» Ethernet SLA Monitoring: Map-out the Health of your network
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Ethernet SLA Monitoring: Map out the health of your network
By Damien Rame, Accedian Networks

May 14, 2007 7:13 PM

Driven by its low cost, affordable bandwidth and its scalability, Ethernet Services are not only in clear expansion but also now reaching mass-market. Two major factors are still preventing a complete adoption of Carrier Ethernet: service availability and service reliability. Needless to say, the latter strongly influences the former. Indeed, without any means of measuring network performance, Service Level Agreements (SLA) cannot be guaranteed from one end to the other end. Network performance, and SLA Verification in particular, come as even more important when considering the growth of demand in IP-based services such as Voice over IP (VoIP), video over IP and Internet protocol television (IPTV) which require very low latency (delay) and jitter (delay variation). Without SLA Verification, there is no way to guarantee a good end-to-end Quality of Service (QoS).

End-to-End SLA Monitoring

Service Level Agreements are defined on an end-to-end basis. Up until now, carriers were unable to measure their Ethernet networks’ quality all the way up to the Last Mile (or the First Mile) properly and efficiently while keeping costs manageable and thus started adopting partial SLAs by taking the access segment out of the loop (Core network efficiency). While early adopters would rely on best-effort services, these are no longer acceptable and major enterprise customers will not move on to an Ethernet Service until Ethernet SLAs are guaranteed, and verified, from one End to the other End (see Figure 1).

Figure 1 : End-To-End SLA Monitoring

Figure 1 : End-To-End SLA Monitoring

The Ethernet Demarcation Device (EDD) creates a clear demarcation point between the carrier’s and the customer’s networks and provides visibility all the way to the customer’s premises. This solution allows the operator to effectively isolate the customer’s network when testing and monitoring the end-to-end link, and thus eliminate diagnostic errors due to end-customer activities.

SLA-Meter Agent

The SLA-Meter Agent is a highly accurate engine included in Ethernet Demarcation Devices (EDD)[1]. It allows constant in-service monitoring of Service Level Agreement (SLA) parameters including: packet loss, latency (delay), jitter (delay variation) and continuous End-To-End path Continuity Check (availability).

Using a silicon-based pass-phrough architecture (as opposed to store-and-gorward), the EDD features an almost negligible intrinsic latency and jitter, thus allowing it to yield the highest-precision measurements with an outstanding 1 microsecond resolution and provide a true view of the end customer experience. Because the EDD has such a low intrinsic latency and jitter (sub-microsecond) at wirespeed for all packet sizes, and because it is sold at a price comparable to that of a single truck roll, it can be installed in-line anywhere without any impact on the network’s performance, and can thus be used to measure SLA parameters in a variety of topologies and applications.

The SLA-meter agent operates in a point-to-point (See Figure 1(, point-to multipoint (See figure 2) or mesh (See figure 4) fashion and is capable of monitoring multiple simultaneous flows (Multi-SLA, see Figure 3). Furthermore, the SLA-meter agent operates at both Layer 2 and Layer 3 (IP) and can assure SLAs on a per-VLAN, per-Class or Service, per-Type of Service and per-Ethernet Virtual Channel basis for optimum flexibility.

Point to Multi-Point SLA Verification

Business Ethernet services are rising and the hub-and-spoke topology many enterprises are using is a typical application of the Point to Multi-Point SLA Verification.

In this scenario, a headquarters office would be connected to a number of branches (warehouses, factories, stores, service centers, etc.) through an Ethernet line. The SLA-meter agent allows monitoring each of these lines independently and can thus measure SLA parameters between the headquarters office and each branch, using only one EDD per location.

Figure 2 : Point to Multi-Point Performance Monitoring

Figure 2 : Point to Multi-Point Performance Monitoring

Multi-SLA Metering

Layer 2 performance monitoring is invaluable when the time comes to measure the complete Ethernet line’s reliability as a whole. Indeed, Carriers transport Layer 2 Ethernet traffic to their customers, and as such, will guarantee their SLA according to such layer parameters.

Because Layer 3 involves an additional layer (notably the IP stack), its performance-monitoring is geared towards applications in particular. For instance, a company may want to monitor several streams at the same time: Voice over IP for its telephony and voice communications, Video over IP for its conferencing solutions, VPN or Best-Effort Internet.

Each of these streams may have a different priority and SLA requirements, and the ability to verify the performance for each of these independently (in addition to the overall Ethernet line’s quality) is a definite advantage and differentiator for Ethernet Service Providers who can now assure SLAs precisely on growing markets such as VoIP and IP Video.

Figure 3 : Multi-SLA Metering

Figure 3 : Multi-SLA Metering

The SLA-Meter Agent as a Wireless Mesh topology Solution
Many applications nowadays require solid and reliable performance. Voice over IP is one of them and wireless mesh networks is a prime example of why performance monitoring needs to be added.

In this scenario, a Mobile Telephone Switching Office (MTSO) is connected to a number of wireless towers, which are also connected to each other (see Figure 4). As if providing a stringent Quality of Service for Voice services wasn’t enough, Wireless providers also need to assure reliability of the entire connection and provide a means to detect link failure in advance in order to replace it without affecting uptime.

The MTSO can monitor the links by using the SLA-meter agent and retrieve all the statistics while building real-time graphs using any software package supporting Simple Network Management Protocol. In addition to the EDD alarms with configurable thresholds, the software package may be used to monitor each link’s performance and thus detect and locate, in advance, when a specific link is starting to degrade, thus allowing the wireless provider to replace the faulty equipment before experiencing any downtime. Again, because the EDD features an almost negligible (sub-microsecond) intrinsic latency and jitter, its inclusion in the network does not impact the performance or quality of the service being delivered.

Figure 4 : SLA-Meter as a Wireless Mesh Topology Solution

Figure 4 : SLA-Meter as a Wireless Mesh Topology Solution


In the growing environment of carrier-grade Ethernet networks and QoS-dependant IP-services such as VoIP and IPTV, ensuring SLAs and assuring the best QoS possible evolved from being a competitive advantage to an absolute necessity. In order to achieve the expected performance, operators need enhanced equipments and capabilities, as well as devices used to actually measure performance of their own network as well as End-to-End links while disregarding the customer’s own network.

Guaranteeing SLAs is the main factor that was preventing mass-market adoption of Ethernet Services and, with Ethernet Demarcation Devices’ SLA-Meter Agent, Service Providers can now measure their SLA parameters in real-time in a variety of scenarios, in Point-to-Point, Point to Multi-Point, Mesh topology, and even measure Multi-SLA for application-specific SLAs, at Layer 2 or Layer 3 (IP), through a platform that adds virtually no delay or jitter to the existing network.

Damien Ramé is Product Marketing Manager for Accedian Networks.

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