low throughput via ppp link of linux routers

low throughput via ppp link of linux routers

Post by Xiangyang H » Sun, 04 Jan 1998 04:00:00



I just set up 2 linux router boxes using the slackware linux 2.0.0.
The system layout looks like this:

                     local CS Net
|-----------------------------------------------------------------------------|

       |                                 |
       |eth0                           |
    ---------------         ------
    | Local Linux  |         | CS |
    |--------------|          |----|
        |
        |
        |  PPP link
        |
        |
    -----------------
    | Remote Linux  |
    |----------------|
       |     |eth0           ethernet            en0-----------
       |     |-------------------------------| Node B  |
       |                                                    | Pentium  |

       | PPP link                                      -----------
       |
       |com A
    -----------
    | Node A  |
    | Pentium  |
    -----------

Node CS is a Sun Sparc II, Node A, B are Pentium 133Mhz PCs.
The two linux boxes are 486 PCs(50Mhz) with enough memory (16M), 10Base
network adaptors(3Com/Intel), and fast serial cards (16550A).

The settings of the serial ports look like this:
            /dev/ttyS0, Line 0, UART: 16550A, Port: 0x03f8, IRQ: 4
                    Baud_base: 115200, close_delay: 50, divisor: 0
                    Flags: spd_vhi skip_test

The local linux router's ppp link is initiated like this:
            pppd -d -detach /dev/ttyS0 115200 asyncmap 0 proxyarp
vj-max-slots 16 &

The remote linux router's ppp link is initiated like this:
            pppd -d -detach defaultroute /dev/ttyS0 115200 asyncmap 0
vj-max-slots 16 &

Also the routing tables look like this:

Routing Table(Local Router):
Destination       Gateway     Genmask           Flags  MSS    Window
Use  Iface
192.103.xx.137    *            255.255.255.255 UH    1500
0              2   ppp0
192.103.xx.136    *            255.255.255.248 U       1500
0              3   ppp0
192.103.xx.0        *            255.255.255.0     U       1500
0          133    eth0
127.0.0.0              *            255.0.0.0             U
3584      0              1       lo
default       192.103.xx.128        *                   UG    1500
0              3    eth0

Routing Table(Remote Router):
Destination      Gateway         Genmask          Flags MSS    Window
Use Iface
192.103.xx.108  *               255.255.255.255  UH    1500
0           1     ppp0
192.103.xx.136  *               255.255.255.248  U       1500
0           3      eth0
127.0.0.0            *               255.0.0.0              U
3584      0           1         lo
default         192.103.xx.108        *                  UG    1500
0         130   ppp0

And now here's the average throughput I get by ftping between node CS
and
node A or B(each transmition was repeated several times):
    download  111kbps
    upload         70kbps (starts at very high speed like even ~240k
then
drops sharply to 40k~50k, then keeps climbing until reaching somewhere
around 70k)

I am expecting 115kbps on both directions. Now I'm very confused by the
70kbps uploading speed. Is there someone who knows why and how?

Thanks in advance.

Bests,

Xiangyang Ha
--------------------------------------------------------
Xiangyang Ha  (515)472-7000x4134/4326

Computer Science Department
       College of Science and Technology
       Maharishi University of Management
      (Maharishi International University 1971-1995)
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