IETF D. Kutscher
Internet-Draft F. Mir
Intended status: Informational R. Winter
Expires: January 12, 2012 NEC
S. Krishnan
Y. Zhang
Ericsson
July 11, 2011
Mobile Communication Congestion Exposure Scenario
draft-kutscher-conex-mobile-01
Abstract
This memo describes a mobile communications use case for congestion
exposure (CONEX) with a particular focus on mobile communication
networks such as 3GPP LTE. The draft describes the architecture of
these networks (access and core networks), current QoS mechanisms and
then discusses how congestion exposure concepts could be applied.
Based on this, this memo suggests a set of requirements for CONEX
mechanisms that particularly apply to mobile networks.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on January 12, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of 3GPP's Evolved Packet System (EPS) . . . . . . . . 3
3. CONEX Use Cases in the Mobile Communication Scenario . . . . . 5
3.1. CONEX as a Basis for Traffic Management . . . . . . . . . 6
3.2. CONEX to Incentivize Scavenger Transports . . . . . . . . 7
3.3. Accounting for Congestion Volume . . . . . . . . . . . . . 8
3.4. CONEX as a Form of Differential QoS . . . . . . . . . . . 8
3.5. Partial vs. Full Deployment . . . . . . . . . . . . . . . 9
3.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. CONEX in the EPS . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Possible Deployment Scenarios . . . . . . . . . . . . . . 11
4.2. Implementing CONEX Functions in the EPS . . . . . . . . . 14
5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . . 18
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Mobile data traffic continues to grow rapidly. The challenge
wireless operators face is to support more subscribers with higher
bandwidth requirements. To meet the bandwidth demand, operators need
to seek for new technologies to efficiently utilize the available
network resources, in particular, this concerns resource allocation
and flow management. Ample statistics for network traffic from
cellular networks are available, stating that many short flows exist,
but that a few large flows constitute a large part of the overall
traffic volume. Measurement studies have shown that a small number
of users is responsible for the most part of the traffic in cellular
networks. With the highly skewed network access behavior, more
expensive resources in cellular networks as compared to other
networks and the rapidly increasing network utilization, resource
allocation and usage accountability are two important issues for
operators to solve in order to achieve a better, accountable network
resource utilization. CONEX, as described in
[I-D.ietf-conex-concepts-uses], is a technology to base this upon.
The CONEX congestion exposure mechanism is intended as a general
technology that could be applied as a key element of congestion
management solutions in a variety of use cases. The IETF CONEX WG
will however work on a specific use case, where the end hosts and the
network that contains the destination end host are CONEX-enabled but
other networks need not be.
A specific example of such a use case can be a mobile communication
network such as a 3GPP LTE network, where UEs (User Equipment, i.e.
mobile end hosts), servers and caches, the access network and
possibly an operator's core network can be CONEX-enabled. I.e.,
hosts support the CONEX mechanisms, and the network provides
policing/auditing functions at its edges.
This draft describes the architecture of such networks (access and
core networks), current QoS mechanisms and then discusses how
congestion exposure concepts can benefit such networks and how they
should be applied. Using this use case as a basis, a set of
requirements for CONEX mechanisms are described.
2. Overview of 3GPP's Evolved Packet System (EPS)
This section provides an overview of 3GPP's "Evolved Packet System"
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(EPS [3GPP.36.300]) as a specific example of a mobile communication
architecture in order to illustrate congestion exposure applicability
in this memo. There are other mobile communication architectures.
The EPS architecture and its standardized interfaces are depicted in
Figure 1. The EPS provides IP connectivity to UEs (user equipment,
i.e., mobile nodes) and access to operator services, such as global
Internet access and voice communications. The EPS comprises the
access (evolved UMTS Terrestrial Radio Access Network, E-UTRAN) and
the core network (Evolved Packet Core, EPC -- all network elements
except the E-UTRAN). QoS is supported through an EPS bearer concept,
providing hierarchical bindings within the network.
