Efm Bonding Overhead Description - ADTRAN Total Access 5000 Deployment Manual

Total Access 5000 Business Services Deployment Guide

EFM Bonding Overhead Description

Before being transported over the physical layer (DS3, T1, etc.), the EFM bonding engine first
encapsulates Ethernet frames into EFM fragments. EFM Fragment payloads can vary from 64
to 512 bytes depending on the Ethernet packet size. If an Ethernet Frame is 512 bytes or
smaller, it is placed into one EFM fragment. If the frame is between 513 and 1024 bytes, it is
split between two EFM fragments. If the frame is 1025 bytes or greater, it is split between three
EFM fragments.
Each EFM fragment has the following overhead:
• There are 2 bytes of overhead per fragment that are the same for all fragments: a start byte
• The frame check sequence (FCS): The size of this depends on technology
• There are 2 additional overhead bonding header bytes
For DS3, this comes out to 8 overhead bytes per fragment. In addition, as part of the 64/65
EFM framing, there are codewords that are 64 payload bytes and 1 sync byte.
Using this information, the following equations can be used to determine the effective
percentage of the EFM bonding group that is available for customer Ethernet transport (for
DS3):
• Ethernet frames 512 bytes or smaller:
• Ethernet frames between 513 and 1024 bytes, inclusive:
• Ethernet frames 1025 bytes or larger:
The equations above assume that the NetVanta is not adding an extra tag to the customer
traffic (ie. when the customer traffic is tagged, and the customer edge tag is not being
preserved). In any case where the customer tag is preserved (the most likely scenario), and the
NetVanta 800 is simply stacking the provisioned service provider tag (s‐tag) to the customer
tag (if present), the calculation must account for the additional 4 bytes for the s‐tag, as follows:
• For Ethernet frames 512 bytes or smaller:
• For Ethernet frames between 513 and 1024 bytes, inclusive:
• Ethernet frames 1025 bytes or larger:
To determine the EFM bonding group bandwidth that needs to be provisioned so that the
customerʹs commissioned rate is provided, divide the customer rate by this percentage:
Required EFM Group Rate = (Customer Commissioned Rate) / (% Utilization.
Following are example calculations for customer throughput percentage, given a fixed frame
size, assuming the NetVanta 800 is adding a VLAN tag:
• For 64 byte Ethernet frames (worst case scenario):
• For an 8 Mbps bonding group, the actual throughput would be:
• If a customer is sold a 4 Mbps service, the required EFM group size calculation would be:
6-12
and Ck byte (an EOF designator)
% Utilization = (Frame Size) / (Frame Size + 8)x (64/65)
% Utilization = (Frame Size) / (Frame Size + 16) x (64/65)
% Utilization = (Frame Size) / (Frame Size + 24) x (64/65)
% Utilization = (Frame Size) / (Frame Size + 12) x (64/65)
% Utilization = (Frame Size) / (Frame Size + 20) x (64/65)
% Utilization = (Frame Size) / (Frame Size + 28) x (64/65)
% Utilization = (64) / (64 + 12) x (64/65) = 82.9%
8 Mbps x .829 = 6.632 Mbps
(4 Mbps) / (.829) = 4.825 Mbps
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