Transcript jgunders_Sem_1v2_Ch_1 - Oakton Community College

1: Review Of Semester 1v2 in
Sem 2v2
1.1.1.1. Provide an overview of
encapsulation.
Networking evolves to support
current and future applications. By
dividing and organizing the
networking tasks into separate
layers/functions, new applications
can be handled without problems.
The OSI reference model organizes
network functions into seven
categories, called layers.
The task of most network
managers is to configure the
three lowest layers.
Peer-to-peer functions use
encapsulation and deencapsulation as the
interface for the layers.
1.1.2.1. Describe three needs that drive enterprise
network improvements.
The enterprise is a corporation, agency, school, or other
organization that ties together its data, communication, computing,
and file servers.
Developments on the enterprise network include:
interconnected LANs that provide access to computers
or file servers in other locations
higher bandwidth on the LANs to satisfy the needs of
the end users
technologies that can be relayed for WAN service
Why Layered Network Model
Each layer uses its own layer protocol to communicate with its
peer layer in another system. Each layer's protocol exchanges
information, called protocol data units (PDUs), with its peer
layers.
For example, in TCP/IP the transport layer of TCP
communicates with the peer TCP function by using segments.
Each layer uses the services of the layer below it in order to
communicate with its peer layer.
Step 1
A computer converts an e-mail message into alphanumeric
characters that can be used by the internetworking system. This is
the data.
Step 2
The message data then changes to segments for transport on the
internetwork system. The transport function ensures that the
message hosts at both ends of the e-mail system can reliably
communicate.
Step 3
The data then forms a packet, or datagram, that also contains a
network header that includes a source and destination logical
address. The address helps the network devices send the packet
across the network along a chosen path.
Step 4
Each network device puts the packet into a
frame. The frame enables the device to connect
to the next directly-connected network device
on the link.
Step 5
The frame changes to a pattern of 1s and 0s for
transmission on the medium (usually a wire).
Some clocking function enables the devices to
distinguish bits as they travel across the
medium.
The physical layer provides access to the network media. The
data link layer provides support for communication over several
types of data links, such as Ethernet/IEEE 802.3 media.
Addressing schemes such as Media Access Control (MAC) and
Internet Protocol (IP) provide a very structured method for
finding and delivering data to computers or to other hosts on a
network.
Bridges that connect LAN segments and help filter traffic
Hubs that concentrate LAN connections and allow use of twisted-pair
copper media
Ethernet switches that offer full-duplex, dedicated bandwidth to
segments or desktops
Routers that offer many services, including internetworking and
broadcast control
Ethernet—The first of the major LAN technologies, it runs
the largest number of LANs.
Token Ring—From IBM, it followed Ethernet and is now
widely used in a large number of IBM networks.
FDDI—Also using tokens, it is now a popular campus LAN.
We will be studying the Ethernet IEEE 802.3 LAN standards.
10Base-2 (thin Ethernet) - allows
coaxial cable network segments up
to 185 m. long
10Base-5 (thick Ethernet) allows coaxial cable network
segments up to 500 m. long
10Base-T - carries Ethernet
frames on inexpensive twisted-pair
wiring
The 10Base-5 and 10Base-2 standards provide access for several
stations to the same LAN segment. Stations are attached to the
segment by a cable that runs from an attachment unit interface
(AUI) in the station to a transceiver that is directly attached to
the Ethernet coaxial cable.
The Ethernet and 802.3 data links prepare data for transport across
the physical link that joins two devices. For example, as this graphic
shows, three devices can be directly attached to each other over the
Ethernet LAN.
The purpose of this target indicator is to show the listening and
transmitting parts of CSMA/CD. The host listens for silence on the
LAN (CS, Carrier Sense). Every host on the LAN is free to transmit
when it hears silence (MA, Multiple Access).
One node’s transmission traverses the entire network and is received
and examined by every node.
Broadcasting is a powerful tool that can send a single frame to many
stations at the same time. Broadcasting uses a data link destination
address of all 1s (FFFF.FFFF.FFFF in hexadecimal).
When improperly used, broadcasting can seriously affect the
performance of stations by unnecessarily interrupting them.
Broadcasts should, therefore, be used only when the MAC address
of the destination is unknown, or when the destination is all stations
When a station wishes to transmit a signal, it checks the network to
determine whether another station is currently transmitting. If the network
is not being used, the station proceeds with the transmission.
While sending a signal, the station monitors the network to ensure that no
other station is transmitting at that time.
If two stations transmit at the same time if this should occur, they would
cause a collision. All stations stop sending frames for a randomly selected
time period.
