Network Working Group | M. Bagnulo |
Internet-Draft | UC3M |
Intended status: Informational | T. Burbridge |
Expires: December 21, 2014 | BT |
S. Crawford | |
SamKnows | |
P. Eardley | |
BT | |
A. Morton | |
AT&T Labs | |
June 19, 2014 |
A Reference Path and Measurement Points for LMAP
draft-ietf-ippm-lmap-path-04
This document defines a reference path for Large-scale Measurement of Broadband Access Performance (LMAP) and measurement points for commonly used performance metrics. The methods for measurement point location may be applicable to similar measurement projects using the extensions described here.
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This document defines a reference path for Large-scale Measurement of Broadband Access Performance (LMAP) or similar measurement projects. The series of IP Performance Metrics (IPPM) RFCs have developed terms that are generally useful for path description (section 5 of [RFC2330]). There are a limited number of additional terms needing definition here, and they will be defined in this memo.
The reference path is usually needed when attempting to communicate precisely about the components that comprise the path, often in terms of their number (hops) and geographic location. This memo takes the path definition further, by establishing a set of measurement points along the path and ascribing a unique designation to each point. This topic has been previously developed in section 5.1 of [RFC3432], and as part of the updated framework for composition and aggregation, section 4 of [RFC5835] (which may also figure in the LMAP work effort). Section 4.1 of [RFC5835] defines the term "measurement point".
Measurement points and the paths they cover are often described in general terms, like "end-to-end", "user-to-user", or "access". These terms alone are insufficient for scientific method: What is an end? Where is a user located? Is the home network included?
The motivation for this memo is to provide an unambiguous framework to describe measurement coverage, or scope of the reference path. This is an essential part of the meta-data to describe measurement results. Measurements conducted over different path scopes are not a valid basis for performance comparisons. We note that additional measurement context information may be necessary to support a valid comparison of results.
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].
The scope of this memo is to define a reference path for LMAP activities with sufficient level of detail to determine the location of different measurement points along a path without ambiguity. These conventions are likely to be useful in other measurement projects as well.
The connection between the reference path and specific network technologies (with differing underlying architectures) is within the scope of this method, and examples are provided. Both wired and wireless technologies are in-scope.
The purpose is to create an efficient way to describe the location of the measurement point(s) used to conduct a particular measurement so that the measurement result will adequately described in terms of scope or coverage. This should serve many measurement uses, including:
This section defines key terms and concepts for the purposes of this memo.
A reference path is a serial combination of routers, switches, links, radios, and processing elements that comprise all the network elements traversed by each packet between the source and destination hosts. The reference path is intended to be equally applicable to all networking technologies, therefore the components are generically defined, but their functions should have a clear counterpart or be obviously omitted in any network technology.
An entity (associated with one or more users) that is engaged in a subscription with a service provider. The subscriber is allowed to subscribe and un-subscribe services, and to register a user or a list of users authorized to enjoy these services. [Q1741] Both the subscriber and service provider are allowed to set the limits relative to the use that associated users make of subscribed services.
All resources of a Dedicated component (typically a link or node on the Reference Path) are allocated to serving the traffic of an individual Subscriber. Resources include transmission time-slots, queue space, processing for encapsulation and address/port translation, and others. A Dedicated component can affect the performance of the Reference Path, or the performance of any sub-path where the component is involved.
A component on the Reference Path is designated a Shared component when the traffic associated with multiple Subscribers is served by common resources.
A point between Dedicated and Shared components on a Reference Path that may be a point of significance, and is identified as a transition between two types of resources.
Service providers are responsible for the portion of the path they manage. However, most paths involve a sub-path which is beyond the management of the subscriber's service provider. This means that private networks, wireless networks using unlicensed frequencies, and the networks of other service are designated as un-managed sub-paths. The Service demarcation point always divides managed and un-managed sub-paths.
This section defines a reference path for Internet communication.
Subsc. -- Private -- Private -- Service-- Intra IP -- GRA -- Transit device Net #1 Net #2 Demarc. Access GW GRA GW ... Transit -- GRA -- Service -- Private -- Private -- Destination GRA GW GW Demarc. Net #n Net #n+1 Host
GRA = Globally Routable Address, GW = Gateway
The following are descriptions of reference path components that may not be clear from their name alone.
Use of multiple IP address families in the measurement path must be noted, as the conversions between IPv4 and IPv6 certainly influence the visibility of a GRA for each family.
In the case that a private address space is used throughout an access architecture, then the Service Demarc. and the Intra IP Access points must use the same address space and be separated by the shared and dedicated access link infrastructure, such that a test between these points produces a useful assessment of access performance.
A key aspect of measurement points, beyond the definition in section 4.1 of [RFC5835], is that the innermost IP header and higher layer information must be accessible through some means. This is essential to measure IP metrics. There may be tunnels and/or other layers which encapsulate the innermost IP header, even adding another IP header of their own.
In general, measurement points cannot always be located exactly where desired. However, the definition in [RFC5835] and the discussion in section 5.1 of [RFC3432] indicate that allowances can be made: for example, it is nearly ideal when there are deterministic errors that can be quantified between desired and actual measurement point.
The Figure below illustrates the assignment of measurement points to selected components of the reference path.
Subsc. -- Private -- Private -- Service-- Intra IP -- GRA -- Transit device Net #1 Net #2 Demarc. Access GW GRA GW mp000 mp100 mp150 mp190 mp200 ... Transit -- GRA -- Service -- Private -- Private -- Destination GRA GW GW Demarc. Net #n Net #n+1 Host mpX90 mp890 mp800 mp900
GRA = Globally Routable Address, GW = Gateway
Figure 1
When communicating the results of measurements using the measurement point designations described here, the measuring organization SHOULD supply a diagram similar to Figure 1 (and the technology-specific examples that follow), and MUST supply it when additional measurement point numbers have been defined and used, with sufficient detail to identify measurement locations in the path. Organizations with similar technologies and architectures are encouraged to coordinate on local numbering and diagrams, when possible.
The measurement point numbering system, mpXnn, has two independent parts:
In order to define the measurement points and the scope of measurements without ambiguity, the operator of the measurement system SHOULD indicate on a diagram (similar to those in this document): the reference path, the numbers (mpXnn) of the measurement points, and the definition of any measurement point other than 00 and 90 (with sufficient detail to clearly define its location).
If the number of intermediate networks (between the source and destination) is not known or is unstable, then this SHOULD be indicated on the diagram and results from measurement points within those networks need to be treated with caution.
Notes:
This section and those that follow are intended to provide a more exact mapping between particular network technologies and the reference path.
We provide an example for 3G Cellular access below.
Subscriber -- Private --- Service ------------- GRA --- Transit ... device Net #1 Demarc. GW GRA GW mp000 mp100 mp190 mp200 |_____________UE______________|___RAN+Core____|___GGSN__| |_____Un-managed sub-path_____|____Managed sub-path_____|
GRA = Globally Routable Address, GW = Gateway, UE = User Equipment, RAN = Radio Access Network, GGSN = Gateway GPRS Support Node.
We next provide an example of DSL access. Consider the case where:
We believe this is a fairly common configuration in some parts of the world and fairly simple as well.
This case would map into the defined reference measurement points as follows:
Subsc. -- Private -- Private -- Service-- Intra IP -- GRA -- Transit device Net #1 Net #2 Demarc. Access GW GRA GW mp000 mp100 mp150 mp190 mp200 |--UE--|------------CPE/NAT--------|------|-BRAS-|------| |------DSL Network---| |_______Un-managed sub-path________|__Managed sub-path__|
GRA = Globally Routable Address, GW = Gateway, BRAS = Broadband Remote Acess Server
Consider next another access network case where:
We believe this is becoming a fairly common configuration in some parts of the world.
This case would map into the defined reference measurement points as follows:
Subsc. -- Private ------------- Service-- Intra IP -- GRA -- Transit device Net #1 Demarc. Access GW GRA GW mp000 mp100 mp150 mp190 mp200 |--UE--|------------CPE/NAT--------|------|-CGN-|------| |--Access Network---| |_______Un-managed sub-path________|_Managed sub-path__|
GRA = Globally Routable Address, GW = Gateway
This section gives an example of Shared and Dedicated portions with the reference path. This example shows two Resource Transition Points.
Consider the case where:
We believe this is a fairly common configuration in parts of the world.
This case would map into the defined reference measurement points as follows:
Subsc. -- Private -- Private -- Access -- Intra IP -- GRA -- Transit device Net #1 Net #2 Demarc. Access GW GRA GW mp000 mp100 mp150 mp190 mp200 |--UE--|------------CPE/NAT--------|------|-CGN-|------| | Wi-Fi | 1000Base-T |--Access Network---| |-Shared--|RT|------Dedicated------| RT |-----Shared------... |_______Un-managed sub-path________|_Managed sub-path__|
GRA = Globally Routable Address, GW = Gateway, RT = Resource Transition Point
Specification of a Reference Path and identification of measurement points on the path represent agreements among interested parties, and they present no threat to the readers of this memo or to the Internet itself.
When considering privacy of those involved in measurement or those whose traffic is measured, there is sensitive information communicated to recipients of the network diagrams illustrating paths and measurement points described above. We refer the reader to the privacy considerations described in the Large Scale Measurement of Broadband Performance (LMAP) Framework [I-D.ietf-lmap-framework], which covers active and passive measurement techniques and supporting material on measurement context.
This memo makes no requests for IANA consideration.
Thanks to Matt Mathis, Charles Cook, Dan Romascanu, and Lingli Deng for review and comments.
[RFC2330] | Paxson, V., Almes, G., Mahdavi, J. and M. Mathis, "Framework for IP Performance Metrics", RFC 2330, May 1998. |
[RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
[RFC3432] | Raisanen, V., Grotefeld, G. and A. Morton, "Network performance measurement with periodic streams", RFC 3432, November 2002. |
[RFC5835] | Morton, A. and S. Van den Berghe, "Framework for Metric Composition", RFC 5835, April 2010. |
[I-D.ietf-lmap-framework] | Eardley, P., Morton, A., Bagnulo, M., Burbridge, T., Aitken, P. and A. Akhter, "A framework for large-scale measurement platforms (LMAP)", Internet-Draft draft-ietf-lmap-framework-06, June 2014. |
[SK] | Crawford, Sam., "Test Methodology White Paper", SamKnows Whitebox Briefing Note http://www.samknows.com/broadband/index.php, July 2011. |
[Q1741] | Q.1741.7, , "IMT-2000 references to Release 9 of GSM-evolved UMTS core network", http://www.itu.int/rec/T-REC-Q.1741.7/en, November 2011. |