WHITE PAPER Layer 2 Protocol Conformance Testing for Ethernet Switches (Version 2.1)

WHITE PAPER Layer 2 Protocol Conformance Testing for Ethernet switches (Version 2.1)

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Introduction

Ethernet's relative simplicity, flexibility, low cost and high bandwidth has ensured its dominance in the enterprise networking market. In addition, there has been a tremendous momentum for use of ethernet in Metropolitan networks, Industrial networks and Residential networks as well.

Ethernet connectivity options extend all the way to 10 Gigabits, on physical media such as wireless, copper and fiber. Accordingly, there are numerous protocols and standards that are employed to adapt the ethernet paradigm to each of these physical media, networks and applications, to address the requirements of functionality, performance, scalability and security.

The rest of the document is organized into two sections: Overview of Bridging protocols and their application Protocol Conformance Testing

This white paper is an updated version of the June 2003 document, providing information on additional protocols and changes to the standards. Overview of bridging protocols and their application

Link Aggregation Control Protocol (LACP)

Link Aggregation Control Protocol (LACP), defined as part of IEEE specification 802.3-2003 – Clause 43 (earlier known as 802.3ad), enables the bundling of physical links to form a logical aggregated link providing a higher effective bandwidth, load-sharing and increased availability. Switches negotiate automatic bundling on their links by exchanging LACP protocol data units (PDUs) with each other.

Aggregated Links Switch 1

Switch 2 Switch 3

Hosts

Figure 1 Aggregation of physical links to provide aggregated links in LACP

Using Link Aggregation allows a Media Access Control (MAC) client to treat a set of one or more switch ports as if it were a single port using the services of an Aggregator. Thus it is the Aggregator that binds to one or more ports within a switch system and distributes frame transmissions from the MAC client to the various ports, and to collect received frames from the ports and pass them to the MAC client. A switch may contain multiple Aggregators, serving multiple MAC clients. A given switch port will bind to (at most) a single Aggregator at any time and a MAC client is served by a single Aggregator at a time. The binding of ports to Aggregators within a System is managed by the Link Aggregation Control function for that System and may be done automatically through use of LACP or manually by direct configuration. Ports are considered for active use in an aggregation in link priority order, starting with the port attached to the highest priority link; thus a port attached to a lower priority link gets selected as a standby. The LACP uses peer exchanges across the links to determine, on an ongoing basis, the aggregation capability of the various links, and continuously provides the maximum level of aggregation capability achievable between a given pair of systems. Also, conversations may be moved among ports within an aggregation, both for load balancing and to maintain availability in the event of link failures.

Layer 2 Protocol Conformance Testing

The use of the Marker protocol provides a means of determining the point at which a given set of conversations can safely be reallocated from one link to another without the danger of causing frames in those conversations to be mis-ordered at the collector. Though the use of the Marker protocol is optional, the ability to respond to Marker Protocol Data Units (PDUs) is mandatory.

Bridging with Spanning Tree Protocol (STP) Spanning Tree Protocol was introduced to allow for dynamic discovery of a topology by bridges which while being loop-free, would also provide a path between every pair of LANs. Bridges transmit special Configuration Bridge Protocol Data Units (or Configuration BPDUs) so that the bridges in the LAN can do the following:

Elect a single Root bridge in the network Choose a Root-port on each bridge that gives the best path from each bridge to the root. Choose Designated Ports for each individual LAN, which forwards frames from the direction of the root onto that LAN and frames from that LAN towards the root. The bridge of which the designated port is part is the Designated Bridge for the LAN. Select ports that are to be included in the topology, as well as identify other ports (called Alternate Ports) that will not participate in reception and forwarding of data.

Physical Topology

Root Bridge Alternate Port Active Topology Root Port Designated Port Downstream Bridge

Figure 2 Determination of Active topology and Port Roles in STP

The root bridge periodically transmits configuration BPDUs every “hello time”. When the other bridges receive this message, they transmit configuration message on each of their ports for which they are designated. In case any bridge notices that the spanning tree algorithm has caused it to transition a port into or out of blocking state, it keeps transmitting Topology Change Notification (TCN) messages towards the root bridge on its root port until it receives an acknowledgement from the designated bridge.

