Services Integrated & RSVP
Types of pplications Basic approach in IntServ Key components Service models
Application types:
Elastic applications
"old-fashioned" applications
Tolerant playback applications.
One-way video streaming, one-way broadcast Delay and delay jitter (Figure 2.1) Removing jitter with play-out buffer (Figure 2.2) Latency .vs. fidelity
Intolerant playback applications: data need to be delievered in real-time
Two way conversations (stringent delay constraint).
Design objective of IntServ:
Preserve datagram model of IP networks Support resource reservation and QoS guarantees for multimedia applications
Protect multimedia traffic from being affected by regular TCP traffic and vice verse
Basic approach: similar to tele. Networks
Before sending, sender describes the traffic and resource requirement and sends the request to the network. The request goes through the network hop-by-hop, each hop will check its resources to decide whether to reject or accept the request. If everyone says ok, the sender will be notified and can start send data along the reserved path.
Key components in IntServ (Figure 2.4):
Control plane:
QoS routing agent (QoS routing)
Can be difficult.
Admission control Reservation setup agent (RSVP) Resource reservation table
Data plane:
Flow identification Packet scheduler
Admission control
To decide whether to accept a new request (done at each router in IntServ). Parameter based
A set of parameters is used to characterize traffic flows. The admission control agent computes the required resources based on the parameters. Difficult to model the traffic.
Measurement based
Measure the actual traffic load for admission control. Probabilistic in nature, no hard guarantees. Trade-off between resource guarantees and resource utilizations.
Common algorithms: simple sum, measured sum, region, acceptance equivalent bandwidth.
Flow Identifications:
Identify to which flow a packet belong to An IP flow is identified by five fields: source IP address, destination IP address, source port, destination port, protocol ID five-tuple The flow identification agent must compare the fivetuple of a packets to all five tuples in the reservation table. Requres fast hardware if performed at wire speed
64 byte packets arrive in a 622Mbps line back to back in less than 1us.
Service Models:
What users can ask and what commitments the network can commit. Flow model in IntServ
Described by a leaky bucket
Token rate ( r ) : 1bps 40tbps Token-bucket depth (b): 1 B to 250GB Peak traffic rate (p): 1bps 40tbps Minimum policed unit (m): packets of size < m bytes will be counted as m bytes. Maximum packet size (M):
What is leaky bucket?
Guaranteed Service and Controlled load Service
Guaranteed Service (RFC 2212)
For applications requiring fixed delay bound and a bandwidth guarantee Control the maximum queuing delay Guarantees that packets will arrive within a certain time and will not be discarded because of queue overflows No control on minimal or average delay (what about jitter?) No packet fragmentation is allowed. Guaranteed service is invoked by a sender specifying a traffic descriptor (Tspec) and a service specification (Rspec)
Rspec has two parameters: Service rate ( R ) and Slack Term ( S)
Worst case queuing delay for guaranteed service: ((b-M)(p-R)) / (R (p-r)) + (M+Ctot)/R + Dtot (M+Ctot) / R + Dtot if (R >=p >= r) if p>R>=r
Controlled load service (RFC 2211)
Provides unloaded network conditions
Closely approximates traditional best-effort in a lightly loaded or unloaded network environment
Intended for adaptive applications Priority service with admission control No fragmentation, packets must comply to MTU