Signaling Transport Options in GMPLS Signaling Transport Options in GMPLS Networks: In-band or Out-of-bandNetworks: In-band or Out-of-band

Malathi Veeraraghavan& Tao Li

Charles L. Brown Dept. of Electrical and Computer EngineeringUniversity of Virginia

Charlottesville, VA 22904, USA

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OutlineOutlineBackground and problem statementAssumptions and delay modelsNumerical resultsConclusions

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BackgroundBackgroundSignaling: needed in connection-oriented

(CO) networks, e.g., PSTN, ATM, GMPLSFunctions 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 protocolsExamples 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) networkResource 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 setupExample: Signaling for call setup

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Host I-A

Host III-B

I

IV V

III

IICall setup (Dest: III-B; BW: OC1)

Routingtable

Connection setup actions at each switch on the path:1. Parse message to extract parameter values2. Lookup routing table for next hop to reach destination3. Read and update CAC (Connection Admission Control) table4. Select timeslots on output port5. Configure switch fabric: write entry into timeslot mapping table6. Construct setup message to send to next hop

call setup call setup

call s

etup

confi

rm

confirmconfirm

confirm

Next hopInterface (Port);

Capacity; Avail timeslots

IV c; OC12; 1, 4, 5

CACtable

INPUTPort /Timeslot

OUTPUTPort/Timeslot

a/1 c/4

Timeslotmapping table

Dest. Next hop

III-* IV

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MotivationMotivationCall 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 Our solution for reducing call setup delaysetup 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-the-

shelf switch, and RESV message takes 8ms.We focus on message transport delay

reduction in this study

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Transport options of signaling Transport options of signaling messagesmessages

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

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S W 1

S W 2 S W 3

S W 6

S W 4 S W 5

S W 2 S W 3

S W 4 S W 5

S W 1 S W 6

IP netw o rk

S ignalingU s er

R 1

R 2 R 3

R 6R 4 R 5

(a) In-band s ignal ing (b) O ut- o f -band s ignal ing

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Problem statementProblem statementWhich one, in-band or out-of-band

transport, is the better option? And, under what circumstances?

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OutlineOutlineBackground and problem statementAssumptions and delay modelsNumerical resultsConclusion

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AssumptionsAssumptions

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IBtxIBtx

IBtx

OOBtxproc proc

(a) In-Band Signaling (b) Out-of-Band Signaling

Signaling protocol processor Transmitter

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 modelsDelay modelsThe 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 engineSoftware-based signaling engineAssume 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

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OOBtx1

proc Delay line

Fixed delay: IBtx1 for IB

for OOB

M/D/1

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Hardware-based signaling Hardware-based signaling engineengine

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

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OOBtxproc1

Delay line

IBtxorDelay:

M/D/1

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Consider retransmissionsConsider retransmissions

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f(T0)

Transmitterλ (1-p)

p

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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OutlineOutlineBackground and problem statementAssumptions and delay modelsNumerical resultsConclusion

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Parameter valuesParameter valuesChange λ so that offered load varies between

0.05 and 0.95µproc: 200k msg/sec for h/w; 20 or 50 msg/sec

for s/wµtx: 500 msg/sec for in-band transport; 10k

msg/sec for out-of-band transport : 0.2ms in metro area; 25ms in wide-area

for s/w; 5ms in wide-area for h/w : 1ms in metro area; 40ms in wide-area

for s/w; 10ms in wide-area for h/w

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IBnT

OOBnT

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Main delay componentsMessage 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 signalingResults 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 signalingResults 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 transportConclusion: 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?Questions, comments?Thanks!

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