Transcript
NEWSLETTER APRIL 2013 Editor Ron Everitt Contact on 020 8394 2123 or
[email protected] The meeting on March 20th was attended by 28 members and guests for a presentation on Networking which was chaired by Seb Welford. He proposed to cover the following topics which are important to most of us running computers / tablets or smartphones on home networks. We are also starting to operate on our TV’s to watch films downloaded over the Internet. These are the topics to be addressed: Ethernet (MAC addressing)Home networks
HomePlug Wireless networks (WiFi) Broadband The Internet (IP addressing)
The Ethernet is a system where all clients are connected to the network by a single cable. This is simple to install but since more than one user is connected then it has problems with keeping the data uncorrupted. Originally this used an RG58 Coaxial cable (10 base 5), connected by BNC connectors to T points on a special cable but this was later replaced by common Coax cable and BNC T pieces (10 base 2). However this still suffered from the contention problem. Bandwidth is wasted and can be as much as 70%, and can even lock up so an alternative solution was sought. This uses RJ45 connectors with multicore ‘CAT 5’ cable instead of coax cable. One pair is send and a second pair is receive. This leaves two spare pairs which can be used for Power (POE) over Ethernet. Using a Switch instead of a Hub removes the contention problem. Messages are broken into packets and each packet contains: A Header byte A Destination address A Source address Data (up to 1023 Bytes) A Checksum (CRC - Cyclic Redundancy Check) byte. If this fails the receiver requests retransmission. There are 8 Bits per Byte plus overhead; Thus for link speeds: 10 Mbits/S gives approx 1 MByte/S
100 Mbits/S gives approx 10 MBytes/S 1000 Mbits/S gives approx 100MBytes/S
Why bother with Home networking –? It is useful if you have several computers which might be your own, someone else’s, a laptop, a tablet or a smartphone as well as a variety of other devices. You can also use other PC’s as backups. One can also be file server. Most modern PC’s have RJ45 (Ethernet) sockets and most laptops have both an RJ45 socket and a wireless link; Most modern routers have both wireless and wired capability which means that you can connect many systems to your network Many PC’s can be connected. Operating systems like Windows, Apple and Linux are all designed to allow networking and enable connection to PC’s, laptops, tablets and smartphones but remember that if you are working with a WiFi system enabled it must be protected by an encryption system to prevent unauthorised users gaining access to your system. Each device has to have a unique name. Each PC has to join a workgroup or homegroup. In Windows this has a default name of MSHOME but it can be changed to your own choice. Every node (PC etc) has its own IP address which is normally assigned automatically by a Dynamic Host Control Protocol (DHCP) setup in the Router. Seb then went on to describe his own Home Network which is a mixture of wired switches, routers and wireless links. He also uses a HomePlug system to connect his Upstairs and Downstairs systems via the
2 mains cables along the neutral line. There was some discussion on how effective these systems were in connecting between Rings in the House. Seb said he was sure that the signal could not cross the electricity meter and would also be stopped where the neutral line is connected to earth. WiFi systems are covered by the IEEE802.11 specification and are available in several versions covering the speed and frequency in the following versions b up to 11 Mb/s
g up to 83 Mb/s n up to 400 (?) Mb/s
The standard uses a 2.4 GHz band for b,g,n speeds and a 5 GHz band for n. It can be shared between many users, with attendant contention problems which are not obvious to the user! Channel allocation for 11b,g There are 13 channels in the 2.4GHz band. However only 3 of these are useable and the channels overlap. Seb showed us a diagram of the overlap. To avoid problem it is wise to use channels not in use nearby. Typically use 1, 6 and 11 or 1, 7 and 13. 802.11 n uses both 2.4Ghz and 5GHz band Some routers offer both bands together but others only allow one at a time. Whatever you choose it is essential to use security. This can be WEP or WPA. WPA2-PSK is much better than WEP From our home network we can connect to the internet which is a collection of other networks. Addresses are of the form of four decimal numbers (0..255) e.g. 192.168.4.6 (for now) but IP Version 6 is coming because the current system has run out of unique addresses. Each packet sent has destination address and source address for response Packets are sent from node to node until it arrives at destination Each packet also has a sequence number which sorts received packets into order Error checking decides if the packet has been accurately received and if not requests a repeat operation, Each packet may take a different route to the destination and return and the loss of a single node does not matter. World Wide Web Because IP numbers are inconvenient to remember Tim Berners-Lee suggested an alternative scheme – the Universal Resource Locator which uses words instead of numbers, mostly in the form www.name.domain, e.g. www.bbc.co.uk/news. 32 bit IP number blocks ran out in 2012 so the system is migrating from IP v4 to IP v6 which is a 128 bit system. Domain Name Server (DNS) URL – the Universal Resource Locator is a specific name followed by a domain name The Domain Name server translates the URL to an IP number. It is generally provided by your ISP
The future of broadband BT has indicated that they will be replacing the link to the local node by Ethernet over optical fibre. This should improve the ADSL speeds for some with long links to the exchange. Eventually the link to the home will be optical fibre (already being installed), however power will still be needed for phones for emergency use.
