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INTRODUCTION TO NETWORK - Coggle Diagram
INTRODUCTION TO NETWORK
CHAPTER 2
NETWORK ACCESS
CHAPTER 2.2
EXPLAIN DATA LINK LAYER PROTOCOLS AND MEDIA ACCESS CONTROL
2.2.1
Describe the purpose and function of the data link layer in preparing communication for transmission on specific media.
De-encapsulation
(used by a receiving device to
remove one or more
of the
protocol headers
.)
Works from
BOTTOM to TOP
.
Data is de-encapsulated as it
moves up the stack toward
the
end-user application
.
Network Addresses
(Responsible for
delivering
the IP packet from the original source to the final destination.)
Devided into two:
Source IP address
Sending device, the original source of the packet.
Destination IP address
Receiving device, the final destination of the packet.
Encapsulation Example
Works from
TOP to BOTTOM
.
The TCP segment is encapsulated in the IP Packet.
The IP packet is encapsulated in the Ethernet Frame.
Data is divided into segments.
Data Link Addresses
(Deliver the data link frame from one network interface to another network interface on the
same network
.)
IP packets is encapsulated in a new data link fram when it is forwarded by each router through its source to destination.
Protocol Data Units
Encapsulation
process
. As application data is passed down the protocol stack, information is added at each level.
Devices on the Same Network
Network layer addresses
(IP addresses)
(indicate the original source and final destination.)
Network portion
The left-most part of the address indicates which network the IP address is a member of who.
Host portion
The remaining part of the address identifies a specific device on the network.
Data link frame
(MAC address)
(sent directly to the receiving device.)
Source MAC address
Address of sending device.
Destination MAC address
Address of receiving device.
Message Segmentation
Large streams of data are divided into smaller, more manageable pieces to send over the network.
Devices on a Remote Network
(Source and destination IP addresses represent hosts on different networks.)
The data link frame
cannot be sent directly
to the
remote destination host
. Therefore the frame is sent to the default gateway
(nearest router interface)
.
The router
removes
the
received Layer 2 information and adds new data link information
before
forwarding out the exit interface
.
2.2.2
The basic characteristics of media access control methods on WAN and LAN topologies.
Controlling Access to Media
Equivalent of traffic rules that regulate the entrance of motor vehicles onto a roadway.
Absence of any media access is equivalent to vehicles ignoring all other traffic and entering the road without regard to the other vehicles.
Not all roads and entrances are the same.
Traffic can enter the road by merging, by waiting for its turn at a stop sign, or by obeying signal lights.
A driver follows a different set of rules for each type of entrance.
Physical and Logical Topologies
Physical Topologies
Physical connections and identifies how end devices including interconnection of infrastructure devices.
Infrastructure Devices
Switches
Wireless Access Points
Routers
Logical Topologies
The way a network transfers frames from one node its next. These logical signal paths are defined by data link layer protocols.
WAN Topologies
Point-to-Point
Permanent link
between two endpoints.
Physical
Frames are placed on the media by the node at one end and taken from the media by the node at the other end of the point-topoint circuit.
Is limited to two nodes.
Logical
However, the use of physical devices in the network does not affect the logical topology.
The logical connection between nodes forms what is called a virtual circuit.
End nodes communicating in a point-to-point network can be physically connected via a number of intermediate devices.
Hub and Spoke
A central site interconnects branch sites using point-to-point links.
Full Mesh
Provides high availability, but requires that every end system be interconnected to every other system. Administrative and physical costs can be significant.
LAN Topologies
Extended Star
A combination of more than 1 Star Topologies.
Bus
Used in legacy network. All end systems are chained to each other and terminated in some form on each end. Uses coax cable instead of switches due to its capability of easy to set up and is inexpensive.
Star
Has a central intermediate device which uses Ethernet switches as it's connector.
Ring
End systems are connected in shape of ring and does not need to be terminated. Were used in legacy Fiber Distributed Data Interface (FDDI) and Token Ring networks.
Half and Full Duplex
Communication
Half-Duplex
Used in legacy bus topologies with Ethernet hubs.
WLANs operate in half-duplex.
Both devices can transmit and receive on the media but cannot do so simultaneously.
Full-Duplex
Data link layer assumes that the media is available for transmission for both nodes at any times.
Operated by Ethernet switches by default but can operate in half-duplex by connecting to a device such as an Ethernet hub.
Both devices can transmit and receive on the media at the same time.
Media Access Control Methods
Contention-Based Access
Nodes operate in halfduplex.
Compete for the use of the medium.
Only one device can
send at a time.
Devided into 2 types
Carrier Sense Multiple Access/Collision
Detection (CSMA/CD)
A collision will occur the moment two devices transmit at the same time.
Both devices will detect the collision on the
network.
Process is used in halfduplex Ethernet LANs.
Data sent by both devices will be corrupted
and will need to be resent.
Carrier Sense Multiple Access With Collision Avoidance CSMA/CA
Uses a method to detect if the media is clear.
The switch and the host NIC operate in full-duplex mode.
Controlled Access
Each node has its own time to use the medium.
Legacy Token Ring LANs are an example
Data Link Frame
The Frame
Consists of 3 basic parts
(its structure depends on Layer 3 protocol)
Data
Trailer
Header
Frame Fields
Type
Identifies the Layer 3
protocol in the data field.
Control
Identifies special flow
control services such as QoS.
Addressing
Indicates the
source and destination nodes.
