Quality-of-Service Routing in IP Networks Donna Ghosh, Venkatesh Sarangan, and Raj Acharya IEEE TRANSACTIONS ON MULTIMEDIA JUNE 2001.

Quality-of-Service Routing in IP Networks

Donna Ghosh, Venkatesh Sarangan, and Raj Acharya

IEEE TRANSACTIONS ON MULTIMEDIA

JUNE 2001

Outline Introduction Two-Level Approach Routing Table Maintenance Packet Forwarding Mechanism Experimental Results and

Discussion Conclusion

Introduction (1/3) QoS routing Goal => To find a loop-less path

satisfying a given set of constraints on parameter like bandwidth, delay, etc.

(optimize the global network resource utilization)

(RSVP + IP) v.s. (RSVP + Qos routing) Need a QoS routing algorithm in IP networ

ks.

Introduction (2/3) Need of QoS Routing Design

Minimal changes to the existing routing protocols. Tradeoff between the average number of messages excha

nged and impreciseness of maintained global state.

Source QoS routing Distributed QoS routing

Maintain global state (source routing) Not Maintain global state (flooding)

Introduction (3/3) Maintain global state

Specify the best next hop. Overhead in maintaining the global state

and state impreciseness.

No Maintain global state High overhead on establishing a connection.

The paper’s method complements this bounded flooding approach.

A

D

E

C

B

F

G

H

I

J

K

Two-Level approach (1/2)

Two-Level approach (2/2) The advantage of Two-Level:

Message overhead and the impreciseness will not be as large as maintaining the global state.

Using the information about the second-degree neighbors, forward intelligently instead blindly flooding.

The approach could extend Nth degree neighbor.

Example network

QoS Routing algorithm Table Maintenance

Building the routing table Update Policies

Packet Forwarding Bounded Two-Level forwarding

Routing Table Maintenance – building the routing table

Building the Routing Table LTN table (Link-to-Node)

Construct by exchanging Hello packets with neighbors.

Forwarding table contains information about the metrics of all the

links in E1(v) and E2(v). Routing table (two-level)

First level entry => copy the LTN table of v Second level entry => updated by Hello2 packet

Routing Table Maintenance – Update Policies (1/2) The update policy used decides when

these Hello2 packets are sent. Based on timers Based on Thresholding (adopt)

Each node remembers the last advertised metric on each link. If the ration is above (or below) a threshold

, an update is triggered.

Routing Table Maintenance – Update Policies (2/2) Advantage of threshold-based update policy the impreciseness could be easily modeled using pr

obabilities. If bandwidth b is advertised on a link ,and say is

2, cab be modeled as a uniform distribution in [b/2, 2b]

There are some approaches[10],[12] to do efficient routing with such imprecise information.

Ref:1.INFOCOM 97, “QoS routing in networks with inaccurate information: Theory and algorithms”2.INFOCOM 98, “QoS routing in networks with uncertain parameters”

Packet Forwarding Mechanism The connection setup process has three ph

ases: probing, ack, failure Probe packet format [k, QoS(Bandwidth=B), s, t, cid, {l}.]K: the router that has forwarded to probe to vQoS(): QoS requirement function

s : Source t :destination cid :unique identifier

{l} :list of neighbors to which v should forward this probe

Fig. Packet forwarding at a node

Receive the message

Message Type

Is this the first copy?

Discard the message

Mark that a probe for this connection has

been received

Am I the destination ?

Send an ack to the upstream neighbor

Is the destination present in my routing

table?

Forward the probe to the destination through all eligible links. Store the

upstream router's id.

Is the neighbor list in the probe empty?

Forward the probe to all eligible second degree neighbors. Store the

upstream router's idForward the probe to all eligible neighbors in the list. Store the upstream

router's id

Request

Yes

No

Yes

Yes

No

No

No

No

Yes

Am I the destination ?

Yes

Release the BW reserved for this connection and forward the

failure to the downstream router

No

Failure

Does the link connecting the downstream router have sufficient BW?

Reserve BW and store the downstream

router's id

Send a failure to the downstream router

Am I the source ?

Connection has been successfully established

Forward the ack to the upstream router

Acknowledgement

Yes

Yes

No

No

Drawback of forwarding mechanism The destination sends an ack only to the firs

t probe it receives and discard all the duplicates.

Improve way: 1. Receiver can retain the best one of probe packet,

besides the first arrive.

2. Failure happened, send failure message to receiver and sender in the same time.

Bounded Two-Level Forwarding(1/2)

If the network load is light, it is not a wise idea to blindly flood the probes on all eligible links.

The shortest eligible path is preferred.

Each probe is assigned an age. Initially, age(p) =0

Bounded Two-Level Forwarding(2/2)

Forward condition on link(i, j) at node i: bandwidth(i,j) B and (age(p) + dj,t +1 L ) Much less overhead when the network load is

light.

First, L = ds,t Second, L = , when network load heavily.

Simulation: Unbounded – without the hop constraint (L = ) Bounded – with the hop constraint (L = ds,t )

Experimental Results and Discussion To have such a reduced overhead, additional

information about the second-degree neighbors must be stored at each router.

Prove: overhead of table maintenance is much less than the savings in probe forwarding.

Summary The savings in the probe forwarding is dependent on resource availability and the network topology.

Simulation Network Topology

Compare manner First set: compare between the unbou

nded versions of flooding and two-level forwarding. (L = )

Second set: compare between the bounded versions of the two approaches. (L = ds,t )

Fig5. Unbounded-flooding

Overhead on Mesh-1

Fig7. Unbounded-flooding

Overhead on ISP

Compare Overhead per Call Admitted (L = )

Fig6. Unbounded-flooding

Bandwidth admitted on Mesh-1

Fig8. Unbounded-flooding

Bandwidth admitted on ISP

Bandwidth admission ratio : the ratio of bandwidth admitted into the network to the total bandwidth requested. (L = )

Compare Overhead per Call Admitted (L = ds,t )

Bandwidth admission ratio : the ratio of bandwidth admitted into the network to the total bandwidth requested. (L = ds,t )

Conclusion Propose a new distributed QoS routing algor

ithm which has a very low call establishment overhead.

Characters: Two-Level routing table maintain Threshold-based update policy The age of a probe is defined