Network Architectures - Basics at TU Berlin | Flashcards & Summaries

Lernmaterialien für Network Architectures - Basics an der TU Berlin

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Forms of delays in Paket-Switched Networks

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1. Transmission delay

2. Propagation delay

3. Queueing delay (wait time in input core)

4. Processing delay (time router needs for lookup)

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How many IP adresses for a subnet?

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1. Number of interfaces (e.g. 255 hosts + 1 router interface)

2. Broadcast IP address (to communicate with all hosts)

3. Network IP address


--> 258 in this example

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UDP 

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"Best effort" service

- No connection establishment (which can add delay)

- it is simple: 

--> no connection state at sender and receiver

--> no handshaking 

--> no sender buffer (but receiver buffer)

- small segment header

- no congestion control: UDP can blast away as fast as desired


Which application use UDP?

- mutimedia apps (loss tolerant, rate sensitve)

- DNS (no connection is necessary)


Disadvantages

- Messages might get lost

- Messages might arrive out of order

- Sender might overwhelm receiver with messages


Advantages


- Simple, no state for sender or receiver necessary

- Small transport layer header

- No additional delay for connection establishment

- UDP can use up all the available bandwidth (because there is no congestion control )

- Allows to communicate with multiple receivers over one socket

- Application has more control over what data is sent and when

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TESTE DEIN WISSEN

Congestion

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“Too many sources sending too much data too fast for network to handle”


prevent collapses at hosts,  not at routers (can still send congestion signals)


Congetion Control and Avoidance:  mechansm which

- Ensures network resources are used efficiently

- Preserves fair network resource allocation

- Prevents or avoids collapse

Lösung ausblenden
TESTE DEIN WISSEN

Classify routing protocols RIP, OSPF and BGP

1. protocol family

2. what they do

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TESTE DEIN WISSEN

RIP : distance vector protocol - the vector is the direction to the destination (next hop); the distance is treated as a metric type.


OSPF : link state protocol and uses Dijkstra algorithm to calculate the shortest path tree.


BGP : Exterior Gateway protocol. typically used to connect autonomous systems (AS) of Internet service providers

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TESTE DEIN WISSEN

Intra vs Inter AS routing

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Intra-AS protocol 

- within an AS (only one admin, no policies --> performace most important)

- helps in the distribution of routing information between routers in an AS


Inter-AS protocol

- policy-oriented (performance of the routes only 2nd importance)

- learn which destinations are reachable thorugh different ASes


BGP (Border Gateway Protocol) is used for inter-AS protocols

selection of best route:

1. Policy decision (local preference value attribute)

2. Shortest AS-PATH

3. closest NEXT-HOP router

4. additional criteria

5. IP-address of peer

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TESTE DEIN WISSEN

Link Layer services

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TESTE DEIN WISSEN

1. Flow control

- Pacing between sending and receiving nodes


2. Error detection

- Errors are caused by signal attenuation and noise

- Receiver detects presence of errors signals sender for retrans. or drops frame


3. Error correction

-Receiver identifies and corrects bit error(s) without resorting to retransmission


4. Sending mode

Half duplex: Nodes at both ends of link can transmit, but not at

same time

Full duplex: Both nodes can send at same time

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TESTE DEIN WISSEN

Circuit vs Packet Switching

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TESTE DEIN WISSEN

Packet:

  • breaks streams of data into smaller blocks, each one sent independently over a shared network

  • allows users to equally share bandwidth resources → more efficient

  • makes no promises concerning quality or latency

  • intelligence in end nodes, with underlying network that only directs packets

  • requires less complicated infrastructure


Circuit:

  • traditional telephone communication

  • temporary and dedicated link of fixed bandwidth between communicating end nodes

    • not enough network resources? → call cannot be established

  • complexities handled in the centralized facilities → telephone itself simple device.

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TESTE DEIN WISSEN

End-to-end priciple

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End to end principle

- Place functionality higher in the stack

- Higher layers = on the endpoints

- Repeat on lower layers only if …

   1. used by/improves performance of many apps

   2. it does not hurt other applications

-Higher layers (endpoints) are complex (“smart”)

-Lower layers (networks) provide simple service (“dumb”)

 --> Success story: Internet

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TESTE DEIN WISSEN

Interior Gateway Protocol (IGP) & Exterior Gateway Protocol (EGP)

What are they and whats the difference?

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TESTE DEIN WISSEN

Interior Gateway Protocol (IGP) is a Routing Protocol which is used to find network path information within an Autonomous System (e.g. Enterprise network). 2 different types: Link-state protocol or distance vector protocol


Exterior Gateway Protocol (EGP) is a Routing Protocol which is used to find network path information between different Autonomous Systems. The protocol is used by ISPs andd is useful to keep the internet running.

Lösung ausblenden
TESTE DEIN WISSEN

Link-state vs distance vector protocl

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TESTE DEIN WISSEN

Both used as IGPs (interior gateway protocol).


Distance Vector protocol:

- router only sends information to directy connected neighbours

- each node has own routing table and relies on information sent by neighbours


Link State protocol:

- router shares knowlegde of whole network with each other router in same area ID

- each node calculates best path to any destination in network

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TESTE DEIN WISSEN

TCP

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TESTE DEIN WISSEN

Transport protocol for in-order reliable data transfer between applications


- point to point communication

   - one sender, one receiver

   - For each tuple of (source IP, dest. IP, source port, dest.  port) a new socket is opened

- TCP take a stream of bytes from the user

   - Segment stream into chucks

   - Reassemble on receivers side

   - No “message boundaries”

- Full duplex data

   - Allows communication in both directions (unlike UDP)


Connection oriented

- Connections are established and terminated

- Handshaking to exchange control messages

- Protocol has to remember state of connection

Flow Control

- Sender will not overwhelm receiver

Congestion Control

- Sender will not overwhelm network

Lösung ausblenden
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Q:

Forms of delays in Paket-Switched Networks

A:

1. Transmission delay

2. Propagation delay

3. Queueing delay (wait time in input core)

4. Processing delay (time router needs for lookup)

Q:

How many IP adresses for a subnet?

