Transport Area Working Group M. Amend
Internet-Draft Deutsche Telekom
Intended status: Informational A. Brunstrom
Expires: September 12, 2019 A. Kassler
Karlstad University
V. Rakocevic
City University of London
March 11, 2019
IP compatible multipath framework for heterogeneous access networks
draft-amend-tsvwg-multipath-framework-mpdccp-00
Abstract
More and more of today's devices are multi-homing capable, in
particular 3GPP user equipment like smartphones. In the current
standardization of the next upcoming mobile network generation 5G
Rel. 16, this is especially targeted in the study group Access
Traffic Steering Switching Splitting [3GPP, TR 23.793]. ATSSS
describes the flexible selection or combination of 3GPP untrusted
access like Wi-Fi and cellular access, overcoming the single-access
limitation of today's devices and services. Another multi-
connectivity scenario is the Hybrid Access [draft-lhwxz-hybrid-
access-network-architecture, draft-muley-network-based-bonding-
hybrid-access], providing multiple access for CPEs, which extends the
traditional way of single access connectivity at home to dual-
connectivity over 3GPP and fixed access. A missing piece in the
ATSSS and Hybrid Access is the access and path measurement for
efficient and beneficial traffic steering decisions. This becomes
particularly important in heterogeneous access networks with a
multitude of volatile access paths. MP-TCP can be employed in such
scenarios and concerning the ATSSS, it is the agreed protocol for the
traffic splitting mode. A decision for MP-TCP though leaves the
increasing share of UDP in today's traffic mix (https://arxiv.org/
abs/1801.05168) unconsidered. In this document, a network
architecture leveraging the MP-DCCP network protocol is proposed,
which enables above scenarios and address the formulated issues
either independent or complementary to MP-TCP.
Status of This Memo
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Internet-Draft MP-DCCP multipath framework March 2019
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. IP compatible multipath framework based on MP-DCCP . . . . . 3
3. Application and placement . . . . . . . . . . . . . . . . . . 5
4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. Informative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Multi-connectivity access networks are evolving. Ongoing
standardization at 3GPP for 5G mobile networks [3GPP, TR 23.793] or
the so called Hybrid Access networks [draft-lhwxz-hybrid-access-
network-architecture, draft-muley-network-based-bonding-hybrid-
access] already provides or will provide in the near future the
ability for multi-connectivity to a broad mass. A superior
resilience against network outages, higher capacities and network
cost optimizations are only some of the reasons why it make sense to
introduce multi-connectivity. Since the multi-connectivity
architectures are almost mature, it requires network protocols
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providing the technology to exploit multi-connectivity. In the
simplest case, multi-connectivity means load-balancing, distributing
individual flows over multiple paths to distribute the load.
However, this has no effect on resilience or capacity gain on those
load balanced individual flows. More complex are those scenarios
where an individual flow can be seamlessly shifted between multiple
paths or can even aggregate those paths for leveraging the sum
capacities. Like [3GPP, TR 23.793] this document refers to the three
distribution schemes Steering (load balancing), Switching (seamless
handover) and Splitting (capacity aggregation).
MP-TCP [RFC6824] is a protocol, which can be applied in the above
mentioned use cases and covers load-balancing, seamless communication
handover and also capacity aggregation. Further, it deals with
heterogeneous and volatile access networks, since it profits from the
TCP inherent congestion control. By design, MP-TCP is limited to TCP
services and excludes any other network protocol, in particular UDP.
For future multi-connectivity systems, it is not sufficient anymore
to rely on supporting only TCP. The increasing share of UPD traffic,
mainly impacted by the QUIC introduction, may significantly reduce
the share from TCP. It might be expected that with HTTP/3 carried
over QUIC [draft-ietf-quic-http], the previous strong dominance of
TCP will be challenged by UDP.
2. IP compatible multipath framework based on MP-DCCP
A new approach, which overcomes MP-TCP's restriction to TCP services
and providing IP compatibility, is depicted in Fig. 1. The
architecture employs MP-DCCP [draft mp-dccp] in combination with an
encapsulation scheme. For simplification, Fig. 1 assumes a traffic
direction from the left (sender) to the right (receiver) and requires
application in each direction for bi-directional transmission. The
architecture in Fig. 1 can replace or complement MP-TCP to reach IP
compatibility.
Service |<- MP-DCCP ->| Service
or Device or Device
+---------+ ___ +------+ DCCP Flow 1 +-------+ +---------+
| | _ |Seq|| Path |--------------| Re- | _ | |
| Sender |___| \___˅__| | : | order |____/ |___|Receiver |
| | IP|_/ | Sched| : | | \_|IP | |
| | VNIF_in | uler |--------------| engine| VNIF_out | |
+---------+ +------+ DCCP Flow n +-------+ +---------+
Figure 1: IP compatible multipath framework based on MP-DCCP
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PDUs generated from the sender and travelling through the
architecture in Fig. 1 passes the components in the following order:
1. Sender: Generates any PDU based on the IP protocol.
2. VNIF_in: IP based Virtual Network Interface as entry point to the
MP-DCCP framework. A simple routing logic in front (between (1)
and (2)) can act as gatekeeper and decides upon redirecting
traffic through the VNIF or bypassing it. The VNIF adds an extra
IP layer to reach the multi-connectivity termination point.
3. Seq: Sequencing of in (2) passed PDUs depending on the incoming
order. Adds an incrementing number, which is later added to the
DCCP encapsulation in (4).
4. Path Scheduler: Decision logic for scheduling sequenced PDUs over
the individual connected DCCP flows for multipath transmission.
