DAY - 2
TCP/IP Internet
Protocol
TCP/IP is a widely used protocol suite for internetworking, a term that
refers to the connection of various physical networks to form one large virtual
network. Any system connected to a TCP/IP internetwork should be able to
communicate with any other system within the internetwork, regardless of the physical
network on which the systems actually reside. Networks are linked together by a
system that functions as a gateway between systems.
While TCP/IP has a closely associated history with UNIX systems, the
TCP/IP protocols themselves are independent of the operating system, the
network topology, and the connection medium. TCP/IP operates on Ethernet and
Token Ring local area networks (LANs), across wide area links such as X.25, and
serial connections. Support for TCP/IP networking has been an integral part of
SunOS in all versions of the operating system.
The TCP/IP protocol suite can be described using a reference model
similar to the OSI reference model.TCP/IP does not delineate the presentation
and session layers as the OSI model does; application code provides the
necessary presentation or session functionality.
The TCP/IP protocols are defined in documents called Requests
for Comments (RFCs). RFCs are maintained by the Network Information
Center (NIC), the organization that handles address registration for the
Internet.
RFCs define a number of applications, the most widely used
being telnet, a terminal emulation service on remote hosts, and ftp,
which allows files to be transferred between systems.
TCP/IP Protocol
Stack Description:
The following sections describes the parts of the TCP/IP protocol stack.
Device Drivers
The device driver layer (also called the Network Interface) is the
lowest TCP/IP layer and is responsible for accepting packets and transmitting
them over a specific network. A network interface might consist of a device
driver or a complex subsystem that uses its own data link protocol.
Internet
Protocol (IP) Layer
The Internet Protocol layer handles communication from one machine to
another. It accepts requests to send data from the transport layer along with
an identification of the machine to which the data is to be sent. It
encapsulates the data into an IP datagram, fills in the datagram header, uses
the routing algorithm to determine how to deliver the datagram, and passes the
datagram to the appropriate device driver for transmission.
The IP layer corresponds to the network layer in the OSI reference
model. IP provides a connectionless, "unreliable" packet-forwarding service
that routes packets from one system to another.
Transport Layer
The primary purpose of the transport layer is to provide communication
from one application program to another. The transport software divides the
stream of data being transmitted into smaller pieces called packets in the ISO
terminology and passes each packet along with the destination information to
the next layer for transmission.
This layer consists of Transport Control Protocol (TCP), a
connection-oriented transport service (COTS), and the user datagram protocol
(UDP), a connectionless transport service (CLTS).
Application
Layer
The application layer consists of user-invoked application programs that
access services available across a TCP/IP Inter
The application program passes data in the required form to the
transport layer for delivery.
Computer Network Toplogies
A Network
Topology is the way computer systems or network equipment connected to each
other. Topologies may define both physical and logical aspect of the network.
Both logical and physical topologies could be same or different in a same
network.
Point-to-point
Point-to-point
networks contains exactly two hosts (computer or switches or routers or
servers) connected back to back using a single piece of cable. Often, the receiving
end of one host is connected to sending end of the other end and vice-versa.
Point-to-point Topology
If the hosts
are connected point-to-point logically, then may have multiple intermediate
devices. But the end hosts are unaware of underlying network and see each other
as if they are connected directly.
Bus Topology
In contrast to
point-to-point, in bus topology all device share single communication line or
cable. All devices are connected to this shared line. Bus topology may have
problem while more than one hosts sending data at the same time. Therefore, the
bus topology either uses CSMA/CD technology or recognizes one host has Bus
Master to solve the issue. It is one of the simple forms of networking where a
failure of a device does not affect the others. But failure of the shared
communication line make all other devices fail.
Bus Topology
Both ends of
the shared channel have line terminator. The data is sent in only one direction
and as soon as it reaches the extreme end, the terminator removes the data from
the line.