The evolved NodeB (eNB), the LTE base station, is part of the access
network that provides radio resource management, header compression,
security and connectivity to the core network through the S1
interface. In an LTE network, the control plane signaling traffic
and the data traffic are handled separately. The eNBs transmit the
control traffic and data traffic separately via two logically
different interfaces.
The Home Subscriber Server, HSS, is a database that contains user
subscriptions and QoS profiles. The Mobility Management Entity, MME,
is responsible for user authentication, bearer establishment and
modification and maintenance of the UE context.
The Serving gateway, S-GW, is the mobility anchor and manages the
user plane data tunnels during the inter-eNB handovers. It tunnels
all user data packets and buffers downlink IP packets destined for
UEs that happen to be in idle mode.
The Packet Gateway, P-GW, is responsible for IP address allocation to
the UE and is a tunnel endpoint for mobility protocols. It is also
responsible for charging, packet filtering, and policy-based control
of flows. It interconnects the mobile network to external IP
networks, e.g. the Internet.
In this architecture, data packets are not sent directly on an IP
network between the eNB and the gateways. Instead, every packet is
sent in a tunneling protocol - the GPRS Tunneling Protocol (GTP
[3GPP.29.060]) over UDP/IP. A GTP path is identified in each node
with the IP address and a UDP port number on the eNB/gateways. The
GTP protocol carries both the data traffic (GTP-U tunnels) and the
control traffic (GTP-C tunnels [3GPP.29.274]).
The above is very different from an end-to-end path on the Internet
where the packet forwarding is performed at the IP level.
Importantly, we observe that these tunneling protocols give the
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operator a large degree of flexibility to control the congestion
mechanism incorporated with the GTP protocols.
+-------+
+-------+ | PCRF |
| HSS | /+-------+\
+-------+ Gx/ \Rx
| / \
| / \
| +-------+ SGi +-------+
| | P-GW |=========|IP Svr |
| +-------+ +-------+
HPMN | |
------------------------------|--------------|----------------------
VPLMN | |
+-------+ |
| MME | |
/+-------+\ |S8
S1-MME / \ |
/ \S11 |
/ \ |
+-----------+ \ |
+----+ LTE-Uu | | \ |
| UE |========| | S1-U +-------+
+----+ | E-UTRAN |==============| S-GW |
| (eNBs) | +-------+
| |
+-----------+
Figure 1: EPS Architecture Overview
3. CONEX Use Cases in the Mobile Communication Scenario
In general, quality of service and good network resource utilization
are important requirements for mobile communication network
operators. Radio access and backhaul networks are considered scarce
resources, and bandwidth (and radio resource) demand is difficult to
predict precisely due to user mobility, radio propagation effects
etc. Hence today's architectures and protocols go to significant
extent in order to provide network-controlled quality of service --
for instance by LTE's EPS bearer model that enables the network to
allocate service data flows (SDFs) to certain EPS bearers with
specific quality of service classes (which can be used for fine-
granular per-application service differentiation).
In the following, we are discussing ways how congestion exposure
could be beneficial for supporting resource management in such
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operated mobile communication networks.
[I-D.ietf-conex-concepts-uses] describes fundamental congestion
exposure concepts and a set of use cases for applying congestion
exposure mechanisms to realize different traffic management
functions, accounting etc. Here, we relate these CONEX use cases to
the general mobile communication scenario in order to validate the
use cases for this scenario.
3.1. CONEX as a Basis for Traffic Management
Traffic management is a very important function in mobile
communication networks. Since wireless resources are considered
scarce and since user mobility and shared bandwidth in the wireless
access create certain dynamics with respect to available bandwidth,
these resources are traditionally managed very tightly (admission
control for bearer establishment etc.).
In LTE, the QoS requirements for different applications running on a
UE is supported by a bearer concept which is managed by the network.
