Data Comm and Computer Networking Ch. 1
What are the difference queuing delays?
La/R ~ 0 (avg. delay small), La/R = 1 (Avg. delay large), La/R > 1 (more "work" arriving) (R link bandwidth bps, L packet length bits, a average packet arrival rate)
What is d(transmission)?
L: packet length (bits), R: link bandwidth (bps). d(transmission) = L/R
What is the software view of the internet?
"Network of networks:" interconnected ISPs, Protocols control sending/receiving of messages, Internet Standards: RFC (Request for Comments)/IETF (Internet Engineering Task Force)
Questions: Quantitative Comparison of Packet Switching and Circuit Switching: A circuit-switching scenario in which Ncs users, each requiring a bandwidth of 25 Mbps, must share a link of capacity 150 Mbps. A packet-switching scenario with Nps users sharing a 150 Mbps link, where each user again requires 25 Mbps when transmitting, but only needs to transmit 30 percent of the time. When one user is transmitting, what fraction of the link capacity will be used by this user?
0.17
Questions: Queuing Delay: Assume a constant transmission rate of R = 800000 bps, a constant packet-length L = 6800 bits, and a is the average rate of packets/second. Traffic intensity I = La/R, and the queuing delay is calculated as I(L/R)(1 - I) for I < 1. Assuming that a = 22 what is the queuing delay?
0.187 * (6,800/800,000)*(1-0.187)*1000 = 1.2923ms
Questions: One-Hop Transmission Delay: Suppose that the packet length is L= 12000 bits, and that the link transmission rate along the link to router on the right is R = 10 Mbps. What is the maximum number of packets per second that can be transmitted by this link?
10,000,000 / 12,000 = 833
Questions: Car - Caravan Analogy: Suppose the caravan has 10 cars, and that the tollbooth services (that is, transmits) a car at a rate of one car per 1 seconds. Once receiving serving a car proceeds to the next tool both, which is 500 kilometers away at a rate of 10 kilometers per second. Also assume that whenever the first car of the caravan arrives at a tollbooth, it must wait at the entrance to the tollbooth until all of the other cars in its caravan have arrived, and lined up behind it before being serviced at the toll booth. (That is, the entire caravan must be stored at the tollbooth before the first car in the caravan can pay its toll and begin driving towards the next tollbooth) How long for all cars to go through first toll booth?
10s
Questions: One-Hop Transmission Delay: Suppose that the packet length is L= 12000 bits, and that the link transmission rate along the link to router on the right is R = 10 Mbps. What is the transmission delay?
12,000/ 10,000,000 = 0.0012s
Questions: Queuing Delay: Assume a constant transmission rate of R = 800000 bps, a constant packet-length L = 6800 bits, and a is the average rate of packets/second. Traffic intensity I = La/R, and the queuing delay is calculated as I(L/R)(1 - I) for I < 1. If the buffer has a maximum size of 896 packets, how many of the 1817 packets would be dropped upon arrival from the previous question?
1817-896 = 921 dropped packets
Questions: Car - Caravan Analogy: Suppose the caravan has 10 cars, and that the tollbooth services (that is, transmits) a car at a rate of one car per 1 seconds. Once receiving serving a car proceeds to the next tool both, which is 500 kilometers away at a rate of 10 kilometers per second. Also assume that whenever the first car of the caravan arrives at a tollbooth, it must wait at the entrance to the tollbooth until all of the other cars in its caravan have arrived, and lined up behind it before being serviced at the toll booth. (That is, the entire caravan must be stored at the tollbooth before the first car in the caravan can pay its toll and begin driving towards the next tollbooth) How long is spent at toll booth?
1s
Questions: Circuit Switching - If we have 11 circuits (A-B) to 17 circuits (A-B) to 18 circuits (C-D) to 10 circuits (D-A), Suppose that every connection requires 2 consecutive hops, and calls are connected clockwise. For example a connection can go from A-C, from B-D, from C-A, and D-B. With these constraints what is the maximum number of connections that can be ongoing in the network at any one time?
27 (B-D is greater than A-C)
What is end-end delay?
2L/R assuming there is zero propagation delay
Questions End-end throughput: Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 200 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 60 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 30 Mbps. What is the max throughput?
