draft-ietf-dime-overload-reqs-07.txt   rfc7068.txt 
Network Working Group E. McMurry Internet Engineering Task Force (IETF) E. McMurry
Internet-Draft B. Campbell Request for Comments: 7068 B. Campbell
Intended status: Informational Tekelec Category: Informational Oracle
Expires: December 8, 2013 June 6, 2013 ISSN: 2070-1721 November 2013
Diameter Overload Control Requirements Diameter Overload Control Requirements
draft-ietf-dime-overload-reqs-07
Abstract Abstract
When a Diameter server or agent becomes overloaded, it needs to be When a Diameter server or agent becomes overloaded, it needs to be
able to gracefully reduce its load, typically by informing clients to able to gracefully reduce its load, typically by advising clients to
reduce sending traffic for some period of time. Otherwise, it must reduce traffic for some period of time. Otherwise, it must continue
continue to expend resources parsing and responding to Diameter to expend resources parsing and responding to Diameter messages,
messages, possibly resulting in congestion collapse. The existing possibly resulting in a progressively severe overload condition. The
Diameter mechanisms, listed in Section 3 are not sufficient for this existing Diameter mechanisms are not sufficient for managing overload
purpose. This document describes the limitations of the existing conditions. This document describes the limitations of the existing
mechanisms in Section 4. Requirements for new overload management mechanisms. Requirements for new overload management mechanisms are
mechanisms are provided in Section 7. also provided.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is not an Internet Standards Track specification; it is
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working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
This Internet-Draft will expire on December 8, 2013. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7068.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction ....................................................4
1.1. Causes of Overload . . . . . . . . . . . . . . . . . . . . 3 1.1. Documentation Conventions ..................................4
1.2. Effects of Overload . . . . . . . . . . . . . . . . . . . 5 1.2. Causes of Overload .........................................5
1.3. Overload vs. Network Congestion . . . . . . . . . . . . . 5 1.3. Effects of Overload ........................................6
1.4. Diameter Applications in a Broader Network . . . . . . . . 5 1.4. Overload vs. Network Congestion ............................6
1.5. Documentation Conventions . . . . . . . . . . . . . . . . 6 1.5. Diameter Applications in a Broader Network .................7
2. Overload Scenarios . . . . . . . . . . . . . . . . . . . . . . 6 2. Overload Control Scenarios ......................................7
2.1. Peer to Peer Scenarios . . . . . . . . . . . . . . . . . . 7 2.1. Peer-to-Peer Scenarios .....................................8
2.2. Agent Scenarios . . . . . . . . . . . . . . . . . . . . . 9 2.2. Agent Scenarios ...........................................10
2.3. Interconnect Scenario . . . . . . . . . . . . . . . . . . 12 2.3. Interconnect Scenario .....................................14
3. Existing Mechanisms . . . . . . . . . . . . . . . . . . . . . 13 3. Diameter Overload Case Studies .................................15
4. Issues with the Current Mechanisms . . . . . . . . . . . . . . 14 3.1. Overload in Mobile Data Networks ..........................15
4.1. Problems with Implicit Mechanism . . . . . . . . . . . . . 15 3.2. 3GPP Study on Core Network Overload .......................16
4.2. Problems with Explicit Mechanisms . . . . . . . . . . . . 15 4. Existing Mechanisms ............................................17
5. Diameter Overload Case Studies . . . . . . . . . . . . . . . . 16 5. Issues with the Current Mechanisms .............................18
5.1. Overload in Mobile Data Networks . . . . . . . . . . . . . 16 5.1. Problems with Implicit Mechanism ..........................18
5.2. 3GPP Study on Core Network Overload . . . . . . . . . . . 17 5.2. Problems with Explicit Mechanisms .........................18
6. Extensibility and Application Independence . . . . . . . . . . 18 6. Extensibility and Application Independence .....................19
7. Solution Requirements . . . . . . . . . . . . . . . . . . . . 18 7. Solution Requirements ..........................................20
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 7.1. General ...................................................20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 23 7.2. Performance ...............................................21
9.1. Access Control . . . . . . . . . . . . . . . . . . . . . . 24 7.3. Heterogeneous Support for Solution ........................22
9.2. Denial-of-Service Attacks . . . . . . . . . . . . . . . . 24 7.4. Granular Control ..........................................23
9.3. Replay Attacks . . . . . . . . . . . . . . . . . . . . . . 24 7.5. Priority and Policy .......................................23
9.4. Man-in-the-Middle Attacks . . . . . . . . . . . . . . . . 25 7.6. Security ..................................................23
9.5. Compromised Hosts . . . . . . . . . . . . . . . . . . . . 25 7.7. Flexibility and Extensibility .............................24
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25 8. Security Considerations ........................................25
10.1. Normative References . . . . . . . . . . . . . . . . . . . 25 8.1. Access Control ............................................25
10.2. Informative References . . . . . . . . . . . . . . . . . . 26 8.2. Denial-of-Service Attacks .................................26
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 26 8.3. Replay Attacks ............................................26
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 27 8.4. Man-in-the-Middle Attacks .................................26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27 8.5. Compromised Hosts .........................................27
9. References .....................................................27
9.1. Normative References ......................................27
9.2. Informative References ....................................27
Appendix A. Contributors ..........................................29
Appendix B. Acknowledgements ......................................29
1. Introduction 1. Introduction
When a Diameter [RFC6733] server or agent becomes overloaded, it A Diameter [RFC6733] node is said to be overloaded when it has
needs to be able to gracefully reduce its load, typically by insufficient resources to successfully process all of the Diameter
informing clients to reduce sending traffic for some period of time. requests that it receives. When a node becomes overloaded, it needs
Otherwise, it must continue to expend resources parsing and to be able to gracefully reduce its load, typically by advising
responding to Diameter messages, possibly resulting in congestion clients to reduce traffic for some period of time. Otherwise, it
collapse. The existing mechanisms provided by Diameter are not must continue to expend resources parsing and responding to Diameter
sufficient for this purpose. This document describes the limitations messages, possibly resulting in a progressively severe overload
of the existing mechanisms, and provides requirements for new condition. The existing mechanisms provided by Diameter are not
overload management mechanisms. sufficient for managing overload conditions. This document describes
the limitations of the existing mechanisms and provides requirements
for new overload management mechanisms.
This document draws on the work done on SIP overload control This document draws on the work done on SIP overload control
([RFC5390], [RFC6357]) as well as on experience gained via overload ([RFC5390], [RFC6357]) as well as on experience gained via overload
handling in Signaling System No. 7 (SS7) networks and studies done by handling in Signaling System No. 7 (SS7) networks and studies done by
the Third Generation Partnership Project (3GPP) (Section 5). the Third Generation Partnership Project (3GPP) (Section 3).
Diameter is not typically an end-user protocol; rather it is Diameter is not typically an end-user protocol; rather, it is
generally used as one component in support of some end-user activity. generally used as one component in support of some end-user activity.
For example, a SIP server might use Diameter to authenticate and For example, a SIP server might use Diameter to authenticate and
authorize user access. Overload in the Diameter backend authorize user access. Overload in the Diameter backend
infrastructure will likely impact the experience observed by the end infrastructure will likely impact the experience observed by the end
user in the SIP application. user in the SIP application.
The impact of Diameter overload on the client application (a client The impact of Diameter overload on the client application (a client
application may use the Diameter protocol and other protocols to do application may use the Diameter protocol and other protocols to do
its job) is beyond the scope of this document. its job) is beyond the scope of this document.
This document presents non-normative descriptions of causes of This document presents non-normative descriptions of causes of
overload along with related scenarios and studies. Finally, it overload, along with related scenarios and studies. Finally, it
offers a set of normative requirements for an improved overload offers a set of normative requirements for an improved overload
indication mechanism. indication mechanism.
1.1. Causes of Overload 1.1. Documentation Conventions
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 defined in [RFC2119], with the
exception that they are not intended for interoperability of
implementations. Rather, they are used to describe requirements
towards future specifications where the interoperability requirements
will be defined.
The terms "client", "server", "agent", "node", "peer", "upstream",
and "downstream" are used as defined in [RFC6733].
1.2. Causes of Overload
Overload occurs when an element, such as a Diameter server or agent, Overload occurs when an element, such as a Diameter server or agent,
has insufficient resources to successfully process all of the traffic has insufficient resources to successfully process all of the traffic
it is receiving. Resources include all of the capabilities of the it is receiving. Resources include all of the capabilities of the
element used to process a request, including CPU processing, memory, element used to process a request, including CPU processing, memory,
I/O, and disk resources. It can also include external resources such I/O, and disk resources. It can also include external resources such
as a database or DNS server, in which case the CPU, processing, as a database or DNS server, in which case the CPU, processing,
memory, I/O, and disk resources of those elements are effectively memory, I/O, and disk resources of those elements are effectively
part of the logical element processing the request. part of the logical element processing the request.
External resources can include upstream Diameter nodes; for example,
a Diameter agent can become effectively overloaded if one or more
upstream nodes are overloaded.
A Diameter node can become overloaded due to request levels that
exceed its capacity, a reduction of available resources (for example,
a local or upstream hardware failure), or a combination of the two.
Overload can occur for many reasons, including: Overload can occur for many reasons, including:
Inadequate capacity: When designing Diameter networks, that is, Inadequate capacity: When designing Diameter networks, that is,
application layer multi-node Diameter deployments, it can be very application-layer multi-node Diameter deployments, it can be very
difficult to predict all scenarios that may cause elevated difficult to predict all scenarios that may cause elevated
traffic. It may also be more costly to implement support for some traffic. It may also be more costly to implement support for some
scenarios than a network operator may deem worthwhile. This scenarios than a network operator may deem worthwhile. This
results in the likelihood that a Diameter network will not have results in the likelihood that a Diameter network will not have
adequate capacity to handle all situations. adequate capacity to handle all situations.
Dependency failures: A Diameter node can become overloaded because a Dependency failures: A Diameter node can become overloaded because a
resource on which it is dependent has failed or become overloaded, resource on which it depends has failed or become overloaded,
greatly reducing the logical capacity of the node. In these greatly reducing the logical capacity of the node. In these
cases, even minimal traffic might cause the node to go into cases, even minimal traffic might cause the node to go into
overload. Examples of such dependency overloads include DNS overload. Examples of such dependency overloads include DNS
servers, databases, disks, and network interfaces. servers, databases, disks, and network interfaces that have failed
or become overloaded.