Each bearer has an associated QoS Class identifier (QCI) and an
Allocation and Retention Policy (ARP) that has been standardized for
uniform traffic handling (across implementations). For the necessary
QoS across the mobile network, an EPS bearer is maintained that
crosses different interfaces in the network and maps to lower layer
bearers for packet forwarding. A radio bearer transports traffic
between a UE and eNB whereas S1 bearer transports traffic between the
eNB and S-GW. Primarily LTE offers two types of bearer: Guaranteed
Bit rate bearer for real time communication, e.g., Voice calls etc.
and Non-Guaranteed bit rate, e.g., best effort traffic for web access
etc. Packets mapped to the same EPS bearer receive the same bearer
level packet forwarding treatment.
In the light of the significant increase of overall data volume in 3G
networks, Deep-Packet-Inspection (DPI) is often considered a
desirable function to have in the EPC -- on, for example, a PDN
(Packet Data Network) gateway, and some operators do in fact deploy
DPI today. 3GPP has a current work item on "Service Awareness and
Privacy Policies" that is chartered to add DPI-related extensions to
the PCC architecture [3GPP.23.203].
Congestion exposure can be employed to address these requirements for
tight resource management in different ways:
1. It can enhance DPI by providing flow policy-based traffic
management. At present, DPI-based resource management is often
used to prioritize certain application classes with respect to
others in overload situations, so that effectively more users can
be served on the network. In overload situations, operators use
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DPI to identify dispensable flows and make them yield to other
flows (of different application classes) through policing. Such
traffic management is thus based on static configuration and some
estimation about the future per-flow bandwidth demand. With
congestion exposure it would be possible to more accurately and
more timely assess the cost that certain flows are causing so
that policing can optimize network utilization (better than a
pure DPI-based approach can do).
2. It can eventually make DPI obsolete by allowing for a bulk packet
traffic management that does not have to consider flows'
application classes and individual sessions. Instead traffic
management would be based on the current cost (contribution to
congestion) incurred by different flows and enable operators to
apply policing/accounting depending on their preference. Such
traffic management would be simpler and more robust (no real-time
flow application type identification required, no static
configuration of application classes) and perform better as
decisions can be taken based on real-time actual cost
contribution.
In summary, it can be said that traffic management in 3GPP EPS and
other mobile communication architectures in very important.
Previously more static approaches based on admission control and
static QoS have been applied, but recently, there has been a
perceived need for more dynamic mechanisms such as DPI. Adding CONEX
support might thus require revisiting the PCC architecture, depending
on the scope and impact of a CONEX-based traffic management approach.
3.2. CONEX to Incentivize Scavenger Transports
As 3G and LTE networks are turning into universal access networks
that are shared between mobile (smart) phone users, mobile users with
laptop PCs, home users with LTE access etc., it is likely that
capacity-sharing among different users and application flows becomes
more important in the mobile communication network as a fine-granular
differentiation would be too costly.
Most of this traffic is likely to be classified as best-effort
traffic, without differentiating (for example) periodic OS updates,
application store downloads from web (browser)-based or other more
real-time communication. Having said that, the general argument for
scavenger transports apply. Especially when wireless and backhaul
resources are scarce, incentivizing users to use less-than best
effort transport for non-interactive background communication would
improve the overall utility of the network. It can be argued that,
if this would be done with a CONEX approach, it could be in a more
effective and cost-efficient way compared to the mentioned DPI
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mechanisms.
This would work best, if the network did not do any traffic class
segregation below the IP layer, i.e., if all traffic would be in the
same traffic class. With current specifications, that would be
possible in principle.
3.3. Accounting for Congestion Volume
3G and LTE networks provide extensive support for accounting and
charging already, for example cf. the PCC architecture. In fact,
most operators today account transmitted data volume on a very fine
granular basis and either correlate monthly charging to the exact
number of packets/bytes transmitted, or employ some form of flat rate
(or flexible flat rate), often with a so-called fair-use policy.
