Chapter 1 Flashcards
URL
Uniform Resource Later
HTTP
Hyper Text Transfer Protocol
TCP
Transmission Control Protocol
17 messages sent for one URL Request
* 6 to find the IP
* 3 to for connection establishment
* 4 for HTTP req. and ACK
* 4 for tearing down TCP connection
Network Providers req.
Require easy-to-manage systems that allow isolation of faults and are easy to monitor.
Network Designers req.
Require cost-effective designs, which means that resources are utilized effectively and fairly between users.
App Programmer req.
Require network services that can be depended on for sending and receiving messages without error in a certain amount of time.
Scalable
A system designed to support growth
Link
A connection between two computers directly connected over a physical medium
Nodes
Refer to the computers in a network
Point-to-point
Physical link between a pair of nodes
Multiple Access
More than 2 nodes share a physical link
Circuit Switched Network
A direct link is switched open for traffic. once the link is established, it is left open until all the data is transmitted.
Store-and-forward
Each node that receives the packet, stores it and sends it to the next
Packet switched network
There is no direct link established, however a link exists. Data is broken into pieces, packets, or messages - which are sent along the network. These find their way to the destination through potentially multiple routes, and are reassembled at the destination end.no
Cloud
Any type of network, a place holder
Packet/message
A block of data sent over a network
Router
A node that connects 2 or more networks
Hosts
Nodes outside the network that use te network
Switches
Nodes on the inside that implement the network
Internetwork
A set of independent networks that are interconnected
Host - to - host connectivity
Each node must say which other node it wants to connect to
Address
A byte string that identifies a node
Routing
The process of determining systematically how to forward message4s toward a destination node
Unicast
Single node sends to all nodes
Broadcast
Single node sends to all nodes
Multicast
Single node wants to sends to a subset of nodes
Multiplexing
Mulitple users share a network with one physical link
De-Multiplexing
When multiple users share a network with one physical link
Synchronous Time Division Multiplexing
Round Robin style, Each flow gets a specific quota
Frequency Division Multiplexing
Transmit each flow at different frequencies over the medium
Statistical Multiplexing
Like STDM, the physical link is shared over time but each flow is chosen on demand
Upper bound on data sent at a time = packet
LAN
Local Area Network
MAN
Metropolitan Area Network
WAN
Wide Area Network
SAN
System Area Network
Request/Reply Communication Channel
- Guarantees the message is entirely delivered
- Used for files
- Privacy
Message Stream Communication Channel
- Used in Video on Demand
- Needs quick messages to be sent
- Not all messages sent
- Not all messages will be received
- Must maintain order
Physical link failures
● Bit Errors
A bit is flipped. Very rare.
● Burst Errors
Several consecutive bits are corrupted. More common.
Packet Level failures
- Congestion
- Corruption (contains an uncorrectable bit)
- Software (the software handling the nodes makes a mistake)
Node/Link Level Failures
- A physical link is cut.
- The computer it is connected to crashes.
- Software crashes
- Power failure
- Misconfiguration of network
- Messages delayed/out of order
- 3rd parties eavesdrop
Layered Network
- Application Programs
- Request/Reply or Message Stream
- Host-to-host connectivity
- Hardware
Protocol
Defines interfaces between the layers in the same system
Service Interface
Operationis on this protocol
Peer-to-peer Interface
Messages exchanged with peer
Interface graph
Host 1:
* High-level object
* < Service Interface >
* Protocol
<- Peer-to-peer interface ->
Host 2:
* Protocol
* < Service Interface >
* High-level object
Internet Engineering Task Force
Standardising body to establish policies for a protocol
Encapsulation
High level messages encapsulated in low level messages
Physical Link Layer OSI - Lower
handles the transmission of raw bits over a communications link.
Data link layer OSI - Lower
- Collects a stream of bits into a larger aggregate called a frame.
- Network adaptors, along with device drivers running in the node’s operating system, typically implement the data link level
- This means that frames, not raw bits, are actually delivered to hosts.
Network Layer OSI - Lower
- handles routing
among nodes within a
packet-switched network. - At this
layer, the unit of data exchanged
among nodes is typically called a
packet rather than a frame, although they are fundamentally the same thing.
Transport Layer OSI
implements what we have up to this point been calling a process-to-process channel. Here, a unit of data exchanged is commonly called a message rather than a packet or frame.
Session Layer OSI
provides a namespace that is used to tie together the potentially different transport streams that are part of a single application.
Presentation Layer OSI
Format the data exchanged between peers
Application Layer OSI
Standardise common type of exchanges
Internet Architecture
FTP: TCP
HTTP: TCP
NV: UDP
TFTP: UDP
TCP: IP
NV: IP
IP: NET1, NET2, … , NET3
ARPANET
Look at diagram
* Does not imply strict layering
* Hour glass shape
* IP Focal Point
* For new protocol to be added
* - Protocol Specification
* - 1 or 2 representative implementations of the spec
Application Programming Interface
- Interface exported by the network
- Network API
Sockets
- Point where local app process attaches to a network
- Interface between an app & network
Socket Interface
- Creating the socket
- Attaching socket to netowrk
- Sending & Receiving messages through socket
- Closing socket
Socket Domain
- The protocol family
- PF_INET: Internet familt
- PF_UNIX: Unix pipe facility
- PF_PACKET: Direct access to the network interface
Socket Type
- Sock_Stream: 4 byte stream
- Sock_DGRAM: message oriented service provided by UDP
Server in Client Server open model
- Performs passive open
- Ready and prepared to accept new connections
Bind command - Server
Binds newly created socket to the address: IP + Port
Listen command - Server
Defines how many connections can be pending on the specified socket
Accept command - Server
- Carries out passive open
- Only returns when a connection is made
- Returns a new socket relating to the client
Client in Client Server Model
- Application performs active open
- Says who it wants to communicate with
Connect Command - Client
- Only returns once a connection has been made
- Address contains remote machines address
Bandiwidth
- Width of frequency band
- Number of bits that can be sent over the comms link
Latency
How long it takes a message from one end of a network to the other end
= propagation + transmit + queue
- propagation = distance / speed of light
- transmit = size / bandwidth
Delay x bandwidth
Volume of the pipe
Latency = length
Bandwidth = width (diameter)
Importance of DxB
Large files need bandwidth
Small files need latency
Round Trip Time
Time it takes to get to one end of the network and back
Throughput
TransferSize/TransferTime
* TransferTime = RTT + TransferSize/Bandwidth
