Network Working Group J. Zhu
Internet Draft M. Zhang
Intended status: Experimental Intel
Expires: August 20,2024 February 20, 2024
A UDP-based GMA (Generic Multi-Access) Protocol
draft-zhu-intarea-gma-control-05
Abstract
A device can simultaneously connect to multiple access networks,
e.g., Wi-Fi, LTE, 5G, DSL, and SATCOM (Satellite Communications).
It is desirable to seamlessly combine multiple connections 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 convergence
protocol for managing data traffic across multiple network paths.
The solution has been developed by the authors based on their
experiences in multiple standards bodies including 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 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.
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This Internet-Draft will expire on August 20, 2024.
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Copyright Notice
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Table of Contents
1 Introduction .................................................3
1.1 Scope of Experiment ...................................4
2 Conventions used in this document ...........................5
3 Use Case ....................................................6
4 UDP-based GMA Encapsulation Protocol ........................7
5 GMA Control Messages .......................................11
5.1 Probe Message ........................................12
5.2 Acknowledgement (ACK) Message ........................15
5.3 Traffic Splitting Update (TSU) Message ...............15
5.4 Traffic Splitting Acknowledgement (TSA) Message ......17
5.5 Delivery Connection Reconfiguration (DCR) Message ....19
5.6 Key Update Message ...................................19
5.7 Traffic Steering Command (TSC) Message ...............20
5.8 Traffic Splitting Command (TSP) Message ..............20
5.9 QoS Testing Request (QTR) Message ....................21
5.10 QoS Testing Response (QTP) Message ...................21
5.11 QoS Testing Notification (QTN) Message ...............21
5.12 QoS Violation Notification (QVN) Message .............22
5.13 Packet Loss Report (PLR) Message .....................22
5.14 First Sequence Number (FSN) Message ..................22
5.15 Coding Configuration Request (CCR) Message ...........23
5.16 Coded GMA SDU (CGS) Message ..........................23
5.17 Connection Priority Reconfiguration (CPR) Message ....24
6 Basic GMA Control Procedures ...............................25
6.1 Initialization .......................................25
6.2 GMA Operation ........................................27
6.3 Termination ..........................................28
7 Advanced GMA Control Procedure .............................29
7.1 Network-based Traffic Steering (Splitting) ...........29
7.2 QoS-aware Traffic Steering ...........................30
7.3 GMA-based Retransmission .............................33
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7.4 Network Coding .......................................34
7.5 Dynamic Connection Management ........................35
7.6 Dynamic One-Way-Delay (OWD) Equalization .............37
8 Security Considerations ....................................38
9 IANA Considerations ........................................38
10 Contributing Authors .......................................38
11 References .................................................38
11.1 Normative References .................................38
11.2 Informative References ...............................38
1 Introduction
A device can simultaneously connect to multiple networks, e.g.,
Wi-Fi, LTE, 5G, DSL, and SATCOM (Satellite Communications). It is
desirable to seamlessly combine multiple connections over these
networks below the transport layer (L4) to improve quality of
experience for applications that do not have built-in multi-path
capabilities.
A new Multi-Access Management Service (MAMS) framework has been
recently specified in [MAMS] to support various multi-access
solutions [ATSSS] [LWIPEP] [GRE1] [GRE2]. As shown in Figure 1,
its user-plane protocol stack 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. 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 | |
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| +-----------------------------------------------------+ |
| MAMS User-Plane Protocol Stack |
+-----------------------------------------------------------+
Figure 1: MAMS User-Plane Protocol Stack [MAMS]
A new Generic Multi-Access (GMA) encapsulation protocol [GMAE] has
been specified to encode additional control information, e.g.,
Timestamp, Sequence Number, to support multi-access operations at
the convergence layer. This document presents a UDP-based GMA
control protocol for the convergence layer, and enhancements to
the GMA encapsulation protocol. The GMA protocol only operates
between endpoints that have been configured to use GMA through
MAMS management messages [MAMS] or other management methods, which
is out of the scope of this document.
From the perspective of applications, the GMA protocol is a multi-
path tunneling protocol operating below the network layer (L3),
and therefore can support any legacy single-path transport
protocol, e.g. TCP, UDP, QUIC, etc. From the perspective of a
underlay access network, it is a light-weight transport protocol
designed specifically for multi-path operation, removing
unnecessary complexity and overhead (e.g., end-to-end encryption,
congestion control, reliable transmission, etc.) as seen in a
modern transport protocol [QUIC]. Moreover, it can be easily
extended to support advanced multi-path operations, e.g., network
coding, network-based traffic steering, in-band QoS monitoring,
etc.
The solution described in this document has been developed by the
authors based on their experiences in multiple standard bodies
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 multi-access requirements [ATSSS2] [Dual3GPP], can
be safely used, and has support for deployment. Particularly, the
proposed GMA protocol addresses the following issues of using QUIC
for ATSSS:
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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 is
16 bytes.
o Multiple Encryptions: the GMA encapsulation protocol does not
mandate encryption to avoid unnecessary encryption overhead
when a delivery connection is secure and trusted.
o Congestion Control in Congestion Control: the GMA control
protocol does not mandate congestion control. All incoming
packets (from higher layer) MAY be sent out without any delay
due to congestion control.
In addition, the GMA protocol makes reliable delivery optional,
assuming it has beenaddressed by the application or transport
layer. Hence, it does not require Acknowledgement (ACK) for data
packets, and can avoid any delay due to retransmission or ACK
overhead on the reverse path.
The GMA protocol supports both out-of-band and in-band path
quality measurements (e.g. one-way-delay, loss, etc.) and
congestion detection. A (out-of-band) control message, e.g. probe,
with acknolwedgement can be used to actively measure round trip
time and reliability of a connection. While the GMA header fields,
e.g. sequence number, timestamp, etc., in the GMA header of a
received data packet can be used for in-band measurement. Another
objective of the experiment is to evaluate state-of-the-art
congestion detection algorithms [GCC] [MPIP] [DCTCP] for multi-
path traffic management.
It is expected that this protocol experiment can be conducted on
the Internet since GMA packets are encapsulated with UDP. Thus,
experimentation is conducted between consenting end systems that
have been mutually configured to participate in the experiment. An
open-source based GMA software implementation [GMA] has been
provided for this experiment. The authors will continually assess
the progress of this experiment and encourage other implementers
to contact them to report the status of their implementations and
their experiences with the GMA 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.
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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 a 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 connections provide multiple
paths between client and gateway to support multi-access traffic
management.
+------- Virtual (anchor) Connection ------+
| |
+-+---+ +---+-+
| | |A|--- LTE (delivery) Connection --|C| | |
Apps ---|X|U|-| |-|S|Z|--- Internet
| | |B|-- Wi-Fi (delivery) Connection--|D| | |
+-+---+ +---+-+
Client 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
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 multiple delivery 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 traffic
management requires additional control message exchange between
client and gateway.
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UDP is used as the adaptation layer protocol in this document.