With such policies, users are typically limited to an
administratively configured maximum bandwidth limit, after they have
used their data contractual volume budget for the charging period.
Changing this data volume-based accounting to a congestion-based
accounting would be possible in principle, especially since there
already is an elaborate per-user accounting system available. Also,
an operator-provided mobile communication network can be seen as a
network domain within such congestion volume accounting would be
possible, without requiring any support from the global Internet.
Traffic normally leaves/enters the operator's network via well-
defined egress/ingress points that would be ideal candidates for
policing functions. Moreover, in most commercially operated
networks, the user is accounted for both received and sent data,
which would facilitate congestion volume accounting as well.
TODO: here we could say something about CONEX leveraging PCC (and/or
enhancing it).
3.4. CONEX as a Form of Differential QoS
As mentioned above, 3GPP mobile communication networks provide an
elaborate QoS architecture. In LTE, the idea is to map different
traffic classes onto different logical channels (bearers) with
individual QoS configuration.
It can be argued whether this approach is sufficient in a world where
most traffic is on TCP port 80 and whether some more application
control would be useful.
With CONEX, accurate downstream path information would be visible to
ingress network operators, which can respond to incipient congestion
in time. This can be equivalent to offering different levels of QoS,
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e.g. premium service with zero congestion response.
Again, CONEX could be used in two different ways:
1. as additional information to assist network functions to impose
different QoS for different application sessions; and
2. as a tool to let applications decide on their response to
congestion notification, while incentivizing them to react (in
general) appropriately, e.g., by enforcing overall limits for
congestion contribution or by accounting and charging for such
congestion contribution.
3.5. Partial vs. Full Deployment
In general CONEX lends itself to partial deployment as the mechanism
does not require all routers and hosts to support congestion
exposure. Moreover, assuming a policing infrastructure has been put
in place, it is not required to modify all hosts. Since CONEX is
about senders exposing congestion contribution to the network,
senders need to be made supporting CONEX (assuming a congestion
notification mechanisms such as ECN is in place).
In mobile communication networks that would for example allow early
partial CONEX deployment in the downlink direction only, i.e.,
servers, gateways and caches would support CONEX but UEs (mobile
hosts) would not.
When moving towards full deployment in a specific operator's network,
different ways for introducing CONEX support on UEs are feasible.
Since mobile communication networks are multi-vendor networks,
standardizing CONEX support on UEs (e.g., in 3GPP specifications)
appears useful. Still, not all UEs would have to support CONEX, and
operators would be free to choose their policing approach in such
deployment scenarios. Leveraging existing PCC architectures, 3GPP
network operators could for example decide policing/accounting
approaches per UE -- i.e., apply fixed volume caps for non-CONEX UEs
and more flexible schemes for CONEX-enabled UEs.
Moreover, it should be noted that network support for CONEX is a
feature that some operators MAY implement to deploy if they wish, but
it is not required that all operators (or all other networks) do so.
Depending on the extent of CONEX support, specific aspects such as
roaming have to be considered. I.e., what happens if a user is
roaming in a CONEX-enabled network, but their UE is not CONEX-enabled
and vice versa. Although these may not be fundamental problems, they
need to be considered. For supporting mobility in general, it can be
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required to shift users' policing state during hand-over. There is
existing work in [raghavan2007] on distributed rate limiting and in
[nec.euronf-2011] on specific optimizations for congestion exposure
and policing in mobility scenarios.
Another aspect to consider is the addition of Selected IP Traffic
Offload (SIPTO) and Local Breakout (LIPA), also see [3GPP.23.829],
i.e., the idea that some traffic (e.g., high-volume Internet traffic)
is actually not passed through the EPC but is offloaded at a "break-
out point" closer to (or in) the access network. On the other hand,
CONEX can also enable more dynamic decisions on what traffic to
actually offload by considering congestion exposure in bulk traffic
aggregates -- thus making traffic offload more effective.
