about the status of the signaling link between the nodes on either end of the link.
*Fill-In Signal Units(FISUs): their purpose is to occupy the link when there is no LSSUs or MSUs to send. FISU facilitate the continuous monitoring of link quality in the absence of signaling traffic.

5. Q13. What is the function of the Flag Octet (Byte) in a signal unit in SS7 ?
and how often should it appears in a signal unit SU ? And where ?
-Flags delimit SUs. A flag defines the end of one SU and the start of the next.
-Flag is defined as the 8-bit pattern “ ” .
-At the end of one SU or the beginning of the next SU
Q14. What is the function of the checksum byte in an SS7 SU.
Used to verify that the SU has passed error-free across the link.
Q15. What is the function of the length indicator LI byte in an SS7 SU ?
Indicate the no. of octets between itself and the checksum,it serves as a check of integrity of the SUs and as a mean of discriminating between different types of SUs at level 2.
Q16. What is the function of the signal unit FISU (Fill-In Signal Unit) ?
Mainly to occupy the link when no need for useful signaling. It indicates that the link is still intact or not.