Component failures: A Diameter node can become overloaded when it is Component failures: A Diameter node can become overloaded when it is
a member of a cluster of servers that each share the load of a member of a cluster of servers that each share the load of
traffic, and one or more of the other members in the cluster fail. traffic and one or more of the other members in the cluster fail.
In this case, the remaining nodes take over the work of the failed In this case, the remaining nodes take over the work of the failed
nodes. Normally, capacity planning takes such failures into nodes. Normally, capacity planning takes such failures into
account, and servers are typically run with enough spare capacity account, and servers are typically run with enough spare capacity
to handle failure of another node. However, unusual failure to handle failure of another node. However, unusual failure
conditions can cause many nodes to fail at once. This is often conditions can cause many nodes to fail at once. This is often
the case with software failures, where a bad packet or bad the case with software failures, where a bad packet or bad
database entry hits the same bug in a set of nodes in a cluster. database entry hits the same bug in a set of nodes in a cluster.
Network Initiated Traffic Flood: Issues with the radio access Network-initiated traffic flood: Certain access network events can
network in a mobile network such as radio overlays with frequent precipitate floods of Diameter signaling traffic. For example,
handovers, and operational changes are examples of network events operational changes can trigger avalanche restarts, or frequent
that can precipitate a flood of Diameter signaling traffic, such radio overlay handovers can generate excessive authorization
as an avalanche restart. Failure of a Diameter proxy may also requests. Failure of a Diameter proxy may also result in a large
result in a large amount of signaling as connections and sessions amount of signaling as connections and sessions are reestablished.
are reestablished.
Subscriber Initiated Traffic Flood: Large gatherings of subscribers Subscriber-initiated traffic flood: Large gatherings of subscribers
or events that result in many subscribers interacting with the or events that result in many subscribers interacting with the
network in close time proximity can result in Diameter signaling network in close time proximity can result in Diameter signaling
traffic floods. For example, the finale of a large fireworks show traffic floods. For example, the finale of a large fireworks show
could be immediately followed by many subscribers posting could be immediately followed by many subscribers posting
messages, pictures, and videos concentrated on one portion of a messages, pictures, and videos concentrated on one portion of a
network. Subscriber devices, such as smartphones, may use network. Subscriber devices such as smartphones may use
aggressive registration strategies that generate unusually high aggressive registration strategies that generate unusually high
Diameter traffic loads. Diameter traffic loads.
DoS attacks: An attacker, wishing to disrupt service in the network, DoS attacks: An attacker wishing to disrupt service in the network
can cause a large amount of traffic to be launched at a target can cause a large amount of traffic to be launched at a target
element. This can be done from a central source of traffic or element. This can be done from a central source of traffic or
through a distributed DoS attack. In all cases, the volume of through a distributed DoS attack. In all cases, the volume of
traffic well exceeds the capacity of the element, sending the traffic well exceeds the capacity of the element, sending the
system into overload. system into overload.
1.2. Effects of Overload 1.3. Effects of Overload
Modern Diameter networks, comprised of application layer multi-node Modern Diameter networks, composed of application-layer multi-node
deployments of Diameter elements, may operate at very large deployments of Diameter elements, may operate at very large
transaction volumes. If a Diameter node becomes overloaded, or even transaction volumes. If a Diameter node becomes overloaded or, even
worse, fails completely, a large number of messages may be lost very worse, fails completely, a large number of messages may be lost very
quickly. Even with redundant servers, many messages can be lost in quickly. Even with redundant servers, many messages can be lost in
the time it takes for failover to complete. While a Diameter client the time it takes for failover to complete. While a Diameter client
or agent should be able to retry such requests, an overloaded peer or agent should be able to retry such requests, an overloaded peer
may cause a sudden large increase in the number of transaction may cause a sudden large increase in the number of transactions
transactions needing to be retried, rapidly filling local queues or needing to be retried, rapidly filling local queues or otherwise
otherwise contributing to local overload. Therefore Diameter devices contributing to local overload. Therefore, Diameter devices need to
need to be able to shed load before critical failures can occur. be able to shed load before critical failures can occur.
1.3. Overload vs. Network Congestion 1.4. Overload vs. Network Congestion
This document uses the term "overload" to refer to application-layer This document uses the term "overload" to refer to application-layer
overload at Diameter nodes. This is distinct from "network overload at Diameter nodes. This is distinct from "network
congestion", that is, congestion that occurs at the lower networking congestion", that is, congestion that occurs at the lower networking
layers that may impact the delivery of Diameter messages between layers that may impact the delivery of Diameter messages between
nodes. The authors recognize that element overload and network nodes. This document recognizes that element overload and network
congestion are interrelated, and that overload can contribute to congestion are interrelated, and that overload can contribute to
network congestion and vice versa. network congestion and vice versa.
Network congestion issues are better handled by the transport Network congestion issues are better handled by the transport
protocols. Diameter uses TCP and SCTP, both of which include protocols. Diameter uses TCP and the Stream Control Transmission
congestion management features. Analysis of whether those features Protocol (SCTP), both of which include congestion management
are sufficient for transport level congestion between Diameter nodes, features. Analysis of whether those features are sufficient for
and any work to further mitigate network congestion is out of scope transport-level congestion between Diameter nodes and of any work to
both for this document, and for the work proposed by this document. further mitigate network congestion is out of scope for both this
document and the work proposed by it.
1.4. Diameter Applications in a Broader Network 1.5. Diameter Applications in a Broader Network
Most elements using Diameter applications do not use Diameter Most elements using Diameter applications do not use Diameter
exclusively. It is important to realize that overload of an element exclusively. It is important to realize that overload of an element
can be caused by a number of factors that may be unrelated to the can be caused by a number of factors that may be unrelated to the
processing of Diameter or Diameter applications. processing of Diameter or Diameter applications.
A element communicating via protocols other than Diameter that is An element that doesn't use Diameter exclusively needs to be able to
also using a Diameter application needs to be able to signal to signal to Diameter peers that it is experiencing overload regardless
Diameter peers that it is experiencing overload regardless of the of the cause of the overload, since the overload will affect that
cause of the overload, since the overload will affect that element's element's ability to process Diameter transactions. If the element
ability to process Diameter transactions. The element may also need communicates with protocols other than Diameter, it may also need to
to signal this on other protocols depending on its function and the signal the overload situation on these protocols, depending on its
architecture of the network and application it is providing services function and the architecture of the network and application for
for. Whether that is necessary can only be decided within the which it is providing services. Whether that is necessary can only
context of that architecture and application. A mechanism for be decided within the context of that architecture and use cases.
signaling overload with Diameter, which this specification details This specification details the requirements for a mechanism for
the requirements for, provides applications the ability to signal signaling overload with Diameter; this mechanism provides Diameter
their Diameter peers of overload, mitigating that part of the issue. nodes the ability to inform their Diameter peers of overload,
Applications may need to use this, as well as other mechanisms, to mitigating that part of the issue. Diameter nodes may need to use
solve their broader overload issues. Indicating overload on this, as well as other mechanisms, to solve their broader overload
protocols other than Diameter is out of scope for this document, and issues. Indicating overload on protocols other than Diameter is out
for the work proposed by this document. of scope for this document and for the work proposed by it.
1.5. Documentation Conventions
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 [RFC2119].
The terms "client", "server", "agent", "node", "peer", "upstream",
and "downstream" are used as defined in [RFC6733].
2. Overload Scenarios 2. Overload Control Scenarios
Several Diameter deployment scenarios exist that may impact overload Several Diameter deployment scenarios exist that may impact overload
management. The following scenarios help motivate the requirements management. The following scenarios help motivate the requirements
for an overload management mechanism. for an overload management mechanism.
These scenarios are by no means exhaustive, and are in general These scenarios are by no means exhaustive and are in general
simplified for the sake of clarity. In particular, the authors simplified for the sake of clarity. In particular, this document
assume for the sake of clarity that the client sends Diameter assumes for the sake of clarity that the client sends Diameter
requests to the server, and the server sends responses to client, requests to the server, and the server sends responses to the client,
even though Diameter supports bidirectional applications. Each even though Diameter supports bidirectional applications. Each
direction in such an application can be modeled separately. direction in such an application can be modeled separately.
In a large scale deployment, many of the nodes represented in these In a large-scale deployment, many of the nodes represented in these
scenarios would be deployed as clusters of servers. The authors scenarios would be deployed as clusters of servers. This document
assume that such a cluster is responsible for managing its own assumes that such a cluster is responsible for managing its own
internal load balancing and overload management so that it appears as internal load-balancing and overload management so that it appears as
a single Diameter node. That is, other Diameter nodes can treat it a single Diameter node. That is, other Diameter nodes can treat it
as single, monolithic node for the purposes of overload management. as a single, monolithic node for the purposes of overload management.
These scenarios do not illustrate the client application. As These scenarios do not illustrate the client application. As
mentioned in Section 1, Diameter is not typically an end-user mentioned in Section 1, Diameter is not typically an end-user
protocol; rather it is generally used in support of some other client protocol; rather, it is generally used in support of some other
application. These scenarios do not consider the impact of Diameter client application. These scenarios do not consider the impact of
overload on the client application. Diameter overload on the client application.
2.1. Peer to Peer Scenarios 2.1. Peer-to-Peer Scenarios
This section describes Diameter peer-to-peer scenarios. That is, This section describes Diameter peer-to-peer scenarios, that is,
scenarios where a Diameter client talks directly with a Diameter scenarios where a Diameter client talks directly with a Diameter
server, without the use of a Diameter agent. server, without the use of a Diameter agent.
Figure 1 illustrates the simplest possible Diameter relationship. Figure 1 illustrates the simplest possible Diameter relationship.
The client and server share a one-to-one peer-to-peer relationship. The client and server share a one-to-one peer-to-peer relationship.
