CompNet 1

Multiplexing

the action of sharing of resources

Concurrency

how resources are shared

Layers

only adjacent layers interact, use services of layer n-1, provide service to layer n+1, embedding/encapsulation

Entities

an independent existence, interact with layers above and below, communicate with peers

Channel

Peers communicate over channels & provide higher-layer peers with higher-layer channels

Symbol type

bits, packets, waveform

Capacity

bandwidth, data-rate, packet-rate Delay: fixed/variable

Fidelity

signal-to-noise, bit error rate, packet error rate

Connectivity

point-to-point, to-many, many-to-many

Internet Protocol Stack

Application: supports network applications - FTP, SMTP, HTTP Transport: process-process data transfer - TCP, UDP Network: routing of datagrams from source to destination - IP, routing protocols

Link

data transfer between neighboring network elements - Ethernet Physical - bits "on the wire"

ISO/OSI Ref Model

IPC with Presentation: allow applications to interpret data - encryption, compression, machine-specific Session: synchronization, checkpointing, recovery of data exchange. Must be implemented by application

Internet

protocols control send/receiving of msgs eg TCP, IP, HTTP, Skype, Ethernet, loosely hierarchical network of networks, public and private, standards RFC: Request for comments and IETF: Internet Engineering Task Force

Protocols

define format, order of msgs sent/received by network entities, actions taken on transmission/receipt

Dial-up Modem

uses telephone infrastructure, < 64kbps, can't use phone

Digital Subscriber Line

uses telephone infrastructure, < 1Mbps U & < 8 Mbps D, dedicated physical line to exchange

Twisted Pair

2 insulated copper wires, Cat3 - 10 Mbps, Cat6 - 100 Mbps Ethernet

Coaxial Cable

2 concentric copper conductors, bidirectional, Hybrid Fiber Coax with multiple channels on broadband

Fiber-optic Cable

High speed, point to point, low error rate, immune to electromagnetic interference

Microwave

45 Mbps

LAN

(wifi) 11 Mbps+ Wide-area: (cellular - 3G) 1 Mbps

Satellite

< 45 Mbps, 270 ms delay

Circuit Switching

dedicated circuit for every connection + guaranteed performance - no sharing, less reliable

Frequency Division Multiplexing

Divide frequency spectrum between users

Time Division Multiplexing

Divide chunks of time between users. Synchronous TDM - same size time slots

Packet Switching

data is sent across network in small blocks, may all take different route across network, same as Asynchronous Time Division Multiplexing + users share connections, resilient to failure - no guaranteed performance

Statistical Multiplexing

sharing does not have fixed pattern, shared on demand

Store-and-Forward

entire packet must arrive at each hop before can be transmitted on next link

Internet Structure

network of networks, ~ hierarchical, Tier 1,2,3 and local ISPs, connect to peers and higher tiers

Per-packet Processing

error checks, lookup output link

Jitter

Difference between min & max delay

Queuing Delay

time waiting for output link

Transmission Delay

packet length / link bandwidth

Throughput

rate (b/s) of transfer from sender-receiver, instantaneous/average

Client

initiates request, sometimes 'on', no direct communication with other clients, knows server address

Server

services client requests, always 'on', needs fixed, well known address

Peer-to-Peer

no central server, all hosts may be clients & server, more reliable, scalable, less management

Hybrid

VoIP, IM, centralised server helps initiate connection, users then communicate directly

Robust

all endpoints can communicate in un-partitioned network, failures (which don't partition) don't interfere

Delivery Service

Application neutral, allow end-based protocols to provide better service

Host attachment

administrative cost of adding hosts is very low (but have to be smart)

Resource Accountability

no coordinated resource accounting, management or resource control - bad!

Network Architecture

how to break systems into modules, where modules are implemented (end-end principle)

Socket

Processes send/receive messages to/from its socket, abstraction which hides layers below needs port & IP

Process Identifier

IP address & port number, needed to receive messages

App-layer protocol

type of messages, syntax, semantics, rules for when & how to send and respond to messages

Transport Service Characteristics

Data loss - some apps can tolerate loss, Timing - some apps need low delay, Throughput - some apps need min throughput to be effective, Security - encryption, data integrity

IP

Internet's global addressing system used by network DNS: Internet's global system of naming, used by app/user

traffic intensity

packet length * avg arrival rate / link bandwith [0,1]

Propagation

physical distance / propagation speed in medium