Tip of the Week – 04 Feb 2011

Tip of the Week: Latency is signal delay which is caused by the transmission equipment and the transmission medium (fiber for this industry).  For Ethernet systems it refers to packet delay.  It’s typically measured in units of milliseconds (“ms” 1E-3 seconds), microseconds (“us” 1E-6 seconds) or nanoseconds (“ns” 1E-9 second). Light travels much slower in a glass fiber than in air and therefore signal latency in a fiber is a much greater in a length of fiber than an equal distance between microwave towers. A 100 km (62 mile) length of standard single mode fiber has a latency of about 0.49 ms.  Therefore, if a fiber communications system is looking for a response from a remote site 100km away, the response will take at least 1 ms to occur if there is no additional delay from the transmission equipment.  Latency for signals passing through equipment such as repeaters, switches, routers, and SONET equipment can vary greatly from a few nanoseconds to more than 1 second. To calculate the overall link latency, sum up all the individual equipment latencies and add it to the overall fiber latency.  Equipment latency is available from the manufacturer.  If you are using standard single mode fiber, its latency is 4.9 us/km. Latency is often specified in service-level agreements (SLA). For voice traffic, a round-trip delay of 250 ms or greater is noticeable by the speakers.  Some SLA require round trip latency to be less than 60 ms. Pertinent Products/Services: Need to expand your fiber network?  Give us a call. Telecom Engineering has products that can expand fiber capacity up to 160 DWDM channels. Some features include:
  • DWDM Channel Tunable XFPs, 44/80 channel, multirate, 10GigE, OC-192, 80 km, 102 channels JDSU
  • Fixed channel DWDM XFPs, 80 km, great price
  •  DWDM Lite Channel Tunable Transponder, 44/80/160 channel, long reach up to 300 km, tunable to any DWDM channel
  • CWDM XFPs, multirate 10GigE / OC-192
  •  DWDM SFPs, various reaches
  •  EDFA Lite optical amplifiers
  •  DWDM channel tunable 10G transponder, latency of only 13 nanoseconds 
To view our products and services, surf to http://www.TelecomEngineering.com/products.htm To learn more about this topic and other fiber optic network topics, refer to my following books (publisher McGraw-Hill): “Planning Fiber Optic Networks”, ISBN 0-07-1499199 available from Amazon.com .  Table of contents can be seen here :  http://www.TelecomEngineering.com/products/resources/planningfibernetworks.htm , “Fiber Optic Installer’s Field Manual”, ISBN 0-07-135604-5 available from Amazon.com. Table of contents can be seen here http://www.TelecomEngineering.com/products/resources/field-manual.htm .  Did you miss last week’s Tip?  If so feel free to peruse this month’s archived Tips at https://www.telecomengineering.com/About_us/Tip_of_week/tipofweek.htm Contacts: For information about our products and pricing contact us at toll free 1-888-250-1562 . If you have any questions regarding this tip or other fiber networking concerns, please feel free to email me at BChomycz@TelecomEngineering.com. To unsubscribe from this email newsletter Click Here or reply to this email and in subject line place “Unsubscribe”. To add a new subscription to this email newsletter Click Here or reply to this email and in subject line place “Subscribe”. Please feel free to forward this email to other industry professionals that may be interested in this newsletter. *Note: All prices shown are in US$ and products are shipped FOB Minnesota, USA. Prices may change without notice. Bob Chomycz, P.Eng. President Telecom Engineering Inc. Toll Free:  1.888.250.1562 www.TelecomEngineering.com