two-tier resource management designed after the internet’s two-tier routing hierarchy separate...
TRANSCRIPT
Two-Tier Resource Management
• Designed after the Internet’s two-tier routing hierarchy
• Separate packet forwarding from admission and resource allocation control
• Resource allocation adjustments can be made on much larger time scales
• Bandwidth Broker (BB) acts as resource manager for each domain
• Neighboring BBs communicate to allocate resources for each aggregate traffic class crossing domain borders according to relatively stable, long-lived SLAs between domains
• BB instructs its border (edge) routers to do aggregate shaping/policing
• End-to-end QoS is concatenation of QoS across originating, transit and receiving domains
Inter-Domain Protocol
• BB informs its egress border router (ER) to shape traffic according to SLA with neighbor domain
• When ER detects an increase in traffic volume to neighbor domain, it notifies its BB specifying address of neighbor ingress router (IR)
• BB contacts the neighbor BB to increase its allocation
• Neighbor BB asks its IR if there are sufficient internal resources
• IR uses its own intra-domain resource allocation protocol
• If enough resources, IR notifies its BB and adjusts its policer parameters
• Reply sent back to requesting BB, which informs its IR to update its shaper parameters
Resource Allocation Requests• If current rate r from ER exceeds w * L (w <= 1), ER asks for
increase
• BB asks for I * r (I > 1)
• I * r > L ==> I * w * L > L ==> I * w > 1
• Lower w means larger spikes in traffic can be absorbed and longer delays in re-negotiation can be tolerated
• Higher I reduces the frequency of increase requests
• If r <= l * L (l < 1), ER asks for decrease
• BB keeps a hysteresis counter H, decremented by one each time ER asks for decrease
• When H = 0, BB sends decrease request of D * L (D <= 1) to neighbor BB
• Decreases happen only when traffic is consistently lower than the allocation
• D close to 1 means gradual decreases
Estimation Process
• Estimate r over a measurement window T
• If a newly computed average load over S < T is larger than r, set r to this value
• At end of T, set r to highest average load for any S period
• Decreasing S makes process more sensitive to bursts
• Increasing T increases the amount of history remembered
Intra-Domain Resource Allocation
• At source domain, source host sends RSVP PATH message toward flow’s receiver host
• First-hop router intercepts PATH message and informs BB of source host
• BB checks if enough resources on border link to downstream domain
• If OK, BB informs IR to send PATH message and ER replies with RESV message to reserve local resources
• Source’s traffic profile is advertised out of band at application level
• If OK, BB informs IR to send PATH message to receiver
• Receiver sends RESV to allocate local resources
Allocation in Transit Domains• Each IR measures amount of traffic toward each ER
• Use RSVP to allocate resources for each IR-ER pair
• O(N^2) state, where N is number of edge routers
• Given each border router participates in BGP, it knows the ER that corresponds to a particular destination
• Based on rate to each ER, IR sends PATH message and ER responds with RESV
• When BB sends increase request to IR, how should this increase distributed among all ER’s?
• Assume newly admitted traffic will follow same distribution as current traffic, IR can send PATH messages with increase requests in same proportion
• ER responds with RESV to allocate local resources
• If assumption not true, notify BB