1. Chapter 16. Internetwork Operation
Routing Protocols
Integrated Services Architecture
Resource Reservation: RSVP
Differentiated Services

2. Protocols in the Chapter

3. Routing Protocols Autonomous systems (AS)
An internet connected by homogeneous routers; generally, the routers are under the administrative control of a single entity
Interior router protocol (IRP)
Passes routing information between routers within an autonomous system
Exterior router protocol (ERP)
Passes routing information between routers in different autonomous systems

4. Routing Protocols (cont)

5. Hierarchical Routing Hosts Interior Gateways Exterior Gateways
Maintain sufficient routing information to forward datagrams to other hosts or an interior gateway(s) that is (are) attached to the same network. (ARP)
Interior Gateways
Maintain sufficient routing information to forward datagrams to hosts or other interior gateways within the same autonomous system
Exterior Gateways
Maintain sufficient routing information to forward datagrams either to an interior gateway, if the datagram is for the same autonomous system, or to another exterior gateway, if it is not.

6. Border Gateway Protocol
Standardized exterior router protocol for the Internet (BGP-4, RFC 1771)
Allows routers (gateways) in different autonomous systems to cooperate in the exchange of routing information.
Operates in terms of messages, which are sent over TCP connections.
Message: Open, Update, Keepalive, Notification
3 functional procedures
Neighbor acquisition, Neighbor reachability
Network reachability (Routing update)

7. BGP (cont) Neighbor acquisition
Neighbor acquisition occurs when two neighboring routers in different autonomous systems agree to regularly exchange routing information
1. One router sends an Open msg to another
2. If the target router accepts the request, it returns a Keepalive msg in response

8. BGP (cont)

9. BGP (cont) Neighbor reachability Network reachability
Used to maintain the neighbor relationship
Two routers periodically issue Keepalive msg to each other
Network reachability
Each router maintains a database of the subnetworks that it can reach and the preferred route for reaching that subnetwork
Whenever a change is made to this database, the router issues an Update msg that is broadcast to all other routers implementing BGP

10. BGP (cont)
For authentication

11. BGP (cont)

12. OSPF Protocol Open Shortest Path First Protocol
Interior routing protocol by ARPANET
Link-state routing algorithm
Each router maintains descriptions of the state of its local links to subnetworks, and from time to time transmits updated state information to all of the routers of which it is aware
Each router maintains a database that reflects the known topology of the autonomous system

13. OSPF Protocol (e.g.)
Sample
autonomous
system

14. OSPF Protocol (e.g.)
Directed
graph of
the sample
autonomous
system

15. OSPF Protocol (e.g.)
SPF tree
for
router R6
Using
Dijkstra’s
Algorithm

16. OSPF Protocol (e.g.)
Routing Table
for
router R6

17. ISA Concept Integrated Services Architecture
Intended to provide QoS transport support over IP-based internets, RFC 1633
Two broad categories of traffic on internet
Elastic Traffic
File transfer (FTP) , (SMTP), Remote Logon (TELNET), Network management (SNMP), Web access (HTTP)
Inelastic Traffic
Real-time traffic
Throughput, Delay, Jitter, Packet loss

18. ISA Approach Traditional (IP) Router mechanisms
Routing algorithm
Packet discard
ISA Enhancements: the concept of flow
Admission control: RSVP
Routing algorithm: QoS-based OSPF
Queuing discipline: For differing requirements of different flow
Discard policy: for managing congestion and meeting QoS guarantees

19. ISA Components
ISA Implemented in Router

20. 2-Level ISA Services 1. General categories of service
Guaranteed
Assured capacity/data rate
Specified upper bound on the queuing delay
No queuing loss
Controlled Load
Best effort
2. Service for a particular flow
Traffic specification (TSpec): Token Bucket
QoS

21. Token Bucket Scheme

22. Queuing Discipline No priority; Larger mean delay
Greedy TCP connections crowd out altruistic ones
Weighted Fair Queuing (WFQ)

23. Resource ReSerVation Protocol
Characteristics
Unicast and Multicast
Simplex
Receiver-initiated reservation
Maintaining soft state in the internet
Providing different reservation styles
Transparent operation through non-RSVP routers
Support for IPv4 and IPv6
Type-of-Service in IPv4
Flow Label in IPv6

24. RSVP Design Characteristics
Receiver-initiated reservation
Sender
Provide the routers with the traffic characteristics of the transmission (data rate, variability)
Receiver
Specify the desired QoS
Router
Aggregate multicast resource reservations for the shared path segments along the distribution tree
Soft State

25. RSVP Data Flows Flow descriptor flowspec: desired QoS
filterspec: defines the set of packets for the reservation
Treatment of packets of one session at one router

26. RSVP Protocol Mechanisms
Two message types
Resv, Path

27. RSVP Operation

28. Differentiated Services (DS)
Goal (RFC 2475)
Provide a simple, easy-to-implement, low-overhead tool to support a range of network services (comparing with ISA)
Key characteristics
IP packets are labeled for differing QoS treatment using the existing IPv4 Type-of-Service octet or IPv6 Traffic Class octet. Thus, no change is required to IP

29. Differentiated Service (cont)
A service level agreement (SLA) is established between the service provider (internet domain) and the customer prior to the use of DS
All traffic with the same DS octet is treated the same by the network service
Routers deal with each packet individually and do not have to save state information on packet flows

30. DS Octet
Packets are labeled for service handling by means of the DS octet
Placed in the Type of Service field of an IPv4 header, or the Traffic Class field of the IPv6 header
RFC 2474: The leftmost 6 bits form a DS codepoint
The DS codepoint is the DS label used to classify packets for differentiated services

31. DS Codepoint (6 bits) xxxxx0 xxxx11 xxxx01
Reserved for assignment as standards
000000: default packet class, i.e. best-effort
xxx000: reserved to provide backward compatibility with the IPv4 precedence service
xxxx11
Reserved for experimental or local use
xxxx01
Reserved for experimental or local use, but may be allocated for future standards action as needed

32. DS Domain
Within a domain, the interpretation of DS codepoints is uniform, consistent service is provided

33. Routers in DS Domain Interior nodes (per-hop behavior: PHB)
Queuing discipline to give preferential treatment depending on codepoint value
Packet-dropping rules to dictate which packets should be dropped first in the event of buffer saturation
Boundary nodes
PHB mechanisms
Traffic conditioning functions
metering, marking, shaping, dropping

34. DS Traffic Conditioner

35. DS Traffic Conditioner (cont)
Classifier
Separates submitted packets into different classes
Based on the DS codepoint or on multiple fields within the packet header
Meter
Measures submitted traffic for conformance to a profile
Determines whether a given packet stream class is within or exceeds the service level guaranteed for that class

36. DS Traffic Conditioner (cont)
Marker
Polices traffic by re-marking packets with a different codepoint as needed
Shaper
Polices traffic by delaying packets as necessary so that the packet stream in a given class does not exceed the traffic rate specified in the profile for that class
Dropper
Drops packets when the rate of packets of a given class exceeds that specified in the profile for that class

37. ISA (IntServ) vs. DS (DiffServ)