Internet DRAFT - draft-daloia-dcn-reliability
draft-daloia-dcn-reliability
Internet Engineering Task Force Carmine Daloia
Internet-Draft Lucent Technologies
Expiration Date: May 2001 November, 2000
Data Communications Network (DCN) Reliability Requirements
draft-daloia-dcn-reliability-00.txt
Status of this Memo
This document is an Internet-Draft and is in full
conformance with all provisions of Section 10 of RFC2026.
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1. Abstract
This contribution provides high-level reliability requirements
for the Data Communications Network (DCN). Thi draft is
intended to initiate work on reliability aspects of the DCN.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as
described in RFC-2119.
3. Introduction
A Data Communications Network (DCN) is necessary to serve as the
transport network for communications related to the signaling
components as well as the routing components within the ASON
control plane. If the ASON control plane includes other components
such as auto discovery, link management, connection admission control,
survivability, the DCN would also provide transport for communications
related to these components as well. Figure 1 illustrates the
logical representation of ASON. As shown in Figure 1, the ASON consists
of the following logical interfaces/links:
(i) S-UNI - User to Network Interface for signaling
The S-UNI as shown in Figure 1 is the protocol between the client
controller component (Client-C) and the server controller component
(Server-C).
(ii) S-NNI - Network to Network Interface for signaling
The S-NNI as shown in Figure 1 is the protocol between two server
controller components (Server-C).
(iii) U-CCI - User Connection Control Interface
The U-CCI as shown in Figure 1 is the protocol between the client
network transport component (Client) and the client controller
component (Client-C).
(iv) N-CCI - Network Connection Control Interface
The N-CCI as shown in Figure 1 is the protocol between the server
network transport component (Server) and the server controller
component (Server-C).
Figure 1
The task addressed in this document is to evaluate the reliability
requirements for the DCN. The reliability requirements of the DCN
depend heavily on the type of communications transported over the
DCN. For example if the DCN supports transport of communications
related to the survivability mechanism than the reliability
requirements of the DCN may be very stringent compared to if the
DCN transported less time-critical messages (e.g., software download).
The following assumptions are made with regard to this draft document.
- The DCN topology is independent of the transport network topology
(e.g., OTN topology). The logical links (i.e., S-UNI, S-NNI, U-CCI,
and N-CCI) may share some common physical routes with the transport
network logical links (i.e.,. O-UNI, O-NNI) but we do not require or
exclude it.
- The DCN can be built on top of any transport technology such as
optical, SONET, or Ethernet.
4. Analysis of Failure Scenarios
There are two types of failure scenarios that need to be discussed.
(A) Failures that effect only the DCN
(B) Failures that effect both the DCN and the underlying transport
network
The following sub-sections provide some discussion on the impact to
overall ASON reliability under each scenario.
4.1 Failure Scenario A
Failure scenario A assumes an independent failure to the DCN that
does not effect the transport network. Such a failure may impact new
connection setup as well as connection teardown requests from being
completed due to an interruption of paths within the DCN. Figure 2
illustrates such an example. A failure occurs between the server
controllers such that there is no communication path between them to
exchange routing or signaling messages.
Figure 2
4.2 Failure Scenario B
Failure scenario B assumes a failure that effects both the DCN and
the Transport Network. Figure 3 illustrates such an example. Such a
scenario would again impact new connection setup as well as teardown
in the transport network since communications paths within the DCN
may not be available. Since the transport network is also effected
by the failure there could be many new connection requests associated
with the connections that were interrupted due to the failure. Also
if the DCN supported communications related to survivability, the DCN
may not be able to provide the necessary communications required to
restore the interrupted connections.
Figure 3
5. Reliability Requirements for the DCN
Section 4 illustrated failure scenarios that could interrupt the
communications in the DCN and its impact to the ASON network. In
addition, some components (e.g., survivability) of the ASON control
plane may require a highly reliable DCN for transport while others
(e.g., software download) which are not as time-critical may not
require reliable transport. The following lists three reliability
requirements for the DCN.
Requirement #1: The DCN shall support resilience between those
communicating components in the ASON control plane in case of DCN
failures.
Requirement #2: The DCN shall support various levels of restoration
depending on the reliability requirements of the communicating
components (i.e., restoration can be supported between those
components requiring highly reliable communications without requiring
restoration to be supported between all communicating components).
Requirement #3: The DCN shall provide restoration speeds which allow
proper operation of the connections for which it controls (e.g.,
restoration speeds for communications between control plane components
related to survivability must be faster than the restoration speed of
the transport connections for which the components are controlling).
6. References
[1] Carmine Daloia, "DCN Reliability Requirements", T1X1.5/2000-204
7. Authors' Contact Information
Carmine Daloia
Lucent Technologies
daloia@lucent.com
Expiration Date: May 2001
