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Communicating over the Network

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Communicating over the
Network
Network Fundamentals – Chapter 2
Sandra Coleman, CCNA, CCAI
Version 4.0
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
1
Objectives

Describe the structure of a network, including the
devices and media that are necessary for successful
communications.

Explain the function of protocols in network
communications.

Explain the advantages of using a layered model to
describe network functionality.

Describe the role of each layer in two recognized
network models: The TCP/IP model and the OSI
model.

Describe the importance of addressing and naming
schemes in network communications.
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
2
Network Structure
 Three elements of communication
• Message source
• The channel
• Message destination
– Data or information networks capable of carrying many different
types of communications
© 2007 Cisco Systems, Inc. All rights reserved.
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3
 How are messages communicated?
– Data is sent across a network in small “chunks” called segments – known as
segmentation
– Multiplexing – describes the process of interleaving multiple digital data
streams into ONE signal (see example in online curriculum 2.1.2)
– It increases the reliability of network communications
– Disadvantage is the amount of encapsulation that must occur with every
segment, especially for large amounts of data!
© 2007 Cisco Systems, Inc. All rights reserved.
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4
Network Components
• Hardware (includes devices and media)
• Software (services and processes)
© 2007 Cisco Systems, Inc. All rights reserved.
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5
End Devices
– End devices form interface with human network &
communications network
– Originate data flow!
– Examples: computers, printers, VoIP Phones,
cameras, cell phones, etc.
– Commonly referred to as hosts (source or destination
of a message)
– Each host has an address that will identify it on the
network
– Role of end devices:
• Client (software installed so they can request & display info from the
server)
• Server (provide information and services to other hosts)
• Both client and server
© 2007 Cisco Systems, Inc. All rights reserved.
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6
Intermediary Devices
–Role of an intermediary device
• Examples: Hubs, switches, access points, routers,
modems, firewalls, etc.
• Provides connectivity and manages data flows
across network
• Works behind the scenes
• Determines the path data will travel to get from
source to destination
• Knows all the paths that exist
• Informs other like devices about errors or
communication failures
• Retimes & retransmits signals as necessary
© 2007 Cisco Systems, Inc. All rights reserved.
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7
Network Media
– this is the channel over which a message travels
– Encoding is different for each type, i.e. electrical
impulses, light pulses, wave patterns
© 2007 Cisco Systems, Inc. All rights reserved.
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8
Network Types
 Local Area Networks (LANs)
– A network serving a home, building or campus is considered a
Local Area Network (LAN)
– Single geographic area, usually a common organization
– Administered by a single organization
– Provides network services to a common organization
© 2007 Cisco Systems, Inc. All rights reserved.
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9
Network Types
 Wide Area Networks (WANs)
– LANs separated by geographic distance are connected by a
network known as a Wide Area Network (WAN)
– Be able to identify a LAN and a WAN given a similar diagram
© 2007 Cisco Systems, Inc. All rights reserved.
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10
Network Types
 Define the Internet
– The internet is defined as a global mesh of interconnected
networks
© 2007 Cisco Systems, Inc. All rights reserved.
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11
Network Symbols – be able to recognize
© 2007 Cisco Systems, Inc. All rights reserved.
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12
Function of Protocol in Network Communication
– A protocol is a set of predetermined rules
– Implemented in software that is loaded on each host and
network device
– View them as a stack – from low to high in a hierarchy
– Outline the functions necessary to communicate between
layers
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
13
Network Protocols
– Network protocols are used to allow devices to communicate
successfully
– Protocols agree on structure of message (specific to PDU’s)
– Protocols agree on the process of sharing, error handling, and
termination procedures – all functions necessary for
communication
– Require layer dependent encapsulations
© 2007 Cisco Systems, Inc. All rights reserved.
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14
Protocols and Industry standards
– A standard is a process or protocol that has been endorsed by
the networking industry and ratified by a standards organization
– Ensures all protocols (open or proprietary) will work together
