Internet Engineering Task Force (IETF) E. Haleplidis
Request for Comments: 6369 O. Koufopavlou
Category: Informational S. Denazis
ISSN: 2070-1721 University of Patras
September 2011
Forwarding and Control Element Separation (ForCES)
Implementation Experience
Abstract
The Forwarding and Control Element Separation (ForCES) protocol
defines a standard communication and control mechanism through which
a Control Element (CE) can control the behavior of a Forwarding
Element (FE). This document captures the experience of implementing
the ForCES protocol and model. Its aim is to help others by
providing examples and possible strategies for implementing the
ForCES protocol.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6369.
Copyright Notice
Copyright (c) 2011 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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Document Goal . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 3
3. ForCES Architecture . . . . . . . . . . . . . . . . . . . . . 4
3.1. Pre-Association Setup - Initial Configuration . . . . . . 5
3.2. TML . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Model . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. Components . . . . . . . . . . . . . . . . . . . . . . 6
3.3.2. LFBs . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.4. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4.1. TLVs . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4.2. Message Deserialization . . . . . . . . . . . . . . . 13
3.4.3. Message Serialization . . . . . . . . . . . . . . . . 15
4. Development Platforms . . . . . . . . . . . . . . . . . . . . 15
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Normative References . . . . . . . . . . . . . . . . . . . 17
7.2. Informative References . . . . . . . . . . . . . . . . . . 17
1. Introduction
Forwarding and Control Element Separation (ForCES) defines an
architectural framework and associated protocols to standardize
information exchange between the control plane and the forwarding
plane in a ForCES Network Element (ForCES NE). [RFC3654] defines the
ForCES requirements, and [RFC3746] defines the ForCES framework.
The ForCES protocol works in a master-slave mode in which Forwarding
Elements (FEs) are slaves and Control Elements (CEs) are masters.
The protocol includes commands for transport of Logical Functional
Block (LFB) configuration information, association setup, status, and
event notifications, etc. The reader is encouraged to read the
Forwarding and Control Element Separation Protocol [RFC5810] for
further information.
[RFC5812] presents a formal way to define FE LFBs using XML. LFB
configuration components, capabilities, and associated events are
defined when LFBs are formally created. The LFBs within the
Forwarding Element (FE) are accordingly controlled in a standardized
way by the ForCES protocol.
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The Transport Mapping Layer (TML) transports the protocol messages.
The TML is where the issues of how to achieve transport-level
reliability, congestion control, multicast, ordering, etc., are
handled. It is expected that more than one TML will be standardized.
The various possible TMLs could vary their implementations based on
the capabilities of underlying media and transport. However, since
each TML is standardized, interoperability is guaranteed as long as
both endpoints support the same TML. All ForCES protocol layer
implementations must be portable across all TMLs. Although more than
one TML may be standardized for the ForCES protocol, all ForCES
implementations must implement the Stream Control Transmission
Protocol (SCTP) TML [RFC5811].
The Forwarding and Control Element Separation Applicability Statement
[RFC6041] captures the applicable areas in which ForCES can be used.
1.1. Document Goal
This document captures the experience of implementing the ForCES
protocol and model, and its main goal is to provide alternatives,
ideas, and proposals as how it can be implemented, not to tell others
how to implement it.
Also, this document mentions possible problems and potential choices
that can be made, in an attempt to help implementors develop their
own products.
Additionally, this document assumes that the reader has become
familiar with the three main ForCES RFCs: the Forwarding and Control
Element Separation Protocol [RFC5810], the Forwarding and Control
Element Separation Forwarding Element Model [RFC5812], and the SCTP-
Based Transport Mapping Layer (TML) for the Forwarding and Control
Element Separation Protocol [RFC5811].
2. Terminology and Conventions
The terminology used in this document is the same as in the
Forwarding and Control Element Separation Protocol [RFC5810]; some of
the definitions below are copied from that document.
Control Element (CE): A logical entity that implements the ForCES
protocol and uses it to instruct one or more FEs on how to process
packets. CEs handle functionality such as the execution of control
and signaling protocols.
