Networking Chapter 8-9 Homework
How does a router differ from a VLAN?
VLAN switches can create multiple subnets, so they act like routers, except the subnets are inside the switch, not between switches. Therefore, broadcast messages sent by computers in one VLAN segment are sent only to the computers on the same VLAN.
What are the advantages and disadvantages of VLANs?
VLANs allow computers in different locations to be in the same subnet while managing the flow of traffic on LAN and backbone. However, VLANs are expensive as well as difficult to manage.
Is a WAN that uses dedicated circuits easier or harder to design than one that uses packet-switched circuits? Explain
WANs that use dedicated circuits are harder to design than WANs that use packet-switched circuits. When making changes to use dedicated circuits, it can be expensive when buildings need to be rewired.
What are common carriers, local exchange carriers, and interexchange carriers?
A common carrier is a private company that sells or leases communication services and facilities to the public. Common carriers are profit-oriented, and their primary products are services for voice and data transmissions, both over traditional wired circuits as well as cellular services. Common carriers often supply a broad range of computer-based services, such as the manufacturing and marketing of specialized communication hardware and software. Common carriers that provide local telephone services are commonly called local exchange carriers (LEC), while carriers that provide long distance services (e.g., Sprint) are commonly called interexchange carriers (IXC). As the LECs move into the long distance market and IXCs move into the local telephone market, this distinction may disappear.
How do VPN services differ from common carrier services?
A type of VAN, called a virtual private network (VPN) (or sometimes software defined network) has emerged. VPNs provide circuits that run over the Internet but appear to the user to be private networks. Internet access is inexpensive compared to the cost of leasing dedicated circuits, circuit switched services, or packet switched services from a common carrier. Different VPNs provide different services, but most offer packet switching hardware that will communicate via the Internet, or VPN services which you lease from the VPN in much the same way as leasing a service from a common carrier. These VPN hardware (or services) take your data, encrypt it, and send it through the Internet through a series of "tunnels" -- a virtual circuit through the Internet which constrains the source and destination to only those within the VPN.
How do Ethernet services work in the WAN?
Any LAN/BN traffic must be translated or encapsulated into a new protocol and destination addresses are generated for the new protocol. This takes time, slowing network throughput.
How do packet-switching services differ from other wide area networks services?
Different locations can have different connection speeds into the common carrier cloud They enable packets from separate messages with different destinations to be interleaved for transmission Permanent Virtual Circuits are changed with software
How does a layer-2 switch differ from a router?
Layer 2 switches operate by using the data link layer address or MAC address to forward packets between network segments. They connect the same or different types of cable. Layer-2 switches (or workgroup switches) operate at the Data Link layer, and typically provide ports for a small set of 16 to 24 computers. Layer-2 switches enable all ports to be in use simultaneously by managing paired combinations of ports as separate point-to-point circuits. Layer-2 switches "learn" addresses; a layer-2 switch builds a forwarding table after it is first turned on. To learn addresses, a layer-2 switch retransmits to all ports (except to the one from which it was received) only for a packet with a destination address not already in the forwarding table. The resulting ACK from the destination computer (that recognized its address) is then used by the layer-2 switch to add the new port number and address to the forwarding table. Routers operate at the network layer. They connect two different TCP/IP subnets. Routers strip off the data link layer packet, process the network layer packet, and forward only those messages that need to go to other networks on the basis of their network layer address. In general, they perform more processing on each message than switches and therefore operate more slowly.
How does a layer-2 switch differ from a VLAN?
Layer 2 switches operate by using the data link layer address or MAC address to forward packets between network segments. They connect the same or different types of cable. Layer-2 switches (or workgroup switches) operate at the Data Link layer, and typically provide ports for a small set of 16 to 24 computers. Layer-2 switches enable all ports to be in use simultaneously by managing paired combinations of ports as separate point-to-point circuits. Layer-2 switches "learn" addresses; a layer-2 switch builds a forwarding table after it is first turned on. To learn addresses, a layer-2 switch retransmits to all ports (except to the one from which it was received) only for a packet with a destination address not already in the forwarding table. The resulting ACK from the destination computer (that recognized its address) is then used by the layer-2 switch to add the new port number and address to the forwarding table. VLAN switches work a little differently. When a VLAN switch receives a frame that is destined for another computer in the same subnet on the same VLAN switch, the switch acts as a traditional layer-2 switch: it forwards the frame unchanged to the correct computer. VLAN switches use Ethernets 802.1q's tagging to move frames from one switch to another. When a VLAN switch receives an Ethernet frame that needs to go to a computer on another VLAN switch, it changes the Ethernet frame by inserting the VLAN ID number and a priority code into the VLAN tag field.
