Internet DRAFT - draft-ravi-icnrg-ccn-notification
draft-ravi-icnrg-ccn-notification
ICN Research Group R. Ravindran
Internet-Draft A. Chakraborti
Intended status: Informational S. Amin
Expires: January 17, 2018 Huawei Technologies
J. Chen
Winlab, Rutgers University
July 16, 2017
Support for Notifications in CCN
draft-ravi-icnrg-ccn-notification-01
Abstract
This draft proposes a new packet primitive called Notification for
CCN. Notification is a PUSH primitive and can be unicast or
multicast to multiple listening points. Notifications do not expect
a Content Object response hence only requires the use of FIB state in
the CCN forwarder. Emulating Notification as a PULL has performance
and routing implications. The draft first discusses the design
choices associated with using current Interest/Data abstraction for
achieving push and challenges associated with them. We follow this
by proposing a new fixed header primitive called Notification and a
CCN message encoding using Content Object primitive to transport
Notifications. This discussion are presented in the context of
CCNx1.0 [1] proposal. The draft also provides discussions on various
aspects related to notification such as flow and congestion control,
routing and reliability considerations, and use case scenarios.
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). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 17, 2018.
Ravindran, et al. Expires January 17, 2018 [Page 1]
Internet-Draft Interest Notification July 2017
Copyright Notice
Copyright (c) 2017 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
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
2. Notification Requirements in CCN . . . . . . . . . . . . . . 3
3. Using Interest/Data Abstraction for PUSH . . . . . . . . . . 4
4. Proposed Notification Primitive in CCN . . . . . . . . . . . 9
5. Notification Message Encoding . . . . . . . . . . . . . . . . 10
6. Notification Processing . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Annex . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Flow and Congestion Control . . . . . . . . . . . . . . . 13
8.1.1. Issues with Basic Notifications . . . . . . . . . . . 13
8.1.2. Flow and Congestion Control Mechanims . . . . . . . . 14
8.1.2.1. End-to-End Approaches . . . . . . . . . . . . . . 14
8.1.2.2. Hybrid Approaches . . . . . . . . . . . . . . . . 15
8.1.3. Receiver Reliability . . . . . . . . . . . . . . . . 17
8.2. Routing Notifications . . . . . . . . . . . . . . . . . . 18
8.3. Notification reliability . . . . . . . . . . . . . . . . 18
8.4. Use Case Scenarios . . . . . . . . . . . . . . . . . . . 19
8.4.1. Realizing PUB/SUB System . . . . . . . . . . . . . . 19
9. Informative References . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
Notification is a PUSH primitive used in the Internet today by many
IoT and social applications. The nature of notifications varies with
the application scenario, ranging from being mission critical to one
that is best effort. Notifications can be unicast or multicast
depending on whether the notification service is aware of all the
consumers or not. A notification service is preceded by a consumer
subscribing to a specific event such as, subscription to hash-tag
feeds, health emergency notification service, or temperature sensor
Ravindran, et al. Expires January 17, 2018 [Page 2]
Internet-Draft Interest Notification July 2017
reading from a room in a building; following this subscription the
service pushes notifications to consuming entities. It has to be
noted that certain IoT applications expects notification end-to-end
latency of few milliseconds [2]. Industrial IoT applications have
more stringent requirement in terms of QoS, timeliness, and
reliability of message delivery. Though we term it as a
Notification, this primitive can also be used for transactional
exchange between two points.
CCN optimizes networking around efficiently distributing already
published content which the consumers learn through mechanisms like
manifests containing the names of published content chunks and their
locations. Applications relying on notifications requires event
driven data to be pushed from multiple producers to multiple
subscribers for which the current Interest/Data primitive is
inefficient. This draft proposes to extend CCN's current primitives
set with a new notification primitive that can be processed in a new
way by the CCN forwarder to serve notification objectives.
Notification here implies a PUSH semantic that is available with IP
today and supported by other FIA architectures like MobilityFirst [3]
and XIA [4].
2. Notification Requirements in CCN
General notification requirements and features have been discussed
have been discussed in protocols such as CoAP's Observe proposal [5]
to push notifications from the server to the clients. Here we
discuss basic notification requirements from CCN's network layer
perspective. Other requirements related to reliability, low latency,
flow control can be engineered by the application or through more
network layer state once the following requirements are met.
o Supporting PUSH Intent: CCN should provide efficient and scalable
support for PUSH, where application's intent is to PUSH content to
listening application without expecting any data in return.
Efficiency relates to minimimizing control and forwarding overhead
and scalability refers to support arbitrary number of producers
and consumers participating in a general pub/sub or multicast
service.
o Multicast Support: CCN network should be able to handle multicast
notifications from a producer to multiple consumers.
o Security: Just as a content object in the context of Interest/Data
primitive provides data authentication and privacy, similar
features should also be offered by notification objects too.
Ravindran, et al. Expires January 17, 2018 [Page 3]
Internet-Draft Interest Notification July 2017
o Routing/Forwarding Support: Name prefixes over which multicast
notifications are managed should be handled in a different manner
from the name prefixes over which Interest/Data primitive is used
for content distribution in order to support the PUSH intent.
This differentiation applies to the control as well as the
forwarding plane.
o Minimizing Processing: Notification processing in the forwarder
should be minimized considering the application's intent to PUSH
data to listening consumers.
