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Description
Capacity
Ethernet Frame Size
MTU Maximum Transmission Unit size (bytes)
The E7 supports the ability to set the MTU Maximum
Transmission Unit size (bytes) on a GE and 10GE port
interface to a maximum of 9600 bytes, not including Ethernet
header and Two VLAN tags for Q-in-Q. GPON ONTs and
xDSL ports have a fixed MTU value.
MTU = 9600 bytes (E7 Ethernet interfaces)
MTU = 9600 bytes (E7 Backplane links)
MTU = 2000 bytes (700GE and 760GX GPON ONTs)
MTU = 1600 bytes (700GX GPON ONTs)
MTU = 1500 bytes (GigaCenter ONTs)
MTU = 1500 bytes (E7 xDSL ports)
The MTU is defined as the maximum size payload of the
Ethernet frame, not the Ethernet frame size. In an IP network,
this is the largest IP packet that can be transmitted on the
Ethernet network without IP packet fragmentation. The
Ethernet frame size varies depending on the number of VLAN
tags applied to the payload, plus allowances for
Preamble/Delimiter and interframe gap.
+ 8 bytes (Preamble/Delimiter)
+ 14 bytes (header not including VLAN tags)
+ 4 bytes (inner VLAN tag)
+ 4 bytes (outer VLAN tag)
+ 4 bytes (trailer)
+ 12 bytes (interframe gap)
For example:
2000 bytes = MTU
2026 = Max Ethernet frame (with two VLAN tags without
Preamble/Delimiter)
2034 = Max Ethernet frame (with two VLAN tags including
Preamble/Delimiter)
2046 = Max Ethernet frame (with two VLANs,
preamble/Delimiter, and Interframe Gap)
Maximum throughput: Protocol efficiency for Ethernet
Protocol efficiency = Payload size ÷ Frame size
Maximum efficiency is achieved with the largest allowed
payload size.
For example:
1500 bytes (Maximum payload size)
+ 8 bytes (preamble)
+ 14 bytes (header)
+ 4 bytes (trailer)
+ 12 bytes (interframe gap)
= 1538
1500 (payload size) ÷ 1538 (frame size) = 97.53%
Maximum throughput: Efficiency for optional 802.1Q tagged
Ethernet packets, include 4 bytes in the frame size
1500 (payload size) ÷ 1542 (frame size) = 97.28%
Maximum throughput: Protocol overhead for Ethernet as a
percentage
Protocol overhead = 1 — Protocol efficiency