Ethernet Testing Overview
Ethernet, standardized by the Institute of Electrical and Electronics Engineers (IEEE), has become the world’s most widely used network technology. Evolving from being a LAN-based network technology, Ethernet is now among the most widely deployed access technology in carrier networks. Supported data rates have also increased over time, reaching speeds of up to 10 Gbit/s. Today’s standard rates range from 10 Mbit/s through to 10 Gbit/s and are supported on both electrical twisted pair or fiber-optic cables.
Figure 1. Typical 10 GigE WAN and LAN PHY applications
10 GigE introduced a departure from standard 10/100/1000 Mbit/s Ethernet, thanks to two variants that are optimized for either LAN or WAN applications. Since most 10 Gbit/s WAN links today are SONET/SDH-based, the 10 GigE specification has a second physical-layer specification allowing it to easily interact with existing SONET/SDH network elements. 10 GigE maintains the standard Ethernet frame size and format, so that Layer 3 and higher protocols are preserved. It operates over point-to-point links in full-duplex mode.
Ethernet Test Applications
EtherSAM: The New Standard in Ethernet Testing
ITU-T Y.156sam is the newly introduced draft standard for turning-up and troubleshooting carrier Ethernet services. This new methodology is completely adapted to today’s Ethernet services especially mobile backhaul and commercial services.
Aligned with the requirements of today’s Ethernet services, the EtherSAM test methodology enables complete validation of all SLA parameters in a single test to ensure optimized quality of service.
Contrary to other methodologies, EtherSAM supports new multiservice offerings. It can simulate all types of services that will run on the network and simultaneously qualify all key SLA parameters for each of these services. Moreover, it validates the quality of service mechanisms provisioned in the network to prioritize the different service types, resulting in more accurate validation and much faster deployment and troubleshooting. EtherSAM is comprised of two phases, the network configuration test and the service test:
The network configuration test consists in sequentially testing each service. It validates that the service is properly provisioned and that all specific KPIs or SLA parameters are met.
The service test simultaneously validates the quality of all the services over time. All services are generated at once at their CIR and all key performance indicators are measured for each service.
EXFO’s EtherSAM approach proves even more powerful as it executes the complete ITU-T Y.156sam test with bidirectional measurements, providing 100% first-time-right service activation.
The following table provides a list and explanation of the other main test applications used in Ethernet testing.
Service-Level Agreements and Ethernet Service Acceptance
Testing
A service-level agreement (SLA) is a legal contract between
a service provider and a customer that specifies a required level of
service. SLAs help service providers attract and retain customers, but
there are also penalties associated with sub-standard service: poor
customer satisfaction, increased spending on maintenance and, often,
direct financial payouts. SLAs typically specify maximum downtime,
mean-time-to-repair (MTTR) when outages occur, and minimum performance
criteria.
Figure 2.
Flow chart of Ethernet service acceptance testing
Ethernet
service-acceptance testing involves specific tests to ensure that SLA
validation can be performed on either part of the network (end-to-core)
or on all of it (end-to-end) using either BERT over Ethernet or RFC 2544
benchmarking (see below for more details on both test).
Figure 3.
End-to-end, end-to-core, and remote testing
Network Installation and Service Turn-Up
Because the transparent transport of Ethernet over
physical media is becoming a common service, Ethernet is
increasingly carried across a variety of Layer 1 media
(e.g., 10Base-FL, 100Base-FX, 1000Base-LX) over longer
distances. There is therefore a growing need to certify
Ethernet transport on a bit-per-bit basis. This can be done
using bit-error-rate testing (BERT).
BERT uses test patterns encapsulated into an Ethernet frame,
making it possible to go from a frame-based error
measurement to a BER measurement. These test patterns can be
pseudo-binary random sequences (PRBS) test signals or
user-defined test patterns. The robustness of optical
network elements can be tested through Ethernet BERT testing
using xPATS (CRPAT, CSPAT, CJTPAT, short and long CRTPAT)
while turning up service over dark fibers, PON or DWDM
networks.
Ethernet BERT provides the bit-per-bit error-count accuracy
required for the acceptance testing of physical-medium
transport systems. BERT over Ethernet should be used when
Ethernet is carried transparently over the following Layer 1
media. Using BERT over Ethernet Layer 2 can be used to test
the error handling capabilities of network elements like
switches, as a user can inject errors within the payload or
in the FCS sequence of the Ethernet frame.
Performance Validation/Qualification
TCP Performance Validation – With the
wide deployment of Ethernet, service providers are now
offering Ethernet connections to most of their customers.
Usually, the service provider will provide an SLA based on
Ethernet bandwidth availability which guarantees the
throughput at Layer 2. Unfortunately, TCP throughput will
not necessarily be equal to its under-layer (Ethernet)
performance since it will be affected by many factors such
as client traffic policing and aggregation. Client traffic
policing refers to bandwidth grooming techniques used to
limit the flow of traffic from clients to the service
provider’s network, while aggregation refers to the practice
of oversubscribing a network in order to take advantage of
the bursty nature of Ethernet data transmission. Other
conditions such as network congestions and frame losses will
have a significant impact on the TCP throughput and must be
taken into account when evaluating TCP performance.
The TCP throughput application is used to determine the
performance of TCP/IP traffic transmission by measuring
statistics for the TCP throughput, TCP window size, total
number of TCP frames transmitted and retransmitted as well
as the round-trip time. These measurements require the use
of two units that emulate a TCP connection between a local
and a remote (similar to a client-server connection) over an
Ethernet network.
Ethernet Performance Validation – The
Internet Engineering Task Force (IETF) has put together a
test methodology to address the issues of performance
verification at the Layer 2 and 3 levels. RFC 2544,
Benchmarking Methodology for Network-Interconnect Devices,
specifies the requirements and procedures for testing
throughput (performance availability), latency (transmission
delay), back-to-back frames (link burstability), and frame
loss (service integrity).
When these measurements are performed, they provide a
baseline for service providers to define SLAs with their
customers. They enable service providers to validate the
quality of the service delivered and can provide them with a
tool to create value-added services that can be measured and
demonstrated to customers. For example, these tests provide
performance statistics and commissioning verification for
virtual LAN (VLAN), virtual private networks (VPNs) and
transparent LAN services (TLS), all of which use Ethernet as
an access technology. The SLA criteria defined in RFC 2544
can be precisely measured using specialized test
instruments. The performance verification is usually done
once the installation is complete. The measurements are
taken when the network is out of service to make sure that
all parameters are controlled.