If the server becomes overloaded, either because the client exceeds If the server becomes overloaded, either because the client exceeds
the server's capacity, or because the server's capacity is reduced the server's capacity or because the server's capacity is reduced due
due to some resource dependency, the client needs to reduce the to some resource dependency, the client needs to reduce the amount of
amount of Diameter traffic it sends to the server. Since the client Diameter traffic it sends to the server. Since the client cannot
cannot forward requests to another server, it must either queue forward requests to another server, it must either queue requests
requests until the server recovers, or itself become overloaded in until the server recovers or itself become overloaded in the context
the context of the client application and other protocols it may also of the client application and other protocols it may also use.
use.
+------------------+ +------------------+
| | | |
| | | |
| Server | | Server |
| | | |
+--------+---------+ +--------+---------+
| |
| |
+--------+---------+ +--------+---------+
| | | |
| | | |
| Client | | Client |
| | | |
+------------------+ +------------------+
Figure 1: Basic Peer to Peer Scenario Figure 1: Basic Peer-to-Peer Scenario
Figure 2 shows a similar scenario, except in this case the client has Figure 2 shows a similar scenario, except in this case the client has
multiple servers that can handle work for a specific realm and multiple servers that can handle work for a specific realm and
application. If server 1 becomes overloaded, the client can forward application. If Server 1 becomes overloaded, the client can forward
traffic to server 2. Assuming server 2 has sufficient reserve traffic to Server 2. Assuming that Server 2 has sufficient reserve
capacity to handle the forwarded traffic, the client should be able capacity to handle the forwarded traffic, the client should be able
to continue serving client application protocol users. If server 1 to continue serving client application protocol users. If Server 1
is approaching overload, but can still handle some number of new is approaching overload, but can still handle some number of new
request, it needs to be able to instruct the client to forward a requests, it needs to be able to instruct the client to forward a
subset of its traffic to server 2. subset of its traffic to Server 2.
+------------------+ +------------------+ +------------------+ +------------------+
| | | | | | | |
| | | | | | | |
| Server 1 | | Server 2 | | Server 1 | | Server 2 |
| | | | | | | |
+--------+-`.------+ +------.'+---------+ +--------+-`.------+ +------.'+---------+
`. .' `. .'
`. .' `. .'
`. .' `. .'
`. .' `. .'
+-------`.'--------+ +-------`.'--------+
| | | |
| | | |
| Client | | Client |
| | | |
+------------------+ +------------------+
Figure 2: Multiple Server Peer to Peer Scenario Figure 2: Multiple-Server Peer-to-Peer Scenario
Figure 3 illustrates a peer-to-peer scenario with multiple Diameter Figure 3 illustrates a peer-to-peer scenario with multiple Diameter
realm and application combinations. In this example, server 2 can realm and application combinations. In this example, Server 2 can
handle work for both applications. Each application might have handle work for both applications. Each application might have
different resource dependencies. For example, a server might need to different resource dependencies. For example, a server might need to
access one database for application A, and another for application B. access one database for Application A and another for Application B.
This creates a possibility that Server 2 could become overloaded for This creates a possibility that Server 2 could become overloaded for
application A but not for application B, in which case the client Application A but not for Application B, in which case the client
would need to divert some part of its application A requests to would need to divert some part of its Application A requests to
server 1, but should not divert any application B requests. This Server 1, but the client should not divert any Application B
requires server 2 to be able to distinguish between applications when requests. This requires that Server 2 be able to distinguish between
it indicates an overload condition to the client. applications when it indicates an overload condition to the client.
On the other hand, it's possible that the servers host many On the other hand, it's possible that the servers host many
applications. If server 2 becomes overloaded for all applications, applications. If Server 2 becomes overloaded for all applications,
it would be undesirable for it to have to notify the client it would be undesirable for it to have to notify the client
separately for each application. Therefore it also needs a way to separately for each application. Therefore, it also needs a way to
indicate that it is overloaded for all possible applications. indicate that it is overloaded for all possible applications.
+---------------------------------------------+ +---------------------------------------------+
| Application A +----------------------+----------------------+ | Application A +----------------------+----------------------+
|+------------------+ | +----------------+ | +------------------+| |+------------------+ | +----------------+ | +------------------+|
|| | | | | | | || || | | | | | | ||
|| | | | | | | || || | | | | | | ||
|| Server 1 | | | Server 2 | | | Server 3 || || Server 1 | | | Server 2 | | | Server 3 ||
|| | | | | | | || || | | | | | | ||
|+--------+---------+ | +-------+--------+ | +-+----------------+| |+--------+---------+ | +-------+--------+ | +-+----------------+|
skipping to change at page 9, line 29 skipping to change at page 10, line 29
`-..__ | _.-'' `-..__ | _.-''
`--._ | _.-'' `--._ | _.-''
``-._ | _.-'' ``-._ | _.-''
+-----`-.-''-----+ +-----`-.-''-----+
| | | |
| | | |
| Client | | Client |
| | | |
+----------------+ +----------------+
Figure 3: Multiple Application Peer to Peer Scenario Figure 3: Multiple-Application Peer-to-Peer Scenario
2.2. Agent Scenarios 2.2. Agent Scenarios
This section describes scenarios that include a Diameter agent, This section describes scenarios that include a Diameter agent, in
either in the form of a Diameter relay or Diameter proxy. These the form of either a Diameter relay or Diameter proxy. These
scenarios do not consider Diameter redirect agents, since they are scenarios do not consider Diameter redirect agents, since they are
more readily modeled as end-servers. more readily modeled as end servers. The examples have been kept
simple deliberately, to illustrate basic concepts. Significantly
more complicated topologies are possible with Diameter, including
multiple intermediate agents in a path connected in a variety
of ways.
Figure 4 illustrates a simple Diameter agent scenario with a single Figure 4 illustrates a simple Diameter agent scenario with a single
client, agent, and server. In this case, overload can occur at the client, agent, and server. In this case, overload can occur at the
server, at the agent, or both. But in most cases, client behavior is server, at the agent, or both. But in most cases, client behavior is
the same whether overload occurs at the server or at the agent. From the same whether overload occurs at the server or at the agent. From
the client's perspective, server overload and agent overload is the the client's perspective, server overload and agent overload are the
same thing. same thing.
+------------------+ +------------------+
| | | |
| | | |
| Server | | Server |
| | | |
+--------+---------+ +--------+---------+
| |
| |
+--------+---------+ +--------+---------+
| | | |
| | | |
| Agent | | Agent |
| | | |
+--------+---------+ +--------+---------+
| |
| |
+--------+---------+ +--------+---------+
| | | |
| | | |
| Client | | Client |
| | | |
+------------------+ +------------------+
Figure 4: Basic Agent Scenario Figure 4: Basic Agent Scenario
Figure 5 shows an agent scenario with multiple servers. If server 1 Figure 5 shows an agent scenario with multiple servers. If Server 1
becomes overloaded, but server 2 has sufficient reserve capacity, the becomes overloaded but Server 2 has sufficient reserve capacity, the
agent may be able to transparently divert some or all Diameter agent may be able to transparently divert some or all Diameter
requests originally bound for server 1 to server 2. requests originally bound for Server 1 to Server 2.
In most cases, the client does not have detailed knowledge of the In most cases, the client does not have detailed knowledge of the
Diameter topology upstream of the agent. If the agent uses dynamic Diameter topology upstream of the agent. If the agent uses dynamic
discovery to find eligible servers, the set of eligible servers may discovery to find eligible servers, the set of eligible servers may
not be enumerable from the perspective of the client. Therefore, in not be enumerable from the perspective of the client. Therefore, in
most cases the agent needs to deal with any upstream overload issues most cases the agent needs to deal with any upstream overload issues
in a way that is transparent to the client. If one server notifies in a way that is transparent to the client. If one server notifies
the agent that it has become overloaded, the notification should not the agent that it has become overloaded, the notification should not
be passed back to the client in a way that the client could be passed back to the client in a way that the client could
mistakenly perceive the agent itself as being overloaded. If the set mistakenly perceive the agent itself as being overloaded. If the set
of all possible destinations upstream of the agent no longer has of all possible destinations upstream of the agent no longer has
sufficient capacity for incoming load, the agent itself becomes sufficient capacity for incoming load, the agent itself becomes
effectively overloaded. effectively overloaded.
On the other hand, there are cases where the client needs to be able On the other hand, there are cases where the client needs to be able
to select a particular server from behind an agent. For example, if to select a particular server from behind an agent. For example, if
a Diameter request is part of a multiple-round-trip authentication, a Diameter request is part of a multiple-round-trip authentication,
or is otherwise part of a Diameter "session", it may have a or is otherwise part of a Diameter "session", it may have a
DestinationHost AVP that requires the request to be served by server Destination-Host Attribute-Value Pair (AVP) that requires that the
1. Therefore the agent may need to inform a client that a particular request be served by Server 1. Therefore, the agent may need to
upstream server is overloaded or otherwise unavailable. Note that inform a client that a particular upstream server is overloaded or
there can be many ways a server can be specified, which may have otherwise unavailable. Note that there can be many ways a server can
different implications (e.g. by IP address, by host name, etc). be specified, which may have different implications (e.g., by IP
address, by host name, etc).
+------------------+ +------------------+ +------------------+ +------------------+
| | | | | | | |
| | | | | | | |
| Server 1 | | Server 2 | | Server 1 | | Server 2 |
| | | | | | | |
+--------+-`.------+ +------.'+---------+ +--------+-`.------+ +------.'+---------+
`. .' `. .'
`. .' `. .'
`. .' `. .'
`. .' `. .'
+-------`.'--------+ +-------`.'--------+
| | | |
| | | |
| Agent | | Agent |
| | | |
+--------+---------+ +--------+---------+
| |
| |
| |
+--------+---------+ +--------+---------+
| | | |
| | | |
| Client | | Client |
| | | |
+------------------+ +------------------+
Figure 5: Multiple Server Agent Scenario Figure 5: Multiple-Server Agent Scenario
Figure 6 shows a scenario where an agent routes requests to a set of Figure 6 shows a scenario where an agent routes requests to a set of
servers for more than one Diameter realm and application. In this servers for more than one Diameter realm and application. In this
scenario, if server 1 becomes overloaded or unavailable, the agent scenario, if Server 1 becomes overloaded or unavailable while
may effectively operate at reduced capacity for application A, but at Server 2 still has available capacity, the agent may effectively
full capacity for application B. Therefore, the agent needs to be operate at reduced capacity for Application A but at full capacity
able to report that it is overloaded for one application, but not for for Application B. Therefore, the agent needs to be able to report
another. that it is overloaded for one application but not for another.
