Download Logical addressing

LECTURE : 5
POINTS TO BE DISCUSSED:
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Addressing
Routing
Network Performance Analysis
ADDRESSING:
In computer networks we are going to connect two nodes or two computers
so we need address of those machines. For example, In case of telephone connection we need
phone numbers or in case of mail we need mailing address.
There are two type of addresses used:
1. Physical addressing
2. Logical addressing
Physical addressing (MAC address):
MAC address stands for Media Access Control address. It is
also called as Ethernet Hardware Address (EHA), hardware address or adapter address is a
unique identifier assigned to most network adapters or network interface cards (NICs) by the
manufacturer for identification. If assigned by the manufacturer, a MAC address usually
encodes the manufacturer's registered identification number. Physical addressing is the
addressing employed by various networking schemes (e.g., Ethernet, ATM, FDDI, AppleTalk,
PPP, HDLC, etc.) These network have different frame formats and use different addressing
scheme.
Logical addressing (IP):
IP stands for Internet Protocol which is used for communicating data
across a packet-switched internetwork using the Internet Protocol Suite, also referred to as
TCP/IP. Logical addressing is an addressing scheme above the physical addressing. This is used
for universal communication between different networks. The most popular logical addressing
protocol is Internet Protocol (IP).
Just, like there’s a need to address source and destination nodes of a communication, it’s also
necessary to identify source and destination application processes as in the end, it is the
applications that are exchanging packets. In an IPv4 address, (comprises of 32 bits) there are
two parts by design.
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Network part
Host Part
An Internet Protocol (IP) address is a numerical identification and logical address that is
assigned to devices participating in a computer network utilizing the Internet Protocol for
communication between its nodes. Although IP addresses are stored as binary numbers, they
are usually displayed in human-readable notations, such as 208.77.188.166 and
2001:db8:0:1234:0:567:1:1.
Communication in same LAN:
The application layer data is prep ended with a transport layer header,
and then an IP header, and lastly with a MAC header. When the destination node (on the same
LAN) receives the frame, it removes the IP address, recognizes its own IP address in the
destination field, demuxes the packet to the right application using the Transport layer (TCP or
UDP) port information. There is no intermediate routing node enroute.
When the distance between the source host and the destination host increases or the number
of nodes increase, switches or bridges can be used. In a hub: a frame is received; it is copied on
all other ports; it’s called a physical layer device.
Internetworking LANs:
A router or a gateway is a specialized device that only implements
functionality up to the network layer. It receives the MAC frame from the source host since the
source host has kept the destination MAC as the MAC address of the router. Once, it has
received the packet, it will inspect the IP address, recognizing that the IP address is not its own,
it will route the packet towards the destination. For this, it will choose a next hop that will take
the packet towards the destination. The router will add a new MAC header, insert its own MAC
address as the source MAC address and the MAC address of the next hop as the destination
MAC address. This process will go on until the packet reaches the destination node. The
destination node will remove the MAC header and recognize that the packet is destined
towards its ownself. It will then use the transport layer port information to deliver the packet to
the right application.
ROUTING:
Routing is the process of selecting paths in a network along which to send network
traffic. Routing is performed for many kinds of networks, including the telephone network,
electronic data networks (such as the Internet), and transportation networks. This article is
concerned primarily with routing in electronic data networks using packet switching
technology.
In packet switching networks, routing directs packet forwarding, the transit of logically
addressed packets from their source toward their ultimate destination through intermediate
nodes; typically hardware devices called routers, bridges, gateways, firewalls, or switches.
General-purpose computers with multiple network cards can also forward packets and perform
routing, though they are not specialized hardware and may suffer from limited performance.
The routing process usually directs forwarding on the basis of routing tables which maintain a
record of the routes to various network destinations. Thus, constructing routing tables, which
are held in the routers' memory, is very important for efficient routing. Most routing algorithms
use only one network path at a time, but multipath routing techniques enable the use of
multiple alternative paths.
NETWORK PERFORMANCE ANALYSIS:
Bandwidth:
It is a measure of available or consumed data communication resources
expressed in bit/s or multiples of it (kbit/s, Mbit/s etc). Bandwidth may refer to bandwidth
capacity or available bandwidth in bit/s, which typically means the net bit rate, channel
capacity of a logical or physical communication path in a digital communication system.
Bandwidth is literally the width of frequency band; e.g., voice-grade telephone can support
frequencies from 300 Hz to 3300 Hz and said to have a bandwidth of 3KHz. When we talk to
bandwidth of a link, we usually refer to the number of bits per second that can be transmitted
on the link. We might say that the bandwidth of an Ethernet link is 10 Mbps.
Throughput:
It can be defined as the measured performance of the system. E.g., due to
various inefficiencies, a pair of nodes connected by a link of 10 Mbps may achieve a throughput
of only 2 Mbps.
Throughput = Transfer Size/ Transfer Time
Latency:
It is also known as delay and depends on the distance covered by the data. It
usually has three components.
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Transmit delay
Queuing delay
Propagation delay
There are certain situations where it’s important to measure time to send a message from one
end of the network to the other end and back. This is called Round Trip Time.
Transmission delay is the time taken by the node to put the links on the medium from its
output buffers.
Queuing delays are because of packet switches since packet switches need to store packets
before forwarding them on a link. If the output queue of a link is already full, the new packets
will have wait.
Propagation delay is the time taken for the signal representing the bit to propagate at the
speed of the light to the other end. Propagation delay = distance/ speed of light which is 3 x
10^8 in vacuum; 2.3 x 10^8 in a cable and 2.0 x 10^8 in a fiber. Bandwidth and delay together
combine to define the performance characteristics of a given link/ channel. The relative
importance, however, depends on the application. For some applications, latency dominates
bandwidth. For example, a client that delivers one byte message and receives one byte
message from the server is latency bound. Assuming no computation is involved (no nodal
delay), the application will perform much different on a 100 ms RTT link than on 1 ms RTT link.
Latency = Propagation + Transmit + Queue
Propagation = Distance/ Speed of Light
Transmit = Size/ Bandwidth
Wajahat Ali Butt
107
BEE-3A
30th April, 2009