Figure 3a and 3b show UDP-based GMA user-plane and control-plane
protocol, respectively. The "UDP Tunnelling" ports at client are
chosen from the dynamic port range, and at gateway are configured
and provided to clients through MAMS messages, e.g., MX UP Setup
Config [MAMS].
+-----------------------------------------------------+
| Virtual Connection (IP, Ethernet, etc.) |
+-----------------------------------------------------+
| UDP-based GMA Encapsulation |
+-----------------------------------------------------+
| UDP | UDP | UDP |
+-----------------+-----------------+-----------------+
| Access #1 IP | Access #2 IP | Access #3 IP |
+-----------------------------------------------------+
Figure 3a: UDP-based GMA User-Plane Protocol Stack
+-----------------------------------------------------+
| GMA Control Messages |
+-----------------------------------------------------+
| UDP-based GMA Encapsulation |
+-----------------------------------------------------+
| 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
+----------------------------------------------------+
| IP hdr | UDP hdr | GMA Header | Payload (GMA SDU) |
+----------------------------------------------------+
Figure 4: UDP-based GMA PDU Format
Figure 4 shows the UDP-based GMA encapsulation format [GMAE]. The
GMA header consists of the mandatory "Flags" field (the first two
bytes), defined as follows:
o Client ID Present (bit 0): If the bit is set to 1, the Client ID
field is present.
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o Payload Type (PT) (bit 1): If the bit is set to 1, the GMA PDU
carries a GMA control message or an encrypted GMA SDU (data).
Otherwise (default), it carries an unencrypted GMA SDU (data).
o Flow ID Present (bit 2): If the bit is set to 1, the Flow ID
field is present.
o Per-Packet Priority (PPP) Present (bit 3): If the bit is set to
1, the PPP field is present.
o Packet Group Identification (PGI) Present (bit 4): If the bit is
set to 1, the PCI field is present.
o Delivery SN Present (bit 5): If the bit is set to 1, the
Delivery SN field is present.
o Flow SN Present (bit 6): If the bit is set to 1, the Flow SN
field is present.
o Timestamp Present (bit 7): If the bit is set to 1, the Timestamp
field is present.
o Reserved (bit 8-15): 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 optional fields
accordingly. The GMA header MAY consist of the following optional
fields:
o Client ID (2 Byte): an unsigned integer to identify the virtual
connection. A client may establish multiple virtual
connections, e.g. MA-PDU, with the gateway, each of which
SHOULD be provided with a unique "Client ID".
o PT (1 Byte)
+ Bit 0: the Key Phase bit to indicate which key is used to
protect the GMA payload.
+ Bit 1~7: the GMA control message type, set to "0" if the
payload is an encrypted GMA SDU
o Flow ID (1 Byte): an unsigned integer to identify the IP flow
+ 0: unknown flows
+ 1~20: reserved for flows using the redundancy mode, with which
a flow may be duplicated over the available delivery
connections.
+ 21~50: reserved for flows using the splitting mode, with which
a flow may be split over the available delivery connections.
+ 51~100: reserved for flows using the steering mode, with which
a flow is steered to only one of the available delivery
connections.
+ Others: reserved for future use
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).
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o Packet Group ID (1 Byte): an unsigned integer to identify the
group of GMA SDUs. If one GMA SDU in the group is dropped,
other GMA SDUs in the same group SHOULD also be dropped. For
example, all GMA SDUs from a video frame MAY be classified
into a same group.
o Delivery SN (1 Byte): an auto-incremented unsigned integer to
indicate the GMA PDU transmission order on a delivery
connection. Delivery SN is used for a flow using the
splitting mode to measure packet loss of each delivery
connection and generated per delivery connection per flow. It
SHOULD be ignored or not used for flows with the reududnancy
or splitting mode
o Flow SN (3 Bytes): an auto-incremented unsigned integer to
indicate the GMA SDU (IP packet) order of a flow. Flow SN is
used for reordering, and generated per flow.
o Timestamp (4 Bytes): an unsigned integer to indicate the value
of the timestamp clock at the transmitter in the unit of 100
microseconds when a GMA PDU is transmitted.
The use of Key Phase bit is similar to what is specified in QUIC
[QUICTLS], allowing a recipient to detect a change in keying
material without needing to receive the first packet that
triggered the change. The Key Phase bit is initially set to 0 and
toggled to signal each subsequent key update. The Key Phase bit
SHALL be ignored if the payload is not encrypted or authenticated.
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
the order of their corresponding flag bits. If a flag bit is not
set, 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PT | Flow ID | PPP | PGI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Delivery SN | Flow SN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 5: GMA Header Format with all Optional Fields Present
Some GMA header fields, e.g. Client ID, Flow ID, and PPP are
designed to support fine granular packet classification. Notice
that GMA header fields (unlike IP header field) won't change
regardless of how a GMA PDU is delivered, since they are
encapsulated as part of UDP payload. Therefore, an intermediate
node, e.g. router, Access Point, Base Station, etc., can perform
active queue management (AQM) based on these GMA header fields
directly.
Other GMA header fields, e.g. Delivery SN, Flow SN, and Timestamp,
are designed to support multi-path 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
especially if a flow uses the splitting mode, and Timestamp allows
in-band one-way-delay (OWD) measurement, which can then be used to
detect congestion and buffer overflow at intermediate nodes.
Moreover, Delivery SN and Flow SN can be used to support the Fast
Packet Loss Detection mechanism as described in [MPSN] for
minimizing multi-path reordering delay.
GMA payload MAY be protected by a symmetric key cipher, e.g.
AES256-GCM. A GMA receiver (e.g. gateway) uses the Client ID field
to determine the corresponding key for decryption. Moreover, the
GMA payload is encrypted and the GMA header is authenticated but
not encrypted.
GMA SDU (data) SHOULD be protected by the symmetric key only if
the delivery connection is "untrusted" and subject to malicious
attacks. If the encrypted GMA payload carries GMA SDU (data), the
PT field MUST be present in the GMA header and the GMA control
message type field MUST be set to "0". In other words, an
encrypted GMA data SDU is encapsulated as a special control
message.
+-------------------------------------------------------------+
| GMA Header | GMA Payload | GCM Tag | IV |
+-------------------------------------------------------------+
|<-authenticated->|<-------encrypted -------->|
Figure 6: AES256-GCM Encrypted GMA Message
Figure 6 shows the format of an AES256-GCM encrypted GMA message,
where IV (initialization vector) is 12 bytes long and GCM Tag is
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16 bytes long. The GMA header is used as additional authenticated
data (AAD).
5 GMA Control Messages
The GMA header of a GMA control message consists of Client ID,
Payload Type, Flow SN, and Timestamp. All GMA control messages
share the same Flow SN space. Table 1 lists all the GMA control
messages specified in this document and their value of "Type" in
the GMA header.
Notice that Coded GMA SDU (CGS) message (5.16) SHOULD be protected
by the symmetric key only if the delivery connection is untrusted.
All other GMA control message SHOULD be protected regardless.
