FUNDAMENTALS OF COMMUNICATION NETWORKS

Presented By:

Vasantha Lakshmi Gutha

Graduate student (CS)

Course: CENG 5931

University of Houston-Clear Lake

Guthav6317@uhcl.edu

Spring 2011

INTRODUCTION SWITCHING TECHNOLOGIES ENCAPSULATION AND MULTIPLEXING NAMING AND ADDRESSING MULTIPLE ACCESS ROUTING AND FORWARDING CONGESTION CONTROL AND FLOW

CONTROL NEW CHALLENGES IN WIRELESS NETWORKS MULTIPLE ACCESS SCHEMES CONGESTION CONTROL IN WIRELESS

NETWORKS CONCLUSION

INTRODUCTION A communication network consists of a set of

interconnected nodes that exchange data with each other. Network nodes exchange control information from a

source device to a destination device. The task of information exchange among communication

networks involves tremendous complexity. The communication task is broken down into subtasks. These subtasks are organized into a number of layers. Each Higher layer uses the service provided by the lower

layer and in turn provides service to the layer above it.

SWITCHING TECHNOLOGIESCommunication networks can be classified into three

categories: Circuit switching: Dedicated communication path is established between

two stations. Communication session involves three phases:

Circuit establishment Data transfer Circuit termination

Packet switching: Data are transmitted as packets or datagrams,

appended with a header or trailer.

SWITCHING TECHNOLOGIES(CONTINUED…) Each packet carries routing information and is

forwarded through the network from node to node. Virtual circuit switching: It is a hybrid technology combining features of both

circuit switching and packet switching. As in circuit switching, a virtual circuit is established. As in packet switching, data are transmitted as

packets. As in circuit switching, all packets of the same session

follow the same path. As in packet switching, packets from different virtual

circuits may be interleaved.

ENCAPSULATION AND MULTIPLEXING When the packets arrives at the destination, it is sent

up through the protocol stack. At each layer, the corresponding header and trailer are

stripped. A communication process running in a host is assigned

a unique port number. This unique port number is carried by all the packets

generated by or designed to this process. A field called frame type in the Ethernet header is used

for multiplexing and demultiplexing.

NAMING AND ADDRESSING A domain name is used to identify a host, such as

www.google.com identifies a Google server. A domain name is more user friendly. Domain names are organized into a tree structure. Port numbers are as addresses for user processes

running in the application layer. In a client-server architecture, a server uses a well-

known port number(smaller than 1024). A client uses ephemeral port numbers that are

randomly chosen and are larger than 1023.

MULTIPLE ACCESS Simplest way of interconnecting two computer hosts is

using a point-to-point link with a host on each end. As the number of hosts increases, this approach may be

inadequate. To share the common media efficiently, all hosts must

follow a set of rules to access the media. Each host should have a fair chance to access the

media. Hosts should not be allowed to take the access media

forever.

ROUTING AND FORWARDING Internet routers are responsible for delivering packets

from source to destination. Routing and forwarding consists of two closely related

parts Maintaining network topology Forwarding packets. Routing information is derived from network topology

and stored in a data structure called routing tables. When there is a packet to deliver, a router consults the

routing table to find out where to forward the packet.

CONGESTION CONTROL AND FLOW CONTROL The receiver will notify the sender how much data it

can receive without causing buffer overflow. Then the sender will not send more data than the

amount allowed by the receiver. The sender may be explicitly notified about the

congestion in the router. then the source will reduce its sending rate until

congestion is dissolved. TCP uses slow start and congestion avoidance to react

to congestion in the network.

NEW CHALLENGES IN WIRELESS NETWORKS Wireless Transmissions: Wireless transmissions consume radio frequency spectrum

in the network area. Mobility: In infrastructure-based wireless networks, each mobile user

is associated with a fixed base station for transmitting and receiving data.

Energy Efficiency: Mobile nodes are usually powered by the batteries they

carry. In infrastructure-based wireless networks, when a node

dies, there is no significant impact on the network topology.

MULTIPLE ACCESS SCHEMES Polling: A polling system is a special types of queuing system

with one server and m stations. Each customer requests service from the server and

departs the system when its service is completed. Any customer that arrives when the buffer is full is

dropped. When the server finishes serving a station, it may

decide which station to serve next. ALOHA and Slotted ALOHA

MULTIPLE ACCESS SCHEMES(CONTINUED..) With pure ALOHA, a station transmits a packet

whenever it wants to. Pure ALOHA is a very simple multiple access

protocol, but its throughput is very low. The exact scheduling of ALOHA is complicated and

hard to analyze. Slotted ALOHA is an extension of pure ALOHA for

improved throughput. Time is divided into slots, and the length of one time

slot is equal to the packet transmission time.

CONGESTION CONTROL IN WIRELESS NETWORKS Congestion control is a key function of the transport

layer. A router buffer is shared by multiple independent

sessions in a store-and-forward communication network.

When the instantaneous arrival rate is higher than the output rate, the router buffer occupancy grows.

Congestion occurs when the buffer is overflow, resulting in packet loss.

CONCLUSION Networks are becoming a strategic cornerstone for

organizations in every industry. As companies explore new global marketplaces and

virtual organizations, they really increasingly on electronic communication.

Access to networks becomes a crucial component of business maneuvers in today’s business environment.

REFERENCESReferences:

1. Cognitive Radio Communications and Networks: Principles and Practice by Alexander M. Wyglinski, Maziar Nekovee, Thomas Hou

2. Local control of cognitive radio networks: Christian Doerr · Dirk Grunwald · Douglas C. Sicker

3. Communication Network http://www.samson.de/pdf_en/l155en.pdf

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