The paper focuses on the Logical link control(LLC) part of the link layer without taking into account improvements that can be made at the Medium access control(MAC) part to reduce non-congestion related errors. A major reason why Ethernet provides better performance is due to a robust collision detection mechanism called carrier sense multiple access(CSMA) with collision detection(CD). This layer prevents hosts from transmitting simultaneously on the channel resulting in damaged frames. So it doesn't allow damaged packets to propagate up the stack and cause unnecessary retransmissions at the LLC layer which can interfere with TCP retransmissions. We know that collision detection is harder in wireless networks due to the “hidden-terminal” problem. But we can still use “collision avoidance” mechanisms to ensure that no two hosts transmit simultaneously. Collision avoidance mechanisms can be conservative – that is they have back off timers that gradually increase the back off intervals when an ack is not received. Instead of backing off, we can employ a more aggressive approach, so that frames are transmitted as soon as an idle channel is sensed. If there is an error, then the sender will not hear an ack within the timeout interval and can retransmit. Issues with End-to-end schemes The major issue in this scheme is that the paper assumes perfect knowledge about wireless losses to generate explicit loss notification(ELN information). This information is then propagated to the TCP sender which takes corrective action based on the type of error. In a real world implementation, it is impossible to accurately identify packets lost due to errors on a lossy network. This is mostly because the only other entity between the source and the ... ... middle of paper ... ...acket. This will require the TCP layer to be enhanced to identify and handle different types of errors. 802.11 uses CSMA/CA to sense if the channel is idle before making a transmission. The exponential back off strategy can adversely impact performance. So in situations where there are more than a certain number('N') of hosts accessing the same wireless link, we can have an arbiter that decides which host has access to the link. In situations where there aren't enough hosts, they can fall back to an aggressive version of CSMA that doesn't have large back off timers. A hybrid approach like this will help reduce non-congestion errors on a wireless link and boost TCP performance. A robust error handling mechanism will make sure that the TCP congestion window size doesn't fluctuate unnecessarily and also avoid duplicate retransmissions and competing retransmissions.
The 802 committee and the OSI model both relate to one another. The OSI model shows how the layers of the internet are able to communicate and function with each other. While the 802 committee will add onto that by showing how network protocols should function. With that being said there are numerous working groups under the 802 committee however the one that I will be writing about is the 802.2 or the logical link control (LLC). The logical link control is in the 2nd layer (data-link) of the OSI model. The purpose of this protocol is flow and error control along with multiplexing and demultiplexing. How multiplexing works is by getting multiple data streams and combining them into one shared stream. This is mainly seen in the common forms
COMP09022 Network Design BSc COMPUTER NETWORKING COMP09022 ICMPv6 Prepared by B00270675 13-03- 2015 WORD COUNT (0000) TABLE OF CONTENTS TITLE PAGE……………………………………………... 1 TABLE OF CONTENTS………………………………….. 2 INTRODUCTION TO THE REPORT……………………. 3 TABLE OF FEATURES.......................................................4
A state variable known as congestion window is implemented by the TCP protocol which stops the clogging of the network by regulating and putting a limit on the data that is sent on the network in turn reducing congestion, timeouts and lost packets.
Ethernet is often built into hardware devices such as network interface controllers, to allow the sending and receiving of data packets to that piece of hardware. Ethernet can be used to create a wired local area network, which can subsequently communicate with other LAN’s, ad infinium, which in turn creates the internet. Ethernet uses a system called CSMA/CD or Carrier Sense Multiple Access with Collision Detection. This system is able to deal with collisions which happen when two messages are sent at the same time. When two nodes on a network attempt to exchange data at the same time, they collide and create an error. When this happens, all nodes involved are notified. The Ethernet protocol will then set a random time interval, after which the node will re-attempt the transmission. This will be done until the message is successfully sent. Just as the hypertext transfer protocol and transmission control protocols will be used every single time a student at PCO’s learning centre accesses internet, so too is the ethernet protocol. This, however, will be done in a slightly different way. As the students will be using Wi-Fi to connect to the modem, ethernet will not be used. In saying this, ethernet will be used to connect to the NAS and the printer. For example, if two students want to print something, and they do so at the exact same time, the messages will collide. As the printer is connected through ethernet, the printer, and two computers will be notified of the collision. The ethernet protocol will then set a random time interval, and the printing request will be sent again at different times for each computer. Although this is a reasonably complex process, in real time, the students will have no idea this is happening, and the printer will print both students documents like nothing has
If the network is badly congested than the ACK for the combined set of packets can be delayed. As the source using the Nagle algorithm awaits the ACK it can introduce an inadvertent additional latency (Wikipedia,
SPI – Stateful Packet Inspection – is a method of monitoring the state of active connections in order to determine what packets to allow access through a firewall.
J. A. Gutierrez ,M. Naeve , E. Callaway , M. Bourgeois ,V. Mitter and B. Heile "IEEE 802.15.4:adeveloping standard for low-power low-cost wireless personal area networks", IEEE Network, vol. 15, no. 5, pp.12 -19 2001
Wireless Local Area Network (WLAN) is one of the most successful technologies in IEEE 802.XX standards family. WLAN provides free connectivity, mobility, and flexibility with a relatively low cost for users. The widespread use of WLAN technology in streaming videos and voice applications stimulated high bandwidth capacity for WLANs. Recently IEEE has announced latest WLAN standard 802.11ac. For 802.11ac to be effective, it requires minimum 80 MHz wide channel with optionally up to 160 MHz. The increase in bandwidth leads to problems like OBSS. OBSS problem occur when two or more BSSs operate in same channel and are close to hear each other. This is an undesirable situation where two or more BSSs compete for channel access and increase contention which ultimately degrades performance/efficiency of the WLAN system [1]. The problem was not critical with 802.11a/b/g/n where the channel bandwidth was reasonable. ...
Wireless local area networks (WLANs) have the potential to improve the flexibility, productivity, and the quality of work life of an enterprise (Sage Research Staff, 2001). Berean Institute is a typical two year college with about a staff of sixty eight employees and 250 students per semester. Berean teaches cosmetology, barbering and the latest software and hardware technology, which is located in Philadelphia, Pennsylvania. Berean currently has two locations in the Philadelphia area and using a Local Area Network (LAN).
Wireless technology has come from the basics of cellular usage to sensors in the medical field. Wires are now a thing of the past in today’s world with technology forever revitalizing. Wi-Fi (Wireless Network) or 802.11 networking is a phenomenal way of providing wireless Internet at a low cost. Using radio waves, a wireless network connects a PC, mobile phone or just about anything that connects to the internet wirelessly via a router.
During the silent period of the communication when the users are not utilizing the bandwidth than this idle bandwidth cannot be used by the other parties as a result this bandwidth gets wastes.
In fact, according to several studies, more than half of all network attacks are committed internally. To determine the best ways to protect against attacks, we should understand the many types of attacks that can be instigated and the damage that these attacks can cause to data. The most common types of attacks include Denial of Service (DoS), password, and root access attacks.... ... middle of paper ... ...
Wireless is everywhere today whether at home working from your WIFI network to work where you might be linked a wireless network or even through your phone through a 3G or 4G network to connecting to an open wireless networks. As you can see for the most part people are connecting to wireless from the moment they leave their home till they get to work and then back. While wireless comm...
The goal of this paper is to define and explore the MD5 checksum utility. It is also my goal to discuss how to use MD5 checksums to support Incident Response.
McCabe, Karen. "IEEE Ratifies 802.11n, Wireless LAN Specification to Provide." 11 September 2009. IEEE Standards Association. 4 April 2010 .