UDP-based Generic Multi-Access (GMA) Control Protocol
draft-zhu-intarea-gma-control-00
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| Authors | Jing Zhu , Menglei Zhang | ||
| Last updated | 2021-10-13 | ||
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draft-zhu-intarea-gma-control-00
Network Working Group J. Zhu
Internet Draft M. Zhang
Intended status: Experimental Intel
Expires: April 13,2022
October 13, 2021
UDP-based Generic Multi-Access (GMA) Control Protocol
draft-zhu-intarea-gma-control-00
Abstract
A device can be simultaneously connected to multiple networks,
e.g., Wi-Fi, LTE, 5G, and DSL. It is desirable to seamlessly
combine the connectivity over these networks below the transport
layer (L4) to improve quality of experience for applications that
do not have built in multi-path capabilities. This document
presents a new control protocol to manage traffic steering,
splitting, and duplicating across multiple connections. The
solution has been developed by the authors based on their
experiences in multiple standards bodies including the IETF and
3GPP, is not an Internet Standard and does not represent the
consensus opinion of the IETF. This document will enable other
developers to build interoperable implementations in order to
experiment with the protocol.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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http://www.ietf.org/ietf/1id-abstracts.txt
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This Internet-Draft will expire on April 13, 2022.
Copyright Notice
Copyright (c) 2021 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 ................................................. 2
1.1. Scope of Experiment ....................................4
2. Conventions used in this document ............................ 5
3. Use Case ..................................................... 5
4. UDP-based GMA Encapsulation Protocol ......................... 6
5. GMA Control Messages ......................................... 9
5.1 Probe Message ........................................10
5.2 Acknowledgement (ACK) Message ........................11
5.3 Traffic Splitting Update (TSU) Message ...............11
5.4 Traffic Splitting Acknowledgement (TSA) Message ......13
5.5 Timestamp Reset Request (TSR) Message ................14
6. GMA Control Flows ........................................... 15
6.1. Initialization ........................................15
6.2. GMA Operation .........................................16
6.3. Termination ...........................................17
7. Security Considerations ..................................... 18
8. IANA Considerations ......................................... 18
9. References .................................................. 18
9.1. Normative References ..................................18
9.2. Informative References ................................18
1. Introduction
A device can be simultaneously connected to multiple networks,
e.g., Wi-Fi, LTE, 5G, and DSL. It is desirable to seamlessly
combine the connectivity over these networks below the transport
layer (L4) to improve quality of experience for applications that
do not have built in multi-path capabilities.
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Figure 1 shows the Multi-Access Management Service (MAMS) user-
plane protocol stack [MAMS], which has been used in today's multi-
access solutions [ATSSS] [LWIPEP] [GRE1] [GRE2]. It consists of
two layers: convergence and adaptation.
The convergence layer is responsible for multi-access operations,
including multi-link (path) aggregation, splitting/reordering,
lossless switching/retransmission, etc. It operates on top of the
adaptation layer in the protocol stack. From the perspective of a
transmitter, a user payload (e.g., IP packet) is processed by the
convergence layer first, and then by the adaptation layer before
being transported over a delivery connection; from the receiver's
perspective, an IP packet received over a delivery connection is
processed by the adaptation layer first, and then by the
convergence layer.
+-----------------------------------------------------+
| User Payload, e.g., IP Protocol Data Unit (PDU) |
+-----------------------------------------------------+
+-----------------------------------------------------------+
| +-----------------------------------------------------+ |
| | Multi-Access (MX) Convergence Layer | |
| +-----------------------------------------------------+ |
| +-----------------------------------------------------+ |
| | MX Adaptation | MX Adaptation | MX Adaptation | |
| | Layer | Layer | Layer | |
| +-----------------+-----------------+-----------------+ |
| | Access #1 IP | Access #2 IP | Access #3 IP | |
| +-----------------------------------------------------+ |
| MAMS User-Plane Protocol Stack |
+-----------------------------------------------------------+
Figure 1: MAMS User-Plane Protocol Stack [MAMS]
A new encapsulation protocol [GMAE] has been specified for the
convergence layer to encode additional control information, e.g.,
Timestamp, Sequence Number, required for multi-access traffic
management. This document presents a UDP-based GMA control
protocol for the convergence layer. The GMA control protocol only
operates between endpoints that have been configured to use GMA.
