Network: Traditional Routing Y. Richard Yang 3/28/2011

Admin Exam Project meetings Mean: 42.67 Std Dev: 10.15 High: 61 Weekly meeting for 15 min Please sign up on the classesv2 server

Recap: Basic Network Layer Model Each node is a network attachment point (e.g., router, base station), to which hosts/user equipment attaches Problems: Location management Routing for wireless A E D C B F User device identified by addressing scheme locator: identifies attachment point identifier: independent of location

Recap: Location Management Two primitives of location management (find out where a MS is) in a cellular network update (a proactive approach) paging (a reactive approach upon request) Hybrid update/paging tradeoff The location area (LA) approach Distributed approaches timer based movement based distance based profile based

Remaining Issue: Handoff A MS may be in a call during mobility Issue: the signal to/from the current serving base station (e.g., Node B in 3G) may gradually degrade as the MS moves away the signal to/from the next base station may become better, but the signal strength is hard to know, if the MS is not actively communicating w/ the next base station

WCDMA Soft Handoff An MS communicates with multiple Node Bs Downlink: multiple base stations send to the MS and the MS combines the received signals Uplink: multiple base stations receive data from the MS and forward to a RNC to combine The combing RNC is called the serving RNC

Serving RNC and Drift RNC Serving RNC handoff RNC1: Serving RNC RNC2: Drift RNC RNC1: Serving RNC

UMTS Serving RNC Handoff Drift RNC

Outline Admin. Location management cellular networks IP networks

Mobile IP: Architecture The current architecture to handle mobility in Internet is Mobile IP Assume the current Internet addressing and routing architecture Design extensions to handle out of network devices Similar to cellular, but simpler Not widely deployed

Mobile IP: Terminology Mobile Node (MN) the node under consideration Home Agent (HA) a stationary network node (e.g., a router) at the home network Foreign Agent (FA) a network node (e.g. a router) in the foreign network Care-of Address (COA) the address in the foreign network Correspondent Node (CN) communication partner

Illustration HA MN FA CN mobile node Internet router home network (physical home network for the MN) FA foreign network router end-system CN router (current physical network for the MN)

Mobile IP Operations Basic idea of Mobile IP: a MN acquires a COA in a foreign network from a foreign agent registers to the home agent (location update) all messages sent to its home address is arrived at the home agent, who forwards to COA

Discovering the Agents and Care-of Address Mobile IP discovery process (home or foreign) agent broadcasts advertisements at regular intervals announce the network list one or more available care-of addresses mobile node takes a care-of address mobile node can also send solicitation to start the process

Registering the Care-of Address Mobile node sends an update (called) registration request) to its home agent with the care-of address information Home agent approves/disapproves the request Home agent adds the necessary information to its routing table Home agent sends a registration reply back to the mobile node

Registration Operations in Mobile IP MH = Mobile Host HA = Home Agent FA = Foreign Agent

Data Transfer from the Mobile Node HA 1 MN Internet home network sender FA foreign network 1. Sender sends to the IP address of the receiver as usual, FA works as default router CN receiver

Data Transfer to the Mobile Node HA 2 MN Internet home network 3 receiver FA foreign network 1. Sender sends to the IP address of MN, HA intercepts packet 2. HA tunnels packet to COA, here FA, by encapsulation 3. FA forwards the packet to the MN 1 CN sender

Tunneling Operations in Mobile IP Correspondent Node X

Discussion Any problems of the Mobile IP approach?

Triangular Routing Triangular Routing “Solution” CN sends all packets via HA to MN higher latency and network load “Solution” CN learns the current location of MN direct tunneling to this location HA or MN informs a CN about the location of MN Problem of the solution big security problems !

Handoff Change of FA (COA) “Solution” packets on-the-fly during the change can be lost “Solution” new FA informs old FA to avoid packet loss, old FA buffers and then forwards remaining packets to new FA this information also enables the old FA to release resources for the MN

Summary: Mobile IP An out-of-network mobile node (MN) registers its current reachable address (COA) with its home agent Home agent forwards packets to the MN Several optimization techniques to improve efficiency and reduce packet losses during mobility

Recap: Key Problems Location management D C B F Location management Routing with lossy and dynamic wireless when infrastructure is wireless discussion: will this be a real issue?

Routing Overview The problem of routing is to find a good path for each source destination pair Issues How to define a path to be good? How do we compute the path? A E D C B F

Link Metric A typical measure for a good path is that it is the shortest path according to some metric One possibility is to assign each link a metric of 1 (hop-count based routing) problems maximizes the distance traveled by each hop low signal strength -> high loss ratio uses a higher TxPower -> interference different links have different qualities A E D C B F

Performance of Shortest Hop Count D C B F

Example Metric: ETX ETX: The predicted number of data transmissions required to successfully transmit a packet over a link the ETX of a path is the sum of the ETX values of the links over that path Examples: ETX of a 3-hop route with perfect links is 3 ETX of a 1-hop route with 50% loss is 2 “A High-Throughput Path Metric for Multi-Hop Wireless Routing” by D. De Couto, D. Aguayo, J. Bicket, R. Morris. Mibicom 2003. http://meraki.com/about/

Acquiring ETX Measured by broadcasting dedicated link probe packets with an average period τ (jittered by ±0.1τ) Delivery ratio: – count(t-w,t) is the # of probes received during window w – w/τ is the # of probes that should have been received

ETX: Example

ETX: Advantage Tends to minimize spectrum use, which can maximize overall system capacity (reduce power too) each node spends less time retransmitting data ETX has problems It considers only ETX, but links may have different rates (how to fix?)

