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Chapter 2
Network
Models
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Components of Communication
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Sender
Receiver
Message
Transmission medium
Protocol
Effectiveness of Communication
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Delivery (correct delivery)
Accuracy
Timeliness
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2.3
Jitter – a subset of timeliness
Data Flow
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2.4
Simplex
Half-Duplex
Duplex
Connection Types
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2.5
Point-to-Point
Multi-point
Physical Topologies
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2.6
Bus
Ring
Star
Mesh
Compound
Physical Topology Links
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Let n=# of nodes. The number of links is:
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2.7
Bus
Ring
Star
Mesh
n-1
n
n-1 (includes the hub)
n*(n-1)/2
Network Types
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2.8
LAN – nodes belonging to an address
space that is part of a well defined domain
(where the domain is an address subdomain).
WAN – When two or more LANs are linked
together.
Chapter 2: Outline
2.1 Protocol Layering
2.2 TCP/IP Protocol Suite
2.3 OSI Model
2-1 PROTOCOL LAYERING
A protocol defines the rules that the sender,
receiver and all intermediate devices must
follow to communicate effectively.
2.10
2.1.1 Scenarios
Consider two scenarios.
Scenario 1: communication is so simple it occurs in
one layer.
Scenario 2: communication takes place in three
layers.
2.11
2-1 PROTOCOL LAYERING
When communication is simple, one simple
protocol may be enough;
When the communication is complex, a
protocol may be required at each “layer”.
2.12
Figure 2.1: A single-layer protocol
2.13
Figure 2.2: A three-layer protocol
Postal carrier facility
2.14
2.1.2 Principles of Protocol Layering
Consider two principles of protocol layering.
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2.1.2 Principles of Protocol Layering
Consider two principles of protocol layering.
1. For half-duplex or full duplex data flow, each
layer must perform a forward operation and the
corresponding inverse operation.
2.16
2.1.2 Principles of Protocol Layering
Consider two principles of protocol layering.
2. The two objects under each layer at both sites
should be identical.
2.17
Figure 2.2: A three-layer protocol
Postal carrier facility
2.18
2.1.3 Logical Connections
The principles of protocol layering lead to a logical
connection between the layers at sending and
receiving ends of the communication.
2.19
Figure 2.3: Logical connection between peer layers
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2-2 TCP/IP PROTOCOL SUITE
A protocol defines the rules that both the
sender and receiver and all intermediate
devices must follow to communicate
effectively.
2.21
2-2 TCP/IP PROTOCOL SUITE
TCP/IP is a five layer protocol suite.
2.22
2-2 TCP/IP PROTOCOL SUITE
TCP/IP is a five layer protocol suite.
•Application Layer
2.23
2-2 TCP/IP PROTOCOL SUITE
TCP/IP is a five layer protocol suite.
•Application Layer
•Transport Layer
2.24
2-2 TCP/IP PROTOCOL SUITE
TCP/IP is a five layer protocol suite.
•Application Layer
•Transport Layer
•Network Layer
2.25
2-2 TCP/IP PROTOCOL SUITE
TCP/IP is a five layer protocol suite.
•Application Layer
•Transport Layer
•Network Layer
•Data Link Layer
2.26
2-2 TCP/IP PROTOCOL SUITE
TCP/IP is a five layer protocol suite.
•Application Layer
•Transport Layer
•Network Layer
•Data Link Layer
•Physical Layer
2.27
Figure 2.4: Layers in the TCP/IP protocol suite
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2.2.1 Layered Architecture
TCP/IP protocol suite example:
Consider three LANs
Each LAN has a group of hosts connected to a
switch (aka 2-level switch).
Each switch is connected to a router (aka 3-level
switch)
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Figure 2.5: Communication through an internet
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2.2.2 Layers in the TCP/IP Protocol Suite
Draw a diagram with multiple nodes in each LAN
Why is it called a 2-level switch?
Why is a router is 3-level switch?
2.31
Figure 2.6: Logical connections between layers in TCP/IP
Logical connections
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Network Data Objects
Data objects:
message
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Network Data Objects
Data objects:
message
segment
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Network Data Objects
Data objects:
message
segment
datagram
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Network Data Objects
Data objects:
message
segment
datagram
frame
2.36
Network Data Objects
Network data object taxonomy:
message
segment
datagram
frame
signals representing bits
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Figure 2.7: Identical objects in the TCP/IP protocol suite
Identical objects (messages)
Identical objects (segment or user datagram)
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Identical objects (datagram)
Identical objects (datagram)
Identical objects (frame)
Identical objects (frame)
Identical objects (bits)
Identical objects (bits)
Network Data Objects
Data Object Taxonomy:
Application layer - message
Transport layer - segment
Network layer - datagram
Data link layer - frame
Physical layer – signals representing bits
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2.2.3 The TCP/IP Layers
Descriptions of the TCP/IP layers will come later;
next,
we will follow a data object through the layers…
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2.2.4 Encapsulation and Decapsulation
One of the important concepts in protocol layering
in the Internet is encapsulation/ decapsulation.
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2.2.4 Encapsulation and Decapsulation
As the object passes through each layer, an
information header (and or trailer) is added to the
object.
The information header is used to assist in any of
these tasks: routing of the object, flow control, error
detection, error correction, etc.
(see next slide)
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Figure 2.8: Encapsulation / Decapsulation
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Encapsulation payload
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Each layer receives an object that is
referred to as the payload, and then
attaches a data header.
Payload can be relative to each layer, or
absolute.
The absolute case refers to the original
object message.
Example Encapsulation
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2.45
Q: What is the efficiency of the link in
figure 2.8, between LANs if each header is
60 bytes and the message is 1000 bytes?
Example Encapsulation
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Q: What is the efficiency of the link in
figure 2.8, between LANs if each header is
60 bytes and the message is 1000 bytes?
A: 84.7%
Example Encapsulation
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2.47
Q: How does the efficiency change if the
message is only 100 bytes?
Example Encapsulation
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2.48
Q: How does the efficiency change if the
message is only 100 bytes?
A: 35.7%
Figure 2.9: Addressing in the TCP/IP protocol suite
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2-3 OSI MODEL
A seven layer protocol model.
It never really caught on due to the success
of TCP/IP
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Figure 2.11: The OSI model
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Figure 2.12: TCP/IP and OSI model
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2.3.1 OSI versus TCP/IP
When we compare the two models, we find that two
layers, session and presentation, are missing from
the TCP/IP protocol suite. These two layers were not
added to the TCP/IP protocol suite after the
publication of the OSI model. The application layer
in the suite is usually considered to be the
combination of three layers in the OSI model, as
shown in Figure 2.12.
2.53