Thursday 28 January 2010

DOCSIS - Data-Over-Cable-Service-Interface-Specification

DOCSIS - Standard certification of cable equipment vendor devices

Sets out the physical and MAC layer standards

Defines RF interface requirements over data systems

Equipment must pass certification by CableLabs, Texas instruments, Netgear, Motorola (et al).

In Europe, EuroDOCSIS is the standard

Physical Specs include channel widths and modulation

MAC Layer specs include Access Method (e.g. TDM or Synchronos Code Division Multiplex Access)

Links :
DOSCIS on Wikipedia
Cisco ITH - Cable Technologies

Wednesday 27 January 2010

Cisco CCNP - TSHOOT 642-832 study materials

Here are links to the study materials for the new Cisco CCNP TSHOOT 642-832 exam:

Cisco CCNP TSHOOT 642-832 Offiicial Certification Guide - Click here
Cisco CCNP TSHOOT 642-832 Cert Kit - Click here
Cisco CCNP TSHOOT 642-832 Cert Flash Cards Online - Click here
Cisco CCNP TSHOOT 642-832 Quick Reference (Coming Soon) - Click here

Cisco CCNP - SWITCH 642-813 study materials

Here is a list of study matierials available for the Cisco CCNP SWITCH 642-813 exam:

Cisco CCNP SWITCH 642-813 Offical Certification Guide - Click here
Cisco CCNP SWITCH 642-813 Cert Kit - Click here
Cisco CCNP SWITCH 642-813 Cert Flash Cards Online - Click here
Cisco CCNP SWITCH 642-813 Portable Command Guide (Coming Soon) - Click here
Cisco CCNP SWITCH 642-813  Quick Reference (Coming Soon) - Click here

Cisco CCNP - ROUTE 642-902 Study materials

Here is a list of Cisco CCNP ROUTE Study materials, presently only available from Cisco Press.

Cisco CCNP ROUTE 642-902 Official Certification Guide - Click here
Cisco CCNP ROUTE 642-902 Cert Kit - Click here
Cisco CCNP ROUTE 642-902 Flash cards online - Click here
Cisco CCNP ROUTE 642-902 Portable Command Guide (Coming Soon) - Click here
Cisco CCNP ROUTE 642-902 Quick Reference Guide (Coming Soon) - Click here

CCNP Revised track

Here it is folks! -

Cisco have announced the new structure for the CCNP and on first glance it looks good.

Reduced from 4 exams to 3, with each one 2 hours long (up from 90 minutes) the emphasis has shifted to more real world application of the subjects including design, deployment, verification and troubleshooting of the subject matter. Expect there to be more configuration type questions on the exam.

If you're like me and are unsure how the new exams affect your studies you can use the Exam Configuration tool - - work out how best to proceed.

For me, I'm taking my ISCW on Friday and am scheduled to start the  BSCI in Feb. So long as I pass the exam first time I think my track will be : BSCI + SWITCH + TSHOOT

So that'll still be 4 exams for me but what you gonna do when the firm is paying :o)

All the best with your studies!

Tuesday 5 January 2010

ADSL Coding Techniques

ADSL has a number of coding techniques:
i) Single Carrier - uses Carrierless Amplitude and Phase Modulation (CAP) - Proprietary
ii) Multiple Carrier - uses Discreet MultiTone Modulation (DMT) - Multiple Carrier Standard
iii) Multiple Carrie with G.lite - uses slower speeds but doesn't require the signals to be split at the subscriber end. Most popular method for mass market.

ADSL Data Rates

ADLS data rates as follows:
ADSL = 8Mbps for 18,000ft
ADSL2= 12Mbps for 8,000ft
ADSL2+= 24Mbps for 5,000ft

1Mbps for upstream data requests.

Monday 4 January 2010

DSL Distance Limits

DSL                       Max Data Rate       Distance (Feet/KM)
ADSL                    8M/1M                   18,000/5.5
VDSL                    52M/13M               4,500/1.4
IDSL                     144k/144k              18,000/5.5
SDSL                    768k/768k              22,000/6.7
G.SHDSL             2.3M/2.3M             28,000/8.5

Factors that affect distance:
Signal Attenuation
Bridge Tap - an extra telephone wirte with an un-terminated cable end connected to the local loop, can cause noise, reflection, raqdiate power to reduce signals and therefore speed
Local Coils - Wrap of excess wire along the local loop
Wire Gauage - thickness of wire, high speeds use thick wire
Impodence Mismatch - noise/echo on the line
Crosstalk - interference
AM Radio interference
Fibre Optics - ADSL signals cannot pass thorugh the conversion from Analog to Digital to Analog that occurs if a portion of the telephone circuit traverses fibre.

DSL Variants

DSL Differs in:
i) Nature - Is it Symmetrical or Asymmetrical?
ii) Max Data Rate - i.e. max speed deployed
iii) Live Coding Technology - technique used to deploy signall to copper wire
iv) Data/Voice Support - Certain DSL types do not support both data and voice at the same time
v) Max Distance - Distance DSL signals can span

DSL            Nature              Max Rate               Data+POTS
ADSL         ASym              8m/1m                     Yes
RADSL      ASym              Adaptable                Yes
VDSL         Both                52m/13m                 Yes
IDSL          Sym                 144k/144k               No
SDSL         Sym                 768k/768k               No
HDSL        Sym                 2M/2M                    No
G.SHDSL  Sym                 2.3M/2.3M              No

Digital Signals over Radio Waves

Frequency - rate at which current (voltage) cycles occur, that is, number of 'waves' per second

Radio waves occur in electromagnetic spectrum between 1Khz and 1Terahertz.
Cable uses part of RF spectrum.
Cable can transmit simultaneously in both directions, RF portion is split in to :
i) Downstream - Head --> Subscriber at 810Mhz of RF Band (50 --> 860Mhz)
ii) Upstream - Subscriber --> Head with 37Mhz of RF Band (5 --> 42Mhz)

Downstream Frequency is split in to channels (6Mhz in US, 7-8Mhz in Europe)
TV Spectrum:
VHF low band = tv channels 2-6
VHF Mid band = tv channels 98,99,+14 to 22
VHF High Band= tv channels 7 to 13
VHF Superband = tv channels 23 to 36
VHF Hyperband = tv channels 37+

No channels for Upstream

New Year - New Updates

Hello, the next few postings are going to be a dump of stats and figures relevant to typical questions that you'd expect to get on the exam.

Apologies if it's a bit dull/brief.