Transcript Lecture 3 and 4 ( ppt )

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Ch 3: Underlying Technologies
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Ch 2: TCP/IP and OSI
Lecture 3 and 4
Dr. Clincy
Lecture 3 and 4
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How TCP/IP maps to OSI ??
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Dr. Clincy
Lecture 3 and 4
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TCP/IP Model
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Explain
Suite and
Stack
Concept
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SCTP
Protocols for
different
underlying
technologies –
this is key
Dr. Clincy
Lecture 3 and 4
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Explain communications at the physical layer
Legend
A
R1
Source
Destination
R3
B
R4
Physical
layer
Physical
layer
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Link 3
Link 1
Link 5
Link 6
011 ... 101
1.
01
1
10
..
011 ... 101
011 ... 101
Signal to bits translation and vice versa (note: digital data is different from digital signal)
Dr. Clincy
Lecture 3 and 4
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Physical addresses
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• Physical address is also known as the link address
• Physical address can be different sizes (depend on the network)
• Unicast type physical addresses – single Rx
• Multicast type physical address – multiple Rxs
• Broadcast type physical address – all Rxs can pickup message
Dr. Clincy
Lecture 3 and 4
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Physical Address Example
Most local area networks use a 48-bit (6
bytes) physical address written as 12
6
hexadecimal
digits,
with
every
2
bytes
0
2 separated by a hyphen as shown below:
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07-01-02-01-2C-4B
A 6-byte (12 hexadecimal digits) physical address
Dr. Clincy
Lecture 3 and 4
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Explain communications at the data link layer
Source
Legend
A
R1
Destination D Data
R3
H Header
B
R4
Data link
Data link
Physical
Physical
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Link 1
Link 5
Link 3
Link 6
D2 H2
Frame
H2
D2 ame
Fr
D2 H2
Frame
D2 H2
Frame
Framing – encapsulation - decapsulation
Dr. Clincy
Lecture 3 and 4
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Explain communications at the network layer
IP Addresses can be either
unicast, multicast or broadcast
types
Going from network A physical
address 10 to network P
physical address 95.
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Can’t use the physical address
because different networks
The network layer address
contains the uniqueness we
need from source to sink.
Network layer address is A-P
Unit at this layer - datagram
Dr. Clincy
Lecture 3 and 4
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IP Address Example
An Internet address (in IPv4) is 32 bits in length,
normally written as four decimal numbers (or 4 octal
numbers), with each number representing 1 byte.
6 How many bits is a byte ? A nibble ??
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The numbers are separated by a dot. Below is an
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example of such an address. Call “dot notation”
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132.24.75.9
Example of IPv6 Address (128 bits):
Dr. Clincy
Lecture 3 and 4
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ADDRESSING
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We explained the physical address.
We explained the need for an Internetworking (IP)
address or Logical address
Are the Physical and Logical addresses enough
?????
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Lecture 3 and 4
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Addresses in TCP/IP
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Converts to a part address
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Lecture 3 and 4
Application
Specific
Address
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“Specific Addresses”
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Dr. Clincy
Lecture 3 and 4
Relationship
between
layers
and
addresses
in TCP/IP
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Port addresses
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Addresses of sending
and receiving processes
(j and k)
Add IP address
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Overhead (H2, T2) added
for what ?
Dr. Clincy
Lecture 3 and 4
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C Port Address Example
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As we will see in Chapters 11 and 12, a
port address is a 16-bit address
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represented
by
one
decimal
number
as
0
2 shown below.
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753
Dr. Clincy
A 16-bit port address
Lecture 3 and 4
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Messages
Segments
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Datagrams (Packets)
Relationship
between
Layers,
Addresses,
and Units
in TCP/IP
Frames
Bits
Dr. Clincy
Signals
Lecture 3 and 4
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Ch 3: Underlying Technologies (1 of 3)
Lecture #3
Dr. Clincy
Lecture 3 and 4
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– Underlying Technologies
C • Internet
As we mentioned before, the Internet is an interconnection of “backbone”
JOINED together via routers, gateways and switches
S • networks
Before getting into the higher level protocols, let’s cover more concerning the
•
•
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•
•
underlying technologies. Let’s talk about LANS and WANS and etc…
Internet is comprised of LANs, Point-to-Point WANs and Switched WANs
We will cover LANS: Ethernet, Token Ring (not in book), Wireless and
FDDI Ring (not in book)
We will cover Pt-to-Pt WANs: Telephony Modem, DSL, Cable/Modem, TLines and SONET
We will cover Switched WANs: X.25, Frame Relay and ATM
Token Ring (not in book)
FDDI Ring (not in book)
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Lecture 3 and 4
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In putting these technologies in
perspective
Most of the technologies we are about to highlight could be covered
as a full blown course – in some cases, multiple courses
We will look at each technology from a high level in gathering a
general appreciation and understanding of the technology
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Lecture 3 and 4
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LOCAL AREA NETWORKS (LANS)
• LAN – a data communication system connecting multiple INDEPENDENT
devices such computers, servers, printers, etc..
