Advanced Networking Flashcards
What is the Internet?
Internet “network of networks” - Interconnected ISPs
Name 2 Internet standards
RFC: request for comments
IETF: Internet Engineering Task Force
Additional info: Request for Comments (RFC), in information and communications technology, is a type of text document from the technology community. … The IETF adopts some of the proposals published as RFCs as Internet Standards. However, many RFCs are informational or experimental in nature and are not standards.
Examples of Protocols?
TCP, IP (network layer)
HTTP (Application layer)
Skype (Application layer)
802.11 (link layer)
Ethernet (data layer)
What are some characteristics of a MAC (or LAN or physical or Ethernet) address?
- Used ‘locally’ to get frame from one interface to another physically-connected interface
- 48 bit MAC address (for most LANs)
- Administered by IEEE
- MAC address like SSN - flat address portable
- IP address like postal address - not portable (depends on IP subnet to which it’s attached)
Address Resolution Protocol (ARP)
A communication protocol used for discovering the link layer address, such as a MAC address, associated with a given internet layer address, typically an IPv4 address.
TRUE/FALSE
Each adapter on LAN has unique LAN address
TRUE
Time to Live (TTL)
Time after which address mapping will be forgotten (typically 20 min) - limits the lifespan or lifetime of data in a computer or network
Ethernet frame structure
7 byte Preamble - used to synchronize receivers, senders clock rates
6 byte Addresses: dest and source
Type: indicates higher layer protocol (mostly IP but others possible, e.g., Novell IPX, AppleTalk)
data (payload)
CRC: cyclic redundancy check at receiver
- error detected: frame is dropped
Explain the following characteristics of Ethernet?
- connectionless
- unreliable
- protocol
connectionless: no handshaking between sending and receiving NICs
unreliable: receiving NIC doesn’t send acks or nacks to sending NIC
- data in dropped frames recovered only if initial sender uses higher layer rdt (e.g., TCP), otherwise dropped data lost
Ethernet’s MAC protocol: unslotted CSMA/CD with binary backoff
What is an Ethernet switch?
link-layer device: takes an active role
- store, forward Ethernet frames
- examine incoming frame’s MAC address, selectively forward frame to one-or-more outgoing links when frame is to be forwarded on segment, uses CSMA/CD to access segment
- Ethernet protocol used on each incoming link, but no collisions; full duplex - each link is its own collision domain - A-to-A’ and B-to-B’
- switches buffer packets
transparent
- hosts are unaware of presence of switches
- hosts have dedicated, direct connection to switch
plug-and-play, self-learning
- switches do not need to be configured
8 facts about TCP
Reliable, in-order delivery
o Congestion control
Point-to-point
o One sender, one receiver
Reliable, in-order byte
o Stream: no message boundaries
Pipelined
o TCP congestion and flow control set window size
Full duplex data
o Bi-directional data flow in same connection
o MSS: max segment size
Connection-oriented
o Handshaking inits sender, receive state before data exchange
Flow controlled
o Sender will not overwhelm receiver
Parity checking
o Single bit parity
Detect single bit errors
Network signal can be unreliable, hence needs error checking
Simplest error checking mechanism with very limited reliability
Can be used tougher with error detection/correction codes
Can only delete, NOT correct, NOR identify if the error was in parity bit or one of the data bits
o 2-dimensional bit parity
Detect and correct single bit errors
A challenge of wireless networks
A challenge of mobile networks
wireless: communication over wireless link
mobility: handling the mobile user who changes point of attachment to network
Examples of wireless hosts
o laptop, smartphone
o run applications
o may be stationary (non-mobile) or mobile
o wireless does not always mean mobility
How does wireless differ from wired link?
decreased signal strength: radio signal attenuates as it propagates through matter (path loss)
interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well
multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times
What are some problems from multiple wireless senders and receivers? (2)
Hidden terminal problem
Signal attenuation (weakening) and interference
What are the differences between 802.11: passive and active scanning?
