| Network Working Group | D. Purkayastha |
| Internet-Draft | A. Rahman |
| Intended status: Informational | D. Trossen |
| Expires: December 31, 2018 | InterDigital Communications, LLC |
| T. Eckert | |
| Huawei | |
| June 29, 2018 |
BIER Multicast Overlay for HTTP Respone
draft-purkayastha-bier-multicast-http-response-00
HTTP Level multicast, using BIER, is described as a use case in BIER Use cases document. HTTP Level Multicast is used in today’s video streaming and delivery services such as HLS, AR/VR etc., generally realized over IP Multicast. A realization of “HTTP Multicast” over “IP Multicast” is described and few problems are identified. Realization over BIER, through a BIER Multicast Overlay Layer, is described. How BIER Multicast Overlay operation improves over IP Multicast is also discussed.
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BIER Use Cases document [I-D.ietf-bier-use-cases] describes an “HTTP Level Multicast” scenario, where HTTP Responses are carried over a BIER multicast infrastructure to multiple clients. Especially rate-adaptive HTTP solutions can benefit from the dynamic multicast group membership changes enabled by BIER. For this, the “server side NAP (Network Attachment Point), creates a list of outstanding client side NAP (Network Attachment Point) requests for the same HTTP resource. When the response is available, the list of NAPs with outstanding client requests are converted into the BIER or BIER-TE bitstring and used to send the HTTP response.
In this draft, we describe how this class of use cases can be realized over IP Multicast and how the operation of the use case can be improved if realized over BIER. The realization over BIER is achieved through what is called in BIER “BIER Multicast overlay” layer: The methods by which the sending BIER router knows what . The requirements for BIER Multicast overlay layer is described. It also describes the necessary functions that form the BIER multicast overlay and the operations that enable the desired “HTTP Level Multicast” behavior. One such operation is generating PATH ID (represents the BFIR and BFER) based on named service relationship and translating it to appropriate BIER header. We describe a list of protocols needed for the realization of the individual operations.
We conclude with future steps and seek input from the WG.
Let us formulate the architecture of the BIER multicast overlay for the scenario outlined in [I-D.ietf-bier-use-cases]. This overlay is shown in Figure 1 below.
+---------+ +------------+
| | | |/
+IP only +---+ SR + BFER +-----|
|receiver | | (CNAP) |\ |
|UE | +----/\------+ |
+---------+ || |
|| +----------+ +---------+
|| | | | |
|-------- | BFR |---| BFR |------|
| | | | | |
| +----------+ +---------+ |
+---------+ +-------+
| |------------------------------------>| BFIR |
+ BIER TE + | + |
| PCE | +---------+ +-------+ | SR |
| |--|| | |----| BFR |----|(SNAP) |
+---------+ || | BFR | +-------+ | |
|| | | +-------+
|| +---------+ /|\
+---------+ +------\/----+ | |
| | | |/ | |
+IP only +---+ SR + BFER +------| +----------+
|receiver | | (CNAP) |\ | IP only |
+---------+ +------------+ | Sender |
|(Server) |
+----------+
[SR : Service Handler, CNAP : Client Network Attachment Point]
[SNAP : Server Network Attachment Point]
[PCE : Path Computation Element]
Figure 1: Deployment over BIER
The multicast overlay is formed by the BFIR and BFER of the BIER layer and the additional SR (Service Handler) and PCE (Path Computation Element) elements shown in the figure. When connecting to a standard IP routed peering network, a special SR, such as Border Gateway may be used
The Service Handler and BFER can be assumed to be collocated and can be viewed as Client Network Attachment Point (CNAP). Clients sends and receives HTTP transactions through CNAP.
On the server side, the Service handling function can be part of the Server Network Attachment Point (SNAP). It also includes the BFIR function. SNAP is responsible for aggregating all HTTP Request and sending BIER Multicasted HTTP response to multiple clients who requested the same content.
As part of POINT/RIFE EU Horizon 2020 project, HTTP Level Multicast use case has been executed on SDN based and ICN based underlay network, as described in the [I-D.irtf-icnrg-deployment-guidelines].
“HTTP multicast” demonstrated benefits in HTTP-level streaming video delivery, when deployed on POINT test bed with 80+ nodes. This draft [I-D.irtf-icnrg-deployment-guidelines] also describes protocol requirements to enable HTTP multicast to work on ICN underlay.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
With the extensive use of “web technology”, “distributed services” and availability of heterogeneous network, HTTP has effectively transitioned into the common transport or session layer for E2E and multi-hop communication across the web that is also called Service signaling. Multi-hop when using a sequence of HTTP instance such as HTTP caches. The draft “On the use of HTTP as a Substrate” [I-D.ietf-httpbis-bcp56bis], describes how HTTP is commonly used among service instances to communicate with each other, thus abstracting the lower layer details to application developers.
