UDP-based Generic Multi-Access (GMA) Control Protocol
draft-zhu-intarea-gma-control-04
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| Authors | Jing Zhu , Menglei Zhang | ||
| Last updated | 2023-08-24 (Latest revision 2023-03-31) | ||
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draft-zhu-intarea-gma-control-04
Network Working Group J. Zhu
Internet Draft M. Zhang
Intended status: Experimental Intel
Expires: February 24,2023 August 24, 2023
UDP-based Generic Multi-Access (GMA) Control Protocol
draft-zhu-intarea-gma-control-04
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 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.
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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Internet-Drafts are draft documents valid for a maximum of six
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http://www.ietf.org/shadow.html
This Internet-Draft will expire on February 24, 2022.
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Copyright Notice
Copyright (c) 2023 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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respect to this document. Code Components extracted from this
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without warranty as described in the Simplified BSD License.
Table of Contents
1 Introduction ...............................................3
1.1 Scope of Experiment ...................................4
2 Conventions used in this document ..........................5
3 Use Case ...................................................5
4 UDP-based GMA Encapsulation Protocol .......................7
5 GMA Control Messages ......................................11
5.1 Probe Message ........................................11
5.2 Acknowledgement (ACK) Message ........................13
5.3 Traffic Splitting Update (TSU) Message ...............14
5.4 Traffic Splitting Acknowledgement (TSA) Message ......15
5.5 Delivery Connection Reconfiguration (DCR) Message ....16
5.6 Key Update Message ...................................17
5.7 Traffic Steering Command (TSC) Message ...............17
5.8 Traffic Splitting Command (TSP) Message ..............18
5.9 QoS Testing Request (QTR) Message ....................18
5.10 QoS Testing Response (QTP) Message ...................19
5.11 QoS Testing Notification (QTN) Message ...............19
5.12 QoS Violation Notification (QVN) Message .............19
5.13 Packet Loss Report (PLR) Message .....................20
5.14 First Sequence Number (FSN) Message ..................20
5.15 Coding Configuration Request (CCR) Message ...........20
5.16 Coded GMA SDU (CGS) Message ..........................21
5.17 Coding Configuration Command (CCC) Message ...........22
6 Basic GMA Control Procedures ..............................23
6.1 Initialization .......................................23
6.2 GMA Operation ........................................25
6.3 Termination ..........................................26
7 Advanced GMA Control Procedure ............................27
7.1 Network-based Traffic Steering .......................27
7.2 QoS-aware Traffic Steering ...........................28
7.3 GMA-based Retransmission .............................30
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7.4 Receiver-based Network Coding ........................31
7.5 Network-based Network Coding .........................32
8 Security Considerations ...................................33
9 IANA Considerations .......................................33
10 Contributing Authors ......................................33
11 References ................................................33
11.1 Normative References .................................33
11.2 Informative References ...............................34
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.
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 | |
| +-----------------------------------------------------+ |
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| 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, for example, Multi-Access Management Services [MAMS].
From individual access network's perspective, the proposed UDP-
based GMA control protocol is a new light-weight transport
protocol designed specifically for multi-path operation, removing
all the 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 features, 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 standards 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 ATSSS [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:
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.
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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 does not mandate Acknowledgement
(ACK) and reliable delivery for data traffic to avoid any delay
due to retransmission as well as ACK 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-path 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. An open-source based GMA software implementation
[GMAsw] is provided for evaluation.
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 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-
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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
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
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 UDP-based GMA user-plane and control-plane
protocol, respectively.
+-----------------------------------------------------+
| Virtual Connection (IP, Ethernet, etc.) |
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+-----------------------------------------------------+
| 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
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 and IP
addresses for "UDP Tunnelling" at multi-access gateway MAY be
configured and provided to client through the MAMS message (MX UP
Setup Config) [MAMS].
+----------------------------------------------------+
| IP hdr | UDP hdr | GMA Header | Payload (GMA SDU) |
+----------------------------------------------------+
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 Client ID Present (bit 0): If the Client ID Present bit is set
to 1, then the Client ID field is present.
