Application: The application layer provides services directly to applications. Functions can include identifying communication partners, determining resource availability, and synchronizing communication.

Presentation: The presentation layer provides a variety of coding and conversion functions that are applied to application layer data. These functions ensure that information sent from the application layer of one system will be readable by the application layer of the another system.

Session: The session layer establishes manages, maintains, and terminates communication sessions between applications. Communication sessions consist of service requests and service responses that occur between applications located in different network devices.

Transport: The transport layer segments and reassembles data into data streams. It is also responsible for both reliable and unreliable end-to-end data transmission. Transport layer functions include flow control, multiplexing, virtual circuit management, and error checking and recovery.

Network: The network layer uses logical addressing to provide routing and related functions that allow multiple data links to be combined into an internetwork. The network layer supports both connection-oriented and connectionless service from higher layer protocols. Network layer protocols are typically routing protocols; however, routed protocols like IP are implemented at the network layer as well.

Data Link: The data link layer provides reliable transmission of data across a physical medium. The data link layer specifies different network and protocol characteristics, including physical addressing, network topology, error notification, sequencing of frames, and flow control. The data link layer is composed of two sublayers known as the Media Access Control Layer and the Logical Link Control Layer. The LLC sublayer manages communications between devices over a single link of a network and the MAC sublayer manages protocol access to the physical network medium. Implementations can be categorizes as either LAN or WAN.

Physical: 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 such characteristics voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, and physical connectors to be used.

In the threaded case study we are using 10 Base T, 100 Base T, and 100 Base FX LAN specifications

The TCP/IP transport-layer provides the following functions:

IP addressing is divided into three main classes of addresses. These classes are defined by the range of the first octet as well as the length of the network and host portions of the address:

Class A 1-127 8 bit Network and 24 bit Host.

Class B 128-191 16 bit Network and 16 bit Host.

Class C 192-223 24 bit Network and 8 bit Host.

Subnetting further divides network addresses by utilizing the first x bits of the host address, where x is between 2 and the maximum host address length minus 2. This results in 2 to the x, –2 potential subnets and 2 to the subnetted host address length, -2 hosts addresses per subnet.

The TCP/IP network-layer provides the following functions:

A MAC address is a data link address that uniquely defines each and every interface so that a communication conflict at the data link layer is prevented.

Data link addresses are burned into the network card and assigned sequentially by the manufacturer resulting in a flat addressing model.

Network addresses are assigned either manually by users or dynamically by DHCP and follow a logical scheme resulting in a hierarchical model.

See description above.

Network congestion can be caused by several factors. Advances in technology producing faster and more intelligent servers and workstations, and more network intensive applications, plus larger file sizes and more users sharing the network all contribute to this problem.

There are basically two options to reduce or eliminate this problem. Increase the bandwidth, or reduce the collision domain.

Full duplex Ethernet can provide twice the bandwidth of traditional ethernet, but requires the use of interfaces on both ends of a point to point link that support it. It is collision free, unlike Half duplex, because there are separate transmit and receive wires. Half duplex, unlike full duplex must provide for collision detection.

Fast Ethernet provides ten times the bandwidth of standard Ethernet. Because of its compatibility with standard 10BaseT, the two standards can be shared on the same network and many Ethernet devices can auto-negotiate between the two standards based upon the device(s) they are attached to.

Fast ethernet provides 10 times the bandwidth of 10 base T ethernet by running at 100 Mbps. It must utilize Category 5 unshielded or shielded twisted pair cabling and not exceed 100 meters in total length, or Multi-mode fiber cabling and not exceed 400 meters in total length.

A bridge segments a LAN by examining the destination MAC address of each frame and only forwards them to the other side of the bridge if the address is not local.

A router segments a LAN by examining the destination layer three protocol address of each packet and forwards them to using the best available route to the destination network based upon the data stored in its routing tables.

A switch segments a LAN by examining the destination MAC address of each frame and forwards them to the appropriate switch port based upon the table of MAC addresses it has built from past data flowing on each of its ports.

Using a bridge to segment a LAN provides more bandwidth per user then the same LAN without the bridge.

Using a router to segment a LAN provides the highest level of segmentation by providing more bandwidth per user in the collision domain as well as isolation of broadcasts to the local segments.

Using a switch to segment a LAN creates micro-segments for each device creating a collision-free domain.

Store-and-Forward – copies the entire frame into the switches buffer, checks for CRC errors, then forwards the frame out the appropriate port.

Cut-Through – reads only the destination MAC address into the buffer, and then forwards the frame out the appropriate port immediately.

