# Reference models
## 1
Which layer packs bits into bytes, bytes into frames, uses hardware addressing and implements error detection? Which device (network hardware) operates on this layer in principle?
- 2nd layer: Data link layer; Switches work on this layer

## 2
At which layer does the assignment of addresses and the forwarding of data packets from one end of the network to another take place? Which network hardware operates on this layer?
- Later 3: Network layer; Router

## 3
 Which layer is responsible for establishing, running and terminating a process communication between 2 systems?
 - Layer 5: Session layer

## 4
At which layer does data stream segmentation take place for communication between endpoints, is a mechanism for establishing/disestablishing virtual connections provided, and does detection and elimination of transport errors as well as flow control or congestion avoidance take place?
- Layer 4: Transport layer

## 5
Which layer determines signal levels, transmission speeds, and connector pinouts, and transmits bits in a transmission channel? Which network hardware operates on this layer?
- Layer 1: Physical layer; Network interface card

## 6
What boundary does the transport layer form between layers 5-7 and 1-3?
- The transport layer forms the boundary between the lower transporting layers, which are primarilly concerned with network tasks, and the application oriented layers

## 7
Contrast the OSI layer model with the widely used TCP/IP layer model. Which layers correspond to each other?
- 

## 8
What are the addressing names of layers 2, 3, 4 and 7?
- Layer 2: MAC-adresses
- Layer 3: IP-adresses
- Layer 4: Port number
- Layer 7: Application specific adresses such as E-Mail or URL

## 9
 Can collisions occur in point-to-point networks?
 - No, the switch sends the data out only at the reciver port. With original Ethernet 10 Mbit/s with CSMA/CD collisions can still happen between switch and connected host

## 10
 How are computer networks classified according to their extent?
 - ![[2023-04-18_11-08.png]]

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