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).
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Otherwise (default), it carries an unencrypted GMA SDU
(data).
o Flow ID Present (bit 2): If the Flow ID Present bit is set to
1, then the Flow ID field is present.
o Per-Packet Priority (PPP) Present (bit 3): If the PPP Present
bit is set to 1, then the PPP field is present.
o Packet Group Identification (PGI) Present (bit 4): If the PCI
Present bit is set to 1, then the PCI field is present.
o Delivery SN Present (bit 5): 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 6): If the Flow SN (Sequence Number)
Present bit is set to 1, then the Flow SN field is present
and contains the valid information.
o Timestamp Present (bit 7): If the Timestamp Present bit is set
to 1, then 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 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
virtual connection.
o PT (1 Byte): this field is present only if the Payload Type
bit is set to 1.
+ 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
of a GMA SDU.
+ 0: default
+ 1~9: reserved for flows using the redundancy mode, with
which a flow is duplicated over all the available
delivery connections.
+ 10~20: reserved for flows using the splitting mode, with
which a flow is split over all the available delivery
connections.
+ 21~100: reserved for flows using the steering mode, with
which a flow is sent over only one of the available
delivery connections.
+ Others: reserved for future use
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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 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 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 unsigned 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 100
microseconds. This field is present only if the Timestamp
Present bit is set to one.
The use of Key Phase bit is similar to QUIC [QUICTLS], and it
allows 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 protected with any encryption.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PT | Flow ID | PPP | PGI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Delivery SN | Flow SN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 hierarchical QoS (hQoS) and fine granular
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-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 one-way-delay measurement, which can then be
used to detect congestion and buffer overflow at intermediate
nodes.
GMA payload MAY be protected by a symmetric key cipher, e.g.
AES256-GCM. The receiver will use the Client ID field to obtain
the corresponding key for decryption. Only GMA payload is
encrypted, and GMA header is authenticated but not encrypted.
GMA SDU (data) SHOULD be protected 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".
+-------------------------------------------------------------+
| GMA Header | GMA Payload | GCM Tag | IV |
+-------------------------------------------------------------+
|<-authenticated->|<-------encrypted -------->|
Figure 6: AES256-GCM Encrypted GMA Message
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Figure 6 shows the format of an AES256-GCM encrypted GMA message,
where IV (initialization vector) is 12 bytes long and GCM Tag is
16 bytes long. 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.
Notice that Coded GMA SDU (CGS) message (5.16) MAY be protected
by the symmetric key only if the delivery connection is
untrusted. All other GMA control message SHOULD be protected
regardless.
5.1 Probe Message
The "Type" field is set to "1" for Probe messages.
Client (or multi-access gateway) MAY send out a Probe message for
initial connection establishment, path quality estimation,
keepalive, time synchronization, and link measurement report. In
response, multi-access gateway (or client) MAY send back the ACK
message. A delivery connection is established after the successful
Probe and ACK handshake, and terminated if any control message
exchange fails.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Link Information Elements |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Probe Message Format
A Probe message consists of the following fields:
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 timestamp SHOULD be
reset (1) or not (0)
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+ Bit #1: a bit flag to indicate if the ACK message is
expected (0) or not (1)
+ Bit #2: 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 #3: a bit flag to indicate if one or more Link
Information Elements (IE) are present.
+ Bit #4: a bit flag to indicate if the client's local clock
is synchronized with the multi-access gateway.
+ Bit #5~7: reserved
A Link IE consists of the following fields:
o Type (1B)
o Length (1B)
o Value (variable)
Multi-access gateway SHOULD update the UDP tunnel end-point of
the client for the delivery connection based on the received
Probe message if the Bit #2 Probing flag is set to 0 (default).
A Probe message with the Bit #0 flag set to "1" is also called
Probe-Sync. Client SHOULD send out a Probe-Sync 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 Probe-Sync message, multi-access gateway SHOULD
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.
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 duration between the last
successful Probe-Sync message exchange and the transmission of the
GMA PDU.
