HP StorageWorks 8/80 HP StorageWorks Fabric OS 6.1.x administrator guide (5697 - Page 378

Compression Data compression can be enabled or disabled on FCIP tunnels. The default setting is to disable compression. Traffic shaping Traffic can be shaped by establishing a rate limit per tunnel. A committed rate can be assigned to a port that guarantees a fixed amount of bandwidth. The committed rate setting insures that a FCIP tunnel will operate at a specific fixed rate (given enough FC traffic to consume it). If too little committed rate is defined, the FCIP tunnel would be limited to that rate and performance could be limited. QoS concepts and implementation over FCIP Quality of Service (QoS) refers to policies for handling differences in data traffic. These policies are based on data characteristics and delivery requirements. For example, ordinary data traffic is tolerant of delays and dropped packets, but voice and video data are not. QoS policies provide a framework for accommodating these differences in data as it passes through a network. FOS versions 6.0.0 and higher provide for Fibre Channel QoS through internal QoS priorities. Those priorities can be mapped to TCP/IP network priorities. There are two options for TCP/IP network based QoS: • Layer three DiffServ code Points (DSCP). • VLAN tagging and Layer two class of service (L2CoS). Layer three DiffServ Code Points (DSCP) Layer three class of service DiffServ Code Points (DSCP) refers to a specific implementation for establishing QoS policies as defined by RFC2475. DSCP uses six bits of the Type of Service (TOS) field in the IP header to establish up to 64 different values to associate with data traffic priority. DSCP settings are useful only if IP routers are configured to enforce QoS policies uniformly within the network. IP routers use the DSCP value as an index into a Per Hop Behavior (PHB) table. Control connections and data connections may be configured with different DSCP values. Before configuring DSCP settings, determine if the IP network you are using implements PHB, and consult with the network administrator to determine the appropriate DSCP values. VLAN tagging and layer two class of service (L2CoS) Devices in physical LANs are constrained by LAN boundaries. They are usually in close proximity to each other, and share the same broadcast/multicast domain. Physical LANs often contain devices and applications that have no logical relationship. Also, when logically related devices and applications reside in separate LAN domains, they must be routed from one domain to the other. A VLAN is a virtual LAN network. A VLAN may reside within a single physical network, or it may span several physical networks. Related devices and applications that are separated by physical LAN boundaries can reside in the same VLAN. Also, a large physical network can be broken down into smaller VLANs. VLAN traffic is routed using 802.1Q compliant tags within an Ethernet frame. The tag includes a unique VLAN ID, and Class of Service (CoS) priority bits. The CoS priority scheme (sometimes called Layer two Class of Service, or L2CoS), uses only the upper three bits of the TOS field, allowing eight priorities. When both DSCP and L2CoS are used If an FCIP tunnel is not VLAN tagged, only DSCP is relevant. If the FCIP tunnel is VLAN tagged, both DSCP and L2CoS are relevant, unless the VLAN is end-to-end, with no intermediate hops in the IP network. 378 Configuring and monitoring FCIP extension services