Application layer functions typically include identifying communication partners, determining resource availability, and synchronizing communication. ...
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Brent R. Hafner
Client - Server
Session service provides four basic services to SS-users.
Five connection-oriented transport layer protocols exist in the OSI suite, ranging from Transport Protocol Class 0 through Transport Protocol Class 4. Connectionless transport service is supported only by Transport Protocol Class 4.
The network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination via one or more networks while maintaining the quality of service requested by the transport layer. The Network layer performs network routing, flow control, network segmentation/desegmentation, and error control functions
i.e. P (IPv4 • IPv6) • ARP • RARP • ICMP • IGMP • RSVP • IPSec •
no call setup at network layer
routers: no state about end-to-end connections
no network-level concept of “connection”
packets forwarded using destination host address
packets between same source-dest pair may take different paths
The Logical Link Control (LLC) sublayer of the data link layer manages communications between devices over a single link of a network. LLC is defined in the IEEE 802.2 specification and supports both connectionless and connection-oriented services used by higher-layer protocols. IEEE 802.2 defines a number of fields in data link layer frames that enable multiple higher-layer protocols to share a single physical data link. The Media Access Control (MAC) sublayer of the data link layer manages protocol access to the physical network medium. The IEEE MAC specification defines MAC addresses, which enable multiple devices to uniquely identify one another at the data link layer.
The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between communicating network systems. Physical layer specifications define characteristics such as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and physical connectors.
Physical layer implementations can be categorized as either LAN or WAN specifications. Figure 1-7 illustrates some common LAN and WAN physical layer implementations.
Workload management is often deployed to proactively shift workload on the basis of the current state of the system, server, and/or networking metrics. This can be done at Level 4 or Level 7 in the OSI model.
For example, consider a service whose Domain Name Server (DNS) name is Service_A.com. Normally, there would be a server set up somewhere with that host name and IP address. With Layer 4 switching, the switch module itself takes ownership of the IP address as a VIP
and has multiple ‘‘real’’ server blades behind it capable of delivering the service Service_A.com, whose addresses can be arbitrarily assigned, since they are of only local significance.
ESX Server installs on the “bare metal” and allows multiple unmodified operating systems and their applications to run in virtual machines that share physical resources.
Each virtual machine represents a complete system, with processors, memory, networking, storage and BIOS.
Advanced resource allocation policies for virtual machines allow you to guarantee resources to even your most resource-intensive applications.
As shown in Figure 8, each of the server blades can
support virtual machine (VM) technology, such as
VMware** virtual infrastructure [34–36], in order to share
the blade physical resources by hosting multiple instances
of OS images. In addition to the blade being shared, the
networking infrastructure can also be shared with the use
of VLAN technology, and security can be maintained
between VMs. For example, each VM shown in Figure 8
can be logically associated with an independent VLAN
configured on the switch, so that with three VMs per
blade, there could be a total of 3 3 m total VLANs
configured internally and trunked out to the uplinks of