CS 439: iClicker Questions (Networks, Lec. 20)
Terms in this set (45)
Networks: Level 1
Physical, e.g. Cables, hubs, USB
Networks: Level 2
Data Link: MAC, Ethernet
Networks: Level 3
Networks: Level 4
Transport: TCP, UDP
Networks: Level 5
Session: NFS, RPC
Networks: Level 6
Presentation: JPEG, ASCII, TLS
Networks: Level 7
Application: SSH, HTTPS
The OS views the network as another ___.
What device is added to the bus?
As another device; transfer of data to/from memory to
(Network Interface Controller) through DMA or memory-mapped I/O
SAN v LAN v WAN
Give an example of each
Rank them in terms of speed
1) System Area Network: Connects clusters or machine room, e.g. Quadrics
2) Local Area Network: Connects nodes in a single building, e.g. Ethernet
3) Wide Area Network: Connects nodes across state, country, planet, universe, e.g. phone lines
Ethernet connects ____ to ____.
Hosts to a hub
How long is the MAC?
Maximum bandwidth of Ethernet?
When you connect many ethernet hubs via ____'s, you get...
Ethernet is to TCP what ____ is to packet/segment
What protocol sits between Ethernet, wireless, DSL, etc, to allow them to communicate? What layer is this at?
IP; Network: Layer 3
IP stands for..
Every packet consists of a ____ and a ____.
Header contains information about...
packet size, source, and destination address
data bits sent form the source host
The information applied by the Ethernet layer is stripped off at...
Maximum bandwidth for Ethernet; Maximum packets per second (pps) of Ethernet; Maximum rate over TCP/IP
/ 84 bytes (size of ethernet frame) = 1,488,095 pps
add 20 bytes (IP header) + 20 bytes (TCP header)
1,488,095 pps * 40 bytes = 476 mb/s
How long is IPv4? IPv6?
32 bits; 64 bits
How many levels does this address have?
Specify which part of the address correlates to each part of the IP address.
4 levels, e.g. 22.214.171.124
128. = edu
83. = cs
Name the Levels of DNS
What is a DNS Resolver?
Handles the request to a domain name, contacting the Internal or ISP Server.
Briefly describe the 8 steps for connecting to an IP address from your machine.
1. Resolver to internal or ISP DNS Server
2. Internal (if not cached) or ISP DNS Server to Root DNS
3. Root DNS back to Internal (caching) or ISP DNS
4. Internal (if not cached) or ISP DNS Server to Top-Level DNS
5. Top-Level DNS back to Internal (caching) or ISP DNS Server
6. Internal (if not cached) or ISP DNS Server to Second-level DNS
7. Second-level DNS back to Internal (caching) or ISP DNS Server
8. Internal (cached) or ISP DNS Server back to resolver
Summary: If domain name mapping to IP is not cached, then go to the closest DNS server (starting at Root) to find the IP and resolve it
resolver -> internal/ISP DNS -> ___ (level) DNS
IP of localhost
What is the logical address (that the OS uses) and what does it map to?
machine name & application
host-id (e.g. IP) & port (e.g. 80)
How many bits is a port?
2^16 = 65,536
UDP stands for..
TCP stands for..
User Datagram Protocol
Transmission Control Protocol
UDP packets may be ___, ___, or ___
dropped, reordered, or duplicated
TCP is used when the connection needs to be ___, as opposed to UDP which is used when the connection can be ___
Name 3 errors that can affect packet delivery:
bit errors (electrical interference, cosmic rays, solar flares, etc)
link and node failure
Name the three steps of the TCP Three-Step Handshake used to establish a connection
What is the biggest problem with this? (not security)
Slow; bandwidth is packet per round trip (RTT)
In networks, PCB is the ___, and it does...
Protocol Control Block; tracks unacknowledged data, i.e.
1) Keep a copy & timer
2) Receiver re-orders out of order segments
3) ACKs received segments (quickly)
4) Decides when to wake process on receipt (more data coming? should it wait?)
5) Decides when to send data (if small, should it wait for more?)
What is the main concerns when using TCP?
Congestive collapse (too many segments building up)
What is the TCP Window?
What does it prevent?
Name sizing ideas for the TCP Window.
the maximum number of bytes that can be sent without ACKing
prevents sender from overflowing receiver's buffer
Large window : high-latency networks (packets can build up)
Small window : high-loss networks (packets are resent frequently, don't want to build up)
What measurements does the sender maintain in TCP Flow Control? Receiver? Describe them.
RcvWindow (estimate of buffer space at receiver), estimated using LastByteSent, LastByteAcked
RcvBuffer, determined by LastByteRead, LastByteRcvd
Formula for measuring overflow in TCP Flow
Formula for measuring size of RcvWindow
LastByteRcvd - LastByteRead <= RcvBuffer
RcvWindow = RcvBuffer - (LastByteRcvd - LastByteRead)
What is a CongWin? Where is it tracked?
Congestion window, packets that build up
Kept on receiver & sender sides
What is Additive Increase and Multiplicative Decrease in the context of TCP Congestion
Multiplicative Decrease: Half CongWin after loss event, until it reached 1 Maximum Segment Size (MSS)
Additive Increase: Increase CongWin by 1 MSS every roundtrip
Latency v Throughput
Give an example of each
Give ideas on how to optimize internet speeds
Latency: time for one byte to go from one place to another
Throughput (bandwidth): Maximum bytes per second
Keep minimum overhead of LAN
Keep pipeline full on WAN
Name the 3 layers of a TCP "packet" and their components
Frame : Frame Header, MAC (dest), MAC (source)
Packet : IP Header, IP (dest), IP (source)
Segment : Segment Header, Port (dest), Port (source), Data
Data sent into the network is chopped into ___.
___ are sent through the network.
But we call everything ___.
Networks make tradeoffs between ___, ___, and ___
speed, reliability, and expense