Capacity Management and Routing Policies for Voice over IP Traffic

1
Capacity Management andRouting Policiesfor
Voice over IP Traffic

• Partho P. Mishra, Gigabit Wireless
• Huzur Saran, Indian Institute of Technology Delhi

2
Outline

• Review the routing algorithm used in
  voice(circuit-switching) and data(IP) network
• Evaluate the performance of two distinct models
  for capacity management
• (on IP-based network)
• Integrated Services Model (SPF, SAPF, WAPF)
• VPN Model (DPO, STT, ASDR)
• Experiment results.

3
Routing Polices Used in Existing Circuit-Switched
Network

• DPO accept only when adequate capacity on
  direct path between originating and terminating
  switches
• Always possible exceed capacity due to transient
  overload
• Alternative routing policy - A two-hop route
• Predetermined order
• Randomize the start point of search
• According to historical load information
• STT (Success To the Top)

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Routing Polices Used in Existing Circuit-Switched
Network
Originating
Intermediate
Terminating
Randomize Start Search Switch
Predetermined
STT
Maintain a stack For success switch Is the top one
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Routing Polices Used in Existing Circuit-Switched
Network

• SDR State Dependent Routing
• Consider the existing state of a link
• Determine intermediate switch
• Ex.
• ASDR Approximate SDR
• Based on predicted link loads (periodic link
  state updates)

K MAX(min(Avail(I, L), Avail(L, J)))
10
10
1
10
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Routing Polices Used in Existing Circuit-Switched
Network

• Alternate path routing can demonstrate
  instability under heavy load. trunk reservation
  always used to address this potential problem.
• Trunk Reservation
• When available capacity is below trunk
  reservation parameter, alternate path routing
  will be refused.

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Routing Polices Used in ExistingIP Network

• Traditionally employ only a single forwarding
  path at a time between a pair of IP routers
  (OSPF).
• Certain extension to OSPF offer multipath routing
  capability.
• More recently, multiprotocol label switching
  (MPLS) offers another mechanism through which
  multiple logical paths or links may be configured.

8
The Integrated Services Model for Capacity
Management
PSTN
IP Network
RSVP Message

• The routing of the RSVP signaling messages
  follows the path determined by the IP layer
  routing protocol.
• Sophisticated QoS-sensitive routing policies may
  be viewed as analogous to STT/SDR-like policies
  in IP world.

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The Integrated Services Model for Capacity
Management

• Two extremes policies for choosing alternative
  path
• SAPF Shortest Available Path First, explored in
  the order of hop count.
• WAPF Widest Available Path First, maximum
  (current) available capacity.
• Not been deployed very widely.
• Because of scalability problem resulting from the
  need to implement per-flow signaling and retain
  per-flow state at every router on the end-to-end
  path of a flow.

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The VPN Model for Capacity Management
router
ISPs network
VPN
VLL

• The VLL(Virtual leased lines) requires the
  customer to request capacity to accommodate the
  worst case traffic requirements for each VLL.
• The use of alternate routing policies can be
  viewed as a way to compensate for traffic
  burstiness and improve the efficiency

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Experiment Environment
12 core routers
42 links
168 PSTN Gateway
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Results (trunk reservation)
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Results (Greater Traffic Aggregation)
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Results (Integrated Service Model)