Data Communications

&
Networking
Lecture 08
LAN Communication Protocols

Lectured by
Nguyễn Đức Thái
1
The Network Layer
 The network layer is concerned with
providing a means for hosts to
communicate with other hosts on different
network segments.
 Data-link layer provides a means for two
hosts on a common network segment to
communicate.
 Technologies such as Ethernet and token
ring provide this intra-segment connectivity

2
Network vs. Data-Link Layer
Addressing
 The data-link layer uses the physical
address (also known as the MAC addresses)
of the NIC to deliver data rather than the
network layer host address.
 For the network and data-link layers to
successfully interact to deliver data, a
direct, one-to-one mapping must be made
between the network layer address and the
data-link layer physical address.

3
Addressing Resolution
 The process of determining the physical
address of an NIC from the network layer
address is known as address resolution.
 Each NIC is assigned a single data-link layer
physical address and one or more network
addresses.

4
Packet Fragmentation

 Fragmentation allows large quantities of data to

be sent across the network in smaller, more
manageable “chunks” of data
5
Network Addressing

6
Network Addressing

7
Network Addressing (2)

8
Network Addressing (3)

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Reserved IP Addresses
 Certain host addresses are reserved and
cannot be assigned to devices on a
network.
 An IP address that has binary 0s in all
host bit positions is reserved for the
network address.
 An IP address that has binary 1s in all
host bit positions is reserved for the
broadcast address

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Public and Private IP Addresses
 No two machines that connect to a public
network can have the same IP address
because public IP addresses are global and
standardized.
 However, private networks that are not
connected to the Internet may use any host
addresses, as long as each host within the
private network is unique.
 Connecting a network using private
addresses to the Internet requires
translation of the private addresses to
public addresses using Network Address
Translation (NAT). 11
Public and Private IP Addresses
 RFC 1918 sets aside three blocks of IP
addresses for private, internal use.

Private IP addresses in class A,B,C

12
 NAT: Network Address Translation
NAT translation table
2: NAT router 1: host 10.0.0.1
WAN side addr LAN side addr
changes datagram sends datagram to
138.76.29.7, 5001 10.0.0.1, 3345 128.119.40.186, 80
source addr from
…… ……
10.0.0.1, 3345 to
138.76.29.7, 5001, S: 10.0.0.1, 3345
updates table D: 128.119.40.186, 80
10.0.0.1
1
S: 138.76.29.7, 5001
2 D: 128.119.40.186, 80 10.0.0.4
10.0.0.2
138.76.29.7 S: 128.119.40.186, 80
D: 10.0.0.1, 3345
4
S: 128.119.40.186, 80
D: 138.76.29.7, 5001 3 10.0.0.3
4: NAT router
3: Reply arrives changes datagram
dest. address: dest addr from
138.76.29.7, 5001 138.76.29.7, 5001 to 10.0.0.1, 3345
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Special IP Addresses

14
Network Addresses

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Direct Broadcast Addresses

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Limited Broadcast Address

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“This Host On This Network”

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“Specific Host On This Network”

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Loopback Address

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IP Subnetting
 Classful network: you define only ONE
network.
 What happens if you want to take one
network address and create six networks
from it?
 You would have to do something called
subnetting, because that’s what allows you
to take one larger network and break it into
a bunch of smaller networks.

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How To Create Subnets
 To create subnetworks, you take bits from
the host portion of the IP address and
reserve them to define the subnet address.
 This means fewer bits for hosts, so the
more subnets, the fewer bits available
for defining hosts.

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Subnet – Default - Supernet Mask

23
Subnets

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IP Subnetting (2)
Benefits of IP Subnetting
 Reduce network traffic

 Optimize network performance

 Simplify management

 Facilitate spanning of large geographical

distances.

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Subnet Masks
 Used to define which part of the host
address will be used as the subnet
address

 A 32-bit value that allows the recipient of

IP packets to distinguish the network ID
portion of the IP address from the host ID
portion.

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Default Subnet Masks
 Not all networks need subnets, meaning
they use the default subnet mask.
 This is basically the same as saying that a
network doesn’t have a subnet address

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Default Subnet Masks

28
Host Addresses

29
Addressing Without Subnets

30
Addressing With Subnets

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Subnet Addressing

32
Subnet Mask

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CIDR
 Classless Inter-Domain Routing
 ISPs use this method to allocate an amount
of addresses to a company, a home—a
customer.
 What you get will look something like this:
192.168.10.32/28. This tells you what your
subnet mask is.
 The slash notation (/) means how many bits
are turned on (1s)

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CIDR - Notes
 Obviously, the maximum could only be /32
because a byte is 8 bits and there are 4
bytes in an IP address: (4×8 = 32).
 But keep in mind that the largest subnet
mask available (regardless of the class of
address) can only be a /30 because you’ve
got to keep at least 2 bits for host bits

35
How Many Subnets?
 Number of subnets = 2x
Where x is the number of masked bits, or
the 1s (in host portion).

 Example:
In 11000000, the number of ones gives us 22
subnets. In this example there are 4
subnets

36
How Many Hosts Per Subnet?
 Number of Hosts per subnet = 2y-2
Where y is the number of unmasked bits, or
the 0s (in host portion).

 Example:
In 11000000, the number of zeros gives us
26-2 hosts. In this example, there are 62
hosts per subnet.

37
Broadcast Address For Subnet
 The broadcast address is all host bits
turned on, which is the number
immediately preceding the next subnet

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Steps To Create Subnets
1. Determine the number of required
network IDs:
 One for each subnet.
 One for each wide area network
connection

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Steps To Create Subnets
2. Determine the number of required
host IDs per subnet:
 One for each TCP/IP host
 One for each router interface

40
Steps To Create Subnets
3. Based on the above requirements,
create following:
 One subnet mask for your entire network
 A unique subnet ID for each physical
segment
 A range of host IDs for each subnet

41
Subnet Masks
 Used to define which part of the host
address will be used as the subnet
address

 A 32-bit value that allows the recipient of

IP packets to distinguish the network ID
portion of the IP address from the host ID
portion.

42
Default Subnet Masks
 Not all networks need subnets, meaning
they use the default subnet mask.
 This is basically the same as saying that a
network doesn’t have a subnet address

43
Transport Layer
Five basic services:
 Segmenting upper-layer application data
 Establishing end-to-end operations

 Transporting segments from one end host

to another end host
 Ensuring data reliability

 Providing flow control

44
Reliability
 Ensure that segments delivered will be
acknowledged to the sender
 Provide for retransmission of any segments
that are not acknowledged
 Put segments back into their correct
sequence at the destination
 Provide congestion avoidance and control

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Flow Control

 Avoids the problem of a host at one side of the

connection overflowing the buffers in the
host at the other side
 Ensures the integrity of the data
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Session Establishment
 One function of the
transport layer is to
establish a
connection-
oriented session
between similar
devices at the
application layer

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Three-Way Handshake

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Windowing
 A method of controlling the amount of
information transferred end-to-end
 Information can be measured in terms of
the number of packets or the number of
bytes

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Transmission Control Protocol
 TCP Protocol
 Connection-oriented
 The protocols that use TCP include:
―FTP (File Transfer Protocol)
―HTTP (Hypertext Transfer Protocol)
―SMTP (Simple Mail Transfer Protocol)
―Telnet

50
User Datagram Protocol
 UDP Protocol
 Connectionless
 The protocols that use UDP include:
―TFTP (Trivial File Transfer Protocol)
―SNMP (Simple Network Management
Protocol)
―DHCP (Dynamic Host Control Protocol)
―DNS (Domain Name System)

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