This may not be the place to ask such a basic question but I thought I would take a chance. What I've learned so far is that the Ethernet TCP/IP environment allows packets in size from 64 bytes to 1518 bytes. What determines these sizes? Is it the originating application, the NIC card or the switch itself? What if a switch does not exist? If your working on an application that communicates with a server are all the packets the same size for that session or application or are they different sizes? If someone answers these questions, thanks for taking the time. Riley
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Packet size and how it is determined
- Thread starter riley3
- Start date
Ok,
From
"payload - Also called the body or data of a packet. This is the actual data that the packet is delivering to the destination. If a packet is fixed-length, then the payload may be padded with blank information to make it the right size. "
"As an example, let's look at how an e-mail message might get broken into packets. Let's say that you send an e-mail to a friend. The e-mail is about 3,500 bits (3.5 kilobits) in size. The network you send it over uses fixed-length packets of 1,024 bits (1 kilobit). The header of each packet is 96 bits long and the trailer is 32 bits long, leaving 896 bits for the payload. To break the 3,500 bits of message into packets, you will need four packets (divide 3,500 by 896). Three packets will contain 896 bits of payload and the fourth will have 812 bits."
I think software decides how much is put in the payload??
But we may have to wait for another expert to come along and fill in the blanks,
Hope someone can help us.
Brett
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NSW, Australia
(Unless you want to pay for our trip?)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
From
"payload - Also called the body or data of a packet. This is the actual data that the packet is delivering to the destination. If a packet is fixed-length, then the payload may be padded with blank information to make it the right size. "
"As an example, let's look at how an e-mail message might get broken into packets. Let's say that you send an e-mail to a friend. The e-mail is about 3,500 bits (3.5 kilobits) in size. The network you send it over uses fixed-length packets of 1,024 bits (1 kilobit). The header of each packet is 96 bits long and the trailer is 32 bits long, leaving 896 bits for the payload. To break the 3,500 bits of message into packets, you will need four packets (divide 3,500 by 896). Three packets will contain 896 bits of payload and the fourth will have 812 bits."
I think software decides how much is put in the payload??
But we may have to wait for another expert to come along and fill in the blanks,
Hope someone can help us.
Brett
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NSW, Australia
(Unless you want to pay for our trip?)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Thread starter
- #3
Thank you very much for the response. It makes sense to me but I now have a few more questions
. You said "The network you send it over uses fixed-length packets of 1,024 bits". Is it our "network" locally, our LAN or our ISP that has the 1,024 fixed-length? Thanks again, Riley
. You said "The network you send it over uses fixed-length packets of 1,024 bits". Is it our "network" locally, our LAN or our ISP that has the 1,024 fixed-length? Thanks again, RileyHey,
From what I read, I may be wrong, but its generally fixed at 1024 for LAN and internet.
Cya,
Brett
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NSW, Australia
(Unless you want to pay for our trip?)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
From what I read, I may be wrong, but its generally fixed at 1024 for LAN and internet.
Cya,
Brett
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NSW, Australia
(Unless you want to pay for our trip?)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Thread starter
- #5
Your information has also helped me do different searches using different words and phrases. From what I'm seeing is the packet on an Ethernet network can be anywhere from the low 64 to the high of 1536 (I think). Also, it appears when you send a URL request it may use the minimum size but when you send a VPN request it may use all of the available room. That would make sense to me and the picture is starting to clear up a little. When I send a URL to the Internet is it my NIC card that packages up the request? Meaning that in a days time I may send many different sizes of packets? Thanks, Riley
Ethernet frame sizes range from 64 bytes (header info only inc. source/destination MAC addresses) up to 1518 bytes (header info + payload aka user data).
The size of the frames that traverse the network are largely responsible to the amount of data being sent (i.e. large FTP packets for instance will always typically be 1518 in size whilst TCP acknowledgement packets will just be 64 bytes in size) or network devices and their respective MTU settings.
Cisco routers default to 1500 bytes MTU on their Ethernet interfaces however this can be changed. Thus if a frame passes through a Cisco device with an MTU of 300 bytes, all frames over 300 bytes will be fragmented prior to being transmitted on this device.
Regarding your last question there, NIC cards exist at something we call Layer 1 and Layer 2. These layers are taken from the OSI reference model ( Thus the NIC is obviously your physical media (layer 1) that connects to the Ethernet network but it also has a burnt in MAC address that is used to function ast layer 2.
Hope some of this helps
The size of the frames that traverse the network are largely responsible to the amount of data being sent (i.e. large FTP packets for instance will always typically be 1518 in size whilst TCP acknowledgement packets will just be 64 bytes in size) or network devices and their respective MTU settings.
Cisco routers default to 1500 bytes MTU on their Ethernet interfaces however this can be changed. Thus if a frame passes through a Cisco device with an MTU of 300 bytes, all frames over 300 bytes will be fragmented prior to being transmitted on this device.
Regarding your last question there, NIC cards exist at something we call Layer 1 and Layer 2. These layers are taken from the OSI reference model ( Thus the NIC is obviously your physical media (layer 1) that connects to the Ethernet network but it also has a burnt in MAC address that is used to function ast layer 2.
Hope some of this helps
- Thread starter
- #7
Thanks KiscoKid for the information. Every answer has helped. Regarding your comment about the NIC card, I'm still not clear on one part. When I hit the enter key to send some sort of "data" to somewhere is the NIC card the initial device that packages the data into a packet? If so does the initial point determine the size of the packet? Also, our network is rather small, a bunch of clients, 5 Win2003 servers; a couple of 3Com managed switches, a MS ISA server and Road Runner cable. When one of the clients sends a URL to a web site are all of the packets that get sent and returned the same size? If so would that apply also to a Terminal Server session to another location? Thanks again for everyone's time and patience. Riley
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