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COMPUTER NETWORKS > LECTURE 2- STEPS TO NETWORKING > Flashcards

LECTURE 2- STEPS TO NETWORKING Flashcards

1
Q

What are the 4 steps to networking?

A 
• Communicating across a link
• Connecting together multiple links
(internetworking)
• Finding and routing data to nodes on
internetwork
• Matching application requirements
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2
Q

Describe the first step of networking

A 
Creating a link between nodes
• Link is  path followed by bits
A link can be:
–Wired or wireless
–Broadcast or point-to-point (or both)
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3
Q

What are the type of packet transmission nodes in the first step

A

Unicast
– Transmission to single specific receiver
• Broadcast
– Transmission to all network nodes
• Multicast
– Transmission to specific subset of nodes
• Anycast
– Transmission to one of a specific subset of
nodes

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4
Q

What is a switched network?

A

A network in which a temporary connection is established from one point to another for either the duration of the session (circuit switching) or for the transmission of one or more packets of data (packet switching).

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5
Q

What is statistical multiplexing?

A

Statistical Multiplexing is a multiplexing technique that allows information from a number of channels to be combined for transmission over a single channel.

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6
Q

What are the characteristics of packet switching?

A

Delays
congestion
reordering- can use alternate paths

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7
Q

What is an internetwork and what are the three units of internetworking

A

A collection of
interconnected
networks

Extranet
Intranet
Internet

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8
Q

What are the main challenges facing internetworking

A 
• Many differences between networks
– Address formats
– Performance – bandwidth/latency
– Packet size
– Loss rate/pattern/handling
– Routing
• How to translate between various
network technologies
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9
Q

What is packet roouting?

A

the forwarding of logically addressed packets from their source toward their ultimate destination through intermediate nodes.

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10
Q

How does a packet get routed?

A

When a packet arrives at a router, the router examines the IP address put there by the IP protocol layer on the originating computer. The router checks it’s routing table. If the network containing the IP address is found, the packet is sent to that network.

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11
Q

What is Address Resolution in networking?

A

The Address Resolution Protocol (ARP) is 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. This mapping is a critical function in the Internet protocol suite(ARP maps IP addresses to Ethernet addresses)

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12
Q

Describe routing in a datagram network

A
  • In datagram networks, each data packet is routed independently from the source to the destination even if they belong to the same message.
  • No prior resource or channel allocation is done for the individual packets. —As the datagrams are treated as independent units, no dedicated path is fixed for data transfer.
  • Each datagram is routed by the intermediate routers using dynamically changing routing tables. So two successive packets from the source may follow completely separate routes to reach destination. -Resources are allocated on demand on a First-Come First-Serve (FCFS) basis. When a packet arrives at a router, the packet must wait if there are other packets being processed, irrespective of its source or destination.
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13
Q

What are the different ways of populating a routing table

A

Static routing
Static route is the term applied to any route in a routing table that has been manually coded (entered). For example, when the routing requirements between networks are very simple, routing tables can easily be coded directly into the host to provide all connectivity requirements.
Static routing has limitations when networks become larger. The number of routes can become difficult to manage. Also, networks can change: routers can become unavailable, causing certain routes to be unusable. At the same time, new routes can become available and these must manually be added to the routing table before they can be utilized. To overcome such limitations, dynamic routing can be used.

Dynamic routing
Dynamic routing involves the usage of routing protocols to communicate information about the status of routes and interfaces. Eg RIP(Routing Information Protocol) and OSPF(Open Shortest Path First ). They populate the routing table of a host with routes. OSPF is more scalable and configurable than RIP.

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14
Q

What are some of the application demands

A 
Reliability
–Corruption
–Lost packets
• Flow and congestion control
• Fragmentation
• In-order delivery
• Etc…
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15
Q

What happens in a network if the data gets corrupted?

A

 Checksum included in header by sender
 Generated by treating data in the packet as numbers and
adding them all up
 Receiver checks checksum
 Performs same operation as sender and checks
checksum field
 Corruption detected when no match

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16
Q

What happens in a network if the data is out of order?

A

Data ‏in‏ each‏ packet‏ is ‏labeled ‏with ‏a‏ ”unique” ‏number
 Establishes ordering amongst packets
 Allows receiver to identify which packets have been received and which have not
 Initialized during connection setup (i.e. 3-way handshake)

17
Q

What happens in a network if the data is lost?

A

he network which uses a combination of acknowledgment and retransmission of damaged or lost packets offers reliability.

Here, retransmission means the data packets have been lost, which leads to a lack of acknowledgment. This lack of acknowledgment triggers a timer to timeout, which leads to the retransmission of data packets. Here, the timer means that if no acknowledgment is received before the timer expires, the data packet is retransmitted.

18
Q

What if receiver has no resources?

A

Flow Control
Flow Control basically means that TCP will ensure that a sender is not overwhelming a receiver by sending packets faster than it can consume.

19
Q

What if Network is Overloaded?

A

Congestion control
Congestion Control is a mechanism that controls the entry of data packets into the network, enabling a better use of a shared network infrastructure and avoiding congestive collapse.

20
Q

What is the difference between flow control and congestion control

A

Although there’s some overlap between the mechanisms TCP uses to provide both services, they are distinct features. Congestion control is about preventing a node from overwhelming the network (i.e. the links between two nodes), while Flow Control is about the end-node.

21
Q

What if the Data Doesn’t Fit?

A

Fragmentation
Fragmentation is a technique implemented on a datagram at the network layer if the size of the datagram is larger than the size of the datagram that the corresponding network can forward. This technique involves the division of the large size datagram into smaller fragments.

22
Q

What is layering?

A

Modular approach to network functionality. (to break up the sending of messages into separate components and activities)

23
Q

What are the characteristics of layering

A

• Each layer relies on services from layer below and exports services to layer above
• Interface defines interaction
• Hides implementation - layers can change without disturbing other layers
(black box)

24
Q

What is demultiplexing?

A

It is the reverse of the multiplexing process. Demultiplex is a process reconverting a signal containing multiple analog or digital signal streams back into the original separate and unrelated signals.

25
Q

What is involved in each of the seven OSI layers?

A
  • Physical: how to transmit bits
  • Data link: how to transmit frames
  • Network: how to route packets
  • Transport: how to send packets end2end
  • Session: how to tie flows together
  • Presentation: byte ordering, security
  • Application: everything else
26
Q

What are the advantages of the layered approach?

A

It provides modularity and clear interfaces
Implementation, simplicity, maintainability, flexibity and scalability are maintained
Layered approach supports portability
It provides stability
It is a time tested approach

27
Q

What are the disadvantages of the layered approach

A

Data overhead and processing due to the duplication of functionality
The more layers you have, the more risks you have for things to breakdown or data to get lost
Various issues regarding Higher Lay

COMPUTER NETWORKS (23 decks)

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