Two important types of addresses are data link layer addresses and
network layer addresses. Data link layer addresses, also called
physical hardware addresses or MAC addresses, are typically unique
for each network connection. In fact, for most LANs, data link layer
addresses are located on the NIC (network interface card).
One way in which the sender can ascertain that MAC address
that it needs is to use an ARP (Address Resolution Protocol).
Router will provide its own MAC address if the host and
destination are on different subnets.
In a TCP/IP environment, end stations communicate with servers or
other end stations. This can occur because each node using the
TCP/IP protocol suite has a unique 32-bit logical address. This
address is known as the IP address.
Subnets improve the efficiency of network addressing. Adding
subnets does not change how the outside world sees the network, but
within the organization, there is additional structure.
From an addressing standpoint, subnets are an extension of a network number.
Network administrators determine the size of subnets based on the expansion
needs of their organizations.
Network devices use subnet masks to identify which part of the address is for
the network and which part represents host addressing.
The 3 bits in the example are enough for the required five hosts per
wire (actually, giving you host numbers 1 - 6).
A host number of 0 is reserved for the wire (or subnet) address, and
a host value of all 1s is reserved because it selects all hosts—that is,
it is a broadcast.
6 host addresses and 30 useable subnets.
Bits
Subnet Mask
Subnets Hosts
2
255.255.255.192
2
62
3
255.255.255.224
6
30
4
255.255.255.240
14
14
5
255.255.255.248
30
6
6
255.255.255.252
62
2
The application layer (Layer 7) supports the
communicating component of an application.
It does not provide services to any other OSI layer.
However, it does provide services to application
processes lying outside the scope of the OSI model
(e.g. spreadsheet programs, Telnet, WWW, etc.)
The presentation layer (Layer 6) formats and converts network application data into text, data
encryption, graphics, video, audio, or whatever format is necessary for the receiving device to
understand it.
The session layer (Layer 5) establishes, manages, and terminates communication interactions
between applications. NFS, SQL and X Windows System all operate at this layer
The transport layer (Layer 4) is responsible for transporting and regulating the flow of
information from source to destination, and for doing it reliably and accurately. Its functions
include:
connection synchronization
flow control
error recovery
reliability through windowing
In the context of the OSI reference model, the application layer
(Layer 7) supports the communicating component of an application.
PICT TIFF JPEG MIDI MPEG QuickTime -
The presentation layer (Layer 6) of the OSI reference model is responsible for presenting data in
a form that a receiving device can understand. It serves as the translator - sometimes between
different formats - for devices that need to communicate over a network, by providing code
formatting and and conversion.
Layer 6 converts and translates the two different formats.
Another function of Layer 6 is the encryption of data
The session layer (Layer 5) establishes, manages, and terminates
sessions between applications. It coordinates the service requests and
responses that occur when applications establish communications
between different hosts.
As the transport layer sends its data segments, it also ensures the integrity of the data.
This transport is a connection-oriented relationship between communicating end
systems. Some of the reasons for accomplishing reliable transport are as follows:
It ensures that senders receive acknowledgement of delivered segments.
It provides for retransmission of any segments that are not
acknowledged.
It puts segments back into their correct sequence at the destination
device.
It provides congestion avoidance and control.
One reason for using a multi-layer model such as the OSI reference
model is so that multiple applications can share the same transport
connection. Transport functionality is accomplished segment by
segment. This means that different data segments from different
applications, being sent to the same destination or to many
destinations, are sent on a first-come, first-served basis.
In concept, one device places a call to another device that the other
device must accept. Protocol software modules in the two operating
systems communicate by sending messages across the network to
verify that the transfer is authorized and that both sides are ready.
While data transfer is in progress, congestion can occur for two
different reasons. First, a high-speed computer might generate
traffic faster than a network can transfer it. Second, if many
computers send datagrams simultaneously to a single destination,
that destination can experience congestion.
Reliable connection-oriented data transfer means that data packets
arrive in the same order in which they are sent. Protocols fail if any
data packets are lost, damaged, duplicated, or received in the wrong
order. In order to ensure transfer reliability, receiving devices must
acknowledge receipt of each and every data segment.
Reliable delivery guarantees that a stream of data that is sent from
one device will be delivered through a data link to another device
without duplication or data loss.
Positive acknowledgment with retransmission is one process that
guarantees reliable delivery of data streams. It requires a recipient to
send an acknowledgment message to the sender whenever it receives
data.
Each of the upper-level layers performs its own functions. However,
their functions depend on lower-layer services.
All four upper layers - application (Layer 7), presentation (Layer 6),
session (Layer 5), and transport (Layer 4) - can encapsulate data in
end-to-end segments
The End