Chap 15, 16, and 17

1. Chap 15, 16, and 17 Dr. John P. Abraham Professor UTRGV, Edinburg, TX

2. Ethernet • Originally invented at Xerox PARC and later standardized by Digital Equipment corp, Intel and Xerox. • Survived over 40 years. Main reason is that newer versions are backward compatible.

3. Ethernet Frame format • Already discussed. However, use the 18 bytes I gave you as the required number of bytes, not 16 as your book says. • Ethernet frame is encoded using Manchester encoding. • Ethernet type used is in hexadecimal, for IP it is 0800 and for ARP it is 0806. See multiplexing and demultiplexing given in fig. 15.2, p 257.

4. LAN connections and Network Interface Cards • Handles address recognition, CRC computation, and frame recognition. • Checks the destination address on a frame and ignores frames not destined for this computer.

5. Ethernet wiring: already covered • Thicknet, thinnet: used bus topology • Remind them about the trancievers and terminators • Logical and physical topology. A hub is seen as a cable logically, but physically you can connect multiple computers to it. • Connectors • Twisted pair

6. 16-Wirless Networking Technologies Dr. John P. Abraham Professor UTRGV

7. Personal area networks (PAN) • Bluetooth – short distance • InfraRed – line-of sight • ISM wireless – communication using frequencies set aside for industrial scientific and medical devices.

8. Wireless Lan Technologies and Wi-Fi • Already discussed speeds and frequency bands. See prior lectures.

9. Spread Spectrum Technologies • Direct sequence spread spectrum (DSSS) • Frequency Hopping spread spectrum (FHSS) • Orthogonal Frequency Division multiplexing • Standards – 802.11e, h, I, k, n, p, r, and s.

10. Wireless LAN architecture • Access Point (base stations) connect to a switch or router. Wireless hosts connects to access points. Those hosts within the range of an access point are called Basic Service Set (BSS) • Ad hoc – wireless hosts communicate among themselves without a base station. • Infrastructure – stations connect to a base station.

11. Overlap, Association and 802.11 frame • If access points are too far apart, we have a dead zone in the middle. • If too close, overlap exist. But a host should only connect to a single access point. In wireless phone service there is a seamless handoff. Access points can coordinate like that. Cheaper access points do not coordinate and the user will have to pick.

12. 17-LAN extensions: Fiber Modems, Repeaters, Bridges and Switches Dr. John P. Abraham Professor UTRGV

13. Distance Limitation • Designing considerations • Capacity • Maximum delay • Distance: hardware emit a fixed amount of energy, so only can travel a certain distance • Cost

14. Fiber Modem extensions • Optical fiber extension require a pair of fiber modems. • Each modem accepts packets from the ethernet interface and sends them over the fiber, And accepts packets that arrive over the optical fiber and send them over the Ethernet Interface.

15. Repeaters • An analog device to propagate LAN signals over long distances. It does not inspect the packets, instead amplifies signals received and transmits over the outputs. • Thick and thinnet used repeaters. An active hub is a repeater. • Repeaters are available for infrared.

16. BRIDGES • Connect multiple LANs • Operate at the Data Link Layer • do not examine the network layer header • doe not care whether it is IP, IPX, or other

17. Purpose of a Bridge • Connect dissimilar networks • Have different networks (different floors) and connect them all together with a bridge • Isolate traffic • Length of cable limitations • Reliability - if one segment goes bad, others work. • Security (not all traffic go through all cables)

18. Bridges and Bridging • Bridges listen in promiscuous mode (listen to all) on each segment. Connects both sides so that it acts like a single LAN. • Learning bridges and frame filtering • Bridge uses MAC addresses to perform filtering to decide either to forward or not. • Bridges learn which computers are connected to which segment by examining source address and then creating a table of its own. As it learns forwarded only to the right one, until then sent to both segments. See fig. 17.4 p.297

20. Distributed Spanning Tree • Views bridges as nodes in a graph and imposes a tree on the graph. 3 steps • Root election – bridge with the smallest ID is chosen • Shortest path computation. Each bridge calculates a shortest path to the root. • Forwarding. Interface that connects to the shortest path is enabled for forwarding packets.

21. VLAN switches • Virtual LAN switch. • Configure one switch to emulate multiple switches. Choose which ports belong to witch virtual switch. • When a computer on VLAN1 broadcasts only computers attached to that VLAN get the packets.

22. VLANs • Virtual LAN. Operates under layer 2, 802.1Q. Physically they could be anywhere, but virtually act like a LAN. Without a VLAN we have to physically run wires as requirements change. • a group of hosts with a common set of requirements that communicate as if they were attached to the same LAN. • 802.1Q header contains a 4-byte tag header containing a 2-byte tag protocol identifier (TPID) and a 2-byte tag control information (TCI). TCI contains Three-bit user priority, One-bit canonical format indicator (CFI), and Twelve-bit VLAN identifier (VID)-Uniquely identifies the VLAN to which the frame belongs • There are Static (port based), Dynamic (VLAN management software using originating MAC address, etc.) and Protocol based VLANs (example ARP traffic).

23. Link-layer Addressing and ARP • Link layer addressing is the MAC address • Sending device does not know MAC address of destination • ARP is used to resolve MAC address • Each host and router keeps an ARP table which includes TTL • More about ARP later