Chapters 1-4 Flashcards
The scripting language invented by Dutch programmer Guido van Rossum
Python
Python has these instead of Arrays
Lists
The way to access values at the end of a string
Negative indexes
What is a host
An end system
What is a packet switch
A device that forwards packets
Communication Links
fiber, copper, radio satellite
Network
A collection of devices, routers, and links managed by an organization
This is called a “network of networks”
The Internet
Protocols
Control sending, receiving of mesages
RFC
Request for Comments
IETF
Internet Engineering Task Force
Network edge
clients and servers
Network core
interconnected routers, network of networks
Frequency Division Multiplexing(FDM)
Different channels transmitted in different frequency bands
Wireless Local Area Networks(WLAN)
Provide connection within or around a building
Wide-area Cellular Access Networks
Provide connection from mobile, cellular network operators, typically within 10’s of Kilometers
Bit
Propagates between transmitter/receiver pairs
Physical link
What lies between transmitter and receiver
Guided media
signals propagate in solid media such as copper, fiber, coax
Unguided media
Signals propagate freely, e.g. radio
Twisted pair (TP)
Two insulated copper wires
Packet-switching
Hosts break application-layer messages into packets
Length (L)
Length of a packet in bits
Transmission rate (R)
How fast bits are being transmitted in bits/sec
Transmission delay
Takes L/R seconds to transmit (push out ) L-bit packet into link at R bps
Store and forward
Entire packet must arrive at router before it can be transmitted on next link
End-end delay
2L/R, assuming zero propagation delay
What happens if arrival rate to link exceeds transmission rate of link for a period of time
Packet queuing and loss, packets will queue and wait to be transmitted on output link, some may be dropped if router fills up
Forwarding
Local action, move arriving packets from router’s input to appropriate router output link
Routing
Global action, determine source-destination paths taken by packets
Time Division Multiplexing (TDM)
Time divided into slots, in which a user can utilize the entire bandwidth for a limited time
How do hosts connect to the internet
Internet Service Providers (ISPs)
“Tier-1” commercial ISPs
National and international coverage
Content Provider Networks (CPNs)
Private network that connects its data centers to Internet, often bypassing tier-1, regional ISPs
What happens when arrival rate to link exceeds output link capacity
Packet Loss
What are the four sources of packet delay?
Nodal Processing, Queueing, Transmission, and Propagation
Throughput
Rate at which bits are being sent from sender to receiver
Instantaneous throughput
Rate at given point in time
Average throughput
Rate over longer period of time
Bottleneck link
Link on end-end path that constrains end-end throughput
Virus
Self-replicating infection by receiving/executing object (e.g., e-mail attachment)
Worm
Self-replicating infection by passively receiving object that gets itself executed
Spyware
Can record keystrokes, websites visited, upload info to collection site
Denial of Service (DoS)
Attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic
Packet sniffing
Promiscuous network interface reads/records all packets, including passwords, passing by
IP spoofing
Send packet with false source address
Layer 5
Application layer, highest in IP stack model, contains supporting network applications such as IMAP, SMTP, HTTP
Layer 4
Transport layer, process-process data transfer, TCP, UDP
Layer 3
Network layer, routing of datagrams from source to destination, IP and routing protocols
Layer 2
Link layer, data transfer between neighboring network elements through things like Ethernet, WiFi, or PPP
Layer 1
Physical layer, bits “on the wire”
Arpanet
The proto version of the Internet developed by DARPA back in the 60’s
ISO/OSI reference model
A model similar to the IP stack, but contains the two extra layers of presentation and session
Wireshark
A type of packet sniffer
Socket
analogous to a door, data is shoved through the socket from the application layer to the transport layer
Identifier
A part of a process which includes both the IP address and port number associated with process on host
Data integrity
Ensures that the data sent is received unchanged, some apps require 100%, other can tolerate some loss
TCP service
A reliable protocol which won’t overwhelm the receiver and maintains integrity, but will go slower
UDP
An unreliable data transfer protocol which doesn’t provide security congestion control or other features, but does go much faster than TCP
Transport Layer Security (TLS)
provides encrypted TCP connections, ensures data integrity
hypertext transfer protocol (HTTP)
Web’s application layer protocol, a client sends a request and the server sends a response
HTTP uses this type of socket
TCP
Non-persistent HTTP
- TCP connection opened
- At most one object sent over TCP connection
- TCP connection closed
Downloading multiple objects required multiple connections
Persistent HTTP
- TCP connection opened to a server
- Multiple objects can be sent over single TCP
connection between client, and that server - TCP connection closed
Round Trip Time (RTT)
Time for a small packet to travel from client to server and back
200
OK
301
Moved Permanently
400
Bad Request
404
Not Found
505