3. Using Interest/Data Abstraction for PUSH
Recent CCN and NDN research [6][7] have studied the problem of
handling notifications and have proposed several solutions to handle
this. Here, we discuss several of them and point out their benefits
and issues:
Long-lived Interest v.1: The most intuitive solution makes the
assumption that the consumers know exactly the names of the
contents that will be published in the future. Yet, it is not
easy since the providers can give arbitrary names to each piece of
content, even though the contents might share a common prefix
(i.e., GROUP_PREFIX). To make it feasible, the providers can
publish the contents with sequential ID, e.g., /GROUP_PREFIX/
SENQUENTIAL_ID[/SEGMENT_ID], so that the consumers can query the
contents with names /GROUP_ID/item_1, /GROUP_ID/item_2, ... (each
name represents a content item). The consumers can pipeline the
requests (always keep some unsatisfied requests in flight, similar
to TCP) to better utilize the network capacity.
However, this solution has several issues, especially in the
multi-provider scenario:
* Since it is unknown to the consumer (and the network) which
provider will use which sequential ID, each request has to be
forwarded to all the possible providers. This solution might
use up a large amount of state (PIT entries) in the network, as
each consumer can keep tens of requests (to all providers) in
flight for each group.
* Since each sequential ID should only be used by one provider,
many PIT entries will not be consumed until timeout (if there
is a timeout mechanism). E.g., P1 and P2 are 2 providers of a
group (/GROUP), the consumers have to send requests /GROUP/
item_1, and /GROUP/item_2 to both providers. Assume that P1
publishes first so he uses the name /GROUP/item_1. The PIT
Ravindran, et al. Expires January 17, 2018 [Page 4]
Internet-Draft Interest Notification July 2017
entries for /GROUP/item_1 towards P2 will not be consumed since
P2 should now publish with name /GROUP/item_2.
* When the PIT entries form loops in the network (it can happen
quite often in the multi-provider, multi-consumer scenario),
the data packets can waste network traffic while following the
loops and get discarded when redundancy happens.
* Other than the inefficiencies mentioned above, one major issue
with this solution is the difficulty of provider
synchronization. It is not easy to make sure that different
providers would use different sequential IDs especially when
the providers are publishing contents at the same time.
Polling v.1: To eliminate the requirement for a sequential ID when
publishing (to address the synchronization issue), the solution
Polling v.1 makes the providers publish contents with name format:
/GROUP_ID/TIMESTAMP. While querying the contents, the consumer
query using name /GROUP_ID/ with "exclude" field <Earliest version
after Tx>, where Tx is the latest version the consumer has
received. E.g., after receiving a content with name /GROUP_ID/
v_1234 (v_1234 is the timestamp of the publication time), the
consumer would send a query with name /GROUP_ID/<Earliest after
v_1234>. He might get the next piece with name /GROUP_ID/v_2345
(assuming that there is no content published between these two
time stamps) without the need to know the exact names of the
contents. The content providers do not have to be synchronized on
the sequential IDs and use the timestamp instead.
While this solution is similar to the one used in NDN for getting
the "latest" version under a prefix, it has several issues when we
need to get "all" versions under a prefix:
* Ambiguity contents will appear when two providers of a same
group publish at the same time.
* Consumers might miss messages when the clocks are not
synchronized on the providers. E.g., one provider (with faster
clock) might publish a content with name /GROUP_ID/v_2345 after
v_1234. When the consumer queries for the earliest version
after v_1234, he will get the content. Yet, another provider
(with slower clock) would publish a content with name
/GROUP_ID/v_2234 after the consumer gets v_2345. The consumer
would miss the content with v_2234 as he will query for
<Earliest after v_2345>.
* Consumers might miss messages due to different delivery latency
(e.g., cache hit vs. no cache hit) even when the clocks on the
Ravindran, et al. Expires January 17, 2018 [Page 5]
Internet-Draft Interest Notification July 2017
providers are perfectly synchronized (e.g., via GPS signals).
E.g., when a client queries for content /GROUP_ID/<Earliest
after v_1234>, and there are two pieces of content exist in the
network (v_2234, and v_2345). It can happen that v_2345 is
returned earlier (either due to a cache hit or because the
provider is closer). The consumer would then query for
<Earliest after v_2345> and miss v_2234 with this solution.
* Also just as with the previous approach, this mechanism also
requires the producers to sync so that they don't produce
content using the same name.
Long-lived Interest v.2: To completely address the issues with
multiple providers sharing a same prefix (e.g., synchronization in
Long-lived Interest v.1, and clock synchronization in Polling
v.1), Long-lived Interest v.2 gives a prefix to each provider.
The providers in this solution provide contents with name
/GROUP_ID/PROVIDER_ID/SEQUENTIAL_ID, and the consumers query the
full names accordingly (similar to Long-lived Interest v.1 but
with an extra prefix PROVIDER_ID). The consumer can still use
pipelining to improve the throughput.
While this solution can avoid packet losses in the previous
solution, it has several other issues:
* Consumers have to know all the potential providers, which might
be difficult in some applications where every user can send
messages in any group that he might be interested in.
* Compared to Long-lived Interest v.1, the consumers in this
solution have to keep multiple pending queries per group per
provider. It might consume even more states in the network,
which makes the solution less scalable.