See above.

VLAN’s reduce administration costs associated with moves, adds and changes.

VLAN’s control broadcasts by only sending them to the ports assigned to the application.

VLAN’s provide workgroup and network security.

VLAN’s can save money by utilizing existing hubs.

An IP address is made up of a network number, a subnet number s, and a host number. The network and subnetwork numbers together are used for routing, while the host number is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork information from the IP address.

When a host application needs to send a packet to a destination on a different network, a data-link frame is received on one of a router’s interfaces. The network layer process examines the packet header to determine the destination network and then references the routing table that associates networks to outgoing interfaces. The packet is again encapsulated in the data-link frame for the selected interface and queued for delivery to the next hop in the path.

See above.

Static routes are useful for isolating an autonomous area utilizing a routing protocol, or for a network with only one path in and out. A Static route is administered manually: A network administrator enters it into the router’s configuration. Therefore, the administrator must manually update this static route entry whenever an internetwork topology change requires an update. Tracking these entries can become an administrative burden.

After the network administrator enters configuration commands to start dynamic routing, route knowledge is updated automatically by a routing process whenever new information is received from the internetwork. Changes in dynamic knowledge are exchanged between routers as part of the update process.

A routed protocol provides enough information in its network layer address to allow a packet to be forwarded from host to host based on the addressing scheme whereas a routing protocol supports a routed protocol by providing mechanisms for sharing routing information.

The network layer process examines the header of each packet to determine the destination network and then references the routing table that associates networks to outgoing interfaces.

The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork. Periodic updates are propagated from router to router with each router adding its own metrics.

The link-state approach re-creates the exact topology of the entire internetwork (or at least the area/zone/partition in which the router is situated). Updates only occur when a change is made or a link goes down at which time the link state change is flooded to every router in the autonomous network.

When all routers in an internetwork, autonomous system, are operating with the same knowledge base, the internetwork is said to have converged.

List kept by and configured in Cisco routers by an administrator to control access to or from the router for specifically assigned network and host numbers and/or one or a number of upper layer services.

Access lists can be utilized to:

As a packet enters an interface, the router checks to see whether it is routable (the act of segmenting). If not, the packet will be dropped. A routing table entry indicates a destination network, some routing metric or state, and the interface to use.

Next the router checks to see whether the destination interface is grouped to an access list. If it is not, the packet can be sent to the output buffer. If it is, its contents are tested against the access list.

If based on the access list tests, the packet can be permitted; for inbound lists, this means continue to process the packet after receiving it on an inbound interface; for outbound lists, this means send it to the output buffer. Otherwise test results can deny permission. This means discard the packet. When discarding packets, some protocols return a special packet to the sender. This notifies the sender of the unreachable destination.

Standard access control lists deal with the source and destination (IPX only) addresses, so they function at layer three exclusively. Since they are only concerned with the source and destination (IPX only) addresses, the only fields in the packet header they inspect are the source and destination (IPX only) addresses.

A connectionless data packet delivery system operates without the existence of a virtual circuit. It is a network system that does not use a sophisticated acknowledgment system to guarantee reliable delivery of information

IPX addressing uses a two-part address, the network number and the node number. The IPX network number can be up to 8 hexadecimal digits in length. The network administrator assigns this number.

The IPX node number is 12 hexadecimal digits in length. This number is usually the MAC address obtained from a network interface that has a MAC address

All the servers on NetWare internetworks can advertise their services and addresses. Adding, finding, and removing services on the internetwork are dynamic because of SAP advertisements. Each SAP service is an object type identified by a hexadecimal number. All servers and routers keep a complete list of the services available throughout the network in server information tables. Like RIP, SAP also uses an aging mechanism to identify and remove table entries that become invalid. By default, service advertisements occur at 60-second intervals.

SAP stands for Service Advertising Protocol. The three major types of services advertised by IPX are routing in the form of RIP, location of the nearest IPX server in the form of GNS, and other services in the form of SAP??

In a Novell network, when a client boots up, it will initiate the connection sequence for the NetWare command shell using SAP. The nearest NetWare file server will respond with a GNS SAP response. From this point on the client can log on to its designated target server, and proceed to use the advertised services.

Get Nearest Server request packets are sent by a client on an IPX network to locate the nearest active server of a particular type. An IPX network client issues a GNS request to solicit either a direct response from a connected server or a response from a router that tells it where on the internetwork the service can be located.

The capability to deliver packets from several routed protocols over the same data links. To do this, routers supporting multiple independent routing protocols by maintaining routing tables for several routed protocols concurrently.