SHEKHAR HMP Assistant Professor, Wireless Networking Laboratory, Department of Computer Science

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SHEKHAR HMPAssistant Professor,Wireless
Networking Laboratory,Department of Computer
Science Engineering,M S Ramaiah Institute of
Technology,Bangalore, INDIAE-mail ID
shekharhmp_at_msrit.edu
NETWORK LAYER
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AGENDA

• Network Layer Design Issues
• Routing Algorithms
• Congestion Control Algorithms
• Quality of Service
• Internetworking
• Internet Protocols (IP, ARP, RARP, DHCP, etc.)

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CONGESTION CONTROL

• Quality of Service
• Requirements
• Techniques for Achieving Good Quality of Service
• Integrated Services
• Differentiated Services
• Label Switching and MPLS

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CONGESTION CONTROL

• Quality of Service
• The collective effect of service performance
  which
• determines the degree of satisfaction of a user
  of a
• service.
• The United Nations Consultative Committee for
  International
• Telephony and Telegraph (CCITT) Recommendation
  E.800
• Typical QoS Metrics available bandwidth, packet
  loss rate, estimated delay, packet jitter, path
  reliability etc.

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CONGESTION CONTROL

• Quality of Service

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CONGESTION CONTROL

• Buffering
• Smoothing the output stream by buffering packets.

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CONGESTION CONTROL

• Traffic Shaping
• Regulating the average rate (and burstiness) of
  data transmission.
• When connection is setup, the user and the subnet
  (i.e. customer and carrier) agree on certain
  traffic pattern (i.e. shape). This is called SLA.
• Traffic shaping reduces congestion and helps the
  carrier to satisfy the customer.

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CONGESTION CONTROL

• Traffic Shaping
• How does carrier ensures that customer is
  following the agreement?
• Traffic policing monitoring the traffic flow.
• Traffic shaping and policing is easier to
  implement in virtual circuit subnets than with
  datagram subnets.
• In datagram subnets, some implementations are
  there at transport layer.

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CONGESTION CONTROL

• Leaky bucket algorithm

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CONGESTION CONTROL

• Leaky bucket algorithm
• Smoothens out bursts and reduces congestion
• It is a single-server queuing system with a
  constant service time.
• If packets are of same size (ATM networks), flow
  is regulated based on packets. When variable
  sized, regulated based on bytes.

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CONGESTION CONTROL

• Leaky bucket algorithm
• Enforces a rigid output pattern at the average
  rate, no matter how bursty the traffic is.
• There are cases where data may be lost.
• Does not allow idle hosts to save up permissions
  to send large bursts later.
• Is not flexible

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CONGESTION CONTROL

• Token bucket algorithm

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CONGESTION CONTROL

• Token bucket algorithm
• Is a flexible algorithm and the output speeds up
  when large bursts arrive.
• If S is the burst length in sec, the token
  capacity C bytes, the token arrival rate ?
  bytes/sec, and the maximum output rate M
  bytes/sec, the output burst contains C ?S
  bytes.
• The number of bytes in a maximum speed burst of
  length S sec is M S

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CONGESTION CONTROL

• Token bucket algorithm
• C ?S MS
• Ex. C 250 KB, M 25 MB/sec and ? 2 MB/sec,
  then burst time is 11 msec.

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(a) Input to a leaky bucket. (b) Output from a
leaky bucket. Output from a token bucket with
capacities of (c) 250 KB, (d) 500 KB, (e) 750
KB, (f) Output from a 500KB token bucket
feeding a 10-MB/sec leaky bucket.
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CONGESTION CONTROL

• Resource reservation
• Traffic shaping to be more effective requires all
  packets to follow the same route.
• Hence would be possible to reserve resources
  along the route to ensure quality of service.
• Resources are generally bandwidth, buffer space
  and CPU cycles
• Ex RSVP

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CONGESTION CONTROL

• Admission control
• Ex

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CONGESTION CONTROL

• Proportional routing
• The source traffic is split over multiple paths
  for each destination to achieve higher quality of
  service.
• Traffic may be divided equally or in proportion
  to the capacity of the outgoing links.

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CONGESTION CONTROL

• Packet scheduling
• Since routers handle multiple flows, one flow may
  starve other flows, thereby reduces quality of
  service.
• To address the above problem, several packet
  scheduling algorithms have been proposed.
• Fair queuing (Nagle, 1987)
• Routers maintain multiple queues for each output
  line, one for each flow.

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CONGESTION CONTROL

• Fair queuing (Nagle, 1987)
• Schedules packet in round robin fashion.
• Limitation hosts that use large packets gets
  more bandwidth than hosts that use small packets.
• Improvement byte-by-byte round robin.
• Limitation all hosts have same priority

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CONGESTION CONTROL

• Fair queuing

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CONGESTION CONTROL

• Weighted Fair queuing (Nagle, 1987)
• Widely used packet scheduling algorithm
• Schedules packets based on priority classes.
• Improvement byte-by-byte round robin.
• Limitation all hosts have same priority