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Forwarding Element (FE): A logical entity that implements the ForCES
protocol. FEs use the underlying hardware to provide per-packet
processing and handling as directed/controlled by one or more CEs via
the ForCES protocol.
LFB (Logical Functional Block): The basic building block that is
operated on by the ForCES protocol. The LFB is a well-defined,
logically separable functional block that resides in an FE and is
controlled by the CE via the ForCES protocol. The LFB may reside at
the FE's data path and process packets or may be purely an FE control
or configuration entity that is operated on by the CE. Note that the
LFB is a functionally accurate abstraction of the FE's processing
capabilities but not a hardware-accurate representation of the FE
implementation.
LFB Class and LFB Instance: LFBs are categorized by LFB classes. An
LFB instance represents an LFB class (or type) existence. There may
be multiple instances of the same LFB class (or type) in an FE. An
LFB class is represented by an LFB class ID, and an LFB instance is
represented by an LFB instance ID. As a result, an LFB class ID
associated with an LFB instance ID uniquely specifies an LFB
existence.
LFB Component: Operational parameters of the LFBs that must be
visible to the CEs are conceptualized in the FE model as the LFB
components. The LFB components include, for example, flags, single
parameter arguments, complex arguments, and tables that the CE can
read and/or write via the ForCES protocol.
ForCES Protocol: While there may be multiple protocols used within
the overall ForCES architecture, the terms "ForCES protocol" and
"protocol" refer to the Fp reference points in the ForCES framework
[RFC3746]. This protocol does not apply to CE-to-CE communication,
FE-to-FE communication, or communication between FE and CE Managers.
Basically, the ForCES protocol works in a master-slave mode in which
FEs are slaves and CEs are masters. This document defines the
specifications for this ForCES protocol.
3. ForCES Architecture
ForCES has undergone two successful interoperability tests, where
very few issues were caught and resolved.
This section discusses the ForCES architecture, implementation
challenges, and ways to overcome these challenges.
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3.1. Pre-Association Setup - Initial Configuration
The initial configuration of the FE and the CE is done by the FE
Manager and the CE Manager, respectively. These entities have not as
yet been standardized.
The simplest solution is static configuration files, which play the
role of the Managers and are read by FEs and CEs.
For more dynamic solutions, however, it is expected that the Managers
will be entities that will talk to each other and exchange details
regarding the associations. Any developer can create any Manager,
but they should at least be able to exchange the details below.
From the FE Manager side:
1. FE Identifiers (FEIDs).
2. FE IP addresses, if the FEs and CEs will be communicating via
network.
3. TML. The TML that will be used. If this is omitted, then SCTP
must be chosen as default.
4. TML priority ports. If this is omitted as well, then the CE must
use the default values from the respective TML RFC.
From the CE Manager side:
1. CE Identifiers (CEIDs).
2. CE IP addresses, if the FEs and CEs will be communicating via
network.
3. TML. The TML that will be used. If this is omitted, then SCTP
must be chosen as default.
4. TML priority ports. If this is omitted as well, then the FE must
use the default values from the respective TML RFC.
3.2. TML
All ForCES implementations must support the SCTP TML. Even if
another TML will be chosen by the developer, SCTP is mandatory and
must be supported.
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There are several issues that should concern a developer for the TML:
1. Security. TML must be secure according to the respective RFC.
For SCTP, you have to use IPsec.
2. Remote connection. While ForCES is meant to be used locally,
both interoperability tests have proven that ForCES can be
deployed everywhere that SCTP/IP is available. In both
interoperability tests, there were connections between Greece and
China, and the performance was very satisfactory. However, in
order for the FE and CE to work in a non-local environment, an
implementor must ensure that the SCTP-TML ports are forwarded to
the CE and/or FE if they are behind NATs; if there is a firewall,
it will allow the SCTP ports through. These were identified
during the first ForCES interoperability test and documented in
the Implementation Report for Forwarding and Control Element
Separation [RFC6053].