The path scheduler can use the information from the DCCP flows
(see (5)) inherent congestion control information like CWND,
packet loss, RTT, Jitter. After selection of a DCCP flow, the
PDU is encapsulated into the individual flow. Further
information, at least the sequencing, is added on top as DCCP
option.
5. DCCP Flow(s): Responsible to transmit the encapsulated PDUs to
the MP-DCCP exit point.
6. Reorder engine: Depending on the sequencing information of (3), a
re-assembly of the PDU stream can be applied. The strictness of
re-ordering shall be configurable up to no re-ordering.
7. VNIF_out: Releases PDUs that have passed the re-ordering engine
and strips the DCCP specific overhead. Again routing is
responsible to deliver the PDUs to the receiver based on the
destination information in the PDU.
8. Receiver: Receive the PDU as generated in (1).
The simple enclosing of the MP-DCCP with Virtual Network Interface
(VNIF) provides the IP compatibility. However, a service or protocol
classifier between sender and VNIF can reduce the scope to particular
traffic, e.g. UDP, by simple routing decisions. The MP-DCCP takes
over responsibility for the multi-path transfer of the traffic, which
is directed through the VNIF_in. For possible re-assembly operations
the IP packets are stamped with a continuously incremented stamped
sequence number. This is not a mandatory operation, but assumed
required in most seamless handover and capacity aggregation use
cases. The path scheduler decides for each IP packet which DCCP flow
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is appropriate, based on a configurable decision logic and supported
by the congestion control information of the DCCP flows available for
transmission. A DCCP flow selection for a PDU leads to its
encapsulation into the respective DCCP flow and adding extra
information required for the multipath transmission, e.g. the
sequence number. Encapsulation also means, that to the original PDU
a DCCP and IP header is added to reach the multi-connectivity end-
point. When the encapsulated PDUs arrive at the multi-path
termination point, they are re-ordered depending on the carried
sequence number and a configurable logic. The re-ordering engine may
also include a logic in which packets are just forwarded (no re-
ordering). Re-ordering needs to be considered carefully since any
active intervention changes the latency responsiveness. The multi-
path termination is finally completed when the DCCP overhead is
stripped and the PDU leaves VNIF_out. Further routing depends again
on the IP layer of the original PDU.
3. Application and placement
The framework of Fig. 1 gives most flexibility in applying multipath
support in different architectures and allows MP-DCCP to be applied
at any place between sender and receiver. Fig2. to Fig. 5 gives an
impression about the universality which covers any imaginable
architecture.
Device Middlebox 1 Middlebox 2 Device
+------+ +-------------+ +------------+ +--------+
|Sender| -> |MP-DCCP entry| -> |MP-DCCP exit| -> |Receiver|
+------+ +-------------+ +------------+ +--------+
Figure 2: Sender and receiver independent MP-DCCP
Device Middlebox Device
+----------------------+ +------------+ +--------+
|Sender + MP-DCCP entry| -> |MP-DCCP exit| -> |Receiver|
+----------------------+ +------------+ +--------+
Figure 3: Sender integrated but receiver independent MP-DCCP
Device Middlebox Device
+------+ +-------------+ +-----------------------+
|Sender| -> |MP-DCCP entry| -> |MP-DCCP exit + Receiver|
+------+ +-------------+ +-----------------------+
Figure 4: Sender independent and receiver integrated MP-DCCP
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Device Device
+----------------------+ +-----------------------+
|Sender + MP-DCCP entry| -> |MP-DCCP exit + Receiver|
+----------------------+ +-----------------------+
Figure 5: Sender and receiver integrated MP-DCCP
4. Conclusion
The specified IP compatible multipath framework based on MP-DCCP in
this document comprises several benefits:
o Pure routing
o Inherent path estimation and measurement
o Imposes no reliability or in-order delivery
o Modular re-ordering
o Modular scheduling
o IP compatible
o Based on the standardized DCCP.
Middle-box traversing, when the framework is applied in uncontrolled
environments, is addressed in [RFC6733] and [draft u-dccp].
5. Security Considerations
[Tbd]
6. Acknowledgments
7. Informative References
[I-D.ietf-quic-http]
Bishop, M., "Hypertext Transfer Protocol Version 3
(HTTP/3)", draft-ietf-quic-http-18 (work in progress),
January 2019.
[I-D.lhwxz-hybrid-access-network-architecture]
Leymann, N., Heidemann, C., Wasserman, M., Xue, L., and M.
Zhang, "Hybrid Access Network Architecture", draft-lhwxz-
hybrid-access-network-architecture-02 (work in progress),
January 2015.
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[I-D.muley-network-based-bonding-hybrid-access]
Muley, P., Henderickx, W., Geng, L., Liu, H., Cardullo,
L., Newton, J., Seo, S., Draznin, S., and B. Patil,
"Network based Bonding solution for Hybrid Access", draft-
muley-network-based-bonding-hybrid-access-03 (work in
progress), October 2018.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<https://www.rfc-editor.org/info/rfc6733>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<https://www.rfc-editor.org/info/rfc6824>.
Authors' Addresses
Markus Amend
Deutsche Telekom
T-Online-Allee 1
Darmstadt
Germany
Email: Markus.Amend@telekom.de
Anna Brunstrom
Karlstad University
Universitetsgatan 2
651 88 Karlstad
Sweden
Email: anna.brunstrom@kau.se
Andreas Kassler
Karlstad University
Universitetsgatan 2
651 88 Karlstad
Sweden
Email: andreas.kassler@kau.se
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Veselin Rakocevic
City University of London
Northampton Square
London
United Kingdom
Email: veselin.rakocevic.1@city.ac.uk
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