Studying Wide Area Networks in the Classroom
Networking currently is taught at many places, and the majority of hands-on learning is done with local area networks (LANs). Even though wide area networks (WANs) are commonly used, course work typically is limited to theory, and students receive little or no practical experience using them. Reasons for this include the high cost of deploying and maintaining a WAN, the lack of WAN test equipment that runs on PC hardware and the impracticality of maintaining commercial data lines for strictly experimental purposes.
One product available for overcoming the obstacles in creating WAN labs is the Sangoma WAN EduKit. Seneca College of Applied Arts & Technology in Toronto is one educational center that is using this toolkit to successfully increase the number of WAN labs available for student use.
A wide area network connects LANs that are typically separated by great distances. The best known example of a WAN is the Internet itself. A smaller-scale example is a network that connects a company's corporate headquarters with branch offices in other cities.
The actual connection (e.g., a leased line or satellite) between the points is handled by a provider, such as the telephone company. The carrier has a point of presence (POP) at each end of the link to which the company connects their equipment.
At each separate site, a company would configure a router containing a WAN adapter card to connect to their carrier's POPs. WAN adapters can communicate over the provider's network using a variety of protocols, including frame relay, HDLC, X.25, SDLC, BSC, PPP and SS7. Because the Sangoma WAN EduKit provides software and sample labs for frame relay and X.25, these protocols are explained briefly below.
Frame relay is a simplified form of packet switching in which synchronous frames of data are routed to different destinations depending on header information. When frame relay is used to communicate over a WAN, the computers containing the WAN adapters are called customer premises equipment (CPE). These connections are identified by a number called a data link connection identifier (DLCI).
Once the hardware is in place to connect each office to the carrier's POPs, a path is established that allows information to be routed between them. This path is called a permanent virtual circuit or PVC, and it is always on as long as the equipment is working. The DLCI is used by the CPE to indicate which of the potentially several different PVCs configured by the provider is the correct recipient of the frame.
The maximum rate at which the carrier guarantees packets can be transmitted over the PVC without packet loss is called the committed information rate (CIR). Some providers offer the capability to specify different CIRs for inbound and outbound traffic along the PVC.
Because frame relay doesn't guarantee packet integrity, it can switch packets end to end much faster than X.25. For packet integrity, the company's routers could use a protocol such as TCP/IP to create packets encapsulated within the frame transmitted over the WAN.
The X.25 protocol is a packet switching protocol that defines an international recommendation for the exchange of data as well as control information. X.25 guarantees data integrity and network managed flow at the cost of some network delays.
The computer connected to the carrier's POP is known as the data terminal equipment (DTE), and the network node is called data circuit terminating equipment (DCE). Connections over the network occur on logical channels of two types: switched virtual circuits (SVCs) and permanent virtual circuits (PVCs).
SVCs are similar to telephone calls; a connection is established, data is transferred and the connection is released. Each DTE on the network is given a unique DTE address that can be used like a telephone number. X.25 PVCs operate in the same manner as the PVCs discussed in the frame relay section.
X.25 uses a store-and-forward mechanism that allows DTEs to have different line speeds, but this can introduce a noticeable delay when the blocks transferred between them are small. The store-and-forward mechanism also has a large requirement for buffering, which can make X.25 less cost-effective than frame relay.
For more information on wide area networks, I recommend reading Linux Routers written by Tony Mancill and published by Prentice Hall PTR.
Practical Task Scheduling Deployment
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
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|The Firebird Project's Firebird Relational Database||Jul 29, 2016|
|Stunnel Security for Oracle||Jul 28, 2016|
|SUSE LLC's SUSE Manager||Jul 21, 2016|
|My +1 Sword of Productivity||Jul 20, 2016|
|Non-Linux FOSS: Caffeine!||Jul 19, 2016|
|Murat Yener and Onur Dundar's Expert Android Studio (Wrox)||Jul 18, 2016|
- Stunnel Security for Oracle
- The Firebird Project's Firebird Relational Database
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- SUSE LLC's SUSE Manager
- Managing Linux Using Puppet
- My +1 Sword of Productivity
- Non-Linux FOSS: Caffeine!
- Doing for User Space What We Did for Kernel Space
- SuperTuxKart 0.9.2 Released
- Google's SwiftShader Released
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide