ALTO WG Y. Yang, Ed.
Internet-Draft Yale University
Intended status: Standards Track July 15, 2013
Expires: January 16, 2014
ALTO Topology Considerations
draft-yang-alto-topology-00.txt
Abstract
The Application-Layer Traffic Optimization (ALTO) Service has defined
Network and Cost maps to provide basic network information. In this
document, we discuss some initial thinking on adding topology in
ALTO.
Requirements Language
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 [RFC2119].
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Motivation using Examples . . . . . . . . . . . . . . . . . . . 4
2.1. Single-Switch . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Multiple Switches . . . . . . . . . . . . . . . . . . . . . 4
2.3. Network Constraints/Policies of a Fixed E2E Path . . . . . 4
2.4. Multi-Layer Topology . . . . . . . . . . . . . . . . . . . 5
2.5. Multicast and Broadcast Topology . . . . . . . . . . . . . 5
3. Sketch of Schema . . . . . . . . . . . . . . . . . . . . . . . 5
4. Graph Transformations to Build Topology/Overlays . . . . . . . 7
5. Operations on Exported Topology . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
Topology is a basic information component that a network can provide
to network management tools and applications. Example tools and
applications that can utilize network topology include traffic
engineering, network services (e.g., VPN) provisioning, PCE,
application overlays, among others [RFC5693,I-D.amante-i2rs-topology-
use-cases, I-D.lee-alto-app-net-info-exchange].
A basic challenge in exposing network topology is that there can be
multiple representations of the topology of the same network
infrastructure, and each representation may be better suited for its
own set of deployment scenarios. For example, the current base ALTO
protocol [I-D.ietf-alto-protocol] is designed for a setting of
exposing network topology using the extreme "my-Internet-view"
representation, which does not report any internal network switches,
and hence is a "single-switch" abstraction. We interpret the word
"switch" in the generic sense of network equipment in this document,
not limited to L2 devices. An issue of this abstraction is that
there are applications who may need details about network elements
(e.g., specific network switches and links), but these are not
exposed in the single-switch topology abstraction. An opposite of
the single-switch representation is the complete raw topology,
spanning across multiple layers, to include all details of network
states such as endhosts attachment, physical links, physical switch
equipment, and logical structures (e.g., LSPs) already built on top
of physical infrastructure devices. A problem of the raw topology
representation, however, is that its exposure may violate privacy
constraints. Also, a large raw topology may be overwhelming and
unnecessary for specific applications.
In this document, we discuss an extension of ALTO for topology
exposure. We focus on a particular network. We assume a raw network
topology, i.e., the ground truth. How the raw topology information
is collected is outside the scope of this document.
The organization of this document is not a typical normative
document. In particular, we first introduce concepts through
examples, to better motivate the design. Then we introduce a sketch
of schema for exposing topology in ALTO. There are details of the
schema that are not specified and the intention is to integrate with
other designs such as [I-D.lee-alto-app-net-info-exchange]. Next we
give a framework of topology transformations to help with the
understanding of deriving multiple representations of the topology of
the same network infrastructure. We finish by pointing out
operations based on new ALTO topology exposure.
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2. Motivation using Examples
We distinguish between endhosts and the network infrastructure of the
network. Endhosts are sources and destinations of data that the
network infrastructure carries. The network itself is neither the
source or the destination of data.
For the given network, it provides "access ports" or access points
where digital signal from endhosts enter and leave the network. One
should understand "access ports" in a general sense. For example, an
access port can be a physical Ethernet port connecting to a specific
endhost, or it can be a port connecting to a CE which connects to a
large number of endhosts. Let AP be the set of access ports that the
network provides.
2.1. Single-Switch
A high-level abstraction of a network topology is only the set AP,
and one can visualize the network as a single switch. At each ap in
AP, a set of endhosts can be reached as destinations. Let dest(ap)
denote the set of endhosts reachable at ap. The base ALTO protocol
introduces PID to represent a partition of the set AP. Each subset
in the partition is named as a PID, and the complete partition is
conveyed as the Network Map. The ALTO base protocol then conveys the
pair-wise connection properties from one PID to another PID through
the "single-switch". This is the Cost Map.
2.2. Multiple Switches
Now, assume that the network actually consists of multiple switches,
and the application needs to know more detailed topology. To help
with the understanding, we consider the example case that the network
has three switches, s1, s2 and s3. Each switch is connected to the
other. The set AP is naturally divided as AP1, AP2, and AP3,
denoting the access ports connected to the three switches
respectively. The topology then exposed is simple to represent:
there are three components: PIDs: {AP1, AP2, AP3}, Switches: {s1, s2,
s3}, and Links: {s1->s2, s2->s1, ..., s2->s3, s3->s2}. It is
straightforward to extend ALTO to represent the two additional
components: Switches and Links.
2.3. Network Constraints/Policies of a Fixed E2E Path
Although the preceding 3-component representation is suited for some
settings, e.g., traffic engineering who works on the raw topology,
some other applications may need to or should only know a topology
that encodes existing network constraints or policies. Note that
such constraints may also come from another network tool or
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application, to allow modular management composition.
For example, there can be a constraint, policy, or modular
composition of the result of another application that endhosts from
ap1 in AP1 connected to s1 must use the path s1 -> s2 -> s3 to reach
endhosts at ap3 in AP3. To encode such a constraint to an
application, there can be two choices: (1) create virtual switches
and links still use the uniform graph-based representation; or (2)
enumerate such a constraint in an end-to-end overlay representation.
