8. Translate the passages in writing:

a) Switches usually work at Layer 2 (Data or Datalink) of the OSI Reference Model, using MAC addresses, while routers work at Layer 3 (Network) with Layer 3 addresses (IP, IPX or Appletalk, depending on which Layer 3 protocols are being used). The algorithm that switches use to decide how to forward packets is different from the algorithms used by routers to forward packets.

b) Broadcasts are used any time a device needs to make an announcement to the rest of the network or is unsure of who the recipient of the information should be. A hub or a switch will pass along any broadcast packets they receive to all the other segments in the broadcast domain, but a router will not.

c) A switch using store-and-forward will save the entire packet to the buffer and check it for CRC errors or other problems before sending. If the packet has an error, it is discarded. Otherwise, the switch looks up the MAC address and sends the packet on to the destination node.

9. Answer the following questions using the information from parts 7, 8 and 9 of the text.

1. What kind of network is called a mixed network? 2. What layer of the OSI Reference Model do switches usually work at? 3. What is the difference in the algorithms between switches and routers? 4. When a new computer or other device comes on to the network, what does it do to announce its presence? 5. What example does the author give to describe the work of a router? 6. What technology do LAN switches rely on? 7. What does an Ethernet frame contain in an Ethernet based LAN? 8. What three methods do packet-based switches use for routing traffic? 9. What is the difference between cut-through and store-and-forward methods of routing traffic? 10. What`s the main idea of fragment-free methods?

10. Look through parts 7, 8 and 9 of the text and mark the statements as true (t) or false (f). If you think a statement is false, change it to make it true.

1.	□	Most networks are not fully switched because it is rather expensive to replace all of the hubs with switches.
2.	□	Switches usually work at Layer 3 of the OSI Reference Model.
3.	□	On any network the concept of a broadcast packet is of no importance to the operability of a network.
4.	□	Whenever a device needs to send out information but doesn`t know who it should send it to, it sends out a broadcast.
5.	□	A switch will never pass along any broadcast packets it receives to all the other segments in the broadcast domain.
6.	□	LAN switches rely on packet-switching.
7.	□	Incoming packets are saved to the switch`s look-up table.
8.	□	Cut-through switches save the entire packet to the buffer and check it for CRC errors or other problems before sending.
9.	□	Many switches combine the two methods, using cut-through until a certain error level is reached and then changing over to store-and-forward.
10.	□	A switch using a fragment-free method stores the first 6 bytes of the packet before sending it on.