LAN Protocol Overview

Published February 3, 2010 David Stahl , Routing & Switching Leave a Comment
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Network technologies can be classified as belonging to one of two basic groups.

  1. Local area network (LAN) technologies connect many devices that are relatively close to each other, many times within the same building. For instance, the computer data terminals in your favorite library have replaced card stacks and are used to display book information. These terminals would normally connect to each other, as well as the data base server, over a local area network.
  2. Wide area network (WAN) technologies connect a number of devices that can be many kilometers apart. For example, if there are two or more libraries in different areas of a large city, and they wanted to share their book catalog information, they would most likely make use of a WAN technology.

As you pursue your studies of the technologies that make up the CCNA core of subjects, you will note that quite a bit of time is dedicated to the subject of LANs. And, most of the study material teaches that there are three primary protocols used in LANs: Token Ring, FDDI, and Ethernet. Continue reading ‘LAN Protocol Overview’

The Beginnings of Ethernet

Published February 1, 2010 David Stahl , Routing & Switching Leave a Comment
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Although not usually covered in training materials, it is interesting to note where Ethernet originally came from. Like many of the early networking protocols, the principles of Ethernet were developed inside a corporation that was looking to solve a specific problem.

Xerox needed an effective way to allow a new invention, called the “personal computer”, to be connected in its offices. In 1973, at the Palo Alto Research Center, researcher Bob Metcalfe designed and tested the first Ethernet network. While working on a way to link Xerox’s Alto computer to a printer, Metcalfe developed the physical method of cabling that connected devices to each other on an Ethernet network.

From that, Ethernet was conceived. Eventually, Xerox teamed with Intel and Digital Equipment Corporation (DEC) to further develop Ethernet, so the original Ethernet became known as DIX Ethernet, referring to DEC, Intel, and Xerox.

The Institute of Electrical and Electronics Engineers (IEEE) took over the LAN standardization process in the early 1980s. And, since that time, the IEEE has defined many Ethernet standards to support the widely varying needs for building a LAN, such as the needs for different speeds, different cabling types, trading off distance requirements versus cost, and other factors.

Ethernet has since become the most widely accepted and deployed LAN network technology in the world. It has grown to encompass new technologies as computer networking has matured. However, the mechanics of operation for every Ethernet network today stem from Metcalfe’s original design.

The original Ethernet concept described communication over a single cable that is shared by all devices on the network. Once a device was attached to the cable, it had the ability to communicate with any other attached device. This process allows the network to expand to accommodate new devices without requiring any modification to those devices already on the network.

Author: David Sthal

Frequently Used UPS Technologies

Published January 28, 2010 David Stahl , Routing & Switching 1 Comment
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As we discussed in a previous post, an Uninterruptible Power Supply (UPS) is an electrical apparatus that provides emergency power to a load when the input power source fails. It does this by means of one or more attached batteries and associated electronic control circuitry. A UPS differs from an auxiliary or emergency power system in that it provides instantaneous (or nearly so) protection from input power interruptions. However, the on-battery runtime of most UPS systems is relatively short, with 5-15 minutes being typical for smaller units. Although this period seems relatively short, it is sufficient to allow time to bring an auxiliary power source on line or to properly shut down the protected equipment.

UPS units are divided into categories that are based on what type, and in some cases the number of different power related problems they address. The general categories of modern UPS systems are online, line-interactive, and standby.

Online
The Online UPS is ideal for environments where electrical isolation is necessary or for equipment that is very sensitive to power fluctuations. Although this technology was once previously reserved for very large installations of 10 kW or more, advances in technology have permitted it to now be available as a common consumer device, usually supplying 500 watts or less. Continue reading ‘Frequently Used UPS Technologies’

Tame the Smartphone Monster

Published January 27, 2010 Unified Communications Leave a Comment
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Cisco’s online TechWise TV channel tackles making smartphone users more productive by giving them access to powerful unified communications and collaboration tools on virtually any mobile device. Take control of the mobility revolution and support your smartphone users while maintaining security policies and reducing mobile communications expenses.

Live Cisco WebCast on TelePresence

Published January 25, 2010 Unified Communications Leave a Comment
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Cisco is holding a live, 1 hour webcast on Thursday, February 18 to discuss the “Engineering Behind TelePresence”. According to their site:

“If you are like many IT professionals, you might be under the impression that this newest collaboration solution requires that you add tons of bandwidth or overhaul your entire network.

“TechWiseTV shatters these and other myths and reveals the realities of TelePresence deployment. Gain the engineering insights and the technical know-how you need for a smooth and successful implementation. Discover the latest innovations behind the technology and why these have made widespread adoption much simpler than you might have thought.”

Register for free at Cisco’s web site.

The Importance of a UPS

Published January 25, 2010 David Stahl , Routing & Switching 1 Comment
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In light of the recent tragic events in Haiti, it might be a good time to review some of the requirements for a well designed Uninterruptible Power Source (UPS) to be included in all of our critical network installations. As a CCNA, we are called upon to help maintain the continued operation of networks during any type of power outage caused by either supplier failures or what is often referred to as “Acts of God,” such as tornados, hurricanes or, in this case, a 7.0 earthquake.