A bridge that discards a packet instead of forwarding it, is said to filter the packet. It is possible to configure the bridge to permanently filter packets based on the input port (either multicast packets or hosts packets) or even source address.

IEEE 802.1D also defines the Generic Attribute Registration Protocol (GARP), which is the basis for its applications -- GARP Multicast Registration Protocol (GMRP) and the GARP VLAN Registration Protocol (GVRP). GARP allows participants in a GARP Application to register attributes with other participants in a bridged LAN. The definition of attribute types, their values, and the semantics associated, are specific to each GARP application.

GMRP allows bridges and end stations to dynamically register Group membership information with other switches in the same LAN segment, and share this information with all other switches in the bridged LAN. In the absence of this implementation, static multicast group addresses need to be configured in the bridge.

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Where the user priority associated with a frame can be signaled by the MAC layer, the STP specification 1 provides for the mapping of user priority to traffic classes in the switch for QoS support.

Changes to the specification in 802.1D – 2004

The original Spanning Tree Protocol (STP) is no longer part of the 802.1D revision of 2004. This new revision incorporates 802.1t-2001 and 802.1w-2001, providing for rapid convergence of the spanning tree.

However, the new revision does provide for functioning in the STP mode, in order to allow compatibility in interoperation with STP-only bridges.

Bridging with Rapid Spanning Tree Protocol (RSTP)

RSTP is specified in 802.1w-2001 and provides rapid convergence of the spanning tree and provides for fast reconfiguration, critical for networks carrying delay-sensitive traffic such as voice and video.

RSTP builds upon STP by defining the following new Port Roles: Alternate port—Offers an alternate path toward the root switch. 2 Backup port—Acts as a backup for a designated port towards downstream switches. A backup port exists only when two ports are connected together in a loopback by a point-to-point link or when a switch has two or more connections to a shared LAN segment.

In a stable topology with consistent port roles throughout the network, RSTP ensures that every root port and designated port immediately transition to the forwarding state, while all alternate and backup ports are always in the discarding state. RSTP also provides faster reconfiguration by means of port handshake mechanisms for rapid transition to forwarding state and new Topology Change mechanisms.

Root Downstream Bridge Bridge Alternate Backup Port Port

Root Port Designated Port

Figure 3 Port Roles and Active Topology in RSTP

The RSTP specification provides interoperability with legacy STP based networks. In addition, RST bridges can be configured to operate in STP mode.

1 This capability which was initially defined by the 802.1p specification has been incorporated as part of 802.1Q. 2 In 802.1D-1998, an Alternate Port is defined as a port that is not a disabled port and is neither a Root Port nor a Designated Port. Such a port does not forward frames onto the LAN to which it is connected. This definition of Alternate Port has been changed in RSTP (i.e., in 802.1w-2001 and 802.1D-2004).

Layer 2 Protocol Conformance Testing

Changes to the specification in 802.1D – 2004

The 2004 revision of 802.1D includes further technical and editorial corrections to 802.1w-2001 and removes the original Spanning Tree Protocol (STP) as a conformance option. Apart from this, there are only some minor changes in the functioning of the protocol:

• An RST bridge sets its own HelloTime in BPDUs sent by it, even though it is not the root bridge • Support for automatically detecting an edge port, on not receiving BPDUs. • A Designated port can transition into forwarding on reception of agreement from the alternate port of a downstream bridge.

Virtual LAN (VLAN)

A VLAN is a switched network that is logically segmented (e.g., by department, function or application), without regard to the physical locations of the users. VLANs have the same attributes as physical LANs, and can be used to group end stations together, though they are not physically located on the same LAN segment. This practically eliminates the need to re-configure switches when end stations are moved about.

Relationship between IEEE Std 802.1D and IEEE 802.1Q

IEEE 802.1Q, extends the concepts of filtering services and bridging in order to provide a set of capabilities that allow bridges to support the Virtual LANs (VLANs). The VLAN Bridging specification contained in 802.1Q is independent of 802.1D, however it makes use of many of the elements of the specification contained in 802.1D, such as the bridge architecture, the forwarding process, spanning tree protocols, GARP and GMRP.

