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Introduction
Basic Concepts
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Line configuration
Topology
Transmission mode
Categories of networks
Internetworks
Line Configuration
• Two or more comm devices attached to a link
• Link is a physical communicating path to transfer data
Point – to – Point
• Dedicated link b/w two devices
• Entire capacity reserved between two devices
• Normally actual path line of wire but microwaves & satellites
links also possible
– E.G Remote of a TV
Multi Point Configuration
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Also called multidrop
More than two devices share common link
Capacity of channel shared
If devices use link simultaneously
– Spatially shared-in terms of space
– Time shared-devices take turns
Topology
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Way a NW is laid out physically or logically
Two or more devices connect to a link
Two or more links form a topology
Geometrical representation of relationship of all links
Possible Relationships
• Peer to Peer : Devices share link equally
– Ring
– Mesh
• Primary-Secondary :One device controls traffic
& other must transmit through it
– Star
– Tree
Mesh Topology
Star Topology
Tree Topology
Bus Topology
Ring Topology
HYBRID TOPOLOGY
The Internet
• Loosely administered network of networks
• Agreed procedures for access and
intercommunication
• Internetworking uses gateways, routers and
firewalls
• Gateways: convert data traffic from one network
format to another. They link LANs to WANs and
WANs to WANs
• An Analog signal is a continuously varying
electromagnetic wave. (Clock with arm)
– Have infinite values
– Used in early telephone systems.
– Analog signals had the drawback that they
attenuate (weaken) over long distances. Needed
amplifiers to boost the signals. However,
amplifiers distort the signal and introduce noise.
• A Digital signal is a sequence of binary voltage
pulses (0’s and 1’s).It is discrete. Have limited
values normally 0 & 1
– Digital transmission avoids the noise problem by
encoding the analog signal into digital form. The
digitized version is then sent across the network.
Periodic & Nonperiodic Signal
• Both analog and digital signal can take two
forms
• Periodic Signal : A signal which completes a
pattern within a measurable time frame called
Period and repeats the pattern. A sine wave is the
simplest Periodic signal
• The completion of one pattern is called Cycle
• Period is amount of time required to complete one
full cycle
• Nonperiodic Signal: Also called Non-periodic
which changes pattern over time.
• In data comm periodic analog signal (use less
bandwidth) and nonperiodic digital signals
Units of Periods & Frequencies
Unit
Equivale
nt
Unit
hertz (Hz)
Equivalen
t
Seconds (s)
1s
1 Hz
Milliseconds
(ms)
10–3 s
kilohertz (KHz)
103 Hz
Microseconds
(ms)
10–6 s
megahertz (MHz)
106 Hz
Nanoseconds
(ns)
10–9 s
gigahertz (GHz)
109 Hz
Picoseconds
(ps)
10–12 s
terahertz (THz)
1012 Hz
Example 1
Express a period of 100 ms in microseconds, and express
the corresponding frequency in kilohertz.
Solution
From Table 3.1 we find the equivalent of 1 ms. We make
the following substitutions:
100 ms = 100  10-3 s = 100  10-3  106 ms = 105 ms
Now we use the inverse relationship to find the
frequency, changing hertz to kilohertz
100 ms = 100  10-3 s = 10-1 s
f = 1/10-1 Hz = 10  10-3 KHz = 10-2 KHz
Wave Length
• Wave length is another characteristic of signal
moving through medium. Distance signal can
travel in one period
• It binds period or frequency of sine wave to the
propagation speed of the medium
• Frequency is in dependent of medium but
wavelength depends upon both frequency and the
medium
• Generally used in Optical Fiber
Wave Length
Wave length = Propagation sp × period
= Propagation / frequency
Wave length is normally measured in
micrometers(microns)
Bandwidth
• Range of frequencies contained in composite signal is
its BW
• The bandwidth is a property of a medium: It is the
difference between the highest and the lowest
frequencies that the medium can satisfactorily pass
If a periodic signal is decomposed into five sine waves with
frequencies of 100,300, 500, 700, and 900 Hz, what is the
bandwidth? Draw the spectrum, assuming all components
have a maximum amplitude of 10 V.
