The Network Layer UNIT-4 snistforum.com

Network Layer Design Issues Store-and-Forward Packet Switching Services Provided to the Transport Layer Implementation of Connectionless Service Implementation of Connection-Oriented Service Comparison of Virtual-Circuit and Datagram Subnets snistforum.com

Store-and-Forward Packet Switching The environment of the network layer protocols. fig 5-1 snistforum.com

Implementation of Connectionless Service Routing within a diagram subnet. snistforum.com

Implementation of Connection-Oriented Service Routing within a virtual-circuit subnet. snistforum.com

Comparison of Virtual-Circuit and Datagram Subnets 5-4 snistforum.com

Routing Algorithms Shortest Path Routing Flooding Distance Vector Routing Link State Routing Hierarchical Routing Broadcast Routing Multicast Routing Routing for Mobile Hosts snistforum.com

Shortest Path Routing The first 5 steps used in computing the shortest path from A to D. The arrows indicate the working node. snistforum.com

Flooding Initially After reaching to nodes finally snistforum.com

Distance Vector Routing (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J. snistforum.com

Distance Vector Routing (2) The count-to-infinity problem. * Check the neighbour value add 1 to its value the delay or cost to each of its neighbors. snistforum.com

Link State Routing Each router must do the following: 1.Discover its neighbors, learn their network address. 2.Measure the delay or cost to each of its neighbors. 3.Construct a packet telling all it has just learned. 4.Send this packet to all other routers. 5.Compute the shortest path to every other router. snistforum.com

Link State Routing snistforum.com

Phase 1: snistforum.com

Phase 2: snistforum.com

Hierarchical Routing Hierarchical routing. snistforum.com

Broadcast Routing  Sending the packets from one host to all other remaining host in the network simultaneously is called Broadcasting  Send a separate packet to each destination Different Methods Use flooding Use multidimensional routing Each packet contains a list of destinations Routers duplicate packet for all matching outgoing lines Use spanning tree routing a subset of the subnet that includes all routers but contains no loops. snistforum.com

spanning tree routing:  If each router knows which of its lines belongs to the spanning tree, it can copy on incoming broad cast packet on to all the spanning tree lines except the one it arrived on.  Uses the minimum number of packets necessary  Routers must be able to compute spanning tree Available with link state routing  The only Problem here is each router must have knowledge of some spanning tree snistforum.com

Method 4: Reverse Path Forwarding or Reverse Path Broadcasting  Use When knowledge of a spanning tree is not available  Provides an approximation of spanning tree routing  Routers check to see if incoming packet arrives from the same line (shortest path) that the router uses to route outgoing packets to the broadcast source  If so, the router duplicates the packet on all other outgoing lines  Otherwise, the router discards the packet snistforum.com

Multicast Routing  A method to broadcast packets to well-defined groups  Hosts can join multicast groups. They inform their routers Routers send group information throughout the subnet  Each router computes a spanning tree for each group. The spanning tree includes all the routers needed to broadcast data to the group snistforum.com

Multicast Routing PIM- Protocol Independent Multicast IGMP- Internet Group Message Protocol snistforum.com

Routing for Mobile Hosts snistforum.com

Hosts Stationary Hosts: Hosts that never move. Migratory Hosts: Stationary hosts who move from one fixed site to another from time to time but use the network only when they are physically connected to it. Roaming Hosts: Need to maintain their connections as they move around. Mobile Hosts: Migratory and Roaming Hosts – that is all host that are away from home and still want to be connected. Routing goal in systems with mobile hosts: To make possible to send packets to mobile hosts using their home address, and Have the packets efficiently reach them wherever they may be. Trick is off course to find them first. Routing for Mobile Hosts snistforum.com

According to the sketch in previous slide world is divided up (geographically) into small units – areas. Areas are typically LANs or wireless cells. Each area has one or more Foreign agents: Processes that keep track of all mobile hosts visiting the area. Home agent: Keeps track of hosts whose home is in the area, but who are currently visiting another area.. snistforum.com

Registration Procedure of Mobile Hosts 1.Each foreign agent broadcasts periodically a packet announcing its existence and address. Newly-arrived mobile host may: 1.Wait for one of these message, or if none arrives quickly enough 2.Can broadcast a packet “saying”: Are there any foreign agents around? 2.The mobile host registers with the foreign agent: Gives its home address, Current data link layer address, and Some security information. 3.The foreign agent contact the mobile host’s home agent and informs it about a mobile host in his area. This message contains: The foreign agent’s network address, Security information (“to convince the home agent that the mobile host is really there”). 4.The home agent authenticates security information containing: Timestamp (to prove that it was generated within the past few seconds), etc. Acknowledges foreign agent by indicating to proceed if everything checks out. 5.Foreign agent registers and informs the mobile host. Checking out when done (typically mobile hosts just turn-off their computers). snistforum.com

Packet routing for mobile users. snistforum.com

Example: Sender wants to send a packet to a host in New York. Packets sent to the mobile host on its home LAN in NEW York are intercepted by the home agent (step 1). Home agent looks up mobile host’s new (temporary) location and finds the address of the foreign agent handling the mobile host (i.e., Los Angeles). Home agent does: 1.It encapsulates the packet in the payload field of an outer packet and sends the latter to the foreign agent (step 2). This mechanism is called tunneling. After getting the encapsulated packet, the foreign agent removes the original packet from the payload field and sends it to the mobile host as a data link frame. 2.The home agent tells the sender to henceforth send packet to the mobile host by encapsulating them in the payload of packets explicitly addressed to the foreign agent instead of just sending them to the mobile host's home address (step 3.) Subsequent packets can now be routed directly to the host via foreign agent (step 4.), snistforum.com

Internetworking snistforum.com

Internetworking How Networks Differ How Networks Can Be Connected Concatenated Virtual Circuits Connectionless Internetworking Tunneling Internetwork Routing Fragmentation snistforum.com

Connecting Networks A collection of interconnected networks. snistforum.com

How Networks Differ Some of the many ways networks can differ snistforum.com

How Networks Can Be Connected (a) Two Ethernets connected by a switch. (b) Two Ethernets connected by routers. snistforum.com

Concatenated Virtual Circuits Internetworking using concatenated virtual circuits. snistforum.com

Connectionless Internetworking A connectionless internet. snistforum.com

Tunneling Tunneling a packet from Paris to London. snistforum.com

Internetwork Routing (a) An internetwork. (b) A graph of the internetwork. snistforum.com

Fragmentation (a) Transparent fragmentation. (b) Nontransparent fragmentation. snistforum.com