Table 1: GMA Control Messages
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type| GMA Control Message |Section|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | Encrypted GMA SDU (data) | N/A |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Probe | 5.1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2 | ACK | 5.2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3 | Traffic Splitting Update (TSU) | 5.3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Traffic Splitting Ack (TSA) | 5.4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | Delivery Connection Reconfiguration (DCR) | 5.5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 | Key Update | 5.6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7 | Traffic Steering Command (TSC) | 5.7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 8 | Traffic Splitting Command (TSP) | 5.8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 9 | QoS Testing Request (QTR) | 5.9 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 10 | QoS Testing Response (QTP) | 5.10 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 11 | QoS Testing Notification (QTN) | 5.11 |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 12 | QoS Violation Notification (QVN) | 5.12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 13 | Packet Loss Report (PLR) | 5.13 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 14 | First Sequence Number (FSN) | 5.14 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 15 | Coding Configuration Request (CCR) | 5.15 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 16 | Coded GMA SDU (CGS) | 5.16 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 17 | Connection Priority Reconfiguration (CPR) | 5.17 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5.1 Probe Message
A client (or gateway) MAY send out a Probe message for initial
connection establishment, path quality estimation, keep-alive,
timestamp synchronization, and link measurement report. In
response, the gateway (or client) SHOULD send back the ACK message
if it is required in the corresponding Probe message.
A control messages may be retransmitted if it is not acknowledged
within a timeout period. It is left to implementation to configure
the retransmission timer and the maximum number of retransmission
attempts. Flow SN SHOULD be adjusted incrementally regardless of
whether a control message is new or retransmitted. A delivery
connection is established after a successful handshake of Probe
and ACK, and terminated if any control message can't be
successfully acknolwedged after retransmissions.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Bitmap | Probing Flag | N | CID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| K | TLV based Link Information Elements |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Probe Message Format
A Probe message consists of the following mandatory fields:
o Link Status (LS) Bitmap (1 Byte): to indicate the status (0:
not connected; 1: connected) of the i-th delivery connection,
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where connections are ordered according to their CID, 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 timestamp needs to be
reset (1) or not (0)
+ Bit #1: a bit flag to indicate if the ACK message is
expected (1) or not (0)
+ Bit #2: a bit flag to indicate if the receiving side
SHOULD update the UDP tunnel end-point (1) or not (0)
based on the Probe message
+ Bit #3: a bit flag to indicate if the client is synchronized
(1) or not (0) with the gateway in time.
+ Bit #4: a bit flag to indicate if Link Information
Elements (IE) are present (1) or not (0).
+ Bit #5~7: reserved
A Probe message with the Bit #0 flag set to "1" is also called
Probe-Sync. A client will send out a Probe-Sync message to reset
timestamp when its local timestamp timer exceeds a pre-defined
threshold, e.g., 0x7FFF0000 and prevent it from overflowing due to
the limited size (4 Bytes). Once receiving a Probe-Sync message,
the gateway will reset the timestamp timer to "0" for the client
and respond with an ACK message. The "Request Type" field in the
ACK message is set to 0, indicating the corresponding Probe message
is Probe-Sync.
The client SHOULD reset its timestamp timer to "0" after the Probe-
Sync message is successfully acknowledged. As a result, the
timestamp field in a GMA PDU indicates the time between the last
successful Probe-Sync message exchange and the transmission of the
GMA PDU.
If the Bit #1 flag is not set, the receiving endpoint SHOULD NOT
send back the ACK message.
If the Bit #2 flag is not set, the probe message is used to test
the reachability of alternative path of the delivery connection,
and therefore the receiving endpoint SHOULD NOT update the UDP
tunnel end-point accordingly.
If the Bit #3 flag is set, indicating the client is already
synchronized with the gateway in time, they SHOULD use their local
clock directly as the timestamp clock without going through the
above "Probe-Sync" procedure. How to maintain time synchronization
between two GMA endpoints is out of the scope of this document.
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If the Bit #4 flag is set, the Probe message consists of the
following optional fields:
o N (1 Byte): the number of delivery connections whose Link IEs
are included in the message.
For each connection, include the following fields:
o Connection ID (1 Byte) to identify the delivery connection
o K (1 Byte): the number of Link IEs for the connection
o TLV(Type-Lenth-Value) encoded Link IEs (variable): a GMA
client MAY use the Probe message to report its link quality,
e.g., signal strength and other information, e.g., Wi-Fi
channel number, as shown in Table 2.
Probe may also be used to measure path quality for a specific
flow. In this case, the Probe message and its corresponding ACK
message SHOULD carry the same QoS classification marking, e.g.
DSCP, as a data packet of the flow. In addition, the "Flow ID"
field SHOULD be included in the GMA header of the flow-specific
Probe and ACK message to identify the flow.
Table 2: GMA Link Information Elements
+---------------------------------------------------------------+
| Name | Type | Length | Value |
+---------------------------------------------------------------+
| Wi-Fi RSSI | 0 | 1 | -255dBm ~ 0dBm |
+---------------------------------------------------------------+
| Wi-Fi Band | 1 | 1 | 0:2.4GHz, 1: 5GHz, 2:6GHz |
+---------------------------------------------------------------+
| Wi-Fi Channel | 2 | 1 | 0~255 |
+---------------------------------------------------------------+
| Wi-Fi BSSID | 3 | 6 | Wi-Fi AP MAC address |
+---------------------------------------------------------------+
| Wi-Fi Bandwidth | 4 | 1 | 0 ~ 255 x 10Mbps |
+---------------------------------------------------------------+
| | | | 0: IEEE 802.11 a/b/g/n |
| Wi-Fi Type | 5 | 1 | 1: Wi-Fi 6 |
| | | | 2: Wi-Fi 7 |
+---------------------------------------------------------------+
| Cellular RSRQ | 30 | 1 | -255dB ~ 0dB |
+---------------------------------------------------------------+
| Cellular RSRP | 31 | 1 | -255dBm ~ 0dBm |
+---------------------------------------------------------------+
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| Cellular RSSI | 32 | 1 | -255dBm ~ 0dBm |
+---------------------------------------------------------------+
| GSM Cell ID | 33 | 4 | 0 ~ 2^32 - 1 |
+---------------------------------------------------------------+
| | | | 0: 3G |
| Cellular Type | 34 | 1 | 1: 4G LTE |
| | | | 2: 5G NR |
+---------------------------------------------------------------+
5.2 Acknowledgement (ACK) Message
An ACK message is used to confirm the successful reception of a
control message unless it is not required or a specific acknolwedge
message, e.g. TSA (5.4), is required. The source IP address and UDP
port of the control message SHOULD be used as its desintation IP
address and UDP port.
The Flow SN field in the GMA header of the ACK message is set to
the Flow SN of the corresponding control message. The ACK message
consists of the following fields:
o Request Type (1 Byte): the corresponding control message type,
e.g. Probe, etc.
o Padding (variable)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Request Type | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Ack Message Format
5.3 Traffic Splitting Update (TSU) Message
A TSU message is used by the receiving endpoint of a data flow to
update traffic splitting or steering configuration at the
transmitting endpoint. Unlike a probe, the gateway SHOULD always
update the UDP tunnel end-point for a client based on a received
TSU message from the client.