Solution
B = fh - fl = 900 - 100 = 800 Hz
The spectrum has only five spikes, at 100, 300, 500, 700,
and 900
Bit rate & Bit Interval
• Most digital signals are aperiodic thus period or
frequency is not appropriate
• Bit Interval is time required to send one single bit
• Bit Rate is no of bits sent per second
• Example: A digital signal has a bit rate of 2000
bps. What is the duration of each bit (bit interval)
• Solution: The bit interval is the inverse of the bit
rate
Bit interval = 1/bitrate =1/ 2000 s = 0.000500
s=500microsec
TRANSMISSION IMPAIRMENT
• Signals travel through media, which are not perfect
• The imperfection causes signal impairment
• This means that the signal at the beginning of the medium is not the same
as the signal at the end of the medium
PERFORMANCE
In networking, we use the term Bandwidth in two contexts:
•The first, bandwidth in hertz, refers to range of frequencies in a
composite signal or the range of frequencies that a channel can pass
• The second, bandwidth in bits per second, refers to the speed of bit
transmission in a channel or link.
Throughput
It is the measure of how fast we can send data. It is different from
BW. We may have B BW but may send only T bps
Example:
A network with bandwidth of 10 Mbps can pass only an average of
12,000 frames per minute with each frame carrying an average of
10,000 bits. What is the throughput of this network?
Solution
We can calculate the throughput as
The throughput is almost one-fifth of the bandwidth in this case.
Propagation Time
Time required for a bit to travel from source to destination
Propagation Time = Distance / Propagation Speed
Example:
What is the propagation time if the distance between the two points
is 12,000 km? Assume the propagation speed to be 2.4 × 108 m/s in
cable.
Solution
We can calculate the propagation time as
The example shows that a bit can go over the Atlantic Ocean in only
50 ms if there is a direct cable between the source and the
destination.
Transmission Time
Time required for transmission of all the bits.
Transmission Time = Message size / Bandwidth
Example:
What are the propagation time and the transmission time for a 2.5kbyte message (an e-mail) if the bandwidth of the network is 1
Gbps? Assume that the distance between the sender and the receiver
is 12,000 km and that light travels at 2.4 × 108 m/s.
Solution
Example
What are the propagation time and the transmission time for a 5Mbyte message (an image) if the bandwidth of the network is 1
Mbps? Assume that the distance between the sender and the
receiver is 12,000 km and that light travels at 2.4 × 108 m/s.
Solution
Latency
Latency or delay is the time for a message to completely arrive at a
destination from the time 1st bit left the source
Latency = Propagation Time + Transmission Time +Queuing Time + Processing delay
Jitter
Variance in delay. More prominent in real time applications
Multiplexing
•When BW of a link is grater than BW
requirement of devices, Link can be shared
•It is technique that allows simultaneous
transmission of multiple signal across single
data link
Dividing a link into channels
•MUX: Combines n lines to 1
•DEMUX: Separates back into its components
•Link refers to physical path
•Channel refers to portion of link that carries transmission
Categories of multiplexing
FDM
• Analog Technique
• Applied when BW of link greater than combined BW of signals to be
transmitted
• Each sending device modulate different CF, which in turn combined
into a composite signal for transmission
• CF separated by sufficient BW to accommodate modulated signal
•Channels are separated by strips of unused BW called GUARDBAND
that prevent signals from overlapping
•To use FDM for digital signal covert it to analog signal first
WDM
• WDM same as FDM except that it involves light signals
• WDM is an analog multiplexing technique to combine
optical signals
• Designed for Fiber optic
• Using Fiber optic cable for one single line wastes available
bandwidth
Synchronous TDM
•Digital process
•Each connection occupies portion of time in a link
•Fig shows only multiplexing and not switching i-e source 1
to any but fixed destination
Statistical TDM
• Ensure no slot is wasted. Slots are not pre-assigned
• Slots are dynamically allocated to improve BW
• Unlike Sync TDM, total speed of input lines can be
greater than capacity of path
• Slots can be less than devices
• Mux scan the input line until slots are filled the transmits
LAN Medium
•Connected directly
•Signal constrained by Physical limit
of media
OSI Model
Please DO NOT Touch Steve’s Pet Alligator
Data Encapsulation
• Data Encapsulation is the process of adding a header
to wrap the data that flows down the OSI model.