+--------------------------------------------+ +--------------------------------------------+
| Application A +----------------------+----------------------+ | Application A +----------------------+----------------------+
|+------------------+ | +----------------+ | +------------------+| |+------------------+ | +----------------+ | +------------------+|
|| | | | | | | || || | | | | | | ||
|| | | | | | | || || | | | | | | ||
|| Server 1 | | | Server 2 | | | Server 3 || || Server 1 | | | Server 2 | | | Server 3 ||
|| | | | | | | || || | | | | | | ||
|+---------+--------+ | +-------+--------+ | +--+---------------+| |+---------+--------+ | +-------+--------+ | +--+---------------+|
| | | | | | | | | | | | | |
skipping to change at page 12, line 37 skipping to change at page 13, line 45
+-------+--------+ +-------+--------+
| |
| |
+-------+--------+ +-------+--------+
| | | |
| | | |
| Client | | Client |
| | | |
+----------------+ +----------------+
Figure 6: Multiple Application Agent Scenario Figure 6: Multiple-Application Agent Scenario
2.3. Interconnect Scenario 2.3. Interconnect Scenario
Another scenario to consider when looking at Diameter overload is Another scenario to consider when looking at Diameter overload is
that of multiple network operators using Diameter components that of multiple network operators using Diameter components
connected through an interconnect service, e.g. using IPX. IPX (IP connected through an interconnect service, e.g., using IPX (IP Packet
eXchange) [IR.34] is an Inter-Operator IP Backbone that provides eXchange). IPX [IR.34] is an Inter-Operator IP Backbone that
roaming interconnection network between mobile operators and service provides a roaming interconnection network between mobile operators
providers. The IPX is also used to transport Diameter signaling and service providers. IPX is also used to transport Diameter
between operators [IR.88]. Figure 7 shows two network operators with signaling between operators [IR.88]. Figure 7 shows two network
an interconnect network in-between. There could be any number of operators with an interconnect network between them. There could be
these networks between any two network operator's networks. any number of these networks between any two network operators'
networks.
+-------------------------------------------+ +-------------------------------------------+
| Interconnect | | Interconnect |
| | | |
| +--------------+ +--------------+ | | +--------------+ +--------------+ |
| | Server 3 |------| Server 4 | | | | Server 3 |------| Server 4 | |
| +--------------+ +--------------+ | | +--------------+ +--------------+ |
| .' `. | | .' `. |
+------.-'--------------------------`.------+ +------.-'--------------------------`.------+
.' `. .' `.
.-' `. .-' `.
------------.'-----+ +----`.------------- ------------.'-----+ +----`.-------------
+----------+ | | +----------+ +----------+ | | +----------+
| Server 1 | | | | Server 2 | | Server 1 | | | | Server 2 |
+----------+ | | +----------+ +----------+ | | +----------+
| | | |
Network Operator 1 | | Network Operator 2 Network Operator 1 | | Network Operator 2
-------------------+ +------------------- -------------------+ +-------------------
Figure 7: Two Network Interconnect Scenario Figure 7: Two-Network Interconnect Scenario
The characteristics of the information that an operator would want to The characteristics of the information that an operator would want to
share over such a connection are different from the information share over such a connection are different from the information
shared between components within a network operator's network. shared between components within a network operator's network. For
Network operators may not want to convey topology or operational example, network operators may not want to convey topology or
information, which limits how much overload and loading information operational information; this would in turn limit how much overload
can be sent. For the interconnect scenario shown, Server 2 may want and loading information can be sent. For the interconnect scenario
to signal overload to Server 1, to affect traffic coming from Network shown in Figure 7, Server 2 may want to signal overload to Server 1,
Operator 1. to affect traffic coming from Network Operator 1.
This case is distinct from those internal to a network operator's This case is distinct from those internal to a network operator's
network, where there may be many more elements in a more complicated network, where there may be many more elements in a more complicated
topology. Also, the elements in the interconnect network may not topology. Also, the elements in the interconnect network may not
support Diameter overload control, and the network operators may not support Diameter overload control, and the network operators may not
want the interconnect network to use overload or loading information. want the interconnect network to use overload or loading information.
They may only want the information to pass through the interconnect They may only want the information to pass through the interconnect
network without further processing or action by the interconnect network without further processing or action by the interconnect
network even if the elements in the interconnect network do support network, even if the elements in the interconnect network do support
Diameter overload control. Diameter overload control.
3. Existing Mechanisms 3. Diameter Overload Case Studies
3.1. Overload in Mobile Data Networks
As the number of smartphone devices that are Third Generation (3G)
and Long Term Evolution (LTE) enabled continues to expand in mobile
networks, there have been situations where high signaling traffic
load led to overload events at the Diameter-based Home Location
Registers (HLRs) and/or Home Subscriber Servers (HSS) [TR23.843].
The root causes of the HLR overload events were manifold but included
hardware failure and procedural errors. The result was high
signaling traffic load on the HLR and HSS.
The 3GPP architecture [TS23.002] makes extensive use of Diameter. It
is used for mobility management [TS29.272], the IP Multimedia
Subsystem (IMS) [TS29.228], and policy and charging control
[TS29.212], as well as other functions. The details of the
architecture are out of scope for this document, but it is worth
noting that there are quite a few Diameter applications, some with
quite large amounts of Diameter signaling in deployed networks.
The 3GPP specifications do not currently address overload for
Diameter applications or provide a load control mechanism equivalent
to those provided in the more traditional SS7 elements in the Global
System for Mobile Communications (GSM); see [TS29.002]. The
capabilities specified in the 3GPP standards do not adequately
address the abnormal condition where excessively high signaling
traffic load situations are experienced.
Smartphones, which comprise an increasingly large percentage of
mobile devices, contribute much more heavily, relative to
non-smartphones, to the continuation of a registration surge, due to
their very aggressive registration algorithms. Smartphone behavior
contributes to network loading and can contribute to overload
conditions. The aggressive smartphone logic is designed to:
a. always have voice and data registration, and
b. constantly try to be on 3G or LTE data (and thus on 3G voice or
Voice over LTE (VoLTE) [IR.92]) for their added benefits.
Non-smartphones typically have logic to wait for a time period after
registering successfully on voice and data.
The aggressive smartphone registration is problematic in two ways:
o first, by generating excessive signaling load towards the HSS that
is ten times the load from a non-smartphone, and
o second, by causing continual registration attempts when a network
failure affects registrations through the 3G data network.
3.2. 3GPP Study on Core Network Overload
A study in the 3GPP System Aspects working group 2 (SA2) on core
network overload has produced the technical report [TR23.843]. This
enumerates several causes of overload in mobile core networks,
including portions that are signaled using Diameter. [TR23.843] is a
work in progress and is not complete. However, it is useful for
pointing out scenarios and the general need for an overload control
mechanism for Diameter.
It is common for mobile networks to employ more than one radio
technology and to do so in an overlay fashion with multiple
technologies present in the same location (such as 2nd or 3rd
generation mobile technologies, along with LTE). This presents
opportunities for traffic storms when issues occur on one overlay and
not another as all devices that had been on the overlay with issues
switch. This causes a large amount of Diameter traffic as locations
and policies are updated.
Another scenario called out by this study is a flood of registration
and mobility management events caused by some element in the core
network failing. This flood of traffic from end nodes falls under
the network-initiated traffic flood category. There is likely to
also be traffic resulting directly from the component failure in this
case. A similar flood can occur when elements or components recover
as well.
Subscriber-initiated traffic floods are also indicated in this study
as an overload mechanism where a large number of mobile devices are
attempting to access services at the same time, such as in response
to an entertainment event or a catastrophic event.
While this 3GPP study is concerned with the broader effects of these
scenarios on wireless networks and their elements, they have
implications specifically for Diameter signaling. One of the goals
of this document is to provide guidance for a core mechanism that can
be used to mitigate the scenarios called out by this study.
4. Existing Mechanisms
Diameter offers both implicit and explicit mechanisms for a Diameter Diameter offers both implicit and explicit mechanisms for a Diameter
node to learn that a peer is overloaded or unreachable. The implicit node to learn that a peer is overloaded or unreachable. The implicit
mechanism is simply the lack of responses to requests. If a client mechanism is simply the lack of responses to requests. If a client
fails to receive a response in a certain time period, it assumes the fails to receive a response in a certain time period, it assumes that
upstream peer is unavailable, or overloaded to the point of effective the upstream peer is unavailable or is overloaded to the point of
unavailability. The watchdog mechanism [RFC3539] ensures that a effective unavailability. The watchdog mechanism [RFC3539] ensures
certain rate of transaction responses occur even when there is that transaction responses occur at a certain rate even when there is
otherwise little or no other Diameter traffic. otherwise little or no other Diameter traffic.
The explicit mechanism can involve specific protocol error responses, The explicit mechanism can involve specific protocol error responses,
where an agent or server tells a downstream peer that it is either where an agent or server tells a downstream peer that it is either
too busy to handle a request (DIAMETER_TOO_BUSY) or unable to route a too busy to handle a request (DIAMETER_TOO_BUSY) or unable to route a
request to an upstream destination (DIAMETER_UNABLE_TO_DELIVER), request to an upstream destination (DIAMETER_UNABLE_TO_DELIVER)
perhaps because that destination itself is overloaded to the point of perhaps because that destination itself is overloaded to the point of
unavailability. unavailability.
Another explicit mechanism, a DPR (Disconnect-Peer-Request) message, Another explicit mechanism, a DPR (Disconnect-Peer-Request) message,
can be sent with a Disconnect-Cause of BUSY. This signals the can be sent with a Disconnect-Cause of BUSY. This signals the
sender's intent to close the transport connection, and requests the sender's intent to close the transport connection and requests that
client not to reconnect. the client not reconnect.
Once a Diameter node learns that an upstream peer has become Once a Diameter node learns via one of these mechanisms that an
overloaded via one of these mechanisms, it can then attempt to take upstream peer has become overloaded, it can then attempt to take
action to reduce the load. This usually means forwarding traffic to action to reduce the load. This usually means forwarding traffic to
an alternate destination, if available. If no alternate destination an alternate destination, if available. If no alternate destination
is available, the node must either reduce the number of messages it is available, the node must either reduce the number of messages it
originates (in the case of a client) or inform the client to reduce originates (in the case of a client) or inform the client to reduce
traffic (in the case of an agent.) traffic (in the case of an agent).
