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SONET or SDH service can be purchased on a monthly basis in
accordance with a negotiated SLA. However, the transport links may
require sufficient BB _Credits to use the purchased bandwidth.
Because of BB_Credit limitations, GFP equipment must provide
buffering and flow control for native FCP or FICON storage data.
Without GFP equipment, iFCP must be used to transmit the data.
Internet Protocol
As demonstrated by the Internet, an infrastructure based on IP and
Ethernet delivers an unrestricted topology that scales to large
geographical distances. IP and Ethernet have well-developed
cross-vendor capabilities, routing, and security, and there is no
inherent distance limitation. This means storage over IP (SoIP) is
well-suited to provide the low to medium bandwidth (over longer
distances) required for asynchronous data replication. Block-based
SoIP protocols include:
•
•
iFCP is an application-layer gateway protocol (FCP-to-iFCP-to-FCP)
solution that connects remote storage devices or SANs across
extended distances that Fibre Channel cannot support. iFCP
effectively replaces a Fibre Channel SAN with an IP network but
continues storage application support.
The protocol can be used over the Internet or a dedicated GbE
network (with IP traffic engineering). Each connected Fibre Channel
fabric (or SAN) is maintained separately, while the IP or GbE network
provides connectivity, congestion control, error detection, and error
recovery.
The technology:
•
•
iFCP - This protocol uses FCP to provide SCSI command set
encapsulation, enabling Fibre Channel device communication
across an IP network.
iSCSI - This protocol encapsulates the SCSI command set directly
to the IP transport network without relying on Fibre Channel
conventions. Refer to
iSCSI Protocol
Figure 4-11
illustrates SoIP extended-distance connectivity.
Is widely deployed and highly-available, and is well suited as an
extension technology for ADR applications over thousands of
kilometers.
Does not require Fibre Channel BB_Credits assigned to the link.
IP and GbE transmit data frames without use of BB_Credits and
enable long-distance transmission of storage traffic.
Implementing SAN Internetworking Solutions
Implementing SAN Internetworking Solutions
for additional information.
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