However, if the Bit #4 flag is set to "1", indicating the client's
local clock is synchronized with the gateway, both client and
gateway SHOULD use their local clock directly as the timestamp
clock without going through the above "Probe-Sync" procedure.
Client MAY use the Probe message to report its link quality, e.g.,
signal strength and other information, e.g. Wi-Fi channel number.
Table 1 list all the supported Link Information Elements.
Table 1: Link Information Elements
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+---------------------------------------------------------------+
| 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 |
+---------------------------------------------------------------+
| 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
The "Type" field is set to "2" for ACK messages. The SN field in
the GMA header is set to the sequence number of the corresponding
request message. The ACK message consists of the following fields:
o Request Type (1 Byte): the corresponding request message type,
e.g. Probe, etc.
o Padding (variable)
0 1 2 3
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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
The "Type" field is set to "3" for TSU messages. Client (Gateway)
may send out a TSU message to change the traffic
splitting/steering/duplicating configuration for downlink
(uplink) flows. Let's use N to denote the number of delivery
connections.
A TSU message consists of the following fields:
o Link Status Bitmap (1 Byte): see 5.1
o Number of Flows (1 Byte): the number of flows that are
configured by the TSU message.
For each flow, the following Traffic Splitting control parameters
are included:
o Flow ID (1 Byte): an unsigned integer to identify the flow.
For a flow using the splitting mode, the following parameters (1
+ 2N Bytes) SHOULD be included:
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 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] = 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.
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For a flow using the steering mode, the following parameter (1
Byte) SHOULD be included:
o C (1 Byte): the CID of the delivery connection that the flow
should be using.
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 |Number of Flows| Flow ID | L |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| K1[1] | K1[2] | K2[1] | K2[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flow ID | C |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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. Gateway (or
client) SHALL send out a TSA message in response to a received TSU
message. The SN field in the GMA header is set to the sequence
number of the corresponding TSU message. A TSA message consists of
the following fields:
o Number of Flows (1 Byte): the number of flows that are
configured by the TSU message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Number of Flows| Flow ID | StartSN
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Flow ID | StartSN
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+
Figure 10: TSA Message Format (Number of Flows = 2)
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 Delivery Connection Reconfiguration (DCR) Message
The "Type" field is set to "5" for DCR messages. Gateway MAY send
out a DCR message to enable or disable a delivery connection for
the client. In response, the client SHALL send out an ACK message
and stop sending any traffic to a disabled 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 similar to Link Status Bitmap (5.1).
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5.6 Key Update Message
The "Type" field is set to "6" for Key Update messages. Gateway
MAY send out a Key Update message to change the symmetric key for
the client. In response, the client SHALL send out an ACK message
and start using the new key to protect GMA control messages. The
gateway SHALL 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): to indicate the type of symmetric key
+ 0: AES256-GCM
+ Others: reserved
If Key Type == 0
o Key Value (32 Bytes): the AES256-GCM key
5.7 Traffic Steering Command (TSC) Message
The "Type" field is set to "7" for TSC messages. Multi-access
gateway MAY send out a TSC message to configure network-based
traffic steering for flows using the steering mode.
Let's use N to denote the number of delivery connections.
A TSC message consists of the following fields:
o Number of Downlink Flows (1 Byte): the number of downlink
flows that are configured in the TSC message.
o Number of Uplink Flows (1 Byte): the number of uplink flows
that are configured in the TSC message.
For each flow, the following (4 Bytes) control parameters are
included:
o Flow ID (1 Byte): an unsigned integer to identify the flow.
o Flag (1 Byte)
+ 0: disable network-based traffic steering (default)
+ 1: enable network-based traffic steering
+ Others: reserved
o CID (1 Byte): the CID of the delivery connection that the
flow will be using (ignored if Flag == 0)
o Reserved (1 Byte)
After receiving a TSC message, client SHALL send out an ACK
message to confirm the successful reception of the TSC message.