• The 5 Steps of Data Encapsulation are:
1. The Application, Presentation and Session layers
create DATA from users' input.
2. The Transport layer converts the DATA to
SEGMENTS
3. The NW layer converts the Segments to Packets
(datagram)
4. The Data Link layer converts the PACKETS to
FRAMES
5. The Physical layer converts the FRAMES to BITS.
Types of Switching
A Datagram Network With 4 Switches (Routers)
•All packets may take different route, arrive out of order, lost or
dropped in the way
•These NWs are called connectionless NWs as Switch does not keep
info about connection state, no setup or tear down phase
A virtual Circuit Network
• A virtual-circuit NW is in between a circuit-switched
and datagram NW. It has some characteristics of
both
• It has setup, data transfer & tear down phases
• Resources are allocated during setup phase as in
circuit switched NW or on demand as in datagram
NWs
• Data are packetized & each packet carries an
address (local jurisdiction only; add of next switch)
in a header
• All packets follow same path & implemented at data
link layer
• Virtual circuit NW is implemented in Datalink layer,
A virtual Circuit Network
Single-bit error
Burst error of length 5
Protocols
• Can not be used in real life
High Level Data Link Control Protocol - HDLC
• High-level Data Link Control (HDLC) is a bitoriented protocol for communication over point-topoint and multipoint links. It implements the ARQ
mechanisms
• HDLC is most important Data link protocol
• It is widely used
• Supports both Half Duplex & Full Duplex TXn and
Both pt– to - pt and pt–to – multipoint
• It has been developed by ISO and the standard is
called (ISO 3309, ISO 4335)
Frame Format
Flag Fields:
Delimit frame at both ends with unique pattern 01111110 for sync
Single frame may be used to close one frame and open another
Receiver hunts for flag sequence to synchronize
Not needed for pt-to-pt link but added for uniformity
HDLC Frame Types
• Information Frames: User data & control info
• Supervisory Frames: Control info only
• Unnumbered Frames: System Management info
Multiple Access
When nodes are connected to a common link, there is a need
of multiple –access protocol to coordinate access to the link.