Diameter requires the use of a congestion-managed transport layer, Diameter requires the use of a congestion-managed transport layer,
currently TCP or SCTP, to mitigate network congestion. It is currently TCP or SCTP, to mitigate network congestion. It is
expected that these transports manage network congestion and that expected that these transports manage network congestion and that
issues with transport (e.g. congestion propagation and window issues with transport (e.g., congestion propagation and window
management) are managed at that level. But even with a congestion- management) are managed at that level. But even with a congestion-
managed transport, a Diameter node can become overloaded at the managed transport, a Diameter node can become overloaded at the
Diameter protocol or application layers due to the causes described Diameter protocol or application layers due to the causes described
in Section 1.1 and congestion managed transports do not provide in Section 1.2, and congestion-managed transports do not provide
facilities (and are at the wrong level) to handle server overload. facilities (and are at the wrong level) to handle server overload.
Transport level congestion management is also not sufficient to Transport-level congestion management is also not sufficient to
address overload in cases of multi-hop and multi-destination address overload in cases of multi-hop and multi-destination
signaling. signaling.
4. Issues with the Current Mechanisms 5. Issues with the Current Mechanisms
The currently available Diameter mechanisms for indicating an The currently available Diameter mechanisms for indicating an
overload condition are not adequate to avoid service outages due to overload condition are not adequate to avoid service outages due to
overload. This inadequacy may, in turn, contribute to broader overload. This inadequacy may, in turn, contribute to broader
congestion collapse due to unresponsive Diameter nodes causing impacts resulting from overload due to unresponsive Diameter nodes
application or transport layer retransmissions. In particular, they causing application-layer or transport-layer retransmissions. In
do not allow a Diameter agent or server to shed load as it approaches particular, they do not allow a Diameter agent or server to shed load
overload. At best, a node can only indicate that it needs to as it approaches overload. At best, a node can only indicate that it
entirely stop receiving requests, i.e. that it has effectively needs to entirely stop receiving requests, i.e., that it has
failed. Even that is problematic due to the inability to indicate effectively failed. Even that is problematic due to the inability to
durational validity on the transient errors available in the base indicate durational validity on the transient errors available in the
Diameter protocol. Diameter offers no mechanism to allow a node to base Diameter protocol. Diameter offers no mechanism to allow a node
indicate different overload states for different categories of to indicate different overload states for different categories of
messages, for example, if it is overloaded for one Diameter messages, for example, if it is overloaded for one Diameter
application but not another. application but not another.
4.1. Problems with Implicit Mechanism 5.1. Problems with Implicit Mechanism
The implicit mechanism doesn't allow an agent or server to inform the The implicit mechanism doesn't allow an agent or server to inform the
client of a problem until it is effectively too late to do anything client of a problem until it is effectively too late to do anything
about it. The client does not know to take action until the upstream about it. The client does not know that it needs to take action
node has effectively failed. A Diameter node has no opportunity to until the upstream node has effectively failed. A Diameter node has
shed load early to avoid collapse in the first place. no opportunity to shed load early to avoid collapse in the first
place.
Additionally, the implicit mechanism cannot distinguish between Additionally, the implicit mechanism cannot distinguish between
overload of a Diameter node and network congestion. Diameter treats overload of a Diameter node and network congestion. Diameter treats
the failure to receive an answer as a transport failure. the failure to receive an answer as a transport failure.
4.2. Problems with Explicit Mechanisms 5.2. Problems with Explicit Mechanisms
The Diameter specification is ambiguous on how a client should handle The Diameter specification is ambiguous on how a client should handle
receipt of a DIAMETER_TOO_BUSY response. The base specification receipt of a DIAMETER_TOO_BUSY response. The base specification
[RFC6733] indicates that the sending client should attempt to send [RFC6733] indicates that the sending client should attempt to send
the request to a different peer. It makes no suggestion that the the request to a different peer. It makes no suggestion that the
receipt of a DIAMETER_TOO_BUSY response should affect future Diameter receipt of a DIAMETER_TOO_BUSY response should affect future Diameter
messages in any way. messages in any way.
The Authentication, Authorization, and Accounting (AAA) Transport The Authentication, Authorization, and Accounting (AAA) Transport
Profile [RFC3539] recommends that a AAA node that receives a "Busy" Profile [RFC3539] recommends that a AAA node that receives a "Busy"
response failover all remaining requests to a different agent or response failover all remaining requests to a different agent or
server. But while the Diameter base specification explicitly depends server. But while the Diameter base specification explicitly depends
on RFC3539 to define transport behavior, it does not refer to RFC3539 on [RFC3539] to define transport behavior, it does not refer to
in the description of behavior on receipt of DIAMETER_TOO_BUSY. [RFC3539] in the description of behavior on receipt of a
There's a strong likelihood that at least some implementations will DIAMETER_TOO_BUSY error. There's a strong likelihood that at least
continue to send Diameter requests to an upstream peer even after some implementations will continue to send Diameter requests to an
receiving a DIAMETER_TOO_BUSY error. upstream peer even after receiving a DIAMETER_TOO_BUSY error.
BCP 41 [RFC2914] describes, among other things, how end-to-end BCP 41 [RFC2914] describes, among other things, how end-to-end
application behavior can help avoid congestion collapse. In application behavior can help avoid congestion collapse. In
particular, an application should avoid sending messages that will particular, an application should avoid sending messages that will
never be delivered or processed. The DIAMETER_TOO_BUSY behavior as never be delivered or processed. The DIAMETER_TOO_BUSY behavior as
described in the Diameter base specification fails at this, since if described in the Diameter base specification fails at this, since if
an upstream node becomes overloaded, a client attempts each request, an upstream node becomes overloaded, a client attempts each request
and does not discover the need to failover the request until the and does not discover the need to failover the request until the
initial attempt fails. initial attempt fails.
The situation is improved if implementations follow the [RFC3539] The situation is improved if implementations follow the [RFC3539]
recommendation and keep state about upstream peer overload. But even recommendation to keep state about upstream peer overload. But even
then, the Diameter specification offers no guidance on how long a then, the Diameter specification offers no guidance on how long a
client should wait before retrying the overloaded destination. If an client should wait before retrying the overloaded destination. If an
agent or server supports multiple realms and/or applications, agent or server supports multiple realms and/or applications,
DIAMETER_TOO_BUSY offers no way to indicate that it is overloaded for DIAMETER_TOO_BUSY offers no way to indicate that it is overloaded for
one application but not another. A DIAMETER_TOO_BUSY error can only one application but not another. A DIAMETER_TOO_BUSY error can only
indicate overload at a "whole server" scope. indicate overload at a "whole server" scope.
Agent processing of a DIAMETER_TOO_BUSY response is also problematic Agent processing of a DIAMETER_TOO_BUSY response is also problematic
as described in the base specification. DIAMETER_TOO_BUSY is defined as described in the base specification. DIAMETER_TOO_BUSY is defined
as a protocol error. If an agent receives a protocol error, it may as a protocol error. If an agent receives a protocol error, it may
either handle it locally or it may forward the response back towards either handle it locally or forward the response back towards the
the downstream peer. If a downstream peer receives the downstream peer. If a downstream peer receives the DIAMETER_TOO_BUSY
DIAMETER_TOO_BUSY response, it may stop sending all requests to the response, it may stop sending all requests to the agent for some
agent for some period of time, even though the agent may still be period of time, even though the agent may still be able to deliver
able to deliver requests to other upstream peers. requests to other upstream peers.
DIAMETER_UNABLE_TO_DELIVER, or using DPR with cause code BUSY also DIAMETER_UNABLE_TO_DELIVER errors, or using DPR with cause code BUSY,
have no mechanisms for specifying the scope or cause of the failure, also have no mechanisms for specifying the scope or cause of the
or the durational validity. failure, or the durational validity.
The issues with error responses in [RFC6733] extend beyond the The issues with error responses described in [RFC6733] extend beyond
particular issues for overload control and have been addressed in an the particular issues for overload control and have been addressed in
ad hoc fashion by various implementations. Addressing these in a an ad hoc fashion by various implementations. Addressing these in a
standard way would be a useful exercise, but it us beyond the scope standard way would be a useful exercise, but it is beyond the scope
of this document. of this document.
5. Diameter Overload Case Studies
5.1. Overload in Mobile Data Networks
As the number of Third Generation (3G) and Long Term Evolution (LTE)
enabled smartphone devices continue to expand in mobile networks,
there have been situations where high signaling traffic load led to
overload events at the Diameter-based Home Location Registries (HLR)
and/or Home Subscriber Servers (HSS) [TR23.843]. The root causes of
the HLR congestion events were manifold but included hardware failure
and procedural errors. The result was high signaling traffic load on
the HLR and HSS.
The 3GPP architecture [TS23.002] makes extensive use of Diameter. It
is used for mobility management [TS29.272] (and others), (IP
Multimedia Subsystem) IMS [TS29.228] (and others), policy and
charging control [TS29.212] (and others) as well as other functions.
The details of the architecture are out of scope for this document,
but it is worth noting that there are quite a few Diameter
applications, some with quite large amounts of Diameter signaling in
deployed networks.
The 3GPP specifications do not currently address overload for
Diameter applications or provide an equivalent load control mechanism
to those provided in the more traditional SS7 elements in (Global
System for Mobile Communications) GSM [TS29.002]. The capabilities
specified in the 3GPP standards do not adequately address the
abnormal condition where excessively high signaling traffic load
situations are experienced.
Smartphones, an increasingly large percentage of mobile devices,
contribute much more heavily, relative to non-smartphones, to the
continuation of a registration surge due to their very aggressive
registration algorithms. Smartphone behavior contributes to network
loading and can contribute to overload conditions. The aggressive
smartphone logic is designed to:
a. always have voice and data registration, and
b. constantly try to be on 3G or LTE data (and thus on 3G voice or
VoLTE [IR.92]) for their added benefits.
Non-smartphones typically have logic to wait for a time period after
registering successfully on voice and data.
