Internet DRAFT - draft-you-traffic-distribution-for-bonding
draft-you-traffic-distribution-for-bonding
Network Working Group J. You
Internet-Draft M. Zhang
Intended status: Informational Huawei Technologies
Expires: September 22, 2016 N. Leymann
C. Heidemann
Deutsche Telekom AG
March 21, 2016
Traffic Distribution for GRE Tunnel Bonding
draft-you-traffic-distribution-for-bonding-00
Abstract
GRE (Generic Routing Encapsulation) Tunnel Bonding as an L3 overlay
tunneling mechanism is used for Hybrid Access (HA) bonding between
HCPE (Hybrid Customer Premises Equipment) and HAG (Hybrid Access
Gateway). The bonding performance depends upon the performance for
each individual link. This document specifies a trying overflow
mechanism to avoid the bonding performance downgrading due to the
situation that an individual link is disrupted or its quality
downgrages too much so that the bonding is no longer applicable.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 22, 2016.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Abbreviations and acronyms . . . . . . . . . . . . . . . 3
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. TCP Throughput Measurement and Issues . . . . . . . . . . . . 4
4. Traffic Distribution Algorithm . . . . . . . . . . . . . . . 4
5. Trying Overflow Mechanism . . . . . . . . . . . . . . . . . . 6
6. Overbooking Considerations . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Service providers want to supply a higher throughput for their
subscribers to provide a better customer experience, especially in
those cases where customers can only be offered with a low bitrate
DSL access. Bonding of fixed broadband and 3GPP access networks
becomes desirable. [I-D.zhang-gre-tunnel-bonding] proposes a GRE
(Generic Routing Encapsulation) tunnel bonding mechanism for bonding
of DSL (Digital Subscriber Line) connection and LTE (Long Term
Evolution) connection. An example of deployment scenario is
illustrated in Figure 1. The Hybrid Access (HA) bonded connection is
established between the HCPE (Hybrid Customer Premises Equipment), in
the customer premises network, and the HAG (Hybrid Access Gateway),
on the service provider's network [WT-348].
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+------+ LTE GRE Tunnel +-------+
+---------+ | +-----------------+ | Internet
|User +----+ HCPE | | HAG +-----
|Equipment| | +-----------------+ |
+---------+ +------+ DSL GRE Tunnel +-------+
Figure 1: GRE Tunnel Bonding
The bonding should not be enabled if the bonding performance is worse
than DSL only. This document proposes a traffic distribution
algorithm named trying overflow to improve the bonding performance.
2. Terminology
2.1. Abbreviations and acronyms
BRAS: Broadband Remote Access Server
CAR: Commit Access Rate
CIR: Committed Information Rate
HA: Hybrid Access
HAG: Hybrid Access Gateway
HCPE: Hybrid Customer Premises Equipment
LTE: Long Term Evolution
2.2. Definitions
Hybrid Access: The bonding of two access paths based on
heterogeneous technologies (e.g., DSL and LTE).
Hybrid Access Gateway: A logical function in the operator network
implementing a bonding mechanism for customer access services.
Hybrid Customer Premises Equipment: A CPE enhanced to support the
simultaneous use of both fixed broadband and 3GPP access networks.
Hybrid Access Gateway: A logical function in the operator network
implementing a bonding mechanism for customer access services.
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3. TCP Throughput Measurement and Issues
The Quality of Experience (QoE) on a hybrid access service depends
upon the performance of each individual link. Generally, TCP
Throughput (T) for a link can be measured as:
Throughput <= min (BW, WindowSize/RTT, MSS/(RTT*sqrt(p)) )
While for hybrid access,
RTT = max(RTT1, RTT2)
p = w1*p1+w2*p2
Therein,
BW: maximum bandwidth
WindowSize: congestion window size
RTT: Round Trip Time; RTT1 for DSL link, RTT2 for LTE link
MSS: maximum segment size (fixed for each Internet path, typically
1460 Bytes)
p: packet loss rate; p1 for DSL link, p2 for LTE link
w: distribution factor; w1 refers to the percentage of total
traffic on DSL link; w2 refers to the percentage of total traffic
on LTE link.
When LTE link becomes congested, the latency may reach up to 400 ms;
while the normal latency on DSL may only be 10 ms. According to the
formula above, the TCP throughput for the hybrid access would be
worse than DSL link only assuming p1 = p2.
4. Traffic Distribution Algorithm
Principle: Traffic distribution over DSL is prior to traffic
distribution over LTE. The bonding mode would be enabled if the
bonding performance is better than DSL only. Otherwise the bonding
should not be enabled.
CAR (Committed Access Rate) with two token buckets is used to
distribute traffic flows on HA-compliant nodes.