Multiple-Access Protocols
Pure ALOHA
• Original ALOHA is called pure ALOHA
• After collision each node waits for random time
before resending frame. After maximum tries node
give up and try later
Slotted ALOHA
• Time is divided in to slots and each node must
transmit at the start of time slot
• If node misses start of slot, it waits until start of
next slot
• There is collision if 2 nodes transmit at start of slot
CSMA / CD
• CSMA does not define procedure for a collision. That's
why it was never implemented
• CSMA / CD adds method to handle collision
• Node uses one of the persistent strategies
• Any station can send frame, then monitors medium, if
senses collision , frames are sent again
• To reduce probability of collision 2nd time, node waits
, it needs to back off
• In the exponential back off method, node waits an
amount of time between 0 and 2 k × max_
propagation_ time where k is the no of attempted
Transmissions
• 1st time = between 0 & 21 × max_ propagation_ time
CSMA / CA
• Why not CSMA/CD in WLAN: In CSMA / CD node is
able to receive while transmitting
– If no collision occurs node receives own signal
(same energy as that of sent signal)
– If collision occurs node receives own plus other
node signal (detected energy is almost double)
• In wireless, sent energy looses its strength so
received signal has little energy, therefore collision
may add only 5-10% of additional energy. This is
not useful for effective collision detection
• Therefore we need to avoid collision as it can not be
detected
• Collisions are avoided through 3 strategies; Inter
frame spaces, contention window and
Reservation
• Node needs to make reservation before sending
data
• Time divided in to intervals
• In each interval reservation frame precedes data
frame in that interval
• If there are N nodes , there are N reservation
minislots in reservation frame
• Each minislot belongs to a node
• When node needs to send data, it makes
reservation in its own minislot
• Node that made reservation can send data after
the reservation frame
Polling
• It works with topologies in which a device is
designated as Primary Station and others as
Secondary Stations
• All data exchange through Primary even if its not
the destination
• Primary controls the link, Secondary follow
instructions
• Primary decides which node may transmit
therefore its always the initiator
• If Primary wants to receive data, its asks
Secondary if they have data – This function is
called POLLING
• If Primary wants to send data, its asks Secondary
Token Passing
• A node is authorized to send data if it receives as
special frame called TOKEN
• Nodes arranged around a ring. Each node has a
predecessor and Successor
• When no data around the ring, Token circulates
• If node needs to send data, it waits fir the token
• Node captures Token and send one or more data
frames either all data frame sent or allocated time
expires
• Then it releases the Token to be captured by next
waiting node (successor)
• Priority or reservation may be added to the process
IEEE STANDARDS
• In 1985, the Computer Society of the IEEE started
a project, called Project 802, to set standards to
enable intercommunication among equipment
from a variety of manufacturers
• Project 802 is a way of specifying functions of the
physical layer and the data link layer of major LAN
protocols
Data Link Layer
• Logical Link Control: Performs flow control, error
control and part of framing duties
– LLC provides one single link control to all IEEE
standards
• MAC layer provides different protocols to different
LANs
• Framing: LLC defines PDU similar to HDLC. Header
contains flow and error control functions
• LLC Header also defines upper layer protocol at
source and dest. that uses LLC called DSAP & SSAP
(not used by IP)
• Other fields including access methods have been
moved to MAC layer. Physical layer is media
Ethernet
• The term Ethernet refers to the family of local-area
network (LAN) products covered by the IEEE 802.3
standard that defines what is commonly known as the
CSMA/CD protocol
• Originally developed by Xerox in 1976
• Later extended by DEC (digital Equipment
Corporation), Intel and Xerox – Called Ethernet
• Three data rates are currently defined for operation
over optical fiber and twisted-pair cables: Standard
Ethernet (10 Mbps), Fast Ethernet (100 Mbps) and
Gigabit Ethernet (1Gbps)
Connecting Devices
• Five kinds of connecting devices; Repeaters, Hubs,
Bridges, Layer Two and Layer Three Switches
• Repeaters and Hubs operate in the 1st layer
• Bridges and layer 2 switches on 1st two layers
• Routers and layer 3 switches on 1st three layers
IPV4 Datagram Format
Supporting Protocols in TCP/IP at NW Layer
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ARP (Address Resolution Protocol )
RARP
ICMP
IGMP
Internet Control Message Protocol (ICMP)
•The IP protocol has no error-reporting or errorcorrecting mechanism. The IP protocol also lacks a
mechanism for host and management queries. The
Internet Control Message Protocol (ICMP) has been
designed to compensate for the above two
deficiencies. It is a companion to the IP protocol
•ICMP is a mechanism used by hosts and routers to
send notification of datagram problems back to the
sender if some thing has gone wrong
•It handles both control and error msg. It only report
problem but not correct it
•Since datagram carries the add of original sender &
final recipient, it does not know the add of previous
IGMP (Internet Group Message
Protocol)
• The IGMP has been designed to help a multicast
router identify the hosts in a LAN that are member
of a multicast group. It is a companion to the IP
protocol.