3.3. Model
The ForCES model is inherently very dynamic. Using the basic atomic
data types that are specified in the model, new atomic (single
valued) and/or compound (structures and arrays) datatypes can be
built. Thus, developers are free to create their own LFBs. One
other advantage that the ForCES model provides is inheritance. New
versions of existing LFBs can be created to suit any extra developer
requirements.
The difficulty for a developer is to create an architecture that is
completely scalable so there is no need to write the same code for
new LFBs, new components, etc. Developers can just create code for
the defined atomic values, and new components can then be built based
on already written code, thus reusing it.
The model itself provides the key, which is inheritance.
3.3.1. Components
First, a basic component needs to be created as the mother of all the
components that has the basic parameters of all the components:
o The ID of the component.
o The access rights of the component.
o If it is an optional component.
o If it is of variable size.
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o Minimum data size.
o Maximum data size.
If the data size of the component is not variable, then the size is
either the minimum or the maximum size, as both should have the same
value.
Next, some basic functions are in order:
o A common constructor.
o A common destructor.
o Retrieve Component ID.
o Retrieve access right property.
o Query if it is an optional component.
o Get Full Data.
o Set Full Data.
o Get Sparse Data.
o Set Sparse Data.
o Del Full Data.
o Del Sparse Data.
o Get Property.
o Set Property.
o Get Value.
o Set Value.
o Del Value.
o Get Data.
o Clone component.
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The Get/Set/Del Full Data, Get/Set/Del Sparse Data, and Get/Set
Property functions handle the respective ForCES commands and return
the respective TLV, for example, Set Full Data should return a
RESULT-TLV. The Get Value, Set Value, and Del Value functions are
called from Get Full/Sparse Data, Set Full/Sparse Data, and Del Full/
Sparse Data respectively and provide the interface to the actual
values in the hardware, separating the forces handling logic from the
interface to the actual values.
The Get Data function should return the value of the data only, not
in TLV format.
The Clone function seems out of place. This function must return a
new component that has the exact same values and attributes. This
function is useful in array components as described further below.
The only requirement is to implement the base atomic data types. Any
new atomic datatype can be built as a child of a base data type,
which will inherit all the functions and, if necessary, override
them.
The struct component can then be built. A struct component is a
component by itself but consists of a number of atomic components.
These atomic components create a static array within the struct. The
ID of each atomic component is the array's index. For a struct
component, the Clone function must create and return an exact copy of
the struct component with the same static array.
The most difficult component to be built is the array. The
difficulty lies in the actual benefit of the model: you have absolute
freedom over what you build. An array is an array of components. In
all rows, you have the exact same type of component, either a single
component or a struct. The struct can have multiple single
components or a combination of single components, structs, arrays,
and so on. So, the difficulty lies in how to create a new row, a new
component by itself. This is where the Clone function is very
useful. For the array, a mother component that can spawn new
components exactly like itself is needed. Once a Set command is
received, the mother component can spawn a new component if the
targeted row does not exist and add it into the array; with the Set
Full Data function, the value is set in the recently spawned
component, as the spawned component knows how the data is created.
In order to distinguish these spawned components from each other and
their functionality, some kind of index is required that will also
reflect how the actual data of the specific component is stored on
the hardware.
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Once the basic constructors of all possible components are created,
then a developer only has to create LFB components or datatypes as a
child of one of the already-created components, and the only thing
the developer really needs to add is the three functions of Get
Value, Set Value, and Del Value of each component, which is platform
dependent. The rest stays the same.
3.3.2. LFBs
The same architecture in the components can be used for the LFBs,
allowing a developer to write LFB handling code only once. The
parent LFB has some basic attributes:
o The LFB Class ID.
o The LFB Instance ID.
o An Array of Components.
o An Array of Capabilities.
o An Array of Events.
Following are some common functions:
o Handle Configuration Command.
o Handle Query Command.
o Get Class ID.
o Get Instance ID.
Once these are created, each LFB can inherit all these from the
parent, and the only thing it has to do is add the components that
have already been created.