A TSU message consists of the following fields:
o Link Status Bitmap (1 Byte): the same as specified in 5.1
o K (1 Byte): the number of TLV-encoded TSU IEs
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o TSU IEs (variable)
A TSU IE consists of the following fields:
o Type (1 Byte)
+ 0: the traffic steering configuration
+ 1: the traffic splitting configuration
+ 2: the minimum OWD (One-Way-Delay) measurement report
+ Others: reserved
o Length (1 Byte): the TSU IE length
o Flow ID (1 Byte): an unsigned integer to identify the flow.
If Type is "0", the TSU IE consists of the following traffic
steering configuration parameters:
o C (1 Byte): the CID of the delivery connection that the flow
should be using.
For a flow with the redundancy mode, the traffic steering
configuration IE MAY consist of multiple CID fields to indicate
which delivery connections will be used to send duplicated packets
of the flow.
If Type is "1", the TSU IE consists of the following traffic
splitting configuration parameters:
o L (1 Byte): 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 S1[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 S2[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 two delivery connections, i.e., N=2, the
configuration of S1[1] = S2[1] = 0, S1[2] = S2[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.
If Type is "2", the TSU IE consists of the following minimum
OWDmeasurement report parameters:
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o D[i] (N Bytes): an unsigned integer (0 ~ 254) to indicate the
minimum OWD measurement (in milliseconds) of the i-th
delivery connection.
+ 255: reserved
Notice that the GMA endpoints (client and gateway) may not be
synchronized in time, and therefore the absolute value of minimum
OWD (d(i)) is not useful. Instead, the difference between the minimum
OWD of a connection and the maximum is reported, i.e.,
D(i) = max(d(i) | i = 1 ~ N) - d(i)
It indicates how much delay should be added by the GMA
transmitting endpoint to equalize minimum OWD across delivery
connections and mitigate the impact of reordering.
Figure 9 shows the TSU message format for two flows with the
splitting mode and the steering mode, respectively. In addition,
the minimum OWD measurement report IE is included for the
splitting flow.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Bitmap | K | IE Type(=0) | IE Length(=4) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID | C | IE Type(=1) | IE Length(=10)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID | L | S1[1] | S1[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| S2[1] | S2[2] | IE Type(=2) | IE Length(=5) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID | D[1] | D[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: TSU Message Format (K = 2, N = 2)
5.4 Traffic Splitting Acknowledgement (TSA) Message
A TSA message is used to confirm the successful reception of a TSU
message. The Flow SN of the TSA message is set to the Flow SN of
the corresponding TSU message. A TSU message consists of the
following fields:
o K (1 Byte): the number of TSA IEs
o TSA IEs
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A TSA IE consists of the following fields:
o Type (1 Byte)
+ 0: the Start SN configuration
+ 1: the OWD adjustment configuration
+ Others: reserved
o Length (1 Byte): the TSA IE length
If Type is "0", a TSA IE consists of the following fields for each
flow configured in the TSU message:
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
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| K | IE Type(=0) | IE Length(=10)| Flow ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| StartSN | Flow ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| StartSN | IE Type(=1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IE Length(=5)| Flow ID | D[1] | D[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: TSA Message Format (K=2, N=2)
If Type is "1", a TSA IE consists of the following fields for the
flow reporting its Minimum OWD in the TSU message:
o Flow ID (1 Byte): an unsigned integer to identify the flow.
o D[i] (N Bytes): a signed integer (-128~127) to indicate the
delay adjustment in milliseconds for the i-th delivery
connection based on the minimum OWD measurement in the TSU
message.
Figure 11 shows the GMA traffic splitting reconfiguration procedure
for downlink traffic, where the client (receiver) performs path
quality measurement based on received packets and reconfigures
traffic splitting parameters at the gateway (transmitter). Once
update is needed, the client will send out a TSU message carrying
the new traffic splitting configuration parameters to the gateway.
The gateway will then send back the TSA message and reconfigure
traffic splitting accordingly.
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client 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 Reconfiguration Procedure
5.5 Delivery Connection Reconfiguration (DCR) Message
The gateway MAY send out a DCR message to enable or disable a
delivery connection for a client. In response, the client SHOULD
stop sending any (control or data) packet to a disabled connection
and set the corresponding bit in the Link Status Bitmap field in
Probe and TSU to "0". If a previously disabled delivery connection
is enabled by the DCR message, the client SHOULD send out a Probe
message to check whether the gateway is reachable via the delivery
connection.
A DCR message consists of the following fields:
o Connection Status Bitmap (1 Byte): to indicate the status (0:
disabled; 1: enabled) of the i-th delivery connection, where
connections are ordered according to their Connection ID the
same way as in Link Status Bitmap (5.1).
5.6 Key Update Message
The gateway MAY send out a Key Update message to change the
symmetric key for a client. In response, the client SHOULD start
using the new key immediately. The gateway SHOULD start using the
new key after receiving the ACK message or a GMA control message
with the toggled Key Phase bit.
A Key Update message consists of the following fields:
o Key Type (1 Byte)
+ 0: AES256-GCM
+ Others: reserved
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If Key Type == 0
o Key Value (32 Bytes): the AES256-GCM key
5.7 Traffic Steering Command (TSC) Message
The gateway MAY send out a TSC message to configure network-based
traffic steering. A TSC message consists of the following fields:
o Flag (1 Byte)
+ 0: disable network-based traffic steering (default)
+ 1: enable network-based traffic steering
+ Others: reserved
o N1 (1 Byte): the number of downlink flows configured in the
TSC message.
o N2 (1 Byte): the number of uplink flows configured in the TSC
message.
If Flag == 1 and N1 > 0, the following control parameters are
included for each downlink flow:
o Flow ID (1 Byte): an unsigned integer to identify the flow.
o CID (1 Byte): the CID of the delivery connection that the
downlink flow will be using.
For uplink flow, the TSC message is only used to enable or disable
network-based traffic steering, and the TSU message is used for
configuration. Therefore, only "Flow ID" fields are included in
the TSC message.
5.8 Traffic Splitting Command (TSP) Message
The gateway MAY send out a TSP message to configure network-based
traffic splitting for downlink traffic. Uplink traffic splitting is
always controlled by the gateway using the TSU message. A TSP message
consists of the following fields:
o Flag (1 Byte)
+ 0: disable network-based traffic splitting (default)
+ 1: enable network-based traffic splitting
+ Others: reserved
o Number of Flows (1 Byte): the number of downlink flows that
are configured in the TSP message
If Flag == 1, the following control parameters are included for each
flow:
o Flow ID (1 Byte): an unsigned integer to identify the flow
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o L (1 Byte): 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 S1[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 S2[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.