HTTP Version Not Supported
Cookie
Used to maintain some state between transactions
Web cache
A copy of an object from another client which is being served to a client by a server
Simple Mail Transfer Protocol (SMTP)
A protocol used by mail servers to send, receive, and relay outgoing email between senders and receivers
Internet Mail Access Protocol (IMAP)
Provides retrieval, deletion, folders of stored messages on server
Domain Name System (DNS)
Distributed database implemented in hierarchy of many name servers. provides hostnames and aliases among other things. Is decentralizeed
Hierarchy of DNS
Root, highest
Top Level Domain, middle
Authoritative, lowest
Root name servers
Contact-of-last-resort by name servers that can not resolve name, incredibly important to internet function. 13 logical root name “servers” worldwide
ICANN (Internet Corporation for Assigned Names and Numbers)
Manages root DNS domain
Top-Level Domain (TLD) servers
Responsible for .com, .org, .net and others, along with top-level country domains such as .cn, .uk, .fr
Authoritative DNS servers
Organization’s own DNS servers, providing authoritative hostname to IP mappings for organization’s named hosts
Local DNS name servers
Does not strictly belong to hierarchy, each ISP has one, when host makes DNS query, query is sent to its local DNS server
Peer-to-peer (P2P) architecture
No always-on server, arbitrary end systems directly communicate as peers who request and send files to each other
Tracker
A server within P2P, while there is not supposed to be an always-on server, there has to be this to let peers find each other
CBR (constant bit rate)
Video encoding rate fixed
VBR (variable bit rate)
Video encoding rate changes as amount of spatial, temporal coding changes
Streaming
Video is being sent played and deleted as user is watching
Apache
A commonly used HTTP server
Multiplexing
Multiple datagrams are combined into one in order to send more efficiently through sockets
Demultiplexing
Splitting up multiplexed datagrams and distributing each datagram to the proper host system
Checksum
The sum of bits in a message which is appended to the end, meant to ensure integrity
ACK
Receiver explicitly tells sender that pkt received OK
NAK
Receiver explicitly tells sender that pkt had errors
Time-to-live (TTL)
In UDP connections is a limit to how many times a packet can hop inside a network before being discarded by a router
Timeout
The amount of time a round trip can take before being reported as lost and requesting a copy from the sender
Flow control
Mitigates one sender sending data too fast for one receiver
Handshake
A client and server introduce each other and identify themselves, establishing a connection that data can be sent through
Congestion control
Mitigates too many senders sending data too fast
QUIC (Quick UDP Internet Connections)
An encrypted transport layer protocol designed by google, meant to get the positives of UDP and TCP without the downsides of either
Data plane
Local, per-router function, determines how datagram arriving on input port is forwarded to output port
Control plane
Network-wide logic, determines how datagram is routed among routers along end-end path from source host to destination host
Software-Defined Networking (SDN)
Remote controller computes, installs forwarding tables in router on the control plane
Per-router control plane
Individual routing algorithm components in each and every router interact in the control plane
Routing table
A data table stored in a router that lists the routes to particular network destinations, can be user defined, or software defined
Longest prefix match
When looking for forwarding table entry for given destination address, use longest address prefix that matches destination address
Multistage switch
(n)x(n) switch from multiple stages of smaller switches
Head-of-the-line (HOL) blocking
Queued datagram at front of queue prevents others in queue from moving forward
Buffering
Required when datagrams arrive from fabric faster than link transmission rate
Drop policy
Defines which datagrams to drop if no free buffers
Scheduling discipline
Chooses among queued datagrams for transmission
Packet scheduling
Deciding which packet to send next on link
IPv4 address
32-bit identifier associated with each host or router interface
IPv6 address
128-bit identifier associated with each host or router interface
Interface
Connection between host/router and physical link
Subnet
Device interfaces that can physically reach each other without passing through an intervening router
CIDR (Classless InterDomain Routing)
Standard that tells how many digits of an IP address are fixed and which can be changed within a subnet
Subnet mask
A standard which tells how many characters in each byte of an IP address can be changed
DHCP (Dynamic Host Configuration Protocol)
Dynamically get IP address from server
NAT (Network Address Translation)
All devices in local network share just one IPv4 address as far as outside world is concerned, but NAT server routes them to the correct end system, meant to save on IPv4 addresses which have run out
Tunneling
IPv6 datagrams are given an IPv4 header in order to be cleanly sent over to the destination port
The internet’s “thin waist”
IP, the only network layer protocol
Middleboxes
Network layer protocols which used to exist before IP was standardized as the one network layer protocol to be used
