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Ethernet & TCP/IP Networking_1 (Communication Model (Each protocol…
Ethernet & TCP/IP Networking_1
Communication Model
Each protocol layer is responsible for a particular set of tasks
As long as the interface btwn layers is well defined, it is possible to
separate the tasks
In each model there is a
suite of different protocols
for the different aspects of communication
An indiv layer needs to be concerned only with the interfaces of the layers immediately
above it
&
below it
Each layer of the stack at the sender node contributes info that is used by the corresponding
peer
layer at the receiver node
Ideally, the operation of a particular layer is
transparent
to other layers
Each model is implemented as a hierarchical
protocol stack
TCP/IP
Based on 5 protocol layers, although layers 1 & 2 are not actually specified in the standard (however, recognises these layers as a necessity)
TCP/IP protocol suite encompasses an integrated suite of numerous protocols that work together & guide all aspects of communication
Transmission Control Protocol/Internet Protocol
Different layers
Layer 3 Network layer
Layer 2 Data Link layer
Layer 4 Transport layer
Layer 1 Physical layer
Layer 5 Application layer
Ethernet Frame
The
destination & source addresses
,
specified as
MAC addresses
;
set in the device's firmware or hardware
A
data length field
to indicate
the amount of data in the frame
A
start frame delimiter
to
indicate the beginning
of the frame contents
A
data field
itself;
requires a min of 46 bytes
Consists of a
preamble
,
used for timing synchronisation
btwn sender & receiver
A field used to confirm
integrity of the frame
Wireless Ethernet (WiFi)
-2 types in use
Ad hoc mode
Based on partial
mesh network topology
Rarely used
Assumes direct
connections btwn nodes
Infrastructure mode
Based on shared access point
CSMA/CA-collision
avoidance MAC protocol
Station waits until channel
is clear plus a short random
amount of time before transmitting
May use "request to send" &
"clear to send" options to
improve collision avoidance
IPv4 Datagram format
Operation of IP
Two major functions
Routes datagrams from node to node
until they reach their destination node
Translates IP addresses to physical
addresses before it passes the packets
to the data link layer for delivery
Address Resolution Protocol
(ARP)
A broadcast of the IP address is
sent to every node on the network;
the
matching node responds
with a physical address
Physical address (MAC address in the
case of Ethernet) is sent in frame
to the
data link layer
Translation of IP address to physical
address at each intermediate node
until destination is reached
At final destination, the packet is
passed up to the transport layer
for deployment to the application layer
Implemented at the
network layer
Address Resolution Protocol (ARP)
Internet Control Message Protocol (ICMP)
-an additional network layer protocol
Error code is encapsulated in an
IP datagram & sent to source
Typical messages: "Destination Host Unknown",
"Time to live exceeded"
Auxiliary protocol that creates error
messages for failures at the network layer
Used for queries by network
tools such as
ping
&
traceroute