osi and tcp ip protocols

1. Network Integration
(Multimedia)

2. Communication Architecture
Strategy for connecting host computers and other communicating
equipment.
Defines necessary elements for data communication between
devices.
A communication architecture, therefore, defines a standard for
the communicating hosts.
A programmer formats data in a manner defined by the
communication architecture and passes it on to the
communication software.
Separating communication functions adds flexibility, for example,
we do not need to modify the entire host software to include
more communication devices.

3. Layer Architecture
Layer architecture simplifies the network design.
It is easy to debug network applications in a layered architecture
network.
The network management is easier due to the layered
architecture.
Network layers follow a set of rules, called protocol.
The protocol defines the format of the data being exchanged, and
the control and timing for the handshake between layers.

4. Open Systems Interconnection (OSI)
Model
International standard organization (ISO) established a committee
in 1977 to develop an architecture for computer communication.
Open Systems Interconnection (OSI) reference model is the result
of this effort.
In 1984, the Open Systems Interconnection (OSI) reference model
was approved as an international standard for communications
architecture.
Term “open” denotes the ability to connect any two systems
which conform to the reference model and associated standards.

5. OSI Reference Model
The OSI model is now considered the primary Architectural
model for inter-computer communications.
The OSI model describes how information or data makes its way
from application programmes (such as spreadsheets) through a
network medium (such as wire) to another application
programme located on another network.
The OSI reference model divides the problem of moving
information between computers over a network medium into
SEVEN smaller and more manageable problems .
This separation into smaller more manageable functions is known
as layering.

6. OSI Reference Model: 7 Layers

7. OSI: A Layered Network Model
The process of breaking up the functions or tasks of networking
into layers reduces complexity.
Each layer provides a service to the layer above it in the protocol
specification.
Each layer communicates with the same layer’s software or
hardware on other computers.
The lower 4 layers (transport, network, data link and physical —
Layers 4, 3, 2, and 1) are concerned with the flow of data from end
to end through the network.
The upper four layers of the OSI model (application, presentation
and session—Layers 7, 6 and 5) are orientated more toward
services to the applications.
Data is Encapsulated with the necessary protocol information as it
moves down the layers before network transit.

8. Physical Layer
Provides physical interface for transmission of information.
Defines rules by which bits are passed from one system to another
on a physical communication medium.
Covers all - mechanical, electrical, functional and procedural -
aspects for physical communication.
Such characteristics as voltage levels, timing of voltage changes,
physical data rates, maximum transmission distances, physical
connectors, and other similar attributes are defined by physical
layer specifications.

9. Data Link Layer
Data link layer attempts to provide reliable communication over
the physical layer interface.
Breaks the outgoing data into frames and reassemble the
received frames.
Create and detect frame boundaries.
Handle errors by implementing an acknowledgement and
retransmission scheme.
Implement flow control.
Supports points-to-point as well as broadcast communication.
Supports simplex, half-duplex or full-duplex communication.

10. Network Layer
Implements routing of frames (packets) through the network.
Defines the most optimum path the packet should take from the
source to the destination
Defines logical addressing so that any endpoint can be identified.
Handles congestion in the network.
Facilitates interconnection between heterogeneous networks
(Internetworking).
The network layer also defines how to fragment a packet into
smaller packets to accommodate different media.

11. Transport Layer
Purpose of this layer is to provide a reliable mechanism for the
exchange of data between two processes in different computers.
Ensures that the data units are delivered error free.
Ensures that data units are delivered in sequence.
Ensures that there is no loss or duplication of data units.
Provides connectionless or connection oriented service.
Provides for the connection management.
Multiplex multiple connection over a single channel.

12. Session Layer
Session layer provides mechanism for controlling the dialogue between
the two end systems. It defines how to start, control and end
conversations (called sessions) between applications.
This layer requests for a logical connection to be established on an end-
user’s request.
Any necessary log-on or password validation is also handled by this
layer.
Session layer is also responsible for terminating the connection.
This layer provides services like dialogue discipline which can be full
duplex or half duplex.
Session layer can also provide check-pointing mechanism such that if a
failure of some sort occurs between checkpoints, all data can be
retransmitted from the last checkpoint.

