Download IP addresses

TCP opening a connection
and closing a connection
SYN sent from client
SYN/ACK sent from server
ACK sent from client
(1)
TCPs three-way handshake in opening a connection
FIN sent from client
FIN/ACK sent from server
ACK sent from client
(2)
TCPs three-way handshake in closing a connection
7 Layer OSI Model
OSI Layer
Function provided
Application
Network application such as file transfer and
terminal emulation
Presentation
Data formatting and encryption.
Session
Establishment and maintenance of sessions.
Transport
Provision for end-to-end reliable delivery.
Network
Delivery of packets of information, which includes
routing.
Data Link
Transfer of units of information, framing and error
checking.
Physical
Transmission of binary data of a medium.
Circuit Switching, Message Switching
and Packet Switching
Circuit Switching : Establishes end-to-end network path before
any data is sent. Network path once set up,
is not shared with other users. Other nodes
have to wait until the transmission is
over to the circuit to be released.
Message Switching : No network path is established. Entire
message is sent to the destination via
network paths that are shared with other
users. Congestions are likely to occur
depending on the size of the message.
Circuit Switching, Message Switching
and Packet Switching
Packet Switching : No network path is established. Messages
are broken down in to smaller size
manageable packets before being sent.
Packets are being sent to the destination
over network paths shared with other
traffic. Destination assembles the packets
retrieving the original message.
Virtual Circuit Switching : Packet switching network that emulates
circuit switching by establishing a
virtual circuit before the packets
are sent. All the packets are
delivered using the same virtual
circuit.
Question 13)
5
3
2
3
5
2
3
1
1
1
1
4
6
2
5
Find the least cost path from node (1) to node (6)
using forward search algorithm.
Network : Network is a set of interconnected computers
Local Area Network : A computer network covering a small
geographic area ( usually less than 1 km2 )
Wide Area Network : A computer network that covers a broad
geographic area ( usually a collection of LANs )
Hub : A Hub is used in a wired network to connected Ethernet cables from number of
workstations together. Data packets sent from one machine are connected to rest of the
machines. The each machine check the header for the destination address. The intended
machine retrieves the packet while other machines discard it. Hubs are prone to packet sniffing
attacks. TCP dump/Net stumbler/ Wireshark(Ethereal) – A hub operates on layer 1 : physical
layer
Switch : A switch is a intelligent hub that forwards incoming frames to a specific port that will
take data to its intended destination. Reads the intended MAC address from the received data
frame and determines the forwarding port from the Switching Table and connect the received
frame to the intended port. Switch operates on MAC sub layer of the layer 2 : the data link
layer.
A network switch constructs its switching table by
extracting the source MAC address from the
received frames. If the entry does not exist the
switch will forward the frames to all its ports.
Prone to ARP poisoning attacks. Cain and Able
Bridge : A bridge is used to partition busy networks into several
collision domains. Bridge operates on the MAC layer, sub layer of the
layer 2 (data link layer). Bridge reads the destination MAC address
from the frame header and decides which partition the frame should
be relayed to.
Once switched on the bridge learns which computer is connected in
each collision domain. The learning process occurs as the bridge
encounters traffic. The bridge extracts the source MAC address from
received frames to determine collision domain that the extracted MAC
address is connected to and constructs a bridging table. If the bridging
table doesn’t have an entry for the MAC address, bridge will forward
the frame to all the domains connected.
Router : A router is an internetworking device commonly used to
connect different network types together. A router has two or more
interface, each interface connecting a different network type and
forwards packets according to its destination address. Router can be
seen as a layer 3 switch (network layer ). Router accepts incoming
packets from one network interface and forwards towards its intended
destination. Routers are the basic building block holding the internet in
place. Routers uses IP address instead of MAC addresses and
constructs routing table from the received packets.
Computer A
Computer B
Modem : A modem is a communication device that converts one form of signal to another
that is suitable for transmission over communication network such as telephone lines, typically
from digital to analogue and from analogue to digital.
