Transport Area Working Group J. Saldana
Internet-Draft University of Zaragoza
Intended status: Standards Track January 5, 2015
Expires: July 9, 2015
Simplemux. A generic multiplexing protocol
draft-saldana-tsvwg-simplemux-01
Abstract
There are some situations in which multiplexing a number of small
packets into a bigger one is desirable. For example, a number of
small packets can be sent together between a pair of machines if they
share a common network path. Thus, the traffic profile can be
shifted from small to larger packets, reducing the network overhead
and the number of packets per second to be managed by intermediate
routers.
This document describes Simplemux, a protocol able to encapsulate a
number of packets belonging to different protocols into a single
packet. It includes the "Protocol" field on each multiplexing
header, thus allowing the inclusion of a number of packets belonging
to different protocols on a packet of another protocol.
The size of the multiplexing headers is kept very low (it may be a
single byte when multiplexing small packets) in order to reduce the
overhead.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on July 9, 2015.
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Copyright Notice
Copyright (c) 2015 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Existing multiplexing protocols . . . . . . . . . . . . . 3
1.3. Benefits of multiplexing . . . . . . . . . . . . . . . . 5
2. Description of the scenario . . . . . . . . . . . . . . . . . 5
3. Protocol description . . . . . . . . . . . . . . . . . . . . 6
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
This document describes Simplemux, a protocol able to encapsulate a
number of packets belonging to different protocols into a single
packet. This can be useful e.g. for grouping small packets and thus
reducing the number of packets per second in a network.
This proposal attempts to be general, meaning that it can be used for
multiplexing packets belonging to a generic protocol on a single
packet belonging to other (or the same) protocol). Thus, we will
talk about the "multiplexed" protocol, and the "multiplexing"
protocol. The "external header" will be the one of the
"multiplexing" protocol (see the figure (Figure 1)).
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+-------------------------------+
| |
| External Header |
| |
+-------------------------------+
| |
| Simplemux |
| |
+-------------------------------+
| |
| Multiplexed Packet |
| |
+-------------------------------+
Figure 1
For example, if a number of IPv6 packets have to travel over an IPv4
network, they can be multiplexed into a single IPv4 packet. In this
case, IPv4 is the "multiplexing" protocol and IPv6 is the
"multiplexed" protocol. The IPv4 header is called in this case the
"external header". The scheme of this packet would be:
|IPv4 hdr||Smux hdr|IPv6 packet||Smux hdr|IPv6 packet|| ...|
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. Existing multiplexing protocols
Different multiplexing protocols have been approved by the IETF in
the past:
o TMux [RFC1692]
TMux is able to combine multiple short transport segments,
independent of application type, and send them between a server and
host pair. As stated in the reference, "The TMux protocol is
intended to optimize the transmission of large numbers of small data
packets. In particular, communication load is not measured only in
bits per seconds but also in packets per seconds, and in many
situation the latter is the true performance limit, not the former.
The proposed multiplexing is aimed at alleviating this situation."
A TMux message appears as:
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|IP hdr||TMux hdr|Transport segment||TMux hdr|Transport segment||...|
So the Transport Segment is not an IP packet, since it does not
include the IP header.
TMux works "between a server and host pair", so it multiplexes a
number of segments between the same pair of machines. However, there
are scenarios where a number of low-efficiency flows share a common
path, but they are not sent between the same pair of machines.
o PPPMux [RFC3153]
PPPMux "sends multiple PPP encapsulated packets in a single PPP
frame. As a result, the PPP overhead per packet is reduced." Thus,
it is able to multiplex complete IP packets, using separators.
However, the use of PPPMux requires the use of PPP and L2TP in order
to multiplex a number of packets together, as done in TCRTP
[RFC4170]. However, this introduces more overhead and complexity.
An IP packet including a number of them using PPPMux appears as:
|IP hdr|L2TP hdr|PPP hdr||PPPMux hdr|packet||PPPMux hdr|packet||...|
The scheme proposed by PPPMux is similar to the Compound-Frames of
PPP LCP Extensions [RFC1570]. The key differences are that PPPMux is
more efficient and that it allows concatenation of variable sized
frames.
***
The definition of a protocol able to multiplex complete packets,
avoiding the need of other protocols as PPP is seen as convenient.
The multiplexed packets can be of any kind, since the "Protocol"
field can be added for each of them. Not all the packets multiplexed
in the same one have to belong to the same protocol. The general
scheme of Simplemux is:
|external hdr||Simplemux hdr|packet||Simplemux hdr|packet||...|
The Simplemux header includes the "Protocol" field, so it permits the
multiplexing of different kinds of packets in the same bundle.
We will also refer to the Simplemux header with the terms
"separator", "Simplemux separator" or "mux separator".
When applied to IP packets, the scheme of a multiplexed packet
becomes:
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|IP hdr||Simplemux hdr|IP packet||Simplemux hdr|IP packet||...|
1.3. Benefits of multiplexing
The benefits of multiplexing are:
- Tunneling a number of packets together. If a number of packets
have to be tunneled through a network segment, they can be
multiplexed and then sent together using a single external header.
