Scalability of Routing Protocols

Transcription

1 Scalability of outing Protocols Internet is large... Need to introduce hierarchy -... into something that naturally does not have one - divide and conquer, abandoning hope for optimality - based on ownership - Autonomous System (AS) Different routing problems: - Intra AS routing - interior gateway routing (IGP) - Inter AS routing - exterior gateway routing (EGP)

2 Examples of outing Protocols Distance Vector Link State IGP IP OSPF EGP BGP-4* * BGP-4 extends the concept of Distance Vector routing to include the path information and is typically referred to as a Path Vector routing protocol

3 IP outing Information Protocol - a distance vector routing protocol - hops used as a measure of distance - 30 second update interval Version history - IPv IPv (includes CID, authentication) - IPng (IPv6 support)

4 OSPF Open Shortest Path First - link state routing protocol - two-level hierarchy - user-defined link weights Version history: - OSPF (1989) Area 0 Area 1 Area 2 Area N - OSPFv2 (1998) - OSPFv3 (2008, IPv6)

5 BGP-4 Border Gateway Protocol - exterior gateway routing protocol - path vector routing - allows policy based routing - AS as a routing hop Version history - Version 4 (1995) - Latest version of version 4 (2006) A B C Paths: SABCD SWXYZD S D W X Y Z

6 QoS Measures Throughput - bits, bytes, packets per second Latency - one way or round trip Latency variation (jitter) - average, max, etc. Probability of successful delivery - packet loss rate - bit error rate

7 Quality of Service in IP Type of Service (TOS) field in IPv4, Traffic Class in IPv6-8 bits - priority (3 bits) - bits to request high throughput, low latency, low loss, and low monetary cost - set by traffic generating applications For most parts, this attempt has failed: - no cost for requesting higher category of service - no broad agreement on how to handle the different categories

8 Differentiated Services Domain-based solution elative guarantees Few classes of service Framework rather than a complete and prescriptive solution euses TOS field (called DSCP - Differentiated Services Code Point)

9 Differentiated Services Src TOS DS Domain DSCP TOS Dst Classifier Meter Marker Shaper Dropper Queuing policy oute selection L2 control egular router Border router Interior router DSCP Differentiated Services Code Point

10 MPLS MultiProtocol Label Switching - a protocol providing virtual circuit service - designed to coexist and complement existing protocols, not to replace them One protocol, many uses: - simplification of forwarding - traffic engineering - protection and restoration - support for legacy services

11 MPLS Terminology Label Switched Path (LSP): a VC Label: VC id Label Switched outer (LS): a switch Typically: Network Layer MPLS Layer Link Layer Forwarding Equivalence Class (FEC) MPLS packet Link header MPLS header IP header Transport and application

12 Link Layer

13 Link Layer Delivers packets using streams of bits Standard services: - addressing - error control - flow control - QoS

14 Components of Link Layer Data Link Control - addressing - framing - error detection and correction - flow control - QoS Media Access Control (MAC) - controlling access to the shared medium

15 Channel Capacity Shannon s (noisy-channel coding) Theorem: C - channel capacity B - channel bandwidth S/N - signal to noise ratio

16 Media Access Control Objective: Arbitration of access to the shared medium - prevention or avoidance of collisions. Deterministic - collisions are prevented - centralized - distributed Stochastic - some collisions are permissible - as long as they are detected and transmissions retried

17 Stochastic (random) MAC ALOHA Transmit at will... Listen to own transmission to detect collisions with transmissions of other nodes andom back-off if collision is detected