Download physical address.

Network Models


Network uses a combination of hardware and software to send data
from one location to another
Performing a task is performed on different layers [Higher ---> Lower]
LAYERED TASKS
 Concept of layers in our daily life
– Two friends communicate through postal mail
Layered Tasks
Layered Tasks
Hierarchy

Task must be done in the order given in the hierarchy
– Sender site from up to down
– Receiver site from down to up
Services

Sender site each layer uses the services of the layer immediately below
it
Higher  Middle  Lower  Carrier
The OSI Model






1947 established ISO : International Standards Organization
ISO model covers network communications is OSI : Open System
Interconnection
Introduced in the late 1970s.
Open system: a set of protocols that allows any two different systems
to communicate regardless of their underlying architecture.
Purpose of the OSI : to show how to facilitate communication between
different systems without requiring changes to the logic of the
underlying hardware and software.
OSI model not a protocol, it is a model for understanding and
designing a network architecture that is flexible, robust, and
interoperable.
ISO is the organization. OSI is the model
THE MODEL



Is a layered framework, for design of computer systems that allows
communication across all types of computer systems
Consists of seven layers each defines a part of the process of moving
information across network
Understanding of the fundamentals of the OSI model provides a solid basis for
exploring data communications.
Seven layers of the OSI model
Layered Architecture



When device A sent message to device B
Message may pass intermediate nodes
Only the first three layers of the model involve
Layered Architecture
At single machine


Each layer defines functions distinct from other layers
Each calls upon the services of the layer below it
– Layer 3 uses services from layer 2
– Layer 3 provides services for layer 4
Between Machines

Layer x on one machine communicates with layer x on another
machine by protocols.
– Communication is governed by an agreed-upon series of rules and
conventions called protocols
– Process that communicate a given layer on one machine are called Peerto-Peer process
– Communication between machines is therefore peer-to-peer process using
the protocols appropriate to a given layer
Peer-to-Peer process
On the sending machine

Each layer in sending device
– adds its own information to the message it receives from the layer
just above it
– pass the whole package to the layer below it
– At layer 1 the message converted to a form that can be transferred
to the receiving machine
On receiving machine
– Message is unwrapped layer by layer

layer 2 removes the data meant for it, then passes the rest to
layer 3 and so on.
Interfaces Between Layers



Between any pair of adjacent layers sending and receiving done by
interface
Each one defines what information and services must provide for layer
above it.
Well-defined interfaces and layer functions provide modularity to a
network ( could modified or replace without affect surrounding )
Organization of the Layers


Seven layers could be belonged to three subgroups
Network support layers: layers 1,2 and 3
– deal with physical aspects of moving data from one device to another


Such as electrical specifications, physical connections, physical addressing,
and transport timing and reliability
User support layer: layer 5, 6, 7
–



It allows interoperability among unrelated software systems
Layer 4, transport layer
– It links the two subgroups
– Ensures that what the lower layers transmitted is in a form that the upper layers can
use
The upper OSI layers are implemented in software
Lower layers implemented in hardware and software except for the physical
layer which is mostly hardware.
Organization of the Layers
Organization of the Layers




Each layer adds a header to data except layer 2 adds also trailer
When data passes physical layer (layer 1) changed into an
electromagnetic signal and transported through physical link
When reaching destination, the signal passes into layer 1 and it
transformed back into digital form.
When data reaches the next higher layer
– header and trailers corresponding sending layer are removed
– Action appropriate to that layer are taken

In layer 7, message will be in appropriate format ( application )
Note
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Physical Layer

The physical layer is responsible for transmitting individual bits
from one node to the next
Physical Layer
The major duties of this layer are:
 Physical characteristics of interfaces and medium :
– Defines :
 characteristic of the interface between the devices and the
transmission medium
 Type of transmission medium
 Representation of bits : Defines the type of encoding (how


0s and 1s are changed to signals: electrical or optical)
Data rate ( transmission rate ) : number of bits sent each
second (duration of a bit)
Synchronization of bits : synchronized at bit level of
sender and receiver
Physical Layer

Line configuration: is concerned with the
connection of the devices to the media
– Point-to-point configuration
– Multipoint configuration