This configuration can be through any management messages and
procedures, including, for example, Multi-Access Management
Services [MAMS].
The solution described in this document was been developed by the
authors based on their experiences in multiple standards bodies
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including the IETF and 3GPP. However, it is not an Internet
Standard and does not represent the consensus opinion of the IETF.
This document presents the protocol specification to enable
experimentation as described in Section 1.1 and to facilitate
other interoperable implementations.
1.1. Scope of Experiment
The protocol described in this document is an experiment. One
objective of the experiment is to determine whether the protocol
meets the 3GPP ATSSS Phase 2 [ATSSS2] requirements, can be safely
used, and has support for deployment. Particularly, the proposed
GMA protocol addresses the following issues of using QUIC for
ATSSS Phase 2:
o Encapsulation Overhead: the GMA encapsulation protocol uses a 2-
bytes Flag field to control all optional header fields instead
of the TLV (Type-Length-Value) based approach. As a result, the
minimum encapsulation overhead is 2 bytes, and the maximum
overhead is 16 bytes.
o Multiple Encryptions: the GMA encapsulation protocol does not
require encryption and avoids redundant encryption overhead.
o Congestion Control in Congestion Control: the GMA control
protocol does not require congestion control. All incoming
packets (from higher layer) are sent over one of the delivery
connections immediately without any delay due to congestion
control.
In addition, the GMA protocol does not require Acknowledgement
(ACK) and reliable delivery for data-plane traffic to avoid any
delay due to retransmission as well as any ACK traffic overhead on
the reverse path.
Path quality measurements (e.g. one-way-delay, loss, etc.) and
congestion detection are performed by receiver based on the GMA
header fields, e.g. sequence number, timestamp, etc. Another
objective of the experiment is to evaluate the usage of various
receiver-based congestion detection algorithms [GCC] [MPIP] in
multi-access traffic management.
It is expected that this protocol experiment can be conducted on
the Internet since the GMA packets are encapsulated with UDP.
Thus, experimentation is conducted between consenting end systems
that have been mutually configured to participate in the
experiment.
The authors will continually assess the progress of this
experiment and encourage other implementers to contact them to
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report the status of their implementations and their experiences
with the protocol.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14 [RFC2119] [RFC8174] when, and only when, they
appear in all capitals, as shown here.
3. Use Case
As shown in Figure 2, a client device (e.g., Smartphone, Laptop,
etc.) may connect to the Internet via both Wi-Fi and LTE
connections, operating as the delivery connection. In addition, a
virtual (e.g. IPv4, IPv6, or Ethernet) connection is established
between client and multi-access gateway. The virtual connection is
the anchor, providing the IP address and connectivity for end-to-
end Internet access, and delivery connection provides multiple
paths between client and multi-access gateway for multi-access
traffic management, aka Access Traffic Steering, Switching, and
Splitting (ATSSS) in 3GPP [ATSSS].
+------- Virtual (anchor) Connection ------+
| |
+-+---+ +---+-+
| | |A|--- LTE (delivery) Connection --|C| | |
Apps ---|X|U|-| |-|S|Z|--- Internet
| | |B|-- Wi-Fi (delivery) Connection--|D| | |
+-+---+ +---+-+
Client multi-access Gateway
o A: The adaptation layer endpoint of the LTE connection in the
client
o B: The adaptation layer endpoint of the Wi-Fi connection in the
client
o C: The adaptation layer endpoint of the LTE connection in the
multi-access gateway
o D: The adaptation layer endpoint of the Wi-Fi connection in the
multi-access gateway
o U: The convergence layer endpoint in the client
o S: The convergence layer endpoint in the multi-access gateway
o X: The virtual connection endpoint in the client
o Z: The virtual connection endpoint in the multi-access gateway
Figure 2: GMA-based Multi-Access Traffic Management
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For example, the virtual connection could be a Multi-Access
Protocol Data Unit (MA-PDU) connection as specified in 3GPP
[ATSSS]. Per-packet aggregation allows the MA-PDU connection to
use the combined bandwidth of the two connections. Moreover,
packets may be duplicated over multiple connections to achieve
high reliability and low latency, where duplicated packets are
eliminated by the receiving side. Such multi-access optimization
requires additional control message exchange between client and
multi-access gateway.