Ingress, Forwarding, Relay Egress GMRP, Learning Station Location

VLAN Topology GVRP, Static

MSTP, RSTP or STP Active Topology

Ethernet Physical Network Topology

Figure 4 Hierarchy of functions in a bridge

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Switches provide filtering of frames in order to confine traffic to recipients that are members of that VLAN. VLAN membership can be configured statically (by manual configuration), or dynamically configured and distributed by means of GVRP.

Router Bridge

VLAN-1 VLAN-3 VLAN-4 (default) (IP) (IPX)

Figure 5 Port and Protocol based VLAN

Most switches support Independent learning, wherein traffic from one VLAN will not be forwarded to another VLAN. Hence if some limited form of forwarding needs to be supported, the switch should implement Shared VLAN learning. If this feature is not supported, layer 3 routing should be used.

Tagging of frames allows frames to carry user priority information across LAN MAC types that are not able to signal user priority. Use of the 802.1Q Priority tagging allows the end-to-end significance of user priority to be maintained regardless of the ability of individual LAN MAC types to signal priority.

The use of GMRP in a VLAN Context allows GMRP registrations to be made that are specific to that VLAN; i.e., it allows the Group filtering behavior for one VLAN to be independent of the Group filtering behavior for other VLANs.

IEEE 802.1u provides the additional capability by which it is possible to support multiple spanning trees – i.e., to implement an independent spanning tree per VLAN. This is made possible by further splitting the 16 bit Bridge Priority component of the Bridge ID into 4 bits of Bridge Priority and the remaining 12 bits as VLAN ID. This feature could be used to provide for redundant links as well as more flexibility in organizing the VLANs.

IEEE 802.1v provides the capability to support Port-and-Protocol-based VLAN classification, including multiple VLAN ID values per port. In addition to the Port VLAN ID, for bridges that implement Port-and- Protocol-based VLAN classification, the VLAN ID associated with an Untagged or Priority-tagged frame is determined based on the Port of arrival of the frame into the bridge and on the protocol identifier of the frame.

VLAN can be considered as an application of STP or RSTP and does not make any assumptions on the type of underlying bridging mechanism.

Layer 2 Protocol Conformance Testing

Changes to the specification in 802.1Q – 2003

802.1Q – 2003 basically incorporates the three amendments namely, 802.1u-2001, 802.1v-2001, and 802.1s-2002, providing:

• Dynamic Group and VLAN registration • VLAN classification according to link layer protocol type and • Support for VLANs over multiple Spanning Tree instances.

Also, since the original STP has been removed from the 2004 revision of 802.1D, an implementation of RSTP is required for any claim of conformance for an implementation of 802.1Q-2003 that refers to the current revision of 802.1D, unless that implementation includes the Multiple Spanning Tree Protocol (MSTP) specified in 802.1Q-2003. MSTP itself is an extension based on RSTP for providing support for multiple spanning trees.

Multiple Spanning Tree (M-STP)

The Multiple Spanning Tree Protocol as defined by IEEE 802.1s-2002, combines the best aspects from both RSTP and VLAN. In MSTP, several VLANs can be mapped to single spanning-tree instance called MST-Instance (MSTI) and each instance is independent of other spanning-tree instances. This approach provides multiple forwarding paths for data traffic, enabling load balancing, and reduces the number of spanning-tree instances required to support a large number of VLANs.

CIST Root Bridge

Region 1

CIST CIST Regional Regional Root Bridge Root Bridge

Region 3 Region 2

Figure 6 MSTP spanning trees with active topology

MSTP establishes and maintains two types of spanning-trees:

An internal spanning tree (IST), which is the spanning tree that runs in an MST region. Within each MST region, MSTP maintains multiple spanning-tree instances. Instance 0 is a special instance for a region, known as the Internal Spanning Tree (IST). A Common and Internal Spanning Tree (CIST), which is a collection of the ISTs in each MST region, and the common spanning tree (CST) that interconnects the MST regions and single spanning trees.

The MSTP algorithm uses extended priority vector components and calculations as compared to RSTP. Also MSTP defines the additional port role Master port, which provides connectivity from a region to a CIST Root outside the region. Copyright 2002-2010 Veryx Technologies. All rights reserved Page 7

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MSTP ensures that frames with a given VLAN ID are assigned to one and only one of the MSTIs or the IST within the Region and that the assignment is consistent amongst all the Bridges within the MST region.