Physical topology: defines how devices are
connected to make a network.
– Mesh, star, ring, bus, or a hybrid.
– Hybrid is a combination of two or more topologies

Transmission mode: defines the direction of
transmission between two devices: simplex, halfduplex, or full-duplex.
Note
The data link layer is responsible for moving
frames from one hop (node) to the next.
Data Link Layer
Data Link Layer
The data link layer is responsible for transmitting frames from one node to
the next
 Framing : divided bits into manageable data units called frames
 Physical addressing : If frames distributed
– On same the network, header (physical address of sender and receiver)
added to frame
– On different networks, receiver address is the address of device that
connects networks

Flow control : controls transmission rate between sender and receiver

Error control : Link layer adds reliability to the physical layer by adding trailer
to frame :
–
–

Mechanisms to detect and retransmit damaged or lost frames
Mechanisms to prevent duplication of frames
Access control : which device has control over at any given time
Hop-to-hop (node-to-node) delivery
Example




A node with physical
address 10 sends a frame
to a node with physical
address 87
Frame contains physical
address in the header
Rest of header contains
other information needed
at this level
The trailer contains extra
bits needed for error
detection
Note
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Network Layer



Responsible for the source-to-destination delivery across multiple networks
Ensures that each packet gets from its point of origin to its final destination
No need for network layer if systems on the same networks
Network Layer

Duties of the network layer:
– Logical addressing : physical address locally but for universal
– A header added to the packet include logical address of sender and
receiver
– Routing : internetwork connected by devices ( routers or gateways ) which
route or switch the packets to their final destination, network layer provide
this mechanism
Source-to-destination delivery
Example

Send from A to P ( network address )
or from 10 to 95 ( physical address )

Different networks

Two addresses required

Network address is universal address

Network address = logical address

Logical address remain the same from
source to destination ( A and P )
Physical address changes

Note
The transport layer is responsible for the delivery
of a message from one process to another.
Transport Layer

Responsible for process-to-process delivery of the entire message
Compare with Network layer

–
–
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Delivery of individual packets
Does not recognize any relationship between those packets
Ensures that whole message
–
–
Intact: not changed or broken
In order ( manage error control + flow control)
Transport Layer
Transport Layer

Service-point addressing: transport layer gets the entire message to the correct process
on that computer (from specific process [ running program ] on one computer to a
specific process [ running program ] on the other.
–
–
–

Segmentation and reassembling: the message is reassembled
–
–

Correctly upon sequence number
Identify and replace packets that lost in the transmission
Connection control : either
–
–
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Transport layer adds header called a service—point address (port address)
Network layer gets each packet to the correct computer
Transport layer gets the entire message to the correct process on that computer
connectionless : each packets treat independent and delivers it to destination
connection-oriented : make connection first then delivers packets then terminated
Flow control: not on single link (data link) But end to end.
Error control: not on single link? But process-to-process
–
–
Sending transport layer ensures message arrives at transport layer in receiving without error
(damage, loss, or duplication)
error correction is achieved by retransmission.
Reliable process-to-process
delivery of a message
The session layer is responsible for dialog control
and synchronization.
Session Layer


The session layer is the network dialog controller.
IT establishes, maintains, and synchronizes the interaction among
communicating systems.
Responsibilities:
 Dialog control:
–
–
Allows two system to enter into a dialog
Allows the communication between two processes to take place in:

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
Half-duplex or
Full-duplex
Synchronization:
– Allows process to add checkpoints (synchronization points) to a stream of
data
– Example : add checkpoint every 100 pages for sending 2000 pages
– If crash happens during the transmission of page 523 retransmission began
at page 501.
Session Layer
The presentation layer is responsible for translation,
compression, and encryption.
Presentation Layer
Concern with the syntax and semantic of the information exchanged between two systems
Presentation Layer
Responsibilities

Translation : Information should change to bits stream before transmit
– Working with different encoding methods ( different computers)
– Presentation layer is responsible for interoperability between these
different encoding methods.
– At sender

Change information ( sender-dependent format to common format)
– At receiving
 Change information (common format to receiver-dependent format)

