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

Ethernet Originally invented at Xerox PARC and later standardized by Digital Equipment corp, Intel and Xerox. Survived over 30 years. Main reason is that newer versions are backward compatible.

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.

802.3 A SNAP header (8bytes) is added (3bytes LLC, 3byte OUI and 2byte type/length) LLC = Logical Link control OUI = Organization unique identifier This reduced the maximum payload of 1500 to 1492.

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.

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

16-Wirless Networking Technologies Dr. John P. Abraham Professor UTPA

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

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

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.

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.

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.

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

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

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.

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.

Bridges and Bridging Discussed in prior lectures. Additional info is given here. 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

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.

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.