QoS. Paul Ferguson and Geoff Huston, Quality of Service: Delivering QoS on the Internet and in Corporate Networks, Wiley, Nixu Oy 2000.

Transcription

1 1 QoS Nixu Oy PL 21 (Mäkelänkatu 91) Helsinki, Finland tel fax Ly tunnus: Kaupparek Paul Ferguson and Geoff Huston, Quality of Service: Delivering QoS on the Internet and in Corporate Networks, Wiley, 1998 info@nixu.fi nixu fi

2 Resource reservation is important Quality of Service - QoS Some of the application require certain QoS level, while others are happy with best effort QoS

3 3 QoS is requested when service is setup Service provider checks resources and provides the QoS Control takes care of internal (isochronous) and external (intramedia) synchronization

4 The requirements are defined with QoS parameters: for example, delay, jitter, error rate, capacity Service user negotiates the service parameters before using the service with the service provider Highest protocol layer Parameters are given to lower protocol layers

5 5 Bandwidth (capacity) Delay (latency) Jitter (variation of delay) Error rate Guaranteed / best effort

6 6 QoS Implementations Nixu Oy PL 21 (Mäkelänkatu 91) Helsinki, Finland tel fax Ly tunnus: Kaupparek Paul Ferguson and Geoff Huston, Quality of Service: Delivering QoS on the Internet and in Corporate Networks, Wiley, 1998 info@nixu.fi nixu fi

7 7 The task of the router is to forward the incoming packets to the correct output This is done by the scheduler Scheduler can be implemented either as software or hardware Individual packets must wait for their turn Similarly, a ATM switch forwards individual cells

8 8 It the queue gets full, the packet have to be discarded Full queues should be avoided Simplest queue is so called FIFO queue The first arrived packet is forwarded to the right output queue first

9 9 Input queue Output queue Packet memory

10 10 FIFO queue works well with burst when load is low When load is high, FIFO queue causes delay for all packets High priority traffic suffers If queue gets full, packets have to be discarded

11 11 Simplest solution is to give different priorities for different kinds of traffic For example, real-time traffic has higher priority Packet classification causes extra load

12 12 Input queue Output queue High priority Normal priority

13 13 Implementation of the scheduler is simple Classification is difficult High priority traffic can block the router Low priority traffic jams

14 14 Different services can have their own output queues High priority traffic does not jam the low priority traffic Several output queues are required

15 15 Input queue Class based queues High Medium Low

16 16 Simple method to divide traffic into different service classes Does not scale well The complexity of scheduling and control of queues slows fast traffic

17 17 Resource Reservation Nixu Oy PL 21 (Mäkelänkatu 91) Helsinki, Finland tel fax Ly tunnus: D. Kosiur, IP Multicasting: The Complete Guide to Interactive Corporate Networks, Wiley, 1998 Kaupparek info@nixu.fi nixu fi

18 18 Real-time transport protocols alone can not guarantee reliable transfer of continuous media Required resources have to be defined separately This can be done with separate resource reservation protocols Best known is Resource reservation Protocol (RSVP)

19 19 Resource reservation Protocol (RSVP) is based on reservations made by the receiver Sender first sends a Path message The routers can reply with PathErr message, in case of error

20 20 Routers store information about the connection Soft state Each connection has cleanup and restart counter Receiver sent Resv reservation At the same time the QoS requirements are defined Resv messages travel via the routers Routers check their resources and make reservations

21 21 Resv messages Target 1 Source Path messages Target 2 Target 3

22 22 Information about each state is stored The information expires after certain time period This is why the state information is called soft

23 23 Not in wide use yet Problems: Scalability (control, connection, updating of connections) Good algorithms for checking of resources do not exist Accounting and billing is difficult to arrange

24 24 Differentiated Services Nixu Oy PL 21 (Mäkelänkatu 91) Helsinki, Finland tel fax Ly tunnus: Kaupparek Chris Metz, IP QoS: Travelling in First Class on the Internet, IEEE Internet Computing, March/April 1999, p info@nixu.fi nixu fi

25 25 Solution has to scale individual micro-flows are aggregated into a single larger aggregated flow the aggregated flow receives special treatment Applicable to all applications no special control protocol (i.e., RSVP) no new application programming interfaces Gigabitrate operation 2.4 and 10 Gbps line rates are coming ISPs want to offer portfolio of service versioning QoS classes

26 26 Individual microflows are classified at the edge of the network Several unique service classes For example, Gold, Silver, and Bronze Per-class service is applied in the middle of network Classification is based on one or more fields in the packets

27 27 DS-field: denotes the service the packet should receive IPv4: Type-of-service IPv6: Traffic class Per-hop behavior (PHB): defines the service the packet receives at each hop Behavior aggregate (BA): group of similar packets

28 28 Boundary router: positioned at the edge of the DiffServ-capable network Packet classification Metering Marking Traffic conditioning Interior router: core switches or routers that provide PHB

29 29 How network policies are managed? Manual configuration Simple Network Management Protocol (SNMP) Lightweight Directory Access Protocol (LDAP) Common Open Policy Server (COPS) How to extend across ISP boundaries? Bilateral agreements Bandwidth brokers