Encryption
– Encryption at sending and Decryption at receiving

Compression :
– Data compression reduces the number of bits to be transmitted
– Compression needs in transmitted multimedia
Note
The application layer is responsible for
providing services to the user.
Application layer
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
Enables the user (human or software) accessing the network
It provides user interfaces and services ( electronic mail, remote file access and
transfer, World Wide Web)
Application layer

Mail services : the basis for e-mail forwarding and storage

File transfer and access: lets user to access file in a remote
host
– Change or read
– Retrieve files
– Manage or control files

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Remote log-in: log into a remote computer and access the resources
Accessing the WWW
Summary of Layers
TCP/IP PROTOCOL SUITE
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Invented before OSI
The layers in the TCP/IP protocol suite do not exactly match those in the
OSI model.
The original TCP/IP protocol suite was defined as having four layers:
–
–
–
–

host-to-network
internet,
transport,
application.
equivalent to
equivalent to
equivalent to
equivalent to
physical + data link
network
part of duties of session
session + presentation + application
However, when TCP/IP is compared to OSI, we can say that the TCP/IP
protocol suite is made of five layers:
–
–
–
–
–
physical,
data link,
network,
transport,
application.
TCP/IP PROTOCOL SUITE

The first four layers provide functions that correspond to the first four layers of
the OSI model:
–
Physical standers
– Network interfaces
– Internetworking
– Transport functions

The three topmost layers functions in the OSI model are represented in TCP/IP
by application layer
TCP/IP and OSI model
TCP/IP PROTOCOL SUITE
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TCP/IP is a hierarchical protocol made up of interactive modules
Each layer in TCP/IP provides specific function
The modules are not necessarily interdependent, but in OSI module specifies
which functions belong to each of its layers.
Each layer has independent protocols
TCP/IP is a hierarchical protocol : each upper-level supported by one or more
lower-level protocols depending on the needs of the system.
AT transport layer, TCP/IP defines three protocols
– Transmission Control Protocol (TCP)
– User Datagram Protocol (UDP)
– Stream Control Transmission Protocol (SCTP)
At network layer, the main protocol defined by TCP/IP is the Internetworking
Protocol (IP)
TCP/IP PROTOCOL SUITE
Physical and Data Link Layers
– TCP/IP does not define any specific protocol but it supports all the
standard protocols.
– A network in TCP/IP internetwork can be local or a wide-area network
Network Layer
– At Internetwork layer, TCP/IP supports the Internetworking Protocol.
IP uses four supporting protocols:

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ARP
RARP
ICMP
IGMP
TCP/IP PROTOCOL SUITE
Internetworking Protocol (IP)
– It is the transmission mechanism used by the TCP/IP protocols.
– It is unreliable and connectionless protocol (a best-effort delivery service).
 A best effort: IP provides no error checking or tracking.
 IP assumes the unreliability of the underlying layers and does its best to get a
transmission through to its destination, but with no guarantees.
– IP transport data in packets separately called datagrams.
– Datatgrams can travel along different routes and can arrive out of
sequence or be duplicated.
– IP does not keep track of the routes and has no facility for reordering
datagrams when they arrive their destination.
– IP provides bare-bones transmission service that free the user to add only
those facilities necessary for a given application and thereby allows for
maximum efficiency. (covers the weakness in its functionality)
TCP/IP PROTOCOL SUITE
Address Resolution Protocol
– Associated a logical address with a physical address.
– On a typical physical network, LAN, each device is identified by a
physical or station address, usually imprinted on the network interface
card (NIC).
– ARP is used to find the physical address of the node when its Internet
address is known.
Reverse Address Resolution Protocol
– RARP allows a host to discover its Internet address when it knows only its
physical address.
– RARP is used when a computer is connected to a network for the first
time or when a diskless computer is booted.
TCP/IP PROTOCOL SUITE
Internet Control Message protocol
–
ICMP is a mechanism used by a host and gateways to send notification of datagram
problems back to the sender.
– ICMP sends query and error reporting messages.
Internet Group Message Protocol
–
IGMP is used to facilitate the simultaneous transmission of a message to a group of
recipients.
Transport Layer
–
–
–
Traditionally the transport layer represented in TCP/IP by TCP and UDP .
IP is host-to-host protocol, deliver a packet from one physical device to another.
UDP and TCP are transport level protocols responsible for delivery of a message
from a process to another process.
– SCTP, has been devised to meet the needs of some newer applications.
TCP/IP PROTOCOL SUITE
User Datagram Protocol
–
–
UDP is the simple of the two standard TCP/IP transport protocol.
UDP is process-to-process adds:



