That's 22 bytes of overhead for a 1500 byte payload (payload size matches the MTU defined in the modem). It's 6 bytes for source MAC, 6 bytes for destination MAC, 4 bytes for 802.1Q QOS/VLAN, 2 bytes for type, and 4 bytes at the end for FCS. VDSL framing encapsulation is similar to Ethernet. This bits per second figure is for ALL traffic that crosses the VDSL line, including framing encapsulation. Your download speed that you're getting is a combination of a bits-to-bytes conversion as well as allowances for protocol overhead.ġ8 Mbps = 18,000,000 bits per second (AT&T and other internet providers use Mega- or Giga- as SI units, which are powers of 10, thus all multipliers are 1000). Then you have to take into account that the data you are requesting may be coming from a server more than 200 miles away with multiple connection points along the way each adding their own set of added overhead as well. There's handshaking, confirmation, and other various other forms of traffic that's traveling along with the raw data of your download. Bytes are bigger than bits.Īs for why you're not getting the full 2.25 MBps that you think you should be getting is that TCP/IP which is the protocol that the whole Internet is based upon has a lot of overhead. "b" stands for bits, "B" stands for bytes. Notice that the last number has a big "B" and not a small "b" like the first number has. Now, we take 2,359,296 and divide it by 1,048,576 (1 Megabyte) which then comes out to be 2.25 Megabytes. Now, since 8 bits are in a byte, we have to take the 18,874,368 bits and divide it by 8, that comes out to be 2,359,296 Bytes. 18 Mbps is equal to 18,874,368 bits per second.
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