Referring to the BIER Use Cases [I-D.ietf-bier-use-cases], multicast is used to scale out HLS (HTTP live streaming) to a large number of receivers that use HTTP. This is used today in solutions like DOCSIS hybrid streaming [TR_IPMC_ABR]. Multicast can speed up both live and high-demand VoD streaming. Adaptive Bit Rate IPMC [TR_IPMC_ABR] describes use of IP multicast towards the CMTS or a box beside it, where the content is converted to HTTP/TCP to stream to the receivers (e.g., homes). A server hosting the HLS content is shown as "NAP Server". The gateways acting as receivers for the multicast from the server are shown as "Client-NAP" (CNAP). Each CNAP can serve multiple clients.
HTTP request and response used in media streaming services like HLS, use HTTP response for delivery of content. In such scenarios, where semi-synchronous access to the same resource occurs (such as watching prominent videos over Netflix or similar platforms or live TV over HTTP), traffic grows linearly with the number of viewers since the HTTP-based server will provide an HTTP response to each individual viewer. This poses a significant burden on operators in terms of costs and on users in terms of likely degradation of quality.
This solution is not limited to traditional TV broadcasting. Consider a virtual reality use case where several users are joining a VR session at the same time, e.g., centered around a joint event. Hence, due to the temporal correlation of the VR sessions, we can assume that multiple requests are sent for the same content at any point, particularly when viewing angles of VR clients are similar or the same. Due to availability of virtual functions and cloud technology, the actual end point from where content is delivered may change.
IPTV or Internet video distribution in CDNs, uses HTTP Level Multicast and realized over IP Multicast (IPMC). Many features of the IPTV service uses IPMC Group dependent state. Besides popular features like PIM, Mldp, in a variable bit rate encoded content source, content consumption also depends on group state.
Assume clients that are consuming the same content (such as a TV program) and that this content has for each block (typically segments worth 2 seconds of content) a set of outstanding requests from its clients. When IP Multicast is used in the domain, such as in aforementioned pre-existing solutions like in Cablelabs/DOCSIS [TR_IPMC_ABR], all possible blocks of the content have to be mapped to some IP multicast group, and the CNAP will need to know the mapping of block to groups. For example, a live stream may have 11 different bitrates available. In the most simple Block to IP multicast group mapping scheme, there could be 11 multicast groups, one for all the blocks of one bitrate (note that this is not necessarily done in deployments of this solution, but we consider it here for the purpose of explanation).
If the multicast domain and especially the links into the CNAP has enough bandwidth, this solution work well with IP multicast. As soon as there is at least one Client connected to a CNAP for one particular content, the CNAP would join all 11 multicast groups for this content.
To realize “HTTP Level Multicast” over “IP Multicast”, some additional functions needs to be supported in an intermediate (overlay) layer.
Support of mapping between FQDN based end points, Multicast Address. Creating multicast group from FQDN based end points.
Control mechanism related to time when to start sending response as the multicast group is created. It is required that the source should not send response immediately to the Multicast address. Wait for some time to build the group sufficiently and then send response.
Support of IGMP signaling between User device, NAPs and Multicast Router.
If the number of clients on a CNAP for a particular program is large, the approach will work fairly well, because the likelihood that each of the 11 bitrates of a content is necessary for at least one Client is then fairly high.
When the number of receivers is not very large, IP multicast runs into two issues. If all the bitrates for the content are sent across the same group, then many of the bitrates may not be required and would have to be received unnecessarily and dropped by the CNAP. If each bitrate was sent on a different IP multicast group, the CNAP could dynamically join/leave each multicast group based on the known receivers, but that would create an extremely high and undesirable amount of IP multicast signaling protocol activity (PIM/IGMP) that is easily overloading the network
For efficiency reasons, the CNAP would need to dynamically join to only those bitrate steams where it does have outstanding requests, therefore achieving the best efficiency. This would mean in the worst case that a CNAP would need to send for each new block, aka.: every two second for every client one IGMP/PIM leave and one IGMP/PIM join towards the upstream router to get a block for an appropriate bitrate (or changed content) whenever bitrate or content on a client have changed. This high rate of control-plane signaling between CNAP and routers, and even between routers inside the multicast Domain is a major pain point and may easily prohibit deployment of these solutions because in many network devices, the performance of PIM/IGMP is not scaled for continuous change in forwarding. Even worse, the limit may not simply be the CPU performance of the routers control plane, but a limitation in the number of changes in forwarding that the forwarding plane units (NPU/ASICs) can support.