After the devastating earthquake in Haiti, it became obvious that the country had lost most of its ability to provide any type of communications, either within the country or with the rest of the world. This blackout covered all of the most commonly used media, including the Internet, telephone, or radio. Although there were isolated instances of messages getting out, Haiti was essentially isolated, even though surrounded by neighboring countries and possible first responders.

Although we are usually only faced with incoming power source problems, they can, by themselves, bring down any normal network operation. Depending on where we live, we normally refer to our power sources as coming from household power, household electricity, power lines, domestic power, wall power, line power, AC power, city power, street power, and grid power. No matter what we call the “power source”, the loss of any normal supply can leave us with dead equipment. It is important to understand the most commonly used terminology when discussing UPS capability. Continue reading ‘The Importance of a UPS’

Quality of Service Part 8: Congestion Management

Published January 22, 2010 Paul Stryer , Unified Communications Leave a Comment
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In part 8 of this series we are going to unravel the mysteries of congestion management and its four main queuing methods.

Congestion is the result of many factors and can occur in many places on the network. A few of the reasons for congestion are traffic aggregation points, network transit points, speed mismatches, oversubscription, and insufficient packet buffers. Aggressive traffic can fill interface queues and starve more time sensitive flows such as voice and video. Increasing bandwidth is not an adequate fix to solve these issues. By using queuing algorithms to sort traffic and determine a method of prioritizing traffic, the routers can solve specific network traffic issues which in turn can increase network performance.

There are two hardware components; hardware and software. Hardware queuing always uses FIFO queueing, and software queueing is used if the hardware queue is full. A full hardware queue indicates interface congestion and a software queue is used to manage that congestion.

To control congestion, the device using the congestion management tools must determine the buffer queues the packets are to be queued in and what order in which packets are sent out an interface based on the priority assigned to those packets. Congestion management tools must perform these tasks to function as suggested.

  • Create Queues
  • Assign packets to queues based on the packet classification
  • Schedule the packets for transmission

There are four types of queuing mechanisms in the congestion management feature set. Each mechanism is fully customizable to specify different number of queues and the order in which the traffic is serviced. Only one queueing mechanism type is allowed to be configured on each interface.

Continue reading ‘Quality of Service Part 8: Congestion Management’

Quality of Service Part 7: Service Policy

Published January 20, 2010 Paul Stryer , Unified Communications 2 Comments
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In part six of this blog series we discussed that Marking was considered to be what will be done with the traffic after it has been classified. Now, we will talk about service policy which are considered as the part of QoS where the policy is implemented.

Service Policy
Once you have defined the class-maps, and policy-maps, the policy is attached to the inbound or outbound packets using the service-policy command. It is possible to assign a single policy map to multiple interfaces or assign multiple policy maps to a single interface. There is a maximum of one service-policy command in each direction, inbound and outbound.

Example 1

Class-map ef
      Match access-group 10
!
Class-map af11
      Match access-group 20
!
Class-map af21
      Match access-group 30
!
Policy-map mark_traffic
      Class ef
      Set ip dscp ef
!
      Class af11
      Set ip dscp af11
!
      Class af21
      Set ip dscp af21
!
Interface serial0/0<
      Service-policy input mark_traffic
!
Access-list 10 permit 192.168.100.0 0.0.0.255
Access-list 20 permit 192.168.101.0 0.0.0.255
Access-list 30 permit 192.168.103.0 0.0.0.255

In the next part of this series on QoS we will look at congestion avoidance.

Author: Paul Stryer

References

UCM IP Phone Services, Part 2

Published January 18, 2010 Joe Parlas , Unified Communications Leave a Comment
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One of the most interesting concepts Cisco came up with is to provide the ability to advertise services to all Cluster IP Phone users without requiring them to subscribe to that service. So, if you company has an “all employee” web service, you can quickly setup the service, and then magically have it automatically show up when the employees search for services by selecting the service button on their respective IP Phones.

But, in order to do this, you must select a box at the beginning of the web service creation to enable it for “Enterprise Subscriptions’. We are going to step through how to configure extension mobility service for all IP Phones in the cluster.
Continue reading ‘UCM IP Phone Services, Part 2′

Routing Protocol Families

Published January 18, 2010 David Stahl , Routing & Switching Leave a Comment
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In packet switching networks, routing directs packet forwarding, the transit of logically addressed packets from their source toward their ultimate destination through intermediate nodes. These nodes are 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 that 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.

The decision of which routing protocol to configure and use must consider many different factors. One of those factors is which branch or family of routing protocols to implement. There are three main branches or families of routing protocol algorithms; Distance Vector, Link-State, and Balanced Hybrid. Each family has distinct functions and features that can provide a desired functionality. Each family also presents certain deficiencies that may preclude its use in modern networks.

Continue reading ‘Routing Protocol Families’

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