CS-09 – Data Communications and Networks
Quiz
SONET/SDH
SWITCHING
ISDN
B-ISDN , ATM
CELLULAR RADIO
SATELLITES
Quiz
1.
Two modems on analog telephone line talk by
a)
Analog Signalling
b)
Digital Signalling
c)
Analog as well as digital signalling
d)
No signalling is required between modems.
2.
QAM (quadrature amplitude modulation) allows transmission over 2400 baud line
at
a)
9600bps b) 2400bps c) 14400 bps d) 33.6Kbps
3.
RLE is useful for Fax Documents. TRUE/FALSE
4.
ASYNC communication over RS232C would use start-stop bits. TRUE/FALSE
5. ‘FTTC’ stands for
a)
Fibre To The Co-axial connection
b)
Fibre To The Cable connection
c)
Fibre To The Curb connection
d)
Frame Transfer Thru Curb
6.
RS-449 allows balanced transmission upto
a) 2
Mb b) 10 Mb c) 10/100 Mb d)
1 Mb
7. RS232C is designed to
transfer information upto
a)
60 Meter b)15 Meter c)100 Meter d)1 Km
8. 24 and 32 channel PCM are
popular in
a)
USA and Europe/Asia respectively
b)
Europe and USA respectively
c)
USA and Japan respectively
d)
Europe and Asia respectively
SONET/SDH
· SONET (Synchronous Optical NETwork) standard to connect long distance networks.
· CCITT equivalent (G.707, G.708, G.709) are called SDH (Synchronous Digital Hierarchy)
Goals:
· Internetwork Different Carriers.
· Unify PCM standards of different countries.
· Provide way to multiplex different digital channels.
· Support for Operations, Administration & Maintenance (OAM)
Features:
· Synchronous transfer of TDM type controlled by a Master clock.
· Section (Connection between two units), Line (Connection between Two Multiplexers) and Path (Connection between source and destination) are defined.
· 810 Byte frame (90x9 bytes) put at 125uSec(8000 frames/sec): 8x810=6480 Bits x8000 = 51.84 Mbps = STS-1 channel.
· SONET Trunks are multiples of above.
STS-1=OC1=51.84 Mbps
STS-3=OC-3=STM-1=155.52 Mbps
STS-9=OC-9=STM-3=466.56 Mbps
STS-12=OC-12=STM-4=622-08 Mbps
STS-24=OC-24=STM-8=1244.1 Mbps
STS-48=OC-48=STM-16=2488.32 Mbps
Switching
· Technology Inside Plant for Information Routing.
Circuit Switching:
· Intermediate points in the system try to give permanent circuit between caller and receiver.
· Pre-connection setup is required.
· After path is set delay is minimal.
· Congestion can not occur after setup.
Message Switching:
· Message is stored on intermediate points and then forwarded to destination.
· Block size is not limited, thus a particular message could block line for other messages.
· Unsuitable for Interactive communication.
Packet Switching:
· Blocks are fixed width = Called packets.
· Message packets travel independent of each other.
· Bandwidth is not reserved in advance.
· Delay could be introduced by the carrier.
· Charging is independent of transmission distance.
· Congestion can occur.
Switch Hierarchy
· Switching Capacity shall have relation with the network usage.
· Switching shall be done in least possible time and cost.
Crossbar
Switching:
· Assumed as Matrix of ‘n’ input and ‘n’ output circuits.
· Required Crosspoints are n(n-1)/2.
· Useful for relatively small end offices.
Space Division
Switching:
· Multistage Crossbar switching to reduce number of cross-points.
· Multi-stage often produces blocking network, but it is good enough for higher level switching offices.
Time Division
Switching:
· Switching is achieved by timeslot interchange.
· Switching limitation comes by access speeds of RAMs used for buffering the data.
ISDN
· Integrated Services Digital Network.
· Sets a goal of integrating voice and non-voice service.
· Two standards for Home and Organisational use were developed.
o NT1 based – For Home use, where ISDN telephone and ISDN terminal can be directly hooked to line.
o NT-2 based – NT2 (Network Terminator PBX) which extends service to various ISDN or normal devices (using Terminal adaptors).
· 4 Reference points R, S, T, U defined
o R – Between Terminal Adapter to Non-ISDN device.
o S – Between NT2 to ISDN device.
o T – Between ISDN Exchange to Customer premises
o U – Between ISDN switch to NT1 at Exchange side.
