Network Working Group S. Salsano
Internet-Draft A. Detti
Intended status: Informational N. Blefari-Melazzi
Expires: November 29, 2012 M. Cancellieri
Univ. of Rome "Tor Vergata"
May 28, 2012
ICTP - Information Centric Transport Protocol for CONET ICN
draft-salsano-ictp-00
Abstract
Let us consider an Information Centric Networking (ICN) solution, in
which an End Node requests for a content sending "content requests"
(or "interest packets"). The content is provided back to the
requestor by the "origin" node or by an intermediate node that had
cached the content. The content is usually divided into "chunks"
that can be individually requested, sent back to the requester,
cached into intermediate nodes. The sending rate of content requests
can be adjusted in order to perform congestion control, implementing
a receiver driven transport protocol. As it can be useful to have
large chunks (significantly larger than the Maximum Tranfer Unit
across the network), the transport protocol should also be used to
further segment the chunks rather than relying to IP fragmentation.
In this memo we define ICTP (Information Centric Transport Protocol),
a receiver driven transport protocol for ICN, which relies on the
CONET ICN solution described in a companion draft.
Status of this Memo
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This Internet-Draft will expire on November 29, 2012.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. CONET Basics . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ICTP Data Structures . . . . . . . . . . . . . . . . . . . . . 5
3.1. Interest CIU Payload Header . . . . . . . . . . . . . . . 5
3.2. DATA CIU Payload Header . . . . . . . . . . . . . . . . . 6
3.3. EVLE Efficient Variable Length Encoding . . . . . . . . . 7
4. ICTP mechanisms . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Congestion control mechanisms . . . . . . . . . . . . . . 9
4.1.1. Fast recovery and fast retransmit . . . . . . . . . . 9
4.1.2. Slow start and congestion avoidance . . . . . . . . . 9
4.2. ICTP specific mechanisms . . . . . . . . . . . . . . . . . 9
4.2.1. Prefetch option . . . . . . . . . . . . . . . . . . . 9
4.2.2. Request chunk information . . . . . . . . . . . . . . 10
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
6. Performance Considerations . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
[I-D.CONET] proposes an approach to Information Centric Networking
[Koponen07][Jacobson09] based on extending the IP protocol by using a
new IP Option called CONET IP option (defined both for IPv4 [RFC0791]
and IPv6 [RFC2460]). The CONET IP option can be used by routers to
support content aware networking, in addition to classical address
based networking. Further information on the proposed solution can
also be found in [CONET11].
In this memo we define a receiver driven transport protocol for CONET
ICN, called ICTP - Information Centric Transport Protocol. The
transport protocol is able to provide a reliable transfer of the
content and to perform congestion control in TCP-friendly way. A
discussion about the definition of a transport protocol for ICN can
be found in [ICTP12].
As shown in Figure 1, the CONET architecture proposed in [I-D.CONET]
foresees End-Nodes, Serving Nodes and CONET nodes. End-Nodes request
for content. Serving Nodes provide content. CONET nodes: i) forward
content requests from End-Nodes to Serving Nodes; ii) deliver content
from Serving Nodes to End-Nodes; iii) may cache content and therefore
provide it to End-Nodes without contacting the Serving Node.
requests for content
------------------->
content is provided
<-------------------
+----+ +----+ +----+
| | --| |------| |
+----+\ / +----+ +----+
\ +----+ +----+ /
----| |------| |/
+----+ +----+
End-Node legacy Intermediate Border Serving
IP router Node Node Node
| |
+---------CONET next hop----------->+
Figure 1: CONET architecture
2. CONET Basics
In this section we recall the basic aspects of the CONET ICN
solution, as needed to introduce the proposed receiver driven
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Information Centric Transport Protocol (ICTP).
The figure below shows the CONET protocol stack. CONET protocol is
divided in two sub-layers, whose data unit are respectively denoted
as "Carrier Packets" and "CONET Information Units". Two types of
CONET Information Units are currently defined ("Interests CIU" and
"Named Data CIU"). The CONET Information Unit Type field in the
CONET IP option differentiates among the two types. A CONET
Information Unit (CIU) can be split into different Carrier Packets.
Each Carrier Packet is transported by an IP packet.
+--------+--------+--------+ \
| CONET Information Units | |
+--------+--------+--------+ |
|
+--------+--------+--------+ |- CONET protocol
| Carrier Packets | |
+--------+--------+--------+ |
|
+--------+--------+--------+ /
| IP (with CONET IP option)|
+--------+--------+--------+
Figure 2: CONET protocol layers
The generic structure of a Carrier Packet (CP) is reported hereafter:
+-------------------------+
| CP Payload header |
+-------------------------+
| CP Payload |
+-------------------------+
| CP Path state |
+-------------------------+
"Interest CIU" are used by End-Nodes to request for content. The
Interest CIUs contain the identifier of the content called ICN-ID and
transported within the IP CONET Option. Optionally, the IP CONET
option can explicitly carry a "Chunk Sequence Number" to identify one
of the chunk in which a content has been split. Another possibility
is that the chunk number is carried within the ICN-ID itself. A
Serving Node or a CONET node that had previously cached the
information can reply to the content request by sending a "Named-data
CIU". These Named-data CIU will also contain the ICN-ID in the IP
CONET Option.