Data
Contains the frame payload
(packet header, segment header, and the data)
Frame start and stop indicator
flags
Identifies the beginning
and end limits of the frame.
Layer 2 Addresses
Contains the source data link address of the NIC card
sending the frame
The destination data link address of the NIC card receiving the frame.
LAN and WAN Frames
Data link layer protocols
includes
Point-to-Point Protocol
(PPP)
High-level Data Link Control
(HDLC)
Ethernet
Frame Relay
802.11 Wireless
Layer 2 protocol used for a topology is determined by the technology.
2.2.3
The characteristics and functions of the data link frame.
The Data Link Layer
Prepares network data for the physical network.
Standards
International Organization for
Standardization (ISO)
International Telecommunication
Union (ITU)
Institute of Electrical and Electronics
Engineers (IEEE)
American National Standards
Institute (ANSI)
Devided into Two Layers
Logical Link Control (LLC)
Communicates with network layer.
Identifies which network layer protocol is being used for the frame.
Allows multiple Layer 3 protocols (IPv4, IPV6) to utilize the same network interface and media.
Media Access Control (MAC)
Defines the media access processes performed by the hardware.
Provides data link layer addressing and access to various network technologies.
Communicates with Ethernet to send and receive frames over copper or fiber-optic cable.
Communicates with wireless technologies such
as Wi-Fi and Bluetooth.
Packets Travelling
From Source Host to Destination Host through physical networks.
Different Physical Networks (media)
Wireless Consisting Electromagnetic Signals
Opticla Fiber
Copper Wire
Radio
Frequencies
Satellite Links
Microwave
Different protocols uses different media.
Packets in a media
De-capsulated frame forward packets in a new frame.
To cross, each frame's headers are formatted for the specific medium.
Providing Access to Media
De-encapsulates the frame.
Re-encapsulates the packet into a new frame.
Accepts a frame from a medium.
Forwards the new frame appropriate to the medium of that segment.
2.2.5
Differentiate the roles of the MAC address and the IP address.
Ethernet MAC Addresses
MAC Addresses and Hexadecimal
An Ethernet MAC address is a 48-bit binary value expressed as 12
hexadecimal digits
(4 bits per hexadecimal digit)
.
Hexadecimal is used to represent Ethernet
MAC addresses and IP Version 6 addresses.
It is easier to express a value as a single hexadecimal digit than as four binary bits.
Hexadecimal is usually represented in text
by the value preceded by 0x
(E.g., 0x73)
.
Hexadecimal is a base sixteen system
(0 to 9 and A to F)
Convert the decimal or hexadecimal value to binary, and then to convert the
binary value to either decimal or hexadecimal as needed.
MAC Addresses: Ethernet Identity
Function to identify the actual source
and destination.
Rules are established by IEEE.
IEEE assign the vendor a 3-byte
(24-bit)
code called the
Organizationally Unique Identifier
(OUI)
.
Requires a vendor to follow two
simple rules:
All MAC addresses assigned to a
NIC
or
other Ethernet
device
must use that vendor's assigned OUI
as the first 3 bytes.
All MAC addresses with the
same OUI
must be assigned a
unique value
in the last 3 bytes.
Frame Processing
Often referred to as a burned-in address
(BIA)
.
Address is encoded into the ROM chip permanently.
When the computer starts up, the first thing the
NIC
does is
copy the MAC address
from
ROM
into
RAM
.
Header information contains the source and destination MAC address.
Header information attached to the frame when a device is forwarding a message to an Ethernet network.
MAC Address Representations
Windows Host
Uses the
ipconfig/all
command to identify the MAC address of an Ethernet adapter
MAC / Linux Host
Uses the
ifconfig
command to identify the MAC address of an Ethernet adapter
Broadcast MAC Address
1 to everyone
Used by
Dynamic Host Configuration Protocol
(DHCP)
and
Address Resolution Protocol
(ARP)
Contains a destination
IPv4 address
that has all ones
(1s)
in the host portion indicating that all hosts on that
local network will receive and process the packet
.
As
IPv4 broadcast packet
is
encapsulated
in the
Ethernet frame
, the destination MAC address is the broadcast MAC address of FF-FF-FF-FF-FFFF
in hexadecimal
(48 ones in binary)
.
Unicast MAC Address
1 to 1
A unique address used when a frame is sent from a single transmitting device to another single destination device.
Sending and Receiving packet
A destination IP address must be in the IP packet header.
A corresponding destination MAC address must also be present in the Ethernet frame header.
Multicast MAC Address
1 to many
Allows a source device to end a packet to a group of devices.
Devices are assigned a multicast group IP address in the range of 224.0.0.0 to 239.255.255.255
(IPv6 multicast addresses begin with FF00::/8)
.
Multicast IP address requires a corresponding multicast MAC address that begins with 01-00-5E in hexadecimal.
MAC and IP
Destination on Same Network
Two primary addresses assigned to a device on an
Ethernet LAN:
Physical address
(the Ethernet MAC address)
.
Logical address
(the IP address)
.
PC-A sends an IP packet to the file server on the same network.
The Layer 2 Ethernet frame contains:
Destination MAC address.
Source MAC address.
The Layer 3 IP packet contains:
• Source IP address
• Destination IP address
Destination on Remote Network
The
destination MAC address
will be the address of the
host’s default gateway
.
PC-A is sending an IP packet to a web server on a remote network.
The destination IP address is that of the File Server.
The destination MAC address is that of Ethernet interface of R1.