Channel Types and ISDN preferred combinations
· A = 4 KHz Analog
· B = 64 Kbps Digital PCM
· C = 8 or 16 Kbps Digital
· D = 16 Kbps Digital for signalling
· E = 64 Kbps Digital for Signalling
· F = 384, 1536, 1920 for digital channel
Preferred:
BASIC Rate = 2B + 1D
Primary Rate = 23 B + 1D (US,Jpn)) or 30B + 1 D (Euro,Ind)
Hybrid = 1A + 1C
· Basic rate is equivalent to 2 x 64Kbps PCM voice channels. Signalling is separate so full band is available.
· Terminal adapters for full 144 Kbps access are now available, which makes ISDN popular for Internet users.
· ISDN is now referred as N-ISDN (due to 64kbps channel) as now B-ISDN of 155 Mbps channel is available.
B-ISDN
·
Basic Channel 155 Mbps
·
Implemented by a small size packet of 53 bytes known as a cell.
·
Cell Switching technology
(ATM–Asynchronous Transfer
Mode).
·
Offers Permanent and Switched virtual circuits.
·
Connection oriented but cells can arrive in any order at the
destination. Thus called asynchronous.
·
ATM switching prepares routing tables for all messages and thus forthcoming
cells can be accordingly routed.
·
Cells can be encased in T1, E1 or Sonet frames.
·
ATM switches: Knockout – Modelled on Crossbar model, Batcher-Banyan
Switch modelled on Space-Division Switch model.
Cellular Radio Technologies - 1
·
Useful for people on the move.
·
Emerging now for Internet connectivity as well.
Paging Systems:
· Paging=Simplex Addressing.
· Beeper, Numeric and AlphaNumeric Types now available.
· 930-932 MHz Band.
· Broadcast mode, so no message contention problem.
Cordless Telephone:
· Base Station and Handset
· Low Power radio of about 100 M range.
· CT-1=Analog Standard, CT-2 Digital Standard, CT-3 (DECT-Digitally Enhanced Cordless Telephone) supports roaming over basestations.
· Broadcast mode, so no message contention problem.
Analog Cellular
Telephone:
· Originally Single Channel Systems, used to work in Push-to-Talk mode.
· IMTS (Improved Mobil Telephone System) utilised different sending and receiving frequencies. Supported 23 channel.
Advanced Mobile
Phone System (AMPS):
· First to use the Cell Technology.
· Frequencies are not used in adjacent cells but can be reused beyond adjacent cells. This allows higher no. of channel availability.
· Uses 832 channels. Half/Half are allocated as A-Side and B-Side to 2 different providers in an area.
· Analog Technology so it can be intruded.
Cellular Radio Technologies - 2
GSM Cellular
Technology:
· GSM=Global Systems for Mobile Communication.
· Digital Technology.
· Uses both FDM and TDM technology.
· Spectrum is broken into 50 nos 200KHz Band. Each band uses TDM for user multiplexing.
· Uses 1.8GHz and 900MHz band wherever available.
Personal
Communication Services:
· Uses Cellular Technology with Microcells 50-100 M wide.
· Radio power in the range of ¼ watt so small phones are possible.
· Infrastructure investment is more but unit costs could be very low.
Wireless in Local
Loop:
· Called as WILL or WLL.
· Support communication upto around 5 Kilometer in wireless mode between base station shared by multiple clients.
· Low cost handset.
· Good for most home segment users.
· Internet connection on this link is not feasible.
Satellite Communication
·
Satellite act as microwave repeater in sky.
·
Useful for Media Broadcasts.
Geosynchronous
Satellites
·
At 36,000 KM above earth Orbital period is same as Earth Revolution Period
of 24 hours.
·
Satellite appears static over earth.
·
To avoid satellite accidents international treaties come in picture.
·
C band 3.7-4.2 GHz (Down) 5.9-6.4 GHz (Up)
·
Ku band 11.7-12.2 GHz (Down) 14-14.5 GHz (Up)
·
Ka band 17.7-21.7 GHz (Down) 27.5-30.5 GHz (Up)
·
C band congested but Ku and Ka are available
·
Rain disturbs Ku and Ka bands but widely separated ground stations can
resolve problems.
·
Multiple Transponders are now put to focus on very narrow spot beam of
satellite coverage.
·
VSAT (Very Small Aperture Terminal) allows low cost Microstation. VSAT
communicate directly or by using Intermediate High gain Antenna.
Low
Orbit Satellites
·
Motorola Iridium Project Proposed 66 Satellites in lower orbits
·
Low Orbit Satellite need to talk to each other to transfer the call
Dynamically.
·
Iridium Failed.
·
More Projects like TeleDesic etc. are still underway.