An example can be seen in Figure 1. The following code creates a
part of FEProtocolLFB:
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//FEID
cui = new Component_uInt(FEPO_FEID, ACCESS_READ_ONLY, FE_id);
Components[cui->get_ComponentId()]=cui; //Add component to array list
//Current FEHB Policy Value
cub = new Component_uByte(FEPO_FEHBPolicy, ACCESS_READ_WRITE, 0);
Components[cub->get_ComponentId()]=cub; //Add component to array list
//FEIDs for BackupCEs Array
cui = new Component_uInt(0, ACCESS_READ_WRITE, 0);
ca = new Component_Array(FEPO_BackupCEs, ACCESS_READ_WRITE);
ca->AddRow(cui, 1);
ca->AddMotherComponent(cui);
Components[ca->get_ComponentId()]=ca; //Add component to array list
Figure 1: Example Code for Creating Part of FEProtocolLFB
The same concept can be applied to handling LFBs as one FE. An FE is
a collection of LFBs. Thus, all LFBs can be stored in an array based
on the LFB's class id, version, and instance. Then, what is required
is an LFBHandler that will handle the array of LFBs. A specific LFB,
for example, can be addressed using the following scheme:
LFBs[ClassID][Version][InstanceID]
Note: While an array can be used in components, capabilities, and
events, a hash table or a similar concept is better suited for
storing LFBs using the component ID as the hash key with linked lists
for collision handling, as the created array can have large gaps if
the values of LFB Class ID vary greatly.
3.4. Protocol
3.4.1. TLVs
The goal for protocol handling is to create a general and scalable
architecture that handles all protocol messages instead of something
implementation specific. There are certain difficulties that have to
be overcome first.
Since the model allows a developer to define any LFB required, the
protocol has been thus created to give the user the freedom to
configure and query any component, whatever the underlying model.
While this is a strong point for the protocol itself, one difficulty
lies with the unknown underlying model and the unlimited number of
types of messages that can be created, making creating generic code a
daunting task.
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Additionally, the protocol also allows two different path approaches
to LFB components, and the CE or FE must handle both or even a mix of
them, making a generic decoding of the protocol message difficult.
Another difficulty also arises from the batching capabilities of the
protocol. You can have multiple Operations within a message; you can
select more than one LFB to command and more than one component to
manipulate.
A possible solution is again provided by inheritance. There are two
basic components in a protocol message:
1. The common header.
2. The rest of the message.
The rest of the message is divided in Type-Length-Value (TLV) units
and, in one case, Index-Length-Value (ILV) units.
The TLV hierarchy can be seen in Figure 2:
Common Header
|
+---------------+---------------+---------------+
| | | |
REDIRECT-TLV LFBselect-TLV ASResult-TLV ASTreason-TLV
|
|
OPER-TLV
|
|
PATH-DATA-TLV ---> Optional KEYINFO-TLV
|
+-------------+-------------+-------------+
| | | |
SPARSEDATA-TLV RESULT-TLV FULLDATA-TLV PATH-DATA-TLV
Figure 2: ForCES TLV Hierarchy
The above figure shows only the basic hierarchical level of TLVs and
does not show batching. Also, this figure does not show the
recursion that can occur at the last level of the hierarchy. The
figure shows one kind of recursion with a PATH-DATA-TLV within a
PATH-DATA-TLV. A FULLDATA-TLV can be within a FULLDATA-TLV and a
SPARSEDATA-TLV. The possible combination of TLVs are described in
detail in the Forwarding and Control Element Separation Protocol
[RFC5810] as well as the data-packing rules.
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A TLV's main attributes are:
o Type.
o Length.
o Data.
o An array of TLVs.
The array of TLVs is the next hierarchical level of TLVs nested in
this TLV.
A TLV's common function could be:
o A basic constructor.
o A constructor using data from the wire.
o Add a new TLV for next level.
o Get the next TLV of next level.
o Get a specific TLV of next level.
o Replace a TLV of next level.
o Get the Data.
o Get the Length.
o Set the Data.
o Set the Length.
o Set the Type.
o Serialize the header.
o Serialize the TLV to be written on the wire.
All TLVs inherit these functions and attributes and either override
them or create new where it is required.
