1. Distributed systems Module 1 -Basic networking Teaching unit 1 – LAN standards Ernesto Damiani Free University of Bozen-Bolzano Lesson 1 – Local network introduction

2. Basic networking DLL (Data Link Layer) management MAC (Medium Access Control) Error control

3. Data Link Layer responsibilities The Data-Link Layer is responsible for: –Multiplexing of data flows –Data frame detection –Medium access control –Error control It ensures reliable point-to-point and point-to- multipoint connections in a communication network

4. Collision free MAC protocols (1) Static channel allocation TDMA (Time Division Multiple Access) FDMA (Frequency Division Multiple Access) CDMA (Code Division Multiple Access).

5. Collision free MAC protocols (2) Dynamic allocation of collision free channels Reservation protocols – bitmap protocol (round robin hand-rising tour for the reservation) – binary countdown protocol (simultaneous hand-rising and the highest bit will come first)

6. Contention MAC protocols (1) Slotted ALOHA It detects a-posteriori collision or lack of ACK – it transmits when it is necessary – it resends lost frames after random time

7. Contention MAC protocols (2) CSMA/CD (Carrier Sensing Multiple Access/Collision Detection) It listens to the channel in advance to avoid collisions, but when they happen it resends the frame (used by Ethernet LAN)  1-persistent: the station resends with probability 1 when the channel is idle  p-persistent: when the channel becomes idle, it transmits with probability p  non-persistent: when the channel idle waits a random time before transmitting

8. When to use MAC protocols DelayEfficiency Low loadALOHA High load COLLISION FREE PROTOCOLS

9. Local network standards Standards are necessary to allow the interoperability among different network devices

10. Advantages of standards They ensure a wide market for devices and software They allow different vendor products to communicate

11. Standard organizations IEEE Internet Society ISO ITU-T, formerly CCITT ATM Forum FINE