Here are the number of broadcast and collision domains for each case: 1. A single switch with 10 connected devices: - Broadcast domain: 1 - Collision domain: 10 (each switch port is its own collision domain) 2. Two switches connected by a single trunk link with 10 devices on each switch: - Broadcast domain: 2 - Collision domain: 20 (each switch port is its own collision domain) 3. A router connected to two switches, with 10 devices on each switch: - Broadcast domain: 3 - Collision domain: 20 (each switch port is its own collision domain)

1. The OSI Model

2. Overview
• When networks first came into being, computers
could typically communicate only with computers
from the same manufacturer. For example,
companies ran either a complete DECnet solution
or an IBM solution—not both together.
• In the late 1970s, the Open Systems
Interconnection (OSI) reference model was created
by the International Organization for
Standardization (ISO) to break this barrier.
• The OSI model was meant to help vendors create
interoperable network devices and software in the
form of protocols so that different vendor
networks could work with each other.

3. • The OSI model describes how data and
network information are communicated from
an application on one computer, through the
network media, to an application on another
computer.
• The OSI reference model breaks this approach
into layers.
• Layers  Departments
• If programmers are developing a protocol for a
certain layer, all they need to concern
themselves with is the specific layer’s
functions, not those of any other layer.

4. Advantages of Reference Models
1. divides the network communication process into
smaller and simpler components, thus aiding
component development, design, and
troubleshooting.
2. allows multiple-vendor development through
standardization of network components.
3. allows various types of network hardware and
software to communicate.
4. prevents changes in one layer from affecting other
layers, so it does not hamper development.

5. The Seven Layers of the OSI Model

6. • The OSI has seven different layers, divided into
two groups.
The top three layers define how the applications
within the end stations will communicate with
each other and with users.
The bottom four layers define how data is
transmitted end-to-end.
• The OSI reference model remains today the
most popular means of comparison for
protocol suites.

8. Typical Layer functions

9. Application Layer (Layer 7)
• where users actually communicate to the
computer.
Take the case of Internet Explorer (IE).
• is also responsible for identifying and
establishing the availability of the intended
communication partner
• Typical protocols
World Wide Web (WWW)
File Transfer Protocol (FTP)
E-mail (SMTP)

10. The Presentation Layer (Layer 6)
• presents data to the Application layer and is
responsible for data translation and code
formatting.
• by providing translation services, the
Presentation layer ensures that data
transferred from the Application layer of one
system can be read by the Application layer of
another one.
• Tasks like data compression, decompression,
encryption, and decryption are associated with
this layer.

11. Presentation Layer Protocols
• TIFF Tagged Image File Format; a standard graphics
format for high-resolution, bitmapped images.
• JPEG Photo standards by the Joint Photographic
Experts Group – compresses images
• MIDI Musical Instrument Digital Interface - used for
digitized music.
• MPEG Moving Picture Experts Group - standard for the
compression and coding of motion video for CDs.
• QuickTime - For use with Macintosh programs;
manages audio and video applications.
• RTF Rich Text Format, a file format that lets you
exchange text files between different word processors,
even in different operating systems.

12. The Session Layer (Layer 5)
• is responsible for setting up, managing, and
then tearing down sessions between
Presentation layer entities.
• provides dialogue control between devices, or
nodes.
• To sum up, the it basically keeps different
applications’ data separate from other
applications’ data.

13. Session layer protocols
• Network File System (NFS) - Developed by Sun
Microsystems and used with TCP/IP and Unix
workstations to allow transparent access to remote
resources.
• Structured Query Language (SQL) - Developed by IBM
to provide users with a simpler way to define their
information requirements on both local and remote
systems.
• Remote Procedure Call (RPC) - A broad client/server
redirection tool used for creating procedures on clients
and performed on servers.
• AppleTalk Session Protocol (ASP) - Another
client/server mechanism, which both establishes and
maintains sessions between AppleTalk client and server
machines.

14. The Transport Layer (Layer 4)
• segments and reassembles data into a data stream.
• provide end-to-end data transport services and
establish a logical connection between the sending
host and destination host
• hides details of any network-dependent information
from the higher layers by providing transparent data
transfer.
• The Transport layer can be connectionless or
connection-oriented.