13. Presentation Layer
Presentation layer defines the format in which the data is to be
exchanged between the two communicating entities.
Also handles data compression and data encryption
(cryptography).

14. Application Layer
1. Application layer interacts with application programs and is the
highest level of OSI model.
2. Application layer contains management functions to support
distributed applications.
3. Examples of application layer are applications such as file
transfer, electronic mail, remote login etc.
OSI Model

15. OSI in Action
A message begins at the top application
layer and moves down the OSI layers to
the bottom physical layer.
As the message descends, each
successive OSI model layer adds a
header to it.
A header is layer-specific information
that basically explains what functions
the layer carried out.
Conversely, at the receiving end,
headers are striped from the message
as it travels up the corresponding
layers.
OSI Model

16. TCP/IP MODEL

17. OSI & TCP/IP Models

18. TCP/IP Model
Application Layer
Application programs using the network
Transport Layer (TCP/UDP)
Management of end-to-end message transmission,
error detection and error correction
Network Layer (IP)
Handling of datagrams : routing and congestion
Data Link Layer
Management of cost effective and reliable data delivery,
access to physical networks
Physical Layer
Physical Media

19. 19
IP Address Classes
• IP addresses are divided into 5 classes, each of
which is designated with the alphabetic letters
A to E.
• Class D addresses are used for multicasting.
• Class E addresses are reserved for testing &
some mysterious future use.

20. 20
IP Address Classes (Cont.)
• The 5 IP classes are split up based on
the value in the 1st octet:

21. 21
IP Address Classes (Cont.)
• Using the ranges, you can determine the class
of an address from its 1st octet value.
• An address beginning with 120 is a Class A
address, 155 is a Class B address & 220 is a
Class C address.

22. 22
Are You the Host or the
Network?
• The 32 bits of the IP address are divided into
Network & Host portions, with the octets
assigned as a part of one or the other.
Network & Host Representation
By IP Address Class
Class Octet1 Octet2 Octet3 Octet4
Class A Network Host Host Host
Class B Network Network Host Host
Class C Network Network Network Host

23. 23
Are You the Host or the
Network? (Cont.)
• Each Network is assigned a network address &
every device or interface (such as a router
port) on the network is assigned a host
address.
• There are only 2 specific rules that govern the
value of the address.

24. 24
Are You the Host or the
Network? (Cont.)
• A host address cannot be designated by all
zeros or all ones.
• These are special addresses that are reserved
for special purposes.

25. 25
Class A Addresses
• Class A IP addresses use the 1st 8 bits (1st
Octet) to designate the Network address.
• The 1st bit which is always a 0, is used to
indicate the address as a Class A address & the
remaining 7 bits are used to designate the
Network.
• The other 3 octets contain the Host address.

26. 26
Class A Addresses (Cont.)
• There are 128 Class A Network Addresses, but
because addresses with all zeros aren’t used &
address 127 is a special purpose address, 126
Class A Networks are available.

27. 27
Class A Addresses (Cont.)
• There are 16,777,214 Host addresses available in a
Class A address.
• Rather than remembering this number exactly, you
can use the following formula to compute the
number of hosts available in any of the class
addresses, where “n” represents the number of bits
in the host portion:
(2n – 2) = Number of available hosts

28. 28
Class A Addresses (Cont.)
• For a Class A network, there are:
224 – 2 or 16,777,214 hosts.
• Half of all IP addresses are Class A addresses.
• You can use the same formula to determine the
number of Networks in an address class.
• Eg., a Class A address uses 7 bits to designate the
network, so (27 – 2) = 126 or there can be 126 Class
A Networks.

29. 29
Class B IP Addresses
• Class B addresses use the 1st 16 bits (two
octets) for the Network address.
• The last 2 octets are used for the Host
address.
• The 1st 2 bit, which are always 10, designate
the address as a Class B address & 14 bits are
used to designate the Network. This leaves 16
bits (two octets) to designate the Hosts.