* When a provider has more than one device (e.g., laptop and
smartphone) that can publish contents under a same name
/GROUP_ID/PROVIDER_ID, the solution would have the same
synchronization issue as Long-lived Interest v.1. If the
solution mandates each device to have a separate provider ID,
it will end up with even more PIT entries (states) in the
network, and the solution becomes less "information-centric".
Polling v.2: To reduce the states and the control overhead in Long-
lived Interest v.2, the solution Polling v.2 allows the provider
process the requests in the application layer. Periodically, the
consumer would query each provider "if there is any update after
Nx" (Nx is name of the last content the consumer has received).
The query would be in the format: /GROUP_ID/PROVIDER_ID/Nx/NONCE.
Ravindran, et al. Expires January 17, 2018 [Page 6]
Internet-Draft Interest Notification July 2017
The provider would reply aggregated results in one response (with
different segments, but under the same name), and an indication of
"no update" if there is no publication after Nx. Since a same
query for /GROUP_ID/PROVIDER_ID/Nx can get different responses
("no update", or aggregated publications), a NONCE has to be added
in the name to prevent possible cache hits in the network. This
solution can be effective in games since the publication rate
(actions of the provider in the game) is much higher than the
polling rate (refresh rate on the consumer). However, it still
has some issues (inefficiencies):
* There is a tradeoff between timeliness vs. in-network traffic
when choosing the polling frequency. The solution can be
inefficient when the polling is too frequent: most of the
polling will get "no update" responses. This can consume a
large amount of traffic in the network and extra computation on
both the providers and the consumers. The timeliness can be
impaired when the polling is infrequent since the publication
can only reach the consumer when the consumer queries. The
average delivery time of a publication in such solution is half
of the polling period.
* In-network cache cannot be used since the response to a same
query (without nonce) can be different according to the time
(and maybe the consumer).
* Consumers still have to know all the potential providers
similar to Long-lived Interest v.2.
Polling with A Server: To relieve the consumers from knowing all
potential providers in Polling v.2, solution Polling with A Server
introduces a server (or broker) as the delegate of all the
providers. The providers would publish data into the server and
the consumers would poll for the updates from the server (similar
to Twitter and Facebook in IP network). In this solution, the
consumers do not have to poll each provider for the updates, which
reduces the overhead in the network. With the aggregated response
on the server, the network traffic is further reduced. However,
it still has several issues:
* Similar to all the server-based solutions like Facebook and
Twitter, the server has to deal with all the polls. This can
cause single point of failure.
* It is not easy for the providers "publish contents to the
server". This becomes another notification problem and has to
be solved by the other solutions mentioned in this section.
Ravindran, et al. Expires January 17, 2018 [Page 7]
Internet-Draft Interest Notification July 2017
* Cache is not used in this solution similar to Polling v.2.
* This solution is not really "information-centric" as the
consumers have to get the location of the content rather than
the content itself.
Interest Overloading: Since all the aforementioned query/response
solutions have issues with efficiency, scalability and/or
timeliness, Interest Overloading tries to modify the communication
pattern by using Interest packets to deliver publications
directly. The consumers in this solution propagate FIB entry of
/GROUP_ID to all potential providers (or simply flood the
network). When a provider sends a publication, he would send an
Interest with name /GROUP_ID/NONCE/<Payload> and the lifetime set
to zero. Since the traditional Interest packets do not have
payload, the solution has to embed (e.g., URL encode [1]) the
payload in the name of the Interest. NONCE is used to prevent PIT
aggregation since providers may publish contents with same payload
(e.g., sensor readings). This solution can address the timeliness
and scalability issues with the Polling and Long-lived Interest
solutions, yet there are still some issues:
* This solution creates ambiguity in the meaning of Interest
packets (and the corresponding forwarding behaviors on the
routers). For a normal Interest packet, the forwarding engines
should perform an anycast (send it to only one of the
providers) according to FIB. However, in this solution, the
forwarding engines should use multicast logic for prefix
/GROUP_ID (and avoid PIT storage). Solution in [8] specifies
some multicast prefixes so that the forwarding engines can
distinguish the publications from the normal requests. Yet,
this places higher overhead on both the forwarding engines and
the network management. It also prevents providers to create
contents under the /GROUP_ID prefix (since the query will be
forwarded using multicast, and not kept in the PIT).
* The routing is also a concern in this solution. When the
consumers propagate FIB, it should reach all potential
providers (in most of the time it will flood the network since
all the users can be potential providers). Naturally, in a
multi-provider, multi-consumer scenario, the FIB entries would
form a mesh in the network. It is less scalable compared to
the tree-based routing in IP multicast (PIM-SM). The network
has to specify another routing policy specifically for these
prefixes, which places even higher overhead on network
management.
Ravindran, et al. Expires January 17, 2018 [Page 8]
Internet-Draft Interest Notification July 2017
* As is mentioned in [9], it is not efficient to embed large
amount of data into the name of the Interest packets. It adds
more computation and storage overhead in the forwarding engines
(PITs).