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3.4.2. Message Deserialization
Following is an algorithm for deserializing any protocol message:
1. Get the message header.
2. Read the length.
3. Check the message type to understand what kind of message this
is.
4. If the length is larger than the message header, then there is
data for this message.
5. A check can be made here regarding the message type and the
length of the message.
If the message is a Query or Config type, then there are LFBselect-
TLVs for this level:
1. Read the next 2 shorts(type-length). If the type is an
LFBselect-TLV, then the message is valid.
2. Read the necessary length for this LFBselect-TLV, and create the
LFBselect-TLV from the data of the wire.
3. Add this LFBselect-TLV to the main header array of LFBselect-
TLVs.
4. Repeat all above steps until the rest of the message has
finished.
The next level of TLVs is OPER-TLVs.
1. Read the next 2 shorts(type-length). If the type is an OPER-TLV,
then the message is valid.
2. Read the necessary length for this OPER-TLV, and create the OPER-
TLV from the data of the wire.
3. Add this OPER-TLV to the LFBselect-TLV array of TLVs.
4. Do this until the rest of the LFBselect-TLV has finished.
The next level of TLVs is PATH-DATA-TLVs.
1. Read the next 2 shorts(type-length). If the type is a PATH-DATA-
TLV, then the message is valid.
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2. Read the necessary length for this PATH-DATA-TLV, and create the
PATH-DATA-TLV from the data of the wire.
3. Add this PATH-DATA-TLV to the OPER-TLV's array of TLVs.
4. Do this until the rest of the OPER-TLV is finished.
Here it gets interesting, as the next level of PATH-DATA-TLVs can be
one of the following:
o PATH-DATA-TLVs.
o FULLDATA-TLV.
o SPARSEDATA-TLV.
o RESULT-TLV.
The solution to this difficulty is recursion. If the next TLV is a
PATH-DATA-TLV, then the PATH-DATA-TLV that is created uses the same
kind of deserialization until it reaches a FULLDATA-TLV or
SPARSEDATA-TLV. There can be only one FULLDATA-TLV or SPARSEDATA-TLV
within a PATH-DATA-TLV.
1. Read the next 2 shorts(type-length).
2. If the Type is a PATH-DATA-TLV, then repeat the previous
algorithm but add the PATH-DATA-TLV to this PATH-DATA-TLV's array
of TLVs.
3. Do this until the rest of the PATH-DATA-TLV is finished.
4. If the Type is a FULLDATA-TLV, then create the FULLDATA-TLV from
the message and add this to the PATH-DATA-TLV's array of TLVs.
5. If the Type is a SPARSEDATA-TLV, then create the SPARSEDATA-TLV
from the message and add this to the PATH-DATA-TLV's array of
TLVs.
6. If the Type is a RESULT-TLV, then create the RESULT-TLV from the
message and add this to the PATH-DATA-TLV's array of TLVs.
If the message is a Query, it must not have any kind of data inside
the PATH-DATA-TLV.
If the message is a Query Response, then it must have either a
RESULT-TLV or a FULLDATA-TLV.
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If the message is a Config, it must contain either a FULLDATA-TLV or
a SPARSEDATA-TLV.
If the message is a Config Response, it must contain a RESULT-TLV.
More details regarding message validation can be read in Section 7 of
the Forwarding and Control Element Separation Protocol [RFC5810].
Note: When deserializing, implementors must take care to ignore
padding of TLVs as all must be 32-bit aligned. The length value in
TLVs includes the Type and Length (4 bytes) but does not include
padding.
3.4.3. Message Serialization
The same concept can be applied in the message creation process.
Having the TLVs ready, a developer can go bottom up. All that is
required is the serialization function that will transform the TLV
into bytes ready to be transferred on the network.
For example, for the creation of a simple query from the CE to the
FE, all the PATH-DATA-TLVs are created. Then they will be serialized
and inserted into an OPER-TLV, which in turn will be serialized and
inserted into an LFBselect-TLV. The LFBselect-TLV will then be
serialized and entered into the Common Header, which will be passed
to the TML to be transported to the FE.
Having an array of TLVs inside a TLV that is next in the TLV
hierarchy allows the developer to insert any number of next-level
TLVs, thus creating any kind of message.