Sending time -

Time to detect collision -
2
Transmitted frame length -
T
Propagation delay to frame length ratio Number of retries needed - K
a  T
Therefore average time for transmitting one frame -
tv
tv  T    2K
 T   1 2K 
 T 1   T 1  2K 
 T 1  a1  2K 
Utilization factor -
U  T tv
U  T tv  1 1  a1  2K 
Wireless LAN - A computer network covering a small
geographic area that communicates with each other
without wires (wireless)
Advantages of wireless LAN Increased mobility of users
Increased flexibility
Instant networking
Availability of LAN technology
Disadvantages of wireless LAN Higher cost
Lower performance
Lower reliability
Multiple standards
Poor security (WEP-Wired Equivalent Privacy- open system authentication- no real authentication but
clients need correct key to encrypt data, shared key authentication – shared key authentication can easily
be cracked)
WPA- Wifi Protected Access – can be cracked passively or actively. Needs several thousand
authentication packets to crack pre shared key. Alternatively you send deauthentication signals to existing
clients, forcing them to reauthenticate with the AP, accelerating the cracking process.
Criteria for LAN Design
Functionality – Speed and Reliability, The network must work with reasonable
speed and reliability
Scalability
– Ability to grow without major changes, The network must be able
to grow without any major changes to the overall design
Adaptability – Easily implements new technologies, The network should include
no element that would limit the use of new technologies as they
become available
Manageability – Facilitates monitoring and ease of Management, The network
must be able to allow ease of monitoring and managing
7 Layer OSI Model
OSI Layer
Function provided
Application
Network application such as file transfer and
terminal emulation
Presentation
Data formatting and encryption.
Session
Establishment and maintenance of sessions.
Transport
Provision for end-to-end reliable delivery.
Network
Delivery of packets of information, which includes
routing.
Data Link
Transfer of units of information, framing and error
checking.
Physical
Transmission of binary data of a medium.
IP addresses
IP Address is 32 bits in length and consists of two parts, prefix denoting network
id. and suffix denoting host id. Since internet might include networks including
from few computers to hundreds of thousands we divide the 32 bit IP address
space into three primary classes with different prefix and suffix sizes
Net id
01234
8
Class A
0
Class B
1 0 prefix
Class C
1 1 0
Class D
1 1 1 0
multicast address
Class E
1 1 1 1
Reserved for future use
prefix
16
24
31
suffix
Primary
Classes
suffix
suffix
prefix
Multicast addresses : To use IP multicasting set of hosts must agree to share a
multicast address. Once the multicast group has been established, a copy of any packet
sent to the multicast address will be delivered to each host in the set.
Although IP addresses are 4-octets, 32 bit numbers we generally represent each
octet by its decimal value separated by a dot. This is known as dotted decimal
notation.
32 bit binary number
10000000 00001010 00000010 00000011
Dotted decimal notation
128 . 10 . 2 . 3
The class of the network must be identified from the first octet.
Class
Range of Values
A
0 through 127
B
128 through 191
C
192 through 223
D
224 through 239
E
240 though 255
IP Address designing parameters
Bits in Suffix
Maximum Number
of Hosts in the
Network
Address Class
Bits in Prefix
Maximum Number
of Networks
A
7
128
24
16777216
B
14
16384
16
65536
C
21
2097152
8
256
Subnet Masking
Rather than allocating address blocks in eight bit boundaries, which in certain cases could be a
waste of address space, arbitrary prefix and suffix lengths are introduced using a subnet mask.
Subnet mask is a 32 bit number in which left hand side ones correspond to prefix and right hand
side zeros correspond to suffix.
IP Address
Subnet Mask
128.10.2.3
10000000 00001010 00000010 00000011
255.255.255.0
11111111 11111111 11111111 00000000
Prefix – first 24 bits – 128.10.2.
Suffix – last 8 bits - 3
This corresponds to a class C network
CIDR : Classless Inter-Domain Routing
Rather than allocating address blocks in eight bit boundaries forcing 8, 16, 24 bit prefixes, it
uses arbitrary length prefixes.
CIDR Notation
192.168.0.3 / 16
Prefix length in bits
32bit IP address
***
Example :- Consider a private intranet of a large organization which consists of 4 physical networks.
One small, two medium sized and one extremely large network. Design suitable IP address scheme.
Medium sized network 1
Medium sized network 2
128.11.0.2
128.10.0.1
128.11.0.1
128.10.0.2
Large Network
Small network
192.168.0.1
192.168.0.2
10.10.0.1
10.10.0.2
ARP : Address Resolution Protocol
ARP is the standard method of finding out hosts layer 2 MAC address when only its
layer 3 IP address is known. If host ‘A’ needs to send a a data packet to host ’B’,
host ‘A’ broadcasts ARP request packet containing ‘A’s MAC address. Host ‘B’ upon
receiving the ARP request replies with its MAC address directly (unicast) to host ‘A’
while other stations discard the ARP request. Host ‘A’ now having the MAC address
of host ‘B’ can directly send the data packet.
