1st Midterm Review

Transmission Delay Formula

T = L(Packet Length)/R(Transmission Rate) T = L/R

Calculate the Maximum number of packets per Second that can be transmitted by the link

N = 1s/T (in seconds)

Propagation Delay Formula

Prop_Delay = d(length of physical link)/s(propagation speed) Prop_Delay = d/s

End-to-End Delay Formula

E2E_Delay(Link 1) = Trans_Delay(Link 1) + Prop_Delay (Link 1) = L/R + d/s To find the end-to-end delay of chained links (ex. 3 links) just do: Tot_E2E_Delay = E2E_Delay(Link 1) + E2E_Delay(Link 2) + E2E_Delay(Link 3)

Maximum Achievable end-end throughput of four client-to-server pairs when middle-link is fair shared

You take the transmission capacity and divide it by 4. So each link should have the same maximum throughput.

Ex. Middle Link R = 100 Mbps Four Servers R_S = 30 Mbps 100 Mbps / 4 = 25 Mbps

Maximum end-end throughput for each link = 25 Mbps

How to find the bottleneck

The bottleneck for a session is the link that causes the other links to not be utilized at full capacity. Typically its the link that is being utilized at 100% but causes other links to not be able to utilize 100%

Ex. R_S Servers = 30 Mbps (Each) R (middle link) = 100 Mbps R_C Computers = 80 Mbps (Each)

Since the middle link is fair shared That means only 25 Mbps can be sent by R_S and R_C is only receiving 25 Mbps, the middle link R is the bottleneck

Calculating Link Utilization Assuming that the Senders are sending at the maximum rate possible

Take the maximum rate the senders are sending and divide it by the transmission capacity of each link

Ex. R_S Servers = 30 Mbps (each) R (middle link) = 100 Mbps R_C Computers = 80 Mbps (each)

Sender links utilization = 25/30 = 83% Client links utilization = 25/80 = 31% Middle link Utilization = 4x25/100 = 100%

Link Layer Addressing and Forwarding

IP datagram sent from node C to node A

1. What is the source mac address at point 6? 41-A0-51-76-0F-6D

2. What is the destination mac address at point 6? 15-8D-D1-C2-C7-08

3. What is the source IP address at point 6? 128.119.88.175

4. What is the destination IP address at point 6? 128.119.156.213

5. Do the source and destination mac addresses change at point 4? No

6. Do the source and destination mac addresses change at point 2? Yes

7. What is the source mac address at point 2? CE-0F-B3-31-3A-FB

8. What is the destination mac address at point 2? 8A-9B-C8-70-B2-51

9. Do the source and destination mac addresses change at point 1? No

Learning Switches 1

1. At t=1, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' F,6

2. At t=1, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' I,7

3. At t=1, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' F,8

4. At t=1, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' I,12

5. At t=2, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' K,7

6. At t=2, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' n/a

7. At t=2, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' K,14

8. At t=2, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' H,11

9. At t=3, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' B,2

10. At t=3, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' Already exists on table (K,7)

11. At t=3, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' B,8

12. At t=3, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' Already exists on table (K,14)

13. At t=4, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' Already exists on table

14. At t=4, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' Already exists on table

15. At t=4, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' Already exists on table

16. At t=4, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' Already exists on table

Learning Switches 2

1. At t=1, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' D,4

2. At t=1, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' J,7

3. At t=1, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' D,8

4. At t=1, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' J,13

5. At t=2, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' H,7

6. At t=2, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' A,1

7. At t=2, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' H,11

8. At t=2, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' A,8

9. At t=3, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' C,3

10. At t=3, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' Already exists on table

11. At t=3, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' n/a

12. At t=3, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' n/a

13. At t=4, what is the source entry for switch 1? Format your answer as letter,number or 'n/a' L,7

14. At t=4, what is the destination entry for switch 1? Format your answer as letter,number or 'n/a' n/a

15. At t=4, what is the source entry for switch 2? Format your answer as letter,number or 'n/a' L,15

16. At t=4, what is the destination entry for switch 2? Format your answer as letter,number or 'n/a' G,10

How many layers does OSI Reference Model have?

7

How many layers does TCP/IP Reference Model have?

5

The IPv4 Address size is

32 bits

The MAC address size is

48 bits

What is the meaning of bandwidth in the network?

Transmission capacity of a communication link

A router operates in which layer of TCP/IP reference model?

Layer 3 (Network Layer)

A switch operate in which layer of TCP/IP Reference Model?

Layer 2 (Link Layer)

Which layers of the TCP/IP model are host-to-host layers?

Transport, Application

What is the broadcast MAC address

FF:FF:FF:FF:FF:FF

How is a Mac address divided

Manufacturer ID coded in 24 first bits, NIC Serial Number coded in last 24 bits

What are the 5 layers of the TCP/IP Model from bottom to top?

Physical Layer -> Link Layer -> Network Layer -> Transport Layer -> Application Layer

What are the 7 layers of the OSI Model from bottom to top

Physical layer -> Data Link Layer -> Network Layer -> Transport Layer -> Session Layer -> Presentation Layer -> Application Layer

What is a Computer Network?

A digital telecommunications network which allows nodes to share resources and exchange data with each other using connections

Communication Links

Things that allow links to communicate to each other (fiber, copper, radio, satellite)

Protocols

Define format, order of messages sent and received among network entities, and actions take on message transmission, receipt (Basically just an algorithm)

bit

Propagates between transmission/receiver pairs

Physical Link

What lies between transmitter & receiver

Guided media

Signals propagate in solid media like copper, fiber, or coax

Unguided Media

Signals propagate freely, e.g., radio

Packet-Switching

Hosts break application layer messages into packets, then forwards packets from one router to the next, across links on path from source to destination. Each packet transmitted at full link capacity (not shared)

ARP (Address Resolution Protocol)

A protocol that connects an ever-changing IP address to a fixed physical machine address (MAC address) in a LAN

Collision

Entire packet transmission time is wasted

Switches vs. Routers

Both are store-and-forward Both have forwarding tables -routers: computer tables using routing algorithms, IP addresses -switch: Learn forwarding using flooding, learning, MAC addresses