Flashcards
ICT169 Week 2 Flashcards
Cards in this deck (30)
- 1Applications- The software tools users interact with
- Provide means to generate and receive data to be transported over network - 2Name & Explain Application Models- Client/Server -
- End user devices (PC, tablet etc.) act as client and dedicated servers as server clients use resources of
- Peer-to-Peer-
- Every device as client/server
- No server aid for data transmission - 3Name 3 Applications & Briefly explain their purposeDNS: Translates human-readable domain names to the associated network IP address
HTTP: Retrieves content from webservers using three commands
FTP: Used for download/upload of large files
DHCP: Automatically obtains IP address from network
SSH (secure shell): Interactive command line for remote management. Encrypts data. - 4Explain the process of resolving domain names by DNS servers1. ISP sends domain name to DNS root server if it cannot be resolved
2. DNS root server directs request to another server if it cannot resolve, and so on
3. When domain is resolved, sent back to ISP and ISP tells user web browser - 5DNS Application + Name two Top Level Domains- Translates human-readable domain names to associated IP address
- Hierarchical system that used UDP(/TCP) port 53
ccTLD = Country code
gTLD = General code - 6HTTP- Retrieves content from webservers using three commands
- 7FTP- Used for downloading/uploading large files over Internet
- 8DHCP (Dynamic Host Config. Protocol)- Automatically obtains IP address from network
- Most home routers have DHCP by default - 9SSH (Secure Shell)- Interactive command line for remote
management. Encrypts data.
- Used by other protocols such as scp (secure copy) to copy files between machines
- TCP port 22 - 10SMTP Simple Mail Transfer Protocol- Used for sending/receiving email between main servers & between client-to-mail servers
- 11Explain what Secure Shell is and why is it used over Telnet?- Both provide interactive command line
- Telnet is unsecure (no encryption)
- Both used for remote management of network devices/servers - 12Explain Presentation layer role in OSI model- Controls coding and conversion of application layer data --> format readable by destination
- Example: MPEG, JPEG, PNG, PDF etc. - 13Session layer- Controls exchange of information over a "conversation", including initiation, restarting,
keeping alive and terminating the CONVERSATION. - 14Transport Layer- Uses port numbers to identify conversations, applications and segments
- reassembles application data
for transmission
- Provides reliability & w/ different protocols to cater to requirements of applications
- Often referred to as an "end-to-end" concept - 15Port Numbers- LOGICAL concept used by OS for identification of applications and concurrent conversations
- Ports are all IDENTICAL, but some "recognised" as specific application
- An app. can have multiple port numbers (destination ports don't need to match) - 16Explain the different Port Classes- Well known (0-1023): For common services & applications (e.g. HTTP, SMTP)
- Registered (1024-49151): Less common services & applications (e.g. OpenVPN, SIP)
- Dynamic/Private (49152-65535): For client-initiated sessions - 17Three-Way Handshake Steps (3)1. Client sends SYN to server asking for synchronisation
2. Server sends SYN-ACK to acknowledge request + asks client to open connection
3. Client sends ACK to let server know it is ready and connection is established
NB: When not ACKed w/in time limit, resent. - 18Why is "ACK" referred to as cumulative?It acknowledges all preceding segments as well.
- 19Network Congestion# of packets arriving at router > # of packets that can be sent to next link
- 20What does Congestion Control do?- Determines the max speed packets can be sent without causing a bottleneck to form
- Manages rate of transmission
- Congestion window specifies max # of unACKed segments that can be in-flight from sender to receiver - 21Congestion Avoidance steps (3)1. Without loss = Increase window by 1 segment each round trip time
2. When low speed link congested = router connected drops packets
3. Packet loss detected = Sender reduces throughput (and congestion) - 22Explain buffering and why buffers should not be set too high- Router buffers outgoing packets, but when filled to limit packets must be dropped
- Bufferbloat: When buffers too high = Latency high (larger buffers take longer to clear)
- Buffers have to be small to maintain low latency - 23Explain active queue management (AQM) and Early Congestion Notification- Tells TCP senders there is congestion at configurable buffer delays
- Marks packets when queue length or est. delay above threshold
- TCP receiver echoes marks to TCP sender & sender reduces congestion window - 24What does flow control do?- Broadcasts "receive window" (# bytes it will accept per ACK or window update)
- Sender restricted to minimum congestion & receive window - 25Explain the process of termination in network communication (4)1. Client send FIN request to server
2. Server returns ACK to client of FIN
3. Server sends FIN request to client
4. Client returns ACK to server of FIN - 26UDP- Timely data delivery
- Connectionless and unreliable
- Used for voice/video comms. and online games - 27Why use UDP over TCP?- Reduced resources used: (CPU, bandwidth etc.)
- Simpler: No handshake, no reliability checks and smaller header
- Better in LAN: b/c chance for packet loss is reduced & DNS queries fit in single packets - 28Why use TCP over UDP?- More reliable: For sending sensitive/crucial information
- When delay doesn't matter: Sending emails, file transfers etc., - 29Encapsulation- Communicates protocol information to end systems & same stack layers
- Adds headers to data, containing important information such as IP of sender/receiver - 30—
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- Year 11 Computer Science Flashcards on ICT169 Week 2 Flashcards, created by Ronan Kavanagh on 03/09/2021.
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- Ronan Kavanagh
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