NEtwork Architecture in Computer networks

1. Unit I
NETWORK ARCHITECTURE
Presentation by:
KAYTHRY P.
Associate Professor, ECE
SSN College of Engineering
Lecture 5

2. Objectives
• At the end of this session, you can able
understand:
• What are the protocols in network layer ?
• What are the various functions of IP?
• Why encapsulation is needed?
• What is protocol?

3. Session Outcome
• At the end of this session, you can able
understand:
• Understand the network architecture.

4. Network Architecture

5. Network Architecture
• Building a network with all the pre
discussed requirements is not an easy
job.
• To get rid of this complexity the networks
are given some architecture. They are
referred to as Blue Prints.
• There are 2 most widely used network
architectures. They are as follows
1. OSI Architecture
2. Internet Architecture

6. Features of Architectures
• The architectural design provides 2 main
features, they are:
It decomposes the problem of building a
network into more components
- Several layers are added and each is
assigned with different functionality.
It provides a more modular design
- Making modifications becomes easier.
- If any new services wanted to be added ,
then the modifications can be done only at 1
respective layer. Other layers can be reused as
such

7. Does Layering Really meets the
expectation..??

8. Introduction to OSI model
• OSI model is introduced by ISO (International Standard
Organization)
• It is a set of protocols that allows any two different systems to
communicate regardless their underlying architecture
• OSI contains 7 layers.
• They are grouped into 3 sub groups
Network Support layers
 Deals with physical aspects of
moving data from one device to
another device
User Support layers
 Deals with the interoperability
among unrelated software
systems
Transport Layer
 Ensures the reliable data
transmission

9. Layering and Protocols
• Use abstractions to hide complexity of
network from application writers.
• Abstraction – define a model to capture
important aspect of the system.
• Identifying the abstraction for each
application to provide service to the
underlying system
• Abstractions naturally lead to layering
• Alternative abstractions at each layer

10. Network Architecture - Layering
 Example of a two layered network system
 Abstraction b/w application programs and
hardware
• Start with services
offered by
underlying
hardware
• Then add a
sequence of layers.
• Each layer provide a
higher level service
• Services provided at
the higher layers
are implemented in
terms of services
provided by lower

11. Network Architecture - Layering
• Advantages:
• Solve small
problems vs.
monolithic
software
• Modularity: easily
add new services
• Drawback:
• May hide
important
Layered system with alternative
abstractions available at a given layer

12. Protocols
• Protocol defines the interfaces between the
layers in the same system and with the layers of
peer system
• Building blocks of a network architecture
• Each protocol object has two different interfaces
– service interface: operations that local objects can
perform on the protocol
– peer-to-peer interface: form & meaning of the
messages exchanged with peer
• Term “protocol” is overloaded
– specification of peer-to-peer interface (rules)
– module that implements this interface

13. Interfaces
 Protocol stack: set of consecutive layers
 Interoperability problems
Service and Peer Interfaces

14. Protocol Graph
• Most peer-to-peer communication is indirect
• Each protocol communicates with its peer by
passing messages to some lower level protocol
– in turn delivers the message to its peer
• Peer-to-peer is direct only at hardware level
• There are multiple protocols at any given level
– each provide different communication
service.
• Suite of protocols make the network –
Protocol Graph

15. Protocol Graph
Example of a protocol graph nodes are the protocols and links the
“depends-on” relation
RRP – Request Reply
protocol
MSP – Message Stream
protocol
HHP- Host to Host
protocol

16. Protocols
• Protocols referred as : abstract interfaces
or module that actually implements the
two interfaces.
• Protocol Specification: prose, pseudo-
code, state transition diagrams, pictures of
packet formats and other abstract
notations.
• Interoperable: when two or more
protocols that implement the specification
accurately
• IETF: Internet Engineering Task Force

17. Encapsulation
High-level messages are encapsulated inside of low-level messages

18. Encapsulation
• RRP receives the message from
application
• RRP must send it to its peer
• RRP must communicate the message with
its control information to its peer – how
to handle the message.
• This is done by attaching header/trailer to
the message.
• Header/trailer – small data structure
• Rest of the message – Payload
• Now we say the application data is

19. Encapsulation
• Encapsulation – repeated at each level of the
protocol graph.
• HHP encapsulates RRP’s message by
attaching its own header.
• HHP sends its message to its peer over some
network.
• At receiver side the message is processed in
opposite side.

20. Multiplexing and Demultiplexing
• RRP multiplexes different application over
the channel at source host.
• Demultiplexed at destination host as
appropriate application (demux key)
• HHP has its own demux key to determine
which message to pass up to RRP and
which to pass up to MSP
•

21. Open System Interconnect (OSI)
Architecture: Reference Model

22. Physical Layer
• Function: provides a “virtual bit pipe” •
How: maps bits into
electrical/electromagnetic signals
appropriate for the channel
• The physical layer module is called a
modem (modulator/demodulator)
• Important issues:
– Timing: synchronous, intermittent
synchronous, asynchronous (characters)
– Interfacing the physical layer and DLC (e.g.,
RS-232, Ethernet, IEEE802.x)

23. Data Link Control Layer (DLC)
• Receives packets from the network layer and
transforms them into bits transmitted by the
physical layer. Generally guarantees order and
correctness.
• Mechanisms of the DLC:
– Framing: header, trailer to separate packets,
detect errors…
– Multiple access schemes: when the link is
shared by several nodes there is a need for
addressing and controlling the access (this
entity is called MAC sublayer)
– Error detection and retransmission (LLC
sublayer)

