Telecom Interview Preparation Guide

Download PDF

Frequency Division Multiple Access or FDMA is a channel
access method used in multiple-access protocols as a
channelization protocol. FDMA gives users an individual
allocation of one or several frequency bands, or channels.
Multiple Access systems coordinate access between multiple
users. The users may also share access via different methods
such as TDMA, CDMA, or SDMA. These protocols are utilized
differently, at different levels of the theoretical OSI model.

Disadvantage: Crosstalk which causes interference on the
other frequency and may disrupt the transmission.

Pole Antenna-for local coverage.
Microwave Antenna-for point to point communication
transreciver,in different area BTS communication...

CDMA means Code Division Multiple access.

It was orginated at USA.

Each user is assigned a unique code and they can use the
entire bandwidth available.It is like Ten persons in a
meeting room are talking at the same time but with
different languages.

GSM is Global System For Mobile Communication.GSM uses
Time Division Multiple Access means Ten persons in a
meeting room and only speaks whenever their turn comes.

IPV6 is advanced version of IPV4.
the address of IPV^ is 128 bits with extend able memory and
that of IPV$ is 32 bits.

Class A 1.0.0.1 to 126.255.255.254 Supports 16 million
hosts on each of 127 networks.
Class B 128.1.0.1 to 191.255.255.254 Supports 65,000 hosts
on each of 16,000 networks.
Class C 192.0.1.1 to 223.255.254.254 Supports 254 hosts on
each of 2 million networks.
Class D 224.0.0.0 to 239.255.255.255 Reserved for multicast
groups.
Class E 240.0.0.0 to 254.255.255.254 Reserved for future
use, or Research and Development Purposes.

Isdn is a type of data and internet service that makes use
of digital signals running along existing copper lines to
increase the data throughput, reduce line noise and enhance
signal quality. Whereas, Internet is a packet-switched
network of interconnected computers, enabling users to
share information along multiple channels. Channels which
can be made available by using ISDN for example! That makes
the difference.

Comma Seperated

Collision domain is the group of hosts in which collision
can occur but broadcast domain consists of all the groups of
hosts that can proceed the broadcast frame. Broadcast domain
may be collision domain but Collision domain may not be
broadcast domain

A collision domain is an Ethernet term used to descrbe a
network,collection of devices in which one particular
device sends a packet on a network segment.
A broadcast domaun is where a set of all device on that
same segment hear all broadcasts sent on that segment.

First SMS is submitted to SMSC. than it is forwarded from
there to SMS gateway. SMS Gateway retrrives Routing info
from HLR and send it to MSC. MSC gets current location from
VLR of receipent mobile and delivers Msg.

If a Roaming Mobile A call to a roaming mobile B,SRI query

will come to Home HLR,which then provides the exact MSC

address of roaming Mobile B.MSC where Raoming mobile B

present will provide a MSRN Which will be provided to MSC

which is current serving Roaming Mobile A via HLR.

MSRN will be used to route the Call.

GSM, which stands for Global System for Mobile communications,
reigns as the world’s most widely used cell phone technology.
Cell phones use a cell phone service carrier’s GSM network by
searching for cell phone towers in the nearby area.

The origins of GSM can be traced back to 1982 when the Groupe
Spécial Mobile (GSM) was created by the European Conference of
Postal and Telecommunications Administrations (CEPT) for the
purpose of designing a pan-European mobile technology.

BTS abbreviated for Base Transiever Station is a collection of transmission and reception card designed for routing of signals from end user to msc and vice versa.
There are many types of BTS depending on the manufacturing companies viz nokia,ericcsion, zte,huwai etc ...i've worked on a few so can tell u about them
in nokia there is practically 2,2,2/4,4,4/8,8,8 configuration but this may vary depending upon the traffic requirement of the circle. mostly composite configurations are used, like 2,3,3 or 2,2,4 etc.
these nos are nothing but no of trx cards in each sector , for example 2,2,2 is 2 trx cards in each of three sectors.
power consumption also is different for each type of BTS, for NOKIA's Flexi indoor BTS running on 222 config power requiremnt will be approx 48 watts per hour
typically on every BTS 48V is supplied with negative polarity.
feel free to mail me for any further doubts

GSM/CDMA
1. CELL and Sector with multiple frequency / CDMA single
frequency as carrier {users are get identifies by codes}
2. used TDMA and FDMA for Accesing /CDMA uses CDMA method
3. GSM is intial 2G technology with intial voice rate of
9.6kbps/same with 14.4kbps
4.GSM emerges into WCDMA/cdma emerges into cdma 2000
5. power control in acces method is comparitively not
efficient (when compare to CDMA)/ cdma as PLL(phase locked
loops for power transmission) better
6.call hand off and network hand off is not smoother in
GSM/ CDMA follows soft handoff and handling call hence more
efficient
7. GSM use less bandwidth and more power comparitively /
CDMA uses less bandwidth and more power

8.cost wise for opeartor GSM is less costlier , but
efficiency wise CDMA is better