– IEEE (Institute of Electrical and Electronic Engineers)
– IETF (Internet Engineering Task Force)
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
15
Function of Protocol in Network Communication
Examples of Protocols
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
16
Function of Protocol in Network Communication
 Technology independent Protocols
– Many diverse types of devices can communicate using the
same sets of protocols
– This is because protocols specify network functionality, not the
underlying technology to support this functionality
© 2007 Cisco Systems, Inc. All rights reserved.
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17
Layers with TCP/IP and OSI Model
 Benefits of using a layered model
•
•
•
•
Assists in protocol design
Fosters competition (different vendors can work together)
Changes in one layer do not affect other layers
Provides a common language
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
18
Layers with TCP/IP and OSI Model
Away
Know the
layers in order!
Pizza
Sausage
Throw
Not
Do
Programmers
© 2007 Cisco Systems, Inc. All rights reserved.
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19
Layers with TCP/IP and OSI Model
 TCP/IP Model – created in early 1970s – KNOW what
each layer is responsible for!
 Open Standard
© 2007 Cisco Systems, Inc. All rights reserved.
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20
Layers with TCP/IP and OSI Model
 Protocol data units (PDU) and encapsulation
PDUs are
SPECIFIC to each
layer!
Know PDUs at
EACH layer!
© 2007 Cisco Systems, Inc. All rights reserved.
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21
Key functions of encapsulation
 Ensure that data pieces get from sending to receiving
device
 Ability to re-assemble the data packets correctly
 Ability to identify data packets that belong together with
the same communication package
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
22
Comparing TCP/IP and OSI Model
Know these layers and how they compare between the
two models
© 2007 Cisco Systems, Inc. All rights reserved.
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23
Addressing and Naming Schemes
 Explain how labels in encapsulation headers are used
to manage communication in data networks
© 2007 Cisco Systems, Inc. All rights reserved.
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24
Addressing and Naming Schemes
 Describe examples of Ethernet MAC Addresses, IP
Addresses, and TCP/UDP Port numbers
© 2007 Cisco Systems, Inc. All rights reserved.
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25
IP: The waist of the hourglass
 IP is the waist of the
hourglass of the Internet
protocol architecture
Applications
HTTP FTP SMTP
TCP UDP
 Multiple higher-layer
protocols
IP
 Multiple lower-layer protocols
 Only one protocol at the
network layer.
Data link layer
protocols
Physical layer
protocols
26
© 2007 Cisco Systems, Inc. All rights reserved.
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26
Application protocol
 IP is the highest layer protocol which is implemented at
both routers and hosts
Application
Application protocol
Application
TCP
TCP protocol
TCP
IP
Data Link
Host
IP
IP protocol
Data
Link
Data
Link
IP
IP protocol
Data
Link
Router
Data
Link
Data
Link
IP protocol
Data
Link
Router
Data
Link
IP
Network
Access
Host
27
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
27
Layers in the Example
HTTP
HTTP protocol
HTTP
TCP
TCP protocol
TCP
IP
Ethernet
IP
IP protocol
Ethernet
argon.tcpiplab.edu
128.143.137.144
Ethernet
IP protocol
Ethernet
Ethernet
router71.tcpip- router137.tcpiplab.edu
lab.edu
128.143.137.1
128.143.71.1
00:e0:f9:23:a8:20
© 2007 Cisco Systems, Inc. All rights reserved.
IP
Ethernet
neon.tcpip-lab.edu
128.143.71.21
28
Cisco Public
28
IP Service
 IP supports the following services:
unicast
one-to-one
(unicast)
one-to-all
(broadcast)
one-to-several
(multicast)
broadcast
multicast
 IP multicast also supports a many-to-many service.
 IP multicast requires support of other protocols (IGMP,
29
multicast routing)
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
29
Layers in the Example
HTTP
HTTP protocol
HTTP
TCP
TCP protocol
TCP
IP
Ethernet
IP
IP protocol
Ethernet
argon.tcpiplab.edu
128.143.137.144
Ethernet
IP protocol
Ethernet
Ethernet
router71.tcpip- router137.tcpiplab.edu
lab.edu
128.143.137.1
128.143.71.1
00:e0:f9:23:a8:20
© 2007 Cisco Systems, Inc. All rights reserved.
IP
Ethernet
neon.tcpip-lab.edu
128.143.71.21
30
Cisco Public
30
Layers in the Example
HTTP
TCP
IP
Frame is an IP
datagram
Ethernet
Send HTTP Request
to neon
Establish a connection to 128.143.71.21 at
port 80Open TCP connection to
128.143.71.21 port 80
IP datagram is a TCP
segment for port 80
Send
IP data-gram
to
Send a datagram (which
contains
a connection
Send IP datagram
to
IP
128.143.71.21
request) to 128.143.71.21
128.143.71.21
Frame is an IP
datagram
Send the datagram to 128.143.137.1
Ethernet
Ethernet
HTTP
TCP
IP
Send the datagram
Ethernet
to 128.143.7.21
argon.tcpipneon.tcpip-lab.edu
router71.tcpip- router137.tcpipSend Ethernet frame
Send Ethernet frame
lab.edu
128.143.71.21
lab.edu
to 00:20:af:03:98:28
to 00:e0:f9:23:a8:20 lab.edu
128.143.137.144
128.143.137.1
128.143.71.1
31
00:e0:f9:23:a8:20
Encapsulation and Demultiplexing