5.9 QoS Testing Request (QTR) Message
A client MAY send out a QTR message to request QoS testing for a
flow. It consists of the following fields:
o Flow ID (1 Byte): an unsigned integer to identify the flow
for QoS testing.
o Traffic Direction (1 Byte): an unsigned integer to indicate
the direction of flow (0: downlink, 1: uplink, 2: both)
o CID (1 Byte): the CID of the delivery connection that the QoS
testing will be performed.
o Test Duration (2 Byte): an unsigned integer to indicate the
testing duration in ms.
5.10 QoS Testing Response (QTP) Message
A QTP message is used by the receiving endpoint of QoS testing to
indicate if the testing is successful or not. It consists of the
following fields:
o Flow ID (1 Byte): an unsigned integer to identify the flow
o CID (1 Byte): the CID of the delivery connection that the QoS
testing has been performed
o Status: an unsigned integer to indicate the result of QoS
testing (0: success; 1: failure)
5.11 QoS Testing Notification (QTN) Message
The gateway MAY send out a QTN message to start QoS testing for a
flow. It consists of the following fields:
o Flow ID (1 Byte): an unsigned integer to identify the flow
for QoS testing.
o Traffic Direction (1 Byte): an unsigned integer to indicate
the direction of flow (0: downlink, 1: uplink, 2: both)
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o CID (1 Byte): the CID of the delivery connection that the QoS
testing will be performed.
o Test Duration (2 Byte): an unsigned integer to indicate the
testing duration in ms.
5.12 QoS Violation Notification (QVN) Message
The gateway MAY send out a QVN message to indicate that QoS violation
has been detected or is expected for a flow. It consists of the
following fields:
o N1 (1 Byte): Number of uplink flows with QoS violation
o N2 (1 Byte): Number of downlink flows with QoS violation
o Uplink Flow ID (1 Byte x N1): an unsigned integer to identify
uplink flow with QoS violation.
o Downlink Flow ID (1 Byte x N2): an unsigned integer to
identify downlink flow with QoS violation.
5.13 Packet Loss Report (PLR) Message
A PLR message is used by the receiving endpoint to report lost GMA
SDUs for example during handover. In response, the transmitter may
retransmit lost GMA SDUs accordingly. A PLR message consists of the
following fields:
o Number of Flows (1 Byte): the number of flows
For each flow, the following control parameters are included:
o Flow ID (1 Byte): an unsigned integer to identify the flow
o ACK number (3 Bytes): the next (in-order) sequence number (SN)
that the sender of the PLR message is expecting
o Number of Loss Bursts (1 Byte)
For each loss burst, include the following
+ Flow SN of the first lost GMA SDU in a burst (3 Bytes)
+ Number of consecutive lost SDUs in the burst (1 Byte)
5.14 First Sequence Number (FSN) Message
A GMA transmitter MAY send out the FSN messages to indicate the
oldest SDU in its buffer if a lost SDU is not found in the buffer
after receiving the PLR message. In response, the GMA receiver SHOULD
NOT report any packet loss with Flow SN < FSN. A FSN message consists
of the following fields:
o Number of Flows (1 Byte): the number of flows
For each flow, the following control parameters are included:
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o Flow ID (1 Byte): an unsigned integer to identify the flow
o First Sequence Number (3 Bytes): the sequence number (SN) of the
oldest SDU in the (retransmission) buffer.
5.15 Coding Configuration Request (CCR) Message
A CCR message is used to support packet loss recovery through
systematic network coding, e.g. XOR [CTCP]. XOR and Reed-Solomon are
supported in this document. Other network coding techniques, e.g.,
Random Linear Network Code (RLNC) [RLNC], Raptor Code [RC], etc., may
be added in the future. A CCR message consists of the following
fields:
o Flag (1 Byte):
+ 0: disable network-based network coding for a downlink flow
+ 1: enable network-based network coding for a downlink flow
+ 2: network coding configuration for a uplink flow
+ 3: network coding configuration for a downlink flow
+ Others: reserved
o Flow ID (1 Byte): an unsigned integer to identify the flow
The Flag field in a CCR message from a client is always set to "3".
If Flag == 1, 2 or 3, include the following fields:
o Coding Type (1 Byte)
+ 0: None
+ 1: XOR
+ 2: (Systematic) Reed-Solomon [RS]
+ Others: reserved
o N (1 Bytes): the number of consecutive (uncoded) GMA SDUs used to
generate the coded GMA SDU
If Coding Type = (Systematic) Reed-Solomon, include the following:
o M (1 Byte): the number of coded (parity) GMA SDUs generated for
every N consecutive uncoded GMA SDUs.
o L (1 Byte): the symbol size for the RS code finite field, i.e.,
the maximum codeword length (N + M) is given by 2^L-1.
If Coding Type == XOR, one coded GMA SDU will be generated by
applying XOR across every N uncoded GMA SDU, and no additional
parameter will be included in the CCR message.
5.16 Coded GMA SDU (CGS) Message
A CGS message is used to encapsulate a coded GMA SDU, generated by
applying the specified network coding method to multiple consecutive
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(uncoded) GMA SDUs. The Flow SN field (as shown in Figure 5) MUST NOT
be included in the GMA header of a CGS message, as it carries a GMA
data SDU. A CGS message SHOULD be encrypted only if the delivery
connection is untrusted.
A CGS message consists of the following fields:
o Flow ID (1 Byte): an unsigned integer to identify the flow.
o Flag (1 Byte)
+ Bit #0: to indicate if the CGS message uses the same coding
configuration as its previous CGS message or not. This bit
is flipped whenever a new configuration is used.
+ Bit #1: to indicate if the FC field is present or not.
+ Bit #2~7: reserved
o Fragmentation Control (FC) (1 Byte): to provide necessary
information for re-assembly.
+ Bit #0: a More Fragment (MF) flag to indicate if the fragment
is the last one (0) or not (1).
+ Bit #1~#7: Fragment Offset (in units of fragments) to specify
the offset of a particular fragment relative to the
beginning of the SDU.
o Flow SN (3 Bytes): the Flow SN of the first (uncoded) GMA SDU used
to generate the coded GMA SDU, updated every N GMA SDUs
o C-SN (1 Bytes): the sequence number (0 ~ M-1) of the coded GMA SDU
carried by the CGS message, reset to "0" every N uncoded GMA
SDUs.
o Coded GMA SDU (variable): if the Coded GMA SDU is too long, it can
be fragmented and transported by multiple CGS messages.
5.17 Connection Priority Reconfiguration (CPR) Message
The gateway MAY send out a CPR message to configure the priority
of a delivery connection for a client or a flow. It consists of
the following fields:
o Client Connection Priority Bitmap (1 Byte): to indicate the
default priority (0: low; 1: high) of the i-th delivery
connection, where connections are ordered the same way as in
Link Status Bitmap (5.1).
o N1 (1 Byte): to indicate the number of downlink flows that are
configured with a flow-specific connection priority bitmap.
o N2 (1 Byte): to indicate the number of uplink flows that are
configured with a flow-specific connection priority bitmap.
