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Internet Infrastructure Measurement: Challenges and Tools

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Internet Infrastructure Measurement: Challenges and Tools Mustafa Zali Internet Measurement Tuesday, 26 Aban 1388 * – PowerPoint PPT presentation

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Title: Internet Infrastructure Measurement: Challenges and Tools


1
Internet Infrastructure Measurement Challenges
and Tools
  • Mustafa Zali
  • Internet Measurement
  • Tuesday, 26 Aban 1388

2
Introduction
  • Review the physical properties of Internet
  • Physical Properties
  • Devices (routers, NAT boxes, firewalls,
    switches), Links (wired, wireless)
  • Topology Properties
  • Various levels Autonomous Systems, Points of
    Presence, Routers, Interfaces
  • Traffic Properties
  • Delays (Transmission, Propagation, Queuing,
    Processing etc.), Losses, Throughput, Jitter

3
Outline
  • Properties
  • Challenges
  • Tools

4
Properties
  • Review the important properties of Internet in
    bottom-up approach
  • Component Devices
  • Topology How devices interconnected
  • Interaction of traffic and infrastructure
  • Our focus in on properties affected by physical
    infrastructure

5
Physical Devices Properties
  • Internet End Systems, Core
  • Core Switch, Router, Link
  • The infrastructure that concerns us here is core
    of internet.

6
Link
  • Viewed at the IP layer propagation of data from
    one node to another is via links.
  • The details of links is hidden from IP layer (ch
    2).
  • Link properties
  • Propagation delay
  • Capacity
  • Packet delay
  • Packet loss
  • jitter

7
Router
  • Routers move packets from one link to another.
  • Drop tail
  • Active Queue Management

8
Router
Forwarding table updates
Routing Protocol Packet
9
Router
10
Wireless
  • The primary goal of wireless connection is to
    link users to wired infrastructure
  • Wireless technology distance, data rate,
    reliability, potential interference, number of
    current users.
  • Security problem very open nature of wireless

11
Wireless- Technologies
  • Narrowband
  • Wideband allows signal to be detected easily by
    receiver.
  • Infrared using high frequency range.

12
Wireless- Standards
  • 802.x 802.11a, 802.11b, 802.11g
  • 802.11b WiFi (Wireless fidelity)
  • Bluetooth shorter distance, less power
    consumption, cheaper
  • WiMAX 802.16

13
Wireless
  • Measurements
  • Signal strength
  • Amount of power consumed
  • Data bite rate
  • Degree of coverage
  • Session related information (duration, set-up
    time)
  • Other traditional measurements

14
Topology properties
  • Four level
  • Autonomous systems Independently operated and
    managed network
  • BGP protocol for routing between them.
  • Point of presence Consists of one or more
    routers in a single location.
  • Router Router graph
  • Vertices are router and edges are links between
    them
  • Interface Interface Graph
  • Vertices are router intreface and edges are links
    one-hop connection

15
Interaction of Traffic and Network
  • Network constrains traffic
  • Minimum possible delay
  • Maximum possible throughput

16
Packet Delay
  • Routing delay
  • Packet processing delay
  • Queuing delay
  • Additional delay
  • Transmission delay
  • Propagation delay

17
Packet Loss
  • In element n
  • Aggregate loss
  • Along pass is aggregate of hops

18
Throughput
  • Throughput
  • Throughput on path

19
Packet Jitter
  • Variability of packet inter arrival times
  • Low jitter more predictable, more reliable

20
Challenges
  • Poor Observability Observability is not built
    into the design of Internet protocols and
    components.
  • Reasons for this
  • Core Simplicity
  • Hidden Layers
  • Hidden Pieces
  • Administrative Barriers

21
Core Simplicity
  • Stateless nature Stupid network
  • Routers is very simple.
  • Explosive growth of Internet
  • As network elements do not track packets
    individually, interaction of traffic with the
    network is hard to observe

22
Hidden Layers
  • Below IP level, packet transmission implemented
    in many ways.
  • These details are hidden from IP level.
  • Detailed measurement can not capture these
    details.