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The CP payload header contains the length of the CP Payload and
allows to identify the start of the CP Path state field. The use of
CP Path state field was explained in [I-D.CONET] and is out of scope
here.
The information contained in the CP Payload header is specific for
each CIU type. The information transported in the CP Payload header
can be used to implement the functionalities of a transport protocol,
providing a reliable transmission of content and performing
congestion control. In this document we define the CP Payload header
for Interest and Data CIUc using the ICTP protocol.
An end-node that wants to retrieve a content (or better a Chunk of a
content) issues an Interest CIU, the ICN-ID and (optionally) the
Chunk Sequence Number of the required Content are respectively
transported in the ICN Identifier (ICN-ID) field and in the CSN field
of the CONET IP option. Assuming for simplicity that the Interest
CIU will fit into a single Carrier Packet, the Interest CIU will be
included in the Carrier Packet that in turn is inserted into an IP
packet. The ICTP comes into play because a Chunk of content may need
to be fragmented in more than one Carrier Packet, as the chunk size
can be much larger than the layer 2 MTU. For example with a chunk
size of 64 KB or 256 KB and an MTU of 1500 bytes, the chunks need to
be split in tens or hundreds of packets. In this case the RDTP
allows to specify in the request the specific segment of the chunk
that is required.
3. ICTP Data Structures
3.1. Interest CIU Payload Header
The structure of the interest CP payload header is reported
hereafter:
+-------------------------+
|TTrrrrrPI| ..Left Edge...|
+-------------------------+
| ...Right Edge... |
+-------------------------+
Flags:
TT : Transport protocol type. It allows to define different
transport protocols. 0 indicates ICTP which is defined in this draft.
1-3 are reserved and can be used to indicate different transport
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protocols. The rest of the bits in this field and in the following
bytes may have a different semantic depending on the transport
protocol, we are providing here only the defintion for TT=0 i.e. the
ICTP protocol. Therefore the number of transport protocols is NOT
limited to 4.
P : Prefetch flag - This flag indicates that this packet comes from a
receiver that asks to perform prefetch on the content chunks.
I : Ask Chunk Info flag - If this flag is set, the serving node is
requested to add chunk-related information to the data CIU payload,
particularly the chunk size.
Left edge/Right edge : These fields contain respectively the value of
first and the last byte of the requested chunk segment. The fields
are encoded with the EVLE (Efficient Variable Lenght Encoding)
mechanim described below
3.2. DATA CIU Payload Header
The structure of the data CP payload header is reported hereafter:
+-------------------------+
|TTrFSSSS| ...Left Edge...|
+-------------------------+
| ...Right Edge... |
+-------------------------+
| (Optional) Chunk size |
+-------------------------+
Flags:
TT : Transport protocol type. It allows to define different
transport protocols. 0 indicates ICTP which is defined in this draft.
1-3 are reserved and can be used to indicate different transport
protocols. The same considerations apply that have been reported
above for the TT subfield in the interest CIU payload header.
F : Final segment flag - If this bit is set to 1 this carrier packet
carries the last segment of a chunk.
SSSS : Chunk size flag - This flag describes the size of a chunk as
follows:
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0 : unspecified (it may have been already indicated
in a previous data)
1 : the chunk size is trasnported in the optional
Chunk size field, encoded with the EVLE variable length
encoding described below
2-16 : let n be the value from 2 to 16, it can represent
14 different chunk sizes from 2KBytes to 8Mbyte
with the following relation:
chunk size = 2 ^ (9+n)
Left edge/Right edge : These fields contains respectively the value
of first and the last byte of the transported chunk segment. The
fields are encoded with EVLE variable length encoding described
below. These fields carry the actual value of the segment
transported that may differ from the request.
3.3. EVLE Efficient Variable Length Encoding
Some of the fields described above are encoded using a variable
lenght encoding that we denote as "Efficient Variable Lenght
Encoding". The same encoding is used for the Chunk Sequence Number
(CSN) field in the CONET IP Option, as described in [I-D.CONET]. To
help the reader, we report the definition of the encoding hereafter.
An EVLE field is represented with a variable number of bytes. An
initial bit pattern determines the length of the EVLE field.
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1 byte EVLE (7 bits range)
+--------+
|0 |
+--------+
2 bytes EVLE (15 bit range)
+--------+--------+
|10 |
+--------+--------+
3 bytes EVLE (21 bit range)
+--------+--------+--------+
|110 | | |
+--------+--------+--------+
4 bytes EVLE (28 bit range)
+--------+--------+--------+--------+
|1110 | | | |
+--------+--------+--------+--------+
5 bytes EVLE (32 bit range)
+--------+--------+--------+--------+
|11110000| | | |
+--------+--------+--------+--------+
| |
+--------+
6 bytes EVLE (40 bit range)
+--------+--------+--------+--------+
|11110001| | | |
+--------+--------+--------+--------+
| | |
+--------+--------+
As explained in in [I-D.CONET], binary patterns from 11110010 to
11111111 are reserved and could be used to extend the EVLE range if
needed. With the above definion the maximum value is 2^40, roughly 1
Tera.