For each downlink flow, include the following fields:
o Downlink Flow ID (1 Byte)
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o Flow Connection Priority Bitmap (1 Byte): to indicate the
priority of the i-th delivery connection for the downlink
flow.
For each uplink flow, include the following fields:
o Uplink Flow ID (1 Byte)
o Flow Connection Priority Bitmap (1 Byte): to indicate the
priority of the i-th delivery connection for the uplink flow.
There are only two priority levels: high and low. Client SHOULD
only use a low-priority connection for its data traffic if all
high-priority connections are disconnected or disabled. The client
SHOULD use the Client Connection Priority Bitmap (CCPB) for a flow
if the flow is not configured with a Flow Connection Priority
Bitmap (FCPB).
6 Basic GMA Control Procedures
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
A GMA 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 MAMS messages.
Client multi-access Gateway
| |
|------- MX Discover Message ----------------------->|
| |
|<----------------------------- MX System Info ------|
| |
|------------------------------ MX Capability REQ -->|
|<----- MX Capability RSP ---------------------------|
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|------------------------------ 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
Moreover, the MX Capability REQ/RSP message SHOULD indicate the
following GMA capabilities for downlink and uplink, respectively:
o Maximum number of flows with the redundancy mode
o Maximum number of flows with the splitting mode
o Maximum number of flows with the steering mode
o Network-based traffic steering (7.1)
o QoS-aware traffic steering (7.2)
o GMA-based retransmission (7.3)
o Network coding (7.4)
o Dynamic Connection Management (7.5)
o Dynamic OWD Equalization (7.6)
o Network coding method (XOR or Reed-Solomon)
The MX UP Setup Config message SHOULD include the following
additional information:
o Client ID: see Figure 5
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 to protect
GMA payload
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o Untrusted CID List: the list of "untrusted" delivery
connections where GMA data SDU MUST be protected by the
symmetric encryption key.
o Best-Effort CID List: the list of "best-effort" delivery
connections where QoS-aware traffic steering procedure (7.2)
SHOULD be used for moving a QoS flow to the connection.
6.2 GMA Operation
After completing the initialization phase successfully, a client
will start the GMA operation phase by sending out probes to decide
if a delivery connection 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.
If the client is already synchronized with the gateway in time, it
will use its local clock as the timestamp clock. Otherwise, the
client will perform the timestamp synchronization procedure by
sending out the Probe-Sync message. Afterwards, the client SHOULD
send out the Probe-Sync message once a while to reset the
timestamp clock.
During the GMA operation, the client SHOULD continuously perform
path quality measurements (e.g. one-way delay, loss, etc.) based
on probing as well as received data packets, and manage 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. Moreover, it is up to
implementation which delivery connection is used to send control
messages, e.g. TSU, etc. However, the ACK message SHOULD use the
same delivery connection as its corresponding control message.
For a downlink flow, if network-based traffic steering (7.1) is
enabled, the gateway SHOULD control how to steer or split the flow
through the TSC or TSP message; otherwise, the client SHOULD
control it through the TSU message.
For an uplink flow using the steering mode, if network-based
traffic steering (7.1) is enabled, the gateway SHOULD control how
to steer traffic through the TSC message (5.7); otherwise, the
client SHOULD control it without any control message.
For an uplink flow using the splitting mode, the gateway SHOULD
control it through the TSU message.
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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 | |
+----------------------------------------+ |
| |
| |
|---------------------------- Probe-Sync ----------->|
| +----------------+
| |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
A 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.
Client multi-access Gateway
| |
|------- MX Termination Request--------------------->|
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| |
|<------------------------ MX Termination Response---|
Figure 14: MAMS-based Termination Procedure
7 Advanced GMA Control Procedure
7.1 Network-based Traffic Steering (Splitting)
Figure 15 and 16 show the network-based traffic steering and
splitting procedure, respectively. It is initiated by the gateway
sending out the TSC (5.7) or TSP (5.8) message.
If the Flag field in the TSC (TSP) message is set to "0", network-
based control is disabled and the client SHOULD decide how to steer
(split) a flow based on its local information.
If the Flag field in the TSC (TSP) message is set to "1", network-
based control is enabled and the traffic steering (splitting)
configuration in the TSC (TSP) message SHOULD be used.
For a downlink flow, the client SHOULD send out a TSU message to
confirm the updated traffic steering (splitting) configuration.
For an uplink flow, the gateway SHOULD use the TSU message to
update the traffic steering (splitting) configuration after
enabling network-based control with the TSC (TSP) message.
Client multi-access Gateway
| |
|<---------- (downlink) flow #1 over link x ---------|
| +-------------------------------------------+
| |collect measurement from network and decide|
| |to steer traffic over link y |
| +-------------------------------------------+
|<---------------- TSC (steer flow #1 to link y)-----|
|------- ACK --------------------------------------->|
| |
|------- TSU --------------------------------------->|
|<-----------------------------------------TSA ------|
| |
|<-------------- flow #1 downlink over link y -------|
| |
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Figure 15: Network-based Downlink Traffic Steering Procedure
Client multi-access Gateway
| |
|<---------- (downlink) flow #1 over link x & y------|
| +-------------------------------------------+
| |collect measurement from network and decide|
| |to update traffic splitting ratio |
| +-------------------------------------------+
|<-------TSP (updated splitting ratio for flow #1)---|
|------- ACK --------------------------------------->|
| |
|------- TSU --------------------------------------->|
|<-----------------------------------------TSA ------|
| |
|<--------- flow #1 (updated splitting ratio)--------|
| |
Figure 16: Network-based Downlink Traffic Splitting Procedure
7.2 QoS-aware Traffic Steering
Figure 17 shows the QoS-aware traffic steering procedure for
steering a flow with QoS requirements, e.g. maximum delay, maximum
loss rate, etc., to a best-effort connection, e.g. Wi-Fi.
At the very beginning, a flow (e.g. uplink flow #1) is delivered
over the connection (e.g. Cellular) that can guarantee its QoS
requirements. Once a best-effort connection (e.g. Wi-Fi) becomes
available, the client SHOULD send out the QTR message to request
QoS testing for the flow. In response, the gateway SHOULD decide
when to start the testing and send out the QTN message. If the
Network-based Traffic Steering (7.1) is enabled for the flow, the
gateway will initiate the procedure by sending out the unsolicited
QTN message directly.
During the QoS testing, the transmitting endpoint SHOULD duplicate
the flow over the testing connection. All duplicated packets SHOULD
be discarded by the receiving endpoint and used only for testing.
In the meantime, they SHOULD be marked with low priority to
minimize their impact to other flows that have already been steered
to the connection.
If the QoS testing fails, the receiving endpoint of the QoS testing
will send out a QTP message to notify the transmitter of the
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testing result. Otherwise, it will send out a TSU message to steer
the flow to the best-effort connection. Afterwards, it will
continue monitoring the QoS performance of the flow. Once detecting
any QoS violation, it will send out a TSU message to steer the flow
back to the QoS-guaranteed connection.