Compare and contrast ring, star, and mesh architecture
Ring Connects all computers in closed loop with full-duplex circuits Computers send data in direction that has shortest vector Star All computers are connected to one central computer Allows easy management because of central computer receives and routes all messages in network Can be faster than ring because less circuits are traversed Since there is only one central computer, managing traffic can be difficult Mesh Every computer is connected to one another High cost if full-mesh is implemented Partial mesh is more commonly used and most WANs use this Loss of circuits/computers may not have large impact on rest of the network But if there are not as many routes, the circuit can shackle the network
What are key advantages and disadvantages of routed and switched backbones?
Routed Backbones - Advantages: Clear segmentation of parts of the network connected to the backbone as each network has a subnet address and can be managed separately; Disadvantages: Slower performance as routing takes more time than bridging or switching. Management and/or software overhead costs due to need to establish subnet addressing and provide reconfiguration when computers are moved (or support dynamic addressing). Switched Backbones - Advantages: Performance is improved. With the traditional backbone network, the backbone circuit was shared among many LANs; each had to take turns sending messages. With the collapsed backbone, each connection into the switch is a separate point-to-point circuit. The switch enables simultaneous access, so that several LANs can send messages to other LANs at the same time. Throughput is increased significantly, often by 200% to 600%, depending upon the number of attached LANs and the traffic pattern. Since there are far fewer networking devices in the network, this reduces costs and greatly simplifies network management. All the key backbone devices are in the same physical location, and all traffic must flow through the switch. If something goes wrong or if new cabling is needed, it can all be done in one place. Software reconfiguration replaces hardware reconfiguration; Disadvantages: Because data link layer addresses are used to move packets, there is more broadcast traffic flowing through the network and it is harder to isolate and separately manage the individually attached LANs. Layer 3 switches can use the network layer address, so future collapsed backbones built with layer 3 will not suffer from this problem. Collapsed backbones use more cable, and the cable must be run longer distances, which often means that fiber optic cables must be used. If the switch fails, so does the entire backbone network. If the reliability of the switch has the same reliability as the reliability of the routers, then there is less chance of an failure (because there are fewer devices to fail). For most organizations, the relatively minor disadvantages of cable requirements and impacts of potential switch failure are outweighed by the benefits offered by collapsed backbones.
Compare and contrast dedicated-circuit services and packet-switched services
With dedicated circuit networks, a circuit is established between the two communicating computers. This circuit provides a guaranteed data transmission capability that was available for use by only those two computers and is assigned solely to that transmission. No other transmission is possible until the circuit is closed. In contrast, packet switched services enable multiple connections to exist simultaneously between computers over the same physical circuit or even over different physical circuits. With a dedicated circuit network, you lease circuits from common carriers for their exclusive use twenty-four hours per day, seven days per week. All connections are point to point, from one building in one city to another building in the same or a different city. The carrier installs the circuit connections at the two end points of the circuit and makes the connection between them. The circuits still run through the common carrier's cloud, but the network behaves as if you have your own physical circuits running from one point to another: Dedicated circuits are billed at a flat fee per month and the user has unlimited use of the circuit. Once you sign a contract, making changes can be expensive because it means rewiring the buildings and signing a new contract with the carrier. Therefore, dedicated circuits require more care in network design than switched circuits both in terms of locations and the amount of capacity you purchase. With packet switched services, the user again buys a connection into the common carrier cloud). The user pays a fixed fee for the connection into the network (depending upon the type and capacity of the service) and is charged for the number of packets transmitted.
