Title: Lord%20Mandelson%20of%20Foy%20and%20Hartlepool%20is%20a%20descendant%20of%20which%20Labour%20leader?
1Lord Mandelson of Foy and Hartlepool is a
descendant of which Labour leader?
- Harold Wilson
- George Brown
- Gordon Brown
- Herbert Morrison
- Clement Attlee
2Herbert Morrison
- Not entirely obvious, I admit.
- Morrison was Mandelsons mothers father, and
Labour leader of London County Council.
3That was the warmup
- Now to check clickers against groups
- IF your group name is shown, please press the
associated number on each individual clicker AND
the group clicker - ELSE wait for next slide(s)
4Please select a TeamIf youre not here, wait.
- Team A
- Team B
- Team C
- Team D
- Team E
5Please select a Team If youre not here, wait.
- Team F
- Team G
- Team H
- Team I
- Team J
6Please select a Team If youre not here, you
should have been done already
- Team K
- Team L
- Team M
- Team N
7Now for your questions
- Im going to show the individual slide please
answer as individuals. - Then Ill ask you to start conferring. Part way
through this, Ill show the individual answers. - Then Ill put up the group slide, and ask groups
to vote using the group clickers only - A group should vote on its own question
8I What would be the biggest impact of removing
the ACK field from TCP?
- Without ACKs reliability benefits, TCP would
become obsolete. - Reliability would always need to be implemented
at application level. - Fewer small packets would result in a faster
Internet. - Lack of self clocking would result in a slower
Internet.
9G What would be the biggest impact of removing
the ACK field from TCP?
- Without ACKs reliability benefits, TCP would
become obsolete. - Reliability would always need to be implemented
at application level. - Fewer small packets would result in a faster
Internet. - Lack of self clocking would result in a slower
Internet.
10What would be the biggest impact of removing the
ACK field from TCP?
- 2. Reliability would always need to be
implemented at application level. - By losing the option to use TCP for reliability,
the feature would need to be implemented at
application level (as in UDP). - Guaranteed Delivery would become less common as
it would be down to the developer to implement
it. - The quality of alternative reliability systems
would vary significantly. - Lack of protocol would make inter-application
communication difficult.
11I When a user performs a DNS query, they often
get back more information than they asked for.
Why?
- Its faster because the DNS server doesnt have
to work out which specific DNS record type the
user needs. - It figures youll ask subsequent questions based
on the same information so it gives you the
answers in advance. - It reduces the likelihood of DNS spoofing,
because we can check that the additional
information backs up the information we did want. - Its useful for debugging purposes, in case there
are errors resolving the address. - Networking enthusiasts find this information
interesting, and it doesnt add much additional
traffic by including it.
12G When a user performs a DNS query, they often
get back more information than they asked for.
Why?
- Its faster because the DNS server doesnt have
to work out which specific DNS record type the
user needs. - It figures youll ask subsequent questions based
on the same information so it gives you the
answers in advance. - It reduces the likelihood of DNS spoofing,
because we can check that the additional
information backs up the information we did want. - Its useful for debugging purposes, in case there
are errors resolving the address. - Networking enthusiasts find this information
interesting, and it doesnt add much additional
traffic by including it.
13When a user performs a DNS query, they often get
back more information than they asked for. Why?
- Its faster because the DNS server doesnt have
to work out which specific DNS record type the
user needs.- The user has already told the DNS
server what record it needs. - It figures youll ask subsequent questions based
on the same information so it gives you the
answers in advance. - It reduces the likelihood of DNS spoofing,
because we can check that the additional
information backs up the information we did
want.- The whole DNS record could still be
spoofed. - Its useful for debugging purposes, in case there
are errors resolving the address.- Debugging is
not its primary purpose. - Networking enthusiasts find this information
interesting, and it doesnt add much additional
traffic by including it.- It wont add much
additional traffic, but it isnt specifically
there just to please networking enthusiasts.
14I Which of these criteria need to be considered
when deciding if an autonomous system is needed?
- You manage a collection of networks
- You have a different routing policy to your
border gateway peers. - You need to send ICMP redirects.
- You need to exchange external routing information.
15G Which of these criteria need to be considered
when deciding if an autonomous system is needed?
- You manage a collection of networks
- You have a different routing policy to your
border gateway peers. - You need to send ICMP redirects.
- You need to exchange external routing information.
16Answer Slide
- The most appropriate criteria is 2. This is
because an AS is only required in this
circumstance. - 1 4 can also be considered. There are scenarios
when ASs can be created. - 3 is incorrect. It isnt relevant.
17I What is the most important algorithm for
preventing packet timeouts occurring in TCP?
- Fast recovery
- Jacobson RTO calculation
- Karns algorithm
- Fast retransmit
18G What is the most important algorithm for
preventing packet timeouts occurring in TCP?
- Fast recovery
- Jacobson RTO calculation
- Karns algorithm
- Fast retransmit
19Answer
- Fast recovery and fast retransmit work together
to ensure lost packets are dealt with more
quickly than allowing the default timeout to
occur. - Jacobson RTO calculation is used to calculate the
default timeout but this does not directly
prevent them occuring. - Karns algorithm is relevant to packet timeouts
but does not directly impact them.
20I Which of the following situations is the
trivial file transfer protocol (TFTP) best suited
for?
- Transferring small files quickly on a secured
network - Transferring files securely over a LAN
- Bootstrapping a networked diskless system
- Transferring a file to multiple clients at once
- Use on systems with limited memory
21G Which of the following situations is the
trivial file transfer protocol (TFTP) best suited
for?
