Video Codec for Multimedia Communications

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COSC 3213 Computer Networks I Instructor Dr.
Amir Asif Department of Computer Science York
University Section M Local Area Networks
Topics LAN Standards IEEE 802.3, IEEE 802.3u,
IEEE 802.3z, IEEE 802.5 Garcia Sections 6.7
6.8
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Review of Number System

• Consider four representations for integers
• Decimal, each digit lies between 0 and 9
• Binary, each bit is either 0 or 1
• Octal, ecah octal digit lies between 0 and 7
• Hexadecimal, each hexadecimal digit lies between
  0 and F
• Activity 1 Convert the decimal number 1500 into
  representations (2) (4).

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IEEE 802.3 - History

1. Developed in the 1970s by Xerox
2. Dec, Intel, and Xerox completed the DIX
   standard for 10Mbps LAN based on coaxial cable.
   DIX standard is referred to as DIX Ethernet
   Standard or simply Ethernet.
3. IEEE 802.3 LAN standard was developed in 1985,
   very similar to DIX.
4. In 1995, the 100Mbps Fast Ethernet standard (IEEE
   802.3u) was approved.
5. In 1998, the 1Gbps Gigabit Ethernet Standard
   (IEEE 802.3z) was approved.
6. Trend of faster and long range Ethernet continues
   

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IEEE 802.3 Protocol (1)

• IEEE 802.3 uses the 1-persistent CSMA/CD protocol
  in the MAC sublayer
• A station with a frame to transmit waits until
  the channel is free (or silent).
• When the channel goes silent, the frame is
  transmitted.
• If a collision is not detected for (2
  propagation time), frame is assumed delivered
• In case of a collision, the station aborts the
  transmission and reattempts after a randomly
  scheduled time
• Rescheduling Algorithm is based on a truncated
  exponential backoff algorithm.
• For nth transmission, the backoff period is
  selected by choosing a length at random between
  (0, 2k 1) minislots where k min(n,10).
• Minislot defined as a duration that is at least
  as long as (2 propagation delay)
• 1st Retransmission (0,1) minislots
• 2nd Retransmission (0,1,2,3) minislots
• 3rd Retransmission (0,1,2,3,4,5,6,7) minislots
• 10th and higher retransmissions (0,1,2, , 210
  1) minislots

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IEEE 802.3 Protocol (2)

• A total of 16 retransmission attempts are
  allowed.
• Activity 2 Show that the total propagation delay
  for a 10Mbps LAN consisting of five segments,
  each 2500m long and connected to each other with
  4 repeaters, is around 51.2 ms. What is the
  minimum length of an Ethernet frame designed for
  the 10Mbps LAN? (Assume a propagation speed of
  2.5 108 m/s) Answer 512 bits
• Activity on the IEEE 802.3 LAN is sum of four
  components
• Idle nearly 0 near saturation.
• Contention multiple of (2tprop)
• Transmission L / R
• Propagation tprop
• The average number of minislots per contention
  period is e minislots.
• The normalized throughput of IEEE 802.3 is given
  by

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IEEE 802.3 Protocol (3)

• Effect of a on performance of IEEE 802.3
• Transfer delays (multiples of slots) grow very
  large as load approaches throughput

a Normalized throughput
0.01 0.94
0.1 0.61
0.2 0.44
CSMA-CD
a 0.01
a 0.1
a 0.2
30
25
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Avg. Transfer Delay
15
10
5
0
0
0.3
0.6
0.9
0.06
0.12
0.18
0.24
0.36
0.42
0.48
0.54
0.66
0.72
0.78
0.84
0.96
Load
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IEEE 802.3 Frame Structure (1)
Preamble has 7 bytes of the bit pattern
10101010 . Used for synchronization Starting
Delimiter (SD) 10101011, indicates start of the
frame Source/Destination Address 6 octets (or 48
bits long) is always used gt 246 global
addresses Length specifies the length of data
(information) in bytes (or octets) Max.
frame length 1518 bytes excluding preamble
SD Information 1518 18 1500
bytes Length field (05DC)16 lt
(0600)16 Min. frame length 512 bits or 64
bytes Pad field ensures that the frame is at
least 64 bytes long Length field ?
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IEEE 802.3 Frame Structure (2)
Source/Destination Address 6 octets (or 48
bytes) are always used Types of Addresses
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IEEE 802.3 Frame Structure (3)
Source/Destination Address 6 octets (or 48
bytes) are always used Types of
Addresses FCS Frame Check Sum Based on
CCITT 32-bit CRC code Structure of DIX Ethernet
Frame is same as IEEE 802.3 frame except for the
length bytes. In DIX Ethernet Frame, length field
is replaced by type field Value of type field gt
(0600)16
1
22 bits
1
24 bits
First 24 bits are specified by the vendor CISCO
(00000C)16 3Comm (02608C)16
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IEEE 802.3 Physical Layer (1)