• Covers up to a certain geographical area – typically within a building or
campus
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• Some Popular LANs: Ethernet, Token Ring, Wireless type LANs, and ATM
LANs
Ethernet LAN
• Ethernet is the more popular LAN protocol
• Designed in 1973 by Xerox
• Started out with a 10 Mbps data rate (bus topology)
• Today, 100 Mbps and 1 gigabit per second exist (gig=1000 Mbps)
• IEEE 802.3 standard describes the Ethernet protocol
Dr. Clincy
Lecture 3 and 4
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CSMA/CD
• The 802.3 standard describes the CSMA/CD standard as the access method for the original Ethernet
• CSMA/CD stands for carrier sense multiple access with collision detection.
• The transport medium is shared – only one station or node can use the medium at a time
• All stations can receive a sent frame however, only the destination station takes it in (the other
stations drop the frame)
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• How can we make sure no two stations are using the transport medium at the same time ? If this
happened, the 2 frames could “collide”
• CSMA/CD solves this problem:
CSMA/CD Process
• Every station has equal access to the medium
• Station listens to or senses the medium before
sending frame – if no data, it can send – if data
exist, wait
• Suppose 2 stations sense at the same time and find
no data on the medium, crash will happen
• In this case, all stations sense the collision and
each Tx send a “jam signal” to delete the data it
sent
• Then each station waits a randomly amount of
time and try it again – this prevents a second
collision
Dr. Clincy
Lecture 3 and 4
Notice that Station Z receives a collision signal 1
20
time period earlier than Station A
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CSMA/CD
• Only one signal can travel down the transport at any time
• Node has to look out and make sure path is clear
• Which can be detected faster – large or small signal ? Why
(sensing)
• Which will clear the hall faster ? Large or small ? Why
(waiting)
• If you wait too little – what’s the problem
• If you wait too long – what’s the problem
• What’s the optimum wait time ?
• If the larger signal is moving very fast – which can be
detected faster ? Why ? Is speed a factor (sensing, waiting)
• Does the length of the transport play a factor in “how fast”
something clears the hall ? (waiting)
Dr. Clincy
Lecture 3 and 4
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CSMA/CD
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3 factors relate to CSMA/CD
1.
Minimum frame length
2.
Data transmission rate
3.
Collision domain (maximum network distance)
•
The amount of time a station needs to wait in making sure no data is on the line) is
minimum frame length divided by the data transmission rate. Why ??
(Speed=Distance/Time) – the larger the frame, the longer the time to wait – however,
sensing is shorter)
•
Amount of time to send the smallest frame (ie. an 8 bit frame at 2 bps will take 8/2 = 4
seconds to send – therefore, need to wait ATLEAST 4 seconds)
•
This time is proportionate to the time it will take the first bit to travel the maximum
network distance (collision domain).
•
Therefore, (max network distance)/(propagation speed) proportionate to (min frame
length)/(transmission-rate)
•
Data transmission rate – data transfer rate – how fast to send a certain amount of bits
from one device to another
•
For the original Ethernet: min frame size=520 bits, transmission rate=10 Mbps and the
max network distance=2500 meters
Dr. Clincy
Lecture 3 and 4
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Increasing Speed of Ethernet
• Decrease collision domain
• Increase minimum frame length
Detect faster
Larger frame
Smaller frame
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Lecture 3 and 4
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Ethernet layers
• Ethernet’s data link layer is sub-divided into MAC Layer and LLC
Layer
• MAC Layer – media access control layer – controls the
CSMA/CD access method. Also performs the “framing” work.
