MIT OCW DATA COMMUNICATION CONTENTS Lectures 2 The Data Link Layer: Framing and Error Detection Lectures 3 4 The Data link layer: arQ Protocols Lectures 5 6 Introduction to Queueing Theory Lectures 8&9 M/G/I Queues

一、SIM卡应用工具 二、无线应用协议

一、主要承载技术GPRS 二、短消息业务

Outline Network Layer and Internetworking The TCP/IP protocol suit ATM

Flow control: end-to-end mechanism for regulating traffic between source and destination Congestion control: Mechanism used by the network to limit congestion The two are not really separable, and I will refer to both as flow control In either case, both amount to mechanisms for limiting the amount of traffic entering the network Sometimes the load is more than the network can handle Eytan Modiano

A packet switch consists of a routing engine(table look-up), a switch scheduler, and a switch fabric. The routing engine looks-up the packet address in a routing table and determines which output port to send the packet. Packet is tagged with port number The switch uses the tag to send the packet to the proper output port Eytan Modiano

Broadcast Routing Route a packet from a source to all nodes in the network Possible solutions: Flooding: Each node sends packet on all outgoing links Discard packets received a second time Spanning Tree Routing: Send packet along a tree that includes all of the nodes in the network

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

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

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