The Service Handler (as in Figure 1) in BIER Multicast Overlay, process the FQDN in the service request. At the service level, e.g. HTTP service, the fixed relationship among consumer and providers may be abstracted using “Service Names”, and the changing relationship at the Service execution endpoints can be managed at the “multicast overlay” level, handing out the exact locations where service request or response needs to be sent to BIER layer.
+-------------+ +-----------+ +-----------+
| | | | | PATH ID |
| Service name| | Multicast | | translates|
| [producer, |------->| Overlay |------>| to BIER |
| consumer] | | Layer | | header |
| | | | | |
+-------------+ +-----------+ +-----------+
Figure 2: Service name to Path ID translation
We illustrate this using HTTP URI as service names. It should be noted, other identifiers can also be used as service name, such as IP address. In the example illustration, other layers such as TCP, IP has been abstracted. Outside BIER domain we terminate TCP/IP session to extract the URI. URI is processed by the “multicast overlay” layer to generate PATH IDENTIFIER, which is used as BIER header. Once the BIER header is determined and added at the BFIR, the rest of the transport layers is assumed to be any underlay technology as supported by BIER.
With reference to Figure 1, the following components are part of BIER Multicast Overlay Layer.
As shown in Figure 3, the “Multicast overlay function” includes a function called PCE (Path Computation Element function), which is responsible for selecting the correct multicast end point and possibly realizing path policy enforcement. The result of the selection is a BIER path identifier, which is delivered to the SR upon initial path computation request (or provided to the ingress router BFIR to be added as BIER header ) (i.e., when sending a request to or response for a specific URL for the first time). The path identifier is utilized for any future request for a given URL-based request.
All service end points indicate availability to the PCE through a registration procedure, the PCE will instruct all SRs to invalidate previous path identifiers to the specific URL. This may result in an initial path computation request at the next service request forwarding. Through this, the newly registered service endpoint might be utilized if the policy-governed path computation selects said service instance.
+-------+ +------+----+ +--------+ +----+-----+
|Apps | |Apps----> | | PCE | | | APP |
|layer |--->|layer | SR | +---/\---+ | SR--> |
|prot | |prot | | || | | LYR |
+-------+ +------+----+ +---------+ +---------+ +----+-----+
| L2 | | L2 |-->|Forwarder|-->|Forwarder|-->| L2 |
+-------+ +------+----+ +---------+ +---------+ +----------+
|--------BIER DOMAIN -------|
Figure 3: Protocol for Multicast Overlay Layer
In the diagram shown above, an HTTP request is sent by an IP-based device towards the FQDN of the server defined in the HTTP request.
At the client facing SR, the HTTP request is terminated at the HTTP level at a local HTTP proxy. We assume termination on the client side at Layer 3 and above protocols, such as TCP. Server side SR at the egress, terminates any transport protocol on the outgoing (server) side. These terminating functions are assumed to be part of the client/server SR. The SR obtains the destination “Service Name” from the received HTTP request.
If no local BIER forwarding information exists to the client side SR, a path computation entity (PCE) is consulted, which calculates a unicast path from the BFIR to which the client SR is connected to the BFER to which the server SR is connected. The PCE provides the forwarding information (Path ID) to the client SR, which in turn caches the result. The Client SR may forward the Path ID to BFIR, which creates the BIER header.
+-------------+--------------+
| | |
| BIER HEADER | HTTP REQUEST |
| | [ENCODED IN |
| | TEXT] |
| | |
+-------------+--------------+
Figure 4: Encapsulation of Service Request
Ultimately, the “HTTP Request” encapsulated by BIER header, as shown in above diagram, is forwarded by the client SR towards the server-facing SR via the local BFIR. We assume a (TCP-friendly) transport protocol being used for the transmission between client and server SR while not mandating the use of TCP for this transmission. A suitable transport or Layer 2 encapsulation, as supported by BIER layer, is added to the above payload as shown in the following diagram.
+-------------+-------------+--------------+
| | | |
| Transport L2| BIER HEADER | HTTP REQUEST |
| HEADER | | [ENCODED IN |
| | | TEXT] |
| | | |
+-------------+-------------+--------------+
Figure 5: Transport Encapsulation of BIER payload
Upon arrival of an HTTP request at the server SR, it forwards the HTTP request as a well-formed HTTP request locally to the server.