Interest Trigger: Similar to Interest Overloading, Interest Trigger
uses an Interest packet as notification. To eliminate the
overhead of embedding the content in the Interest, this solution
places the name of the publication in the name of the notification
(Interest) packet. On receiving the notification, the consumers
can extract the content name and send another query (Interest) for
the real content. While this solution reduces the overhead of
embedding the payload, it still has the ambiguity and routing
issues similar to Interest Overloading solution. It also incurs
additional round trip delay before the produced data arrives at
the listening consumer.
To summarize CCN and NDN operates on PULL primitive optimized for
content distribution applications. Emulating PUSH operation over
PULL has the following issues:
o It is a mismatch between an application's intent to PUSH data and
the PULL APIs currently available.
o Unless Interests are marked distinctly, overloading Interests with
notification data will undergo PIT/CS processing and are also
subjected to similar routing and forwarding policies as regular
Interests which is inefficient.
o Another concern in treating PUSH as PULL is with respect to the
effect of local strategy layer routing policies, where the intent
to experiment with multiple faces to fetch content is not required
for notification messages.
This motivates the need for treating notifications as a separate
class of traffic which would allow a forwarder to apply the
appropriate routing and forwarding processing in the network.
4. Proposed Notification Primitive in CCN
Notification is a new type of packet hence can be subjected to
different processing logic by a forwarder. By definition, a
notification message is a PUSH primitive, hence is not subjected to
PIT/CS processing. This primitive can also be used by any other
transactional or content distribution application towards service
authentication or exchanging contextual information between end
points and the service.
Ravindran, et al. Expires January 17, 2018 [Page 9]
Internet-Draft Interest Notification July 2017
5. Notification Message Encoding
The wire packet format for a Notification is shown in Fig. 1 and Fig.
2. Fig. 1 shows the Notification fixed header considering the
CCNx1.0 encoding, and Fig. 2 shows the format for the CCN
Notification message, which is used to transport the notification
data. We next discuss these two packet segments of the Notification
message.
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
+---------------+---------------+---------------+--------------+
| Version | PacketType= | PacketLength |
| | Notification | |
+---------------+---------------+---------------+--------------+
| HopLimit | Reserved | Flags | HeaderLength |
+---------------+---------------+---------------+--------------+
/ Optional Hop-by-hop header TLVs /
+---------------+---------------+---------------+--------------+
/ Content Object as Notification Message /
+---------------+---------------+---------------+--------------+
Figure 1: CCN Notification fixed header
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
+---------------+---------------+---------------+--------------+
| MessageType = Content Object | MessageLength |
+---------------+---------------+---------------+--------------+
| Name TLV |
+---------------+---------------+---------------+--------------+
| Optional MetaData TLVs |
+---------------+---------------+---------------+--------------+
| Message Payload Type | Message Type Length |
+---------------+---------------+---------------+--------------+
| Payload or Optional Content Object |
+---------------+---------------+---------------+--------------+
/ Optional CCNx ValidationAlgorithm TLV /
+---------------+---------------+---------------+--------------+
/ Optional CCNx ValidationPayload TLV (ValidationAlg required) /
+---------------+---------------+---------------+--------------+
Figure 2: CCN Notification Message
Ravindran, et al. Expires January 17, 2018 [Page 10]
Internet-Draft Interest Notification July 2017
Notification Fixed Header: The fields in the fixed header that have
new meaning in the context of notifications are discussed next, while
the other fields follow the definition in [1].
o Packet Type: This new type code identifies that the packet is of
type Notification [TBD].
o Optional Hop-by-hop header TLVs : Encodes any new hop-by-hop
headers relevant to notifications [TBD].
CCN Notification message: The CCN Notification message is a Content
Object as in [1]. Notifications are always routed on the top level
Content Object (outer CO) name. Notification itself can be encoded
in two forms depending on the application requirement:
o Notification with single name: In this case the notification
contains a single content object. Here the producer generates
notification using the same name used by consumers on which they
listen on.
o Notification with two names: In this case the notification
contains a top level Content Object (outer CO), that encapsulates
another Content Object (inner CO). With an encapsulated Content
Object, the meaning is that notification producers and consumers
operate on different name-spaces requiring separate name-data
security binding. A good application of the encapsulation format
is a PUB/SUB service, where the consumer learns about the
notification service name offline, and the producer who is
decoupled from the consumer generates a new Content Object using
its own name and pushes the notification to the consumer.
The interpretation of the fields shown in Fig. 2 are as follows:
o MessageType : The CCN message type is of type Content Object.
o Name TLV : Name TLV in the Content Object is used to route the
Notification.
o Optional Metadata TLV: These TLVs carry metadata used to describe
the Notification payload.
o Message Payload Type: This is of type T_PAYLOADTYPE defined in
CCNx.1.0 or a new encapsulation type (T_ENCAP) that indicates the
presence of another encapsulated Content Object [TBD].
o Optional Encapsulated Content Object: This is an optional
encapsulated Content Object newly defined for the Notification
primitive. The name in the encapsulated Content Object
Ravindran, et al. Expires January 17, 2018 [Page 11]
Internet-Draft Interest Notification July 2017
corresponds to the producer's name-space, or anything else based
on the application logic. The rational for an encapsulated
Content Object was discussed earlier.
o Optional Security Validation data: The Content Object optionally
carries security validation payload as per CCNx1.0.
