Internet architecture, addressing, encapsulation, reliable
transport and the TCP/IP protocol suite
To introduce the concept of an address space in
general and the address space of IPv4 in particular.
 To discuss the classful architecture, classes in this
model, and the blocks of addresses available in each
class.
 To discuss the idea of hierarchical addressing and how
it has been implemented in classful addressing.
 To explain subletting and super netting for classful
architecture and show how they were used to
overcome the deficiency of classful addressing.
 To discuss the new architecture, classless addressing,
that has been devised to solve the problems in classful
addressing such as address depletion.
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Interconnect heterogeneous networks and
provide universal service
 Hardware: routers connect different networks
 Internet protocols: provide universal service by
creating a single virtual network
•
Although a single router can connect many
networks, most organisations use multiple
routers

The illusion
that there is a
single
universal
network

The TCP/IP Internet Protocols
 begun in the 1970s
 The Internet has emerged into the public
domain in the 1990s
Application Layer
The application layer of the TCP/IP model corresponds to the application layer of the OSI
reference model. Some well known examples of application level entities within the TCP/IP
domain are:
• FTP/Telnet
• HTTP/Secure HTTP (SHTTP)
• POP3/SMTP
• SNMP
Transport Layer
The transport layer of the TCP/IP model maps fairly closely to the transport layer of the OSI
model. Two commonly used transport layer entities are TCP and User Datagram
Protocol(UDP)
Internet Layer
The Internet layer of the TCP/IP model maps to the network layer of the OSI model.
Consequently, the Internet layer is sometimes referred to as the network layer. The primary
component of the Internet layer is the Internet Protocol (IP).
Network Access Layer
The lowest layer of the TCP/IP protocol stack is the network access layer.
The network access layer contains two sublayers, the media access control
(MAC) sublayer and the physical sublayer. The MAC sublayer aligns closely
with the data link layer of the OSI model, and is sometimes referred to by
that name. The physical sub layer aligns with the physical layer of the OSI
model.
Note: Some references divide the TCP/IP model into 5 layers, with the MAC
and physical layers occupying the lowest two layers.
Examples of the network access layer :
• Ethernet
• Wireless Fidelity (Wi-FI)/WiMAX
• ATM/Frame Relay
Uniform addressing, the IP address hierarchy, address
classes, dotted decimal notation, special addresses, routers
and addresses, address resolution

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Internet protocols deal in packets and provide
uniform addressing
Internet addressing is specified in the IP
protocol
Each host is assigned a unique 32 bit address

Each 32 bit address is divided into two parts
 prefix: physical network to which the host is
attached - the network number
 suffix: a host attached to a given physical network

Prefixes are coordinated globally and suffixes
locally
The address space of IPv4 is 4,294,967,296. is it enough? 
IPv4 addresses are unique. They are unique in the
sense that each address define one, and only one,
connection to the Internet. Two devices on the
Internet can never have the same address at the
same time. However, if a device has two
connections to the Internet, via two networks, it
has two IPv4 addresses. The IPv4 addresses are
universal in the sense that the addressing system
must be accepted by any host that wants to be
connected to the Internet.
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Size of prefix and suffix determines
maximum number of networks and
maximum number of hosts per network
IP defines different classes of address with
different sized prefixes and suffixes
The first four bits of the address specify its
class

Makes it easier to for humans to use
addresses (names are also possible)

Public Internet network numbers are assigned by
Internet Service providers (ISPs)
The idea of network mask in classless addressing is the
same as the one in classful addressing. A network mask is
a 32-bit number with the n leftmost bits all set to 0s and
the rest of the bits all set to 1s.
Example
The following addresses are defined using slash notations:
a. In the address 12.23.24.78/8, the network mask is
255.0.0.0. The mask has eight 1s and twenty-four 0s.
The prefix length is 8; the suffix length is 24.
b. In the address 130.11.232.156/16, the network mask is
255.255.0.0. The mask has sixteen 1s and sixteen
0s.The prefix length is 16; the suffix length is 16.