If no BIER forwarding information exists for the reverse direction towards the requesting client SR, this information is requested from the PCE, similar to the operation in forward direction.
Upon arrival of any further client SR request at the server SR to an HTTP request whose response is still outstanding, the client SR is added to an internal request table. Optionally, the request is suppressed from being sent to the server.
Upon arrival of an HTTP response at the server SR, the server SR consults its internal request table for any outstanding HTTP requests to the same request. The server SR retrieves the stored BIER forwarding information for the reverse direction for all outstanding HTTP requests and determines the path information to all client SRs through a binary OR over all BIER forwarding identifiers with the same SI field. This newly formed joint BIER multicast response identifier is used to send the HTTP response across the network.
BIER makes the solution scalable. Instead of IP multicast with IGMP/PIM, BIER is being used between Server NAP (SNAP) and CNAP, the SNAP simply coalesces the forwarded HTTP requests from the CNAP, and determines for every requested block the set of CNAPs requesting it. A set of CNAPs corresponds to a set of bits in the BIER-bitstring, one bit per CNAP. The SNAP then sends the block into BIER with the appropriate bitstring set.
This completely eliminates any dynamic multicast signaling between CNAP and SNAP. It also avoid sending of any unnecessary data block, which in the IP multicast solution is pretty much unavoidable.
Furthermore, using the approach with BIER, the SNAP can also easily control how long to delay sending of blocks. For example, it may wait for some percentage of the time of a block (e.g, 50% = 1 second), therefore ensuring that it is coalescing as many requests into one BIER multicast answer as possible.
BIER-TE (BIER Traffic Engineering [I-D.ietf-bier-te-arch]) forwards and replicates packets like BIER based on a BitString in the packet header. Where BIER forwards and replicates its packets on shortest paths towards BFER, BIER-TE allows (and requires) to also use bits in the bitstring to indicate the paths in the BIER domain across which the BIER-TE packets are to be sent. This is done to support Traffic Engineeringfor BIER packets via explicit hop-by-hop and/or loose hop forwarding of BIER-TE packets. A BIER-TE controller calculates explicit paths for this packet forwarding.
The Multicast Flow Overlay operates as in BIER. Instead of interacting with the BIER layer, it interacts with the BIER-TE Controller.
In this draft, “Name-based” service forwarding over BIER, is described to handle changes in service execution end points and manage adhoc relationship in a multicast group. BIER-TE is another way of doing this, while integrated with BIER architecture. The PCE function described earlier in the BIER Multicast Overlay, may become part of BIER-TE Controller. The SR function in the CNAP and SNAP communicates with BIER TE controller. SR sends the service name to the controller, which process the request using the PCE function and returns the “bitstring” to be used as BIER header for delivery of the HTTP response to multiple clients.
A realization for the “HTTP multicast” use case may have the following requirements:
This Applicability Statement document describes how name based service forwarding can be realized over BIER. Name based service forwarding helps in handling the change of service execution end points. This document describes the functionalities in the multicast overlay layer to enable the name based forwarding. We would like to get feedback from the WG if this is relevant and would like to get support to continue this work. We will like to elaborate further on the functions of the overlay layer and list the involved protocols by the next IETF after Montreal. We also plan to implement in our H2020 projects.
This document requests no IANA actions.
TBD.
| [I-D.ietf-bier-te-arch] | Eckert, T., Cauchie, G., Braun, W. and M. Menth, "Traffic Engineering for Bit Index Explicit Replication (BIER-TE)", Internet-Draft draft-ietf-bier-te-arch-00, January 2018. |
| [I-D.ietf-bier-use-cases] | Kumar, N., Asati, R., Chen, M., Xu, X., Dolganow, A., Przygienda, T., Gulko, A., Robinson, D., Arya, V. and C. Bestler, "BIER Use Cases", Internet-Draft draft-ietf-bier-use-cases-06, January 2018. |
| [I-D.ietf-httpbis-bcp56bis] | Nottingham, M., "On the use of HTTP as a Substrate", Internet-Draft draft-ietf-httpbis-bcp56bis-05, May 2018. |
| [I-D.irtf-icnrg-deployment-guidelines] | Rahman, A., Trossen, D., Kutscher, D. and R. Ravindran, "Deployment Considerations for Information-Centric Networking (ICN)", Internet-Draft draft-irtf-icnrg-deployment-guidelines-03, June 2018. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [TR_IPMC_ABR] | CableLabs, "IP Multicast Adaptive Bit Rate Architecture Technical Report", OC-TR-IP-MULTI-ARCH-V01-141112 C01, October 2016. |