24. Network Layer
• Provides naming/addressing, routing, flow
control, and scheduling/queuing in a
multi-hop network
• Makes decisions based on packet header
(e.g., destination address) and module
stored information (e.g., routing tables)
• General comment: each layer looks only at
its corresponding header (here packet
header)
• Routing is different on virtual circuit
networks than on datagram networks

25. Transport Layer
• Provides a reliable mean to transmit
messages between two end-nodes through:
– Messages fragmentation into packets
– Packets reassembly in original order
– Sessions multiplexing and splitting
– Retransmission of lost packets
– End-to-end flow control
– Congestion control

26. Session Layer
• Was intended to handle the interaction
between two end points in setting up a
session:
– multiple connections
– Service location (e.g., would achieve load
sharing)
– Check pointing
– Control of access rights
• In many networks these functionalities are
inexistent or spread over other layers

27. Presentation Layer
• Provides data encryption, data
compression, and code conversion

28. Application Layer
• What’s left …
• Examples
– http (web), smtp (mail), telnet, rtp (voip)

29. Internet Architecture
• Defined by Internet Engineering Task
Force (IETF)
• IETF requires working implementations
for standard adoption
• They are also called as TCP / IP
Architecture or TCP / IP Protocol Suite.
• This model uses various protocols at
different layers.

30. Internet Architecture
Alternative view of the Internet architecture.
The “Network” layer shown here is sometimes
referred to as the “sub-network” or “link” layer.

31. Internet Architecture
Internet Protocol Graph
 NET – combination of
network adapter &
network device drivers
 IP – supports
interconnection of
multiple networking
technologies single,
logical internetwork
 TCP& UDP – provide
alternative logical
channels to application
programs
 TCP – reliable byte
stream
 UDP – unreliable

32. 1. Network interface layer
• The physical and datalink layer of the OSI
model are jointly known as Network Interface
layer in TCP / IP Model
• There is no specific protocols in this layers and
they supports all standards
• They particularly deals with the physical
connection between the nodes

33. 2. Network Layer
• They are also called as Internet layer.
• This layer defines the official packet format.
• Protocol used is Internet Protocol (IP)
• They are responsible for successful delivery of
packets from one host to another host

34. Internet Protocol (IP)
• It is an transmission mechanism used for sending the
packets. It uses connection less protocol. IP in turn uses 4
protocols.
• Address Resolution Protocol (ARP):
It is used to find the physical address of the node when
the logical address is known.
• Reverse Address resolution Protocol (RARP):
It is used to find the logical address of the node when the
physical address is known.
• Internet Control Message Protocol (ICMP):
It is an mechanism used by the hosts and gateways to
send notifications about the datagram problem to the
sender.
It contains control and error messages.
• Internet Group Message Protocol (IGMP):

35. Address Resolution Protocol - ARP

36. Reverse Address Resolution Protocol -
RARP

37. ARP Vs RARP

38. Internet Control Message Protocol - ICMP

39. Internet Group Message Protocol - IGMP

40. 3. Transport layer
• Transmission Control Protocol (TCP):
This is an reliable Connection Oriented protocol which
allows the segments of one machine to another machine
without any error.
A connection is established between the sender and
receiver before the transmission starts. This is called as
handshaking.
Each segments are numbered and on successful receipt of
segments they are acknowledged by the receiver.
• User Datagram Protocol (UDP):
It is an unreliable , connection less protocol.
No hand shaking process is done before transmission.
No acknowledgement is received after delivery of segments.
segments.

41. 4. Application Layer
• It is a combination of session layer,
presentation layer and application layers of
OSI model.
• It supports various protocols.
TELNET
FTP – File Transfer Protocol
SMTP – Simple Mail Transfer Protocol
DNS – Domain Name System
HTTP – Hyper Text Transfer Protocol.

42. Telnet
This protocol allows the
user of one machine to
log on to another
machine and can work
from here

43. FTP – File Transfer Protocol
This protocol
provides a
procedure to
move data from
one machine to
another machine
more efficiently

44. SMTP – Simple Mail Transfer Protocol
This protocol is mainly
used for mail transfers
from various servers.

45. DNS – Domain Name System
This protocol is
helpful in
mapping their
host name with
their network
address

46. Internet Architecture
• Three main features
– Does not imply strict layering. The
application is free to bypass the
defined transport layers and to directly
use IP or other underlying networks
– An hour-glass shape – wide at the top,
narrow in the middle and wide at the
bottom. IP serves as the focal point for
the architecture
– In order for a new protocol to be
officially included in the architecture,
there needs to be both a protocol
specification and at least one (and
preferably two) representative
implementations of the specification

47. SUMMARY
• Thus a computer network must provide a
general, cost effective, fair and robust
connectivity among the group of computers.
• It must also deal with the varying environments
to adopt the changes and latest technologies.
• They must be manageable by any humans with
varying skill sets.

48. Self Assessment
• What is meant by a network?
• What is function of RARP?
• State the difference between logical
addressing and physical addressing?

49. References
• 1. Larry L. Peterson ,”Computer networks
– A system approach” fifth edition.
• 2.Forouzon, “Data communication and
Networking”, 5th edition.