Active scan
- The client radio transmits a probe request and listens for a probe response from an AP.
Passive scan
- The client radio listens on each channel for beacons sent periodically by an AP.
- Generally takes more time, since the client must listen and wait for a beacon.
- Another limitation with a passive scan is that if the client does not wait long enough on a channel, then the client may miss an AP beacon.
How to avoid collisions?
RTS/CTS
11 facts about UDP
Unreliable, unordered delivery
o No-frills extension of “best-effort” IP
Segments may be lost
Segments may be delivered out of order
Connectionless
o No handshaking between UDP sender, receiver
o Each UDP segment handled independently of others
Uses:
o Streaming multimedia apps (loss tolerant, rate sensitive)
o DNS
o SNMP
Add reliability at application layer - Application-specific error recovery
Use checksum to check if error-free
o Detect “errors” (e.g., flipped bits) in transmitted segment
o Simple method of error detection
o Calculates the aggregate sum of all data bits – Data sum
Small header size
No congestion control
o UDP can blast away as fast as desired
No connection establishment (which can add delay)
What services are not available with UDP?
- Delay guarantees
* Bandwidth guarantees
3 facts about Reliable Data Transfer (RDT)
- stop-and-wait operation
- High overhead
- Network protocol limits use of physical resources
Pipelining
Sender allows multiple “in-flight” yet to be acknowledged packets
o Range of sequence numbers must be increased
o Buffering at sender and/or receiver
2 generic forms of pipelined protocols
Go-Back-N
Sender can have up to N unacknowledged packets in pipeline
Receiver only sends cumulative acknowledgement - Doesn’t ack packet if there’s a gap
Sender has timer for older unacked packet - When timer expires, retransmit all uancked packets
Selective Repeat
Sender can have up to N unack’d packets in pipeline
Receiver sends individual ack for each packet
Sender maintains timer for each unacked packet - When timer expires, retransmit only that unacked packet
What do Network protocols govern?
All Internet communication activity o Defines format o Order of messages sent and received among network entities o Actions taken on message transmission o Receipt
Example
TCP connection request
TCP connection response
Get
What are 2 components of a Network Structure?
Network edge
Network core
Network edge
Also known as the WAN edge, is where an enterprise network connects to third-party network services
(E.g., for remote offices)
Hosts: clients and servers
Servers often in data centers
Access networks, physical media
- Wired, wireless communication links
Network core
o Interconnected routers
o Network of networks
o packet-switching: hosts break application-layer messages into packets
- forward packets from one router to the next, across links on path from source to destination
- each packet transmitted at full link capacity
Packet switching vs circuit switching
Circuit Switching is connection oriented that means a path is established between source and destination before the transmission occurs. On the other hand, Packet Switching is Connectionless that means a dynamic route is decided for each packet while transmission.
Circuit Switching was originally designed for voice communication whereas, Packet Switching was originally designed for data communication.
Circuit Switching is inflexible as once a path is established for transmission, it doesn’t change while the duration of the session. On the other hand, Packet Switching is flexible as each packet may travel through a different route to reach its destination.
In packet switching, as each packet travels a different path hence, the packet are received out of order at the receiver side and later arranged in order. On the other hand, in circuit switching the entire message is received as it is as sent from a sender to receiver.
Space Division Switching or Time-Division Switching can be used to implement Circuit Switching whereas, Packet Switching can be implemented using two approaches Datagram Approach and Virtual Circuit Approach.
Circuit Switching is always implemented at physical layer whereas, Packet Switching is implemented on the network layer.
Is packet switching a “slam dunk winner?”
o Great for bursty data - Resource sharing
- Simpler, no call setup
o Excessive congestion possible: packet delay and loss
- Protocols needed for reliable data transfer, congestion control
- BUT bandwidth guarantees needed for audio/video apps
When does queueing delay loss occur with Packet switching?
