ERPS is a protocol defined by the International Telecommunication Union – Telecommunications Standardization Sector (ITU-T) – to eliminate loops in Layer 2 while providing traffic recovery switching in ring topology networks.
ERPS implements the convergence of reliability standards and allows all devices compatible with it to be deployed.
The internet is a global system of interconnected computers in networks, which use their own set of protocols, with the purpose of progressively serving users around the world.
Over the years, access has grown on a large scale, both for entertainment and for the corporate market.
All this connectivity infrastructure requires high availability in communication, and fulfilling this role is the function of network protocols, among them ERPS (Ethernet Ring Protection Switch).
Are there differences?
The main differences between ERPS and other Ethernet network protocols, such as Spanning Tree for example, are stability, reliability, and high convergence, minimizing downtime in the logical circuit.
Spanning Tree and Rapid Spanning Tree are also Ethernet layer protocols that provide redundancy for Ethernet networks, but they encounter low convergence issues in a high-scale backbone at the operator level.
It is important to emphasize that the concept of a stable and available network is related to the shortest possible downtime.
With these two protocols, we cannot obtain satisfactory results, as they have relatively high convergence and circuit switching indices.
ERPS uses the RPL (Ring Protection Link) mechanism to protect the entire ring. When a failure occurs at one end of the link, there is an exchange of RAPS (Ring Auto Protection Switching) PDUs (Protocol Data Units) between all neighbors to notify each other of the changes in the link status.
RAPS messages are transmitted over a control VLAN.
The VLAN only carries self-protection ring messages, not service packets, and all nodes in the ring must be configured with the same VLAN in the protocol.
With a port configured with the RPL mechanism, under normal conditions, this ring is blocked. That is, it is not used for service traffic, only for control RAPS messages.
When a ring node fails, the port with the configured RPL owner receives a RAPS indicating the failure in one of the nodes.
The node configured with RPL automatically unlocks the owner's port, allowing that interface to be used for service traffic.
Switching in ERPS is reversible, and when the fault is resolved, the RPL mechanism blocks traffic on the activated port with the protection link.
In an ERPS ring, a port enabled with this protocol has two statuses:
- Routing: routes user traffic and sends and receives RAPS PDUs.
- Discarding: only sends and receives RAPS PDUs.
Why implement the ERPs?
Implementing this protection ring requires that the network topology be planned in advance, taking into account future bandwidth expansions and increases in the number of devices that are part of its structure.
The major advantage of ERPS is its interoperability between manufacturers, as this protocol is available from the main telecommunications equipment manufacturers (Cisco, Huawei, Datacom, among others).
Therefore, planning and implementing a ring backbone project, in addition to enabling stability, scalability, and fault correction standards, makes the project financially viable, since the ERP (Environmental Risk Prevention Program) is already available in entry-level equipment from these manufacturers.
João Calixto – NIS Specialist