3.6. Summary
In summary, the 3GPP EPS is a system architecture that can benefit
from congestion exposure in multiple ways, as we have shown by this
brief description of CONEX use cases in this environment. Dynamic
traffic and congestion management is an acknowledged important
requirement for the EPS, also illustrated by the current DPI work for
EPS.
Moreover, we believe that networks such as an LTE mobile
communication network would be quite amenable for deploying CONEX as
a mechanism, since they represent clearly defined and well separated
operational domains, in which local CONEX deployment would be
possible. Aside from roaming (which needs to be considered for a
specific solution), a single mobile network deployment is under full
control of a single operator, which can enable operator-local
enhancement without the need to change the complete architecture.
In 3GPP EPS, interfaces between all elements of the architecture are
subject to standardization, including UE interfaces and eNodeB
interfaces, so that a standardized approach can be feasible as well.
4. CONEX in the EPS
The CONEX mechanism is still work in progress in the IETF working
group. Still, we would like to discuss a few options for how such a
mechanism (and possibly additional policing functions) could
eventually be deployed in 3GPP's EPS. Note that this description of
options is not intended as a complete set of possible approaches --
it is merely intended for discussing a few options. More details
will be provided in a future revision of this document.
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4.1. Possible Deployment Scenarios
There are different possible ways how CONEX functions on hosts and
network elements can be used. For example, CONEX could be used for a
limited part of the network only -- e.g., for the access network --
congestion exposure and sender adaptation could involve the mobile
nodes or not, or, finally, the CONEX feedback loop could extend
beyond a single operator's domain or not.
We present three different deployment scenarios for congestion
exposure in the figures below:
1. In Figure 2 CONEX is supported by servers for sending data (here:
web servers in the Internet and caches in an operator's network)
but not by UEs (neither for receiving nor sending). An operator
who chooses to run a policing function on the network ingress
(e.g., on the P-GW) can still benefit from congestion exposure
without requiring any change on UEs.
2. CONEX is universally employed between operators (as depicted in
Figure 3), with an end-to-end CONEX feedback loop. Here,
operators could still employ local policies, congestion
accounting schemes etc., and they could use information about
congestion contribution for determining interconnection
agreements.
3. Isolated CONEX domains as depicted in Figure 4, CONEX is solely
applied locally, in the operator network, and there is no end-to-
end congestion exposure. This could be the case when CONEX is
only implemented in a few networks, or when operators decide to
not expose ECN and account for congestion for inter-domain
traffic. Independent of the actual scenario, it is likely that
there will be border gateways (as in today's deployments) that
are associated with policing and accounting functions.
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+------------+
| Web server |
| w/ CONEX |
+------------+
|
|
|
-----------------------
| | |
| Internet | |
| | |
-----------------------
|
--------------------------------------------|--------
| | |
| +-----------+ |
| | Web cache | |
| | w/ CONEX | |
| +-----------+ |
| | |
| +----+ +-------+ +-------+ +-------+ |
| | UE |=====| eNB |=====| S-GW |=====| P-GW | |
| +----+ +-------+ +-------+ +-------+ |
| |
| Operator B |
-----------------------------------------------------
Figure 2: CONEX support on servers and caches
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-----------------------------------------------------
| +----+ +-------+ +-------+ +-------+ |
| | UE |=====| eNB |=====| S-GW |=====| P-GW | |
| +----+ +-------+ +-------+ +-------+ |
| | |
| Operator A | |
--------------------------------------------|--------
|
-----------------------
| |
| Internet |
| |
-----------------------
|
--------------------------------------------|--------
| +----+ +-------+ +-------+ +-------+ |
| | UE |=====| eNB |=====| S-GW |=====| P-GW | |
| +----+ +-------+ +-------+ +-------+ |
| |
| Operator B |
-----------------------------------------------------
Figure 3: CONEX deployment across operator domains
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-----------------------------------------------------
| |--- CONEX path ---| |
| v v
| +----+ +-------+ +-------+ +-------+ |
| | UE |=====| eNB |=====| S-GW |=====| P-GW | |
| +----+ +-------+ +-------+ +-------+ |
| | |
| Operator A | |
--------------------------------------------|--------
|
-----------------------
| |
| Internet |
| |
-----------------------
|
--------------------------------------------|--------
| +----+ +-------+ +-------+ +-------+ |
| | UE |=====| eNB |=====| S-GW |=====| P-GW | |
| +----+ +-------+ +-------+ +-------+ |
| |
| Operator B |
-----------------------------------------------------
Figure 4: CONEX deployment in a single operator domain
We consider all three scenarios to be relevant and believe that both
of them are within the scope of the CONEX WG charter. A more
detailed description will be provided in a future version of this
document.
