Service availability platform interface specification The Service Availability Forum is a consortium of communications industry leaders and innovative startups dedicated to producing standards to enable development of carrier-grade communications systems from off-the-shelf hardware platforms and middleware. The key characteristic of a carrier grade system is its ability to provide uninterrupted user access to the services it is designed to deliver, with no loss to the continuity of those services. To meet this goal, the Service Availability Forum is developing two layers of standard, carrier-grade interfaces: an application interface and a platform interface.
The Service Availability Forum Application Interface provides access to a standard set of tools for application software to use to distribute processing over multiple computing elements, and to respond to failures of those elements without loss of service delivery or continuity to any user. Management middleware that conforms to the Service Availability Forum Application Interface provides these tools. Specification middleware that conforms to this specification is called service availability middleware.
Service availability middleware provides these tools to application software in part by monitoring and controlling the physical components of a high-availability computing platform via the Service Availability Forum Platform Interface. By using a standard interface to manage the physical platform, developers can write the service availability middleware independently of any particular hardware. This independence, in turn, allows application developers to choose the best hardware platform and the best service availability middleware to fit their needs.
Carrier Grade Linux Specification The OSDL Carrier Grade Linux Working Group formed in January 2002. It consists of several equipment providers including Nokia, Alcatel, Cisco, Ericsson, and NEC, and platform providers such as IBM, HP, and Intel. MontaVista Software, SuSE, and Red Hat are Linux distributors that are also part of the Carrier Grade Working Group. These companies are committed to developing and promoting a common standard definition for Carrier Grade Linux. The specification promotes portability, ease of programming, and software availability for telecom developers looking to implement Linux in an equipment design. This standard focuses on high availability, performance, and adopting new leading edge technologies that promote high availability and service ability. Additionally, the working group hopes to develop standards that make it easier to avoid problems in coding, and thus improve the reliability of systems. These standards will ensure that companies have choices for Carrier Grade Linux but that all of them will meet the specification, will support a rich set of high availability features, and will have consistent interfaces and functionality.
Some of the standards on which the OSDL Working Group is focusing are LSB compliance, IPv6 (including IPSECv6 and MIPv6) compliance, SNMP support, and POSIX interface compliance in the areas of timers, signals, message queues, semaphores, event logging, and threads.
High availability One important characteristic of highly available systems is redundancy of key subsystems. A highly available system should include redundant Ethernet to ensure constant networking connections and disk mirroring to ensure high levels of data reliability. Carrier Grade Linux also includes an enhanced kernel with hardened device drivers and fault response behaviors, such as panic handler improvements, that ensure the application logs appropriate messages and sends notifications before a kernel panic.
Hardware redundancy Hardware redundancy is commonly achieved by deploying CompactPCI chasses that support failover and hot-insertion and removal of field replaceable units. CompactPCI and its successor, AdvancedTCA, are preferred platforms for carrier grade solutions. CompactPCI offers the most flexibility in terms of processor choice and overall architecture. From an application software perspective, the choice of form factor is often transparent. The Linux OS kernel, drivers, and interfaces encapsulate support for CompactPCI. Linux is very much at home on these architectures, and solid commercial ports are available for the embedded architectures represented thereon, specifically IA-32/x86, PowerPC, and sometimes MIPS. The same cannot be said of Windows and most RTOS platforms. Carrier Grade Linux requires full support of PICMG 2.12 and full device enumeration.
When defining the high availability platform, the main requirement is to support hot swap, remote boot, diskless operation, and headless operation (no console). The Carrier Grade Linux definition of hot swap also includes the concept of hot insert (adding cards to the system not originally in place at boot time), hot remove (not replacing cards that are removed), and identity maintenance (maintaining device identities across hot swaps and system boots). Today, different implementations of embedded Linux support these features.
Redundant Ethernet Redundant Ethernet refers to a driver, the bonding driver, which permits grouping of LAN connections to provide for link failover, link throughput aggregation, or both. All links in a bond have the same Ethernet and MAC addresses. Link failover refers to the process by which a failure of one component of a redundant link can be transparently masked by having its traffic routed to another link. The bonding driver accomplishes this task by continuously monitoring all links available to it and removing any links from service that are no longer operative. With the proper sort of switch, the system can aggregate the redundant links to provide better throughput, but it can offer failover operation with any class of switch.
