Our thoughts and prayers are with everyone in London. with regard to telecommunications services, Tim Richardson writes in The Register: [snip] Phone networks have been jammed today following a series of blasts that hit London's public transport network this morning. Mobile networks in particular have been put under pressure as people use their phones to contact friends and family following the explosions. In a statement Vodafone said: "Understandably we are experiencing significant network congestion but we are working closely with the emergency services. "In these circumstances, we would ask all of our customers in Central London to avoid making unnecessary or lengthy phone calls. BT has also reported that its network is intact although it is witnessing a massive spike in calls. [snip] http://www.theregister.co.uk/2005/07/07/london_phone/ - ferg -- "Neil J. McRae" <neil@DOMINO.ORG> wrote: Mobile networks have been switched in to emergency services only owing to congestion and concern that devices may be activated by mobile. However the cause of some of the these incidents is still not clear. -- "Fergie", a.k.a. Paul Ferguson Engineering Architecture for the Internet fergdawg@netzero.net or fergdawg@sbcglobal.net ferg's tech blog: http://fergdawg.blogspot.com/
Mobile networks in particular have been put under pressure as people use their phones to contact friends and family following the explosions.
Luckily, I was 10 minutes late leaving home otherwise I could very well have been on that first train which was attacked near Aldgate. When the Central Line shut down, I tried to get a bus, and when all the bus service into central London was shut down I gave up and started walking home. I suspected that the rumours of terrorist attack were true. All this while I was trying unsuccessfully to use my mobile to ring the office. Finally, I decided to try sending a text message and this worked. Text messages normally are delivered virtually instantaneously and there is a time stamp indicating when the message was sent. During the morning and early afternoon of Thursday, I was receiving text messages that had been sent between 20 minutes and one hour previous. Some of the problems on the mobile networks were the result of a protocol to reserve mobile capabilities for the emergency services. The police have the authority to switch cells to emergency service and then people with specially registered SIM cards in their mobile can take priority. Presumably, some amount of capacity is also held in reserve for these people as well. I had moved the weekend before and my landline was not yet installed. Also, I live near a large hospital. I noticed that my mobile didn't function at all even late on Thursday unless I left home and travelled a kilometer or two from the hospital. Presumably, the cells in this suburban location had also been switched to emergency service. --Michael Dillon
On 11-jul-2005, at 11:40, Michael.Dillon@btradianz.com wrote:
I had moved the weekend before and my landline was not yet installed. Also, I live near a large hospital. I noticed that my mobile didn't function at all even late on Thursday unless I left home and travelled a kilometer or two from the hospital. Presumably, the cells in this suburban location had also been switched to emergency service.
A hospital using up "emergency mode" GSM capacity doesn't make much sense to me. You're not supposed to use cell phones in many places in hospitals, and the ones that I've seen have an ample supply of fixed lines that are cheaper, more reliable and pose less risk of interference with the equipment. It's probably just congestion. Cellular networks don't come close to being able to absorb the burstiness of the (potential) usage patterns in situations like this. (The bean counters don't like cell towers that are idle 99% of the time.) When all the time slots on all the sites in range are filled up you can't get through with voice or data, but SMS which just uses signalling still works. When it gets really bad the random access channel gets clogged and all mobile- intiated communication, including SMS, is dead in the water. (The random access channel is the one not under control of the network: handsets use it to signal their desire to communicate. As such, it is very prone to collisions and congestion collapse under heavy loads.)
A hospital using up "emergency mode" GSM capacity doesn't make much sense to me. You're not supposed to use cell phones in many places in hospitals, and the ones that I've seen have an ample supply of fixed lines that are cheaper, more reliable and pose less risk of interference with the equipment.
This was just a guess on my part because the congestion in this suburban area lasted well into the evening. The only time I was able to make phonecalls on my mobile was when I took a bus out of the area. I planned to travel away from the city to get away from mobile congestion but the phone started working again before I had gotten any further from the centre. However I had moved a km or two from the hospital. Later, I returned home and lost the ability to use the mobile even as late as 11:30 p.m.
It's probably just congestion. Cellular networks don't come close to being able to absorb the burstiness of the (potential) usage patterns in situations like this.
This, I understand. But it doesn't explain why this area would have suffered such a prolonged problem.
When it gets really bad the random access channel gets clogged and all mobile- intiated communication, including SMS, is dead in the water.
I never had a problem sending or receiving SMS other than the long delays. The people on the other end were near Aldgate on the edge of central London so even there, SMS was still functioning. It was an interesting experience which seems to show that it is better to have several completely different communications channels to choose from. In my case I had lost landline and DSL Internet access due to moving house, and I lost mobile voice access due to congestion. But SMS still functioned. I haven't heard of any Internet outages caused by the attacks although everyone who has travelled on the tube knows that there are lots of cables in the tunnels. Presumably, there are so many tunnels with cables that breaks in three places are easily covered by protection switching. --Michael Dillon
On 11-jul-2005, at 13:31, Michael.Dillon@btradianz.com wrote:
A hospital using up "emergency mode" GSM capacity doesn't make much sense to me.
This was just a guess on my part because the congestion in this suburban area lasted well into the evening.
Could be lots of things. Maybe it was really the hospital, but then simply the people in the waiting area calling all over the place. Or maybe some completely unrelated problem with the cell network in your area.
When it gets really bad the random access channel gets clogged and all mobile- intiated communication, including SMS, is dead in the water.
I never had a problem sending or receiving SMS other than the long delays. The people on the other end were near Aldgate on the edge of central London so even there, SMS was still functioning.
Follow the money... At several hundreds of your favorite currency unit per megabyte, I'm not surprised they manage to keep this service running. Here in the Netherlands we had free airtime for a few hours at the beginning of the new year several times, and it was interesting to see what this did to the networks.
On Mon, Jul 11, 2005 at 12:31:35PM +0100, Michael.Dillon@btradianz.com wrote:
It was an interesting experience which seems to show that it is better to have several completely different communications channels to choose from. In my case I had lost landline and DSL Internet access due to moving house, and I lost mobile voice access due to congestion. But SMS still functioned.
The lower the bandwidth channel, the less likely it is to break. Cheers, -- jr 'cf: Morse Code' a -- Jay R. Ashworth jra@baylink.com Designer Baylink RFC 2100 Ashworth & Associates The Things I Think '87 e24 St Petersburg FL USA http://baylink.pitas.com +1 727 647 1274 If you can read this... thank a system administrator. Or two. --me
Some of the problems on the mobile networks were the result of a protocol to reserve mobile capabilities for the emergency services. The police have the authority to switch cells to emergency service and then people with specially registered SIM cards in their mobile can take priority. Presumably, some amount of capacity is also held in reserve for these people as well.
Requests from the police on specific SIM numbers on certain mobile networks whilst others applied such that you got no access to a cell site, others deployed a limit on normal SIM cards to limit the access down by 50% so that there was some level of service. Regards, Neil.
participants (5)
-
Fergie (Paul Ferguson) -
Iljitsch van Beijnum -
Jay R. Ashworth -
Michael.Dillon＠btradianz.com -
Neil J. McRae