6. Notification Processing
The following steps are followed by a CCN forwarder to process the
Notification packet.
o Notification packet type is identified in the fixed header of a
CCN packet with a new type code. The Notification carries a
Content Object, whose name is used for routing. This name is
matched against the FIB entries to determine the next hop(s).
Novel strategy layer routing techniques catering to the
notification traffic can be applied here.
o CCN forwarder also processes the optional metadata associated with
the Notification meant for the network to help with the forwarding
strategy, for e.g., mission critical notifications can be given
priority over all other traffic.
o As mentioned earlier, CCN forwarder MUST NOT cache the Content
Objects in the notifications.
7. Security Considerations
The proposed processing logic of Notifications that bypass the
processing of PIT/CS has the following security implications:
Flow Balance : PIT state maintains the per-hop flow balance over all
the available faces by enforcing a simple rule, that is, one Content
Object is send over a face for a single Interest. Bypassing PIT
processing compromises this flow balancing property. For scenarios
where the notification traffic volume is not high such as for IoT
applications, the impact may not be significant. However, this may
not be the case considering the plethora of social networking and
emerging IoT applications in a general Internet scenario. This flow
balance tradeoff has to be understood considering an application's
intent to PUSH data and the latency introduced by processing such
traffic if a PULL primitive is used. Also PIT offers a natural
defense mechanism by throttling traffic at the network edge,
considering the provisioned PIT size, and bypassing it could
exacerbate DDOS attacks on producing end points.
Ravindran, et al. Expires January 17, 2018 [Page 12]
Internet-Draft Interest Notification July 2017
Cache Poisoning: This draft doesn't recommend the caching of the
Content Object in the Notification payload, though doing so might
help in increasing the availability of notification information in
the network. A possible exception would be if the inner CO is a
nameless object [10]. as those can only be fetched from CS by hash We
leave this possibility of applying policy-based caching of
Notification Content Objects for future exploration. The
recommendation for not caching these Content objects is that, in a
regular Interest/Content Object exchange, content arrives at the
forwarder and is cached as a result of per-hop active Interest
expression. Unsolicited Content Objects, as in the case of the
Notification, violates this rule, which could be exploited by
malicious producers to generate DDOS attack against the cache
resource of a CCN infrastructure.
8. Annex
8.1. Flow and Congestion Control
8.1.1. Issues with Basic Notifications
As mentioned in the previous sections, one of the main issues with
notification is the flow and congestion control. One naive way to
solve this issue is the routers drop the packets from aggressive
flows. Flow-based fair queueing (and its variation stochastic
fairness queueing) maintain queues for flows (or the hash of flows)
and try to give a fair share to each flow (or a hash). Flows can be
classified by the prefixes in the ICN case. However, according to
[11], the overall network throughput will be affected when there are
multiple bottlenecks in the network. Therefore, [11] promotes an
end-to-end solution for congestion control. Flow balance is a key
requirement to an end-to-end (or end-driven) flow and congestion
control. In the case of CCN query/response, flow balance entails
that an Interest pulls at most one Data object from upstream. The
data consumer can therefore control the amount of traffic coming from
the data source(s) either it is a data provider or a cache in the
network. However, the basic notification does not follow the rule of
flow balance (each Subscription can result in more than one
Notifications disseminated in the network). In the absence of a
proper feedback mechanism to notify the data sender or the network
the available bandwidth and local resource the consumer has, the
sender can easily congest the bottleneck link of the receivers
(causing congestion collapse) and/or overflow the buffer on the
receiver side. In the later sections, we will describe the possible
congestion control mechanisms in ICN and how to deal with packet loss
when both congestion control and reliability are required.
Ravindran, et al. Expires January 17, 2018 [Page 13]
Internet-Draft Interest Notification July 2017
However, the basic notification does not follow the rule of flow
balance (each Subscription can result in more than one Notifications
disseminated in the network). There is no way a receiver can notify
the data sender or the network the available bandwidth and local
resource it has. As a result, the sender can easily congest the
bottleneck link of the receivers (causing congestion collapse) and/or
overflow the buffer on the receiver side.
8.1.2. Flow and Congestion Control Mechanims
Here we discuss broad approaches towards achieving flow and
congestion control in CCN as applied to Notification traffic. Since
the forwarding logic of the Notification packets are quite similar to
that of IP multicast, existing multicast congestion control solutions
can be candidates to solve the flow/congestion control issue with
Notification. In addition we also summarize recent ICN research to
address this issue.
8.1.2.1. End-to-End Approaches
In the multicast communication, it is not scalable to have direct
receiver-to-sender feedback loop similar to TCP since this would
result in each receiver sending ACKs (or NACKs) to the data sender
and cause ACK (NACK) implosion. To address the ACK implosion issue,
two types of solutions have been proposed in multicast congestion
control, namely, sender-driven approaches and receiver-driven
approaches.
8.1.2.1.1. Sender-driven Multicast
In the first category, the sender controls the sending rate and to
ensure the network friendliness, the sender usually align the sending
rate to the slowest receiver.
To avoid the ACK implosion issue, TCP-Friendly Multicast Congestion
Control (TFMCC [12]) uses rate based solution. This solution uses
TCP-Friendly Rate Control (TFRC) to get a proper sending rate based
on the RTT between sender and each receiver. The sender only needs
to collect the RTTs periodically instead of per-packet ACKs.