4.2. Implementing CONEX Functions in the EPS
We expect a CONEX solution to consist of different functions that
should be considered when implementing congestion exposure in 3GPP's
EPS. [I-D.ietf-conex-abstract-mech] is describing the following
congestion exposure components:
o Modified senders that send congestion exposure information in
response to congestion feedback).
o Receivers that generate congestion feedback (leveraging existing
behavior or requiring new functions).
o Audit functions that audit CONEX signals against actual
congestion, e.g., by monitoring flows or aggregate of flows.
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o Policy devices that monitor congestion exposure information and
act on the flows according to the operator's policy.
In the following, we discuss some possible placement strategies for
CONEX functional entities (addressing both policing and auditing
functions) in the EPS and for possible optimizations for both the
uplink and the downlink.
In general, CONEX information (exposed congestion) is declared by a
sender and remains unchanged on the path, hence reading CONEX
information (e.g., by policing functions) is placement-agnostic.
Auditing CONEX normally requires assessing declared congestion
contribution and current actual congestion. If the latter is, for
example, done using ECN, such a function would best be placed at the
end of the path.
In order to provide a comprehensive CONEX-based capacity management
framework for LTE, it would be advantageous to consider user
contribution to congestion for both the radio access and the core
network. For a non-invasive introduction of CONEX, it can be
beneficial to combine CONEX functions with existing logical EPS
entities. For example, potential places for CONEX policing and
auditing functions would then be eNBs, S-GWs or the P-GWs. Operator
deployments may of course still provide additional intermediary
CONEX-enabled IP network elements.
For a more specific discussion it will be beneficial to distinguish
downlink and uplink traffic directions (also see [nec.globecom2010]
for a more detailed discussion). In today's networks and usage
models, downlink traffic is dominating (also reflected by the
different maximum capacity provided by the air interface). That does
however not imply that uplink congestion is not an issue, since the
asymmetric maximum bandwidth configuration can create a smaller
bottleneck for uplink traffic -- and there are of course backhaul
links, gateways etc. that can be overloaded as well.
For managing downlink traffic -- e.g., in scenarios such as the one
depicted in Figure 2, operators can have different requirements for
policing traffic. Although policing is in principle location-
agnostic, it is important to consider requirements related to the EPS
architecture (Figure 1) such as tunneling between P-GWs and eNBs.
Policing can require access to subscriber information (e.g.,
congestion contribution quota) or user-specific accounting, which
suggests that the CONEX function could be co-located with the P-GW
that already has a PCRF interface.
Still, policing can serve different purposes. For example, if the
objective is to police bulk traffic induced by peer networks,
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additional monitoring functions can be placed directly at
corresponding ingress points to monitor traffic and possible drive
out-of-band functions such as triggering border contract penalties.
The auditing function which should be placed at the end of the path
(at least after/at the last bottleneck) would likely be placed best
on the eNB (wireless base station).
For the uplink direction, there are naturally different options for
designing monitoring and policy enforcement functions. A likely
approach can be to monitor congestion exposure on central gateway
nodes (such as P-GWs) that provide the required interfaces to the
PCRF, but to perform policing actions in the access network, i.e., in
eNBs, e.g., to police traffic at the ingress, before it reaches
concentration points in the core network.