This will avoid the need for adding a tunneling header to each of the
packets, thus reducing the overhead.
- Reduction of the amount of packets per second in the network. It
is desirable for two main reasons: first, network equipment has a
limitation in terms of the number of packets per second it can
manage, i.e. many devices are not able to send small packets back to
back due to processing delay.
- Bandwidth reduction. The presence of high rates of tiny packets
translate into an inefficient usage of network resources, so there is
a need for mechanisms able to reduce the overhead introduced by low-
efficiency flows. When combined with header compression, as done in
TCRTP [RFC4170] multiplexing may produce significant bandwidth
savings, which are interesting for network operators, since they may
alleviate the traffic load in their networks.
- Energy savings: a lower amount of bandwidth packets per second will
reduce energy consumption in network equipment since, according to
[Bolla], internal packet processing engines and switching fabric
require 60% and 18% of the power consumption of high-end routers
respectively. Thus, reducing the number of packets to be managed and
switched will reduce the overall energy consumption. The
measurements deployed in [Chabarek]on commercial routers corroborate
this: a study using different packet sizes was presented, and the
tests with big packets showed that energy consumption gets reduced,
since a non-negligible amount of energy is associated to header
processing tasks, and not only to the sending of the packet itself.
2. Description of the scenario
Simplemux works between a pair of machines. It creates a tunnel
between the ingress and the egress. They MAY be the endpoints of the
communication, but they MAY also be middleboxes able to multiplex
packets belonging to different flows. Different mechanisms MAY be
used in order to classify flows according to some criteria (sharing a
common path, kind of service, etc.) and to select the flows to be
multiplexed and sent to the egress (see Figure 2).
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+-------+
| | +---------+ +---------+
| | ---> |Simplemux| _ _ |Simplemux| -->
|classif| ---> | ingress | ===> ( ` )_ ===> | egress | -->
| | +---------+ ( Network `) +---------+
| | --------------------> (_ (_ . _) _) ----------------->
+-------+
<--------Simplemux-------->
Figure 2
3. Protocol description
A Simplemux packet consists of:
- An external header which is used as the tunneling header for the
whole packet.
- A series of pairs "Simplemux header" + "packet".
This is the scheme of a Simplemux packet:
|external hdr||Smux hdr|packet||Smux hdr|packet||...|
The Simplemux header has two different forms: one for the First
Simplemux header, and another one for the rest of the Simplemux
headers (Non-first Simplemux headers).
o First Simplemux header (before the first multiplexed packet):
| Protocol (8 bits)|SPB(1 bit)| LXT(1 bit) | length (6 or 14 bits) |
- Protocol (8 bits) is the Protocol field of the multiplexed packet,
according to IANA "Assigned Internet Protocol Numbers".
- Single Protocol Bit (SPB, one bit) only appears in the first
Simplemux header. It is set to 1 if all the multiplexed packets
belong to the same protocol (in this case, the "Protocol" field will
only appear in the first Simplemux header). It is set to 0 when each
packet MAY belong to a different protocol.
- Length Extension (LXT, one bit) is 0 if the length of the first
packet can be expressed in 6 bits, and 1 in other case.
- Length (LEN, 6 or 14 bits): This is the length of the multiplexed
packet in bytes not including the length field. If the length of the
multiplexed packet is less than 64 bytes (less than or equal to 63
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bytes), LXT is set to 0 and the 6 bits of the length field are the
length of the multiplexed packet. If the length of the multiplexed
packet is greater than 63 bytes, LXT is set to 1 and the 14 bits of
the length field are the length of the multiplexed packet. The
maximum length of a multiplexed packet is 16,383 bytes. Packets
larger than 16,383 bytes will need to be sent in their native form.
A Simplemux ingress is not required to multiplex all packets smaller
than 16,383 bytes. It may choose to only multiplex packets smaller
than a configurable size into a Simplemux multiplexed packet.
As an example, a First Simplemux header before a packet smaller than
64 bytes would be 16 bits long:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |S|L| |
| Protocol |P|X| Length |
| (8 bits) |B|T| (6 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LXT = 0
Figure 3
And a First Simplemux header before a packet bigger than 63 bytes
would be 24 bits long:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |S|L| |
| Protocol |P|X| Length |
| (8 bits) |B|T| (14 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LXT = 1
Figure 4
o Subsequent (Non-first) Simplemux headers (before the other
packets):
| Protocol(8 bits, optional) |LXT(1 bit) | length (7 or 15 bits) |
- Protocol (8 bits) is the Protocol field of the multiplexed packet,
according to IANA "Assigned Internet Protocol Numbers". It only
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appears in Non-first headers if the Single Protocol Bit (SPB) of the
First Simplemux header is set to 1.