30 Mbps
Questions: Car - Caravan Analogy: Suppose the caravan has 10 cars, and that the tollbooth services (that is, transmits) a car at a rate of one car per 1 seconds. Once receiving serving a car proceeds to the next tool both, which is 500 kilometers away at a rate of 10 kilometers per second. Also assume that whenever the first car of the caravan arrives at a tollbooth, it must wait at the entrance to the tollbooth until all of the other cars in its caravan have arrived, and lined up behind it before being serviced at the toll booth. (That is, the entire caravan must be stored at the tollbooth before the first car in the caravan can pay its toll and begin driving towards the next tollbooth) After the first care leaves the tollbooth how long does it take until it arrives at the next tollbooth?
50s
Questions: Circuit Switching - If we have 11 circuits (A-B) to 17 circuits (A-B) to 18 circuits (C-D) to 10 circuits (D-A) what is the maximum number of connections that can be ongoing in the network at any one time?
56
Questions: Car - Caravan Analogy: Suppose the caravan has 10 cars, and that the tollbooth services (that is, transmits) a car at a rate of one car per 1 seconds. Once receiving serving a car proceeds to the next tool both, which is 500 kilometers away at a rate of 10 kilometers per second. Also assume that whenever the first car of the caravan arrives at a tollbooth, it must wait at the entrance to the tollbooth until all of the other cars in its caravan have arrived, and lined up behind it before being serviced at the toll booth. (That is, the entire caravan must be stored at the tollbooth before the first car in the caravan can pay its toll and begin driving towards the next tollbooth) Once the first car leaves the tollbooth, how long does it take until it enters service at the next tollbooth?
59s
Questions: Quantitative Comparison of Packet Switching and Circuit Switching: A circuit-switching scenario in which Ncs users, each requiring a bandwidth of 25 Mbps, must share a link of capacity 150 Mbps. A packet-switching scenario with Nps users sharing a 150 Mbps link, where each user again requires 25 Mbps when transmitting, but only needs to transmit 30 percent of the time. When circuit switching is used what is the maximum number of users that can be supported?
6
What is a botnet?
A network of bots in a DDoS attack.
What is the internet structure: network of networks look like?
Access ISPs connect to regional ISPs, that connect to global ISPs, that connect to content provider networks.
What is an enterprise access network (ethernet)?
Access network typically used in companies and universities, 10/100 Mbps or 1/10 Gbps transmission rates, today the end systems typically connect into ethernet switch
What is presentation in the ISO/OSI model?
Allows application to interpret meaning of data by encryption, compression, machine-specific conventions, etc.
Questions: The IP Stack and Protocol Layering: What layer in the IP stack best corresponds to the phrase: 'handles messages from a variety of network applications?
Application Layer
What makes up the ISO/OSI Reference model?
Application, Presentation, Session, Transport, Network, Link, Physical
What makes up internet protocol stack?
Application, Transport, Network, Link, and Physical
What is malware?
Bad software that can get in host from a virus or worm
What is transmission rate?
Bandwidth
What is the hardware view of the internet?
Billions of connected computing devices: hosts = end systems/running network apps, Communication links: fiber/copper/radio/satellite, Packet Switches: forward packets (chunks of data)/routers and switches
What is a bit?
Binary digit that propagates between transmitter/receiver pairs
What is physical in IPStack?
Bits "on the wire"
What is packet sniffing?
Broadcast media, Network interface reads/records all the packets that pass by
What is DoS?
Denial of service when attackers make resources(server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic.
What is d(nodal processing)?
Checking bit errors, determine output link, typically < ms
What is Link in IPStack?
Data transfers between neighboring network elements: Ethernet, 802.11 (WiFi), PPP
Why do we use layering?
Dealing with complex systems we have an explicit structure that allows for identification, relationship of complex system's pieces, modularization eases maintenance/updating of system
What is routing?
Determining source-destination route taken by packets with routing algorithms
What is DSL?
Digital subscriber line: It uses existing telephone line to central office DSLAM, upstream transmission rate is typically < 1 Mbps, downstream transmission rate is typically < 10 Mbps
What are layers?
Each layer implements a service via its own internal-layer actions, relying on services provided by layer below
What are hosts?
End systems
What is circuit-switching?