Such a setup would enable all the CONEX use cases described in
Section 3, without requiring significant changes to the EPS
architecture, while enabling operators to re-use existing
infrastructure, specifically wireless base stations, PCRF and HSS
systems.
For CONEX functions on elements such as the S-GWs and P-GWs, it is
important to consider mobility and tunneling protocol requirements.
LTE provides two alternative approaches: Proxy-Mobile-IP (PMIP,
[3GPP.23.402]) and GPRS Tunneling Protocol (GTP). For the
propagation of congestion information (responses) tunneling
considerations are therefore very important.
In general, policing will be done based on per-user (per subscriber)
information such as congestion quota, current quota usage etc. and
network operator policies, e.g., specifying how to react to
persistent congestion contribution etc. In the EPS, per-user
information is normally part of the user profile (stored in the HSS)
that would be accessed by PCC entities such as the PCRF for dynamic
updates, enforcement etc.
A more detailed description of the different approaches and their
respective advantages will be provided in a future revision of this
document.
5. Summary
We have shown how congestion exposure can be useful for efficient
resource management in mobile communication networks. The premise
for this discussion was the observation that data communication,
specifically best-effort bulk data transmission, is becoming a
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commodity service whereas resources are obviously still limited --
which calls for efficient, scalable, yet effective capacity sharing
in such networks.
CONEX can be a mechanism that enables such capacity sharing, while
allowing operators to apply this mechanisms in different ways, e.g.,
for implementing different use cases as described in Section 3. It
is important to note that CONEX is fundamentally a mechanism that can
be applied in different ways -- to realize different operators
policies.
We have described a few possibilities for adding CONEX as a mechanism
to 3GPP LTE-based networks and have shown how this could be done
incrementally (starting with partial deployment). It is quite
feasible that such partial deployments be done on a per-operator-
domain basis, without requiring changes to standard 3GPP interfaces.
For a network-wide deployment, e.g., with congestion exposure between
operators, more considerations might be needed.
We have also identified a few implications/requirements that should
be taken into consideration when enabling congestion exposure in such
networks:
Performance: In mobile communication networks -- with more expensive
resources and more stringent QoS requirements -- the feasibility
of applying CONEX as well as its performance and deployment
scenarios need to be examined closer. For instance, a mobile
communication network may encounter longer delay and higher loss
rates, which can impose specific requirements on the timeliness
and accuracy of congestion exposure information.
Mobility: One of the unique characteristics in cellular network is
the presence of user mobility compared to wired networks. As the
user location changes, the same device can be connected to the
network via different base stations (eNodeBs) or even go through
switching gateways. Thus, the CONEX scheme must to be able to
carry latest congestion information per user/flow across multiple
network nodes in real time.
Multi-access: In cellular network, multiple access technologies can
co-exist. In such cases, a user can use multiple access
technologies for multiple applications or even a single
application simultaneously. If the congestion policies are set
based on each user, then CONEX should have the capability to
enable information exchange across multiple access domains.
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Tunneling: Both 3G and LTE networks make extensive usage of
tunneling. The CONEX mechanism should be designed in a way to
support usage with different tunneling protocols such as PMIP and
GTP. For ECN-based congestion notification, [RFC6040] specifies
how the ECN field of the IP header should be constructed on entry
and exit from IP-in-IP tunnels.
Roaming: Independent of the specific architecture, mobile
communication networks typically differentiate between non-roaming
and roaming scenarios. Roaming scenarios are typically more
demanding regarding implementing operator policies, charging etc.
It can be expected that this would also hold for deploying CONEX.
A more detailed analysis of this problem will be provided in a
future revision of this document.