"UDP" is used for the adaptation layer in this document. Figure 3a
and 3b show the UDP-based GMA user-plane and control-plane
protocol, respectively.
+-----------------------------------------------------+
| Virtual Connection (IP, Ethernet, etc.) |
+-----------------------------------------------------+
| UDP-based GMA Encapsulation protocol |
+-----------------------------------------------------+
| UDP | UDP | UDP |
+-----------------+-----------------+-----------------+
| Access #1 IP | Access #2 IP | Access #3 IP |
+-----------------------------------------------------+
Figure 3a: UDP-based GMA User-Plane Protocol Stack
+-----------------------------------------------------+
| GMA Control Protocol |
+-----------------------------------------------------+
| UDP-based GMA Encapsulation protocol |
+-----------------------------------------------------+
| UDP | UDP | UDP |
+-----------------+-----------------+-----------------+
| Access #1 IP | Access #2 IP | Access #3 IP |
+-----------------------------------------------------+
Figure 3b: UDP-based GMA Control-Plane Protocol Stack
4. UDP-based GMA Encapsulation Protocol
Figure 4 shows the UDP-based GMA encapsulation format as specified
in [GMAE]. The ports for "UDP Tunnelling" at Client are chosen
from the Dynamic Port range, and the ports for "UDP Tunnelling" at
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multi-access gateway are configured and provided to client through
the MAMS message (MX UP Setup Config) [MAMS].
+------------------------------------------------+
| IP hdr | UDP hdr | GMA Header | Payload |
+------------------------------------------------+
Figure 4: UDP-based GMA PDU Format
The GMA (Generic Multi-Access) header MUST consist of the
mandatory "Flags" field (the first two bytes), defined as follows:
o Payload Type (bit 0): to indicate the GMA PDU payload type
+ 0: control message
+ 1: user-plane message
o Client ID Present (bit 1): If the Client ID Present bit is set
to 1, then the Client ID field is present
o Slice ID Present (bit 2): if the Slice ID Present bit is set, to
1, then the Slice ID field is present
o Connection ID Present (bit 3): If the Connection ID Present bit
is set to 1, then the Connection ID field is present
o Flow ID Present (bit 4): If the Flow ID Present bit is set to 1,
then the Flow ID field is present
o Per-Packet Priority (PPP) Present (bit 5): If the PPP Present
bit is set to 1, then the PPP field is present
o Delivery SN Present (bit 6): If the Delivery SN (Sequence
Number) Present bit is set to 1, then the Delivery SN field is
present and contains the valid information
o Flow SN Present (bit 7): If the Flow SN Present bit is set to 1,
then the Sequence Number field is present
o Timestamp Present (bit 8): If the Timestamp Present bit is set
to 1, then the Timestamp field is present
o Concatenation Present (bit 9): If the Concatenation Present bit
is set to 1, then the PDU carries multiple SDUs
o Reserved (bit 10-15): set to "0" and ignored on receipt
Bit 0 is the most significant bit (MSB), and Bit 15 is the least
significant bit (LSB).
The Receiver SHOULD first decode the Flags field to determine the
length of the GMA header, and then decode each optional field
accordingly. The GMA (Generic Multi-Access) header MAY consist of
the following optional fields:
o Client ID (2 Byte): an unsigned integer to identify the client
o Slice ID (1 Byte): an unsigned integer to identify the network
slice of the GMA SDU
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o Connection ID (1 Byte): an unsigned integer to identify the
anchor connection of the GMA SDU.
o Flow ID (1 Byte): an unsigned integer to identify the IP flow
of the GMA SDU.
o Per-Packet Priority (1 Byte): an unsigned integer to identify
the relative priority of the GMA SDU in the flow (smaller
value means higher priority).
o Delivery SN (1 Byte): an auto-incremented integer to indicate
the GMA PDU transmission order on a delivery connection.
Delivery SN is used to measure packet loss of each delivery
connection and therefore generated per delivery connection
per flow. This field is present only if the Delivery SN
Present bit is set to one.
o Flow SN (3 Bytes): an auto-incremented integer to indicate the
GMA SDU (IP packet) order of a flow. Flow SN is used for
reordering, and therefore generated per flow. This field is
present only if the Flow SN Present bit is set to one.
o Timestamp (4 Bytes): to contain the current value of the
timestamp clock of the transmitter in the unit of 1
millisecond. This field is present only if the Timestamp
Present bit is set to one.