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+-------+ (RTT2, p2, T2) +-------+
| | LTE GRE Tunnel | |
| +-----------------------+ |
| HPCE | | HAG |
| | +-----+ | |
| +----------+BRAS +------+ |
+-------+ +-----+ +-------+
DSL GRE Tunnel
(RTT1, p1, T1)
Figure 2: Deployment Scenario
1. Start DSL only, and measure RTT1, p1 and T1 periodically; get
<RTT1_min, p1_min>, <T1_max, RTT1_t1max, p1_t1max>. Here RTT1_t1max
refers to the RTT when the throughput reaches maximum (T1_max) in a
period. Likewise, p1_t1max refers to the p when the throughput
reaches maximum (T1_max) in a period.
2. Estimate the usage of DSL according to RTT1 and P1; If there's no
congestion (i.e. RTT1=RTT1_min and p1=p1_min), bonding is not
enabled.
3. If DSL is congested (i.e. RTT1>RTT1_min or p1>p1_min), start the
"trying overflow" procedure (detailed in Section 5).
1) The bonding mode is on. Tentatively distribute a small amount
of traffic onto the LTE link at the initial stage, assuming CIR2 =
LTE_MIN (minimum committed access rate). LTE_MIN is configurable
and its default value is 64Kbps.
2) Measure the throughput of the bonded links (T12) periodically.
a) If T12 < T1_max and the DSL link is not congested, the
bonding mode should be off.
b) If T12 < T1_max and the DSL link is congested, the bonding
mode is open, the CIR adjustment (i.e. decreasing) of the DSL
link is triggered.
c) Otherwise, the bonding mode is on. Set CIR1 = T1_max, the
overflow traffic is distributed to LTE tunnel.
i. If the DSL link is not congested and T12 is increasing
rapidly, the CIR adjustment (i.e. increasing) of the DSL
link is triggered.
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5. Trying Overflow Mechanism
The "Trying Overflow" mechanism is implemented using the token bucket
mechanism on, as shown in Figure 3.
|
|CIR2=LTE_MIN
|
\|/
+---+----+
+--------+
| | Mark color
|Trying | (Yellow, #1)
|Overflow+---------------------+
|Bucket | |
| | \|/
+---+----+ +---+----+
|Mark color +--------+ Mark color
| (Green) | | (Yellow, #2)
\|/ | +--------------+
+----------+ |DSL | CIR1=T1_max |
|Forward to| |Bucket | \|/
|LTE tunnel| | | +----------+
+----------+ +---+----+ |Forward to|
Mark color | |LTE tunnel|
(Green) \|/ +----------+
+----------+
|Forward to|
|DSL tunnel|
+----------+
Figure 3: Trying Overflow
o Trying Overflow Bucket: In this step, all the incoming traffic will
be distributed to the trying overflow bucket. Its CIR can be set to
LTE_MIN.
HA node has no knowledge of the quality of the LTE tunnel at
first. If the LTE tunnel is congested, the bonding may impair the
customer experience. So trying overflow is performed. If the
trying is successful, then it means the LTE tunnel can be used for
bonding.
The green packets will be distributed into the LTE tunnel, while
yellow packets of #1 will be put into the DSL bucket.
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o DSL Bucket: Its CIR can be set to T1_max. The green packets will
be distributed into DSL tunnel, and yellow packets of #2 will be
distributed into LTE tunnel.
Theoretically, if the LTE tunnel is suitable for bonding, the bonding
TCP throughput T12 will increase continuously; and will exceed T1_max
immediately. Yellow packets of #2 can be continuously observed
obviously in a period of time.
6. Overbooking Considerations
DSL bandwidth can be overbooked on the BRAS (Broadband Remote Access
Server). Overbooking may cause long delay or high packet loss rate.
When bandwidth downgrading happens on the BRAS due to overbooking,
the CIR of the DSL link needs to be decreased. At that time, the
bonding performance is worse than using DSL only and the DSL link is
congested.
When the bandwidth is restored, the CIR of the DSL link needs to be
increased. At that time, the bonding performance improves, and the
congestion on the DSL link can be relieved.
7. Security Considerations
TBD.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References
[I-D.zhang-gre-tunnel-bonding]
Leymann, N., Heidemann, C., Zhang, M., Sarikaya, B., and
M. Cullen, "GRE Tunnel Bonding", draft-zhang-gre-tunnel-
bonding-01 (work in progress), October 2015.
[WT-348] "BBF WT-348 Part-A: Hybrid Access for Broadband Networks",
12 2015.
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Authors' Addresses
Jianjie You
Huawei Technologies
101 Software Avenue, Yuhuatai District
Nanjing 210012
China
Email: youjianjie@huawei.com
Mingui Zhang
Huawei Technologies
No.156 Beiqing Rd. Haidian District
Beijing 100095
China
Email: zhangmingui@huawei.com
Nicolai Leymann
Deutsche Telekom AG
Winterfeldtstrasse 21-27
Berlin 10781
Germany
Email: n.leymann@telekom.de
Cornelius Heidemann
Deutsche Telekom AG
Heinrich-Hertz-Strasse 3-7
Darmstadt 64295
Germany
Email: heidemannc@telekom.de
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