Transcript 20001012

Capacity Management and
Routing Policies
for Voice over IP Traffic
Partho P. Mishra, Gigabit Wireless
Huzur Saran, Indian Institute of Technology Delhi
2000/10/02
Chin-Kai Wu, CS, NTHU
1
Outline


Review the routing algorithm used in voice(circuitswitching) 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.
2000/10/02
Chin-Kai Wu, CS, NTHU
2
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




2000/10/02
Predetermined order
Randomize the start point of search
According to historical load information
STT (Success To the Top)
Chin-Kai Wu, CS, NTHU
3
Routing Polices Used in Existing
Circuit-Switched Network
Originating
Predetermined
Intermediate
Terminating
Randomize Start
Search Switch
STT
N-Clique
N-Clique
N-Clique
Search each switch
Search each switch
Maintain a stack
From 1 to N
From Random Switch
For success switch
Is the top one
2000/10/02
Chin-Kai Wu, CS, NTHU
4
Routing Polices Used in Existing
Circuit-Switched Network

SDR – State Dependent Routing


Consider the existing state of a link
Determine intermediate switch:
K = MAX(min(Avail(I, L), Avail(L, J)))


Ex.
10
10
1
10
ASDR – Approximate SDR

2000/10/02
Based on predicted link loads (periodic link state updates)
Chin-Kai Wu, CS, NTHU
5
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

2000/10/02
When available capacity is below trunk reservation
parameter, alternate path routing will be refused.
Chin-Kai Wu, CS, NTHU
6
Routing Polices Used in Existing
IP 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.
2000/10/02
Chin-Kai Wu, CS, NTHU
7
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.
2000/10/02
Chin-Kai Wu, CS, NTHU
8
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.

2000/10/02
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.
Chin-Kai Wu, CS, NTHU
9
The VPN Model for Capacity
Management
router
VPN


VLL
ISP’s
network
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
2000/10/02
Chin-Kai Wu, CS, NTHU
10
Experiment Environment
12 core routers
42 links
168 PSTN Gateway
2000/10/02
Chin-Kai Wu, CS, NTHU
11
Results (trunk reservation)
2000/10/02
Chin-Kai Wu, CS, NTHU
12
Results (Greater Traffic Aggregation)
2000/10/02
Chin-Kai Wu, CS, NTHU
13
Results (Integrated Service Model)
2000/10/02
Chin-Kai Wu, CS, NTHU
14