Transition Networks, Inc.
S4224 Web User Guide
33595 Rev. C
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links. The mechanisms and protocol defined in G.8032 provide highly reliable and stable protection; and avoid
loops which would prove fatal to network operation and service availability.
Each Ethernet Ring Node is connected to adjacent Ethernet Ring Nodes participating in the same Ethernet
Ring, using two independent links. A ring link is bounded by two adjacent Ethernet Ring Nodes, and a port for a
ring link is called a ring port. The minimum number of Ethernet Ring Nodes in an Ethernet Ring is two.
The basis of this RPS architecture are a) the principle of loop avoidance, and b) the use of learning, forwarding,
and Filtering Database (FDB) mechanisms defined in the Ethernet flow forwarding function (ETH_FF).
Loop avoidance in an Ethernet Ring is done by guaranteeing that at all times, traffic may flow on all but one of
the ring links. This particular link is called the Ring Protection Link (RPL), and under normal conditions this ring
link is blocked (i.e., not used for service traffic). One designated Ethernet Ring Node, the RPL Owner Node, is
responsible for blocking traffic at one end of the RPL. Under an Ethernet ring failure condition, the RPL Owner
Node is responsible for unblocking its end of the RPL (unless the RPL has failed) allowing the RPL to be used
for traffic. The other Ethernet Ring Node adjacent to the RPL, the RPL Neighbor Node, may also participate in
blocking or unblocking its end of the RPL.
An Ethernet Ring failure results in protection switching of the traffic. This is achieved under the control of the
ETH_FF functions on all Ethernet Ring Nodes. An APS protocol is used to coordinate the protection actions
over the ring.
ERPS Performance
Note from Rec. ITU-T G.8032/Y.1344 (03/2010): “Ethernet ring protection switching performance: In an Ethernet
ring, without congestion, with all Ethernet ring nodes in the idle state (i.e., no detected failure, no active
automatic or external command, and receiving only "NR, RB" R-APS messages), with less than 1200 km of ring
fibre circumference, and fewer than 16 Ethernet ring nodes, the switch completion time (transfer time as defined
in [ITU-T G.808.1]) for a failure on a ring link will be less than 50 ms. On Ethernet rings under all other
conditions, the switch completion time may exceed 50 ms (the specific interval is under study), to allow time to
negotiate and accommodate coexisting APS requests. In case of interconnection of sub-rings with R-APS virtual
channel to a major ring, the R-APS messages of the sub-ring that are inserted into the R-APS virtual channel
take on performance characteristics (e.g., delay, jitter, packet drop probability, etc.) of the ring links and
Ethernet ring nodes it crosses over the interconnected Ethernet ring. In this case, if the R-APS channel and R-
APS virtual channel exceed the number of Ethernet ring nodes or fibre circumference defined above, the
protection switching of the sub-ring may exceed 50 milliseconds. NOTE – The inclusion of the completion of
FDB flush operation within the transfer time is for further study.”
ESP
The IP Encapsulating Security Payload (ESP) protocol provides a mix of security services in IPv4 and IPv6.
ESP supports two modes of operation: tunnel mode and transport mode.
The ESP header is designed to provide a mix of security services in IPv4 and IPv6. ESP may be applied alone,
in combination with AH, or in a nested fashion.
Security services can be provided between a pair of communicating hosts, between a pair of communicating
security gateways, or between a security gateway and a host. The ESP header is inserted after the IP header
and before the next layer protocol header (transport mode) or before an encapsulated IP header (tunnel mode).
ESP can be used to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay
service (a form of partial sequence integrity), and (limited) traffic flow confidentiality. The set of services
provided depends on options selected at the time of Security Association (SA) establishment and on the
location of the implementation in a network topology. See
IETF
Ethernet ring
A collection of Ethernet ring nodes forming a closed physical loop whereby each Ethernet ring node is
connected to two adjacent Ethernet ring nodes via a duplex communications facility. From ITU-T
Rec.G.8032/Y.1344 (03/2010).
