diff --git a/usecases/sbc.rst b/usecases/sbc.rst new file mode 100644 index 0000000..bbbbda3 --- /dev/null +++ b/usecases/sbc.rst @@ -0,0 +1,311 @@ +.. + +This work is licensed under a Creative Commons Attribution 3.0 Unported License. +http://creativecommons.org/licenses/by/3.0/legalcode + +================================================= + Perimeta Session Border Controller by Metaswitch +================================================= + +This use case is specifically about deploying the Perimeta Session Border +Controller (SBC) Virtual Network Function (VNF) from Metaswitch Networks in +OpenStack, but is more generally representative of the issues involved in +deploying in OpenStack any VNF utilising a fast data plane or high scale SIP. +The use case focuses on those elements rather than more generic issues like +orchestration and high availability (HA). + +Perimeta, like other SBCs, sits on the edge of a service provider's network and +polices SIP and RTP (i.e. VoIP) control and media traffic passing over both +* the access network between end-users and the core network +* the trunk network between the core and another service provider. + +:: + + Access + SP A core + Trunk + SP B core + network | network | network | network + | | | + | | | + +-------+ +-+--+ +---------+ +-+--+ +-+--+ +---------+ + |User | |SBC | |Network | |SBC | |SBC | |Network | + |device |--| |---|function |--| |------------| |---|function | + +-------+ +-+--+ +---------+ +-+--+ +-+--+ +---------+ + | | | + + + + + +Glossary +======== + +**NFV** + Network Functions Virtualization, the vision of deploying telecoms functions + as virtual applications running on commercial off the shelf hardware. + +**VNF** + Virtual Network Function - a telecoms or other network function running as + a virtual application. + +**SIP** + Session Initiation Protocol (RFC 3261) - a common application-layer control + protocol for creating, modifying and destroying sessions between two or more + participants. + +**RTP** + Real-time Transport Protocol (RFC 3550) - an end-to-end network transport + protocol for transmitting real-time data like audio and video. + +**VoIP** + Voice over Internet Protocol - delivering voice and multimedia sessions over + IP networks, commonly through the use of SIP + RTP. + +**SBC** + Session Border Controller, a telecoms function which polices SIP and RTP + flows, providing security, quality of service, admission control and interop + services. + +**DDoS** + Distributed Denial of Service - a form of packet flood attack. + +**SLA** + Service Level Agreement - contractual commitment to reach certain performance + and availability targets. + +**SR-IOV** + Single Root I/O Virtualisation - a technique for presenting a single physical + PCIe device (such as a NIC) as multiple virtual devices, directly presented + to VMs. + +**DPDK** + Data Plane Development Kit - a set of libraries and drivers for fast packet + processing. + +Problem description +=================== + +In order to implement its security and admission control functions (e.g. DDoS +protection), Perimeta must perform line-rate processing of received packets. +For RTP streams, this equates to several million VoIP packets (each ~64-220 +bytes depending on codec) per second per core. Perimeta must be able to +guarantee this performance and offer SLAs. + +Perimeta must be fully HA, with no single points of failure, and service +continuity over both software and hardware failures (i.e. all SIP sessions and +RTP sessions must continue with minimal interruption over software or hardware +failures). + +Perimeta must be elastically scalable, enabling an NFV orchestrator to add and +remove instances in response to applied load. + +To apply different policies to traffic from different customers, Perimeta must +be able to distinguish and separate traffic from different customers via VLANs +or similar mechanism. + +Perimeta must separate networks carrying live customer traffic from networks +carrying management or other internal data. + +Perimeta signaling instances must be able to support large numbers of +concurrent TCP connections (hundreds of thousands) to cater for large numbers +of clients using TCP. + +Perimeta must be able to coexist with VMs which do not have these requirements +on the same host, so long as it can provide sufficient dedicated resources. +For example, just because Perimeta may not require security group function it +does not mean this can be disabled at a host scope, or just because Perimeta +uses SR-IOV or DPDK it does not mean that all VMs on that host must do so. + +Affected By +----------- + +The following bps in progress will affect this use case (see Gaps): +* https://blueprints.launchpad.net/nova/+spec/virt-driver-cpu-pinning +* https://blueprints.launchpad.net/nova/+spec/input-output-based-numa-scheduling +* https://blueprints.launchpad.net/nova/+spec/virt-driver-large-pages +* https://blueprints.launchpad.net/neutron/+spec/ml2-ovs-portsecurity +* https://blueprints.launchpad.net/neutron/+spec/nfv-vlan-trunks +* https://blueprints.launchpad.net/neutron/+spec/ovs-optimization-redundant-bridge + +The following etherpads are also relevant: +* https://etherpad.openstack.org/p/kilo_sriov_pci_passthrough +* https://etherpad.openstack.org/p/telcowg-usecase-openstack-ha + +Requirements +============ + +The problem statement above leads to the following requirements. + +* Achieving packets per second target - networking implications + + A standard OpenStack/OpenvSwitch platform allows VMs to drive NICs to full + bandwidth if using large packet sizes typical for Web applications. What + makes VoIP different is the small packet size, which means order of magnitude + more packets and permits only a few hundred CPU instructions per packet - + nowhere near enough to drive a packet through the standard OpenStack + networking stack from VM to NIC. Instead, this requires technologies such + as SR-IOV (https://blueprints.launchpad.net/nova/+spec/pci-passthrough-sriov + - completed in 2014.2, though with some technical debt remaining) or a DPDK + or similar poll mode based vSwitch in the host. Note that SR-IOV in + particular imposes some limitations (e.g. prevents live migration) so may not + be a desirable option for some SPs. + + Ideally the network would support and respect QoS rules on traffic priority + and bandwidth limits. + +* Security - networking implications + + Security groups must be disabled for network technologies where they are + not bypassed completely. + + The network should protect against ARP poisoning attacks from other VMs. + +* High scale TCP - networking implications + + For ports with security group function disabled, it is desirable that host + connection tracking function is disabled to avoid performance and occupancy + hits for large numbers of TCP connections and the need to tune host + parameters unnecessarily. + +* Achieving packets per second target - compute implications + + * To achieve line rate all the working data for processing RTP streams + (active flows etc.) must be kept in L3 cache - main memory look-ups are too + slow. That requires pinning guest vCPUs to host pCPUs. + + * To optimise the data flow rate it is desirable to bind to a NIC on the host + CPU's bus. + + * To offer performance SLAs rather than simply "best efforts" we need to + control the placement of cores, minimise transaction lookaside buffer (TLB) + misses and get accurate info about core topology (threads vs. hyperthreads + etc). + +* HA + + Perimeta must be deployable to provide a 5 9's level of availability. If + deployed in a single cloud instance, that instance must therefore itself be + more than 5 9's available. As that is hard to achieve with today's state of + the art, Perimeta is designed to be able to span multiple independent cloud + instances, so that the failure of any one cloud has a minor impact. The + requirements that creates are still being discussed and will be addressed in + a future use case. + + When deploying Perimeta within a single cloud instance, Perimeta uses an + active/standby architecture with an internal heartbeat mechanism allowing the + standby to take over within seconds of failure of the active, including + taking over its IP address. To support these application level HA mechanisms + requires: + + * support for anti-affinity rules to permit the active and standby being + instantiated on the same host + + * support for application-controlled virtual IPs via gratuitous ARP based + scheme (for IPv4) and NDP Neighbour Advertisements (for IPv6); in both + cases the standby sends messages saying it now owns the virtual IP address. + + The former is supported through standard anti-affinity nova scheduler rules, + and the latter through the neutron allowed-address-pairs extension. + + If using SR-IOV, Perimeta does not need multiple SR-IOV ports, as + application level redundancy copes with the failure of a single NIC. However, + it can take advantage of local link redundancy using multiple SR-IOV vNICs. + For this to be of any benefit requires the SR-IOV VFs forming a redundant + pair to be allocated on separate PFs. + + Additionally, it is clearly desirable that the underlying cloud instance is + as available as possible e.g. no single points of failure (SPOFs) in the + underlying network or storage infrastructure. + +* Elastic scaling + + An NFV orchestrator must be able to rapidly launch or terminate new Perimeta + instances in response to applied load and service responsiveness. This is + basic OpenStack nova function. + +* Support for a scalable mechanism to support multiple networks in a VM + + There must be a scalable mechanism to present multiple networks to Perimeta, + of order hundreds or thousands, so far exceeding the number of vNICs that can + be attached. Various mechanisms are possible; a common one, and the one + that Perimeta supports, is for different customer networks to be presented + over VLANs. This creates a guest requirement for VLAN trunking support. + + There are multiple possible ways of mapping networks to these VLANs within + OpenStack, for example, trunking external VLAN networks directly to the VMs + with minimal OpenStack knowledge or configuration (already supported in Kilo) + or configuring the mapping between OpenStack networks and VLANs as covered in + VLAN aware VMs: https://blueprints.launchpad.net/neutron/+spec/vlan-aware-vms + +Related Use Cases +================= + +None as yet, but any VNF that needs to do line rate processing of VoIP packets +will likely have similar requirements and gaps. + +Gaps +==== + +The above requirements currently suffer from these gaps. + +* SR-IOV + + Initial support for this has been released, but there remains technical debt + being tracked at https://etherpad.openstack.org/p/kilo_sriov_pci_passthrough + which would improve the usability and robustness of an SR-IOV-based solution. + + Making use of multiple bonded SR-IOV VFs requires the following two bps: + + * SR-IOV VFs distributed across multiple pNICs + + * https://blueprints.launchpad.net/nova/+spec/distribute-pci-allocation + + * Allow user to control setting of spoof checking for the SR-IOV ports + + * http://specs.openstack.org/openstack/neutron-specs/specs/liberty/sriov-spoofchk.html + + Allowing link redundancy with SR-IOV requires the following bp: + + * https://blueprints.launchpad.net/nova/+spec/distribute-pci-allocation + + Additional minor enhancements that would be useful: + + * http://specs.openstack.org/openstack/nova-specs/specs/liberty/approved/pci-passthrough-whitelist-regex.html + +* QoS + + * http://specs.openstack.org/openstack/neutron-specs/specs/liberty/qos-api-extension.html + +* Security protection + + * http://specs.openstack.org/openstack/neutron-specs/specs/liberty/arp-spoof-filtering-ebtables.html + +* CPU pinning + + https://blueprints.launchpad.net/nova/+spec/virt-driver-cpu-pinning + http://specs.openstack.org/openstack/nova-specs/specs/liberty/approved/virt-driver-cpu-pinning.html + +* VLAN aware VMs + + http://specs.openstack.org/openstack/neutron-specs/specs/liberty/vlan-aware-vms.html + +The following are not yet addressed. + +* Removing redundant bridge + + https://blueprints.launchpad.net/neutron/+spec/ovs-optimization-redundant-bridge + +* Disabling connection tracking in host + + [No current blueprint] + +* HA + + As above, to deliver 5 9's service Perimeta expects to be deployed spanning + multiple cloud instances, but if deployed in a single instance it is + desirable for that cloud to be available as possible. + +This use case also implicitly places requirement on elements outside core +OpenStack, such as the DPDK OVS mechanism driver +(https://github.com/stackforge/networking-ovs-dpdk). + +References +========== + +N/a. +