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• LLC Layer – logical link control layer – performs the error and
flow control routines
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Lecture 3 and 4
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Ethernet frame
• The Ethernet frame consist of 7 fields: preamble, SFD, DA, SA,
length/type of PDU, 802.2 frame (the actual data) and CRC
• Frame doesn’t provide acknowledgment or “hand shaking” fields –
unreliable medium
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• Preamble – alternating 1s and 0s t alert
and synchronize the Rx
• SFD – start field delimiter – signals the
beginning of the frame
• Length of protocol data unit – if less than
1518, defines the length up-and-coming
data field – if greater than 1536, tells the
protocol that uses the service
• Destination address – contains the
address of the next node( intermediate or
Rx)
• Data & padding – data encapsulated from
higher layers – size ranges between 46
bytes to 1500 bytes
• Source address – contains the address of
the sending node (Tx or intermediate)
• CRC – cyclic redundancy check – error
detection info
Dr. Clincy
Lecture 3 and 4
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Ethernet implementation
Each device on an Ethernet
network has a NIC
(network interface card)
Contains the physical address –ah ha, this is
how I can change locations and still get
emails
Ethernet addressing:
• Unicast
• Multicast
• Broadcast
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Some implementations of
Ethernet:
• 10BASE5 (thick ethernet)
• 10BASE2 (thin ethernet)
• 10BASE-T (twisted pair)
• 10BASE-FL (fiber link)
Dr. Clincy
British naval connector or
bayonet nut connector – for
coaxial cable
Lecture 3 and 4
Connects host to
medium and perform
CSMA/CD
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Ethernet implementation
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Lecture 3 and 4
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Ethernet implementation
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Unshielded
twisted pair
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Lecture 3 and 4
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Ethernet implementation
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Lecture 3 and 4
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Fast Ethernet implementation
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100 Mbps
Ethernet
2-wire type
(100BASE-TX or
100BASE-FX)
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4-wire type (only
100BASE-T4)
To make faster,
collision domain
was decreased 10
fold (250 meters vs
2500 meters)
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Lecture 3 and 4
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Fast Ethernet implementation
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Lecture 3 and 4
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Fast Ethernet implementation
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Lecture 3 and 4
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Gigabit Ethernet implementation
Need for data rates higher than 100 Mbps resulted in a 1000 Mbps Ethernet
called gigabit Ethernet
Again, we had the choice to either decrease the collision domain or increase
the minimum frame size
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Because 25 meters for the 100 Mbps Ethernet was short enough, the
minimum frame size was increased to get the desired speed
Another option is to do away with the CSMA/CD overhead by connecting
every station to the hub using 2 separate paths (this will do away with
collisions) – called full-duplex Ethernet
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Lecture 3 and 4
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Gigabit Ethernet implementation
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Lecture 3 and 4
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Ten-Gigabit Ethernet implementation
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Lecture 3 and 4
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Token Ring LAN
• Token Ring is a protocol defined by IEEE 802.5
• Use a token passing ACCESS method
Token Passing Method
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Dr. Clincy
Lecture 3 and 4
•
During idle times (network not
being used), a token circulates
•
The token is passed station to
station until a station needs to send
data
•
When the station sends it’s data, it
holds the token
•
The data (or frame) circulates and
get re-generated by each station
•
The Rx takes in and COPY the
frame (based on destination
address)
•
The data then continues back to the
original Tx
•
Token is then release to circulate
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Token Ring layers
• Uses the same layers as Ethernet (MAC and LLC)
• LLC Layer – logical link control layer – performs the error and flow
control routines (same as Ethernet)
• MAC Layer – media access control layer –it implements the Token
Passing Access Method (versus Ethernet’s CSMA/CD access method)
Token Ring
Dr. Clincy
Lecture 3 and 4
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Token Ring Data frame
• Token Ring frame defines 3 types of frames: data, token and abort
• Data Frame – carries a protocol data unit (actual data) and is addressed to a specific Rx
(not broadcasted)
• Token Frame – is the placeholder frame (token) and uses only 3 of the 9 fields (SD, AC
and ED)
• Abort Frame – doesn’t carry any info and is used to stop transmission
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• SD – start delimiter – alert and synch the
Rx
• DA – Destination address
• SA – Source Address
• AC – Access control - 3 bits set priority, 1
bit tells what type of frame, 1 bit is a
monitor bit tells which station is monitoring
or sending at the time, and 3 reservation bits
for station wishing for access
• FC – Frame control – 1 bit tells if PDU is
control info or data, 7 bits is used by Token
Ring (ie. tells how to use AC field info)
Dr. Clincy
• Data
• CRC – cyclic redundancy check – error checking
• ED – end delimiter – signals end of data
• FS – frame status – intermediate stations can set it
letting the Tx know they read it, Rx can set it letting
the Tx know it was copied and can be discarded now
Lecture 3 and 4
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Token Ring Implementation
• Token Ring is a series of shielded twisted pair transport medium linking each station into a ring
• Because the token needs to pass through each station with in the ring, if a station is down, it could
be a problem
• Therefore, for each station, a switch is used to by pass the down (or disabled) station
• These bypass switches are packaged together as a MAU – multi-station access unit
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NOTE: As we covered last lecture, don’t confuse the Ring Token
technology with the Ring topology. With a ring topology approach,
you would want to traverse in either direction (this is the main
benefit of a ring topology) – explain Ethernet in ring topology.