RARP : Reverse Address Resolution Protocol
RARP is the reverse process of ARP. It’s the process of finding out the layer 3 network address from
layer 2 MAC address. RARP was subsequently replaced by DHCP.
DHCP : Dynamic Host Configuration Protocol
DHCP is a protocol used by clients to obtain various necessary parameters for its operation. DHCP
allows clients to be configured automatically over the network. New machines can be added to the
network more easily. Less chance of error.
DNS : Domain Name System
DNS associates domain names with difficult to remember IP address. Mapping domain name to an IP
address is called domain name translation. When a host requires a domain name translation it makes
a request to its assigned DNS server.
WiMax, WLAN and Bluetooth Comparison
Parameters
802.16a
(WiMax)
802.11
(WLAN)
802.15
(Bluetoo
th)
Frequency Band
2-11GHz
2.4GHz
Varies
Range
~31miles
~100meter
s
~10meters
Data transfer rate
70 Mbps
11 Mbps –
55 Mbps
Number of Users
Thousands
Dozens
20Kbps –
55 Mbps
Dozens
Aloha System
ALOHA was a pioneering computer networking system developed at the University
of Hawaii. Although the network itself is no longer used, the ALOHA project is quite
important as one of the core concepts in the ALOHA net is the basis for widely used
Ethernet technology.
Aloha key concept : If you have data send data. If the message collides try
resending the data later. The waiting time must be random
or the same frames will collide over and over again, in a
deadlock.
N – Number of frames generated by all the users connected per frame time
G – Total Number of frames generated per frame time (New and retransmitted) G ≥ N
G is also known as the channel traffic
S – Channel throughput per frame time, number of successful transmission per frame time
Channel throughput is equal to number of total packets generated in the system per
given time into the probability of a frame does not suffer collision
Aloha Capacity
S – Channel throughput per frame time, number of successful transmission per frame time
Channel throughput is equal to number of total packets generated in the system per
given time into the probability of a frame does not suffer collision
P0 – Probability of a frame does not suffer collision
S=G. P0
Therefore
If (number of users connected) → ∞, N and G takes
the shape of Poisson distribution. P0 = e-2G
S = G.e-2G
Aloha Capacity
S – Channel throughput per frame time, number of successful transmission per frame time
Channel throughput is equal to number of total packets generated in the system per
given time into the probability of a frame does not suffer collision
P0 – Probability of a frame does not suffer collision
S=G. P0
If (number of users connected) → ∞, N and G takes
the shape of Poisson distribution. P0 = e-2G
Therefore
S = G.e-2G
Capacity is the maximum throughput
We can see the throughput is maximum at G = 0.5
S=0.5 x e-2x0.5 = 0.1839
The channel Utilization is Approximately 18%
Slotted Aloha
Slotted Aloha divides the time into discrete time intervals, each interval corresponding to
one frame time. Rather than trying to send data at any given time, users are forced to
send data only at the beginning of a time slot. This minimises probability of collision and
increase the channel throughput. The users must know the beginning of the time slot to
begin transmitting data. The system uses a pilot signal to inform the workstations of the
beginning of the time slot.
The channel throughput
S=G. P0
In slotted Aloha the probability of
frame not colliding improves
Therefore
P0 = e-G
S = G.e-G
We can see the throughput is maximum at G = 1
Capacity is the maximum throughput
S=1 x e-1 = .368
The channel Utilization is Approximately 37%
The channel capacity doubles
Capacity is the maximum throughput
We can see the throughput is
maximum at G = 0.5
S=0.5 x e-2x0.5 = 0.1839
The channel Utilization is Approximately 18%
If an ALOHA system has a total generated capacity of 14400 bits/s,
a.) Compute the maximum capacity a pure ALOHA system can reach
b.) Compute the maximum capacity a slotted ALOHA system can reach
Pure ALOHA system has a utilization factor of 18%, and therefore can reach a
maximum capacity of 14400x0.1839 = 2648 bits/s
Pure ALOHA system has a utilization factor of 37%, and therefore can reach a
maximum capacity of 14400x0.386 = 5558 bits/s