If arrival rate (in bits) to link exceeds transmission rate of link for a period of time
o Packets will queue, wait to be transmitted on link
o Packets can be dropped (lost) if memory (buffer) fills up
Wireless access networks (3)
Shared wireless access network connects end system to router
o Via based station aka “access point”
Wireless LANs
o Within building (100 ft)
o 802.11 b/g/n (WiFi_: 11, 54, 450 Mbps transmission rate
Latest is dual band routers 802.11se, higher capacity
Wide-area wireless access (cellular)
o Provided by telco (cellular) operator, 10’s km
o Between 1 and 10 Mbps
o 3G, 4GL:LTE
3 parts of a Bluetooth Packet signature
Access Code
o Composite key -> Piconet ID + channel ID
Header
o Composite key -> defines
Payload
o Defines data
Throughput (end to end)
Rate (bits/time unit) at which bits transferred between sender/receiver
o Instantaneous: rate at given point in time
o Average: rate over longer period of time
Bottleneck link
o Link on end-end path that constrains end-end throughput
4 Bluetooth throughput methods
SDR – standard data rate
o Original rate of v.1.0 and how fallback mode
EDR – enhanced data rate
o Short range, high quality streaming
HS – high speed
o Uses wi-fi 802.11 to transfer files fast
LE – low energy
o Retains sleep mode between connections
o Short connection bursts w/ high data rates
o Devices retain months of battery life
Factors that affect sound velocity underwater
Temperature
Pressure
Salinity
5 layers in TCP/IP protocol stack
Application layer (RDP) o Supporting network applications: FTP, SMTP, HTTP
Transport layer (end to end) o Process-process data transfer: TCP, UDP
Network layer
o Routing of datagrams from source to destination: IP, routing protocols
Data link layer (Bluetooth, cell)
o Data transfer between neighboring network elements: Ethernet, 802.11(WiFi), PPP
Physical layer (media device) o Bits “on the wire”
DSRC
Dedicated short range communication technology
USDOT’s vision for DSRC
USDOT’s vision is to have Connected and Autonomous Vehicles (CAVs)
Not currently used by autonomous vehicles
Describe DSRC Technology
Uses 5.9 GHz freq band specifically allocated for automotive use by FCC (Federal Communications Commission)
Provides an omnidirectional range of about 300 to 1200 m
Can communicate reliably up to at least 155 mph
Standards defined by IEEE 802.11p, IEEE 1609.x, SAE J2735
What is DSRC’s Protocol Implementation?
3-way handshake protocol using DSRC
• Control messages
• Synchronization messages
• Acknowledgement messages
Applications of Underwater Sensor Networks
Ocean Sampling Networks
Pollution Monitoring and other environmental monitoring (chemical, biological)
Disaster Prevention (tsunami warnings)
Assisted Navigation
Distributed Tactical Surveillance
Mine Reconnaissance
What is QoS and why is it important?
QoS refers to any technology that manages data traffic to reduce PACKET LOSS, LATENCY and JITTER on the network
Some applications running on your network are sensitive to delay
These applications commonly use the UDP protocol as opposed to the TCP protocol.
Links become overly congested - routers and switches start dropping packets because they are coming in/out faster that what can be processed
How does QoS work?
Classification and Queuing
Classification identifies and marks traffic to ensure network devices know how to identify and prioritize data as it traverses a network.
Queues are buffers in devices that hold data to be processed. Queues provide bandwidth reservation and prioritization of traffic as it enters or leaves a network device. If the queues are not emptied, they overflow and drop traffic.
identify the traffic
o Class of Service (CoS) - Will mark a data stream in the layer 2 frame header
o Differentiated Services Code Point (DSCP) - Will mark a data stream in the layer 3 packet header
What is Edge computing?
When edge device is between data source and cloud service
Allows for computations to be performed on edge device
o Computations can be performed faster
o Frees up previously used bandwidth
What created the need for Edge computing?
The success of cloud computing
The rapid growth of devices connecting to IoT - 50 billion devices expected on IoT by 2020
Advancement of data-processing speed does NOT equal advancement of bandwidth available
What are early problem areas in Edge computing?