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5.8 Traffic Splitting Command (TSP) Message
The "Type" field is set to "8" for TSP messages. Multi-access
gateway MAY send out a TSP message to configure network-based
traffic splitting for downlink flows using the splitting mode.
Let's use N to denote the number of delivery connections.
A TSC message consists of the following fields:
o Number of Flows (1 Byte): the number of downlink flows that
are configured in the TSP message
For each flow, the following control parameters are included:
o Flow ID (1 Byte): an unsigned integer to identify the flow
o Flag (1 Byte)
+ 0: disable network-based traffic splitting (default)
+ 1: enable network-based traffic splitting
+ Others: reserved
If (Flag == 1), include the following 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 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.
After receiving a TSP message, client SHALL send out an ACK
message to confirm the successful reception of the TSP message.
5.9 QoS Testing Request (QTR) Message
The "Type" field is set to "9" for QTR messages. Multi-access
client MAY send out a QTR message to request QoS testing for a
flow. A QTR message 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.
5.10 QoS Testing Response (QTP) Message
The "Type" field is set to "10" for QTP messages. Multi-access
gateway MAY send out a QTP message to indicate if QoS testing for
an uplink flow is successful or not. A QTP message 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 "Type" field is set to "11" for QTN messages. Gateway MAY send
out a QTN message to start QoS testing for a flow.
A QTN message 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.
5.12 QoS Violation Notification (QVN) Message
The "Type" field is set to "12" for QVN messages. Gateway MAY send
out a QVN message to indicate that QoS violation has been detected
or is expected for a flow. A QVN message 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.
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5.13 Packet Loss Report (PLR) Message
The "Type" field is set to "13" for PLR messages.
Client (Gateway) MAY send out the PLR messages to report lost GMA SDUs
for example during handover. In response, gateway (client) 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
The "Type" field is set to "14" for FSN messages.
Client (Gateway) 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 from multi-access gateway (client). In
response, gateway (client) MUST NOT report packet loss with Flow SN
smaller than 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:
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 of the sender of
the FSN message.
5.15 Coding Configuration Request (CCR) Message
The "Type" field is set to "15" for CCR messages.
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Client (Gateway) MAY send out the CCR message to support downlink
(or uplink) packet loss recovery through systematic network coding,
e.g. XOR [CTCP]. In response, gateway (client) SHALL send out the
ACK message to indicate the successful reception. It supports XOR
and Reed-Solomon currently. 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 Flow ID (1 Byte): an unsigned integer to identify the flow
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:
+ M (1 Bytes): the number of coded (parity) GMA SDUs
generated for every N consecutive uncoded GMA SDUs.
+ L (1 Bytes): the symbol size for the RS code finite field,
i.e., the maximum codeword length (N + M) is given by 2^L-
1.
5.16 Coded GMA SDU (CGS) Message
The "Type" field is set to "16" for CGS messages.
Client (or gateway) may send out the CGS message to support downlink
(or uplink) packet loss recovery through systematic network coding
[CTCP]. A coded GMA SDU is generated by applying a network coding
method to multiple consecutive (uncoded) GMA SDUs, which are
transmitted as is without any changes. It is used for fast recovery
without retransmission if any of the GMA SDUs is lost.
The Flow SN field (as shown in Figure 5) MUST NOT be included in the
GMA header of a CGS message. A CGS message MAY be protected with
authentication or encryption only if the delivery connection is
untrusted.
A Coded GMA SDU message consists of the following fields:
o Flow ID (1 Byte): an unsigned integer to identify the flow.
o Flag (1 Byte)
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+ 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 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 Coding Configuration Command (CCC) Message
The "Type" field is set to "17" for CCC messages. Multi-access
gateway MAY send out a CCC message to configure network coding for
downlink flows. A CCC message consists of the following fields:
o Flow ID (1 Byte): an unsigned integer to identify the flow
o Flag (1 Byte)
+ 0: disable network-based network coding (default)
+ 1: enable network-based network coding
+ Others: reserved
If "Flag == 1", include the following fields
o Coding Type (1 Byte)
+ 0: None
+ 1: XOR
+ 2: Reed-Solomon
+ Others: reserved
o N (1 Bytes): the number of consecutive (uncoded) GMA SDUs
used to generate the coded GMA SDU
If Coding Type = Reed-Solomon, include the following:
+ M (1 Byte): the number of coded (parity) GMA SDUs generated
for every N consecutive uncoded GMA SDUs.