23
Hidden Pieces - Middleboxes
  • End-to-end argument.
  • Firewalls provide security
  • Traffic Shapers assist in traffic management
  • Proxies improve performance by terminating TCP
    inside network. (Cache proxy)
  • NAT boxes utilize IP address space efficiently
  • Each of these impedes visibility of network
    components.
  • firewalls may block active probing requests
  • NATs hide away the no. of hosts and the structure
    of the network on the other side

24
Administrative Barriers
  • Owing to the competition-sensitive nature of the
    data required (topology, traffic etc.), ISPs
    actively seek to hide these details from outside
    discovery
  • Information that they do provide are often
    simplified.
  • E.g. Instead of publishing router-level
    topologies, ISPs often publish PoP-level
    topologies

25
Tools Classification
  • Active Measurement
  • Passive Measurement
  • Fused/Combined Measurement
  • Bandwidth Measurement

26
Active Measurement Tools
  • Methods that involve adding traffic to the
    network for the purposes of measurement
  • Ping Sends ICMP ECHO_REQUEST and captures
    ECHO_REPLY
  • Useful for measuring RTTs
  • Only sender needs to be under experiment control
  • Zing Sends at random, exponential time

27
Traceroute
  • Useful for determining path from a source to a
    destination
  • Uses the TTL (Time To Live) field in the IP
    header in a clever but distorted way
  • A large scale measurement system called skitter
    uses traceroute to discover network topology
    (Chapter 10)

28
IP Header and the TTL field
29
Traceroute Problem
  • Suppose the path between A and D is to be
    determined using traceroute

X
Y
D
A
B
C
30
Traceroute Process

X
Y
D
A
B time exceeded
Dest D TTL 1
B
C
31
Traceroute Process

X
Y
D
A
C time exceeded
Dest D TTL 2
B
C
32
Traceroute Process

X
Y
D
A
D echo reply
Dest D TTL 3
B
C
33
Traceroute issues
  • Path Asymmetry (Destination -gt Source need not
    retrace Source -gt Destination)
  • Unstable Paths and False Edges
  • Aliases
  • Measurement Load

34
Unstable Paths and False Edges
  • Inferred path A -gt B -gt Y

Y time exceeded
Dest D TTL 2
X
Y
D
A
B time exceeded
Dest D TTL 1
B
C
35
Aliases
  • IP addresses are for interfaces and not routers
  • Routers typically have many interfaces, each with
    its own IP address
  • IP addresses of all the router interfaces are
    aliases
  • Traceroute results require resolution of aliases
    if they are to be used for topology building

36
Aliases
  • Alias resolution
  • Send packet to both interface.
  • Close IP ID field and same TTL field.
  • Record Route Option. (The address of interface
    that is packet sent.)
  • Guess difference in last bits.

37
Measurement Load
  • Traceroute inserts considerable load on network
    links if attempting a large-scale topology
    discovery
  • Optimizations reduce this load considerably
  • Track interfaces visited already
  • Assumption Routers are stable and only one path
    exists.
  • If single source is used, instead of going from
    source to destination, a better approach is to
    retrace from destination to source.
  • If multiple sources and multiple destinations are
    used, sharing information among these would bring
    down load considerably (A-gtB-gtC-gtD, X-gtB)

38
System Support
  • Injecting and capturing packets, has several
    security problems.
  • Efficient packet injection and accurate
    measurement of arrival and departure times are
    best done at kernel level
  • Using scriptroute, unprivileged users can inject
    and capture packets
  • Periscopes API helps define new probing
    structures and inference techniques for
    extracting results from arrival patterns of
    responses
  • Unrestricted access to the network interface
    raises security concerns

39
Passive Measurement
  • Methods that capture traffic generated by other
    users and applications to build the topology

40
BGP
  • A BGP routing table is the set of paths.
  • Each path is the sequence of ASes.
  • Each AS advertises the routes that it knows.
  • Routeviews repository is useful for passive
    internet analysis and monitoring.