2.4. Multi-Layer Topology
Now assume that the link s1 -> s2 is actually a given optical path,
and s1 -> s3 is another given optical path, and the deployment
scenario requires that this detail be exposed to the tool or
application on top of topology exposure, for example, to evaluate
reliability considering shared risk link groups. To handle such a
case, one can encode the optical topology in a graph representation,
and also include (layer 3) end-to-end entries s1 -> s2 and s1 -> s3
to specify the paths or some transformation of the paths such as
encoded, opaque shared-risk-link group numbers for each of the s1 ->
s2 and s1 -> s3 paths.
2.5. Multicast and Broadcast Topology
Next consider more complexity. Assume that the link from s1 -> s2 is
actually a wireless link and the application may benefit in knowing
that s1 -> s2 and s1 -> s3 can be active simultaneously. In other
words, s1 -> [s2, s3] is a broadcast link. Knowing such links can be
beneficial in settings such as wireless opportunistic routing.
3. Sketch of Schema
Given the preceding, we consider the following schema, which consists
of EndhostMap, Topology, and Overlays.
EndhostMap: which encodes PIDs representing endhosts.
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object {
VersionTag map-vtag;
EndhostMapData map; // CHANGE: rename NetworkMap
// to EndhostMap??
} InfoResourceEndhostMap;
object-map {
PIDName -> EndpointAddrGroup; // already defined in base ALTO
} EndhostMapData;
Topology: A network can define 0 to multiple topology maps, where
each topology consists of switches and links:
object {
VersionTag map-vtag;
SwitchMapData switches;
LinkMapData links;
} InfoResourceTopology;
object-map {
JSONString -> SwitchProperties; // switch name to properties
} SwitchMapData;
object {
AccessLinks alinks; // between a PID to a switch
TransportLinks tlinks; // between two switches
} LinkMapData;
(Overlay) paths: A network can define 0 to multiple overlays on top
of a given topology, and path can be recursive:
object {
PathType type; // E2ECostMap; LSPs; ...
[PathMapData map;] // depends on type,
// if it is E2ECostMap,
// it is InfoResourceCostMap
// defined in [alto-protocol]
} PathMap;
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4. Graph Transformations to Build Topology/Overlays
The preceding sections give a top-down derivation. In this section,
we give a graph transformation framework to build the schema from a
raw topology G(0). The network conducts transformations on G(0) to
obtain other topologies, with the following objectives:
1. Simplification: G(0) may have too many details that are
unnecessary for the receiving app (assume intradomain, and hence
no security problem); and
2. Preservation of privacy: there are details that the receiving app
should not be allowed to see; and
3. Convey of logical structure (e.g., MPLS paths already computed);
and
4. Convey of capability constraints (the network can have
limitations, e.g., it uses only shortest path routing); and
5. Allow modular composition: path from one point to another point
is delegated to another app.
The transformation of G(0) is to achieve/encode the preceding. For
conceptual clarity, we assume that the network uses a given set of
operators. Hence, given a sequence of operations and starting from
G(0), the network builds G(1), to G(2), ...
Below is a list of basic operators that the network may use to
transform from G(n-1) to G(n):
o O1: Deletion of a switch/port/link from G(n-1);
o O2: Switch aggregation: a set Vs of switches are merged as one new
(logical) switch, links/ports connected to switches in Vs are now
connected to the new logical switch, and then all switches in Vs
are deleted;
o O3: Path representation: For a given extra path from A to R1 to R2
... to B in G(n-1), a new (logical) link A -> B is added; if the
constraint is that A -> must use the path, it will be put into the
Overlay;
o O4: Switch split: A switch s in G(n-1) becomes two (logical)
switches s1 and s2. The links connected to s1 is a subset of the
original links connected to s; so is s2.
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5. Operations on Exported Topology
Going beyond the basic topology exposure from the network and
applications/tools, we anticipate that applications and tools can
derive results and feed to topology. In particular, we consider the
following operations:
o Instantiation of app guidance in real network: The details of
instantiation will be outside the scope of this document. Example
protocols include PCEP Extensions for Stateful PCE [I-D.ietf-pce-
stateful-pce], RSVP LSP's and their associated characteristics,
(i.e.: head and tail-end LSR's, bandwidth, priority, preemption,
etc.). The reason that we choose the preceding operator set is
that they are "implementable".
o We also anticipate topology guided mapping of other data: to allow
applications to subscribe to statistics and link status from the
derived topology.
6. Security Considerations
This document has not conducted its security analysis.
7. IANA Considerations
This document does not specified its IANA considerations, yet.
8. Acknowledgments
The author thanks discussions with Erran Li, Tianyuan Liu, Andreas
Voellmy, Haibin Song, and Yan Luo.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[I-D.amante-i2rs-topology-use-cases]
Amante, S., Medved, J., Previdi, S., and T. Nadeau,
"Topology API Use Cases",
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draft-amante-i2rs-topology-use-cases-00 (work in
progress), February 2013.
[I-D.ietf-alto-protocol]
Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
draft-ietf-alto-protocol-17 (work in progress), July 2013.
[I-D.lee-alto-app-net-info-exchange]
Lee, Y., Bernstein, G., Choi, T., and D. Dhody, "ALTO
Extensions to Support Application and Network Resource
Information Exchange for High Bandwidth Applications",
draft-lee-alto-app-net-info-exchange-02 (work in
progress), July 2013.
[RFC5693] Seedorf, J. and E. Burger, "Application-Layer Traffic
Optimization (ALTO) Problem Statement", RFC 5693,
October 2009.
Author's Address
Y. Richard Yang (editor)
Yale University
51 Prospect St
New Haven CT
USA
Email: yry@cs.yale.edu
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