Outline Admin and recap Routing Overview Routing metric Computing shortest path routing A E D C B F 2 1 3 5 How does Internet (Yale) computes shortest path routing?

Design Dimensions What does each node know? When to know? Whole network topology and per link cost Set of neighbors that can reach dest Neighbors’ costs to destination When to know? All the time (proactive) Upon a need to forward a data packet (reactive/on demand)

Design Dimensions What does each node know? Whole network topology and per link cost (link state)

Link-State Routing Algorithms Separation of topology distribution from route computation Used in OSPF, the dominant intradomain routing protocol used in the Internet Net topology, link costs are distributed to all nodes Link state distribution accomplished via “link state broadcast” Each node (locally) computes its paths to all destinations

Link State Broadcast B A S E F H J D C G I K M N L represents a node that has received update represents link

Link State Broadcast S E F B C M L J A G H D K I N

Link State Broadcast S E F B C M L J A G H D K I N To avoid forwarding the same update multiple times, each update has a sequence number. If an arrived update does not have a higher seq, discard! - The packet received by E from C is discarded - The packet received by C from E is discarded as well - Node H receives packet from two neighbors, and will discard one of them

Summary of Link State Routing Separation of topology distribution from route computation Whenever a link metric changes, the node broadcasts new value Q: What is the scope of updates when a link changes status? Q: Does link state routing work well in a network with dynamic link status?

Design Dimensions What does each node know? Whole network topology and per link cost Set of neighbors that can reach dest. Link reversal

Motivation Link reversal algorithms maintain a mesh (hopefully) local adaptation

Links and DAG up stream down stream A B F Links are bi-directional But algorithm imposes logical directions on them C E G Maintain a directed acyclic graph (DAG) for each destination, with the destination being the only sink This DAG is for destination node D D C E up stream down stream

Link Reversal Algorithm: Illustration of Idea B F C E G Link (G,D) broke D Any node, other than the destination, that has no outgoing links reverses some incoming links. Node G has no outgoing links

Link Reversal Algorithm: Illustration B F C E G Represents a link that was reversed recently D Now nodes E and F have no outgoing links, the process continues.

Link Reversal Algorithm: Illustration B F C E G Represents a link that was reversed recently D Now nodes B and G have no outgoing links

Link Reversal Algorithm: Illustration B F C E G Represents a link that was reversed recently D Now nodes A and F have no outgoing links

Link Reversal Algorithm: Illustration B F C E G Represents a link that was reversed recently D Now all nodes (other than destination D) have an outgoing link

Link Reversal Algorithm: Illustration B F C E G D DAG has been restored with only the destination as a sink

Summary: Link Reversal Motivations maintain a mesh (hopefully) local adaptation Remaining questions: how to implement it? will reversal stop? Next we will look into the questions using partial reversal (not full reversal, as the preceding example)

Link Direction Through Heights A node i contains a triple (i, i, i) i : an integer (the major integer) i : another integer (the minor integer) i : node index (to impose a total order) The triple of a node is called the height of the node Suppose there is a link from node i to node j, the direction is determined by their heights i -> j: if (i, i, i) > (j, j, j) For destination D, the height is (0, 0, D)

Illustration of Heights

Partial Reversal Algorithm If the height of node i is lower than all of its neighbors, i.e., (i, i, i) < (j, j, j) for all j in Ni, Increases i to where Ni is the neighbors of i. Set i to if there exists a neighbor j with the same  value after i has increased its ; otherwise i not changed

min  of all neighbors with new  Illustration min  of all neighbors with new  min  of all neighbors

Example (0,4,1) (0,3,2) (0,2,3) (0,5,4) (0,1,6) (0,2,5) Destination: (0,0,0)

Example: Link from 6 to 0 is down (0,4,1) (0,3,2) (0,2,3) (0,5,4) (0,1,6) (0,2,5) Destination: (0,0,0)

Example: After Node 6 Reverses (0,4,1) (0,3,2) (0,2,3) (0,5,4) (1,1,6) (0,2,5) 1 = min{0,0}+1 Destination: (0,0,0)

Example: After Nodes 3 and 5 Reverse 1 = min{0,1}+1; 0 = min{1}-1 (0,4,1) (0,3,2) (1,0,3) (0,5,4) (1,1,6) (1,0,5) Destination: (0,0,0)

Example: After Nodes 2 Reverses (0,4,1) (1,-1,2) (1,0,3) (0,5,4) (1,1,6) (1,0,5) Destination: (0,0,0)

Example: After Nodes 1 Reverses (1,-2,1) (1,-1,2) (1,0,3) (0,5,4) (1,1,6) (1,0,5) Destination: (0,0,0)

Backup Slides

Change of Foreign Agent CN HA FAold FAnew MN Data Data Data Update ACK Data Data MN changes location Registration Update ACK Data Data Data Warning Request Update ACK Data Data t

Micro Mobility A very typical scenario of Mobile IP is that a MN visits a company or university the MN may change foreign networks multiple times in the foreign network, generating much control traffic

Handoff Aware Wireless Access Internet Infrastructure (HAWAII) Operation: MN obtains co-located COA and registers with HA Handover: MN keeps COA, new BS answers Reg. Request and updates routers MN views BS as foreign agent Backbone Router Internet BS MN Crossover DHCP Server HA Mobile IP 1 2 4 1 2 3 4 BS 3