FIBRE CHANNEL and IP SAN INTEGRATION(9)

The maturity and mission-critical deployment of Fibre Channel (FC) in storage area networks (SANs) creates a unique class of multi-terabit networks with demanding throughput, latency, scalability, robustness, and availability requirements. This paper revie

fabrics without requiring fabric address changes. A gateway manages the session state, addresses translation and mapping, and provides proxy functions for remote devices. In addition, a gateway performs security functions (like authentication of devices), and works with an iSNS server for registry and discovery functions. The configuration and management of an iFCP gateway is more involved than for an FCIP gateway, as each device-device session has to be set up. Also, an iFCP gateway has more device proxy-related states to manage. As the number of device-to-device sessions increases, an iFCP gateway design becomes more complex and may result in performance and stability issues. However, one can use admission control techniques to limit the number iFCP sessions allowed for a gateway. Since an iFCP gateway is managing device-to-device communications, it can enforce some degree of flow control by pacing command forwarding at the time of congestion. The iFCP specification allows an optional unbounded connection feature, which sets up and uses a pool of backup TCP connections for fast-session fail-over support. This assists a gateway in providing faster connection fail-over.3.5 TCP/IP & Transport Protocol DiscussionsSome classes of applications have different requirements for transport services and protocols. For example, applications that prefer timeliness in delivery over reliable data delivery (such as RealAudio, Voice over IP) prefer a different transport service and protocol design [17] than that of TCP. Also, for applications that prefer a different type of fault tolerance, reliability, and a non-byte stream-oriented transport service, a different type of transport protocol might be needed (such as Stream Control Transmission Protocol (SCTP) [18]). These are examples of new transport protocol research and standard development activities. TCP protocol is undergoing many enhancements to improve performance under different operating conditions, and these enhancements include High Performance Extensions (TCP Window Scaling Option, Round-Trip Time Measurements, Protect Against Wrapped Sequence Numbers) [19], Selective Ack Option [20, 21], Explicit Congestion Notification [22, 23], Eifel Detection Algorithm [24], and High Speed TCP (HSTCP) [25]. As part of the design considerations for an IP SAN, the design and tuning of TCP for the SAN is critical. For iSCSI servers and storage devices, the design and tuning of protocol off-load, zero-copy, interrupt coalescing, and buffer-MTU-MSS tuning are critical (MTU is the maximum transfer unit, MSS is the maximum segment size). For iSCSI, FCIP, and iFCP gateway design, buffer-MTU-MSS tuning is very critical and several of the aforementioned TCP enhancements are important considerations for scaling the IP SAN for 1 to 10 Gbps speeds. For long and fast network (LFN), HSTCP enhancement is an important design. Multiple TCP connections for iSCSI, FCIP link, and unbounded iFCP connections are critical considerations for load balancing and high availability. In addition to the IP based transport, there are developments for operating Gigabit Ethernet and FC protocol directly over SONET-based transports for Generic Frame Protocol ITU-T G.7041 standards [26].109