Bottlenecks The connection to the server is only as fast as the slowest link. With broadband the ADSL link is probably the weakest link. WiFi can also be a limit Homeplug can also be a limit.
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Ethernet Communication Over Mains - or perhaps not. A few days ago I tried getting a new DVD Blu-Ray Player upstairs to connect to my Draytek 2110 router for access to the Internet. Having initially registered the two plug-in TP-Link 500Mps devices placed side by side on a mains extension strip, together with an RJ45 cable connector from one of the link devices to a laptop, everything worked fine. I then took the second of these Ethernet-over-mains devices upstairs, leaving the first one connected to the router, and reconnected the RJ45 cable to a DVD player, foolishly expecting it to work. At my age and having started to use a PC before the introduction of the mouse, I really should have known better. Having tried many options, including re-registration of the devices by pressing the reset button on each device within two minutes, as per the instruction leaflet, I still could not get all three indicator lights to switch on either link device (ie mains on, device connected and Ethernet cable attached). I spoke with my eldest son, a senior programmer with a former West German bank, who came over to help. I had already realized that the MAC address of the DVD could not be seen by the router to assign an IP address by the routers DHCP table. However, I had discovered that my Draytek router could bind the DVD;s MAC to an IP setting, creating a single static IP address at the highest permitted number within the allowed IP range in order to avoid any auto DHCP assignment. My son spent some considerable time with me trying to get the two devices to re-register themselves, including moving the one upstairs to different mains sockets and a various extension leads. I then explained that initially when placed side by side in an extension block and hardwired to a laptop everything seemed to work. On trying this again, then removing one device and moving it upstairs, the DVD finally connected to the Internet, but only YouTube. I wish I hadn’t bothered, the DVD wasn’t as Smart as I’d been led to believe, as I really wanted to get to IPlayer, the same as my Sony TV downstairs. For anyone wanting an incredibly flexible router I can recommend the Draytek Vigor 2110Vn which has lots of functions, such as a ability to use a USB hard drive plugged into the router as a NAS drive (The WD Passport drive which I couldn’t get working with 64biit Win 7, for example) and VoIP. Be prepared though - the PDF manual is 217 pages, surprisingly only in English, which takes a lot of understanding. This includes DOS (Denial of Service) filtering like I’ve never seen before, Virtual Private Networking (VPN), connection of analogue phones for using VoIP (eg Skype) and up to four SSID’s and lots more. Newer Vigor models should result in my Vigor model 2110Vn being sold for a lot cheaper price than a year ago. You can if you wish download the manual from the Support Tab on the Draytek web-site and get a lot more advice on networking in general, without having to register ownership of an appropriate router, I’m still experimenting with my WD Passport drive, but at least the light comes on now, whereas it didn’t when plugged into my PC. Finally a word of caution about the 802.11n wireless standard. It is not as a most people imagine, a guarantee of a fast connection speed. In fact “n” devices are being sold as either 150,200,300 or 500Mbs (Megabits/sec) and you should compare the ratings for a sustained data throughput. Also starting to appear are Gigabit (1000Mbs) devices which use twinned 500Mbs channels. Remember the above quoted figures, like everything in communications, is a maximum speed under ideal conditions and are used to promote sales. If you want to stream video from the Internet the higher speeds are essential, especially if you want HD resolution, which is due to double within a few years. However, the “n” standard does give a higher powered “cleaner” signal permitting “up to” four times the transmission distance of a “g” device. Just by using an “n” device may obviate the use of additional signal boosters etc. and therefore work out a cheaper option.
