Capacity Unit 26 Design a small or home office network HND in Computing and Systems Development

Capacity bandwidth to internet local internet contention ratio Internal network bandwidth internal network contention ratio bandwidth requirements applications users devices

Internet bandwidth Web bandwidth means the amount of data transferred in a prescribed period of time Web – need to know: Number of pages on the site Average file size of a page Number of visitors per day Web bandwidth = Pages x File size x Visitors 10 x 40k x 60 = 2.4MB/day or 72MB/month

Web bandwidth Typical page sizes BBC News, about 650kB CNN, 900kB The Verge 7.36MB Determine the page sizes and number of pages for http://www.carved.com/ Then calculate and graph the web bandwidth required for 10, 100, 1000 page hits/month (use a spreadsheet) 

e-mail Average message size 50kB Owners could send up to 100 per day Attachments Drawing or solid model files up to 10MB Say every 10th email has an attachment email traffic = 5MB + 100MB = 105MB An on site email server will have 10 times as much spam as legitimate traffic So email traffic could be 1GB per 8 hour working day Or about 34kBps = 272 kbps Amend your spreadsheets to add these calculations and calculate total web and email transfer rates (Mbps)

Streaming 320 x 240 or 384 x 216 = 500kbps HD 1280 x 720 = 2000kbps Calculate the effects of both types of streaming on the peak demand

Actual speeds There are five main types in the UK, generally offering : FTTH (Fibre to the Home) - 1Gb Virgin FTTC (Fibre to the Cabinet) - Up to 152Mb BT FTTC (Fibre to the Cabinet) - Up to 78Mb ADSL2+ - Up to 24Mb ADSLMax - Up to 8M The key word here is “up to”

ADSL Distance from exchange The further away a property is from a telephone exchange the weaker broadband signal can become and the slower your actual connection This is due to : attenuation, the signal getting weaker as it moves further away from its source the quality of the lines themselves electromagnetic background 'noise' which interferes with the signal

ADSL Contention ratio Contention ratio is the number of users sharing one unit of data capacity. A 50:1 contention ratio would mean that up to 50 broadband customers are sharing the same bandwidth at any one time Average contention ratios home user 50:1 business 20:1

Asymmetry Upload speeds about 10% of download speeds on ADSL What is the line speed available at MWS? Is ADSL a suitable solution for the business? Consider Limiting streaming Off site web serving Uploading to cloud services

Internal network File sizes Wired or wireless or both? 10MB drawings/models Wired or wireless or both? Wired speeds – 1Gbps standard Wireless 802.11a and 802.11g offer up to 54 Mbps 802.11n offers up to 300 Mbps 802.11ac offers up to 1 Gbps Farm buildings in Herefordshire have thick stone walls

LAN contention ratio Ethernet uses Carrier Sense Multiple Access With Collision Detection (CSMA/CD) A device accessing the LAN senses other transmissions, stops if there is a “collision”, waits a random time then retransmits If there are a lot of devices, there are a lot of collisions This is contention and the overall transmission rates drop Can be fixed by sub-netting to limit the number of devices – typically 254 devices Will this be needed at MWS?

Activity For MWS you now know: Create a communications plan for MSW The applications (web, email, CAD/CAM) The users The devices (from the previous session) Create a communications plan for MSW Internet connection, speed, data usage LAN provision Justify all your choices and demonstrate judgement in selecting from alternatives