- Transferring small files quickly on a secured
network - Transferring files securely over a LAN
- Bootstrapping a networked diskless system
- Transferring a file to multiple clients at once
- Use on systems with limited memory
22Answer
- Best Bootstrapping a networked diskless system
- The main use of TFTP is for booting multiple
networked devices such as thin clients. - Possibly Transferring a file to multiple clients
at once - Despite using UDP TFTP does support parallel
access to a file by using multiple ports. - Possibly Systems with limited memory
- TFTP can fit in read only memory and is
therefore useful where resources are limited. - Possibly Transferring small files quickly on a
secured network - There is no real speed increase using TFTP other
than the fact it is lightweight, and the timeouts
are lousy. - Incorrect Transferring files securely over a LAN
- TFTP has no security features and therefore
should only be used over a network where the
security is carefully controlled, or via another
secure method such as a VPN.
23I The triggering of fast retransmission of data
is based on a key assumption "if three or more
duplicate ACKs are received in a row, it is a
strong indication that a segment has been
lost (Stevens, TCP/IP Illustrated, Volume 1
The Protocols, 2003).Is this assumption safe?
- Yes, it's always true - its even written in an
RFC. - Yes, although this could signal reordered rather
than lost segments, the consequences are not
serious - No, although it's unlikely the ACKs could signal
something else, such as reordering of segments,
unnecessary retransmissions could potentially
flood the network. - No, it's a completely flawed assumption that has
yet to be removed from implementations of TCP.
24G The triggering of fast retransmission of data
is based on a key assumption "if three or more
duplicate ACKs are received in a row, it is a
strong indication that a segment has been
lost (Stevens, TCP/IP Illustrated, Volume 1
The Protocols, 2003).Is this assumption safe?
- Yes, it's always true - its even written in an
RFC. - Yes, although this could signal reordered rather
than lost segments, the consequences are not
serious - No, although it's unlikely the ACKs could signal
something else, such as reordering of segments,
unnecessary retransmissions could potentially
flood the network. - No, it's a completely flawed assumption that has
yet to be removed from implementations of TCP.
25And the most likely answer isB
- A duplicate ACK may be a sign of segments getting
reordered or a packet being lost. In the case of
reordering however, it is unlikely that more than
two would be received. - Even if a packet was mistakenly retransmitted it
would not be processed more than once - the
receiver would send out a duplicate ACK
thereafter.
26I Which is the more suitable option out of the
following
- All Multicasting should be handled at the Network
layer - All Multicasting should be handled at the
Application layer - Either is fine and both layers should be able to
handle multicasting - Either is fine and if it cant handle
multicasting, then the loss is acceptable
27G Which is the more suitable option out of the
following
- All Multicasting should be handled at the Network
layer - All Multicasting should be handled at the
Application layer - Either is fine and both layers should be able to
handle multicasting - Either is fine and if it cant handle
multicasting, then the loss is acceptable
28No right answer!
- Any one of them can be justified.
- Currently performed in Network layer, but does
not have to be. - Just as justifiable to use Application Layer,
which is used for Mobile Devices. - Can argue that separation is important, but can
also argue that depends on context. - Forcing all network layer components to handle it
would be expensive though.
29I Historically Nagles algorithm was developed
to reduce network congestion for applications
like rlogin and telnet. With today's networks why
would someone wish to disable it?
- It increases network latency
- It conflicts with other TCP congestion avoidance
techniques - It is not relevant anymore with todays high
bandwidth connections - A newer algorithm has been developed that is now
used
30G Historically Nagles algorithm was developed
to reduce network congestion for applications
like rlogin and telnet. With today's networks why
would someone wish to disable it?
- It increases network latency
- It conflicts with other TCP congestion avoidance
techniques - It is not relevant anymore with todays high
bandwidth connections - A newer algorithm has been developed that is now
used
31Answer more than one correct
- 1) Yes it can increase latency but only when the
network is lightly loaded. For heavily loaded
networks Nagles algorithm is relevant. - 2) Yes, Nagle algorithm can cause extended
waiting when used in combination with the delayed
ACK algorithm - 3) No, bandwidth does not play a part. It depends
on the load of the network (see point 1) and the
type of data being sent. Small packets which
require a fast response time (interactive such as
mouse movements in x-windows) are unsuitable for
Nagles algorithm. An unloaded network can often
lead to many delayed ACKs not being sent until
the timer fires, again useless for highly
interactive applications. - 4) No, no newer algorithm has been widely
accepted. However, newer propositions and
enhancements to Nagles algorithm have been
suggested, like for example Minshalls algorithm.
32I Given the current technology, should Delayed
ACKs be used?
- No, because advances in technology have rendered
them obsolete. - Yes, because they reduce the number of segments
sent. - Yes, because it says so in RFC2581.
- Yes, but only on WANs.
- No, because they can disturb round-trip timing
and packet clocking algorithms.
33G Given the current technology, should Delayed
ACKs be used?
- No, because advances in technology have rendered
them obsolete. - Yes, because they reduce the number of segments
sent. - Yes, because it says so in RFC2581.
- Yes, but only on WANs.
- No, because they can disturb round-trip timing
and packet clocking algorithms.
34Given the current technology, should Delayed ACKs
be used?
- Wrong. WANs can still suffer congestion.
- Delayed ACKs can reduce the number of segments
sent over a network. - Wrong. RFC2581 only states that an acknowledgment
must be sent within 500ms, thus making a delay
possible, not enforcing it. - Delayed ACKs can reduce congestion on WANs by
reducing the number of segments sent. - Wrong. Only seriously delayed ACKs will cause
trouble like this. RFC2581 says that ACKs should
be sent within 500ms so this should not be a
problem.