Figure 5 shows the GMA header format with all the fields present,
and the order of the GMA control fields SHALL follow the bit order
in the Flags field. Note that the bits in the Flags field are
ordered with the first bit transmitted being bit 0 (MSB). All
fields are transmitted in regular network byte order and appear in
order to their corresponding flag bits. If a flag bit is clear,
the corresponding optional field is absent.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags | reserved | Client ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Slice ID | Conn ID | Flow ID | PPP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delivery SN | Flow SN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: GMA Header Format with all Optional Fields Present
Some GMA header fields, e.g. Slice ID, Conn ID, Flow ID, and PPP
are designed to support hierarchical QoS (hQoS) and fine granular
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packet classification. Notice that GMA header fields (unlike IP
header field) won't change regardless how a GMA PDU is delivered
on the way, since they are encapsulated as part of UDP payload.
Therefore, an intermediate node, e.g. router, Access Point, Base
Station, etc., can perform hQoS scheduling and active queue
management (AQM) directly based on these GMA header fields without
additional packet classification processing.
Other GMA header fields, e.g. Delivery SN, Flow SN, and Timestamp,
are designed to support multi-access traffic management. For
example, Flow SN allows reordering at the receiver when a flow is
split over multiple connections. In the meantime, Delivery SN is
needed for packet loss measurement per delivery connection, and
Timestamp allows one-way-delay measurement, which can then be used
to detect congestion and buffer overflow at intermediate nodes.
If concatenation is supported, a GMA PDU MAY carry multiple GMA
SDUs with the same Slice ID, Connection ID, Flow ID, and PPP.
However, concatenation is only applicable to IP-based virtual
(anchor) connection. Please refer to [GMAE] for more details on
concatenation.
5. GMA Control Messages
A GMA control message is encapsulated as the payload of a GMA PDU
(see Figure 4) and indicated by setting Bit 0 in the Flags field
of the GMA header to 0. Moreover, the GMA header MUST include the
Client ID field, but not any other optional fields. As a result,
the Flag in the GMA header is always set to 0x4000 for a GMA
control message.
GMA control message MAY be encrypted with a symmetric key cipher,
e.g. AES256-GCM. If a GMA control message is encrypted, the
receiver will use the Client ID field to obtain the corresponding
key for decryption. Notice that only the GMA control message is
encrypted. The GMA header is authenticated but not encrypted.
Figure 6 shows the format of an encrypted GMA control message,
where IV (initialization vector) is 12 bytes long and GCM Tag is
16 bytes long. The GMA header (Flag (2B) + Client ID (2B)) is used
as additional authenticated data (AAD).
+---------------------------------------------------------------+
|Flag(0x4000) | Client ID | GMA control message | GCM Tag | IV |
+---------------------------------------------------------------+
|<------authenticated---->|<----encrypted ----->|
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Figure 6: Encrypted GMA Control Message
A GMA control message consists of the following fields:
o Header (2 Bytes)
+ Type (1 Byte): the GMA control message type
+ Connection ID (1 Byte): an unsigned integer to identify
the anchor connection for the GMA control message
o Payload (variable): the payload of the GMA control message
5.1 Probe Message
The "Type" field is set to "1" for Probe messages.
Client (or multi-access gateway) may send out Probe message for
path quality estimation or keepalive. In response, multi-access
gateway (or client) may send back the ACK message.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | LS Bitmap | Probing Flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Probe Message Format
A Probe message consists of the following fields:
o Sequence Number (2 Bytes): the sequence number of the message
o Link Status (LS) Bitmap (1 Bytes): to indicate the status (0:
not connected; 1: connected) of the i-th delivery connection,
where connections are ordered according to their Connection ID,
bit #7 (LSB) corresponds to the 1st delivery connection and bit
#0 (MSB) corresponds to the 8th delivery connection.
o Probing Flag (1 Byte):
+ Bit #0: a bit flag to indicate if the ACK message is
expected (0) or not (1)
+ Bit #1: a bit flag to indicate if multi-access Gateway
SHOULD update the UDP tunnel end-point (0) or not (1) based
on the received Probe message.
+ Bit #2~7: reserved
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o Timestamp (4 Bytes): the current value of the timestamp clock of
the sender
o Padding (variable)
The "Padding" field is used to control the length of a Probe
message.