The smartphone aggressive registration is problematic in two ways:
o first by generating excessive signaling load towards the HSS that
is ten times that from a non-smartphone,
o and second by causing continual registration attempts when a
network failure affects registrations through the 3G data network.
5.2. 3GPP Study on Core Network Overload
A study in 3GPP SA2 on core network overload has produced the
technical report [TR23.843]. This enumerates several causes of
overload in mobile core networks including portions that are signaled
using Diameter. This document is a work in progress and is not
complete. However, it is useful for pointing out scenarios and the
general need for an overload control mechanism for Diameter.
It is common for mobile networks to employ more than one radio
technology and to do so in an overlay fashion with multiple
technologies present in the same location (such as 2nd or 3rd
generation mobile technologies along with LTE). This presents
opportunities for traffic storms when issues occur on one overlay and
not another as all devices that had been on the overlay with issues
switch. This causes a large amount of Diameter traffic as locations
and policies are updated.
Another scenario called out by this study is a flood of registration
and mobility management events caused by some element in the core
network failing. This flood of traffic from end nodes falls under
the network initiated traffic flood category. There is likely to
also be traffic resulting directly from the component failure in this
case. A similar flood can occur when elements or components recover
as well.
Subscriber initiated traffic floods are also indicated in this study
as an overload mechanism where a large number of mobile devices
attempting to access services at the same time, such as in response
to an entertainment event or a catastrophic event.
While this 3GPP study is concerned with the broader effects of these
scenarios on wireless networks and their elements, they have
implications specifically for Diameter signaling. One of the goals
of this document is to provide guidance for a core mechanism that can
be used to mitigate the scenarios called out by this study.
6. Extensibility and Application Independence 6. Extensibility and Application Independence
Given the variety of scenarios Diameter elements can be deployed in, Given the variety of scenarios in which Diameter elements can be
and the variety of roles they can fulfill with Diameter and other deployed and the variety of roles they can fulfill with Diameter and
technologies, a single algorithm for handling overload may not be other technologies, a single algorithm for handling overload may not
sufficient. This effort cannot anticipate all possible future be sufficient. For purposes of this discussion, an algorithm is
scenarios and roles. Extensibility, particularly of algorithms used inclusive of behavior for control of overload but does not encompass
to deal with overload, will be important to cover these cases. the general mechanism for transporting control information. This
effort cannot anticipate all possible future scenarios and roles.
Extensibility, particularly of algorithms used to deal with overload,
will be important to cover these cases.
Similarly, the scopes that overload information may apply to may Similarly, the scopes to which overload information may apply may
include cases that have not yet been considered. Extensibility in include cases that have not yet been considered. Extensibility in
this area will also be important. this area will also be important.
The basic mechanism is intended to be application-independent, that The basic mechanism is intended to be application independent, that
is, a Diameter node can use it across any existing and future is, a Diameter node can use it across any existing and future
Diameter applications and expect reasonable results. Certain Diameter applications and expect reasonable results. Certain
Diameter applications might, however, benefit from application- Diameter applications might, however, benefit from application-
specific behavior over and above the mechanism's defaults. For specific behavior over and above the mechanism's defaults. For
example, an application specification might specify relative example, an application specification might specify relative
priorities of messages or selection of a specific overload control priorities of messages or selection of a specific overload control
algorithm. algorithm.
7. Solution Requirements 7. Solution Requirements
This section proposes requirements for an improved mechanism to This section proposes requirements for an improved mechanism to
control Diameter overload, with the goals of improving the issues control Diameter overload, with the goals of addressing the issues
described in Section 4 and supporting the scenarios described in described in Section 5 and supporting the scenarios described in
Section 2 Section 2. These requirements are stated primarily in terms of
individual node behavior to inform the design of the improved
mechanism; solution designers should keep in mind that the overall
goal is improved overall system behavior across all the nodes
involved, not just improved behavior from specific individual nodes.
REQ 1: The overload control mechanism MUST provide a communication 7.1. General
method for Diameter nodes to exchange load and overload
information.
REQ 2: The mechanism MUST allow Diameter nodes to support overload REQ 1: The solution MUST provide a communication method for Diameter
control regardless of which Diameter applications they nodes to exchange load and overload information.
support. Diameter clients must be able to use the received
load and overload information to support graceful behavior
during an overload condition. Graceful behavior under
overload conditions is best described by REQ 3.
REQ 3: The overload control mechanism MUST limit the impact of REQ 2: The solution MUST allow Diameter nodes to support overload
overload on the overall useful throughput of a Diameter control regardless of which Diameter applications they
server, even when the incoming load on the network is far in support. Diameter clients and agents must be able to use the
excess of its capacity. The overall useful throughput under received load and overload information to support graceful
load is the ultimate measure of the value of an overload behavior during an overload condition. Graceful behavior
control mechanism. under overload conditions is best described by REQ 3.
REQ 4: Diameter allows requests to be sent from either side of a REQ 3: The solution MUST limit the impact of overload on the overall
connection and either side of a connection may have need to useful throughput of a Diameter server, even when the
provide its overload status. The mechanism MUST allow each incoming load on the network is far in excess of its
side of a connection to independently inform the other of capacity. The overall useful throughput under load is the
its overload status. ultimate measure of the value of a solution.
REQ 5: Diameter allows nodes to determine their peers via dynamic REQ 4: Diameter allows requests to be sent from either side of a
discovery or manual configuration. The mechanism MUST work connection, and either side of a connection may have need to
consistently without regard to how peers are determined. provide its overload status. The solution MUST allow each
side of a connection to independently inform the other of its
overload status.
REQ 6: The mechanism designers SHOULD seek to minimize the amount REQ 5: Diameter allows nodes to determine their peers via dynamic
of new configuration required in order to work. For discovery or manual configuration. The solution MUST work
example, it is better to allow peers to advertise or consistently without regard to how peers are determined.
negotiate support for the mechanism, rather than to require
this knowledge to be configured at each node.
REQ 7: The overload control mechanism and any associated default REQ 6: The solution designers SHOULD seek to minimize the amount of
algorithm(s) MUST ensure that the system remains stable. At new configuration required in order to work. For example, it
some point after an overload condition has ended, the is better to allow peers to advertise or negotiate support
mechanism MUST enable capacity to stabilize and become equal for the solution, rather than to require that this knowledge
to what it would be in the absence of an overload condition. be configured at each node.
Note that this also requires that the mechanism MUST allow
nodes to shed load without introducing non converging
oscillations during or after an overload condition.
REQ 8: Supporting nodes MUST be able to distinguish current 7.2. Performance
overload information from stale information, and SHOULD make
decisions using the most currently available information.
REQ 9: The mechanism MUST function across fully loaded as well as REQ 7: The solution and any associated default algorithm(s) MUST
quiescent transport connections. This is partially derived ensure that the system remains stable. At some point after
from the requirement for stability in REQ 7. an overload condition has ended, the solution MUST enable
capacity to stabilize and become equal to what it would be in
the absence of an overload condition. Note that this also
requires that the solution MUST allow nodes to shed load
without introducing non-converging oscillations during or
after an overload condition.
REQ 10: Consumers of overload information MUST be able to determine REQ 8: Supporting nodes MUST be able to distinguish current overload
when the overload condition improves or ends. information from stale information.
REQ 11: The overload control mechanism MUST be able to operate in REQ 9: The solution MUST function across fully loaded as well as
networks of different sizes. quiescent transport connections. This is partially derived
from the requirement for stability in REQ 7.
REQ 12: When a single network node fails, goes into overload, or REQ 10: Consumers of overload information MUST be able to determine
suffers from reduced processing capacity, the mechanism MUST when the overload condition improves or ends.
make it possible to limit the impact of this on other nodes
in the network. This helps to prevent a small-scale failure
from becoming a widespread outage.
REQ 13: The mechanism MUST NOT introduce substantial additional work REQ 11: The solution MUST be able to operate in networks of different
for node in an overloaded state. For example, a requirement sizes.
for an overloaded node to send overload information every
time it received a new request would introduce substantial
work. Existing messaging is likely to have the
characteristic of increasing as an overload condition
approaches, allowing for the possibility of increased
feedback for information piggybacked on it.
REQ 14: Some scenarios that result in overload involve a rapid REQ 12: When a single network node fails, goes into overload, or
increase of traffic with little time between normal levels suffers from reduced processing capacity, the solution MUST
and overload inducing levels. The mechanism SHOULD provide make it possible to limit the impact of the affected node on
for rapid feedback when traffic levels increase. other nodes in the network. This helps to prevent a small-
scale failure from becoming a widespread outage.
REQ 15: The mechanism MUST NOT interfere with the congestion control REQ 13: The solution MUST NOT introduce substantial additional work
mechanisms of underlying transport protocols. For example, for a node in an overloaded state. For example, a
a mechanism that opened additional TCP connections when the requirement for an overloaded node to send overload
network is congested would reduce the effectiveness of the information every time it received a new request would
underlying congestion control mechanisms. introduce substantial work.
REQ 16: The overload control mechanism is likely to be deployed REQ 14: Some scenarios that result in overload involve a rapid
incrementally. The mechanism MUST support a mixed increase of traffic with little time between normal levels
environment where some, but not all, nodes implement it. and levels that induce overload. The solution SHOULD provide
for rapid feedback when traffic levels increase.
REQ 17: In a mixed environment with nodes that support the overload REQ 15: The solution MUST NOT interfere with the congestion control
control mechanism and that do not, the mechanism MUST result mechanisms of underlying transport protocols. For example, a
in at least as much useful throughput as would have resulted solution that opened additional TCP connections when the
if the mechanism were not present. It SHOULD result in less network is congested would reduce the effectiveness of the
severe congestion in this environment. underlying congestion control mechanisms.
REQ 18: In a mixed environment of nodes that support the overload 7.3. Heterogeneous Support for Solution
control mechanism and that do not, the mechanism MUST NOT
preclude elements that support overload control from
treating elements that do not support overload control in a
equitable fashion relative to those that do. Users and
operators of nodes that do not support the mechanism MUST
NOT unfairly benefit from the mechanism. The mechanism
specification SHOULD provide guidance to implementors for
dealing with elements not supporting overload control.