MSTP provides interoperability with RSTP and legacy STP based networks. In addition, an MST bridge can be configured to operate in RSTP or STP mode. The MSTP specification 802.1s-2002 has been now incorporated in 802.1Q – 2003.

Port-Based Network Access Control

The IEEE 802.1X standard defines a client-server-based access control and authentication protocol that restricts unauthorized hosts from connecting to a LAN through publicly accessible ports. An authentication server (typically a RADIUS server), is used to authenticate each client (called the ‘supplicant’ entity) connected to a switch port (which performs the authenticator role), before making available any services offered by the switch.

Workstation (WLAN client) WLAN Access Point

Authentication Workstation Switch (wired client) Server (RADIUS)

Figure 7 Application of Port-based Network Access Control

Until the client is authenticated, 802.1X access control allows only Extensible Authentication Protocol over LAN (EAPOL) traffic through the port to which the client is connected. After authentication is successful, normal traffic can pass through the port.

Changes to the specification in 802.1X – 2004

802.1X-2004 extends the original specification by providing for a two-step authentication process, as would be the requirement in a Wireless LAN scenario, in order to mitigate the risk of rogue WLAN access points (WLAN-APs). Thus, the new WLAN-APs or switches that enter the network need to be authenticated first, before even providing authentication services to hosts connecting through them. Hence the supplicant and authenticator entities in the WLAN-AP ports would need to be authenticated before data transfer can occur. However, the configuration support for inactivating the first step of authenticating the supplicant is provided for situations when host is directly attached.

Application Scenarios

LACP is being widely used in ethernet switches to aggregate multiple physical links – in all types of applications since it also provides for some level of robustness at data link layer.

Ethernet switches being deployed in medium to large enterprise applications and industrial applications increasingly support Rapid Spanning Tree Protocol (RSTP) for networks carrying traffic such as voice and video. Since RSTP inherently supports STP, compatibility with legacy switches with STP support can

Layer 2 Protocol Conformance Testing

easily be provided. For better security, use of 802.1X-based authentication of the clients (such as stations, WLAN Access Points, WiMAX gateways) accessing the ports of ethernet switches is mandatory.

Port-based VLAN support is useful for logically segmenting the network without regard to the physical locations of the nodes in the network, thus also eliminating the need to reconfigure switches when nodes are moved. VLANs inherently provide for added security since communication across VLANs is disallowed by default.

Switches supporting per-VLAN spanning trees allow for redundant links and load balancing but are pre- standard. For a standards-based solution, large enterprise networks need to support Multiple Spanning Tree Protocol (MSTP), since it not only provides rapid reconfiguration but also better scalability and control due to the support of regions and multiple instance support within each region. MSTP allows frames assigned to different VLANs to follow separate paths each based on an independent Multiple Spanning Tree Instance (MSTI) support, providing redundancy and load balancing.

Switches being deployed in Metro Ethernet networks need to support MSTP and VLAN. A current limitation in using VLANs however is that the maximum number of VLAN IDs supported (4094) is too low for use in Metro applications 3. Similarly, ethernet switches being used in access applications such as in DSLAMs will need to support a suitable spanning tree protocol with VLAN.

3 While not standardized by IEEE, VLAN Stacking is a solution being used by many vendors to overcome this limitation. Providing a two-level VLAN tag structure (i.e., assigning a second VLAN tag) extends the VLAN ID space to over 16 million VLANs. The second VLAN tag is inserted in the frames at the ingress edge device, and removed at the egress edge device. The stacked frame, wherein several customer VLAN frames are multiplexed over a service provider VLAN ID, appears as an Ethernet jumbo frame, and is seen by only the intermediate switches. IEEE 802.1ad – VLAN Provider Bridges specification when finalized, will provide a standardized method of demarcation of the VLAN as S-VIDs (Provider’s Service VLAN IDs) and C-VIDs (Customer VLAN IDs).

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Protocol Conformance Testing

Testing for LACP

Conformance testing for LACP should test the Receive State Machine to ensure that the switch peers have synchronized the LACP operational parameters such that the port can be safely used, either in aggregation with other ports or as an individual port. Also, the Transmit Machine should be verified for correct transmission of LACP PDUs, both on demand and on a periodic basis.

