UNIT 1
FUNDAMENTALS AND PHYSICAL LAYER
1.1 Building a Network
 By clicking on one URL, as many as 17 messages may be exchanged over
the internet.
 Up to 6 messages to translate the server name (www.xyz.com) into its
internet address 128.112.136.35
 3 messages to set up a TCP connection between your browser and this server
 4 messages for the browser to send the HTTP”GET” request and the respond
with the request page and 4 messages to tear down the Tcp connection.
1.2 REQUIREMENTS
The 1st step is to identify the set of constraints and requirements that influence
network design.
Application Engineer
 List the services the application needs.
 Ex: Guarantee that each message the application sends will be delivered
without error within certain amount of time.
Network Designer
 It List the properties of a cost effective design.
 Ex: Network resources are efficiently utilized and fairly allocated to
different users.
Network Provider
 It List the characteristics of the system that is easy to administer and
manage.
 Ex: In which false can be easily isolated and when it is easy to account for
usage.
Connectivity
 A network must provide connectivity among a set of computers.
 A system that is designed to support growth to all arbitrarily large size is
said to scale.
1.2.1 LINKS, NODE AND CLOUDS
 A network can consist of two or more computers directly connected by some
physical medium, such as coaxial cable or an optical fibre.
 We call such a physical medium a link and the computers connect as nodes.
Point-to-point: physical links between pair of computers.
Multiple accesses: single physical link shared by more nodes.
Switched network
 Nodes have at least two point-to-point links.
 They run software that forwards data received on one link out on another.
Types:
 Circuit-switched (Telephone system)
 Packet-switched (computer network)
Packet-Switched Network
 It Stores and forwards the packets.
 Receives complete packet, stores and then forwards it to next node.
Circuit-Switched Network
 Establishes a dedicated circuit across sequence of links and then allows the
source node to send a stream of bits across this circuit to the destination
node.
Internetwork
 It is the Collection of independent networks connected together (internet).
Router or Gateway
 A node that is connected to two or more networks is commonly called as a
router.
Address
 A node is assigned a unique IP address in the network.
 When the source node wants the network to deliver a message to the
destination node, it should specify the address of the destination node.
 If the source and destinations are not directly connected, then the switches
and routers use this address to decide how to forward the message toward
the destination.
Routing
 The process of determining systematically how to forward messages toward
the destination node based on its address is called “Routing”
Classifications of Routing
 Unicast - Source to destination routing.
 Broadcast - Source to all nodes in the network..
 Multicast – Source to specific group of nodes.