Use Cases of
Computing-aware Service Function Chaining (SFC)China UnicomBeijingChinazhangs366@chinaunicom.cnHuawei TechnologiesBeijingChinajescia.chenxia@huawei.comMultiple occurrences of the same service function(SF) can exist in
the same administrative domain and each occurrence of SF is called SF
instance. A Service Function Path(SFP) is determined by composing
selected SF instances and overlay links. The SF instances are selected
according to the computing power of SFs in addition to the network
information and this is defined as the computing-aware SFC in this
document.This document describes the use cases for computing-aware Service
Function Chaining(SFC).The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.defines the architecture for SFC and mentions
load-balancing considerations of the scenario that is same service
function may be reachable through multiple SFFs.The selection of which
SFF to use to reach SF may be made by the control logic in defining the
SFP, or may be left to the SFFs themselves, depending upon policy,
solution, and deployment constraints. indicates that
implementing a (logically) centralized path computation engine requires
information to be dynamically communicated to the central SFC Control
Element, such as the list of available SF instances, SFF locators, load
status, SFP availability, etc. SF load update information such as the
performance threshold or stress level of SF can be exchanged between an
SF and the SFC control plane to establish or adjust an SFP.In this document the computing power of SF includes computing
resources and computing load of SF. For example, the compute resource
can be the vCPUs allocated to SF, and the compute load can be the CPU
utilization of SF or the ratio of the number of SFPs currently using SF
to the maximum number of SFPs supported by SF.Multiple instances of the same service function(SF) can exist in the
same administrative domain. A Service Function Path(SFP) is determined
by composing selected SF instances and overlay links.The SF instances
can be selected according to the computing power of SFs in addition to
the network information and this is defined as the computing-aware
SFC.This document describes the use cases for computing-aware Service
Function Chaining(SFC).In carrier networks, operators may deploy multiple data centers or
computing resource pools dispersed geographically. These data centers
can host diverse types of value-added services(VASes) such as
FW(Firewall), IPS(Intrusion Prevention System), WOC(Web Optimization
Control) and VO(Video Optimizer) shared by the enterprise leased line
services, internet services etc.Each data center may have different types of service functions. For
example, high usage service functions are deployed in edge or regional
data centers while other low usage service functions are deployed in
global or central data centers. So SFCs with different types of
service functions may span multiple data centers.The same service function can be deployed in multiple data centers.
In such deployments the SF in one data center is called a SF instance.
SFPs are constructed with the ordered chain of SFs each of which is
from specific data center.The path computation of SFP should consider the computing load of
SFs and the cost or latency of network paths between the DCs hosting
the SFs in order to get the good service experience of SFs and the
optimal end to end network path.In Figure 1, A enterprise tenant orders SFC with a chain of two
value-added services for its access to internet service. The sequenced
services of SFC are FW and VO.The current computing load status of the FW SFs in DC1 and DC2 is
as follows: each SF uses 6 vCPUs. The load of DC1 is 50%. The load of
DC2 is 20%. Considering lightly loaded SF the computed SFP is
represented as: DC2 FW -> DC3 VO. Traffic follows the path: CPE
-> R1 -> R2 -> DC2 FW -> R2 -> R3 ->DC3 VO -> R3
-> R4 -> internetThe procedures for SFP creation according to computing power of SFs
and network topology may be handled by the control plane as
follows:1.Collect computing power which are computing resources and
computing load of of SFs in DCs2.Associate the DC location and computing power of the available
SFs with topological information of network connecting all the data
centers to allow control plane to construct the overall mapThe following potential solutions could be considered:Collect the SF's location and computing power by BGP-LS or
Netconf from the router connecting the data centers and
dynamically get the association relationship.Independently collect the SF location and computing power by
other means and statically configure the association with the
network on the control plane.3.Compute the actual sequence of specific routers and selected SFs
in the network for SFPIf the same SF is deployed in multiple data centers the control
plane selects one SF instance for SFP considering the computing load
of SF and the cost or latency of network paths between the DCs hosting
the SFs.4.Deliver the actual computed path called Rendered Service Path
(RSP) to the routers to steer the traffic
from classifier to destinationIn some cases SFP adjustments can be handled. For example, a SF in
the selected DC fails, the load of the same SF in each DC varies
greatly, and the delay is caused among routers connected to the
DC.TBDThere are no IANA considerations in this document.