Dr. Clincy
Lecture 3 and 4
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FDDI Ring
C
S • FDDI stands for Fiber Distributed Data
•
•
•
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Interconnect
Data rate is the same as Fast Ethernet (100 Mbps)
Light signals versus electrical signals are used
Uses a token passing access method with selfhealing
What do we mean by “self healing” ? Ability to
detect and fix problems. The hardware
automatically recognizes and fix problems
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Lecture 3 and 4
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FDDI Ring
• How does the “self-healing” works ?
• Two independent rings connecting all stations are used – dual
counter-rotating rings
• The second ring is used only if a failure occurs
• Functions like a Token Ring LAN until a failure (ie. fiber cut, node
failure)
• In this case, the intermediate (non-Rx) nodes keep copies of the sent
frame too
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Lecture 3 and 4
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FDDI Ring
• When the station detects it can’t communicate with the
adjacent station, it uses the second ring to bypass the
adjacent station
• Given a fiber cut or node failure, this station is
bypassed and the ring is closed
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Lecture 3 and 4
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FDDI Frame
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Lecture 3 and 4
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C WIRELESS LANS
S Wireless communication is one of the fastest growing
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technologies. The demand for connecting devices
without the use of cables is increasing everywhere.
Wireless LANs can be found on college campuses, in
office buildings, and in many public areas.
In this section, we concentrate on two wireless
technologies for LANs:
1) IEEE 802.11 wireless LANs, sometimes called
wireless Ethernet,
2) and Bluetooth, a technology for small wireless
LANs.
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Lecture 3 and 4
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Wireless Transmission (not in book)
• Wireless devices can transmit signals using radio
frequency narrow band, infrared waves and radio
frequency spread spectrum.
• The frequency spread spectrum technique is typically
used for internet applications
• Two types of frequency spread spectrum techniques:
(1) FHSS- Frequency Hopping Spread Spectrum and
(2) DSSS – Direct Sequence Spread Spectrum
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Lecture 3 and 4
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FHSS- Frequency Hopping Spread Spectrum
(not in book)
• Tx transmits at different carrier frequencies for the same period of time
(rotates between a set of frequencies)
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• The required bandwidth must be N times the original bandwidth, where N is
the number of different carrier frequencies
• Tx and Rx must agree to the hopping pattern. In this case, the first bit signal
is transmitted in spectrum 2.01-2.02Ghz, 2nd bit transmitted in the 2.03-2.04
Ghz spectrum, 3rd bit transmitted in the 2.04-2.05 GHz spectrum, etc..
• Good technique for security reasons – if someone tunes to one of the 5
frequency spectrums below, they would only get 1/5 of the info being
transmitted.
