Fiche: Réseaux informatiques EPFL (document en anglais)

Switch: Buffers(Store data), Forwarding table(store meta-data, indicate where to send data)Queuing delay>buffer full>packet loss

“Con° switching”: Dedicated end-end conn° Ressources reserved in advance. Admi° ctrl and forward per con°.

“Packet switching”: Packets treated on demand. Admi° ctrl and forward per packet. = wait for all bits of a packet before processing it

CS: Inefficient ressource use, perf guar°. PS: Efficient ressource use, no perf guar°, simpler but requires congestion ctrl

PS allows more users in the network, and if only 1 user, quicker than CS

Circuit Switching: CS though several physical circuits - Virtual multiple links on 1 phys link

TDM, each user’s circuit gets all of the bandwidth periodically during brief

timeslots. User is always ass° the same dedi° timeslot in the revolving TDM frames

Multi-homing: An ISP that connects with 2 or more provider ISPs

PoP: Physical location that houses servers, routers, ATM sw°, aggregators..

Layer: Part of a system with well defined interfaces to other parts

Two layers interest only through the interface between them

One layer interacts only with the layer above and the layer below it

Application: applications that exchange messages. it defines

The types of messages exchanged, for example, request messages and response messages 
The syntax of the various message types, such as the fields in the message and how the fields are delineated. The semantics of the fields, that is, the meaning of the information in the fields 
Rules for determining when and how a process sends messages and responds to messages

Transport: transports segments between end-systems

Network: moves datagrams around the network

Link: moves frames accros a link

Physical: moves data across a physical medium

Why layer ? Reduce complexity and improve flexibility

Delay: How long does it take to send a packet from its src to dst?

Transmission delay : How long does it take to push all the bits of a packet into a link ?

Propagation delay: How long does it take to move one bit form one end of a link to the other ?

Queuing delay: How long does a packet have to sit in a buffer before it is processed ? UB: N*(L/R)

Processing delay: How long does it take to process a packet ? N +1= size buffer

The bandwidth-delay product of a link is the maximum number of bits that can be in the link. 
QD: Statistical mesures > average QD, variance of QD, prob that it exceeds a certain value

QD: Depends on traffic pattern > arrival rate, nature of arriving traffic(burst, or not), TR of outgo° link

If LA > R QD => ∞ (L length A arrival rate, R transmission Rate)

If LA ≤ R QD => 0 Buffer size = n+1: QD upper bound = N*(L/R)

Without store and forward (i.e. phone call) only 1 TD, instead of #Link*TD

Loss: What fraction of the packets sent from a source to a destination are dropped ?

Throughput: At what rate is the destination receiving data from the source ?

Avg throughput: DataSize/TransferTime (Avg throughput = R)

Avg throughput and bottleneck link: (Avg throughput = min{R, R’})

Eavesdropper: Tries to listen in on the com° to obtain copies of the data (wired(less)) - Sniffing

Impersonator: Pretends she is Alice to extract information form Bob - Spoofing / v dos-ing

DOS attacker: Makes Alice or Bob crash or disconnect and disrupts the com° (vulnerability attack / bandwidth flooding /conn° floo°)

Malware Master: Infects Alice of Bob with a malware (i.e. delete files, copy/export perso data, send spam mail, launch DOS)

Self-propagating malware : virus (requires user interaction), worm (does not)

Botnet : army of compromised end-systems (bots) Processes: pieces of code that belong to the application layer

A process can be thought of as a program that is running within an end system 192.168.1.1:80 = IP:port

A process sends messages into, and receives messages from, the network through a software interface called a socket

Server: Process that is always running - reachable at a fixed, known process addr, - answers(denies) requests for services

Client: Process that requests services

C/S Arch°: Clear separation of the roles - servers runs on dedicated infrastructure

Peer: Process that may both make and answer requests (act as client and/or server)

P2P Arch°: Peer runs on personally owned end-system - no dedicated infrastructure (PC, laptop, smartphone)

Challenges of P2P: ISPs designed for asymmetrical bandwidth usage (DL>UL) - Security - based on volunteering

Protocol ⊂ Application (App = comm° protocol + client&server (or peer) processes + …) ie Web = HTTP comm° protocol + web browser & server processes + HTML languages

Reliable message delivery (TCP): The transport delivers the msg to the dst process or signals failure (loss sensitive apps)

Guaranteed performances (neither): Minimum throughput (bandwidth sensitive apps) (voice few kbps, video few Mbps)

Minimum end-to-end delay (delay sensitive apps) (voice & video 10ms)

Guaranteed Security: Confidentiality : msg is revealed only to the dust - Data Integrity : msg not changed

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