Similarly, in ICN, the sender can create another channel (namespace)
to collect the RTT measurement from the receivers. However, due to
the dynamics on each path, it is difficult to calculate the proper
sending rate.
To address the rate calculation issue, pgmcc [13], a window-based
solution is proposed. It uses NACKs to detect the slowest receiver
(the ACKer). The ACKer sends an ACK back to the sender on receiving
each multicast packet. A feedback loop similar to TCP is formed
Ravindran, et al. Expires January 17, 2018 [Page 14]
Internet-Draft Interest Notification July 2017
between the sender and the ACKer to control the sending rate. Since
the ACKer is the slowest receiver, the sender adapts its sending rate
to the available bandwidth of the slowest receiver, the solution can
therefore ensure the network friendliness. In the ICN case, the
receivers can send NACKs in the form of Notification packets through
another namespace, and the ACKer can also use the same mechanism to
send ACKs.
However, since the sender is always aligning the sending rate to the
slowest receiver to ensure the network friendliness, the performance
of the solutions can be dramatically affected by a very slow
receiver.
8.1.2.1.2. Receiver-driven Multicast
Unlike the sender-driven solutions, the receiver-driven solutions
[14] choose to use layered-multicast to satisfy heterogeneous
receivers. The sender first initiates several multicast groups
(namespaces in the case of ICN) with different sending rates. Each
receiver would choose to join a multicast group with the highest
sending rate that it can afford. The sender can also adapt the
sending rate of each multicast group according to the receiver
status.
These solutions can support applications like video streaming (with
layered codecs) efficiently. However, they also have some issues: 1)
they complicate the sender and receiver logic, especially for simple
applications like file transfer; and 2) the receivers are limited by
the sending rates initiated by the provider and would therefore
under-utilize the available bandwidth.
8.1.2.2. Hybrid Approaches
In this approach, flow balance of Notification is achieved by the
receivers notifying the network (rather than the sender or other
receivers) about the capacity it can receive. Here, we take
advantage of operating the Notification service through a receiver-
driven approach and get support from the network.
A solution based on this approach is proposed in [15], which we
summarize next.
To retain flow balance, the consumers in this solution send out one
subscription for only one next Notification instead of the original
logic (that receives all the Notifications). Similar to the flow and
congestion control in query/response, the receivers can now maintain
a congestion window to control the amount of traffic coming from
upstream.
Ravindran, et al. Expires January 17, 2018 [Page 15]
Internet-Draft Interest Notification July 2017
Here, instead of maintaining a (name, outgoing face) pair in FIB (or
subscription table), the routers now adds a third field --
accumulated count -- for each entry. The accumulated count is
increased by 1 on receiving such a subscription and decreased by 1 on
sending a Notification to that face. The routers should also
propagate the maximum accumulated count upstream till the 1st hop
router of the provider (or the rendezvous point in the network). The
subscribers sends a subscription for every successfully received
notification. Here we also assume that, the subscribers operate
based on the AIMD scheme.
If the dissemination of Notification follows a tree topology in the
network, we define the branching point of a receiver R (BP_R) as the
router closest to R which has another outgoing face that can receive
data faster than R. For receivers that has bandwidth/resources to
receive all the data from the provider, BP_R is the 1st hop router of
the provider (or the rendezvous point).
In this solution, we can prove that there is a feedback loop between
each receiver and its branching point. Therefore, when a receiver
maintains its congestion window size using AIMD, the traffic between
the branching point and the receiver is similar to TCP. It can get a
fair share at the bottleneck on the path, even if the bottleneck is
not directly under the branching point. In the multicast tree, the
solution can ensure the fairness with other (TCP-like) flows on each
branch.
The solution can thus allow the sender to send at an application-
efficient rate rather than being affected by the slowest receiver
like pgmcc [13].
It is true that the solution requires more packets and more states in
the network compared to the basic notification solution, but the cost
is similar to (and smaller than) that of query/response. Since we
are using one notification per subscription pattern, the amount of
traffic overhead is the same as query/response. As for the states
stored in the router, the solution only requires 1 entry per prefix
per face, which is smaller than the query/response which requires 1
entry per packet per face. Therefore, the overhead of the solution
is acceptable in CCN.
8.1.2.2.1. Other Challenges
o Sender Rate Control: The sender in the solution does not have to
limit the sending rate to the slowest receiver to maintain network
friendliness. Therefore, the choice of sending rate is a tradeoff
between network traffic and session completion time. In the case
where the application does not require a certain sending rate
Ravindran, et al. Expires January 17, 2018 [Page 16]
Internet-Draft Interest Notification July 2017
(like file transfer), the sender can align the sending rate to the
slowest receiver (similar to pgmcc) to minimize the repair
traffic, but at the cost of longer session completion time. He
can also send at the rate of the fastest receiver and try to get
peer repair in the network. This allows faster receivers finish
the session earlier but causing higher network traffic due to the
repair. An ACKer-based solution similar to pgmcc can be adopted
to allow the sender align the rate at a proportion of users (e.g.,
top 30%). The sender can collect feedback (throughput, latency,
etc.) from all the receivers periodically and pick an ACKer
according to the proportion it desires. On receiving a
Notification packet, the ACKer would send an ACK just like TCP.
