|
|
|
|
Home / Computers / Computer Certification
Cisco CCNA Certification: Error Detection vs. Error Recovery
By:Chris Bryant, CCIE #12933
Passing the CCNA, Intro, and ICND exam is all about knowing and noticing the details. (Which makes perfect sense, since becoming a master networking administrator or engineer is also about noticing the details!) One such detail knows the difference between error detection and error recovery. While the terms are sometimes used interchangeably, they are not the same thing.
Error detection is just that - error detection only. Two common error detection methods are found at the Data Link layer of the OSI model, the FCS (Frame Check Sequence) and CRC (Cyclical Redundancy Check). A mathematical equation is run against the data in the frame, and the result is sent along with the data. The receiver runs the equation again, but this time. If the result is the same, the frame is considered valid; if the result is different, the frame is considered corrupt and is discarded.
Note that the FCS and CRC do nothing in regards to retransmission. They are strictly error detection schemes.
For an example of error recovery, we look to the Transport layer, where TCP runs. TCP performs reliable delivery, and the reason we call it "reliable" is that TCP uses sequence numbers to detect missing segments. If the sender determines from the sequence numbers that the remote host did not receive transmitted segments, the sender will retransmit the missing segments.
The key to keeping the terms straight in your head is to remember that while both error detection and error recovery both detect problems, only error recovery does anything about it. It's also worth reading an exam question twice when you see either term!
Article Source: http://www.dailynewarticles.com
Chris Bryant, CCIE #12933, is the owner of The Bryant Advantage (www.thebryantadvantage.com), home of free CCNA and CCNP tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages. Video courses and training, binary and subnetting help, and corporate training are also available. Pass the CCNA exam and BSCI exam with Chris Bryant, CCIE #12933!
For a copy of his FREE ebooks, “How To Pass The CCNA” and “How To Pass The CCNP”, visit the website and download your copies! Get your CCNA certification with The Bryant Advantage!
More Articles from Computer Certification Category:
Cisco CCNP Certification / BCMSN Exam Tutorial: Writing QoS Policy
Cisco CCNP / BCSI Exam Tutorial: Configuring EIGRP Packet Authentication
Cisco CCNP / BSCI Certification: Introduction To ISIS Terminology
What To Expect When Taking Your First Cisco Certification Exam
Cisco CCNA / CCNP Home Lab: Why You Need An ISDN Simulator
Be Certifiable! The Basics Of MCSE And MCP
Cisco CCNP / BCSI Exam Tutorial: Broadcasts And The IP Helper-Address Command
Webroot Window Washer
Cisco CCNA / CCNP Home Lab Tutorial: Using 2520 Routers
CCNA / CCNP Home Lab Tutorial: The VLAN.DAT File
Cisco CCNP / BCMSN Exam Tutorial: Changing Root Bridge Election Results
CCNP Certification / BCMSN Exam Tutorial: HSRP MAC Addresses And Timers
Cisco CCNP / BCMSN Exam Tutorial: Switches, QoS, And Cisco's Networking Model
Cisco CCNA Exam Tutorial: Troubleshooting Directly Connected Serial Interfaces
How To Earn Cisco’s Firewall Specialist Certification
|
|