Bridging is a forwarding technique used in packet-switched computer networks. Unlike routing,
bridging makes no assumptions about where in a network a particular address is located. Instead,
it depends on flooding and examination of source addresses in received packet headers to locate
unknown devices. Once a device has been located, its location is recorded in a table where the
MAC address is stored so as to preclude the need for further broadcasting. The utility of bridging
is limited by its dependence on flooding, and is thus only used in local area networks.
Bridging generally refers to Transparent bridging or Learning bridge operation which
predominates in Ethernet. Another form of bridging, Source route bridging, was developed for
token ring networks.
A network bridge connects multiple network segments at the data link layer (Layer 2) of the OSI
model. In Ethernet networks, the term bridge formally means a device that behaves according to
the IEEE 802.1D standard. A bridge and switch are very much alike; a switch being a bridge with
numerous ports. Switch or Layer 2 switch is often used interchangeably with bridge.
Bridges are similar to repeaters or network hubs, devices that connect network segments at the
physical layer (Layer 1) of the OSI model; however, with bridging, traffic from one network is
managed rather than simply rebroadcast to adjacent network segments. Bridges are more
complex than hubs or repeaters. Bridges can analyze incoming data packets to determine if the
bridge is able to send the given packet to another segment of the network.

ROUTER interconnecting on layer 3, and SWITCH does it on layer 2.
ROUTER can access to different LANs, versus that the SWITCH can work only in the same LAN.
ROUTER changes the MAC addresses when pass from one LAN to another, versus that the
SWITCH can’t change it.
ROUTER do look on the IP address, versus that the SWITCH don’t care form the IP address,
SWITCH look on IP address as regular Data inside the frame.
ROUTER is defining the border of Broadcast Domain; versus that SWITCH define the border of
Collision Domain.

RSL is very low due to fading and other path losses. Hence
when signal is received at REceiver it is very low. To
amplify this low signal LNA is used as first stage amlifier
in all the receivers.

I think you have to study SDH network to understand the answer of this question.I am giving the formulae by which the STM-N is generated.

STM-64: 64 VC-4 or 16 VC-4-4c or 4 VC-4-16c or 1 VC-4-64c
STM-16: 16 VC-4 or 4 VC-4-4c or 1 VC-4-16c
STM-4: 4 VC-4 or 1 VC-4-4c
STM-1: 1 VC-4


Higher-level STM-N frames can be simplistically perceived as *4 multiples of a basic STM-1. An STM-4 is constructed by byte-interleaved multiplexing of 4 STM-1s into a frame that is 9 rows by 1080 columns wide. The STM-4 signal has a line rate of 622.080 Mbps (4 * 155.520 Mbps). The four STM-1s (STM-1(1), STM-1(2), STM-1(3), and STM-1(4)) are frame aligned before multiplexing. Frame alignment is achieved by ensuring that the first 12 bytes of the STM-4 signal are A1 framing bytes drawn from STM-1(1), the next 3 from STM-1(2), then 3 from STM-1(3), and finally 3 from STM-1(4). The 12 A1 framing bytes are followed by 12 A2 framing bytes that are obtained from the 4 STM-1s in a process, similar to the way that the A1 bytes were obtained.

GSM is a circuit switched network which is used for voice
call.for data call we use GPRS.Gprs uses network elements of
gsm but it has two additional nodes (SGSN,GGSN).by using
these two nodes we can connect to PDN(packet data network)
and make packet call(downloadig)
data speeds of gsm 13kb/s
while in gprs 171kb/s

In india its 1920-1980
and 2110-2170 MHZ

In Gsm We use routing number towards the calling subscriber
and tldn towards the calling subscriber , but in cdma the
subcriber will not be allocated any routing number for the
internal routing, i..e.. for the itra cell or intra msc
routing there will be no token issued, but for the inter
msc there will be token only towards called party.

Crankback is a mechanism used by ATM networks when a
connection setup request is blocked because a node along a
selected path cannot accept the request. In this case, the
path is rolled back to an intermediate node, which attempts
to discover another path to the final destination

There are four RRC states present in UMTS .
1.CELL_DCH STATE
2.CELL_FACH STATE
3.CELL_PCH STSTE
4.URA_PCH STATE

WHEN MOBILE IS MOVING FROM IDLE MODE TO DEDICATED MODE AND
DATA TRANMISSION IS OF LARGE AMOUNT OF DATA THEN CELL_DCH
STATE COMES IN TO PICTURE .

IF DATA TRANSMISSION IS OF SMALL AMOUT OF DATA THEN
CELL_FACH STATE WILL COME IN TO PICTURE

WHEN MOBILE IS MOVING FROM ONE CELL TO ANOTHER CELL IT
SHOULD PERFORM HANDOVER THEN MOBILE RRC STATE WILL BE IN
CELL_PCH STATE.

URA MEANS UTRAN REGISTRATION AREA

THE AREA COVERED BY ONE RNC IS KNOWN AS URA

SO WHEN MOBILE IS MOVING FROM URA AREA TO ANOTHER URA AREA
THEN LOCATION UPDATION SHOULD PERFORM THEN MOBLIE RRC STATE
COMES TO URA_PCH STATE .


THESE ARE THE FOUR RRC STATES PRESENT IN UMTS NETWORK