MTU (Maximum Transmission Unit)
The MTU (Maximum Transmission Unit) is the size of the largest datagram that can be sent over a network.
If a datagram is larger than an MTU, the datagram must be fragmented into multiple smaller datagrams.
Default MTU Sizes
Most network technologies have default MTU sizes which may be changed by the network administrator.
| Network | Default MTU |
|---|---|
| PPP | 296 |
| X.25 | 576 |
| IEEE 802.3 | 1,492 |
| Ethernet | 1,500 |
| FDDI | 4,352 |
| 4Mb Token Ring | 4,464 |
| 16Mb Token Ring | 17,914 |
| Hyperchannel | 65,535 |
The term PMTU (Path MTU) is sometimes used to describe the MTU along an entire network path. The PMTU will always be equal to the smallest MTU along the entire path which the datagram must travel.
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Dear Sir/Madam
We have a satellite network (including some remote sites and a hub) connected to a LAN network. Our LAN network is Gigabit Ethernet, but Sat. network backbone has limited bandwdth (from 64 kbps for remote sites and 2Mbps for the hub). Our satellite modems don’t support QoS. So, voice packets, vidoe packets, and file sharing applications compete to communicate and have unpredictably transmission charasteristics. The MTU of our Sat. modem is 1520 bytes.
Prioritizing and preserving voice applicatons quality, could we change the MTU size? Do you think the MTU size has effect on the congestion (or QoS)?