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 networks.

Introduction (2/3) Need of QoS Routing Design Minimal changes to the existing routing protocols. Tradeoff between the average number of messages exchanged 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.

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 N th 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 E 1 (v) and E 2 (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 probabilities. 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 phases: probing, ack, failure Probe packet format [k, QoS(Bandwidth=B), s, t, cid, {l}.] K: the router that has forwarded to probe to v QoS(): 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

Drawback of forwarding mechanism The destination sends an ack only to the first 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) + d j,t +1 L ) Much less overhead when the network load is light. First, L = d s,t Second, L =, when network load heavily. Simulation: Unbounded – without the hop constraint (L = ) Bounded – with the hop constraint (L = d s,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 unbounded versions of flooding and two-level forwarding. (L = ) Second set: compare between the bounded versions of the two approaches. ( L = d s,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 = d s,t )

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

Conclusion Propose a new distributed QoS routing algorithm 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