Star Topology
All hosts in
star topology are connected to a central device, known as Hub device, using a
point-to-point connection. That is, there exists a point to point connection
between hosts and Hub. The hub device can be Layer-1 device (Hub / repeater) or
Layer-2 device (Switch / Bridge) or Layer-3 device (Router / Gateway).
As in bus
topology, hub acts as single point of failure. If hub fails, connectivity of
all hosts to all other hosts fails. Every communication happens between hosts,
goes through Hub only. Star topology is not expensive as to connect one more
host, only one cable is required and configuration is simple.
Ring Topology
In ring
topology, each host machine connects to exactly two other machines, creating a
circular network structure. When one host tries to communicate or send message
to a host which is not adjacent to it, the data travels through all
intermediate hosts. To connect one more host in the existing structure
administrator may need only one more extra cable.
Failure of any
host results in failure of the whole ring. Thus every connection in the ring is
point of failure. There exists methods which employs one more backup ring.
Mesh Topology
In this type of
topology, a host is connected to one or two or more than two hosts. This
topology may have hosts having point-to-point connection to every other hosts
or may also have hosts which are having point to point connection to few hosts
only.
Hosts in Mesh
topology also work as relay for other hosts which do not have direct
point-to-point links. Mesh technology comes into two flavors:
Full Mesh: All
hosts have a point-to-point connection to every other host in the network. Thus
for every new host n(n-1)/2 cables (connection) are required. It provides the
most reliable network structure among all
network topologies.
Partially Mesh:
Not all hosts have point-to-point connection to every other host. Hosts connect
to each other in some arbitrarily fashion. This topology exists where we need
to provide reliability to some host whereas others are not as such necessary.
Tree Topology
Also known as
Hierarchical Topology is the most common form of network topology in use
present day. This topology imitates as extended Star Topology and inherits
properties of Bus topology.This topology divides the network in to multiple
levels/layers of network. Mainly in LANs, a network is bifurcated into three
types of network devices. The lowest most is access-layer where user’s computer
are attached. The middle layer is known as distribution layer, which works as
mediator between upper layer and lower layer. The highest most layer is known
as Core layer, and is central point of the network, i.e. root of the tree from
which all nodes fork.
All neighboring
hosts have point-to-point connection between them. Like bus topology, if the
root goes down, the entire network suffers. Though it is not the single point
of failure. Every connection serves as point of failure, failing of which
divides the network into unreachable segment and so on.
Daisy Chain
This topology
connects all its hosts in a linear fashion. Similar to Ring topology, all hosts
in this topology are connected to two hosts only, except the end hosts. That is
if the end hosts in Daisy Chain are connected then it represents Ring topology.
Each link in
Daisy chain topology represents single point of failure. Every link failure
splits the network into two segment. Every intermediate host works as relay for
its immediate hosts.
Hybrid Topology
A network structure
whose design contains more than one topology is said to be Hybrid Topology.
Hybrid topology inherits merits and demerits of all the incorporating
topologies.
Hybrid Topology
The above
picture represents an arbitrarily Hybrid topology. The combining topologies may
contain attributes of Star, Ring, Bus and Daisy-chain topologies. Most WANs are
connected by means of dual Ring topology and networks connected to them are
mostly Star topology networks. Internet is the best example of largest Hybrid topology
A protocol is a
set of rules that governs the communications between computers on a network.
These rules are guidelines that regulate the access method, allowed physical
topologies, types of cabling, and speed of data transfer.
The most common
protocols are:
1. Ethernet
2. Local Talk
3. Token Ring
4. FDDI
5. ATM
1.
ETHERNET
This is the
most widely used protocol. This protocol uses an access method called CSMA/CD
(Carrier Sense Multiple Access/Collision Detection). In this system each
computer listens to the cable for any transmitting node before sending anything
through the network. If the network is clear, the computer will transmit. Else
wait and try again when the line is clear. Sometimes, two computers attempt to
transmit at the same instant (causing a collision). Each computer then backs
off and waits a random amount of time before attempting to retransmit. The
delay by collisions and retransmitting is very small and does not normally
affect the speed of transmission on the network.
