Main Flashcards
How does a client-server model look?
What type of network is a network of scale: Vicinity?
(PAN) Personal Area Network
Connect devices over the range of a person:
Example of a Bluetooth PAN:
(The word Vicinity means: “the area near or surrounding a particular place”)
What type of network is a network of scale: Building?
(LAN) Local Area Network
Connect devices in a home or office building
Called enterprise network in a company
What type of network is a network of scale: City?
(MAN) Metropolitan Area Networks
Connect devices over a metropolitan area
Example of a MAN based on cable TV:
What type of network is a network of scale: Country?
(WAN) Wide Area Network
Three different kinds:
- Connect devices over a country
- Example of a WAN conneting three branch offices:
- An Internet Service Provider (ISP) network.
- Customers buy connectivity from the ISP to use it.
- A Virtual Private Network (VPN) is built from virtual links that run on top of the Internet.
What type of network is a network of scale: Planet?
The Internet (the network of all networks)
What are protocol layers?
Protocol layering is the main structuring method used to divide up network functionality.
- Each protocol instance talks virtually to its peer
- Each layer communicates only by using the one below
- Lower layer services are accessed by an interface
- At bottom, messages are carried by the medium (means: data are then sent over physical cables)
How does headers work with protocol layers?
Each lower layer adds its own header (with control information) to the message to transmit and removes it on recieve.
What is a Connection-Oriented service?
Must be set up for ongoing use (and torn down after use), e.g. a phone call
What is a Connectionless service?
Messages are handled separately, e.g. postal delivery
What are the different Reference Models?
- OSI reference model
- TCP/IP reference model
- Model used for this course
Name the layers of the OSI reference model
A principled, international standard, seven layer model to connect different systems
- Application
- Presentation
- Session
- Transport
- Network
- Data link
- Physical
Explain the TCP/IP reference model:
A four layer model; omits some OSI layers and uses the IP as the network layer.
Explain the reference model used in this course:
It is based on the TCP/IP model but we call out the physical layer and look beyond Internet protocols.
What is a distributed system?
Definition:
A distributed system is the one in which hardware and software components at networked computers communicate and coordinate their activity only by passing messages.
What are service layers?
It is a conceptual layer within a network service provider architecture.
What is Middleware?
It is computer software that provides services to software applications beyond those available from the operating system. It can be described as “software glue”.
Middleware makes it easier for software developers to perform communication and input/output, so they can focus on the specific purpose of their application.
- Masks heterogenity
- Provides a convenient programming model
- Objects / processes
- Communication primitives
- Synchronization
- Group and multicasting
- Naming and Localization services
- Event notification
What is an Asynchronous interaction model?
The most significant aspect of asynchronous communications is that data is not transmitted at regular intervals, thus making possible variable bit rate, and that the transmitter and receiver clock generators do not have to be exactly synchronized all the time.
- No known bounds for:
- The execution speed of a process
- Message delay on the network
- Clock drift
What is a (partly) Synchronous interaction model
- Known upper and lower bound for each process step
- Known upper bound for the time it takes for a message to be recieved
- Known upper bound for clock drift
What does Heterogeneity mean?
A heterogeneous network is a network connecting computers and other devices with different operating systems and/or protocols.
For example, local area networks (LANs) that connect Microsoft Windows and Linux based personal computers with Apple Macintosh computers are heterogeneous.
What are Timing failures?
- Class of Failure: Clock
- Affects: Processes
- Process’s local clock exceeds the bounds on its rate of drift from real time
- Class of Failure: Performance
- Affects: Processes
- Process exceeds the bounds on the interval between two steps
- Class of Failure: Performance
- Affects: Channel
- A message’s transmission takes longer than the stated bound
What is the MAC Sublayer?
- Responsible for deciding who sends next on a multi-access link
- An important part of the link layer, especially for LANs
Explain Static channel allocation
- You divide up the bandwidth using FTM, TDM, CDMA, etc.
- Like radio (different channels)
- Static allocation performs poorly for busy traffic
- Allocation to a user will also sometimes go unused
Explain dynamic allocation
Dynamic allocation gives the channel to a user when they need it. Potentially N times as efficient for N users.

