RESERVATION SYSTEMS Single channel shared by multiple users Only one user can use the channel at a time Need to coordinate transmissions between users Polling systems Polling station polls the users in order Polling to see if they have something to send station A scheduler ca

An interesting property of an M/M/ 1 queue, which greatly simplifies combining these queues into a network, is the surprising fact that the output of an M/M/ queue with arrival rate is a Poisson process of rate This is part of Burke's theorem, which follows from reversibility A Markov chain has the property that P[future present, past] P[future present] Conditional on the present state, future states and past states are independent

Queueing Systems Used for analyzing network performance In packet networks, events are random Random packet arrivals Random packet lengths While at the physical layer we were concerned with bit-error-rate, at the network layer we care about delays How long does a packet spend waiting in buffers

Service times Poisson arrivals at rate n Service time has arbitrary distribution with given E[X] and E[X2I Service times are independent and identically distributed (ID) Independent of arrival times E[service time]=1/u Single Server queue

Automatic Repeat ReQuest(ARQ) When the receiver detects errors in a packet, how does it let the transmitter know to re-send the corresponding packet? Systems which automatically request the retransmission of missing packets or packets with errors are called ARQ systems Three common schemes Stop Wait

Data Link Layer (DLC) Responsible for reliable transmission of packets over a link Framing: Determine the start and end of packets(sec 2.5) Error Detection: Determine when a packet contains errors ( sec 2.3) Error recovery: Retransmission of packets containing errors(sec 2. 4) DLC layer recovery May be done at higher layer

Computer Science 6.111-Introductory Digital Sy Laborator How to Make Your 6.1ll Project Work There are a few tricks of the trade \which allow an experienced digital designer to fix problems quickly. This note is an attempt to fill you in on some with which you might not

Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science 6. 111-Introductory Digital Systems Laboratory Project Information Introduction The term project in 6 1 1 1 is your opportunity to specify a small digital system. You will

Massachusetts Institute of Technology Department of Electrical Engineering and Computer Science 6.111-Introdi igital Systems Labo Report guide Introduction The purpose of this memorandum is to describe general requirements for the reports you

assachusetts Institute of Technology Department of Electrical Engineering and Computer Science 6. 111-Introductory Digital Systems Laboratory Project resources Project resources are allocated on a per student basis. This means that a two-person