Programmability
o Current solutions custom made
o Need frameworks
Naming
o No current standard for name edge devices
o Hard for edge devices to be found
Privacy and Security
o Hackers can gather info from IoT devices with poor security
o Need to ensure encryption of data on network and edge devices
What are 4 sources of packet delay?
Nodal processing
o Check bit errors
o Determine output link
o Typical < msec
Queueing delay
o Time waiting at output link for transmission
o Depends on congestion level of router
Transmission delay
o L: packet length (bits)
o R: link bandwidth (bps)
o = L/R
Propagation delay
o D: length of physical link
o S: propagation speed (~2x10^8 m/sec)
o = D/S
What is CRC?
Cyclic Redundancy Check
- More powerful error-detection coding
- Widely used in practice (Ethernet, 802.11 WiFi, ATM) – looks like long division
- View data bits, D, as a binary number - based on the remainder of a polynomial division of their contents.
Hamming code
Error correction code (single bit)
Can detect 2-bit error and correct 1-bit error
Cannot fix 2-bit
Condition for 2 bit errors
If 2 bits have been altered, then
o At least one of the circles will have odd number of ones
o The total number of ones including the overall parity bit will be even
If 1 bits has been altered, then
o At least one of the circles will have odd number of ones
o The total number of ones including the overall parity bit will be odd
Base station
o typically connected to wired network
o relay - responsible for sending packets between wired network and wireless host(s) in its “area”
o e.g., cell towers, 802.11 access points
Wireless link
o typically used to connect mobile(s) to base station
o also used as backbone link
o multiple access protocol coordinates link access
o various data rates, transmission distance
Infrastructure mode
wireless devices can communicate with each other or can communicate with a wired network
Ad hoc mode
o no base stations
o nodes can only transmit to other nodes within link coverage
o nodes organize themselves into a network: route among themselves
What OSI layer is bluetooth?
Physical/MAC
What’s band frequency does Bluetooth operate?
2.4 GHz
What is Bluetooth’s 3-step pairing process?
Inquiry
Paging
Bonding
Functions of a Host?
Send packets of data
- takes application message
- breaks into smaller chunks, known as packets, of length L bits
- transmits packet into access network at transmission rate
Packet-switching: store-and-forward
Entire packet must arrive at router before it can be transmitted on next link
end-end delay = 2 L/R (assuming zero propagation delay)
2 key network-core functions
Routing - determines source-destination route taken by packets
Forwarding - move packets from router’s input to appropriate router output
What is Multiplexing?
The process of sending two or more individual signals over a single communication channel
This is usually achieved by an electronic circuit known as a multiplexer
FDM vs TDM
TDM
- share the timescale for the different signals
- more efficient
- can be used for both Analog and Digital signals.
FDM
- shares the frequency scale for the different signals.
- can be used for Analog signals only.
point-to-point
one sender, one receiver
full duplex data
bi-directional data flow in same connection
connection-oriented
handshaking (exchange of control msgs) before data exchange
flow controlled
sender will not overwhelm receiver
IP address
32-bit
network-layer address for interface
used for layer 3 (network layer) forwarding
MAC address
48 bit (For most LANs) burned into NIC ROM
used ‘locally’ to get frame from one interface to another physically-connected interface
4 elements of a wireless network
wireless hosts - laptops, smartphones
base station - typically connected to wired network
wireless link - typically used to connect mobile(s) to base station
infrastructure mode - base station connects mobiles into wired network
5G Security Concerns (4)
Authentication - needs to be fast, low latency, high data rates - can’t be based on only symmetric key
Integrity - prevent manipulation when modifying data
Availability - call reception, signal scrambling, DoS
Confidentiality - vehicle routing data, health monitoring data
5G over DSRC
5G has:
higher throughput higher reliability cheaper (existing cellular infrastructure) lower latency wider range symmetric better with NLOS