End-end resources allocated to, reserved for "call" between source and destination. There are dedicated resources, no sharing with a circuit-like (guaranteed) performance. Circuit segment idle if not used by call due to no sharing. This is commonly used in traditional telephone networks.
How do access network: cable networks work?
Frequency division multiplexing: different channels transmitted in different frequency bands, HFC (hybrid fiber coax): asymmetric with up to 30Mbps downstream transmission rate and 2 Mbps upstream transmission rate, Network of cable, fiber attaches homes to ISP router where homes share access network to cable headend
What is fiber optic cable?
Glass fiber carrying light pulses where each pulse is a bit. High speed operation: high-speed point to point transmission (e.g. 10's-100's Gbps transmission). Low error rate due to repeaters being spaced far apart and immunity to electromagnetic noise
What is a content provider network?
Google, etc.: Private network that connects its data centers to internet, often bypassing tier-1, regional ISPs
How is cable network different from DSL?
Homes share access network to cable headend unlike DSL, which has dedicated access to central office
What is 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 and each pack is transmitted at full link capacity
What is network edge?
Hosts: clients and servers (servers are often in data centers)
What is in the field of network security?
How bad guys can attack computer networks, how we can defend networks against attacks, and how to design architectures that are immune to attacks.
What is queuing and loss?
If arrival rate (in bits) to link exceeds transmission rate of link for a period of time packets will queue and wait to be transmitted on link, and then packets can be dropped (lost) if memory (buffer) fills up
What is the service view of the internet?
Infrastructure that provides services to applications and provides programming interface to apps
Why is packet switching not always good?
It's great for bursty data, resource sharing, simpler. However, excessive congestion is possible: packet delay and loss is possible (protocols are needed for reliable data transfer/congestion control
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission rate: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is transmission delay of link 1?
L/R = 4,000/10Mbps = 0.0004s
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission rate: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is transmission delay of link 2?
L/R = 4000 bits / 10 Mbps = 0.0004 seconds
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission rate: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is transmission delay of link 3?
L/R = 4000 bits / 10 Mbps = 0.0004 seconds
What is a "tier-1" commercial ISP?
Level 3, Sprint, AT&T, NTT: National and international coverage
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission raterm-96te: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is total delay of link 2?
Link 2 total delay = d_t + d_p = 0.0004 seconds + 0.017 seconds = 0.017 seconds
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission raterm-96te: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is total delay of link 3?
Link 3 total delay = d_t + d_p = 0.0004 seconds + 1.00E-5 seconds = 0.00041 seconds
Questions: The IP Stack and Protocol Layering: What layer in the IP stack best corresponds to the phrase: 'passes frames from one node to another across some medium'?
Link Layer
Questions: The IP Stack and Protocol Layering: What layers do the switches use?
Link Layer and Physical Layer
What is bottleneck link?
Link on end-end path that constrains end-end throughput
What is forwarding?
Moving packets from router's input to appropriate router output
Questions: The IP Stack and Protocol Layering: What layer in the IP stack best corresponds to the phrase: 'moves datagrams from the source host to the destination host'?
Network Layer
What are protocol "layers"?
Networks are complex with many "pieces": Hosts, routers, links of various media, applications, protocols, hardware/software
Questions: Car - Caravan Analogy: Suppose the caravan has 10 cars, and that the tollbooth services (that is, transmits) a car at a rate of one car per 1 seconds. Once receiving serving a car proceeds to the next tool both, which is 500 kilometers away at a rate of 10 kilometers per second. Also assume that whenever the first car of the caravan arrives at a tollbooth, it must wait at the entrance to the tollbooth until all of the other cars in its caravan have arrived, and lined up behind it before being serviced at the toll booth. (That is, the entire caravan must be stored at the tollbooth before the first car in the caravan can pay its toll and begin driving towards the next tollbooth) Are there ever two cars in service at the same time, one at the first toll booth and one at the second toll booth?
No
Questions: Circuit Switching - If we have 11 circuits (A-B) to 17 circuits (A-B) to 18 circuits (C-D) to 10 circuits (D-A), Suppose that the maximum number of connections are all ongoing. What happens when another call connection request arrives to the network, will it be accepted?