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+ 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.
After receiving a CCC message, client SHALL send out an ACK
message to confirm the successful reception of the CCC message.
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
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
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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 Receiver-based network coding (7.4)
o Network-based network coding (7.5)
o Network coding method (XOR, Reed-Solomon, or others)
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
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 flow with specific QoS
requirements (maximum delay or loss rate) to the connection.
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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.
If client's local clock is already synchronized with multi-access
gateway, both client and gateway SHOULD use their local clock as
the timestamp clock directly. Otherwise, client will send out the
Probe-Sync message to reset the timestamp clock. Afterwards,
client MAY send out the Probe-Sync message periodically to reset
the timestamp clock.
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 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, 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,
etc. However, the ACK message SHALL use the same delivery
connection as its corresponding control 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.
For uplink flow using the steering mode, client SHOULD control
how to steer traffic without any GMA control message exchange
with multi-access gateway. For uplink flow using the splitting
mode, multi-access gateway SHOULD perform measurements 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 | |
+--------------+ |
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|---------------------------- 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
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--------------------->|
| |
|<------------------------ MX Termination Response---|
Figure 14: MAMS-based Termination Procedure
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7 Advanced GMA Control Procedure
7.1 Network-based Traffic Steering
Multi-access gateway may trigger steering a flow from one delivery
connection to another, aka Network-based Traffic Steering. Figure
15 shows the procedure with the TSC (Traffic Steering Command)
message as defined in 5.7.
For downlink traffic, client SHALL send out a TSU message to
confirm changing the delivery connection. For uplink traffic, no
additional control message exchange is required.
If the Flag field in the TSC message is set to "0", network-based
traffic steering is disabled for the flow and client SHALL decide
how to steer the flow based on its local information.
If the Flag field in the TSC message is set to "1", network-based
traffic steering is enabled for the flow and the delivery
connection specified in the TSC message SHOULD be used for the
flow.
Client multi-access Gateway
| |
|<-------------- 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 --------------------------------------->|
+-----------+ |
|accept TSC | |
+-----------+ |
|--------------- flow #1 uplink over link y -------->|
| |
|------- TSU --------------------------------------->|
|<-----------------------------------------TSA ------|
| |
|<-------------- flow #1 downlink over link y -------|
| |
Figure 15: Network-based Traffic Steering Procedure
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Figure 16 shows the similar procedure to support network-based
downlink traffic splitting with the TSP message as defined in 5.8.
Network-based uplink traffic splitting is always controlled by
multi-access gateway using the TSU/TSA message exchange.
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 --------------------------------------->|
+-----------+ |
|accept TSP | |
+-----------+ |
| |
|------- TSU --------------------------------------->|
|<-----------------------------------------TSA ------|
| |
|<--------- flow #1 (updated splitting ratio)--------|
| |
Figure 16: Network-based Downlink Traffic Splitting Procedure
7.2 QoS-aware Traffic Steering
Client SHOULD request QoS testing for a flow that has specific QoS
requirements, e.g. maximum delay or/and loss rate, over a (best-
effort) delivery connection, e.g. Wi-Fi, that can not guarantee
QoS, before steering the flow to the connection. Figure 17 shows
the QoS-aware traffic steering procedure.
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, client SHOULD send out the QTR message to request QoS
testing. In response, multi-access gateway SHOULD decide when to
start the testing and send out the QTN message.
During QoS testing, multi-access gateway (or client) SHOULD
duplicate downlink (or uplink) traffic of the flow over the
testing connection as indicated in the QTN message. All duplicated
packets SHALL be discarded by the receiving side, and only used
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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 best-effort connection.
