IT6601 - Mobile Computing - 2 Marks Questions and Answers - 2

1.    Write the congestion avoidance algorithm.
•    TCP Tahoe and Reno
•    TCP Vegas
•    TCP New Reno
•    TCP Hybla
•    TCP BIC

2.    State the mechanism used in improvement of TCP Performance.
•    Slow start
•    Mobile TCP
•    Indirect TCP
•    Snooping TCP
•    Fast Transmit/Fast Recovery
3.    Explain Slow start Algorithm.
Slow-start algorithm works by increasing the TCP Window by one segment for each acknowledged segment. This behavior effectively doubles the TCP Window size each round trip of the network. The algorithm continues increasing until this "congestion window" (cwnd) reaches the size of the receivers advertised TCP Receive Window (RWIN), or until packet loss occurs.

4.    Define Round Trip Time.
Round-trip time (RTT), also called round-trip delay, is the time required for a signal pulse or packet to travel from a specific source to a specific destination and back again. In this context, the source is the computer initiating the signal and the destination is a remote computer or system that receives the signal and retransmits it.

5.    Explain any two protocols used in the application layer.
•    SNMP
•    FTP
•    DNS
•    HTTP

6.    Define GSM.
GSM (Global System for Mobile communication) is a digital mobile telephony system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephony technologies (TDMA, GSM, and CDMA).

7.    Elaborate the category of GSM services.
•    Supplementary Services
•    Bearer Services
•    Tele Services
8.    State the Functions of Data Link Layer.
•    Error Control- The end to end transfer of data from a transmitting application to a receiving application involves many steps, each subject to error.
•    Flow Control- Sender sends data at higher rate and receive is too sluggish to support that data rate.
9.    Write the three main elements of UMTS.
•    User Equipment (UE): The User Equipment or UE is the name given to what was previous termed the mobile, or cellphone.
•    Radio Network Subsystem (RNS): It provides and manages the air interface for    the overall network.
•    Core Network:  The core network provides all the central processing and management for the system. It is the equivalent of the GSM Network Switching Subsystem or NSS.

10.    Define SS7.
Signaling System 7 (SS7) is an architecture for performing out-of-band signaling in support of the call-establishment, billing, routing, and information-exchange functions of the public switched telephone network (PSTN).

11.    Write the Subsystems of GSM.
•    Network Switching Subsystem (NSS)
•    Radio Switching Subsystem (RSS)
•    Operation Switching Subsystem (OSS)

12.    List the types of services used in GPRS.
•    Authentication
•    Encryption
•    Anonymity

13.    State the two elements used in GPRS.

•    Gateway GPRS Support Node (GGSN)- The Gateway GPRS Support Node acts as an interface and a router to external networks. It contains routing information for GPRS mobiles, which is used to tunnel packets through the IP based internal backbone to the correct Serving GPRS Support Node.
•    Serving GPRS Support Node (SGSN)- The Serving GPRS Support Node is responsible for authentication of GPRS mobiles, registration of mobiles in the network, mobility management, and collecting information on charging for the use of the air interface.

14.    Define Handover.
A handover is a process in telecommunications and mobile communications in which a connected cellular call or a data session is transferred from one cell site (base station) to another without disconnecting the session.

15.    Draw the protocol of GSM.