4 Finally, be aware that laptops and netbooks are advertised having 802.11n Ethernet capability, but that commonly only applies to the hard-wired RJ45 port, the inbuilt wireless device running at the slower, and less powerful, “g” standard. A number of years ago, Microsoft laid on a three day conference to show off their new online Internet service. After three days of total failure an investigation was held and the result was that nearly all the delegates (being “techies”) had mobiles switched on , which resulted in swamping of the wireless modem channel that Microsoft was trying to use. Similar problem groups are mini-cab operators, schools, stations and groups where a mass of people may all use mobile phones at once. Other modern devices such as microwaves, central heating systems, fridges and many other things can also use the same range of frequencies your modem is trying to use, but the bandwidth is split into channels! Hence, check those wireless Channel numbers as congestion and errors can result in a request to the server to resend the packets of information, severely reducing the data reception speed, if a connection can be established at all! After all you are paying for a service, so you want to get the best service that matches your needs. There are many free WiFi checkers available on line or as mobile phone apps, or like my Draytek router, built into the router setup options. Paul Sedgwick
Just for info:http://www.tp-link.us/support/emulators/ There are 18 different models include under the 802.11n standard !!! Paul Sedgwick
MEETINGS ARE ON THE THIRD WEDNESDAY OF EACH MONTH THE MEETINGS WILL BE IN THE VILLAGE HALL AT NEWDIGATE (grid ref TQ 195 422) (A map and directions are available from David
Goddard Tel 01428 683925 email
[email protected] ) The hall is available from 9.00 a.m until 1.00 p.m. The meeting commences at 10.00 am for 10.30 a.m. The next meeting is on Wednesday April 17th and will be our AGM followed by an open forum.
FUTURE MEETINGS Wednesday May 15th Wednesday June 19th
Ladies Lunch Emails A Chaired discussion with Tony Barnes
For the latest information on the program please see http://www.ietrms-surrey.org.uk/pc_group.html We are looking for contributions to either the program or the Newsletter so if any member would like to give a talk or know anyone else capable please talk to the committee. A short note on your experiences might also make a useful addition to the newsletter and could provide a solution to someone else’s problem. Please do not be shy and remember that what may seem obvious to you may help someone else to solve a difficult problem
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PUZZLE PAGE As you may know, Leslie is not available at present to provide material for the puzzle page. He wishes to produce joint solutions with me to the masses and springs problem set in the last but one Newsletter so there will of necessity be a delay in publication. However, he has asked me to provide a couple of problems to keep you occupied so here they are: SUM OF DIGITS Find the sum of all the digits in the integers from 1 to 1,000,000,000 inclusive.
BOX OF EGGS A trader dropped a box of eggs and every one was broken. He couldn’t remember how many eggs were lost but he did know that when they were divided by 2,3,4,5 or 6 there was always one egg left over and when he put them in the box he recalled putting in a whole number of groups of seven. What is the least number of eggs that were broken? Chris Rosenberg
MINUTES OF THE NINEEENTH ANNUAL GENERAL MEETING OF THE IET SURREY RMS PC GROUP HELD AT THE NEWDIGATE VILLAGE HALL ON 18th APRIL 2012 at 10.30am
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Members Present
Twenty-two members were present. The meeting was chaired by Chris Rosenberg. In the absence of Seb Welford, Guy Meakin acted as Secretary of the Meeting. •
Apologies for Absence
Roy Stevens, Seb Welford th
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Minutes of the last A.G.M. Held on 20 April 2011.
There were no comments on the Minutes of the 18th AGM. Mike French proposed acceptance of the Minutes, seconded by Roland Polding. Acceptance was agreed.
