Transport Layer (Layer 4)
DATA (PDU(Protocol Data Unit)) + PORT NUMBER = SEGMENT
Transport Layer segment and reassemble data from upper-layer applications and unite it into the same data stream. They provide end-to-end data transport services and can establish a logical connection between the sending host and destination on an internetwork.
The Transport Layer is responsible for providing mechanisms for multiplexing the upper-layer applications, establishing sessions, and tearing down virtual circuits.
The Transport Layer can bt connectionless(UDP) or connection-oriented(TCP).
Flow Control:
•
The segments delivered
are acknowledged back to the sender upon their reception.
•
Any segments not
acknowledged are retransmitted.
•
Segments are sequenced
back into their proper order upon arrival at their destination.
•
A manageable data flow
is maintained in order to avoid congestion, overloading, and data loss.
Connection-Oriented Communication:
•
A service is
considered connection-oriented if it has the following characteristics:
•
A virtual circuit is set up (e.g., a three-way
handshake like Synchronize, Negotiate connection and Acknowledge).
•
It uses sequencing.
•
It uses acknowledgments.
•
It uses flow control
Windowing and Buffering:
•
The quantity of data
segments (measured in bytes) that the transmitting machine is allowed to send
without receiving an acknowledgment for them is called a window.
•
Windows are used to
control the amount of outstanding, unacknowledged data segments.
Acknowledgments:
•
Reliable data delivery
ensures the integrity of a stream of data sent from one machine to the other
through a fully functional data link. It guarantees that the data won’t be
duplicated or lost. This is achieved through something called positive acknowledgment with retransmission.
Network Layer (Layer 3)
SEGMENT + IP/IPX/APPLETALK = PACKET(DATAGRAM)
•
The Network layer (also called layer 3)
manages device addressing, tracks the location of devices on the network, and
determines the best way to move data, which means that the Network layer must
transport traffic between devices that aren’t locally attached. Routers (layer
3 devices) are specified at the Network layer and provide the routing services
within an internetwork.
•
Two types of packets
are used at the Network layer: data and route updates:
•
Data packets Used to
transport user data through the internetwork. Protocols used to support data
traffic are called routed protocols;
examples of routed protocols are IP and IPv6.
•
Route update packets
Used to update neighboring routers about the networks connected to all routers
within the internetwork. Protocols that send route update packets are called
routing protocols; examples of some common ones are RIP, RIPv2, EIGRP, and
OSPF. Route update packets are used to help build and maintain routing tables
on each router.
•
Logical addressing .
•
It also define the
route .
Data link layer (Layer 2)
CRC = Cyclic Redundancy Check (For Error Detection)
PACKET + MAC ADDRESS + CRC = FRAME
CRC = Cyclic Redundancy Check (For Error Detection)
•
The Data Link layer provides the physical
transmission of the data and handles error notification, network topology, and
flow control. This means that the Data Link layer will ensure that messages are
delivered to the proper device on a LAN using hardware addresses and will
translate messages from the Network layer into bits for the Physical layer to
transmit.
•
The Data Link layer
formats the message into pieces, each called a data frame, and adds a customized header containing the hardware
destination and source address.
The IEEE Ethernet Data Link layer has two sublayers:
•
Media Access Control
(MAC) 802.3 Defines how packets are placed on the media. Contention media
access is “first come/first served” Physical addressing is defined here, Line
discipline, error notification (not correction), ordered delivery of frames,
and optional flow control can also be used at this sublayer.
•
Logical Link Control
(LLC) 802.2 Responsible for identifying Network layer protocols and then
encapsulating them.
•
An LLC header tells
the Data Link layer what to do with a packet once a frame is received.
Physical layer (Layer 1)
•
At the bottom, we find
that the Physical layer does
two things: It sends bits and receives bits. Bits come only in values of 1 or 0
— a Morse code with numerical values.
•
The Physical layer
communicates directly with the various types of actual communication media.
•
The Physical layer
specifies the electrical, mechanical, procedural, and functional requirements
for activating, maintaining, and deactivating a physical link between end
systems.
Made By : P & V
No comments :
Post a Comment