CS-09 – Data Communications and Networks

 

 

AGENDA (Session 8)

 

 

Quiz

 

FDDI

 

TCP-UDP

 

MultiMedia Data Compression

 

 

 

 

                                     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Quiz

 

 

1. In Sliding Window Protocol When frame is acknowledged, Upper Edge of the Window is advanced.   TRUE/FALSE

 

2. Sliding Window Protocol

a)    Works on Half Duplex Channel Only.

b)   Allows Acknowledgement to be clubbed with Data frame.

c)    Is primarily meant for flow control.

d)   Allows different window sizes at receiving and sending end.

 

3. When HDLC line is ideal what information can be found on channel.

a)    Destination address.

b)   Flag Byte.

c)    Ack of Last Frame.

d)   Supervisory Frame.

 

4. SLIP uses 0xC0 byte for frame start/end.  TRUE/FALSE

 

 

5. Primary Advantage of PPP over slip is

a)    PPP allows point to point connection, SLIP doesn’t.

b)   Start/End on PPP is not required.

c)    PPP allows dynamic IP address allocation.

d)   PPP is connection oriented, SLIP is not.

 

6. The primary purpose of Header Only checksum in ATM frame is.

a)    Higher Efficiency.

b)   Better Frame Detection.

c)    Better Error Detection.

d)   Better Traffic Congestion Control.

 

 

 

 

 

FDDI – Fibre Distributed Data Interface

 

 

·        Token Ring LAN.

·        100 Mbps, 200 KM, 1000 Nodes.

·        Useful for workstation or backbone of LANs.

·        Uses Multimode fibres for Lower Cost.

·        LED’s used for Lower cost and safety.

·        2 RINGS (one operates clockwise, Second Anti-clockwise

 

 

 

 

 

 

 

 

 

 

 

 

 


·        Type A station is connected to both rings, so it keeps working even if one ring fails.

·        Type B is connected to one ring only.

·        All frames in window are buffered for retransmission.

·        If any type A station fails, They have Relays to join the 2 rings as one long ring.

 

 

 

 

 

 

 

 

 

FDDI – Contd.

 

·        Frame similar to 802.5

 

 

Preamble

(>=8)

Start

 

Frame Control

 

Destin-ation

Source

Data

End

Frame Status

 

·        Preamble-wait time for synchronisation.

·        Frame Status holds ACK bits.

·        Token Holding Timer, Token Rotation Timer, Valid Transmission timer used.

·        Token regenerated as soon as frame transmission is finished (Unlike 802.5 where it is done when frame is heard back on the ring).

·        Priority classing is possible.

 

 

FDDI-II:

 

·        Permits synchronous frames, Circuit Switched Data.

·        16 Bytes of Non-Circuit Switched Data, 96 Bytes of Ckt Switched data (PCM Data for e.g.).

·        96 bytes equiv. To 96 PCM channels per frame

·        4x24 for T1 channel, 3x32 for E1 channel.

·        Time slot allotment is reserved, whether used or unused by data.

·        Unused slots on demand may be allotted to other type of data.

 

 

 

 

 

 

 

 

 

TCP vs UDP

 

TCP/UDP:

·        Meant for Connection Oriented Service.

·        Reliable Connection over unreliable lower layers.

·        TCP Entity = User Data broken as less than 64 Kbytes.

·        Entity send as separate IP datagrams.

·        Receiver regenerates TCP entity and subsequently user data.

·        TCP handles retransmission or re-ordering for proper sequencing.

·        Header as per diagram on page 526.

 

UDP:

·        Meant for connectionless service.

·        Just a small header added to IP.

·        Header as per page 542.

·        Source destination port functionality same as TCP.

·        UDP length = 8 byte header+Data.

·        UDP Checksum includes pseudo header same as TCP.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Multimedia Data Compression

 

Compression:

·        Representation of Information by fewer number of Bits (Encoding).

·        Decoding always required at receiver.

·        Efficiency requirement for encoding and decoding could be different owing to its usage.

·        Multimedia compression could be lossy if quality produced after decoding is acceptable.

·        Various compression methods relate to type of multimedia data Text, Images, Audio, Video etc.

·        Text compression follows principles of file compression. Font based compression techniques are a type of Source Encoding covered under Image compression.

 

Image Compression Techniques:

·        ENTROPY ENCODING : manipulate bit stream without going thru its meaning (Run-Length Encoding, Statistical Encoding, CLUT). Is always a lossless encoding.

·        SOURCE ENCODING: encoding may be dependent of meaning of bit values (Differential Encoding, Transformations, Vector Quantization).

·        JPEG performs, source/entropy encoding in many steps.

 

 

 

 

 

 

 

 

 

 

 

 

Audio-Video Compression

 

Audio-Visual Telephony:

·        H.200 series recommendations of ITU

o       CIF (Common Intermediate Format) for 352x288 pixel image.

o       QCIF (Quarter CIF) for 176x144

o       H.261 codecs for px64Kbits/sec streams. P>6 is ok for CIF

o       ISDN OK CIF format.

·        H.320 series

o       For Narrowband Telephony <1920 Kbits/sec channel.

o       QCIF at 7.5 fps min. support.

o       CIF upto 15 fps implemented as optional.

 

Audio Video Applications:

·        MPEG-1.

o       Fits into bitstream of 1.5 Mbits/sec (Good for CD, DAT etc).

o       Allows Manufacturer customisation upto (4095x4095 by 60fps)

o       Practical Implementation (CPB-Contrained Parameter bitstream) as 352x240 at 25 fps or 352x288 at 30 fps. Just better than VHS.

o       Philips adaptation CD-I (CD-Interactive).

o       16 bit PCM audio at 44.1 KHz, 48 KHz, 32 KHz.

o       Audio Layer 1 – 448 Kbit/sec on 192 Kbit/sec channel.

o       Audio Layer 2– 385 Kbit/sec on 128 Kbit/sec channel.

o       Audio Layer 3– 320 Kbit/sec on 64 Kbit/sec channel.

 

 

 

 

 

 

Audio-Video Compression (contd)

·        MPEG-2.

o       Broadcast quality upto 4-6 mbps stream.

o       Suitable for NTSC, PAL and later extended to HDTV.

o       DSM-CC (Digital Storage Media Command and Control ) Protocol between set-top terminals and video servers.

o       Interlaced Video Formats Allowed.

o       Backward Compatible with MPEG-1. MPEG-2 Can be played on MPEG-1 Player with limitation.

o       Profile Available:

Low – 352x288, 30fps, 4Mbps

Main – 720x576, 30fps, 15Mbps

High1440 – 1440x1152, 60fps, 60Mbps

High – 1920x1152, 60fps, 80Mbps

o       Transport Stream – Multiple Programs broadcast.

o       Programme Stream – Application Multimedia and MPEG-1 Compatibility.

o       Surround Sound Channels added in Audio.

 

·        MPEG-4

o       Low Bit rate Encoding for narrow band.

o       10 fps at 64 Kbps.

o       Video Conference on N-ISDN B Channel.

 

·        Proprietary

o       DVI – Digital Video Interactive of Intel has RTV (Real Time Video) and PLV (Presentation Level Video) an assymmetric standard.

o       Quicktime – Apple, 160x120 at 15 fps, Compact Video, 320x240 upto 15fps, 160x120 upto 30fps.

o       Video for Windows (VfW) , Video & RLE are Microsoft Implementation and Indeo is Intels Implementation using DVI. Stored as AVI files.