REQ 19: It MUST be possible to use the mechanism between nodes in REQ 16: The solution is likely to be deployed incrementally. The
different realms and in different administrative domains. solution MUST support a mixed environment where some, but not
all, nodes implement it.
REQ 20: Any explicit overload indication MUST be clearly REQ 17: In a mixed environment with nodes that support the solution
distinguishable from other errors reported via Diameter. and nodes that do not, the solution MUST NOT result in
materially less useful throughput during overload as would
have resulted if the solution were not present. It SHOULD
result in less severe overload in this environment.
REQ 21: In cases where a network node fails, is so overloaded that REQ 18: In a mixed environment of nodes that support the solution and
it cannot process messages, or cannot communicate due to a nodes that do not, the solution MUST NOT preclude elements
network failure, it may not be able to provide explicit that support overload control from treating elements that do
indications of the nature of the failure or its levels of not support overload control in an equitable fashion relative
congestion. The mechanism MUST result in at least as much to those that do. Users and operators of nodes that do not
useful throughput as would have resulted if the overload support the solution MUST NOT unfairly benefit from the
control mechanism was not in place. solution. The solution specification SHOULD provide guidance
to implementors for dealing with elements not supporting
overload control.
REQ 22: The mechanism MUST provide a way for a node to throttle the REQ 19: It MUST be possible to use the solution between nodes in
amount of traffic it receives from a peer node. This different realms and in different administrative domains.
throttling SHOULD be graded so that it can be applied
gradually as offered load increases. Overload is not a
binary state; there may be degrees of overload.
REQ 23: The mechanism MUST provide sufficient information to enable REQ 20: Any explicit overload indication MUST be clearly
a load balancing node to divert messages that are rejected distinguishable from other errors reported via Diameter.
or otherwise throttled by an overloaded upstream node to
other upstream nodes that are the most likely to have
sufficient capacity to process them.
REQ 24: The mechanism MUST provide a mechanism for indicating load REQ 21: In cases where a network node fails, is so overloaded that it
levels even when not in an overloaded condition, to assist cannot process messages, or cannot communicate due to a
nodes making decisions to prevent overload conditions from network failure, it may not be able to provide explicit
occurring. indications of the nature of the failure or its levels of
overload. The solution MUST result in at least as much
useful throughput as would have resulted if the solution were
not in place.
REQ 25: The base specification for the overload control mechanism 7.4. Granular Control
SHOULD offer general guidance on which message types might
be desirable to send or process over others during times of
overload, based on application-specific considerations. For
example, it may be more beneficial to process messages for
existing sessions ahead of new sessions. Some networks may
have a requirement to give priority to requests associated
with emergency sessions. Any normative or otherwise
detailed definition of the relative priorities of message
types during an overload condition will be the
responsibility of the application specification.
REQ 26: The mechanism MUST NOT prevent a node from prioritizing REQ 22: The solution MUST provide a way for a node to throttle the
requests based on any local policy, so that certain requests amount of traffic it receives from a peer node. This
are given preferential treatment, given additional throttling SHOULD be graded so that it can be applied
retransmission, not throttled, or processed ahead of others. gradually as offered load increases. Overload is not a
binary state; there may be degrees of overload.
REQ 27: The overload control mechanism MUST NOT provide new REQ 23: The solution MUST provide sufficient information to enable a
vulnerabilities to malicious attack, or increase the load-balancing node to divert messages that are rejected or
severity of any existing vulnerabilities. This includes otherwise throttled by an overloaded upstream node to other
vulnerabilities to DoS and DDoS attacks as well as replay upstream nodes that are the most likely to have sufficient
and man-in-the middle attacks. Note that the Diameter base capacity to process them.
specification [RFC6733] lacks end to end security and this
must be considered.
REQ 28: The mechanism MUST NOT depend on being deployed in REQ 24: The solution MUST provide a mechanism for indicating load
environments where all Diameter nodes are completely levels, even when not in an overload condition, to assist
trusted. It SHOULD operate as effectively as possible in nodes in making decisions to prevent overload conditions from
environments where other nodes are malicious; this includes occurring.
preventing malicious nodes from obtaining more than a fair
share of service. Note that this does not imply any
responsibility on the mechanism to detect, or take
countermeasures against, malicious nodes.
REQ 29: It MUST be possible for a supporting node to make 7.5. Priority and Policy
authorization decisions about what information will be sent
to peer nodes based on the identity of those nodes. This
allows a domain administrator who considers the load of
their nodes to be sensitive information to restrict access
to that information. Of course, in such cases, there is no
expectation that the overload control mechanism itself will
help prevent overload from that peer node.
REQ 30: The mechanism MUST NOT interfere with any Diameter compliant REQ 25: The base specification for the solution SHOULD offer general
method that a node may use to protect itself from overload guidance on which message types might be desirable to send or
from non-supporting nodes, or from denial of service process over others during times of overload, based on
attacks. application-specific considerations. For example, it may be
more beneficial to process messages for existing sessions
ahead of new sessions. Some networks may have a requirement
to give priority to requests associated with emergency
sessions. Any normative or otherwise detailed definition of
the relative priorities of message types during an overload
condition will be the responsibility of the application
specification.
REQ 31: There are multiple situations where a Diameter node may be REQ 26: The solution MUST NOT prevent a node from prioritizing
overloaded for some purposes but not others. For example, requests based on any local policy, so that certain requests
this can happen to an agent or server that supports multiple are given preferential treatment, given additional
applications, or when a server depends on multiple external retransmission, not throttled, or processed ahead of others.
resources, some of which may become overloaded while others
are fully available. The mechanism MUST allow Diameter
nodes to indicate overload with sufficient granularity to
allow clients to take action based on the overloaded
resources without unreasonably forcing available capacity to
go unused. The mechanism MUST support specification of
overload information with granularities of at least
"Diameter node", "realm", and "Diameter application", and
MUST allow extensibility for others to be added in the
future.
REQ 32: The mechanism MUST provide a method for extending the 7.6. Security
information communicated and the algorithms used for
overload control.
REQ 33: The mechanism MUST provide a default algorithm that is REQ 27: The solution MUST NOT provide new vulnerabilities to
mandatory to implement. malicious attack or increase the severity of any existing
vulnerabilities. This includes vulnerabilities to DoS and
DDoS attacks as well as replay and man-in-the-middle attacks.
Note that the Diameter base specification [RFC6733] lacks
end-to-end security, and this must be considered (see
Security Considerations in this document (Section 8)). Note
that this requirement was expressed at a high level so as to
not preclude any particular solution. Is is expected that
the solution will address this in more detail.
REQ 34: The mechanism SHOULD provide a method for exchanging REQ 28: The solution MUST NOT depend on being deployed in
overload and load information between elements that are environments where all Diameter nodes are completely trusted.
connected by intermediaries that do not support the It SHOULD operate as effectively as possible in environments
mechanism. where other nodes are malicious; this includes preventing
malicious nodes from obtaining more than a fair share of
service. Note that this does not imply any responsibility on
the solution to detect, or take countermeasures against,
malicious nodes.
8. IANA Considerations REQ 29: It MUST be possible for a supporting node to make
authorization decisions about what information will be sent
to peer nodes based on the identity of those nodes. This
allows a domain administrator who considers the load of their
nodes to be sensitive information to restrict access to that
information. Of course, in such cases, there is no
expectation that the solution itself will help prevent
overload from that peer node.
This document makes no requests of IANA. REQ 30: The solution MUST NOT interfere with any Diameter-compliant
method that a node may use to protect itself from overload
from non-supporting nodes or from denial-of-service attacks.
9. Security Considerations 7.7. Flexibility and Extensibility
REQ 31: There are multiple situations where a Diameter node may be
overloaded for some purposes but not others. For example,
this can happen to an agent or server that supports multiple
applications, or when a server depends on multiple external
resources, some of which may become overloaded while others
are fully available. The solution MUST allow Diameter nodes
to indicate overload with sufficient granularity to allow
clients to take action based on the overloaded resources
without unreasonably forcing available capacity to go unused.
The solution MUST support specification of overload
information with granularities of at least "Diameter node",
"realm", and "Diameter application" and MUST allow
extensibility for others to be added in the future.
REQ 32: The solution MUST provide a method for extending the
information communicated and the algorithms used for overload
control.
REQ 33: The solution MUST provide a default algorithm that is
mandatory to implement.
REQ 34: The solution SHOULD provide a method for exchanging overload
and load information between elements that are connected by
intermediaries that do not support the solution.
8. Security Considerations
A Diameter overload control mechanism is primarily concerned with the A Diameter overload control mechanism is primarily concerned with the
load and overload related behavior of nodes in a Diameter network, load-related and overload-related behavior of nodes in a Diameter
and the information used to affect that behavior. Load and overload network, and the information used to affect that behavior. Load and
information is shared between nodes and directly affects the behavior overload information is shared between nodes and directly affects the
and thus is potentially vulnerable to a number of methods of attack. behavior, and thus the information is potentially vulnerable to a
number of methods of attack.
Load and overload information may also be sensitive from both Load and overload information may also be sensitive from both
business and network protection viewpoints. Operators of Diameter business and network protection viewpoints. Operators of Diameter
equipment want to control visibility to load and overload information equipment want to control the visibility of load and overload
to keep it from being used for competitive intelligence or for information to keep it from being used for competitive intelligence
targeting attacks. It is also important that the Diameter overload or for targeting attacks. It is also important that the Diameter
control mechanism not introduce any way in which any other overload control mechanism not introduce any way in which any other
information carried by Diameter is sent inappropriately. information carried by Diameter is sent inappropriately.
Note that the Diameter base specification [RFC6733] lacks end to end Note that the Diameter base specification [RFC6733] lacks end-to-end
security, making verifying the authenticity and ownership of load and security, making it difficult for non-adjacent nodes to verify the
overload information difficult for non-adjacent nodes. authenticity and ownership of load and overload information.
Authentication of load and overload information helps to alleviate Authentication of load and overload information helps to alleviate
several of the security issues listed in this section. several of the security issues listed in this section.
This document includes requirements intended to mitigate the effects This document includes requirements intended to mitigate the effects
of attacks and to protect the information used by the mechanism. of attacks and to protect the information used by the mechanism.
This section discusses potential security considerations for overload
control solutions. This discussion provides the motivation for
several normative requirements described in Section 7. The
discussion includes specific references to the normative requirements
that apply for each issue.