As data is moving down the protocol stack, each
protocol is adding layer-specific control
information
User data
HTTP
HTTP Header
User data
HTTP Header
User data
TCP
TCP Header
IP
TCP segment
IP Header
Ethernet
TCP Header
HTTP Header
User data
IP datagram
Ethernet
Header
IP Header
TCP Header
HTTP Header
Ethernet frame
User data
Ethernet
Trailer
32
Encapsulation and Demultiplexing
6 bytes
destination address
source address
type
4 bytes
CRC
33
Encapsulation and Demultiplexing:
Ethernet Header
6 bytes
00:e0:f9:23:a8:20
4 bytes
0:a0:24:71:e4:44
0x0800
Ethernet Header
CRC
IP Header
TCP Header
Application data
Ethernet Trailer
Ethernet frame
34
Encapsulation and Demultiplexing:
IP Header
32 bits
version
(4 bits)
header
length
DS
flags
(3 bits)
Identification (16 bits)
TTL Time-to-Live
(8 bits)
Total Length (in bytes)
(16 bits)
ECN
Protocol
(8 bits)
Fragment Offset (13 bits)
Header Checksum (16 bits)
Source IP address (32 bits)
Destination IP address (32 bits)
Ethernet Header
IP Header
TCP Header
Application data
Ethernet Trailer
Ethernet frame
35
Encapsulation and Demultiplexing:
IP Header
32 bits
0x4
0x5
0x0
0x0
9d08
12810
4410
0102
00000000000002
0x06
8bff
128.143.137.144
128.143.71.21
Ethernet Header
IP Header
TCP Header
Application data
Ethernet Trailer
Ethernet frame
36
Encapsulation and Demultiplexing:
TCP Header
32 bits
Source Port Number
Destination Port Number
Sequence number (32 bits)
Acknowledgement number (32 bits)
header
length
0
Flags
TCP checksum
option
type
Ethernet Header
IP Header
length
window size
urgent pointer
Max. segment size
TCP Header
Application data
Option:
maximum
segment
size
Ethernet Trailer
Ethernet frame
37
Encapsulation and Demultiplexing:
TCP Header
32 bits
162710
8010
60783510
010
610
0000002
0000102
0x598e
210
Ethernet Header
IP Header
819210
00002
410
TCP Header
146010
Application data
Ethernet Trailer
Ethernet frame
38
Encapsulation and Demultiplexing:
Application data
No Application Data
in this frame
Ethernet Header
IP Header
TCP Header
Application data
Ethernet Trailer
Ethernet frame
39
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