Download Pres 2 Internet Addressing and Layers

Operating Systems
Internet Addresses
Universal Identifiers
• Universal Communication Service Communication system which allows any
host to communicate with any other host
– Name : what an object is
– Address : where it is
– Route : how to get there
IP Address
• Unique 32-bit address
IP Classes
IP Classes
Layers
TCP/IP vs OSI
Open System Interconnect
• The layers of the OSI model provide a
framework for understanding networking.
• The OSI model is not a protocol, but rather
a reference model (abstract structure) that
describes the functions and interactions of
various data communication protocols.
OSI Stack
• Layers 5 through 7, the
"higher" layers, are
concerned with
communication between
applications.
• Layers 1 through 4, the
"lower" layers, are
concerned with
transmitting raw data
between computers.
Physical Layer
• The Physical Layer deals with
transmitting and receiving bits
across a physical medium.
• Includes the following types of
hardware devices that send and
receive signals over each type
of physical medium:
– Network interface cards
(NICs)
– Fiber optic transceivers
– Radio transceivers
– Modems
Physical Layer (cont.)
• Concerned only with transmitting and receiving physical signals that
represent data bits.
• Demo
• Most error detection and all error correction are the responsibility of
higher layers.
Data Link Layer
• The Data Link Layer deals with frames
over a single physical link. A Data Link
Layer address is the unique address
built into a NIC.
• It uses the signaling services of the
Physical Layer below it.
• To Layer 3 above, it provides the
service of addressing a message to a
device located across a single physical
transmission path.
Data Link Layer (cont.)
• Network Layer handles data in units called
"packets.“
• Network Layer passes a packet to the Data
Link Layer, which encapsulates the packet
by placing a header and trailer around it
(frame).
• Frame header includes the unique NIC
addresses of the sending and receiving
nodes.
• Frame trailer contains error-checking
information
Data Link Layer (cont.)
• Network Layer handles data in units called
"packets.“
• Network Layer passes a packet to the Data
Link Layer, which encapsulates the packet
by placing a header and trailer around it
(frame).
• Frame header includes the unique NIC
addresses of the sending and receiving
nodes.
• Frame trailer contains error-checking
information
Data Link Layer (cont.)
Transmitting Node
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Accepts data packets of arbitrary length
from the Network Layer.
Accepts the address of an adjacent node to
which it is to transmit the data.
Adds sequence information to the frame in
case they get out of sequence during error
recovery.
Adds error detection and correction codes
to the frames.
Does not send frames to the Physical Layer
at a faster rate than the receiving Data Link
Layer process can handle them.
Data Link Layer (cont.)
Receiving Node
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Receives bits passed up from the Physical
Layer and interprets groups of bits as frames.
Checks each frame for errors and takes
corrective measures if necessary.
Handles problems, such as missing frames,
through handshaking with its peer process.
Puts the frames back in the correct sequence to
reconstruct the packet.
Passes each decapsulated packet up to the
Network Layer.
Demo
Network Layer
• The Network Layer deals with packets.
• Responsible for transmitting data packets
between source and destination nodes that
may not be connected by the same
physical link
• Message may pass through an
"intermediate node." Network Layer's job
is to use intermediate nodes to transmit a
packet to its destination.
• Demo
Transport Layer
• The Transport Layer carries messages
between processes (remember - multitasking).
• Transport Layer addresses are process
addresses called "port numbers."
• The lowest layer in which peer software
processes at either end of a connection
carry on a conversation.
• Demo
Transport Layer (cont.)
Services
• Addressing
– deliver data to a specific process within a node.
• Connection management
– responsible for establishing and releasing
connections between processes.
– During data transfer, processes on both hosts
communicate to verify that data is being
received without errors or loss.
– When communication is complete, the peer
processes terminate the connection to free up
resources for other processes.
• Flow Control and Buffering
– responsible for ensuring that the receiving node
has enough memory buffers to store the
incoming data
– data is not transmitted faster than the receiving
node can accept it.
Session Layer
• Where a conversation starts and stops
• The rules of the conversation are agreed
upon.
• Facilitates a step-by-step interaction or
session between two entities.
– Example - an interactive user session
begins with a user logging on to the
computer and ends with the user logging
off.
Session Layer (cont.)
Electronic Conversation
• Parties first agree to talk to one another.
• They (usually) do not talk
simultaneously.
• Divide the conversation into parts.
• End the conversation in an orderly
fashion.
Presentation Layer
• The process concerned with how data is
presented on the computer and represented
inside the computer.
• The "representation" layer.
– deals with the format of stored computer
information.
• Three main services:
– Data representation
– Data security
– Data compression
Presentation Layer (cont.)
Services
• Data Representation - resolves differences between different types of
encoding systems.
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Byte ordering within integers
Character coding (EBCDIC and ASCII)
Format of floating point numbers
Boolean
• Data Security - encrypts and decrypts data
– Authentication
– data encryption
• Data Compression - reduces the number of bytes that must be
transmitted by translating the data into a more efficient form that
requires less storage.
Application Layer
• Includes some programs that interact
directly with users, and some that provide
services to user applications.
• E-mail
• USENET newsgroups
• File transfer and access
• Virtual terminals
• Web browsers and servers