The number of addresses in the block can be
found as:
 Note: in which n is the prefix length and N is the number of addresses
in the block.

The first address (network address) in the block can be found
by ANDing the address with the network mask:

The last address in the block can be found by either adding
the first address with the number of addresses or, directly, by
ORing the address with the complement (NOTing) of the
network mask:
Example
One of the addresses in a block is 167.199.170.82/27. Find
the number of addresses in the network,
the first address, and the last address.
Solution
The value of n is 27. The network mask has twenty-seven 1s
and five 0s. It is 255.255.255.240.
a. The number of addresses in the network is
232 − n = 232 − n = 25 = 32.
b. We use the AND operation to find the first address (network
address).The first address is
167.199.170.64/27.
c. To find the last address, we first find the
complement of the network mask and then OR
it with the given address: The last address is
167.199.170.95/27.
One of the addresses in a block is
7.63.110.114/24
Find the number of addresses, the first address,
and the last address in the block.
The network mask is 255.255.255.0.
a. The number of addresses in the network is
232 − 24 = 256.
b. The first address is 17.63.110.0/24.
c. The last address is 17.63.110.255/24.
The Internet is running out of addresses
Allow division between prefix and suffix to appear at
an arbitrary boundary
 Consider network with only 9 hosts


 Only need 4 bits for host suffix
 Class C (smallest) address uses 8 bits for host suffix
 Sol: Can subdivide a class C address into 16 addresses with
a 28 bit prefix and 4 bit suffix

Extend dotted decimal notation
 193.68.138.0/28, 193.68.138.16/28, …,193.68.138.240/28
Routers are assigned two
or more IP addresses
 So are multi-homed
computers
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An Internet packet passes through a series
of routers
 each hop takes it over a particular network,
either to a specific computer on that network
or to the next router
 in either case, the sending router has to map
between the protocol (IP) address and a
hardware address
 this is called Address Resolution
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Table lookup
Closed-form computation
Message exchange
 send message to specific server computers
 broadcast message, only the required computer
responds

TCP/IP defines the Address Resolution
Protocol (ARP) which defines the format of
resolution requests and responses
Special DHCP server that assigns IP addresses to
hosts
 Newly booted machine broadcasts a DHCP discover
packet
 DHCP server sends back an IP address

 Permanent IP addresses
▪ Manually assigned by administrator
 Automatic IP address from a pool of addresses to be
allocated on demand
▪ Leased for a finite period of time

DHCP server does not need to be on the same
network as the host
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Uniform addressing
Address classes
Dotted decimal notation
Classless addressing
Special IP addresses
Service paradigm, IP datagrams, routing, encapsulation,
fragmentation and reassembly

TCP/IP supports both connectionless and
connection-oriented services
 fundamental delivery service is connectionless
at the Internet layer
 optional reliable connection-oriented service is
layered on top of this at the transport layer
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Packets of data are sent across multiple
physical networks via routers
Internet protocols define a universal virtual
packet - the IP datagram
The amount of data carried in a datagram is
not fixed and is determined by an application
•
•
Each router forwards a virtual packet by using
a local routing table
Each entry is:
– destination address
– mask
– next hop
• IP address of a router or
• Deliver direct
•
Then does address resolution

IP attempts best effort delivery and does not
guarantee to deal with:
 datagram duplication
 delayed or out of order delivery
 corruption of data
 datagram loss

These issues are dealt with other protocol
layers

When an IP datagram is sent across a
physical network it is placed in the data
area of a frame and the frame type is set to
IP

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Maximum transmission unit - max of data
that a frame can carry on a given network
A packet may have to cope with different
MTU sizes as is passes over an internet

A datagram that is larger than MTU is
fragmented into smaller datagrams

Is done at the final host
 routers require less state information
 fragments can take different routes
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Header fields indicate when the data is a
fragment and also where it belongs
Whole datagram is lost if any fragment is lost