Multi-Access Gateway SHOULD update the UDP tunnel end-point of the
client based on the received Probe message if the Bit #1 Probing
flag is set to 0 (default).
5.2 Acknowledgement (ACK) Message
The "Type" field is set to "2" for ACK messages. The ACK message
consists of the following fields:
o Acknowledgment Number (2 Bytes): the sequence number of the
corresponding request message
o Reserved (1 Byte)
o Request Type (1 Byte): the corresponding request message type,
e.g. Probe, etc.
o Timestamp (4 Bytes): the current value of the timestamp clock
of the sender
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ack Number | Reserved | Request Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Ack Message Format
5.3 Traffic Splitting Update (TSU) Message
The "Type" field is set to "3" for TSU messages.
Client (or multi-access gateway) may send out a TSU message to
change the traffic splitting/steering/duplicating configuration
for downlink flows. Let's use N to denote the number of delivery
connections.
A TSU message consists of the following fields:
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o Sequence Number (2 Bytes): the sequence number of the TSU
message
o Link Status Bitmap (1 Byte): to indicate the status (0: not
connected; 1: connected) of the i-th delivery connection,
where connections are ordered according to their Connection
ID
o Number of Flows (1 Byte): the number of flows that are
configured by the TSU message
o Timestamp (4 Bytes): the current value of the timestamp clock
of the sender
For each flow, the following Traffic Splitting control parameters
are included:
o Flow ID (1 Byte): an unsigned integer to identify the flow
o L (1 Bytes): the total number of packets per traffic
splitting cycle, e.g. L = 32, and each packet is assigned an
index from 0 to L-1.
o K1[i] (N Bytes): the index of the first packet sent over the
i-th delivery connection per traffic splitting cycle, where
connections are ordered according to their Connection ID and
i = 1, 2, ..., N.
o K2[i] (N Bytes): the index of the last packet sent over the
i-th delivery connection per traffic splitting cycle, where
connections are ordered according to their Connection ID and
i = 1, 2, ..., N.
For example, with N = 2, i.e. two delivery connections, the
configuration of K1[1] = K1[2] = 0, K2[1] = K2[2] = 1, and L = 2
indicates sending every packet of the flow over both connections,
i.e. duplication. In another example, the configuration of K1[1] =
K2[1] = 0, K1[2] = K2[2] = 1 and L = 2 indicates sending one
packet of every two packets over the first connection, and the
other one over the second connection.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number | LS Bitmap |Number of Flows|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID | L | K1[1] | K1[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| K2[1] | K2[2] | Flow ID | L |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| K1[1] | K1[2] | K2[1] | K2[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: TSU Message Format (N = 2, Number of Flows = 2)
Multi-access gateway SHALL always update the UDP tunnel end-point
of the client based on the received TSU message.
5.4 Traffic Splitting Acknowledgement (TSA) Message
The "Type" field is set to "4" for TSA messages. Multi-access
gateway (or client) SHALL send out a TSA message in response to a
received TSU message. A TSA message consists of the following
fields:
o Acknowledgment Number (2 Bytes): the sequence number of the
corresponding TSU message
o Reserved (1 Byte)
o Number of Flows (1 Byte): the number of flows that are
configured by the TSU message
o Timestamp (4 Bytes): the current value of the timestamp clock
of the sender in the unit of 1 millisecond
For each flow, the message further consists of the following
fields:
o Flow ID (1 Byte): an unsigned integer to identify the flow
o StartSN (3 Bytes): the Flow SN of the first GMA SDU
using the traffic splitting configuration provided by the
corresponding TSU message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ack Number | Reserved |Number of Flows|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID | StartSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID | StartSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: TSA Message Format (Number of Flows = 2)
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Figure 11 shows the traffic splitting update procedure for downlink
traffic, where client performs path quality measurement based on
received packets and determines traffic splitting parameters. Once
update is needed, client will send the TSU message carrying the new
traffic splitting parameters to multi-access gateway. Multi-access
gateway will send back the TSA message in response, and perform
traffic splitting accordingly. The TSA message carries the
"StartSN" parameter to indicate the first packet using the new
configuration so that client can perform measurements accordingly.
client multi-access gateway
| |
|<------------------ GMA SDU #1 ------------------|
|<------------------ GMA SDU #2 ------------------|
+--------------------------+ |
| path quality measurement | |
+--------------------------+ |
|------------------ TSU ------------------------->|
|<------------------------- TSA(StartSN: 3) ------|
|<------------------ GMA SDU #3 ------------------|
|<------------------ GMA SDU #4 ------------------|
Figure 11: Downlink Traffic Splitting Update Procedure
5.5 Timestamp Reset Request (TSR) Message
The "Type" field is set to "5" for TSR messages.