41
(No Transcript)
42
BGP Advantages and Disadvantages
  • Large set of AS-AS, router-router connections can
    be learned by simply processing captured tables
  • However, especially using BGP views, there could
    be potential loss of cross-connections between
    ASes which are along the path
  • Secondly, route aggregation and filtering tends
    to hide some connections
  • Also, multiple connections between ASes will be
    shown as a single connection in the graph

43
OSPF
  • Capture link state announcements within routing
    domain.
  • Announcements
  • Topology changes
  • External routes change availability

44
Fused Measurement
  • Combine both active and passive measurements.
  • Active large amount of traffic.
  • One way is to using passive measurement
  • Another way is to augment passively obtained BGP
    topologies with additional inter AS connections.

45
Bandwidth Measurement
  • Bandwidth amount of data the network can
    transmit per unit time
  • Bandwidth measure requirements
  • Streaming media applications
  • Server selection
  • Estimating the bandwidth for TCP flow control
  • Verification of service level agreement

46
Bandwidth Measurement
  • Bandwidth measurement is a active process
  • Bottleneck link with minimum bandwidth
  • Three kinds of bandwidth
  • capacity max throughput a link can sustain,
  • available bandwidth capacity used bandwidth
    and
  • bulk transfer capacity rate that a new single
    long-lived TCP connection would obtain over a
    path

47
Bandwidth Measurement
  • Tight link Link with minimum available bandwidth
  • Narrow link Link with minimum capacity

48
Bandwidth Measurement Methods
  • These focus on observing how packet delay
    (queuing and transmission) is affected by link
    properties
  • Four types
  • Packet-pair Methods
  • Size-delay Methods
  • Self-induced Congestion
  • Bulk Transfer Capacity Measurement

49
Packet-Pair Methods
  • Methods to measure capacity and available
    bandwidth
  • Involve sending probe packets with known
    inter-packet gaps and measuring the same gap
    downstream
  • where C is the capacity, L is the length of probe
    packets, max delta is the maximum inter-packet
    gap measured downstream

50
Packet-Pair Methods- Capacity
51
Packet-Pair Methods- Capacity
  • Capacity of narrow link can be estimated
  • The packets should be queued at bottleneck link
  • Cross traffic sending many probe packets

52
Packet-Pair Methods- Bandwidth
  • Assumption
  • FIFO queuing
  • Router queue is not empty between first and
    second probe packet
  • Tight link is narrow link

53
Size Delay Methods
  • Useful for measuring link capacities on each link
    along a path
  • Based on the observation that transmission delay
    is affected by link capacity and packet size
  • The idea is to send many different sized packets
    and measure the difference in delays affected by
    packet size.
  • Then the capacity of each link will be a function
    of these differences
  • Method assumes there is no cross-traffic, no
    variation in packet size
  • Measurements become less accurate if the length
    of the path grows

54
Size Delay Methods
  • Queuing delay
  • Transmission delay
  • Propagation delay

55
Size Delay Methods
56
Self Induced Congestion
  • Find the maximum probe rate that create
    congestion
  • Increase R until congestion occurs
  • Problem cross traffic

57
Bulk Transfer Capacity Management
  • One opens a TCP connection over the path and
    sends as much as data that the path can handle

58
Caveats in Bandwidth Measurements
  • High rate links make it difficult to measure
    bandwidth accurately because of small delays
  • Wireless links affect rate dramatically on fine
    timescales
  • FIFO order is not guaranteed in wireless links
  • Layer 2 devices can cause underestimation of a IP
    hops capacity by introducing additional
    transmission delays

59
Conclusion
  • Internet Measurement is key to designing the next
    generation communication network
  • Fundamental design principles of the current
    internet make it harder for measuring various
    aspects of it
  • Preliminary research has resulted in a set of
    basic tools and methods to measure aspects like
    topology, traffic etc.
  • Accuracy of such methods is still an open
    question
  • There is still a lot of ground to cover in this
    direction and this is where researchers like you
    come into the equation!
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