No
Questions: Quantitative Comparison of Packet Switching and Circuit Switching: A circuit-switching scenario in which Ncs users, each requiring a bandwidth of 25 Mbps, must share a link of capacity 150 Mbps. A packet-switching scenario with Nps users sharing a 150 Mbps link, where each user again requires 25 Mbps when transmitting, but only needs to transmit 30 percent of the time. Suppose packet switching is used. If there are 11 packet switching user, can this many users be supported under circuit switching?
No
Questions: Circuit Switching - If we have 11 circuits (A-B) to 17 circuits (A-B) to 18 circuits (C-D) to 10 circuits (D-A), Suppose that 13 connections are needed from A-C and 20 connections are needed from B-D. Can we route these calls through the four links to accommodate all 33 connections?
No the max connections is 27
What is packet transmission delay equal to?
Pack transmission delay = time needed to transmit L-bit packet into link. L (bits) / R (bits/sec)
How is packet switching different from circuit switching?
Packet switching allows for more users to use the network at a time. There is no guaranteed access
How does loss and delay occur?
Packets get queued up in router buffers: packet arrival to link (temporarily) exceeds the output link capacity and packets queue while waiting for their turn
Questions: Queuing Delay: Assume a constant transmission rate of R = 800000 bps, a constant packet-length L = 6800 bits, and a is the average rate of packets/second. Traffic intensity I = La/R, and the queuing delay is calculated as I(L/R)(1 - I) for I < 1. Assuming the router's buffer is infinite, the queuing delay is 1.6022 ms, and 1817 packets arrive. How many packets will be in the buffer 1 second later?
Packets left = a - (1000/delay) = 1817 - (1,000/1.6022) = 1193 packets
Questions: The IP Stack and Protocol Layering: What layer in the IP stack best corresponds to the phrase: 'bits live on the wire'?
Physical Layer
Questions: The IP Stack and Protocol Layering: What layers do the routers use?
Physical Layer, Link Layer, Network Layer
What is transport in IPStack?
Process-process data transfer: TCP, UDP
What do protocol do?
Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission.
What is throughput?
Rate (bits/time unit) at which bits transferred between sender/receiver. Instantaneous is the rate at given point in time. Average is the rate over a longer period of time.
Questions End-end throughput: Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 200 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 60 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 30 Mbps. Which link is the bottleneck?
Rc
How are end systems connected to edge router?
Residential access nets, institutional access networks (School/Company), and mobile access networks
What are the two key network-core functions?
Routing and forwarding
What is network in IPStack?
Routing on datagrams from source to destination: IP, routing protocols
What are the steps of DoS?
Select target, break into hosts around the network, and send packets to target from compromised hosts.
What is a virus?
Self-replicating infection by receiving/executing object (email attachment)
What is a worm?
Self-replication infection by passively receiving object that gets itself executed
What is IP spoofing?
Sending packets with a false source address
What is the host?
Sends the packets of data. When host is sending function: takes application message, breaks it into smaller chunks known as packets of length L bits, transmits packets into access network at transmission rate R.
What are wireless access networks?
Shared wireless access network connects end system to router via an access point. Wireless LANs are within a building (100ft.), 80.11b/g/n (WiFi) 11, 54, 450 Mbps transmission rate
What is radio?
Signal carried in electromagnetic spectrum, no physical "wire," bidirectional, affected by reflection/obstruction by objects/interference
What is guided media?
Signals propagate in solid media: copper, fiber, coax
What is unguided media?
Signals that propagate freely, like radio
What is session in the ISO/OSI model?
Snychronization, checkpointing, recovery of data exchange
What is spyware malware?
Software that can record keystrokes, web sites visited, and upload info to collection site
What is application in IPStack?
Supporting network applications: FTP, SMTP, HTTP
What is packet-switching: store-and-forward?
Takes L/R seconds to transmit L-bit packet into link at R bps. The entire packet must arrive at router before it can be transmitted on the next link. E
What are the different radio link types?
Terrestrial microwave, LAN, wide-area, satellite
Questions End-end throughput: Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 200 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 60 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 30 Mbps. Assuming that the servers are sending at the maximum rate possible, what are the link utilizations for the server links (RC)?
The client's utilization = Rbottleneck / RC = 30 / 30 = 1
Questions End-end throughput: Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 200 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 60 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 30 Mbps. Assuming that the servers are sending at the maximum rate possible, what are the link utilizations for the server links (RS)?