15. Connection-Oriented Communication
• Three way
handshake.
Setup a call
Transfer Data
Terminate the
call

16. Too much traffic for too small a capacity?
Solution -> flow control

17. Wouldn’t it be slow
if the transmitting machine had to wait for an acknowledgment
after sending each segment?
Solution  Windowing

18. Transport Layer Protocols
• TCP - a full-duplex, connection-oriented,
reliable protocol
– Too much overhead
• UDP - doesn’t offer all the bells and whistles of
TCP either, but it does do a fabulous job of
transporting information that doesn’t require
reliable delivery—and it does so using far
fewer network resources.

19. The Network Layer (Layer 3)
• manages device addressing, tracks the location of
devices on the network, and determines the best way to
move data
• transports traffic between devices that aren’t locally
attached.
• Concerned about network addressing
– Network addresses allow a system to be identified on the
network by a logically assigned address.
– The logical assignment of addresses allows a more
hierarchical approach to addressing than MAC addresses
provide.
• Routers are layer 3 devices

20. Switching Methods
• describes how the data sent from one node reaches another.
1. Circuit switching – just like is a telephone call.
– The link between caller and receiver is created, then a dedicated
communications link between the two points (hence the term circuit) is
created. The circuit cannot be broken, meaning no one else can use the
line.
– In a data communications environment, however, this is a disadvantage
because the data often originates from various sources.
2. Packet switching – widely used in a modern network
environment.
– data is broken down into packets that can then be transported around the
network.
– all messages travel over the same path, or it might be that messages travel
on different paths.
– At each point in the journey, a node stores the message before it is
forwarded to the next hop on the journey - store and forward.
– Due to store and forward, there is some delay.

21. Network Layer Protocols
• IPX - Part of Novell's IPX/SPX protocol suite,
which provides a connectionless transport
mechanism.
• IP - IP performs much the same function as
IPX, but IP is part of TCP IP protocol suite.

22. The Data Link Layer (Layer 2)
• provides the physical transmission of the data and handles
error notification, network topology, and flow control.
• will ensure that messages are delivered to the proper device
on a LAN using hardware addresses, and translates messages
from the Network layer into bits for the Physical layer to
transmit.
• formats the message into pieces, each called a data frame, and
adds a customized header containing the hardware destination
and source address.
• For a host to send packets to individual hosts on a local
network as well as transmitting packets between routers, the
Data Link layer uses hardware addressing.
• Switches and Bridges are layer 2 devices – they pass data using
MAC address
• WAPs are also considered data-link layer devices because their
primary function is to provide connectivity to the network.

23. • has two distinct sublayers
1. Logical Link Control (LLC) sublayer - controls the
access of the media, allowing multiple high-level
protocols to use a single network link.
 tells the Data Link layer what to do with a packet once a
frame is received
2. Media Access Control (MAC) - manages and
controls access to the network media for the
protocols trying to use it.
 The MAC address (Physical address) is defined at this
layer, as well as logical topologies.
 Defines how packets are placed on the media.
 “first come/first served” access where everyone shares
the same bandwidth
 Line discipline, error notification (not correction),
ordered delivery of frames are used at this layer

24. • The layer 2 device puts the source hardware address
in a filter table and keeps track of which port the
frame was received on. This information (logged in
the bridge’s or switch’s filter table) is what helps the
machine determine the location of the specific
sending device.
• The biggest benefit of using switches instead of hubs
in a network is that each switch port is actually its
own collision domain.

26. The Physical Layer (Layer 1)
• defines the physical characteristics of the network.
– physical characteristics can include the cable and connector type, the
format for pinouts for cables, and so on.
• also defines how the data actually travels across the network.
• defines the voltage used on the cable and the frequency at
which the signals that carry the data are transitioned from one
state to another  (speed and maximum distance)
• defines the physical topology of the network.
• Hubs and repeaters are layer 1 devices
• although NICs are physical components, they are defined as
data-link layer devices because they are used in physical media
access (which is handled at the MAC sublayer) and the logical
access of the network media (which is handled at the LLC
sublayer).

28. Encapsulation and decapsulation
• As data is passed up or down through the OSI
model structure, headers are added (going
down) or removed (going up) at each layer a
process called encapsulation (addition) or
decapsulation (removal).

32. Exercise – Identify the number of broadcast and
collision domains in each case.