One important thing to note here is that CONEX is intended to be used
as a supplement and not a replacement to the existing QoS mechanisms
in mobile networks. For example, CONEX deployed in 3GPP mobile
networks can provide useful input to the existing 3GPP PCC mechanisms
by supplying more dynamic network information to supplement the
fairly static information used by the PCC. This would enable the
mobile network to make better policy control decisions than is
possible with only static information.
6. IANA Considerations
No IANA considerations.
7. Security Considerations
Security considerations will be provided in a future version of this
document.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[3GPP.23.203]
3GPP, "Policy and charging control architecture", 3GPP
TS 23.203 10.4.0, June 2011.
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[3GPP.23.402]
3GPP, "Architecture enhancements for non-3GPP accesses",
3GPP TS 23.402 10.4.0, June 2011.
[3GPP.23.829]
3GPP, "Local IP Access and Selected IP Traffic Offload
(LIPA-SIPTO)", 3GPP TR 23.829 10.0.0, March 2011.
[3GPP.29.060]
3GPP, "General Packet Radio Service (GPRS); GPRS
Tunnelling Protocol (GTP) across the Gn and Gp interface",
3GPP TS 29.060 3.19.0, March 2004.
[3GPP.29.274]
3GPP, "3GPP Evolved Packet System (EPS); Evolved General
Packet Radio Service (GPRS) Tunnelling Protocol for
Control plane (GTPv2-C); Stage 3", 3GPP TS 29.274 10.3.0,
June 2011.
[3GPP.36.300]
3GPP, "Evolved Universal Terrestrial Radio Access (E-UTRA)
and Evolved Universal Terrestrial Radio Access Network
(E-UTRAN); Overall description; Stage 2", 3GPP TS 36.300
10.4.0, June 2011.
[I-D.ietf-conex-abstract-mech]
Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)
Concepts and Abstract Mechanism",
draft-ietf-conex-abstract-mech-01 (work in progress),
March 2011.
[I-D.ietf-conex-concepts-uses]
Moncaster, T., Leslie, J., Briscoe, B., Woundy, R., and D.
McDysan, "ConEx Concepts and Use Cases",
draft-ietf-conex-concepts-uses-01 (work in progress),
March 2011.
[RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, November 2010.
[nec.euronf-2011]
Mir, Kutscher, and Brunner, "Congestion Exposure in
Mobility Scenarios", in proceedings of 7th EURO-NF
CONFERENCE ON NEXT GENERATION INTERNET, June 2011.
[nec.globecom2010]
Kutscher, Lundqvist, and Mir, "Congestion Exposure in
Mobile Wireless Communications", in proceedings of IEEE
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Internet-Draft CONEX Mobile Scenario July 2011
GLOBECOM 2010, December 2010.
[raghavan2007]
Raghavan, Vishwanath, Ramabhadran, Yocum, and Snoeren,
"Cloud Control with Distributed Rate Limiting", in
proceedings of ACM SIGCOMM 2007, 2007.
DOI: http://doi.acm.org/10.1145/1282427.1282419
Appendix A. Acknowledgments
We would like to thank Bob Briscoe and Ingemar Johansson for their
support in shaping the overall idea and in improving the draft by
providing constructive comments.
Authors' Addresses
Dirk Kutscher
NEC
Kurfuersten-Anlage 36
Heidelberg,
Germany
Phone:
Email: kutscher@neclab.eu
Faisal Ghias Mir
NEC
Kurfuersten-Anlage 36
Heidelberg,
Germany
Phone:
Email: faisal.mir@neclab.eu
Rolf Winter
NEC
Kurfuersten-Anlage 36
Heidelberg,
Germany
Phone:
Email: winter@neclab.eu
Kutscher, et al. Expires January 12, 2012 [Page 20]
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Suresh Krishnan
Ericsson
8400 Blvd Decarie
Town of Mount Royal, Quebec
Canada
Phone:
Email: suresh.krishnan@ericsson.com
Ying Zhang
Ericsson
200 Holger Way
San Jose, CA 95134
USA
Phone:
Email: ying.zhang@ericsson.com
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