If uplink testing is performed, multi-access gateway SHALL send
out the QTP message to indicate the testing result. If the testing
is successful, client SHOULD send out the TSU message to steer the
flow to the best-effort connection.
Afterwards, multi-access gateway SHOULD continue measuring and
monitoring the QoS performance of the flow. Once detecting any QoS
violation, multi-access gateway MAY send the QVN message to
client. In response, client SHOULD send the TSU message to steer
the flow back to the QoS-guaranteed connection.
For downlink flow, client SHOULD perform QoS measurement and
violation detection, and send the TSU message to steer the flow
back to the QoS-guaranteed connection once detecting QoS
violation.
Client multi-access Gateway
| |
|-------- (uplink) flow #1 over link x ------------->|
+--------------+ |
| link y is up | |
+--------------+ |
| |
|------- 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 |
| +-------------------------------------------+
| |
|<--------------------- QTP (result: success)--------|
|--------------------- ACK ------------------------->|
| |
|--------------------- TSU ------------------------->|
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|<--------------------- TSA -------------------------|
| |
|-------- flow #1 over link y ---------------------->|
| |
| +--------------------------------------------+
| |collect measurement and detect QoS violation|
| +--------------------------------------------+
|<-------------------- QVN (flow #1)-----------------|
|--------------------- ACK ------------------------->|
| |
|--------------------- TSU ------------------------->|
|<--------------------- TSA -------------------------|
|-------- flow #1 over link x ---------------------->|
| |
Figure 17: QoS-aware Traffic Steering Procedure
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 | |
+----------------------+ |
| |
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|----- PLR Message ------------------------->|
| +---------------------+
| |Lost packet not found|
| +---------------------+
|<-------------FSN message ------------------|
Figure 18: GMA-based Retransmission Procedure
7.4 Receiver-based Network Coding
Figure 19 shows the receiver-based network coding procedure (using
XOR) for downlink traffic. In this example, client first detects
packet loss, and then sends out a CCR message to activate network
coding, including all the required parameters, e.g. Network Coding
Type, N, and M. 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 with Network
Coding Type set to "None" to deactivate network coding for a
downlink flow.
Client Gateway
| |
|<------------------ GMA SDUs(data packets)--|
| |
+---------------------+ |
|Packet Loss detected | |
+---------------------+ |
| |
|------CCR Message (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 -------------|
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|<------------------ GMA SDU #5 -------------|
Figure 19: Receiver-based Network Coding Procedure for Downlink
7.5 Network-based Network Coding
Figure 20 shows the network-based network coding procedure (using
XOR) for downlink traffic. In this example, gateway first collect
measurements and then sends out a CCC message to activate network
coding with the required parameters, e.g. Network Coding Type, N,
and M. In this example, XOR is configured as the coding method
with N = 2. After the CCC message is successfully acknowledged,
gateway starts sending one CGS message carrying the coded GMA SDU
for every two (uncoded) GMA SDUs. Afterwards, gateway MAY send out
a CCC message with Network Coding Type set to "None" to deactivate
network coding for the flow.
Notice that network-based network coding for uplink follows the
receiver-based procedure as in 7.4 using the CCR message, because
gateway is the receiver for uplink traffic.
Client Gateway
| |
|<------------------ GMA SDUs(data packets)--|
| |
| +-------------------------------------------+
| |collect measurement from network and decide|
| |to activate network coding |
| +-------------------------------------------+
| |
|<-----CCC Message (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 | |
+----------------------+ |
| |
|<-----CCC Message (None) -------------------|
|-------------------- ACK Message ---------->|
|<------------------ GMA SDU #3 -------------|
|<------------------ GMA SDU #4 -------------|
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|<------------------ GMA SDU #5 -------------|
Figure 20: Network-based Network Coding Procedure for Downlink
8 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.
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>
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11.2 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
[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,
[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
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[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.
Authors' Addresses
Jing Zhu
Intel
Email: jing.z.zhu@intel.com
Menglei Zhang
Intel
Email: menglei.zhang@intel.com
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