port addresses
Checksum error control
Length information to the data from the upper layer
Transmission Control Protocol
–
–
–
TCP provides full transport-layer services to applications.
TCP is a reliable stream (connection-oriented) transport protocol.
At sending end of each transmission:

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

–
TCP divides a stream of data into smaller units called segments
Each segment includes a sequence number for recording after receipt
An acknowledgment number for the segments received
Segments carried across the internet inside of IP datagrams.
At receiving end

TCP collects each datagram as it comes in and reorders the transmission based on
sequence numbers
TCP/IP PROTOCOL SUITE
Stream Control Transmission Protocol
– SCTP provides support for newer applications as voice over the Internet.
– SCTP is a transport layer protocol that combines the best features of UDP
and TCP.
Application Layer
– Application layer in TCP/IP is equivalent to the combined session,
presentation, and applications layers in the OSI model.
– Many protocols are defined at this layer.
ADDRESSING
Four levels of addresses are used in an internet employing the TCP/IP
protocols:
ADDRESSING
Each address is related to a specific layer in the TCP/IP architecture.
ADDRESSING
Physical Addresses
– It is known as the link address.
– It is the address of a node as defined by its LAN and WAN.
– It is included in the frame used by the data link layer.
– It is the lowest-level address.
– It has authority over the network (LAN or WAN).
– The size and format of these addresses vary depending on the network.
 The Ethernet uses a 6-byte (48 bit) physical address that is imprinted on NIC.
 LocalTalk (Apple) has 1-byte dynamic address.
ADDRESSING
In Figure 2.19 a node with physical address 10 sends a frame to a node with physical
address 87. The two nodes are connected by a link (bus topology LAN). As the figure
shows, the computer with physical address 10 is the sender, and the computer with
physical address 87 is the receiver.
ADDRESSING
As we will see in Chapter 13, most local-area
networks use a 48-bit (6-byte) physical address
written as 12 hexadecimal digits; every byte (2
hexadecimal digits) is separated by a colon, as
shown below:
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.
ADDRESSING
Logical Addresses
– It is necessary for universal communications.
– Physical addresses are not adequate in an internetwork environment where
different networks can have different address format.
– A universal addressing system is needed in which each host can be
identified uniquely, regardless of the underlying physical newtwork.
– A logical address in the Internet is currently a 32-bit address.
– No two publicly addressed and visible hosts on the Internet can have the
same IP address.
IP Addresses
Figure 2.20 shows a part of an internet with two routers connecting three LANs.
Each device (computer or router) has a pair of addresses (logical and
physical) for each connection. In this case, each computer is connected to
only one link and therefore has only one pair of addresses. Each router,
however, is connected to three networks (only two are shown in the figure).
So each router has three pairs of addresses, one for each connection.
Port Addresses



The end objective of Internet communication is a process communicating with
another process.
In TCP/IP architecture, the label assigned to a process is called a port address.
A port address in TCP/IP is 16 bits in length.
Port Addresses
Figure 2.21 shows two computers communicating via the Internet. The sending
computer is running three processes at this time with port addresses a, b,
and c. The receiving computer is running two processes at this time with
port addresses j and k. Process a in the sending computer needs to
communicate with process j in the receiving computer. Note that although
physical addresses change from hop to hop, logical and port addresses
remain the same from the source to destination
Addresses
The physical addresses will change from hop to hop,
but the logical addresses usually remain the same.
Port Addresses
As we will see in Chapter 23, a port address is a 16-bit
address represented by one decimal number as shown.
753
A 16-bit port address represented
as one single number.
Specific Addresses
E-mail address
Universal Resource Locator (URL)