A TSR message consists of only one field:
o Sequence Number (2 Bytes): the sequence number of the TSR
message.
Client SHOULD send out a TSR message to reset timestamp and
prevent it from overflowing for one-way delay measurement due to
the limited size (4 Bytes) when its local timestamp timer exceeds
a pre-defined value, e.g. 0x7FFF0000.
Once receiving a TSR message, multi-access gateway SHOULD reset
the timestamp timer to "0" for the client and respond with a ACK
message. Client SHOULD reset its timestamp timer to "0" after the
TSR message is successfully acknowledged. As a result, the
timestamp field in a GMA PDU indicates the duration between the
last successful TSR message exchange and the transmission of the
GMA PDU.
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6. GMA Control Flows
GMA control sequence consists of the following three phases:
o Phase 1 (Initialization): client and gateway exchange MAMS
messages [MAMS] to configure the GMA-based multi-access
traffic management.
o Phase 2 (GMA Operation): client and gateway exchange GMA
control messages as defined in this document to manage traffic
steering/splitting/duplicating across multiple connections.
o Phase 3 (Termination): client and gateway exchange MAMS
messages to terminate the GMA operation.
6.1. Initialization
Client may trigger the initialization procedure once detecting any
one of the delivery connections, e.g. Wi-Fi, LTE, etc., becomes
available. Figure 12 shows the MAMS message exchange sequence to
activate the GMA operation. Please refer to [MAMS] for more
details about the MAMS messages.
Client multi-access Gateway
| |
|------- MX Discover Message ----------------------->|
| |
|<----------------------------- MX System Info ------|
| |
|------------------------------ MX Capability REQ -->|
|<----- MX Capability RSP ---------------------------|
|------------------------------ MX Capability ACK -->|
| |
|<-------------------- MX UP Setup Config -----------|
|-------- MX UP Setup Confirmation ----------------->|
| |
Figure 12: MAMS-based Initialization Procedure
To support the virtual (anchor) connection specified in this
document, the MX Capability REQ message SHOULD include the
following additional information:
o Last IP address: the virtual IP address used in the last MAMS
session
o Last MAMS session ID: the unique session id of the last MAMS
session
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The MX UP Setup Config message SHOULD include the following
additional information:
o Client IP address: the client IP address of the virtual anchor
connection.
o Gateway IP address: the gateway IP address the virtual anchor
connection
o DNS server: the DNS server IP address of the virtual anchor
connection
o Subnet mask: the subnet mask of the virtual anchor connection
o MAMS port: the TCP port number at the multi-access Gateway for
exchange MAMS messages over the virtual anchor connection
o Key: the symmetric encryption (e.g. AES256-GCM) key for GMA
control message.
6.2. GMA Operation
After completing the initialization phase successfully, client
will start the GMA operation phase by sending out probes to decide
if a delivery connection is connected and can be used for data
transfer.
After successful probing, client will activate the virtual anchor
connection based on the information in the MX UP Setup Config
message and start (GMA-based) multi-access traffic management.
First of all, client will send out the TSR message to reset the
timestamp clock. Afterwards, client SHOULD only send out the TSR
message to reset timestamp when its local timestamp clock exceeds
a pre-defined value, e.g. 0x7FFF0000.
During the GMA operation, client SHOULD continuously perform path
quality measurements (e.g. one-way delay, loss, etc.) based on
probing as well as received user-plane packets, and manage user-
plane traffic across all available connections accordingly. How
and when to trigger probing as well as how to perform path quality
measurements are left to implementation, and not considered in
this document. Moreover, it is up to client implementation which
delivery connection is used to send control messages, e.g. TSU,
TSR, etc. However, the ACK message SHALL use the same delivery
connection as its corresponding request message.