The sender can maintain a congestion window also like TCP. The
feedback loop between the sender and the ACKer can align the
sending rate at the ACKers's available bandwidth.
o Receiver Window Control: Slightly different from one-sender one-
receiver window control in TCP, the sending rate in the hybrid
approach is not controlled by any of the receivers. Receiving
intermittent packets can indicate both congestion (similar to TCP)
and not enough window size (since the sending rate is higher). In
the first case, the receiver should reduce the window size while
in the second case, the receiver should increase the window size.
An indication of congestion (e.g., Random Early Detection, RED)
should be provided directly from the network.The receivers with
available bandwidth higher than the sending rate would have too
large window size since it does not see any packet loss. Please
refer to [15] for a detailed solution on this issue.
8.1.3. Receiver Reliability
The receiver would miss packets when the available bandwidth/resource
of the receiver is lower than the sending rate of the Notification
provider. Some applications (like gaming and video conferencing) can
tolerant such kind of packet loss while the others (like file
transfer) cannot. Therefore, another module that ensures the
reliability is needed. However, reliability should be separated from
the flow and congestion control since it is not a universal
requirement.
With the solution described in the receiver-driver or the hybrid
approach, the slower consumers would receive intermittent packets
since the sending rate can be faster than their fair share. The
applications that require reliable transfer can query the missing
packets similar to the normal query/response. This also requires
that each content in the Notifications should have a unique Content
Name (or hash in the nameless scenario). The clients should also be
able to detect the missing packets either based on the sequence
Ravindran, et al. Expires January 17, 2018 [Page 17]
Internet-Draft Interest Notification July 2017
number or based on a pre-acquired meta-file. Caching in CCN can be
leveraged to achieve availability and reliability.
The network can forward the requests (Interests) of the missing
packets towards the data provider, the other consumers and/or the in-
network cache to optimize the overall throughput of the consumers.
This solution is similar to Scalable Reliable Multicast (SRM [16]).
However, as mentioned in [17], solutions like SRM requires the
consumers communicate directly with each other and therefore lose the
privacy and trust. CCN can ensure the privacy since the providers
cannot get the information of the identity of the consumers. Trust
(data integrity) is also maintained with the signature in the Data
packets.
8.2. Routing Notifications
Appropriate routing policies should be employed to ensure reliable
forwarding of a notification to its one or many intended receivers.
The name in the notification identifies a host or a multicast service
being listened to by the multiple intended receivers. Two types of
routing strategies can be adopted to handle notifications, depending
on whether or not an explicit pub/sub state is maintained in the
forwarder.
o Stateless forwarding: In this case the notification only relies on
the CCN FIB state to route the notification. The FIB entries are
populated through a routing control plane, which distinguishes the
FIB states for the notification service from the content fetching
FIB entries. Through this logical separation, Notifications can
be routed by matching its name with the matching FIB policy in the
CCN forwarder, hence processed as notification multicast.
o Stateful forwarding: In this case, specific subscription state is
managed in the forwarder to aid notification delivery. This is
required to scale notifications at the same time apply
notification policies, such as filter notifications or to improve
notification reliability and efficiency to subscribing users [18].
8.3. Notification reliability
This proposal doesn't provide any form of reliability. Reliability
can be realized by the specific application using the proposed
notification primitive, for instance using the following potential
approaches:
Caching: This proposal doesn't propose any form of caching. But
caching feature can be explored to improve notification reliability,
and this is a subject of future study. For instance, consumers,
Ravindran, et al. Expires January 17, 2018 [Page 18]
Internet-Draft Interest Notification July 2017
which expect notifications and use external means (such as periodic
updates or by receiving manifests) to track notifications, can
recover the lost notifications using the PULL feature of CCN.
Notification Acknowledgment: If the producer maintains per-receiver
state, then the consumer can send back notification ACK or NACK to
the producer of having received or not received them.
8.4. Use Case Scenarios
Here we provide the discussions related to the use of Notification in
different scenarios.
8.4.1. Realizing PUB/SUB System
A PUB/SUB system provides a service infrastructure for subscribers to
request update on a set of topics of interest, and with multicast
publishers publishing content on those topics. A PUB/SUB system maps
the subscribers' interests to published contents and pushes them as
Notifications to the subscribers. A PUB/SUB system has many
requirements as discussed in [19] which include low latency,
reliability, fast recovery, scalability, security, minimizing false
(positive/negative) notifications.
Current IP based PUB/SUB systems suffer from interoperability
challenges because of application-defined naming approach and lack of
support of multicast in the data plane. The proposed Notification
primitive can be used to realize large scale PUB/SUB system, as it
unifies naming in the network layer and support for name-based
multicasting.
Depending on the routing strategy discussed earlier, two kind of PUB/
SUB approaches can be realized : 1) Rendezvous style approach ; 2)
Distributed approach. Each of these approaches can use the
Notification primitive to implement their PUSH service.
In the Rendezvous style approach, a logically centralized service
maps subscriber's topic interest with the publisher's content and
pushes it as notifications. If stateless forwarding is used, the
routing entries contain specific application-ID's requesting a given
notification, to handle scalability, a group of these application can
share a multicast-ID reducing the state in the FIB.