4. ICTP mechanisms
The transport protocol described in this draft mimics the TPC
mechanisms described in [RFC2581], with the required adaptations for
a receiver driven approach. In fact, while in TCP the sender sends
data segment and implements retransmissions and congestion control
based on the reception of ACKs, in ICN based content download the
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receiver asks for content sending the Interests and implements re-
sending of Interests and congestion control based on the reception of
Data.
4.1. Congestion control mechanisms
4.1.1. Fast recovery and fast retransmit
The receiver bases its flow control on the received data CP. The out
of sequence recognition is based on the expected chunk number and
segment bytes. When three out-of-sequence data CP are received the
slow start threshold (ssthresh, see [RFC2581]) is set to half the
window plus the 3 data carrier packet already received and the
interest for the missing segment is retransmitted.
4.1.2. Slow start and congestion avoidance
To manage the increase of congestion window slow start and congestion
avoidance mechanism are performed. During slow start, (e.g. the
beginning of the connection), the congestion window increases of an
amount equal to the received data CP. This corresponds to an
"exponential" growth of the window. During congestion avoidance, the
growth of the window is aproximately "linear" with time. Let us
define a "segment" as the portion of content transported in a data
CP. We define the congestion window cwnd in segments. During slow
start cwnd = cwnd + 1 for each received data CP. During congestion
avoidance cwnd = cwnd + 1/cwnd for each received data CP.
4.2. ICTP specific mechanisms
4.2.1. Prefetch option
In a ICN based network, we can have applications separately
requesting the download of each chunk of content. In our ICTP
approach this means that we can only request the segments of a given
chunk after that we have received the request for the chunk coming
from the application. The application may implement retransmission
and congestion control, therefore the ICTP could receive requests for
more than a chunk of the same content in parallel. Anyway the
interaction between the congestion control performed at application
level and the congestion control performed at ICTP level could prove
inefficient. Therefore we believe that the API offered to the
application should allow the application to request for a whole
content (or for the content starting from a given chunk number).
Then the ICTP protocol can handle the retrieval of all the (rest of)
the content. Therefore the ICTP protocol offers also a "prefetch
option". Whit the prefetch option active, if the congestion window
has space left, the mechanism allow to issue requests for segments of
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next expected chunks, without waiting for an explicit request from
application level.
4.2.2. Request chunk information
When the transmission start, the receiver must issue a request for at
least the chunk size. Receiver should set the flags in carrier
packet accordingly to Section 3.1. The data ciu requested will carry
at least the chunk size, receiver should use this information to
create data structure best suited for the chunk size.
5. Acknowledgments
We acknowledge the financial support by the EU in the context of the
CONVERGENCE research project.
6. Performance Considerations
7. IANA Considerations
This document requires the allocation of one IP option by the IANA.
This document requires the allocation of one IP protocol number by
the IANA.
This document requires that IANA will maintain the registry of CONET
namespaces.
8. Security Considerations
Security considerations to be provided
9. References
9.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
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June 1999.
9.2. Informative References
[CONET11] A. Detti, et al., "CONET: A Content Centric Inter-
Networking Architecture", ACM SIGCOMM Workshop on
Information-Centric Networking (ICN-2011), Toronto,
Canada , August 2011.
[I-D.CONET]
Detti, A., Salsano, S., and N. Blefari-Melazzi, "An IPv4
Option to support Content Networking",
draft-detti-conet-ip-option-01 (work in progress),
September 2011.
[ICTP12] S. Salsano, et al., "Transport-layer issues in Information
Centric Networks", ACM SIGCOMM Workshop on Information-
Centric Networking (ICN-2012), Helsinki, Finland ,
August 2012.
[Jacobson09]
V. Jacobson, et al., "Networking named content", Proc. of
ACM CoNEXT 2009 , 2009.
[Koponen07]
T. Koponen et al., "A data-oriented (and beyond) network
architecture", Proc. of ACM SIGCOMM 2007 , 2007.
[RFC2581] Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
Control", RFC 2581, April 1999.
Authors' Addresses
Stefano Salsano
Univ. of Rome "Tor Vergata"
Via del Politecnico, 1
Rome 00133
Italy
Email: stefano.salsano@uniroma2.it
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Andrea Detti
Univ. of Rome "Tor Vergata"
Via del Politecnico, 1
Rome 00133
Italy
Email: andrea.detti@uniroma2.it
Nicola Blefari-Melazzi
Univ. of Rome "Tor Vergata"
Via del Politecnico, 1
Rome 00133
Italy
Email: blefari@uniroma2.it
Matteo Cancellieri
Univ. of Rome "Tor Vergata"
Via del Politecnico, 1
Rome 00133
Italy
Email: matteo.cancellieri@gmail.com
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