Note: When the TLV is serialized to be written on the wire,
implementors must take care to include padding to TLVs as all must be
32-bit aligned.
4. Development Platforms
Any development platform that can support the SCTP TML and the TML of
the developer's choosing is available for use.
Figure 3 provides an initial survey of SCTP support for C/C++ and
Java at the present time.
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/-------------+-------------+-------------+-------------\
|\ Platform | | | |
| ----------\ | Windows | Linux | Solaris |
| Language \| | | |
+-------------+-------------+-------------+-------------+
| | | | |
| C/C++ | Supported | Supported | Supported |
| | | | |
+-------------+-------------+-------------+-------------+
| | Limited | | |
| Java | Third Party | Supported | Supported |
| | Not from SUN| | |
\-------------+-------------+-------------+-------------/
Figure 3: SCTP Support on Operating Systems
A developer should be aware of some limitations regarding Java
implementations.
Java inherently does not support unsigned types. A workaround can be
found in the creation of classes that do the translation of unsigned
types to Java types. The problem is that the unsigned long cannot be
used as-is in the Java platform. The proposed set of classes can be
found in [JavaUnsignedTypes].
5. Acknowledgements
The authors would like to thank Adrian Farrel for sponsoring this
document and Jamal Hadi Salim for discussions that made this document
better.
6. Security Considerations
Developers of ForCES FEs and CEs must take the Security
Considerations of the Forwarding and Control Element Separation
Framework [RFC3746] and the Forwarding and Control Element Separation
Protocol [RFC5810] into account.
Also, as specified in the Security Considerations section of the
SCTP-Based Transport Mapping Layer (TML) for the Forwarding and
Control Element Separation Protocol [RFC5811], transport-level
security has to be ensured by IPsec.
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7. References
7.1. Normative References
[RFC5810] Doria, A., Hadi Salim, J., Haas, R., Khosravi, H., Wang,
W., Dong, L., Gopal, R., and J. Halpern, "Forwarding and
Control Element Separation (ForCES) Protocol
Specification", RFC 5810, March 2010.
[RFC5811] Hadi Salim, J. and K. Ogawa, "SCTP-Based Transport Mapping
Layer (TML) for the Forwarding and Control Element
Separation (ForCES) Protocol", RFC 5811, March 2010.
[RFC5812] Halpern, J. and J. Hadi Salim, "Forwarding and Control
Element Separation (ForCES) Forwarding Element Model",
RFC 5812, March 2010.
[RFC6041] Crouch, A., Khosravi, H., Doria, A., Wang, X., and K.
Ogawa, "Forwarding and Control Element Separation (ForCES)
Applicability Statement", RFC 6041, October 2010.
[RFC6053] Haleplidis, E., Ogawa, K., Wang, W., and J. Hadi Salim,
"Implementation Report for Forwarding and Control Element
Separation (ForCES)", RFC 6053, November 2010.
7.2. Informative References
[JavaUnsignedTypes]
"Java Unsigned Types",
<http://nam.ece.upatras.gr/index.php?q=node/44>.
[RFC3654] Khosravi, H. and T. Anderson, "Requirements for Separation
of IP Control and Forwarding", RFC 3654, November 2003.
[RFC3746] Yang, L., Dantu, R., Anderson, T., and R. Gopal,
"Forwarding and Control Element Separation (ForCES)
Framework", RFC 3746, April 2004.
Haleplidis, et al. Informational [Page 17]
RFC 6369 ForCES Implementation Experience September 2011
Authors' Addresses
Evangelos Haleplidis
University of Patras
Department of Electrical & Computer Engineering
Patras 26500
Greece
EMail: ehalep@ece.upatras.gr
Odysseas Koufopavlou
University of Patras
Department of Electrical & Computer Engineering
Patras 26500
Greece
EMail: odysseas@ece.upatras.gr
Spyros Denazis
University of Patras
Department of Electrical & Computer Engineering
Patras 26500
Greece
EMail: sdena@upatras.gr
Haleplidis, et al. Informational [Page 18]