1. Presented By: Vasantha Lakshmi Gutha Graduate student (CS) Course: CENG 5931 University of Houston-Clear Lake Guthav6317@uhcl.edu Spring 2011

2.  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

3.  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.

4. Communication 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.

5.  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.

6.  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.

7.  A domain name is used to identify a host, such as www.google.com identifies a Google server. www.google.com  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.

8.  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.

9.  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.

10.  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.

11.  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.

12.  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

13.  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.

14.  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.

15.  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.

16. References: 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