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Advanced Networks > Lecture 3 > Flashcards

Lecture 3 Flashcards

1
Q

What is circuit switching?

A

A dedicated channel (known as circuit) is established for the duration of the transmission.

That circuit between the hosts can be made of one or more physical links.

An example being the PSTN Telephony system - where multiple wire segments are linked together to create an unbroken line for each phone call.

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2
Q

What is packet switching?

A

Data is transferred by dividing the data into individual (small) packets and are transmitted via a medium that may share multiple communication sessions.

No path or resources are reserved, packets are routed on-the-fly.

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3
Q

What does ATM stand for?

A

Asynchronous Transfer Mode (ATM).

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4
Q

What is ATM?

A

A Layer 2 cell relay protocol designed by the ATM Forum.

A telecom concept for the carriage of complete user traffic, including voice, data and video signals.

Similar to circuit switching, ATM uses signaling protocol to establish circuit before data communication commences.

Similar to packet switching as well, ATM is based on statistical multiplexing.

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5
Q

How does ATM benefit itself?

A

It uses both circuit and packet switching.

It has a small packet (cell) size meaning less transmission delay.

Fixed route for all packets of the connection.

Flexible bandwidth and statistical multiplexing.

High transmission efficiency

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6
Q

What does logical connection first established mean?

A

Route from the source to the destination is chosen.

The same route is used for all cells (fixed size) of the connection.

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7
Q

Benefits of virtual circuit?

A

No routing decision for every cell

No dedicated path reserved

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8
Q

What is the transmission path (TP)?

A

TP is hte physical transmission connection medium - the cable, wireless /etc.

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9
Q

What is a virtual path (VP)?

A

VP provides connection(s) between switches.

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10
Q

What does a VP consist of?

A

Multiple Virtucal Circuits (VCs) that logically connect the same two points.

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11
Q

What is the fixed size of a cell?

A

53 Bytes - 48 bytes payload + 5 bytes header.

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12
Q

What are the problems with a cell?

A

They have a reduced header functionality.

There is no sequence number or destination and source address.

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13
Q

What does UNI stand for?

A

User-Network Interface (UNI)

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14
Q

What does NNI stand for?

A

Network-Network Interface (NNI)

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15
Q

What is the cell format at UNI?

A 
GFC - 4 - Generic Flow Control
VPI - 8 - Virtual Path Identifier
VCI - 16 - Virtual Circuit Identifier
PT - 3 - Payload Type
CLP - 1 - Cell Loss Priority
HEC - 8 - Header Error Check
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16
Q

What is the cell format at NNI?

A 
VPI - 12 - Virtual Path Identifier
VCI - 16 - Virtual Circuit Identifier
PT - 3 - Payload Type
CLP - 1 - Cell Loss Priority
HEC - 8 - Header Error Check
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17
Q

How is switching done in ATM?

A

Based on the VPI / VCI.

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18
Q

What does AAL stand for?

A

Application Adaptation Layer

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19
Q

What is the point in AAL?

A

ATM must be able to accept different types of payload for example, phone calls, data frames and bit streams.

AAL is a layer which sits on top of the ATM Layer to allow for different types of traffic to be sent.

20
Q

How many versions of AAL are there?

A

Four

AAL1, AAL2, AAL3/4, and AAL5

21
Q

Which types of AAL are used today?

A

AAL1 (audio/video stream) and AAL5 (data communication).

22
Q

What are the two sublayers of AAL?

A 
Segmentation and Reassembly (SAR)
Convergence Sublayer (CS)
23
Q

What does the CS Layer do?

A

Guarantees the integrity of data.

24
Q

What does SAR layer do?

A

At source segments the paylaod in to 48-byte segments.

At destination reassembles the segments back into the payload.

25
Q

If you have a constant bit rate which AAL needs to be used?

A

AAL1 - you are likely sending video / data.

26
Q

Which AALs are connection oriented?

A

AAL1/AAL2

27
Q

Which AALs are connectionless oriented?

A

AAL(3/4)/AAL5

28
Q

What is cell rate?

A

The number of ATM cells created per a second.

29
Q

What are the 5 service categories?

A 
Constant Bit Rate (CBR)
Real-time Variable Bit Rate (rt-VBR)
Non Real-time Variable Bit Rate (nrt-VBR)
Available Bit Rate (ABR)
Unspecified Bit Rate (UBR)
30
Q

What are the 6 QoS parameters?

A

Peak Cell Rate (PCR)
Minimum Cell Rate (MCR)
Sustainable Cell Rate (SCR)

Cell Transfer Delay (CTD)
Cell Delay Variation (CDV)

Cell Loss Ratio (CLR)

31
Q

What does MPLS stand for?

A

Multiprotocol Label Switching

32
Q

What does multi protocol allow?

A

Allows switching operations on different protocols (IPv4, IPv6, Ethernet, Point-to-Point Protocol (PPP), Frame Relay)

33
Q

What does Label Switching do?

A

Forwards packets based on short labels instead of looking up destination in the routing table.

34
Q

What is an LSR?

A

Label Switch router, it’s the routers within an MPLS network. LSRs route data packets based on labels.

35
Q

What is an LER?

A

Label Edge Router the router that resides at the entry and exit points of an MPLS network.

Acts as a gateway and handles both labeled and unlabeled packets.

36
Q

What is LDP?

A

Label distribution protocol, used in MPLS networks for exchanging label mapping information.

37
Q

What is LSP?

A

Label-Switched path, it’s a unidirectional path through an MPLS network, there will be at least one for each label.

38
Q

Where does the MPLS header sit?

A

Sits between the L2 and L3 headers, it’s a 32-bit shim header.

Sometimes referred to as a 2.5 layer protocol.

39
Q

Are multiple labels allowed in MPLS?

A

Yes, when multiple labels are used they are grouped into a label stack.

40
Q

What are multiple labels grouped into in an MPLS network?

A

A label stack.

41
Q

Which part of a label stack do the LSRs use?

A

The top part.

42
Q

What is an example of MPLS traffic which uses multiple labels?

A

MPLS Virtual Private Networks (MPLS-VPN), top label is the egress router, the next label identifies the VPN.

43
Q

What does FEC stand for?

A

Forwarding Equivalence Class - refers to a set of packets that are able to receive the same treatment in a particular router.

44
Q

What is a typical example of an FEC?

A

Thye are bound to the same MPLS label.

45
Q

What does MPLS packet forwarding involve?

A

Assigning a packet to a specific FEC (using labels)

Determining the next hop of each FEC

46
Q

What does MPLS allow non IP hardware to do?

A

Route IP based packets without understanding IP packets, for example ATM switches.

Advanced Networks (6 decks)

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