Topologies are
bus star or tree and transmission is via twisted pair, coaxial, or fibre optic
cable at a speed of 10 Mbps.
Fast Ethernet
Support 100Mbps
and are more expensive network concentrators/hubs and network interface cards
is requires for Fast Ethernet. Category 5 twisted pair or fibre optic cable is
necessary.
Gigabit Ethernet
The Ethernet
has a standard protocol of 1Gbps transmission speed but used primarily for
backbones on a network.
Media Access Control layer (MAC layer)
In the Open
Systems Interconnection (OSI) model of
communication, the Media Access Control layer is one of two sublayers of the
Data Link Control layer and is concerned with sharing the physical connection
to the network among several computers. Each computer has its own unique MAC address. Ethernet is
an example of a protocol that
works at the Media Access Control layer level.
LAN & MAC
(Medium Access Control) protocols
Two basic types of networks:
Switched networks: transmission lines, multiplexers, and switches;
routing, hierarchical address for scalability.
Broadcast networks: a single shared medium, simpler, no routing, messages
received by all stations, flat address; however, when users try to transmit
messages into the medium, potential conflict, so MAC is needed to
orchestrate the transmission from various users.
LAN is a typical
broadcast network.
In the
seven-layer OSI model of computer networking, media access control (MAC) data
communication protocol is a sublayer of the data link layer (layer 2). The MAC
sublayer provides addressing and channel access control mechanisms that make it
possible for several terminals or network nodes to communicate within a
multiple access network that incorporates a shared medium, e.g. Ethernet. The
hardware that implements the MAC is referred to as a medium access controller.
The MAC sublayer
acts as an interface between the logical link control (LLC) sublayer and the
network's physical layer. The MAC layer emulates a full-duplex logical
communication channel in a multi-point network. This channel may provide unicast,
multicast or broadcast communication service.
The local
network addresses used in IEEE 802
networks and FDDI networks are called MAC addresses;
they are based on the addressing scheme used in early Ethernet
implementations. A MAC address is a unique serial number. Once a MAC address
has been assigned to a particular network interface (typically at time of
manufacture), that device should be uniquely identifiable amongst all other
network devices in the world. This guarantees that each device in a network
will have a different MAC address (analogous to a street address). This makes
it possible for data packets to be delivered to a destination within a sub network,
i.e. Hosts interconnected by some combination of repeaters, hubs, bridges and switches, but not by network layer
routers. Thus, for example, when an IP packet reaches its destination (sub) network,
the destination IP address (a layer 3 or network layer concept) is resolved
with the Address Resolution Protocol for ipv4, or by Neighbour Discovery
Protocol (ipv6) into the MAC address (a layer 2 concept) of the destination
host. Examples of physical networks are Ethernet networks and Wi-Fi networks,
both of which are IEEE 802 networks and use IEEE 802 48-bit MAC addresses.
A MAC layer is
not required in full-duplex point-to-point communication, but address fields
are included in some point-to-point protocols for compatibility reasons.
Channel access control mechanism
The channel
access control mechanisms provided by the MAC layer are also known as a
multiple access protocol. This makes it possible for several stations connected
to the same physical medium to share it. Examples of shared physical media are bus networks, ring networks,
hub networks, wireless networks and half-duplex point-to-point links. The
multiple access protocol may detect or avoid data packet collisions if a packet
mode contention based channel access method is used, or
reserve resources to establish a logical channel if a circuit-switched
or channelization-based channel access method is used. The channel access
control mechanism relies on a physical layer multiplex scheme.
The most
widespread multiple access protocol is the contention based CSMA/CD protocol
used in Ethernet networks. This mechanism is only utilized within a network
collision domain, for example an Ethernet bus network or a hub-based star
topology network. An Ethernet network may be divided into several collision
domains, interconnected by bridges and switches.
A multiple
access protocol is not required in a switched full-duplex network, such as
today's switched Ethernet networks, but is often available in the equipment for
compatibility reasons.
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