In the Distributed approach, the CCN/NDN protocol is further enhanced
with new subscription primitive for the subscription interested
consumers. When a consumer explicitly susbcribes to a multicast
topic, its subscription request is forwarded to the upstream
forwarder which manages this state mapping between subscription names
Ravindran, et al. Expires January 17, 2018 [Page 19]
Internet-Draft Interest Notification July 2017
to the downstream faces which has expressed interest for
Notifications being pushed under that prefix. An example of the
network layer based approach is the COPSS notification proposal [19].
Here a PUB/SUB multi-cast state state, called the subscribers
interest table, is managed in the forwarders. When a Notification
arrives at a forwarder, the content descriptor in the notification is
matched to the PUB/SUB state in the forwarder to decide the faces
over which the Notification has to be forwarded.
9. Informative References
[1] CCN Wire format, CCNX1., "http://www.ietf.org/id/
draft-mosko-icnrg-ccnxmessages-00.txt.", 2013.
[2] Osseiran, A., "Scenarios for 5G Mobile and Wireless
Communications: The Vision of the METIS Project.", IEEE
Communication Magazine , 2014.
[3] NSF FIA project, MobilityFirst.,
"http://www.nets-fia.net/", 2010.
[4] NSF FIA project, XIA., "https://www.cs.cmu.edu/~xia/",
2010.
[5] Observing Resources in CoAp, observe.,
"https://tools.ietf.org/html/draft-ietf-core-observe-16.",
2015.
[6] Amadeo, M., Campolo, C., and A. Molinaro, "Internet of
Things via Named Data Networking: The Support of Push
Traffic", Network of the Future (NOF), 2014 International
Conference and Workshop on the , 2014.
[7] Shang, W., Bannis, A., Liang, T., and Z. Wang, "Named Data
Networking of Things.", IEEE IoTDI 2016, 2016.
[8] Zhu, Z. and A. Afanasyev, "Let's chronosync: Decentralized
dataset state synchronization in named data networking",
The 21st IEEE International Conference on Network
Protocols ICNP, 2013.
[9] Moiseenko, I. and O. Oran, "TCP/ICN: Carrying TCP over
Content Centric and Named Data Networks", Proceedings of
the 3rd ACM Conference on Information-Centric
Networking ICN, 2016.
[10] Mosko, M., "Nameless Objects.", IETF/ICNRG, Paris
Interim 2016, 2016.
Ravindran, et al. Expires January 17, 2018 [Page 20]
Internet-Draft Interest Notification July 2017
[11] Floyd, S. and F. Kevin, "Promoting The Use of End-to-End
Congestion Control in The Internet.", IEEE ToN vol. 7(4),
pp. 458-472, 1999.
[12] Widmer, J. and M. Handley, "TCP-Friendly Multicast
Congestion Control (TFMCC): Protocol Specification.", IETF
RFC 4654, 2006.
[13] Rizzo, L., "pgmcc: A TCP-Friendly Single-Rate Multicast
Congestion Control Scheme.", SIGCOMM CCR vol. 30.4, pp.
17-28, 2000, 2000.
[14] McCanne, S., Jacobson, V., and M. Vetterli, "Receiver-
driven Layered Multicast.", SIGCOMM CCR pp. 117-130, 1996.
[15] Chen, J., Arumaithurai, M., Fu, X., and KK. Ramakrishnan,
"SAID: A Control Protocol for Scalable and Adaptive
Information Dissemination in ICN.", arXiv vol. 1510.08530,
2015.
[16] Floyd, S., Jacobson, V., Liu, C., McCanne, S., and L.
Zhang, "A Reliable Multicast Framework for Light-Weight
Sessions and Application Level Framing.", IEEE TON vol.
5(6), pp. 784-803, 1997.
[17] Floyd, N., Grossglauser, M., and KK. Ramakrishnan,
"Distrust and Privacy: Axioms for Multicast Congestion
Control.", Distrust and Privacy: Axioms for Multicast
Congestion Control NOSSDAV, 1999.
[18] Francois et al, J., "CCN Traffic Optimization for IoT",
Proc. of NoF , 2013.
[19] Chen, J., Arumaithurai, M., Jiao, L., Fu, X., and K.
Ramakrishnan, "COPSS: An Efficient Content Oriented
Publish/Subscribe System.", ACM/IEEE Symposium on
Architectures for Networking and Communications Systems
(ANCS 2011) , 2011.
[20] DNS Security Introduction and Requirements, DNS-SEC.,
"http://www.ietf.org/rfc/rfc4033.txt.", 2005.
[21] Cisco System Inc., CISCO., "Cisco visual networking index:
Global mobile data traffic forecast update.", 2009-2014.
[22] CCNx Label Forwarding, CCNLF., "http://www.ccnx.org/pubs/
ccnx-mosko-labelforwarding-01.txt.", 2013.
Ravindran, et al. Expires January 17, 2018 [Page 21]
Internet-Draft Interest Notification July 2017
Authors' Addresses
Ravishankar Ravindran
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: ravi.ravindran@huawei.com
Asit Chakraborti
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: asit.chakraborti@huawei.com
Syed Obaid Amin
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: obaid.amin@huawei.com
Jiachen Chen
Winlab, Rutgers University
671, U.S 1
North Brunswick, NJ 08902
USA
Email: jiachen@winlab.rutgers.edu
Ravindran, et al. Expires January 17, 2018 [Page 22]