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Matters Arising
The only Matter Arising was the then Chairman’s concern over the future of the PC Group owing to the lack of volunteers for its Committee. The Chairman stated that, now that nominations had now been received for all necessary Officers and Members of the Committee, he was content that this matter had been resolved. •
Chairman’s Report
As Acting Chairman, Chris Rosenberg had prepared the Chairman’s Report. He presented the Report: “We continue to get a good attendance at our monthly meetings, and our membership now stands at 45. “We had another varied programme of presentations and discussions throughout the year as follows: 2011 20 April 18 May 15 June 20 July 17 August 21 September
AGM & open forum Ladies’ Lunch GIMP (Gnu image manipulation Don Andrews program) Spreadsheets Seb Welford et al
19 October
Open Forum Photon to JPEG – digital cameras Network Encryption
16 November
Spreadsheets (continued)
14 December 2012 19 January
Mince Pies & Open Forum
15 February
Presentation on Presentations Brian Arthur
Website Creation
Chris Rosenberg Guy Meakin Chr i s Ros e n b e r g & Tony Barnes
Jan Spencer
21 March Tables CPU – the beating heart of Seb Welford in Word, Excel & Access computers Les Haddow Leslie “We continue to be indebted to Ron Everitt for the production of the monthly Newsletter and to Leslie Haddow for keeping the Problem Page going. “The difficulties associated with attracting outside experts to come and give presentations remain and are likely to get worse as pressure increases on people to attract the highest remuneration for their time. Thus we remain dependent on members to give talks and participate in discussions. The visual aspect of presentations has improved through use of the ceilingmounted projector but we still suffer from relatively poor audio projection. “We are still getting IET funding for all of our meetings, with the exception of the
7 Ladies’ Lunch. Without this support our subscription rate would be significantly higher. “Despite the changes that have taken place at the Six Bells, Don Andrews and David Goddard have between them managed to keep us fed and watered for which we owe thanks. David Goddard has again stepped in to organise the Ladies Lunch this year. “The Constitution of the PC Group had been reviewed and minor editorial amendments made.” After some discussion on the revised Constitution, it was agreed that it would be published on the website and distributed with the next Newsletter, so that Members could review it themselves. At the start of the PC Group Meeting on 20 June 2012, a short Extraordinary General Meeting would be held to seek agreement to the document. •
Treasurer’s Report & Accounts
David Goddard presented his Treasurer’s Report and Accounts for the year ending 30 September 2011: “The end of year accounts which have been examined by Peter Dulley show a Bank Balance of £2398.59 plus cash in hand of £109.46 with an operating surplus of £410.10 over the previous year. These figures include membership subscriptions of £338 for the subsequent year of 2011-2012. Membership is slightly down on last year at 45. “There has been no significant expenditure during the year other than general administrative expenses, so our balance is gradually creeping up. The major item of expenditure (ie Hall Hire) is currently reimbursed by the IET. “We nevertheless need to keep a reasonable balance to fund the purchase of hardware / software when needed as we cannot guarantee that the IET would meet these costs. Our laptop for instance is probably nearing the end of its useful life. “There is therefore no recommendation that we should make any adjustments to the membership subscription which stands at £9 pa. There is still a shortfall in covering the cost of a hard copy of the newsletter despite the increase authorised last year and this will worsen in view of the impending rise in second class postage, I propose we do nothing about it at this stage. “The Bank Balance as at the date of this meeting is £2688.59 which includes monies collected for the Ladies Lunch. “I would like to extend my thanks to Peter Dulley for once again examining the accounts and I understand he is willing to continue in this role.” He added that the Accounts would not be available on the website for security reasons and similarly would not be generally distributed. However, any Member wishing to receive a copy should let him know. •
Election of Officers
(to take effect from October 2012) The following had been nominated by the present committee; all had agreed to serve: Chairman: Vice-Chairman: Hon. Secretary: Hon. Treasurer:
Roy Stevens - a new nomination Chris Rosenberg - a new nomination Seb Welford David Goddard
8 Election of these Officers was proposed by Peter Dulley and seconded by David Neish. The Meeting elected these Officers.
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Election of Ordinary Committee Members
(to take effect from October 2012) The following had been nominated by the present committee; all had agreed to serve: Tony Barnes Leslie Haddow Guy Meakin - a new nomination Ron Everitt News Letter Editor Election of these Committee Members was proposed by Don Andrews and seconded by Peter Davis. The Meeting elected these Committee Members.
• Effective Date of Appointments as Officers and Committee Members (an additional Agenda Item) Guy Meakin proposed that the appointments of the newly nominated Officers and Committee Member should take immediate effect, with any formal period of tenure beginning in October 2012. David Neish seconded this proposal. The Meeting agreed. •
Suggestions for topics for further meetings
Members offered a welcome number of topics for further meetings: 1. The Cloud. (Afternote: at its meeting that afternoon, the Committee noted that this topic was already in the programme.) 2. Home networks and the setting up of routers, especially wireless routers. 3. A review of the history of mobile devices. 4. The history of computers – the proposer knew of a potential presenter and agreed to notify Seb Welford of his contact details. 5. Computers in cars. 6. Android – the operating system. 7. System recovery for PCs. 8. Solving the encryption system of the Lorenz Geheimschreiber (Fish and Tunny at Bletchley Park?) 9. Microsoft
Access 2010. 10. A visit to Bletchley Park. It was suggested that the PC Group by itself might not produce a viable number of visitors to fill a coach and that such a visit should be undertaken either with or by the main RMS.
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Any other business
The Meeting thanked the outgoing and incoming Officers and Committee Members for their diligent work in supporting the Group.
(signed) Guy Meakin Secretary of the AGM