• What is multicasting ?
Addressing
• Each device on the Internet id identified through IP
add
• An IP address is a 32-bit address
• The IP addresses are unique and universal
• The address space of IPv4 is2 32 or
4,294,967,296
• Dotted-decimal notation
Netid & Hostid
Subnetting
• Without subnetting, IP address with 2-level of
hierarchy (consist of netid and hostid) is not enough.
• Consider the org. which has 2-level of hierarchy
cannot have more than one physical network.
• With this scheme, the org. is limited to two levels of
hierarchy. The hosts cannot be organized into
groups, and all of the hosts are at the same level.
The org. has one network with many hosts.
• One solution to this problem is subnetting, the further
division of a network into smaller networks called
subnetworks. Network is divided into 3-subnetworks.
• In next fig., the rest of the Internet is not aware that
the network is divided into 3 physical subnetworks:
the three subnetworks still appear as a single
network to the rest of Internet. E.g. A packet destined
Subnetting
• Subnetting is done borrowing bits form host portion.
Mask of all zero’s in the host field specify the entire
network
• Number of bits borrowed from the host portion are
identified by subnet mask. Example: Network
131.10.0.0, Mask for Class B 255.255.0.0. An eight bit
mask will be 255.255.255.0. You can have 254
subnets and 254 hosts per subnet
• How to find Subnet add: Use bit wise AND operator
• Rules:
1. Bytes in IP add that correspond to 255 in the mask
will be repeated in Sub Net add
2. Bytes in IP add that correspond to 0 in the mask will
Default Masks
Network address can be found by applying the
default mask to any address in the block
(including itself). It retains the netid of the block
and sets the hostid to 0s.
Private IP Addresses
• Another approach to conservation of the IP address
space
• IP addresses are globally unique by reserving part of
the address space for networks which are used
exclusively within a single organization and which do
not require IP connectivity to the Internet
• There are three ranges of addresses which have
been reserved by IANA for this purpose:
TCP/IP and the OSI Model
Process to Process Comm
• TPT layer provides process to process comm through
Client Server methodology
– Process on local host is called Client and it gets
services from remote host called Server
– OS support no of processes to be run concurrently
Addressing
• Processes are delivered to transport layer add called
Port Number which are 16 bits integers from 0 –
65535
• Client process randomly chose a Port No where as
Server Process are designated a predefined No
called Well known ports assigned by central
authority (1-1023)
– User-defined ports (range 1024 or greater)
IANA(I/N Assigned No Authority) Ranges
•Registered: Not assigned or controlled by IANA. Can be
registered to avoid duplication
•Dynamic: Neither controlled nor registered
Socket Add
• Each process need two identifiers – IP add & Port no called Socket
• A transport layer protocol needs a pair of Socket add i.e. Client Socket
and Server Socket – Part of TCP / UDP Header
User Datagram Protocol (UDP)
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UDP is called connectionless unreliable protocol.
It has no flow & error control mechanism
UDP message called user datagram
It is very simple protocol with no over heads thus
suitable for protocols that requires simple request response comm with little flow & error control
concerns
• Not used for app such a FTP that send bulk of data
UDP Header
• Fixed header size of 8 bytes
• Checksum is over entire datagram. Calculation is optional
TCP
• It is reliable connection oriented protocol that
creates virtual connection
• TCP Services:
– Process to process comm
– Stream Delivery Service
– Buffered Service
– Full Duplex Service
– Connection Oriented Service
• TCP provides reliable, end-to-end data Txn with
flow and error control. E.G Telnet, FTP, WWW,
POP, IMAP, etc.
TCP Segment Format
Three-step Connection Establishment
Not actual but imaginary byte
What is Sync Flooding Attack? How cookies
help in overcoming it?
Connection Termination using ThreeWay Handshaking
Four - Way Handshaking Half-Close