Title: Chapter 1: Internetworking
1Chapter 1 Internetworking
- Internetworking Basics
- Network segmentation
- How bridges, switches, and routers are used to
physically segment a network - How routers are used to create internetwork
- OSI model
2Internetworking Models
- Most networks are designed as a stack of layers,
each one built upon the one below it. Why?
Host 1
Host 2
Layer 3 protocol
Layer 3
Layer 3
Layer 2/3 interface
Layer 2 protocol
Layer 2
Layer 2
Layer 1/2 interface
Layer 1 protocol
Layer 1
Layer 1
Physical Medium
3- Each layer provides services to the higher
levels. - Each layer behaves as a black box.
- Layer n on one machine talks to layer n on
another machines. - The corresponding layer in the layered structure
are called peers. - The communication between peers must follow
certain rules, known as protocol. - No data are directly transferred between layers.
Actual communication is through a physical medium
below layer 1.
4An Analogy
Professor A
Professor B
I like rabbits
Jaime bien les lapins
Message
Chinese French
Information for the remote translator
Urdu English
Translator
Translator
L Dutch
L Ducth
Ik vind konijnen leuk
Ik vind konijnen leuk
use Dutch
Secretary
Secretary
Information for the remote secretary
Fax
Fax
L Ducth
L Ducth
Ik vind konijnen leuk
Ik vind konijnen leuk
use fax
5Open Systems Interconnection (OSI) Reference Model
Application
- Provides user interface
- Initiates services
Presentation
- Transfer data into standard format before
transmission
The upper levels
Session
- Keeps data different applications data separate
- Control the data exchange
Transport
- End-to-end data error free data transmission
Network
- Logical addressing for data packets Routing and
error handling
The lower levels
Data Link
- NIC software function
- How data in packaged
- Error detection
Physical
- Moves bits between devices
- Specifies voltages, cables, and cables
6Reasons for Layering
- Simplifies the network model
- Enables programmers to specialize in a particular
level or layer of the networking model - Provides design modularity
- Encourages interoperability
- Allows for standardized interfaces to be produced
by networking vendors
7The Application Layer (Layer 7)
- The layer where users communicate to the computer
- Contains protocols and utilities that provides
services to network applications - (True/False) MsWord, Eudora Mail, Netscape are in
the application layer. - Eudora (application) uses SMTP (Simple Mail
Transfer Protocol) (protocol). - E-mail
- Message formats such as RFC 822
- SMTP, POP3 (Post Office Protocol Version 3), IMAP
(Internet Message Access Protocol) - WWW
- HTML (The HyperText Markup Language), XML
(eXtensible Markup Language), XSL (eXtensible
Style Language) - HTTP (The HyperText Transfer Protocol)
8The Presentation Layer (Layer 6)
- The presentation layer prepares the data from the
application layer for transmission over the
network or from the network to the application
layer. - Include protocols specifying how to represent
data (MPEG, JPEG, PIC, WAV) - Responsible for data translation, formatting,
encryption, compression. - We need these services because different
computers use different internal representation
for data (integers and characters)
9The Session Layer (Layer 5)
- Enables two applications on the network to have
an ongoing conversation - Provide following services
- Communication setup and teardown
- Control for data exchange
- Data synchronization definition
- Failure recovery
- Examples
- Structured Query Language (SQL)
- X Windows
- AppleTalk Session Protocol (ASP)
10The Transport Layer (Layer 4)
- Provides
- end-to-end error free data transport services
- establish a logical connection
- data segmentation into maximum transmission unit
size - messaging service for session layer
- Protocols in this layer can be
- connection-oriented require an acknowledgment
of the receipt of data packets. - connectionless do not require an acknowledgment
of the receipt of data packets.
11- Connection-oriented protocols
sender
receiver
Synchronize
Negotiate connection
Synchronize
Acknowledge
Connection Establish
Virtual Circuit
Data Transfer
12- The segments delivered back to the sender upon
their reception - Any segment not acknowledged are retransmitted.