If client decides to update the traffic splitting configuration
for downlink flows, it SHOULD send out the TSU message to gateway,
notifying the updated configuration, and gateway SHOULD send out
the TSA message to confirm the update and also indicate the Flow
SN Of the first packet with the updated configuration.
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For uplink traffic, if splitting is not enabled, client SHOULD
control how to steer traffic without any GMA control message
exchange with multi-access gateway. Otherwise, if splitting is
enabled, multi-access gateway SHOULD perform measurements for the
splitting-enabled uplink flow based on received data packets and
send the TSU message to client for updating the traffic splitting
configuration.
Client multi-access Gateway
| |
+--------------+ |
| Link x is up | |
+--------------+ |
|---------------------------- Probe (over Link x) -->|
|<----- ACK (over Link x) ---------------------------|
| |
+----------------------------------------+ |
| activate the virtual anchor connection | |
| and start the GMA operation | |
+----------------------------------------+ |
|---------------------------- TSR ------------------>|
| +---------------+
| |reset timestamp|
| +--------------+
|<----- ACK -----------------------------------------|
+---------------+ |
|reset timestamp| |
+---------------+ |
| |
+----------------------------------------+ |
| perform path quality measurement based | |
| on probes and data packets, and decide | |
| to steer traffic over Link x | |
+----------------------------------------+ |
|------------------------------ TSU (over Link x)--->|
|<----- TSA (over Link x)----------------------------|
Figure 13: GMA-based Multi-Access Traffic Management Procedure
6.3. Termination
Client may trigger the termination procedure to stop the GMA
operation at any time. Figure 14 shows the MAMS message exchange
sequence to terminate the GMA operation.
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Client multi-access Gateway
| |
|------- MX Termination Request--------------------->|
| |
|<------------------------ MX Termination Response---|
Figure 14: MAMS-based Termination Procedure
7. Security Considerations
Security in a network using GMA should be relatively similar to
security in a normal IP network. GMA is unaware of IP or higher
layer end-to-end security as it carries the IP packets as opaque
payload. Deployers are encouraged to not consider that GMA adds
any form of security and to continue to use IP or higher layer
security as well as link-layer security.
8. IANA Considerations
This document makes no requests of IANA.
9. References
9.1. 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, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[GRE1] Dommety, G., "Key and Sequence Number Extensions to GRE",
<https://www.rfc-editor.org/info/rfc2890> .
9.2. Informative References
[MAMS] S. Kanugovi, F. Baboescu, J. Zhu, and S. Seo "Multi-Access
Management Services
(MAMS)https://tools.ietf.org/rfc/rfc8743.txt
[IANA] https://www.iana.org/assignments/protocol-
numbers/protocol-numbers.xhtml
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[LWIPEP] 3GPP TS 36.361, "Evolved Universal Terrestrial Radio
Access (E-UTRA); LTE-WLAN Radio Level Integration Using
Ipsec Tunnel (LWIP) encapsulation; Protocol
specification"
[RFC791] Internet Protocol, September 1981
[ATSSS] 3GPP TR 23.793, Study on access traffic steering, switch
and splitting support in the 5G system architecture.
[GRE2] RFC 8157, Huawei's GRE Tunnel Bonding Protocol, May 2017
[RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan,
O., and F. Gont, "IP Fragmentation Considered Fragile",
BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020,
<https://www.rfc-editor.org/info/rfc8900>.
[ATSSS2] M. Boucadair, et al. 3GPP Access Traffic Steering
Switching and Splitting (ATSSS) - Overview for IETF
Participants, <
https://datatracker.ietf.org/doc/html/draft-bonaventure-
quic-atsss-overview-00>
[GMAE] J. Zhu, et al. Generic Multi-Access (GMA) Encapsulation,
Protocolhttps://www.ietf.org/archive/id/draft-zhu-
intarea-gma-10.txt
[GCC] S. Holmer, et al. A Google Congestion Control Algorithm for
Real-Time Communication,
https://www.ietf.org/archive/id/draft-ietf-rmcat-gcc-
02.txt
[MPIP] L. Sun, et al. Multipath IP Routing on End Devices:
Motivation, Design, and Performance,
https://eeweb.engineering.nyu.edu/faculty/yongliu/docs/M
PIP_Tech.pdf
Authors' Addresses
Jing Zhu
Intel
Email: jing.z.zhu@intel.com
Menglei Zhang
Intel
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Email: menglei.zhang@intel.com
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