30. 30
Class B IP Addresses (Cont.)
• So how many Class B Networks can there be?
• Using our formula, (214 – 2), there can be
16,382 Class B Networks & each Network can
have (216 – 2) Hosts, or 65,534 Hosts.

31. 31
Class C IP Addresses
• Class C addresses use the 1st 24 bits (three
octets) for the Network address & only the
last octet for Host addresses.the 1st 3 bits of
all class C addresses are set to 110, leaving 21
bits for the Network address, which means
there can be 2,097,150 (221 – 2) Class C
Networks, but only 254 (28 – 2) Hosts per
Network.

32. 32
Class C IP Addresses (Cont.)

33. 33
Special Addresses
• A few addresses are set aside for specific
purposes.
• Network addresses that are all binary zeros, all
binary ones & Network addresses beginning
with 127 are special Network addresses.

34. 34
Special Addresses (Cont.)

35. 35
Special Addresses (Cont.)
• Within each address class is a set of addresses
that are set aside for use in local networks
sitting behind a firewall or NAT (Network
Address Translation) device or Networks not
connected to the Internet.

36. 36
Special Addresses (Cont.)
• A list of these addresses for each IP
address class:

37. 37
Subnet Mask
• An IP address has 2 parts:
– The Network identification.
– The Host identification.
• Frequently, the Network & Host portions of the
address need to be separately extracted.
• In most cases, if you know the address class, it’s easy
to separate the 2 portions.

38. 38
Subnet Mask (Cont.)
• With the rapid growth of the internet & the ever-
increasing demand for new addresses, the
standard address class structure has been
expanded by borrowing bits from the Host
portion to allow for more Networks.
• Under this addressing scheme, called Subnetting,
separating the Network & Host requires a special
process called Subnet Masking.

39. 39
Subnet Mask (Cont.)
• The subnet masking process was developed to
identify & extract the Network part of the
address.
• A subnet mask, which contains a binary bit
pattern of ones & zeros, is applied to an address
to determine whether the address is on the local
Network.
• If it is not, the process of routing it to an outside
network begins.

40. 40
Subnet Mask (Cont.)
• The function of a subnet mask is to determine
whether an IP address exists on the local network
or whether it must be routed outside the local
network.
• It is applied to a message’s destination address to
extract the network address.
• If the extracted network address matches the
local network ID, the destination is located on the
local network.

41. 41
Subnet Mask (Cont.)
• However, if they don’t match, the message
must be routed outside the local network.
• The process used to apply the subnet mask
involves Boolean Algebra to filter out non-
matching bits to identify the network address.

42. 42
Default Standard Subnet Masks
• There are default standard subnet
masks for Class A, B and C addresses:

43. Subnetting Concepts
• Revise: binary nos., boolean operators AND
• Phone number analogy still works!
(401) 555-7777
• Host ID: divided into Subnet ID and Host ID
• Need to communicate which part is subnet ID
• 32 bit binary number called “Subnet mask”
• The bits of the mask in any given subnetted network
are chosen so that the bits used for either the
network ID or subnet ID are ones, while the bits used
for the host ID are zeroes.

44. Subnetting Concepts (Cont)
• Subnet Bit Is A One: In this case, we are ANDing either a 0 or 1 in the IP address
with a 1. If the IP address bit is a 0, the result of the AND will be 0, and if it is a 1,
the AND will be 1. In other words, where the subnet bit is a 1, the IP address is
preserved unchanged.
Subnet Bit Is A Zero: Here, we are ANDing with a 0, so the result is always 0
regardless of what the IP address is. Thus, when the subnet bit is a 0, the IP
address bit is always cleared to 0.
• A router that performs this function is left with the address of the subnet. Since it
knows from the class of the network what part is the network ID, it also knows
what subnet the address is on.
• Bit Allocation Example
– We can decide to use 1 bit for the subnet ID and 15 bits for the host
ID. If we do this, then the total number of subnets is 21 or 2: the first
subnet is 0 and the second is 1. The number of hosts available for each
subnet is 215-2 or 32,766.

