Transcript Signaling Transport Options in GMPLS Networks: In

Signaling Transport Options in GMPLS
Networks: In-band or Out-of-band
Malathi Veeraraghavan
& Tao Li
Charles L. Brown Dept. of Electrical and
Computer Engineering
University of Virginia
Charlottesville, VA 22904, USA
Outline
Background and problem statement
 Assumptions and delay models
 Numerical results
 Conclusions

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Background
Signaling: needed in connection-oriented
(CO) networks, e.g., PSTN, ATM,
GMPLS
 Functions of signaling:

◦ Call setup:
 route selection
 bandwidth reservation on each link of end-to-end
path
 switch fabric configuration of each switch
◦ Call release
 release bandwidth for use by others
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Examples of signaling protocols

ISDN User Part of the SS7 (Signaling System
No. 7) protocol stack
◦ to set up and release DS0 (64kbps) circuits in a
telephone (circuit-switched) network

Resource reSerVation Protocol with Traffic
Engineering (RSVP-TE)
◦ used in CO packet-switched networks, such as MPLS
and ATM
◦ used in circuit-switched networks, such as
SONET/SDH and WDM
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Example: Signaling for call setup
Call setup
(Dest: III-B; BW: OC1)
Host IA
confirm
Routing
table
CAC
table
Dest.
III-*
Timeslot
mapping
table
INPUT
Port /Timeslot
a/1
IV
V
IV
Interface (Port);
Next hop Capacity; Avail timeslots
IV
III
I
Next hop
Host IIIB
II
c; OC12; 1, 4, 5
OUTPUT
Port/Timeslot
c/4
Connection setup actions at each switch on the path:
1. Parse message to extract parameter values
2. Lookup routing table for next hop to reach destination
3. Read and update CAC (Connection Admission Control) table
4. Select timeslots on output port
5. Configure switch fabric: write entry into timeslot mapping table
6. Construct setup message to send to next hop
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Motivation

Call setup delay is an overhead in CO networks
◦ Reserved bandwidth is idle during call setup
 Setup message processing delay measured at 91ms on an
off-the-shelf SONET switch
 If 10 hops, call setup delay > 91x10 =910ms
 Transmission time of a 100Mbyte file over a 1Gbps-rate
circuit is just 800ms
 To use circuits for file transfers, need to reduce call setup
delay

Why is this not a major concern for others?
◦ Signaling is used to reduce turn-around time for
leased lines, which will be held for hours/days
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Our solution for reducing call
setup delay

Components of call setup delay
◦ message processing delay + message transport delay

Message processing delay reduction
◦ Past work: We implemented a hardware-accelerated
signaling processor
 Result: 3 s processing delay for a RSVP PATH message;
total of 5 s per call
 Processing of the PATH message takes 91ms on an off-theshelf switch, and RESV message takes 8ms.

We focus on message transport delay reduction
in this study
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Transport options of signaling
messages

In-band: e.g., DCC channels in SONET
◦ Typical rate: Line DCC - 576kbps for a single OC1
◦ Low rate may lead to queueing delays at high message loads

Out-of-band: e.g., Internet
◦ Typical rate: 10Mbps/100Mbps Ethernet
◦ Queueing delays for the transmitter unlikely
◦ But, can suffer from longer path and delay variations across IP network
Signaling
User
R2
R3
R1
SW2
SW3
R4
R5
SW2
SW1
R6
IP network
SW3
SW6
SW1
SW4
SW5
(a) In-band signaling
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SW6
SW4
SW5
(b) Out-of-band signaling
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Problem statement

Which one, in-band or out-of-band
transport, is the better option? And, under
what circumstances?
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Outline
Background and problem statement
 Assumptions and delay models
 Numerical results
 Conclusion

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Assumptions
Signaling protocol processor
Transmitter
txIB

 proc
txIB
 proc

txOOB
txIB
(a) In-Band Signaling




(b) Out-of-Band Signaling
Two stages of servers: protocol processor and transmitter
 Protocol processor: can be software-based or hardware-based
 Transmitter:
 In-band option: several neighbors/transmitters
 Out-of-band option: one control-plane link to the Internet
Message arrival: Poisson process with rate λ
Message processing delay: fixed at 1/µproc
Message transmission delay: fixed at 1/µtx
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Delay models