The server's utilization = Rbottleneck / RS = 30 / 60 = 0.5
Questions End-end throughput: Consider the scenario shown below, with four different servers connected to four different clients over four three-hop paths. The four pairs share a common middle hop with a transmission capacity of R = 200 Mbps. The four links from the servers to the shared link have a transmission capacity of RS = 60 Mbps. Each of the four links from the shared middle link to a client has a transmission capacity of RC = 30 Mbps. Assuming that the servers are sending at the maximum rate possible, what is the link utilizations for the shared link (R)?
The shared link's utilization = Rbottleneck / (R / 4) = 30 / (200 / 4) = 0.6
Where do radio links reach?
Their line of sight
What must be done if the Internet stack doesn't have presentation or session layers?
They must be implemented if needed in the application.
Why is connecting every access ISP together not plausible?
This leads to O(N^2) connections
What is d(queuing)?
Time waiting at output link for transmission and depends on congestion level of router
What is "real" internet delay and loss look like?
Traceroute program can provide delay measurement from source to router along end-end internet path towards destination. For all i routers three packets are sent on path towards destination, then router i will return packets to sender, then sender time interval between transmission and reply
Questions: The IP Stack and Protocol Layering: What layer in the IP stack best corresponds to the phrase: 'handles the delivery of segments from the application layer, may be reliable or unreliable?
Transport Layer
What is coaxial cable?
Two concentric copper conductors, bidirectional, broadband: multiple channels on cable/HFC
What is twister pair (TP)?
Two insulated copper wires, category 5: 100 Mbps, 1 Gbps, category 6: 10 Gbps
What is terrestrial microwave?
Up to 45 Mbps channels
What is the physical link?
What lies between transmitter and receiver
What is wide-area wireless access?
Wide-area wireless access provided by telco (cellular) operator, 10's km between 1 and 10 Mbps, 3G/4G/LTE
What are access networks, physical media?
Wired/wireless communication links
Questions: Queuing Delay: Assume a constant transmission rate of R = 800000 bps, a constant packet-length L = 6800 bits, and a is the average rate of packets/second. Traffic intensity I = La/R, and the queuing delay is calculated as I(L/R)(1 - I) for I < 1. In practice does the queuing delay tend to vary a lot?
Yes
Questions: Car - Caravan Analogy: Suppose the caravan has 10 cars, and that the tollbooth services (that is, transmits) a car at a rate of one car per 1 seconds. Once receiving serving a car proceeds to the next tool both, which is 500 kilometers away at a rate of 10 kilometers per second. Also assume that whenever the first car of the caravan arrives at a tollbooth, it must wait at the entrance to the tollbooth until all of the other cars in its caravan have arrived, and lined up behind it before being serviced at the toll booth. (That is, the entire caravan must be stored at the tollbooth before the first car in the caravan can pay its toll and begin driving towards the next tollbooth) Are there ever zero cars in service at the same time, i.e., the caravan of cars has finished at the first toll both but not yet arrived at the second tollbooth?
Yes (the last car)
What are the four sources of packet delay?
d(nodal) = d(processing) + d(queuing) + d(transmission) + d(propagation)
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission raterm-96te: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is total delay of link 1?
d(transmission) + d(propagation) = 0.0004s + 1.00*10^-5s = 0.00041s
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission rate: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is propagation delay of link 3?
d/s = (3 Km) * 1000 / 3*10^8 m/sec = 1.00E-5 seconds
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission rate: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is propagation delay of link 2?
d/s = (5000 Km) * 1000 / 3*10^8 m/sec = 0.017 seconds
Questions: End-end delay: Link 1 (Transmission rate: 10 Mbps, Link Length: 3 Km), Link 2 (Transmission rate: 10 Mbps, Link Length: 5000 Km), Link 3 (Transmission rate: 10 Mbps, Link Length: 3 Km).Assume the length of a packet is 4000 bits. The speed of light propagation delay on each link is 3x10^8 m/sec. What is propagation delay of link 1?
d/s = 3,000m/(3*10^8) = 1.00*10^-5s
What is d(propagation)?
d: length of physical length, s: propagation speed (2*10^8 m/s), d(propagation) = d/s
What is network core?
interconnected routers network of networks