- Length Extension (LXT, one bit) is 0 if the length of the first
packet can be expressed in 7 bits, and 1 in other case.
- Length (LEN, 7 or 15 bits): This is the length of the multiplexed
packet in bytes not including the length field. If the length of the
multiplexed packet is less than 128 bytes (less than or equal to 127
bytes), LXT is set to 0 and the 7 bits of the length field represent
the length of the multiplexed packet. If the length of the
multiplexed packet is greater than 127 bytes, LXT is set to 1 and the
15 bits of the length field are the length of the multiplexed packet.
The maximum length of a multiplexed packet is 32,768 bytes. Packets
larger than 32,768 bytes will need to be sent in their native form.
However, this will have to be reduced to 16,383 bytes taking into
account that the maximum size of the First header is 14 bits. A
Simplemux ingress is not required to multiplex all packets smaller
than 32,768 bytes. It may choose to only multiplex packets smaller
than a configurable size into a Simplemux multiplexed packet.
As an example, a Non-first Simplemux header before a packet smaller
than 128 bytes, when the protocol bit has been set to 0 in the first
header, would be 8 bits long:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|L| |
|X| Length |
|T| (7 bits) |
+-+-+-+-+-+-+-+-+
LXT = 0
SPB = 0 in the first header
Figure 5
A Non-first Simplemux header before a packet bigger than 127 bytes,
when the protocol bit has been set to 0 in the first header, would be
16 bits long:
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| |
|X| Length |
|T| (15 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LXT = 1
SPB = 0 in the first header
Figure 6
A Non-first Simplemux header before a packet smaller than 128 bytes,
when the protocol bit has been set to 1 in the first header, would be
16 bits long:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |L| |
| Protocol |X| Length |
| (8 bits) |T| (7 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LXT = 0
SPB = 1 in the first header
Figure 7
And a Non-first Simplemux header before a packet bigger than 127
bytes, when the protocol bit has been set to 1 in the first header,
would be 24 bits long:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |L| |
| Protocol |X| Length |
| (8 bits) |T| (15 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LXT = 1
SPB = 1 in the first header
Figure 8
These would be some examples of the whole bundles:
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Case 1: All the packets belong to the same protocol: The first
Simplemux header would be 2 or 3 bytes, and the other Simplemux
headers would be 1 or 2 bytes. For small packets (< 128 bytes), the
Simplemux header would only require one byte.
|ext hdr||Protocol|0|0|len|pkt||0|len|pkt||1|len|pkt||...|
| | |
v v v
(6bits) (7bits) (15bits)
|ext hdr||Protocol|0|1|len|pkt||0|len|pkt||1|len|pkt||...|
| | |
v v v
(14bits) (7bits) (15bits)
Figure 9
Case 2: Each packet may belong to a different protocol: All the
Simplemux headers would be 2 or 3 bytes.
|ext hdr||Prot|1|0|len|pkt||Prot|0|len|pkt||Prot|1|len|pkt||...|
| | |
v v v
(6bits) (7bits) (15bits)
|ext hdr||Prot|1|1|len|pkt||Prot|0|len|pkt||Prot|1|len|pkt||...|
| | |
v v v
(14bits) (7bits) (15bits)
Figure 10
4. Acknowledgements
5. IANA Considerations
A protocol number should be requested to IANA for Simplemux.
As a provisional solution for IP networks, the ingress and the egress
optimizers may agree on a UDP port, and use IP/UDP as the
multiplexing protocol.
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6. Security Considerations
7. References
7.1. Normative References
[RFC1570] Simpson, W., "PPP LCP Extensions", RFC 1570, January 1994.
[RFC1692] Cameron, P., Crocker, D., Cohen, D., and J. Postel,
"Transport Multiplexing Protocol (TMux)", RFC 1692, August
1994.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3153] Pazhyannur, R., Ali, I., and C. Fox, "PPP Multiplexing",
RFC 3153, August 2001.
[RFC4170] Thompson, B., Koren, T., and D. Wing, "Tunneling
Multiplexed Compressed RTP (TCRTP)", BCP 110, RFC 4170,
November 2005.
7.2. Informative References
[Bolla] Bolla, R., Bruschi, R., Davoli, F., and F. Cucchietti,
"Energy Efficiency in the Future Internet: A Survey of
Existing Approaches and Trends in Energy-Aware Fixed
Network Infrastructures", IEEE Communications Surveys and
Tutorials vol.13, no.2, pp.223,244, 2011.
[Chabarek]
Chabarek, J., Sommers, J., Barford, P., Estan, C., Tsiang,
D., and S. Wright, "Power Awareness in Network Design and
Routing", INFOCOM 2008. The 27th Conference on Computer
Communications. IEEE pp.457,465, 2008.
Author's Address
Jose Saldana
University of Zaragoza
Dpt. IEC Ada Byron Building
Zaragoza 50018
Spain
Phone: +34 976 762 698
Email: jsaldana@unizar.es
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