Testing should also verify that the Selection Logic selects a compatible Aggregator for a port, using the Port’s LAG (Link Aggregation Group) ID. The Selection Logic may determine that the link should be operated as a standby link if there are constraints on the simultaneous attachment of ports that have selected the same aggregator.

Tests may verify the ability to respond to Marker PDUs. Also, if Marker Protocol is supported, tests may verify the distribution function of the Link Aggregation sublayer for transmission of Marker PDUs.

See Table 11 below, for the Conformance test categories for LACP.

Table 1 Tests for LACP Conformance Test Description Frame Format Format and processing of LACP PDU & Marker PDU Receive State Actor and Partner states Machine Recoding and updating default Partner information Transmit State Actor and Partner states Machine Slow /Fast Periodic Transmission Rapid Transmission Group selection Support for aggregator(s) logic Assignment of operational keys for ports attached to the same or different LAG(s) Attachment / Detachment of link to/ from LAG LACP Configuration of Admin Key values, System and Management Port priorities, loopback selection, etc. Marker Protocol Distribution function Transmission of Marker PDUs

Testing for STP

Conformance testing for STP should test for election of the bridge entity as the Root bridge and the Designated bridge based on the assigned priority and that the required loop free topology is maintained in all the scenarios. Election of the Root bridge and the propagation of parameters such as Root ID, Root Path Cost and Forward Delay should be performed consistently.

Also, the roles of individual ports in the bridge should be verified for various scenarios for transitions from/to blocked state and forwarding state. Relay and filtering of frames should be supported and aging of dynamic entries should occur. The bridge should detect and respond to Topology changes. All the required bridge parameters and port parameters should be maintained properly. See Table 22 below, for the Conformance test categories for STP.

Layer 2 Protocol Conformance Testing

Table 2 Tests for STP Conformance

Test Description Frame Format Format and processing of Configuration BPDU & Topology Change Notification (TCN) BPDU Active Topology Selection of Root and Designated Bridge Recording and Propagation of Configuration Port Roles Assignment and role transitions for the Root Port Designated Port and Alternate Port. Port State Blocking/ Listening / Learning/ Forwarding states Transitions between states Relay and Static entries Filtering Dynamic entries Ageing of Dynamic entries Topology Change in Bridge/Port priority and path costs Change Reception and propagation of TC notifications Bridge Reading and setting of Bridge and Port Protocol Management parameters with Range checks GMRP Ingress rules for received GMRP frames Transmission according to Egress rules for GMRP frames

Testing for RSTP

As in the case of STP, Conformance testing for RSTP should test for election as the Root bridge and the Designated bridge based on the assigned priorities. Also propagation of parameters such as Root ID, Root Path Cost and Forward Delay should be performed consistently by all bridges not just the Root bridge. The bridges should detect and respond to Topology changes in accordance with the changed specification in RSTP – topology changes when detected are propagated on all ports other than the one which detected it.

Roles of individual ports in the bridge should be verified for various scenarios for transitions from/to discarding state and forwarding state. Rapid transitions from Discarding to Forwarding state should occur in cases where the handshake with the neighboring RSTP bridge is successful, in cases where handshake is not complete, the transition should occur slowly, as in STP.

As in the case of STP, Relay and filtering of frames should be supported and aging of dynamic entries should occur. All the required bridge parameters and port parameters should be maintained properly.

RSTP bridges should also maintain compatibility with legacy STP bridges. If a legacy bridge is detected on any port, RSTP should behave in the STP compatible mode. See Table 33 below, for the Conformance test categories for RSTP.

Table 3 Tests for RSTP Conformance Test Description Frame Format Frame Format and processing of RST BPDU, Configuration BPDU Topology Change Notification (TCN) BPDU Active Topology Selection of Root and Designated Bridge Recording and Propagation of Configuration Port Roles Assignment and role transitions for the Root Port Designated Port, Alternate Port, Backup Port and Disabled Port.

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Test Description Port State Discarding/ Learning/ Forwarding states Transitions between states Relay and Static entries Filtering Dynamic entries Ageing of Dynamic entries Topology Change in Bridge/Port priority and path costs Change Reception and propagation of TC notifications STP Forced Migration Compatibility Transmission/Reception of Config and TCN PDUs Disabling of Rapid Transitions in STP mode Detection of Legacy STP bridge Bridge Reading and setting of Bridge and Port Protocol Management parameters with Range checks

VLAN Testing

Conformance Testing for VLANs should test for correct tagging frames for Access and Trunk ports, based on the VLAN membership. It is also mandatory that the bridge provide support for VLAN Registration - Static configuration and optionally Dynamic Registration using GVRP.