45. Example: IP Subnetting
• Requirements
– Class, how many hosts, scalability, min, max
Subnetting Design Trade-Off For Class C Networks

46. • Class C Custom Subnet Mask Calculation Example
– 3 for subnet ID and 5 for host ID
Express Subnet Mask In “Slash Notation”: 255.255.255.224 is equivalent
to “/27”.

47. Determining Host Address for each Subnet

48. VLSM
• Variable-length subnet masks were developed to
allow multiple levels of subnetted IP addresses
within a single network
• The routing protocol you use must support VLSM
– Open Shortest Path First (OSPF)
– Enhanced Interior Gateway Routing Protocol (EIGRP)
– Routing Information Protocol version 2 (RIPv2)
• VLSM is crucial for an effective IP addressing plan

49. VLSM
Benefits of VLSM
• More efficient use of IP addresses
– Without use of VLSM, a single subnet mask must be
implemented with an entire Class A, B, or C network
• Greater capacity to use router summarization
– Allows more hierarchical levels within an addressing plan
• Isolation of topology changes from other routers

50. VLSM
Benefits of VLSM
VLSM Permits Flexible, Efficient Subnet Address Allocation

51. VLSM
CIDR and Route Summarization
• The definition of classless inter-domain routing (CIDR):
– Allocation of one or more blocks of Class C network numbers to each
network service provider
– Organizations using the network service provider for Internet
connectivity are allocated bitmask-oriented subsets of the provider’s
address space as required
• CIDR (“cider”) was developed to address the problem of IP
address space running out and core Internet routers running
out of capacity
• Route summarization is the representation by a single network
of a group of contiguous networks

52. VLSM
CIDR and Route Summarization
Route
Summarization of
Contiguous
Subnets of a Class
B Network

53. VLSM
CIDR and Route Summarization
Route Summarization of Contiguous Subnets of a Class B Network
(continued)
• Router D in previous slide has these networks in its routing
table
– 172.16.12.0/24
– 172.16.13.0/24
– 172.16.14.0/24
– 172.16.15.0/24
• To calculate the summary route:
– Find the number of highest-order bits that match in all addresses
– Locate where the common pattern of digits ends
– Count the number of common bits; this is the length of the summary
route

54. VLSM
CIDR and Route Summarization
Route Summarization of Contiguous Subnets of a Class B Network
(continued)
• Follow these guidelines when calculating summary routes:
– Addresses that do not share the same number of bits as the prefix length
of the summary route are not included in the summarization block
– The IP addressing plan is hierarchical in nature to allow router to
aggregate the largest number of IP addresses into a single summary
route
– IP networks can only be summarized in 2n networks (for some n), where
the last octet of the first network in the sequence is divisible by 2n

55. VLSM
Route Aggregation
• By using a prefix length instead of an address class to determine
the network portion of the address, CIDR allows routers to
aggregate routing information
– Shrinks routing table
– One address and mask combination can represent the routes to multiple
networks
• Route aggregation is used more loosely than CIDR; describes
the summarization of classful networks
• Without CIDR, routers must maintain tables for individual
networks

56. VLSM
Supernetting
• The practice of using a summary network to group multiple
classful networks into a single address is called
supernetting
– Subnetting breaks down a classful network
– Supernetting pastes together classful networks
• With Class A and B address space almost exhausted, large
organizations requested multiple Class C network addresses
from their service providers
• A block of contiguous Class C addresses can appear as a
single large network, or supernet

57. VLSM
Supernetting
• Supernetting and route aggregation are similar
– Route aggregation is used in the context of summarizing
routes with BGP
– Supernetting is a term used when the summarized
networks are under common administrative control
• Many networking professionals use the terms
“route summarization” and “route aggregation”
interchangeably

58. VLSM
CIDR Example
CIDR Permits the Aggregation of Several Classful Networks
into a Single Route Advertisement