The first server, i.e., protocol processor,
can be analyzed with the classical M/D/1
model
◦ Problem: output process of the first stage
(input to the second stage) is not Poisson
◦ Our solution approach: simplify the two-stage
models by taking into account practical
considerations
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Software-based signaling engine

Assume processing rate µproc ≤ trans. rate µtx
◦ Msg processing time of an off-the-shelf switch: 91ms
◦ 1000-bit msg emission time: 1.7ms over 576Kbps
DCC channel; even smaller over 10/100Mbps
Ethernet

Implication: no queueing delay at the 2nd server
◦ Two-stage model can be approximated with an
M/D/1 queue plus constant delay
M/D/1

 proc
Delay line
Fixed delay:
1 txIB for IB
1  txOOB for OOB
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Hardware-based signaling
engine

Call arrival rate, λ, determined by data-plane considerations:
◦ Minimum call holding time needed (given call setup delay) due to
utilization considerations
◦ Link capacity in channels, which determines traffic load
◦ Number of data-plane links on the switch
We estimate λ in 103 calls/s region for a 200Gbps switch
 µproc =20000 >> λ

◦ Call proc. time in a hardware-accelerated signaling processor: 5 µs
◦ Implication: approximate the first server with a delay line
Delay: 1

 proc
txOOB or txIB
Delay line
M/D/1
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Consider retransmissions
λ
Transmitter
(1-p)
p
f(T0)
p: packet loss probability
 T0: time-out limit - 3Tn, where Tn is one-way network delay
 Combine M/D/1 results, the simplified queueing models with
delay line, and the retransmission model, we obtain:

◦ E[Tsw] – average per-switch delay for software-based signaling
engine
◦ E[Thw] – average per-switch delay for hardware-based signaling
engine
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Outline
Background and problem statement
 Assumptions and delay models
 Numerical results
 Conclusion

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Parameter values
Change λ so that offered load varies between
0.05 and 0.95
 µproc: 200k msg/sec for h/w; 20 or 50
msg/sec for s/w
 µtx: 500 msg/sec for in-band transport; 10k
msg/sec for out-of-band transport
 TnIB : 0.2ms in metro area; 25ms in wide-area
for s/w; 5ms in wide-area for h/w
OOB
 Tn : 1ms in metro area; 40ms in wide-area
for s/w; 10ms in wide-area for h/w

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Main delay components

Message processing delay:
◦ Queueing delay + service time: software implementation
◦ Negligible: Hardware implementation

Message transport delay:
◦ Message transmission delay:
 Queueing delay possible with in-band (e.g., 576kbps)
 if number of in-band channels is insufficient relative to signaling
message load
 Negligible: Out-of-band signaling (e.g., 10Mbps)
◦ Network delay:
 Propagation delay only: in-band
 Propagation delay + queueing delay at IP routers: out-of-band
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Results with software signaling

Software signaling processor; plots show the effect of metro-area
vs. wide-area, in-band (IB) vs. out-of-band (OOB) transport, with
two values of message processing service rate, µproc
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Results with hardware signaling

Hardware signaling: plots show the effect of metro-area vs.
wide-area, and in-band vs. out-of-band transport
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Conclusion: Use in-band transport

Software signaling engine
 Message processing delay on the same order as network delay
 So both message processing delay + message transport delay matter
 Preferred transport option: IN-BAND
 Why?
 Message transmission delay is low (10Mbps transmitter); no queueing
 Network delay is higher in out-of-band

Hardware signaling engine
 Message processing delay negligible, which makes message transport
delay even more important than with software signaling
 Preferred transport option: IN-BAND
 Given that higher call loads can be handled (based on data-plane
considerations), a larger number of in-band channels are needed to
keep load to the transmitters low to avoid transmitter queueing delays.
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Questions, comments?

Thanks!
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