- Segments are sequence back into their proper
order upon arrival at their destination - Manageable data flow is maintained in order to
avoid congestion
sender
receiver
Buffer full
GO
13- Windowing The quantity of data segment (in
bytes) is sent without receiving an
acknowledgment (ack) is called a window.
sender
receiver
sender
receiver
Window size of 3
Window size of 1
receive 1
send 1
send 1
ack. 2
send 2
send 2
receive 2
send 3
ack. 3
ack. 4
send 3
send 4
14sender
receiver
Positive Acknowledgment with retransmission
1
2
3
4
5
6
1
2
3
4
5
6
send 1
send 2
send 3
ack. 4
send 4
send 5
Connection lost!
send 6
ack. 5
send 5
ack. 7
15The Network Layer (Layer 3)
- Provides services
- to manage devices addressing
- to tracks the location of devices on the network
- to determine the best way to move data on the
network - The network layer must transport traffic between
devices that are not directly connected. - Routers are specified at this layer.
16The Data Link (Layer 2)
- Services
- Identification of the source and destination
nodes via their physical address (Media Access
Control (MAC) address) - Definition of how data is packaged for transport
as frames - Error detection
- Flow control of information sent across the link
- Has two sublayers
- Media Access Control (MAC) 802.3
- Logical Link Control (LLC) 802.2
17The Physical Layer (Layer 1)
- This layer communicates directly with the various
types of actual communication media - Services
- definition of the physical characteristics of the
network hardware, including cable and connector - Encoding
- Transmission of signals on the wire
18Example568B twisted pair wiring scheme
19Layer 1 Network Devices Repeaters
- The number of nodes on a network and the length
of cable used influence the quality of
communication on the network - Attenuation
- Natural degradation of a transmitted signal over
distance - Repeaters work against attenuation by repeating
signals that they receive on a network - Why are repeaters Layer 1 devices?
20Layer 1 Network Devices Hubs
- Generic connection device used to tie several
networking cables together to create a link
between different stations on a network
21- Hubs that are plugged into electric power are
called active hubs - A hub that merely connects different cables on a
network and provides no signal regeneration is
called a passive hub and is not a repeater - Hub is a generic term applied to many different
network-connection devices - If a hub in some way segments or subdivides the
traffic on a network, it is an intelligent, or
switching, hub - For the purpose of the CCNS exam, the term hubby
itselfis a device that does not segment the
network
22Network Segmentation
- Segmentation
- Process of breaking a network into smaller
broadcast or collision domains - Ethernet network, which are characterized by IEEE
802.3 standard, define the use of a Carrier Sense
Multiple Access with Collision Detection
(CSMA/CD) access method - Backoff algorithm Mathematical calculation
performed by computers after a collision occurs
on a CSMA/CD network - Backoff period Random time interval used after
a collision has been detected on an Ethernet
network
23Network Segmentation via Bridges
24Layer 2 Devices Bridges
- Operate at the Data Link layer of the OSI model
- Filters traffic between network segments by
examining the destination MAC address - Based on this destination MAC address, the bridge
either forwards or discards the frame - When a client sends a broadcast frame to the
entire network, the bridge will always forward
the frame
25- Transparent Bridges Also called learning
bridges because they build a table of MAC
addresses as they receive frames - This means that they learn which addresses are
on which segments - Ethernet networks mainly use transparent bridges
- Source-routing bridges Rely on the source of
the frame transmission to provide the routing
information - Usually employed by Token Ring networks
- Translation bridges Can connect networks with
different architectures
26Layer 2 Devices Switches
- Increase network performance by reducing the
number of packets transmitted to the rest of the
network - Like bridges, operate at the Data Link layer of
the OSI model - In an Ethernet network, computers are usually
connected directly to a switch - Virtual circuit
- Private connections between two points created by
a switch that allows the two points to use the
entire available bandwidth between those two
points without contention