If network-based traffic steering is enabled, the gateway MAY steer
a QoS flow from a best-effort connection back to the QoS-guaranteed
connection anytime. However, when the gateway decides to steer a
QoS flow to a best-effort connection, it SHOULD first send out the
QTN message to initiate QoS testing and steer the flow only if the
QoS testing succeeds.
Client Gateway
| |
|-------- (uplink) flow #1 over link x ------------->|
+--------------+ |
| link y is up | |
+--------------+ |
| |
+-----skipped if network-based traffic steering is enabled -------+
| |------- QTR (req testing flow #1 over link y)------>| |
| |<------------------- ACK ---------------------------| |
+-----------------------------------------------------------------+
| |
|<------ QTN (start testing flow #1 over link y)-----|
|--------------------- ACK ------------------------->|
| |
|----duplicating flow #1 over link y --------------->|
| |
| +-------------------------------------------+
| |collect measurement and drop all duplicated|
| |packets received from link y |
| +-------------------------------------------+
| |
|<--------------------- TSU -------------------------|
|--------------------- ACK ------------------------->|
| |
|-------- flow #1 over link y ---------------------->|
| |
| +--------------------------------------------+
| |collect measurement and detect QoS violation|
| +--------------------------------------------+
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|<-------------------- TSU --------------------------|
|--------------------- ACK ------------------------->|
| |
|-------- flow #1 over link x ---------------------->|
| |
Figure 17: QoS-aware Traffic Steering Procedure
It is pretty straightforward to measure packet loss rate using the
Flow SN field in the GMA header and detect QoS violation accordingly.
Next, we will introduce a simple method to detect QoS violation based
on OWD measurement.
Define the following notations:
o d0: the (true) OWD of a received data packet
o d1: the OWD measurement of a received data packet
o d2: the OWD measurement of the received ACK message for the last
probe
o d3: the (true) OWD of the probe message on the reverse path
o r: the round trip time (RTT) measurement of the last probe
o D: the maximum OWD threshold for QoS violation detection.
If client and gateway are not synchronized in time, we can't measure
OWD directly. Moreover, we can't measure RTT of a data packet either
because the data packet does not have acknowledgement. Thus, we
propose to use the RTT measurement of the last probe as the reference
to estimate the RTT of a received data packet, and use it as the OWD
upper-bound, i.e.,
d0 = r - d3 + d1 - d2 < r + d1 - d2
Then, we detect OWD QoS violation as follows:
r + d1 - d2 > D
We MAY send the flow-specific probe message with high priority to
reduce d3 and minimize its impact.
Notice that the above QoS-aware traffic steering procedure SHOULD be
used only if the QoS requirement of a flow can be guaranteed by at
least one delivery connection. Otherwise, the flow SHOULD be
configured with the redundancy mode, and the GMA receiver SHOULD
measure and detect QoS violation based on data packets received from
each delivery connection and determine which delivery connections
will be used to send duplicated packets of the flow. At the very
beginning, a flow MAY be duplicated over all the available
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connections. Afterwards, if a connection is found sufficient for
meeting the QoS requirement by itself, the GMA receiver MAY steer the
flow to the single connection and stop duplication to improve
efficiency. If detecting any QoS violation, it will reconfigure the
flow to start duplicating over multiple connections again. The TSU
message (5.3) with the traffic steering configuration IE (Type = 0)
SHOULD be used for reconfiguration.
7.3 GMA-based Retransmission
Figure 7 shows the GMA-based retransmission procedure in an example.
The first lost packet is found and retransmitted. However, the second
lost packet is not found, and the FSN message is sent out to notify
the client.
Client Gateway
| |
|<------------------ GMA SDU (data packets)--|
| |
+---------------------+ |
|Packet Loss detected | |
+---------------------+ |
| |
|----- PLR Message ------------------------->|
| +---------------------+
| |Lost packet found |
| +---------------------+
|<-------------retransmit(lost)MX SDUs ------|
|<------------------ GMA SDU (data packets)--|
| |
+----------------------+ |
|Packet Loss detected | |
+----------------------+ |
| |
|----- PLR Message ------------------------->|
| +---------------------+
| |Lost packet not found|
| +---------------------+
|<-------------FSN message ------------------|
Figure 18: GMA-based Retransmission Procedure
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7.4 Network Coding
Network coding for an uplink flow is always configured by the gateway
using the CCR message with the Flag field set to "2".
For a downlink flow, it may be configured by gateway (network-based)
or client. Figure 19 shows the client-based procedure, where the
client detects packet loss and sends out a CCR message with the Flag
field set to "3" to activate network coding along with all the
required parameters. In this example, XOR is configured as the coding
method with N = 2. In response, gateway starts sending one CGS
message carrying the coded GMA SDU for every two (uncoded) GMA SDUs.
Afterwards, client MAY send out a CCR message to deactivate network
coding for the flow.
Figure 20 shows the network-based procedure. Wherein, the gateway
will send out a CCR message with the Flag field set to "1" to provide
all the configuration parameters. Notice that network coding MAY be
used for a flow regardless of its operation modes: splitting,
steering, or duplicating.
Client Gateway
| |
|<------------------ GMA SDUs(data packets)--|
| |
+---------------------+ |
|Packet Loss detected | |
+---------------------+ |
| |
|------CCR Message (Flag = 3, XOR, N=2)----->|
|<------------------- ACK Message -----------|
| |
|<------------------ GMA SDU #1 -------------|
| lost<-------- GMA SDU #2 -------------|
|<-- CGS Message (GMA SDU #1 XOR GMA SDU #2)-|
+----------------------+ |
| GMA SDU #2 recovered | |
+----------------------+ |
| |
|------CCR Message (None) ------------------>|
|<------------------- ACK Message -----------|
|<------------------ GMA SDU #3 -------------|
|<------------------ GMA SDU #4 -------------|
|<------------------ GMA SDU #5 -------------|
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Figure 19: Client-based Network Coding Procedure for Downlink
Client Gateway
| |
|<------------------ GMA SDUs(data packets)--|
| |
| +-------------------------------------------+
| |collect measurement from network and decide|
| |to activate network coding |
| +-------------------------------------------+
| |
|<-----CCR Message (Flag = 1, XOR, N=2)------|
|-------------------- ACK Message ---------->|
Figure 20: Network-based Network Coding Procedure for Downlink
7.5 Dynamic Connection Management
The gateway MAY use a DCR message (5.5) to disable or enable one or
multiple delivery connections. For example, if the gateway detects or
predicts significant performance degradation of a network, it may
proactively disable the connection for clients that are connected to
the network. The gateway gains knowledge of which network a client is
connected to via Link IEs in a Probe message.
On the other hand, the gateway MAY use a CPR message (5.17) to
provide guidance for a client to steer traffic especially when
network-based traffic steering (7.1) is disabled or a flow is
configured with the redundancy mode. The key difference between DCR
and CPR are:
o A DCR message provide the configuration for all traffic while a CPR
message applies only to data traffic and may provide a flow-
specific configuration.
o A disabled connection (by DCR) MUST NOT be used for any traffic
until it is enabled by another DCR message. Unlikely, a low
priority connection (by CPR) MAY be used for data traffic if all
high priority connections are lost.
