Overhead need to be conside

Overhead need to be consider
when calculate traffic performance
Issue 0: Feb/18/2003 by tasuka@tailyn.com.tw
Describe:
When we say the traffic performance, almost people did not consider about the
protocol’s overhead, because that is less the the traffic, but the overhead actually need
to be consider because protocol to protocol transfer and transmitter media change.
Every different media require different transmit function.
Here is a example:

Host A send a file via FTP to Host B through the Ethernet/ADSL/IMA/Ethernet networks.
the scenario like below.

Some protocol format and header describe below.

A. IP Packet to IMA E1 Interface Over Head Formula

1. 64 byte IP packet, via 1483 Bridge mode.
Known conditions:
IP packet size 64 byte
LLC SNAP: LLC frame bridge mode 18 byte
AAL5 :CPCS PDU tail 8 bytes
IMA frame size = per 127 cell plus 1 IMA ICP cell
Packet in ATM = 64+8+18=90/48=2 cell
ATM Size = 2 x 53 = 106 byte
4 E1 bandwidth = 2048 x 4 =8192 Kbps

overhead rate = 64/106 = 0.60378
Rate = 8192 Kbps x 0.60378 = 4946.166 Kbps
IMA Cell =((53/(53*127))byte but too small

2. 64 byte IP packet via 1483 Route Mode
Known conditions:
LLC SNAP: LLC frame route mode 8 byte
AAL5 : CPCS PDU tail 8 byte

overhead rate = 64/106 = 0.60378
Rate = 8192 Kbps x 0.60378= 4946.166 Kbps

3. 1500 byte IP packet with 1483 Bridge Mode
Known conditions:
ATM size 32x53 = 1696 byte

Overhead rate = 1500/1696 = 0.8844
IMA Cell =((53*32/(53*127))byte but too small
Actually rate = 8192 Kbps x 0.8844 = 7245.005 Kbps #

4. 1500 byte IP packet with 1483 Route Mode
Known conditions:
ATM size = 32x53 = 1696 byte

Overhead rate = 1500/1696 = 0.8844

B. TCP Packet to IMA E1 Interface Over Head Formula

1. 24 byte data via TCP, through 1483 Bridge mode.
Known conditions:
TCP packet size 24 byte
TCP header 20 bytes
IP header 20 bytes
Packet in ATM = 24+20+20+8+18=90/48=2 cell

overhead rate = 24/106 = 0.2264
Rate = 8192 Kbps x 0.2264 = 1854.669 Kbps

2. 24 byte data via TCP through 1483 Route Mode
Known conditions:
Data size 24 bytes
TCP header 20 bytes
IP header 20 bytes

overhead rate = 24/106 = 0.2264
Rate = 8192 Kbps x 0.2264 = 1854.669 Kbps

3. 1460 byte data via TCP through 1483 Bridge Mode
Known conditions:
Data size 1460 bytes
TCP header 20 bytes
IP header 20 bytes

Overhead rate = 1460/1696 = 0.8609

4. 1460 byte IP packet with 1483 Route Mode
Known conditions:
TCP header 20 bytes
IP header 20 bytes

Overhead rate = 1460/1696 = 0.8609

C. UDP Packet to IMA E1 Interface Over Head Formula

1. 36 byte data via UDP, through 1483 Bridge mode.
Known conditions:
Data size 36 bytes
UDP header 8 bytes
IP header 20 byte

overhead rate = 36/106 = 0.3396
Rate = 8192 Kbps x 0.3396 = 2782.003 Kbps

2. 36 byte IP packet via 1483 Route Mode
Known conditions:
Data size 36 bytes
UDP header 8 bytes
IP header 20 bytes

overhead rate = 36/106 = 0.3396
Rate = 8192 Kbps x 0.3396 = 2782.003 Kbps

3. 1472 byte UDP packet with 1483 Bridge Mode
Known conditions:
UDP header 8 bytes
IP header 20 bytes

Overhead rate = 1472/1696 = 0.8679

4. 1472 byte UDP packet with 1483 Route Mode
Known conditions:
Data size 1472
UDP header 8 bytes
IP header 20 bytes

Overhead rate = 1472/1696 = 0.8679

IP packet TCP packet UDP packet
Size
Bridge Route Bridge Route Bridge Route
Small pkt 4946 4946 1854 1854 2782 2782
Large pkt 7245 7245 7052 7052 7109 7109

These 3 kinds of packet test result but still not consider about any detail, such
like the TCP traffic will has handshake algorithm so, after a window size packet
transmitted, the transmit will stop and wait until the receiver side send a ACK
packet back for confirm the data is correct, and continue send next window, so
the current TCP traffic will below the rate for this table.

So if you are test the traffic performance via IP packet ( send ICMP echo and
reply), then you need to consider that the host send out ICMP packet’s rate, in
normal, the MS Windows is send a ICMP packet 1 second by default, but if you
are use Linux, the you can use this command for fast send
“ping -i0.01 IP_address”, that it could send ICMP packet every 0.01 second.

So if your ICMP packet is 32 bytes, in MS Windows will send out :
32 byte* 1 Sec = 32 * 8 * 1 = 256 bps
but with Linux with “-i” condition :
32 bytes * (1/0.01) = 32 * 8 * 100 = 25600 bps

That is very different test condition.

So when you are test traffic performance with FTP application, that you will see
the traffic rate from FTP application, that need to be consider about the server
round trip time for that FTP service. FTP is work with TCP packet, so the
overhead is more then others packet, and need to consider the TCP windows
size and handshake. That is very complex to calculate in real life, but one true is
that FTP protocol can make sure your file is correctly send and received but it
need more overhead to make sure that.

So when you are calculate the TCP/IP packet performance rate, please consider
what media you have and what kind of traffic you send and receive when the
packet size different, the performance will change.

Overhead need to be conside

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