11. Make summary of parts 13 and 14 of the text.

12. Read the text and insert articles where necessary. A) Give definitions to the word combinations in bold type. Spanning Trees

Spanning trees are __ standard technique used in local area network (LAN) switching. __ Spanning tree algorithms were developed to prevent redundant transmission of data along intermediate hops between __ source and destination host on __ mesh network topology. Without spanning trees, __ mesh network can be flooded and rendered unusable by __ messages circulating in __ infinite loop between hosts.

__ primary Spanning Tree Protocol (STP) is IEEE standard 802.1D, an algorithm commonly used on __ Ethernet networks. This algorithm works by limiting the paths messages can travel at any given time to __ fully connected tree rather than __ mesh. As hosts join and leave __ network, this protocol dynamically updates the tree accordingly.

__ variant of STP called Rapid Spanning Tree Protocol (RSTP) is also now part of __ IEEE standard and is the recommended version for use today. RSTP improves __ performance of spanning tree updates when the network configuration changes.

(By Bradley Mitchell)

13. Read the following text and fill in words from the box. Each word can be used once only.

directs assigns half-duplex firewall software accommodates arrive

difference signals antenna eavesdropping trick increase

interface transmits mode device broadcasts cost

A Networking Switch

¹A networking switch is the central _____ in a wired or wireless LAN (local area network). It receives _____ from each computer on the network via Ethernet cables in a wired network or radio waves in a wireless LAN. In both cases, the networking switch _____ traffic across the LAN, enabling the computers to talk to each other and share resources.

²All computers included in the LAN must contain a network _____ card (NIC). The card _____ a unique address to the machine in which it is installed. This address is called a MAC (Medium Access Control). A wired NIC _____ an Ethernet cable, which runs to a port on the back of the networking switch. If the NIC is wireless, the card will feature a small _____ instead of an Ethernet port. The antenna _____ signals to the wireless networking switch, which also bears an antenna rather than ports. Whether wireless or wired, the networking switch acts as a relay, reading traffic packets as they _____ from the various machines and directing the packets to the proper MAC address.

³A networking switch runs in full-duplex _____, meaning a machine on the LAN can receive and transmit data simultaneously. This is much faster than a networking hub, an alternate device that serves the same purpose as a switch but operates in _____ mode, allowing each machine or node either to send or receive at any given time. Another key _____ between a networking switch and a hub is that the switch sends traffic discriminately, using addresses to direct traffic packets exactly where they are supposed to go. Conversely, a networking hub _____ all traffic on the network to all nodes, relying on filters within each machine to discard packets not addressed to it. This makes networks that use a hub particularly vulnerable to "packet sniffers" or _____.

⁴For the above reasons, a networking switch is considered superior to a networking hub. However, a networking switch is also not foolproof. It can be "tricked" into accommodating packet sniffers, but the methods used to _____ the switch will leave telltale traffic signatures, unlike the passive methods that can be used on a hub. Anti-sniffing _____ can be installed on a switched network to detect packet sniffers.

⁵Network switches are inexpensive devices that _____ in price with the number of ports featured. A basic Ethernet networking switch might come with five ports at a _____ of about US$30. For those with cable modem or DSL service, a broadband router with a built-in switch and _____ can be used in lieu of a stand-alone networking switch.

(By Bradley Mitchell)