For example, if a client has 4 concurrent delivery connections, the
gateway may configure two of them as high priority and the other two
as low priority for its flow with the redundancy mode. As a result,
the flow SHOULD be duplicated over the two high priority connections
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when they are available. Only if both high priority connections are
lost, the flow will be duplicated over the two low priority
connections. If only one high-priority connection remains, the flow
will be sent over the remaining high-priority connection until the
gateway configures more connections as high priority.
When network-based traffic steering is disabled, a client will decide
how to steer a flow over all available connections. However, the
gateway may detect or predict that a network is experiencing
performance degradation so that the QoS requirements of a flow can't
be met. In this scenario, the gateway MAY use CPR to prevent a client
from using "bad" connections for the flow.
Figure 21 shows an example of CPR-based dynamic connection
management. At the very beginning, a flow is split over two
connections: x and y. Once the gateway detects performance
degradation of x, it sends out a CPR message with x set to low
priority and y set to high priority. In response, the client will
steer the flow to y. Afterwards, y is lost and the client steers the
flow to x.
Client Gateway
| |
|<--------- flow #1 split over x & y --------------->|
| +-------------------------------------------+
| |collect measurement from network and detect|
| |performance degradation of x |
| +-------------------------------------------+
|<------- CPR (x: low priority and y: high-priority)-|
|--------------------- ACK ------------------------->|
|------- TSU (steer flow #1 to y)------------------->|
|<--------------------- ACK -------------------------|
|<--------- flow #1 over y ------------------------->|
| |
+-----------+ |
| y is lost | |
+-----------+ |
|------- TSU (steer flow #1 to x)------------------->|
|<-------------------- ACK --------------------------|
|<--------- flow #1 over x ------------------------->|
| |
Figure 21: CPR-based Dynamic Connection Management Example
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7.6 Dynamic One-Way-Delay (OWD) Equalization
A GMA transmitting endpoint MAY add an extra "delay" to each of the
packets before sending it to a delivery connection for mitigating the
impact of reordering due to OWD difference among the delivery
connections, aka "Delay Equalization" in [MPSN].
When enabled, the GMA receiving endpoint SHOULD measure and report
minimum OWD measurement based on data packets of the flow
periodically, e.g., every 12 seconds, or immediately when receiving a
data packet of the flow with its OWD (d) meeting the following
criteria:
d < t - c
Where t is the last minimum OWD estimation and c is a configurable
constant (margin), e.g. 10ms.
In response, the GMA transmitter SHOULD update the delay (T(i)) added
to the i-th connection using the following two-step procedure:
o step 1: T(i) = T(i) + D(i), where i = 1 ~ N
o step 2: T(i) = T(i) - min(T(i) | i = 1 ~ N)
Wherein, step 1 is for equalizing the minimum OWD for all the
connections, and step 2 is for minimizing the delay added to each
connection. The GMA transmitter MAY apply the above procedure only to
the connections that are actively being used to send data packets of
a flow and set T(i) = 0 for others. In this case, N indicates the
total number of active connections. Moreover, the GMA receiver MAY
request to reset the delay for a connection by setting its D(i) to
"255" in a TSU message. In response, the GMA transmitter SHOULD
simply set T(i)=0 for the i-th connection, and exclude it from the
procedure above.
Moreover, the GMA transmitting endpoint SHOULD use the OWD adjustment
configuration IE in the TSA message (5.4) to indicate how much one-
way delay has been added or reduced for a connection following the
above procedure. In response, the GMA receiving endpoint SHOULD
adjust its minimum OWD estimation accordingly, i.e. t'=t + q, where
the notations are defined as follows:
o t: the minimum OWD estimation before receiving the TSA message
o q: the OWD adjustment in the TSA message
o t': the minimum OWD estimation after receiving the TSA message
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8 Security Considerations
A method is provided to protect GMA control messages with a symmetric
key (e.g. AES256). It can also be used to protect GMA data packets if
a delivery connection is "untrusted".
9 IANA Considerations
This document makes no requests of IANA.
10 Contributing Authors
The editors gratefully acknowledge the following additional
contributors in alphabetical order: Wei Mao/Intel, Hosein
Nikopour/Intel.
11 References
11.1 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>.
[QUIC] RFC 9000, "QUIC: A UDP-Based Mutiplexed and Secure
Transport", <https://www.rfc-editor.org/rfc/rfc9000.txt>
11.2 Informative References
[MAMS] RFC 8743, "Multi-Access Management Services (MAMS)"
<https://tools.ietf.org/rfc/rfc8743.txt>
[LWIPEP] 3GPP TS 36.361, "Evolved Universal Terrestrial Radio
Access (E-UTRA); LTE-WLAN Radio Level Integration Using
Ipsec Tunnel (LWIP) encapsulation; Protocol
specification"
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[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
[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. RFC 9188 Generic Multi-Access (GMA)
Encapsulation Protocol <https://www.rfc-
editor.org/rfc/rfc9188.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,
[QUICTLS] M. Thomson and S. Turner, Using TLS to Secure QUIC,
https://www.rfc-editor.org/rfc/rfc9001.txt
[GMA] https://github.com/IntelLabs/gma
[CTCP] Simone Ferlin, et al., MPTCP meets FEC: Supporting
Latency-Sensitive Applications over Heterogeneous
Networks, IEEE Transactions on Networking, Oct 2018
[RLNC] T. Ho, M. Medard, R. Koetter, D. Karger, M. Effros, J. Shi
and B. Leong, "A random linear network coding approach
to multicast," IEEE Transactions on Information Theory,
vol. 52, no. 10, pp. 4413-4430, 2006.
[RC] A. Shokrollahi, "Raptor codes," in IEEE Transactions on
Information Theory, vol. 52, no. 6, pp. 2551-2567, June
2006, doi: 10.1109/TIT.2006.874390.
[RS] I. Reed and G. Solomon, "Polynomial codes over certain finite
fields," Journal of the Society for Industrial and
Applied Mathematics, vol. 8, no. 2, pp. 300-304, 1960.
[DCTCP] RFC 8257, "Data Center TCP (DCTCP): TCP Congestion Control
for Data Centers",
<https://datatracker.ietf.org/doc/html/rfc8257>
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[Dual3GPP] 3GPP TR 22.841, "Study on Upper Layer Traffic Steer,
Switch and Split over Dual 3GPP Access", 2023-12
[MPSN] M. Amend, D. Von Hugo, Multipath Sequence Maintenance,
<https://www.ietf.org/archive/id/draft-amend-iccrg-
multipath-reordering-03.txt>
Authors' Addresses
Jing Zhu
Intel
Email: jing.z.zhu@intel.com
Menglei Zhang
Intel
Email: menglei.zhang@intel.com
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