9.1. Access Control 8.1. Access Control
To control the visibility of load and overload information, sending To control the visibility of load and overload information, sending
should be subject to some form of authentication and authorization of should be subject to some form of authentication and authorization of
the receiver. It is also important to the receivers that they are the receiver. It is also important to the receivers that they are
confident the load and overload information they receive is from a confident the load and overload information they receive is from a
legitimate source. Note that this implies a certain amount of legitimate source. REQ 28 requires that the solution work without
configurability on the nodes supporting the Diameter overload control assuming that all Diameter nodes in a network are trusted for the
mechanism. purposes of exchanging overload and load information. REQ 29
requires that the solution let nodes restrict unauthorized parties
from seeing overload information. Note that this implies a certain
amount of configurability on the nodes supporting the Diameter
overload control mechanism.
9.2. Denial-of-Service Attacks 8.2. Denial-of-Service Attacks
An overload control mechanism provides a very attractive target for An overload control mechanism provides a very attractive target for
denial-of-service attacks. A small number of messages may affect a denial-of-service attacks. A small number of messages may effect a
large service disruption by falsely reporting overload conditions. large service disruption by falsely reporting overload conditions.
Alternately, attacking servers nearing, or in, overload may also be Alternately, attacking servers nearing, or in, overload may also be
facilitated by disrupting their overload indications, potentially facilitated by disrupting their overload indications, potentially
preventing them from mitigating their overload condition. preventing them from mitigating their overload condition.
A design goal for the Diameter overload control mechanism is to A design goal for the Diameter overload control mechanism is to
minimize or eliminate the possibility of using the mechanism for this minimize or eliminate the possibility of using the mechanism for this
type of attack. type of attack. More strongly, REQ 27 forbids the solution from
introducing new vulnerabilities to malicious attack. Additionally,
REQ 30 stipulates that the solution not interfere with other
mechanisms used for protection against denial-of-service attacks.
As the intent of some denial-of-service attacks is to induce overload As the intent of some denial-of-service attacks is to induce overload
conditions, an effective overload control mechanism should help to conditions, an effective overload control mechanism should help to
mitigate the effects of an such an attack. mitigate the effects of such an attack.
9.3. Replay Attacks 8.3. Replay Attacks
An attacker that has managed to obtain some messages from the An attacker that has managed to obtain some messages from the
overload control mechanism may attempt to affect the behavior of overload control mechanism may attempt to affect the behavior of
nodes supporting the mechanism by sending those messages at nodes supporting the mechanism by sending those messages at
potentially inopportune times. In addition to time shifting, replay potentially inopportune times. In addition to time shifting, replay
attacks may send messages to other nodes as well (target shifting). attacks may send messages to other nodes as well (target shifting).
A design goal for the Diameter overload control mechanism is to A design goal for the Diameter overload control solution is to
minimize or eliminate the possibility of causing disruption by using minimize or eliminate the possibility of causing disruption by using
a replay attack on the Diameter overload control mechanism. a replay attack on the Diameter overload control mechanism.
(Allowing a replay attack using the overload control solution would
violate REQ 27.)
9.4. Man-in-the-Middle Attacks 8.4. Man-in-the-Middle Attacks
By inserting themselves in between two nodes supporting the Diameter By inserting themselves between two nodes supporting the Diameter
overload control mechanism, an attacker may potentially both access overload control mechanism, an attacker may potentially both access
and alter the information sent between those nodes. This can be used and alter the information sent between those nodes. This can be used
for information gathering for business intelligence and attack for information gathering for business intelligence and attack
targeting, as well as direct attacks. targeting, as well as direct attacks.
A design goal for the Diameter overload control mechanism is to REQs 27, 28, and 29 imply a need to prevent man-in-the-middle attacks
minimize or eliminate the possibility of causing disruption man-in- on the overload control solution. A transport using Transport Layer
the-middle attacks on the Diameter overload control mechanism. A Security (TLS) and/or IPsec may be desirable for this purpose.
transport using TLS and/or IPSEC may be desirable for this.
9.5. Compromised Hosts 8.5. Compromised Hosts
A compromised host that supports the Diameter overload control A compromised host that supports the Diameter overload control
mechanism could be used for information gathering as well as for mechanism could be used for information gathering as well as for
sending malicious information to any Diameter node that would sending malicious information to any Diameter node that would
normally accept information from it. While is is beyond the scope of normally accept information from it. While it is beyond the scope of
the Diameter overload control mechanism to mitigate any operational the Diameter overload control mechanism to mitigate any operational
interruption to the compromised host, a reasonable design goal is to interruption to the compromised host, REQs 28 and 29 imply a need to
minimize the impact that a compromised host can have on other nodes minimize the impact that a compromised host can have on other nodes
through the use of the Diameter overload control mechanism. Of through the use of the Diameter overload control mechanism. Of
course, a compromised host could be used to cause damage in a number course, a compromised host could be used to cause damage in a number
of other ways. This is out of scope for a Diameter overload control of other ways. This is out of scope for a Diameter overload control
mechanism. mechanism.
10. References 9. References
10.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn, [RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
"Diameter Base Protocol", RFC 6733, October 2012. "Diameter Base Protocol", RFC 6733, October 2012.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, September 2000. RFC 2914, September 2000.
[RFC3539] Aboba, B. and J. Wood, "Authentication, Authorization and [RFC3539] Aboba, B. and J. Wood, "Authentication, Authorization and
Accounting (AAA) Transport Profile", RFC 3539, June 2003. Accounting (AAA) Transport Profile", RFC 3539, June 2003.
10.2. Informative References 9.2. Informative References
[RFC5390] Rosenberg, J., "Requirements for Management of Overload in [RFC5390] Rosenberg, J., "Requirements for Management of Overload
the Session Initiation Protocol", RFC 5390, December 2008. in the Session Initiation Protocol", RFC 5390,
December 2008.
[RFC6357] Hilt, V., Noel, E., Shen, C., and A. Abdelal, "Design [RFC6357] Hilt, V., Noel, E., Shen, C., and A. Abdelal, "Design
Considerations for Session Initiation Protocol (SIP) Considerations for Session Initiation Protocol (SIP)
Overload Control", RFC 6357, August 2011. Overload Control", RFC 6357, August 2011.
[TR23.843] [TR23.843] 3GPP, "Study on Core Network (CN) overload solutions",
3GPP, "Study on Core Network Overload Solutions", TR 23.843 1.2.0, Work in Progress, October 2013.
TR 23.843 0.6.0, October 2012.
[IR.34] GSMA, "Inter-Service Provider IP Backbone Guidelines", [IR.34] GSMA, "Inter-Service Provider IP Backbone Guidelines",
IR 34 7.0, January 2012. IR 34 9.1, May 2013.
[IR.88] GSMA, "LTE Roaming Guidelines", IR 88 7.0, January 2012. [IR.88] GSMA, "LTE Roaming Guidelines", IR 88 9.0, January 2013.
[IR.92] GSMA, "IMS Profile for Voice and SMS", IR 92 7.0, [IR.92] GSMA, "IMS Profile for Voice and SMS", IR 92 7.0,
March 2013. March 2013.
[TS23.002] [TS23.002] 3GPP, "Network Architecture", TS 23.002 12.2.0,
3GPP, "Network Architecture", TS 23.002 12.0.0, June 2013.
September 2012.
[TS29.272] [TS29.272] 3GPP, "Evolved Packet System (EPS); Mobility Management
3GPP, "Evolved Packet System (EPS); Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) related
Entity (MME) and Serving GPRS Support Node (SGSN) related interfaces based on Diameter protocol", TS 29.272 12.2.0,
interfaces based on Diameter protocol", TS 29.272 11.4.0, September 2013.
September 2012.
[TS29.212] [TS29.212] 3GPP, "Policy and Charging Control (PCC) over Gx/Sd
3GPP, "Policy and Charging Control (PCC) over Gx/Sd reference point", TS 29.212 12.2.0, September 2013.
reference point", TS 29.212 11.6.0, September 2012.
[TS29.228] [TS29.228] 3GPP, "IP Multimedia (IM) Subsystem Cx and Dx interfaces;
3GPP, "IP Multimedia (IM) Subsystem Cx and Dx interfaces; Signalling flows and message contents", TS 29.228 12.0.0,
Signalling flows and message contents", TS 29.228 11.5.0, September 2013.
September 2012.
[TS29.002] [TS29.002] 3GPP, "Mobile Application Part (MAP) specification",
3GPP, "Mobile Application Part (MAP) specification", TS 29.002 12.2.0, September 2013.
TS 29.002 11.4.0, September 2012.
Appendix A. Contributors Appendix A. Contributors
Significant contributions to this document were made by Adam Roach Significant contributions to this document were made by Adam Roach
and Eric Noel. and Eric Noel.
Appendix B. Acknowledgements Appendix B. Acknowledgements
Review of, and contributions to, this specification by Martin Dolly, Review of, and contributions to, this specification by Martin Dolly,
Carolyn Johnson, Jianrong Wang, Imtiaz Shaikh, Jouni Korhonen, Robert Carolyn Johnson, Jianrong Wang, Imtiaz Shaikh, Jouni Korhonen, Robert
Sparks, Dieter Jacobsohn, Janet Gunn, Jean-Jacques Trottin, Laurent Sparks, Dieter Jacobsohn, Janet Gunn, Jean-Jacques Trottin, Laurent
Thiebaut, Andrew Booth, and Lionel Morand were most appreciated. We Thiebaut, Andrew Booth, and Lionel Morand were most appreciated. We
would like to thank them for their time and expertise. would like to thank them for their time and expertise.
Authors' Addresses Authors' Addresses
Eric McMurry Eric McMurry
Tekelec Oracle
17210 Campbell Rd. 17210 Campbell Rd.
Suite 250 Suite 250
Dallas, TX 75252 Dallas, TX 75252
US US
Email: emcmurry@computer.org EMail: emcmurry@computer.org
Ben Campbell Ben Campbell
Tekelec Oracle
17210 Campbell Rd. 17210 Campbell Rd.
Suite 250 Suite 250
Dallas, TX 75252 Dallas, TX 75252
US US
Email: ben@nostrum.com EMail: ben@nostrum.com
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