A:

1. Number of interfaces (e.g. 255 hosts + 1 router interface)

2. Broadcast IP address (to communicate with all hosts)

3. Network IP address


--> 258 in this example

Q:

UDP 

A:

"Best effort" service

- No connection establishment (which can add delay)

- it is simple: 

--> no connection state at sender and receiver

--> no handshaking 

--> no sender buffer (but receiver buffer)

- small segment header

- no congestion control: UDP can blast away as fast as desired


Which application use UDP?

- mutimedia apps (loss tolerant, rate sensitve)

- DNS (no connection is necessary)


Disadvantages

- Messages might get lost

- Messages might arrive out of order

- Sender might overwhelm receiver with messages


Advantages


- Simple, no state for sender or receiver necessary

- Small transport layer header

- No additional delay for connection establishment

- UDP can use up all the available bandwidth (because there is no congestion control )

- Allows to communicate with multiple receivers over one socket

- Application has more control over what data is sent and when

Q:

Congestion

A:

“Too many sources sending too much data too fast for network to handle”


prevent collapses at hosts,  not at routers (can still send congestion signals)


Congetion Control and Avoidance:  mechansm which

- Ensures network resources are used efficiently

- Preserves fair network resource allocation

- Prevents or avoids collapse

Q:

Classify routing protocols RIP, OSPF and BGP

1. protocol family

2. what they do

A:

RIP : distance vector protocol - the vector is the direction to the destination (next hop); the distance is treated as a metric type.


OSPF : link state protocol and uses Dijkstra algorithm to calculate the shortest path tree.


BGP : Exterior Gateway protocol. typically used to connect autonomous systems (AS) of Internet service providers

Mehr Karteikarten anzeigen
Q:

Intra vs Inter AS routing

A:

Intra-AS protocol 

- within an AS (only one admin, no policies --> performace most important)

- helps in the distribution of routing information between routers in an AS


Inter-AS protocol

- policy-oriented (performance of the routes only 2nd importance)

- learn which destinations are reachable thorugh different ASes


BGP (Border Gateway Protocol) is used for inter-AS protocols

selection of best route:

1. Policy decision (local preference value attribute)

2. Shortest AS-PATH

3. closest NEXT-HOP router

4. additional criteria

5. IP-address of peer

Q:

Link Layer services

A:

1. Flow control

- Pacing between sending and receiving nodes


2. Error detection

- Errors are caused by signal attenuation and noise

- Receiver detects presence of errors signals sender for retrans. or drops frame


3. Error correction

-Receiver identifies and corrects bit error(s) without resorting to retransmission


4. Sending mode

Half duplex: Nodes at both ends of link can transmit, but not at

same time

Full duplex: Both nodes can send at same time

Q:

Circuit vs Packet Switching

A:

Packet:

  • breaks streams of data into smaller blocks, each one sent independently over a shared network

  • allows users to equally share bandwidth resources → more efficient

  • makes no promises concerning quality or latency

  • intelligence in end nodes, with underlying network that only directs packets

  • requires less complicated infrastructure


Circuit:

  • traditional telephone communication

  • temporary and dedicated link of fixed bandwidth between communicating end nodes

    • not enough network resources? → call cannot be established

  • complexities handled in the centralized facilities → telephone itself simple device.

Q:

End-to-end priciple

A:

End to end principle

- Place functionality higher in the stack

- Higher layers = on the endpoints

- Repeat on lower layers only if …

   1. used by/improves performance of many apps

   2. it does not hurt other applications

-Higher layers (endpoints) are complex (“smart”)

-Lower layers (networks) provide simple service (“dumb”)

 --> Success story: Internet

Q:

Interior Gateway Protocol (IGP) & Exterior Gateway Protocol (EGP)

What are they and whats the difference?

A:

Interior Gateway Protocol (IGP) is a Routing Protocol which is used to find network path information within an Autonomous System (e.g. Enterprise network). 2 different types: Link-state protocol or distance vector protocol


Exterior Gateway Protocol (EGP) is a Routing Protocol which is used to find network path information between different Autonomous Systems. The protocol is used by ISPs andd is useful to keep the internet running.

Q:

Link-state vs distance vector protocl

A:

Both used as IGPs (interior gateway protocol).


Distance Vector protocol:

- router only sends information to directy connected neighbours

- each node has own routing table and relies on information sent by neighbours


Link State protocol:

- router shares knowlegde of whole network with each other router in same area ID

- each node calculates best path to any destination in network

Q:

TCP

A:

Transport protocol for in-order reliable data transfer between applications


- point to point communication

   - one sender, one receiver

   - For each tuple of (source IP, dest. IP, source port, dest.  port) a new socket is opened

- TCP take a stream of bytes from the user

   - Segment stream into chucks

   - Reassemble on receivers side

   - No “message boundaries”

- Full duplex data

   - Allows communication in both directions (unlike UDP)


Connection oriented

- Connections are established and terminated

- Handshaking to exchange control messages

- Protocol has to remember state of connection

Flow Control

- Sender will not overwhelm receiver

Congestion Control

- Sender will not overwhelm network

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