• Physical layers defined by the IEEE 802.3 Standard

10Base5 10Base2 10BaseT 10BaseF
Medium Thick Coaxial Thin Coaxial Twisted Pair Optical Fiber
Segment length (max) 500m 185m 100m 2km
Topology Bus Bus Star Point to Point
Data Rate 10Mbps 10Mbps 10Mbps 10Mbps
Miscellaneous Transceiver needed to attach NIC card to coax T-shaped BNC junctions used Twisted pair connects NIC card to hub responsible for comm.
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IEEE 802.3 Physical Layer (2)

• 10Base5
• 10Base2

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IEEE 802.3 Physical Layer (3)

• 10 Base T
• Read more about Fast and Gigabit Ethernet .

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IEEE 802.5 - History

• Set of protocols at the physical and data link
  layer (MAC sublayer)
• Developed by IBM in 1980s
• IEEE 802.5 standard modeled after IBM Token Ring
  in 1990s
• IBM and IEEE specifications differ in minor ways
• IBMs Token Ring specifies a star IEEE 802.5
  does not specify a topology but most IEEE 802.5
  implementations are based on a star
• IBMs Token Ring uses twisted-pair wire IEEE
  802.5 does not specify a media type
• Speed 4 Mbps and 16 Mbps
• Signalling Differential Manchester
• Size max 250 stations

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IEEE 802.5 Token Ring

• Token Passing Systems decenteralized approach
  with no central controller
• In ring topology, each station is connected in a
  ring using an interface
• Interface operates in two modes

listen mode
transmit mode
input from ring
output to ring
delay
delay
to device
from device
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MAC Scheduling Approaches Token Ring (2)

• Interface operates in two modes

listen mode
transmit mode
input from ring
output to ring
delay
delay
to device
from device
1. Each bit is reproduced on the ring with a
delay2. Delay is a multiple of (one bit
duration)3. Delay allows to check for certain
bit patterns
1. Station transmits a message bit by bit on
ring 2. Station receives a message bit by bit
from ring3. No forwarding of bits is done
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MAC Scheduling Approaches Token Ring (3)

• When no station is transmitting, there is a free
  token floating on the ring
• When a free token is received (T 0), the
  interface changes the passing token bit (T 1)
  and starts transmitting

Token Frame Format
ED
SD
AC
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MAC Scheduling Approaches Token Ring (4)

• When a free token is received (T 0), the
  interface changes the passing token bit (T 1)
  and starts transmitting
• Each transmitted bit is removed by the
  destination station or by the source station
• After the transmission is complete, the source
  station inserts the free token back onto the ring
  with (T 0)

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MAC Scheduling Approaches Token Ring (5)

• Ring Latency Maximum number of bits in
  transition around the ring
• If frame size gt ring latency, a complete frame
  cannot be present on the ring at one time
• If frame size lt ring latency, complete frame is
  on transition in the ring.
• Ring Latency (t) in seconds t Mb/R
• Ring Latency in bits (t Mb/R)R
• where t is total propagation delay around the
  ring, M is the number of stations in the ring, b
  is the number of bit-delays in an interface.
• Approaches to Token Reinsertion
• Single token operation (delayed token release)
  in which the token is released only after a
  complete frame is received by the transmitting
  station. Suitable when frame size is nearly equal
  to ring latency.
• Multiple token operation (early token release)
  in which token is released after the transmission
  of a frame is completed by the transmitting
  station. Suitable when frame size is less than
  ring latency.

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MAC Scheduling Approaches Token Ring vs Token Bus

1. Cost Ethernet is generally less expensive and
   easier to install than Token Ring .
2. Stability Token Ring is generally more secure
   and more stable than Ethernet.
3. Scalability It is usually more difficult to add
   more computers on a Token Ring LAN than it is to
   an Ethernet LAN. However, as additional computers
   are added, performance degradation will be less
   pronounced on the Token Ring LAN than it will be
   on the Ethernet LAN.
4. QoS Ethernet uses CSMA/CD media access control
   and Token Ring uses token passing. This makes
   Ethernet better suited in a situation where there
   are a large number of computers sending fewer,
   larger data frames. Token Ring is better suited
   for small to medium size LANs sending many,
   smaller data frames.