Dr. Clincy
Lecture 3 and 4
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S•
DSSS – Direct Sequence Spread Spectrum
(not in book)
Each bit sent by the Tx is replaced with a set of bits called a “chip code”
• For the time it takes to send the original single bit, it now will take more time to
send the chip code
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• Therefore, the data rate must be N times the original data rate, where N is the #
of bits of the chip code
• Also, the bandwidth for the chip code should N times greater than the original bit
stream’s BW
Example of original bits
being transmitted as 6-bit
chip codes
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Lecture 3 and 4
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ISM bands (not in book)
• In 1985, the FCC modified the radio spectrum to allow
unlicensed devices (operating at 1 watt or less) to ISM
bands – Industrial, Scientific and Medical bands
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• Stimulated growth in wireless technology
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Lecture 3 and 4
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Wireless LANs Architecture
• IEEE 802.11 covers 2 services – (1) BSS - Basic service set and (2)
ESS – Extended service set
• BSS – is the base architecture for a wireless LAN – it contains a
stationary or mobile stations and a central access point (optional)
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• Without central access point, the BSS can’t transmit to other BSS’s
Dr. Clincy
example ?
Lecture 3 and 4
example ?
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Wireless LANs Architecture - ESS
• Contains 2 or more BSS’s with central access points
• The BBS’s central access points are connected via a distribution
system (could be a wired LAN) – this network is called an
Infrastructure network
• BBS’s within reach of one another can communicate
• BBS’s not within reach have to communicate via the central access
points
Dr. Clincy
Lecture 3 and 4
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Wireless LANs Access Method
• Wireless LANs use an access method similar to CSMA/CD access method discussed
last lecture
• The access method is called CSMA/CA (vs CSMA/CD) and stands for carrier sense
multiple access with collision avoidance
• With CSMA/CA, all nodes have equal access and the medium is sensed before data is
sent
• However, collision detection is not applicable because the environment is wireless –
THEREFORE, COLLISIONS MUST BE AVOIDED.
CSMA/CA Process
Dr. Clincy
•
Each station determines how long it needs
the medium and all other stations refrain
from using it
•
After the Tx detects the medium is free, it
sends a RTS (request to send) and it contains
the amount of time
•
The Rx acknowledges the request by issuing
a CTS (clear to send) to all stations
•
Tx sends data
•
Rx acknowledges the receipt of data
Lecture 3 and 4
Example
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and NAV
C CSMA/CA
Source
Destination
S
After Rx receive RTS, it waits amount of time called short
interframe space (SIFS), before send a CTS
All other stations
•••
If free, Tx waits amount of time
called distributed interframe space
(DIFS)
DIFS
1
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RTS
SIFS
CTS
2
SIFS
3
NAV
(No carrier sensing)
Data
ACK
4
SIFS
Time
Time
Time
Time
The way collisions are prevented is: when the Tx issues a RTS, a timer called Network Allocation
Vector (NAV) is created for the duration of time for (1) to (4) above – all stations affected by this
transmission uses the NAV in letting it know when it can check the channel for idleness
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Lecture 3 and 4
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C Frame format
Carries the NAV value
or ID of the frame
Defines the frame type
and some control info
Depends on To DS and
From DS fields
S
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Defines sequence # of
frame for flow control
CRC-32 error
detection
Can carry up to
2312 bytes
DS- Distribution System
Dr. Clincy
Lecture 3 and 4
For wireless, some time
the protocol recommends
“fragmentation” due to
corrupted frames (the
smaller the better) or
frames being too large
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C Frame Types
LANs have three categories of frames: (1) Management Frames, (2)
S • Wireless
Control Frames, and (3) Data frames
• Mgmt frames – used for the initial communications between stations and
access points
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• Data Frames – used for carrying data and control info
• Control Frames – used for accessing the channel and acknowledging frames
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Lecture 3 and 4
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C Bluetooth
S • Wireless LAN technology designed to:
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– connect devices of different functions (ie phone, camera, printer,
etc)
– spontaneously form (devices find each other)
– connect to the Internet
– be small by nature – large size will cause chaos
– Handle data rate of 1 Mbps with 2.4 GHz of bandwidth
– Can be interference between 802.11b wireless LAN and Bluetooth
LANS (802.15)
• The networks are called “Piconet”
• Defined by standard 802.15 (PAN)
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Lecture 3 and 4
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C Bluetooth Architectures (2 types)
• Can have up to 8 stations
S
• One station is the primary and the
rest are secondary stations
• all secondary stations synch their
clock to the primary station.
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• The communications with the
primary can be 1-to-1 or 1-to-many
• Can have an unused 8th secondary –
must be activated to use and some
existing secondary must be
deactivated
• Multiple piconets combined is a
Scatternet
• A secondary station in one
piconet can be a primary station
in a 2nd Piconet
Dr. Clincy
Lecture 3 and 4
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