Learning, Filtering and Relay of frames should be verified. Filtering support may vary depending on the type of learning support –Independent, Shared or both. See Table 44 below, for the Conformance test categories for VLAN.

Table 4 Tests for VLAN Conformance

Test Description Frame Format Frame Format and processing of Tagged frames VLAN Tagging Reception and relay of frames based on port type (port-based) VLAN Tagging Reception and relay of frames based on port of (port and reception and protocol type protocol-based) VLAN Static Registration Dynamic (using GVRP) Filtering Static entries Dynamic entries Ageing of Dynamic entries Frame Relay Classification of frames based on VLAN Relay of Frames depending on Ingress/Egress rules Learning Independent vs. Shared Learning methods VLAN-ID to Filtering ID (FID) allocation GMRP Ingress rules for received GMRP frames Transmission according to Egress rules for GMRP frames Bridge Reading and setting of VLAN Bridge and Port Management Protocol parameters with Range checks

Testing for MSTP

Conformance testing for MSTP should verify for establishment and behavior of both the Internal Spanning Tree (IST), and the Common and Internal Spanning Tree (CIST) and the propagation of configuration

Layer 2 Protocol Conformance Testing

information between them. Roles of individual ports in the switch should be verified for various scenarios for transitions from/to discarding state and forwarding state.

Though the selection of the CIST Root Bridge and computations of port roles for CIST use the same fundamental algorithm as RSTP, MSTP uses extended priority vector and components and hence results in more scenarios.

Testing should verify that MSTP implementations support VLAN features such as tagging of frames, VLAN Registration and learning/filtering/relay, the key difference being that VLANs should now be tested in the context of MST instances. See Table 55 below, for the Conformance test categories for MSTP.

Table 5 Tests for MSTP Conformance

Test Description Frame Format Frame Format and processing of MST BPDU, RST BPDU, Configuration BPDU Topology Change Notification (TCN) BPDU Active Topology Selection of CIST and MSTI Root and Designated Bridge Recording and Propagation of Configuration Port Roles Assignment and role transitions for the CIST and MSTI Root Port, Designated Port, Alternate Port, Backup Port and Disabled Port. Port State Discarding/ Learning/ Forwarding states Transitions between states Relay and Static entries Filtering Dynamic entries Ageing of Dynamic entries Topology Change in Bridge/Port priority and path costs Change Reception and propagation of TC notifications STP/RSTP Forced Migration Compatibility Transmission/Reception of Config and TCN BPDUs in STP mode and RST BPDUs in RSTP Mode Disabling of Rapid Transitions in STP mode Detection of Legacy STP/RSTP bridges Bridge Reading and setting of MST Bridge and Port Management Protocol parameters with Range checks

Testing for Port-Based Network Access Control

Conformance testing for 802.1X should verify that the Authenticator Port Access Entity on the switch, only allows Extensible Authentication Protocol over LAN (EAPOL) traffic through switch ports until client authentication. The Authenticator should communicate with the Authentication Server using implementation dependent mechanisms. Where the Supplicant role is also supported, the switch should communicate the Client credentials to the Authenticator, in response to requests from the Authenticator.

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Table 6 Tests for 802.1X Conformance

Test Description Frame Format EAPOL Frame Formats

Packet EAPOL Packet Processing Processing Port Roles Supplicant Authenticator Management Reading and setting of Port Access Control parameters

Conclusion Many protocols and standards are being implemented in Ethernet switches to cater to various networks and applications, mandating a comprehensive approach to testing for Protocol Conformance to address the challenge of releasing consistently well-tested standards-based products in the marketplace. IEEE is actively developing standards required for a wide range of applications.

As more protocols are being added to provide support for more demanding application scenarios, implementers have to ensure conformance to the standards and interoperability with other vendor implementations, with the added challenge of maintaining compatibility with legacy protocols. Automation of the test setup makes testing a manageable and predictable process, apart from the huge savings on resources and time.

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About Veryx Technologies

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