Why do 56K modems have higher pings than cable and ADSL

[Tontoman]

Ok, dumb general question for the techies :P.  56K and lower modems have longer ping times (I had to live through it playing quake and such)  around 200+ms where as ADSL can get down into the 20,30s for local sites.  Now I know ADSL/cable has higher bandwidth, but why the faster response time.  I though it might be the modem but both go through a modem attached to the PC.  Is it just the amount of switches and junk it has to go through before getting to the fiber?

Thanks

 

[theo_wyvern]

As far as I'm concerned its this - you can get more data through ADSL/cable that is why the response is faster.

Compare 512k ADSL and 56k Modem, almost ten times more bandwidth.

[GeordieSteve]

True but pings are measure in mili seconds so there shouldn't be too much of a differnece

[OBonio]

Bandwidth is the speed at which you can receive data.  Theoretically 512 kilobits/sec for ADSL, 56 kilobits/sec for modem.  Ping is simply a measurement of time for one bit of data to reach its destination.  Naturally this would be quicker for ADSL than a modem, unless there was something seriously wrong with the network infrastructure on the journey to the desination.

[Gandy]

When you "ping" a website or server, your PC sends a packet of data. The receiving server then checks that the packet is complete by referring to the checksum file that is sent as part of the packet. If the packet is complete and no data is missing the server will then send a message back to your PC to request the next piece of data. The only control you have over the journey of this data packet is where it travels from your PC into your modem and then into your phone socket. Every other part of the journey it takes can be affected by outside influences such as busy networks, downed servers etc. This however can also be true of ADSL.

[Tontoman]

Think people are confusing bandwidth with speed.  You have a thin and fat pipe (for water say).  The fat pipe will move more water even if the water flows at the same speed in both pipes.  So it doesn't necessarily have to be faster. For eg. my old 56k would usually get around 200ms ping and 3-4KB/s download. My ADSL now gets 300KB/s download or 100 times faster.  If it was all due to speed I'd have to be at 2ms ping and unfortunately I don't get that.  Plus remember we are talking electrical and light signals in the cables which are all the same speed whether it comes from a 56k modem or DSL.

Obonio, why would it naturally be faster?  If it's only one bit it doesn't hit the limit on either channel.  If it was 112Kb than the ADSL would still be a second and then the 56K would be 2 seconds... now you get some difference.

Gandy, so if those factors can effect both why is it that ADSL 99% of the times comes out way faster unless someones got a congested channel or a crap ISP.

[Tontoman]

Ok got it from another source :P. Apparently the bandwidth still comes into effect when building the packet that is to be sent.  So a 56K modem takes longer to build the packet before it is sent and thus this lag gets included in the ping time.  Once the packet is sent it would/should be just as fast traveling along the fiber (at the speed of light in glass) but the initial setup is slower.

http://techrepublic.com.com/5100-6265_11-1042973-2.html

All circuits have a common characteristic known as serialization delay, which is the time it takes some unit of data to be serialized onto the circuit. It�s directly related to the bandwidth of the circuit and the technology employed. For instance, if I have a DS3, DS1, and a DS0, and I want to send a 1,500-byte packet (the maximum payload for a TCP/IP packet), the approximate serialization delay will be:
DS3: (1500 bytes * 8 bits/byte) / 44040192 bits/sec = .27 ms (approx)
DS1: (1500 bytes * 8 bits/byte) / 1572864 bits/sec = 8 ms (approx)
DS0: (1500 bytes * 8 bits/byte) / 65536 bits/sec = 183 ms (approx)